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Sample records for pulse electron paramagnetic

  1. Multifrequency pulsed electron paramagnetic resonance on metalloproteins.

    Science.gov (United States)

    Lyubenova, Sevdalina; Maly, Thorsten; Zwicker, Klaus; Brandt, Ulrich; Ludwig, Bernd; Prisner, Thomas

    2010-02-16

    Metalloproteins often contain metal centers that are paramagnetic in some functional state of the protein; hence electron paramagnetic resonance (EPR) spectroscopy can be a powerful tool for studying protein structure and function. Dipolar spectroscopy allows the determination of the dipole-dipole interactions between metal centers in protein complexes, revealing the structural arrangement of different paramagnetic centers at distances of up to 8 nm. Hyperfine spectroscopy can be used to measure the interaction between an unpaired electron spin and nuclear spins within a distance of 0.8 nm; it therefore permits the characterization of the local structure of the paramagnetic center's ligand sphere with very high precision. In this Account, we review our laboratory's recent applications of both dipolar and hyperfine pulsed EPR methods to metalloproteins. We used pulsed dipolar relaxation methods to investigate the complex of cytochrome c and cytochrome c oxidase, a noncovalent protein-protein complex involved in mitochondrial electron-transfer reactions. Hyperfine sublevel correlation spectroscopy (HYSCORE) was used to study the ligand sphere of iron-sulfur clusters in complex I of the mitochondrial respiratory chain and substrate binding to the molybdenum enzyme polysulfide reductase. These examples demonstrate the potential of the two techniques; however, they also highlight the difficulties of data interpretation when several paramagnetic species with overlapping spectra are present in the protein. In such cases, further approaches and data are very useful to enhance the information content. Relaxation filtered hyperfine spectroscopy (REFINE) can be used to separate the individual components of overlapping paramagnetic species on the basis of differences in their longitudinal relaxation rates; it is applicable to any kind of pulsed hyperfine or dipolar spectroscopy. Here, we show that the spectra of the iron-sulfur clusters in complex I can be separated by this

  2. In vivo imaging of a stable paramagnetic probe by pulsed-radiofrequency electron paramagnetic resonance spectroscopy

    DEFF Research Database (Denmark)

    Murugesan; Cook; Devasahayam

    1997-01-01

    Imaging of free radicals by electron paramagnetic resonance (EPR) spectroscopy using time domain acquisition as in nuclear magnetic resonance (NMR) has not been attempted because of the short spin-spin relaxation times, typically under 1 μs, of most biologically relevant paramagnetic species...... to minimize motional artifacts from cardiac and lung motion that cause significant problems in frequency-domain spectral acquisition, such as in continuous wave (cw) EPR techniques...

  3. Bulk Quantum Computation with Pulsed Electron Paramagnetic Resonance: Simulations of Single-Qubit Error Correction Schemes

    Science.gov (United States)

    Ishmuratov, I. K.; Baibekov, E. I.

    2016-12-01

    We investigate the possibility to restore transient nutations of electron spin centers embedded in the solid using specific composite pulse sequences developed previously for the application in nuclear magnetic resonance spectroscopy. We treat two types of systematic errors simultaneously: (i) rotation angle errors related to the spatial distribution of microwave field amplitude in the sample volume, and (ii) off-resonance errors related to the spectral distribution of Larmor precession frequencies of the electron spin centers. Our direct simulations of the transient signal in erbium- and chromium-doped CaWO4 crystal samples with and without error corrections show that the application of the selected composite pulse sequences can substantially increase the lifetime of Rabi oscillations. Finally, we discuss the applicability limitations of the studied pulse sequences for the use in solid-state electron paramagnetic resonance spectroscopy.

  4. Comparison of pulse sequences for R1-based electron paramagnetic resonance oxygen imaging

    Science.gov (United States)

    Epel, Boris; Halpern, Howard J.

    2015-05-01

    Electron paramagnetic resonance (EPR) spin-lattice relaxation (SLR) oxygen imaging has proven to be an indispensable tool for assessing oxygen partial pressure in live animals. EPR oxygen images show remarkable oxygen accuracy when combined with high precision and spatial resolution. Developing more effective means for obtaining SLR rates is of great practical, biological and medical importance. In this work we compared different pulse EPR imaging protocols and pulse sequences to establish advantages and areas of applicability for each method. Tests were performed using phantoms containing spin probes with oxygen concentrations relevant to in vivo oxymetry. We have found that for small animal size objects the inversion recovery sequence combined with the filtered backprojection reconstruction method delivers the best accuracy and precision. For large animals, in which large radio frequency energy deposition might be critical, free induction decay and three pulse stimulated echo sequences might find better practical usage.

  5. Design and implementation of an FPGA-based timing pulse programmer for pulsed-electron paramagnetic resonance applications.

    Science.gov (United States)

    Sun, Li; Savory, Joshua J; Warncke, Kurt

    2013-08-01

    The design, construction and implementation of a field-programmable gate array (FPGA) -based pulse programmer for pulsed-electron paramagnetic resonance (EPR) experiments is described. The FPGA pulse programmer offers advantages in design flexibility and cost over previous pulse programmers, that are based on commercial digital delay generators, logic pattern generators, and application-specific integrated circuit (ASIC) designs. The FPGA pulse progammer features a novel transition-based algorithm and command protocol, that is optimized for the timing structure required for most pulsed magnetic resonance experiments. The algorithm was implemented by using a Spartan-6 FPGA (Xilinx), which provides an easily accessible and cost effective solution for FPGA interfacing. An auxiliary board was designed for the FPGA-instrument interface, which buffers the FPGA outputs for increased power consumption and capacitive load requirements. Device specifications include: Nanosecond pulse formation (transition edge rise/fall times, ≤3 ns), low jitter (≤150 ps), large number of channels (16 implemented; 48 available), and long pulse duration (no limit). The hardware and software for the device were designed for facile reconfiguration to match user experimental requirements and constraints. Operation of the device is demonstrated and benchmarked by applications to 1-D electron spin echo envelope modulation (ESEEM) and 2-D hyperfine sublevel correlation (HYSCORE) experiments. The FPGA approach is transferrable to applications in nuclear magnetic resonance (NMR; magnetic resonance imaging, MRI), and to pulse perturbation and detection bandwidths in spectroscopies up through the optical range.

  6. Field-swept pulsed electron paramagnetic resonance of Cr{sup 3+}-doped ZBLAN fluoride glass

    Energy Technology Data Exchange (ETDEWEB)

    Drew, S.C. [School of Physics and Materials Engineering, Monash University, VIC (Australia)]. E-mail: simon.drew@spme.monash.edu.au; Pilbrow, J.R. [School of Physics and Materials Engineering, Monash University, VIC (Australia); Newman, P.J.; MacFarlane, D.R. [Department of Chemistry, Monash University, VIC (Australia)

    2001-10-07

    Field-swept pulsed electron paramagnetic resonance (EPR) spectra of a ZBLAN fluoride glass doped with a low concentration of Cr{sup 3+} are obtained using echo-detected EPR and hole-burning free induction decay detection. We review the utility of the pulsed EPR technique in generating field-swept EPR spectra, as well as some of the distorting effects that are peculiar to the pulsed detection method. The application of this technique to Cr{sup 3+}-doped ZBLAN reveals that much of the broad resonance extending from g{sup eff}=5.1 to g{sup eff}=1.97, characteristic of X-band continuous wave EPR of Cr{sup 3+} in glasses, is absent. We attribute this largely to the variation in nutation frequencies across the spectrum that result from sites possessing large fine structure interactions. The description of the spin dynamics of such sites is complicated and we discuss some possible approaches to the simulation of the pulsed EPR spectra. (author)

  7. Electron paramagnetic resonance

    CERN Document Server

    Al'tshuler, S A

    2013-01-01

    Electron Paramagnetic Resonance is a comprehensive text on the field of electron paramagnetic resonance, covering both the theoretical background and the results of experiment. This book is composed of eight chapters that cover theoretical materials and experimental data on ionic crystals, since these are the materials that have been most extensively studied by the methods of paramagnetic resonance. The opening chapters provide an introduction to the basic principles of electron paramagnetic resonance and the methods of its measurement. The next chapters are devoted to the theory of spectra an

  8. Site directed spin labelling and pulsed dipolar electron paramagnetic resonance (double electron-electron resonance) of force activation in muscle

    Energy Technology Data Exchange (ETDEWEB)

    Fajer, Piotr G [Institute of Molecular Biophysics, Department of Biological Science, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310 (United States)

    2005-05-11

    The recent development of site specific spin labelling and advances in pulsed electron paramagnetic resonance(EPR) have established spin labelling as a viable structural biology technique. Specific protein sites or whole domains can be selectively targeted for spin labelling by cysteine mutagenesis. The secondary structure of the proteins is determined from the trends in EPR signals of labels attached to consecutive residues. Solvent accessibility or label mobility display periodicities along the labelled polypeptide chain that are characteristic of {beta}-strands (periodicity of 2 residues) or {alpha}-helices (3.6 residues). Low-resolution 3D structure of proteins is determined from the distance restraints. Two spin labels placed within 60-70 A of each other create a local dipolar field experienced by the other spin labels. The strength of this field is related to the interspin distance, {proportional_to} r{sup -3}. The dipolar field can be measured by the broadening of the EPR lines for the short distances (8-20 A) or for the longer distances (17-70 A) by the pulsed EPR methods, double electron-electron resonance(DEER) and double quantum coherence (DQC). A brief review of the methodology and its applications to the multisubunit muscle protein troponin is presented below.

  9. Pulse saturation recovery, pulse ELDOR, and free induction decay electron paramagnetic resonance detection using time-locked subsampling

    Science.gov (United States)

    Froncisz, W.; Camenisch, Theodore G.; Ratke, Joseph J.; Hyde, James S.

    2001-03-01

    Time locked subsampling (TLSS) in electron paramagnetic resonance (EPR) involves the steps of (i) translation of the signal from a microwave carrier to an intermediate frequency (IF) carrier where the (IF) offset between the signal oscillator and local oscillator frequencies is synthesized, (ii) sampling the IF carrier four times in an odd number of cycles, say 4 in 3, where the analog-to-digital (A/D) converter is driven by a frequency synthesizer that has the same clock input as the IF synthesizer, (iii) signal averaging as required for adequate signal to noise, (iv) separating the even and odd digitized words into two separate signal channels, which correspond to signals in phase and in quadrature with respect to the IF carrier, i.e., I and Q, and (v) detecting the envelope of I and also of Q by changing the signs of alternate words in each of the two channels. TLSS detection has been demonstrated in three forms of pulse EPR spectroscopy at X band: saturation recovery, pulse electron-electron double resonance, and free induction decay. The IF was 187.5 MHz, the A/D converter frequency was 250 MHz, the overall bandwidth was 125 MHz, and the bandwidths for the separate I and Q channels were each 62.5 MHz. Experiments were conducted on nitroxide radical spin labels. The work was directed towards development of methodology to monitor bimolecular collisions of oxygen with spin labels in a context of site-directed spin labeling.

  10. Pulse radiolysis of alkanes: A time-resolved electron paramagnetic resonance study

    Energy Technology Data Exchange (ETDEWEB)

    Shkrob, I.A.; Trifunac, A.D. [Argonne National Lab., IL (United States). Chemistry Division

    1994-02-14

    Time-resolved spin-echo-detected electron paramagnetic resonance (EPR) was applied to examine short-lived alkyl radicals formed in pulse radiolysis of liquid alkanes. It was found that the ratio of yields of penultimate and interior radicals in n-alkanes at the instant of their generation is temperature-independent and is ca. 1.25 times greater than the statistical quantity. This higher-than-statistical production of penultimate radicals indicates that the fast ion molecule reactions involving radical cations are a significant route of radical generation. The analysis of spin-echo kinetics in n-alkanes suggests that the alkyl radicals are emissively polarized in spur reactions. this initial polarization rapidly increases with shortening of the aliphatic chain. Another finding is that a long-chain structure of these radicals results in much higher rate of Heisenberg spin exchange relative to the recombination rate. The relative yields of hydrogen abstraction and fragmentation for various branched alkanes are estimated. It is concluded that the fragmentation occurs prior to the formation of radicals in an excited precursor species. Effects of phenolic and alkene additives in radiolysis of n-alkanes are examined. It is demonstrated that phenoxy radicals are produced in dissociative capture of electrons and alkane holes. Another route is a reaction of phenols with free hydrogen atoms. A rapid transfer of singlet correlation from the geminate radical ion pairs is responsible for unusual polarization patterns in the phenoxy and cyclohexadienyl radicals. The significance of these results in the context of cross-linking in polyethylene and higher paraffins is discussed. 56 refs.

  11. Kissing G domains of MnmE monitored by X-ray crystallography and pulse electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Meyer, Simon; Böhme, Sabine; Krüger, André; Steinhoff, Heinz-Jürgen; Klare, Johann P; Wittinghofer, Alfred

    2009-10-01

    MnmE, which is involved in the modification of the wobble position of certain tRNAs, belongs to the expanding class of G proteins activated by nucleotide-dependent dimerization (GADs). Previous models suggested the protein to be a multidomain protein whose G domains contact each other in a nucleotide dependent manner. Here we employ a combined approach of X-ray crystallography and pulse electron paramagnetic resonance (EPR) spectroscopy to show that large domain movements are coupled to the G protein cycle of MnmE. The X-ray structures show MnmE to be a constitutive homodimer where the highly mobile G domains face each other in various orientations but are not in close contact as suggested by the GDP-AlF(x) structure of the isolated domains. Distance measurements by pulse double electron-electron resonance (DEER) spectroscopy show that the G domains adopt an open conformation in the nucleotide free/GDP-bound and an open/closed two-state equilibrium in the GTP-bound state, with maximal distance variations of 18 A. With GDP and AlF(x), which mimic the transition state of the phosphoryl transfer reaction, only the closed conformation is observed. Dimerization of the active sites with GDP-AlF(x) requires the presence of specific monovalent cations, thus reflecting the requirements for the GTPase reaction of MnmE. Our results directly demonstrate the nature of the conformational changes MnmE was previously suggested to undergo during its GTPase cycle. They show the nucleotide-dependent dynamic movements of the G domains around two swivel positions relative to the rest of the protein, and they are of crucial importance for understanding the mechanistic principles of this GAD.

  12. Kissing G domains of MnmE monitored by X-ray crystallography and pulse electron paramagnetic resonance spectroscopy.

    Directory of Open Access Journals (Sweden)

    Simon Meyer

    2009-10-01

    Full Text Available MnmE, which is involved in the modification of the wobble position of certain tRNAs, belongs to the expanding class of G proteins activated by nucleotide-dependent dimerization (GADs. Previous models suggested the protein to be a multidomain protein whose G domains contact each other in a nucleotide dependent manner. Here we employ a combined approach of X-ray crystallography and pulse electron paramagnetic resonance (EPR spectroscopy to show that large domain movements are coupled to the G protein cycle of MnmE. The X-ray structures show MnmE to be a constitutive homodimer where the highly mobile G domains face each other in various orientations but are not in close contact as suggested by the GDP-AlF(x structure of the isolated domains. Distance measurements by pulse double electron-electron resonance (DEER spectroscopy show that the G domains adopt an open conformation in the nucleotide free/GDP-bound and an open/closed two-state equilibrium in the GTP-bound state, with maximal distance variations of 18 A. With GDP and AlF(x, which mimic the transition state of the phosphoryl transfer reaction, only the closed conformation is observed. Dimerization of the active sites with GDP-AlF(x requires the presence of specific monovalent cations, thus reflecting the requirements for the GTPase reaction of MnmE. Our results directly demonstrate the nature of the conformational changes MnmE was previously suggested to undergo during its GTPase cycle. They show the nucleotide-dependent dynamic movements of the G domains around two swivel positions relative to the rest of the protein, and they are of crucial importance for understanding the mechanistic principles of this GAD.

  13. A high-frequency electron paramagnetic resonance spectrometer for multi-dimensional, multi-frequency, and multi-phase pulsed measurements

    Energy Technology Data Exchange (ETDEWEB)

    Cho, F. H. [Department of Physics, University of Southern California, Los Angeles, California 90089 (United States); Stepanov, V. [Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States); Takahashi, S., E-mail: susumu.takahashi@usc.edu [Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States); Department of Physics, University of Southern California, Los Angeles, California 90089 (United States)

    2014-07-15

    We describe instrumentation for a high-frequency electron paramagnetic resonance (EPR) and pulsed electron-electron double resonance (PELDOR) spectroscopy. The instrumentation is operated in the frequency range of 107−120 GHz and 215−240 GHz and in the magnetic field range of 0−12.1 T. The spectrometer consisting of a high-frequency high-power solid-state source, a quasioptical system, a phase-sensitive detection system, a cryogenic-free superconducting magnet, and a {sup 4}He cryostat enables multi-frequency continuous-wave EPR spectroscopy as well as pulsed EPR measurements with a few hundred nanosecond pulses. Here we discuss the details of the design and the pulsed EPR sensitivity of the instrumentation. We also present performance of the instrumentation in unique experiments including PELDOR spectroscopy to probe correlations in an insulating electronic spin system and application of dynamical decoupling techniques to extend spin coherence of electron spins in an insulating solid-state system.

  14. Electron Paramagnetic Resonance Imaging: 1. CW-EPR Imaging

    Indian Academy of Sciences (India)

    2016-07-01

    Twentieth century bore witness to remarkable scientists whohave advanced our understanding of the brain. Among them,EPR (Electron Paramagnetic Resonance) imaging is particularlyuseful in monitoring hypoxic zones in tumors which arehighly resistant to radiation and chemotherapeutic treatment.This first part of the article covers aspects of CW(continuous wave) imaging with details of FT (pulsed FourierTransform)-EPR imaging covered in Part 2, to be publishedin the next issue of Resonance.

  15. Electron paramagnetic resonance of transition ions

    CERN Document Server

    Abragam, A

    2012-01-01

    This book is a reissue of a classic Oxford text, and provides a comprehensive treatment of electron paramagnetic resonance of ions of the transition groups. The emphasis is on basic principles, with numerous references to publications containing further experimental results and more detailed developments of the theory. An introductory survey gives a general understanding, and a general survey presents such topics as the classical and quantum resonance equations, thespin-Hamiltonian, Endor, spin-spin and spin-lattice interactions, together with an outline of the known behaviour of ions of each

  16. Electron Paramagnetic Resonance Study of Pr

    Energy Technology Data Exchange (ETDEWEB)

    Tezuka, Keitaro; Hinatsu, Yukio

    2001-01-01

    Electron paramagnetic resonance (EPR) spectra of tetravalent praseodymium ions doped in the cubic perovskite compound BaHfO{sub 3} have been measured at 4.2 K. A very large hyperfine interaction with the {sup 141}Pr nucleus was observed in the spectrum of Pr{sup 4+}/ BaHfO{sub 3}. The results were analyzed based on the weak field approximation, and the g value (|g|=0.619) and a hyperfine coupling constant (A=0.0589 cm{sup {minus}1}) were obtained. The measured g value is much smaller than |-10/7|, which indicates that the crystal field effect on the behavior of a 4f electron is large. These g and A values were compared with the EPR results for other f{sup 1} ions in an octahedral crystal field.

  17. Electron paramagnetic resonance dosimetry using synthetic hydroxyapatite

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Kwon; Kim, Hwi Young; Ye, Sung Joon [Seoul National University, Seoul (Korea, Republic of); Hirata, Hiroshi [Hokkaido University, Sapporo (Japan); Park, Jong Min [Seoul National University Hospital, Seoul (Korea, Republic of)

    2014-11-15

    The victims exposed doses under 3.5-4.0 Gy have chance to survive if treated urgently. To determine the priority of treatment among a large number of victims, the triage – distinguishing patients who need an urgent treatment from who may not be urgent – is necessary based on radiation biodosimetry. A current gold standard for radiation biodosimetry is the chromosomal assay using human lymphocytes. But this method requires too much time and skilled labors to cover the mass victims in radiation emergencies. Electron paramagnetic resonance (EPR) has been known for its capability of quantifying radicals in matters. EPR dosimetry is based on the measurement of stable radiation-induced radicals in tooth enamel. Hydroxyapatite (HAP) (Ca10(PO4)6(OH)2) contained in tooth enamel is a major probe for radiation dose reconstruction. This HAP dosimetry study was performed using a novel EPR spectrometer in Hokkaido University, Japan. The EPR dose-response curve was made using HAP samples. The blind test using 250 cGy samples showed the feasibility of EPR dosimetry for the triage purpose.

  18. Multifrequency Electron Paramagnetic Resonance Theory and Applications

    CERN Document Server

    Misra, Sushil K

    2011-01-01

    Filling the gap for a systematic, authoritative, and up-to-date review of this cutting-edge technique, this book covers both low and high frequency EPR, emphasizing the importance of adopting the multifrequency approach to study paramagnetic systems in full detail by using the EPR method. In so doing, it discusses not only the underlying theory and applications, but also all recent advances -- with a final section devoted to future perspectives.

  19. Study of metalloproteins using continuous wave electron paramagnetic resonance (EPR).

    Science.gov (United States)

    Gambarelli, Serge; Maurel, Vincent

    2014-01-01

    Electron paramagnetic resonance (EPR) is an invaluable tool when studying systems with paramagnetic centers. It is a sensitive spectroscopic method, which can be used with dilute samples in aqueous buffer solutions. Here, we describe the basic procedure for recording an X-band EPR spectrum of a metalloprotein sample at low temperature. We also discuss basic optimization techniques to provide spectra with a high signal to noise ratio and minimum distortion.

  20. Pulse electron paramagnetic resonance studies of the interaction of methanol with the S2 state of the Mn4O5Ca cluster of photosystem II.

    Science.gov (United States)

    Oyala, Paul H; Stich, Troy A; Stull, Jamie A; Yu, Fangting; Pecoraro, Vincent L; Britt, R David

    2014-12-23

    The binding of the substrate analogue methanol to the catalytic Mn4CaO5 cluster of the water-oxidizing enzyme photosystem II is known to alter the electronic structure properties of the oxygen-evolving complex without retarding O2-evolution under steady-state illumination conditions. We report the binding mode of (13)C-labeled methanol determined using 9.4 GHz (X-band) hyperfine sublevel-correlation (HYSCORE) and 34 GHz (Q-band) electron spin-echo electron nuclear double resonance (ESE-ENDOR) spectroscopies. These results are compared to analogous experiments on a mixed-valence Mn(III)Mn(IV) complex (2-OH-3,5-Cl2-salpn)2Mn(III)Mn(IV) (salpn = N,N'-bis(3,5-dichlorosalicylidene)-1,3-diamino-2-hydroxypropane) in which methanol ligates to the Mn(III) ion ( Larson et al. (1992) J. Am. Chem. Soc. , 114 , 6263 ). In the mixed-valence Mn(III,IV) complex, the hyperfine coupling to the (13)C of the bound methanol (Aiso = 0.65 MHz, T = 1.25 MHz) is appreciably larger than that observed for (13)C methanol associated with the Mn4CaO5 cluster poised in the S2 state, where only a weak dipolar hyperfine interaction (Aiso = 0.05 MHz, T = 0.27 MHz) is observed. An evaluation of the (13)C hyperfine interaction using the X-ray structure coordinates of the Mn4CaO5 cluster indicates that methanol does not bind as a terminal ligand to any of the manganese ions in the oxygen-evolving complex. We favor methanol binding in place of a water ligand to the Ca(2+) in the Mn4CaO5 cluster or in place of one of the waters that form hydrogen bonds with the oxygen bridges of the cluster.

  1. In-situ electron paramagnetic resonance studies of paramagnetic point defects in superconducting microwave resonators

    Science.gov (United States)

    Zhang, Shengke; Kopas, Cameron; Wagner, Brian; Queen, Daniel; Newman, N.

    2016-09-01

    The physical nature and concentration of paramagnetic point defects in the dielectrics of superconducting planar microwave resonators have been determined using in-situ electron paramagnetic resonance spectroscopy. To perform this work, the quality factor of parallel plate and stripline resonators was measured as a function of the magnitude of a magnetic-field applied parallel to the electrode surfaces. YBa2Cu3O7-δ thin film electrodes proved to be a preferred choice over Nb and MgB2 because they are readily available and have a small surface resistance (Rs) up to high temperatures (˜77 K) and magnetic fields (i.e., dielectric, Co2+-doped Ba(Zn1/3Nb2/3)O3, are shown to have losses dominated by d-electron spin-excitations in exchange-coupled Co2+ point-defect clusters, even in the absence of an applied magnetic field. A significant enhanced microwave loss in stripline and parallel plate resonators is found to correlate with the presence of paramagnetic Mn2+ dopants in Ba(Zn1/3Ta2/3)O3 ceramics and dangling bond states in amorphous Si thin films, although the identification of the dominant loss mechanism(s) in these dielectrics requires further investigation.

  2. Introduction to Spin Label Electron Paramagnetic Resonance Spectroscopy of Proteins

    Science.gov (United States)

    Melanson, Michelle; Sood, Abha; Torok, Fanni; Torok, Marianna

    2013-01-01

    An undergraduate laboratory exercise is described to demonstrate the biochemical applications of electron paramagnetic resonance (EPR) spectroscopy. The beta93 cysteine residue of hemoglobin is labeled by the covalent binding of 3-maleimido-proxyl (5-MSL) and 2,2,5,5-tetramethyl-1-oxyl-3-methyl methanethiosulfonate (MTSL), respectively. The excess…

  3. Introduction to Spin Label Electron Paramagnetic Resonance Spectroscopy of Proteins

    Science.gov (United States)

    Melanson, Michelle; Sood, Abha; Torok, Fanni; Torok, Marianna

    2013-01-01

    An undergraduate laboratory exercise is described to demonstrate the biochemical applications of electron paramagnetic resonance (EPR) spectroscopy. The beta93 cysteine residue of hemoglobin is labeled by the covalent binding of 3-maleimido-proxyl (5-MSL) and 2,2,5,5-tetramethyl-1-oxyl-3-methyl methanethiosulfonate (MTSL), respectively. The excess…

  4. Electron paramagnetic resonance of material properties and processes

    Energy Technology Data Exchange (ETDEWEB)

    Brower, K. L.

    1980-01-01

    This paper demonstrates, primarily for the non-specialist and within the context of new and recent achievements, the diagnostic value of electron paramagnetic resonance (EPR) in the study of material properties and processes. I have selected three EPR studies which demonstrate the elegance and uniqueness of EPR in atomic defect studies and exemplify unusual achievements through the use of new techniques for material measurement and preparation. A brief introduction into the origin, interaction, and detection of unpaired electrons is included.

  5. The Electron Paramagnetic Resonance in the study of tissue specimens

    OpenAIRE

    Stefaniuk, Ireneusz; Wróbel, Dagmara; Skrȩt, Andrzej; Skrȩt-Magierło, Joanna; Góra, Tomasz; Szczerba, Piotr

    2014-01-01

    The Electron Paramagnetic Spectroscopy (EPR) is the most direct and powerful method for the detection and identification of free radicals and other species with unpaired electrons. Statistics disorders are a common gynaecological disorder occurring in women. The condition afflicts around 15% of women to the extent of impairing the quality of living. According to scientific reports as many as 50% of women experiencing problems related to genital statistics disorders. The aim of this work was t...

  6. Tetrachloridocuprates(II—Synthesis and Electron Paramagnetic Resonance (EPR Spectroscopy

    Directory of Open Access Journals (Sweden)

    Peter Strauch

    2012-02-01

    Full Text Available Ionic liquids (ILs on the basis of metal containing anions and/or cations are of interest for a variety of technical applications e.g., synthesis of particles, magnetic or thermochromic materials. We present the synthesis and the results of electron paramagnetic resonance (EPR spectroscopic analyses of a series of some new potential ionic liquids based on tetrachloridocuprates(II, [CuCl4]2−, with different sterically demanding cations: hexadecyltrimethylammonium 1, tetradecyltrimethylammonium 2, tetrabutylammonium 3 and benzyltriethylammonium 4. The cations in the new compounds were used to achieve a reasonable separation of the paramagnetic Cu(II ions for EPR spectroscopy. The EPR hyperfine structure was not resolved. This is due to the exchange broadening, resulting from still incomplete separation of the paramagnetic Cu(II centers. Nevertheless, the principal values of the electron Zeemann tensor (g║ and g┴ of the complexes could be determined. Even though the solid substances show slightly different colors, the UV/Vis spectra are nearly identical, indicating structural changes of the tetrachloridocuprate moieties between solid state and solution. The complexes have a promising potential e.g., as high temperature ionic liquids, as precursors for the formation of copper chloride particles or as catalytic paramagnetic ionic liquids.

  7. The Electron Paramagnetic Resonance in the study of tissue specimens

    CERN Document Server

    Stefaniuk, Ireneusz; Skrȩt, Andrzej; Skrȩt-Magierło, Joanna; Góra, Tomasz; Szczerba, Piotr

    2014-01-01

    The Electron Paramagnetic Spectroscopy (EPR) is the most direct and powerful method for the detection and identification of free radicals and other species with unpaired electrons. Statistics disorders are a common gynaecological disorder occurring in women. The condition afflicts around 15% of women to the extent of impairing the quality of living. According to scientific reports as many as 50% of women experiencing problems related to genital statistics disorders. The aim of this work was to investigate tissue taken from women with genital statistics disorders using the Electron Paramagnetic Resonance method. The studies on the tissue of women is one of the first studies in this area. In this work we observed a close relationship between the observed EPR signal and the consumption of omega 3 acids.

  8. Pulsed Plasma Electron Sources

    Science.gov (United States)

    Krasik, Yakov

    2008-11-01

    Pulsed (˜10-7 s) electron beams with high current density (>10^2 A/cm^2) are generated in diodes with electric field of E > 10^6 V/cm. The source of electrons in these diodes is explosive emission plasma, which limits pulse duration; in the case E Hadas and Ya. E. Krasik, Europhysics Lett. 82, 55001 (2008).

  9. Electron paramagnetic resonance of some {gamma}-irradiated drugs

    Energy Technology Data Exchange (ETDEWEB)

    Koeseoglu, R.; Koeseoglu, E.; Koeksal, F. E-mail: koksalf@ttnet.net.tr

    2003-01-01

    Some drugs, used mainly in treatment of some neurological diseases and hypertension were exposed to {gamma}-irradiation, and the samples were investigated by electron paramagnetic resonance (EPR). The observed spectra were interpreted in terms of some type of alkyl and amine radical fragments. The spectra were computer simulated and the g values of the radicals and the hyperfine structure constants of the free electron with nearby protons were determined. The species were found to be stable at room temperature for more than a year. The samples were found to display no EPR signal without irradiation.

  10. Electron Paramagnetic Studies Of Diluted Magnetic Semiconductor Nanostructures

    CERN Document Server

    Montes, L A

    1999-01-01

    In this thesis we investigate the Electron Paramagnetic Resonance (EPR) of Diluted Magnetic Semiconductor (DMS) nanostructures. The first chapter studies the appearance of strain-induced magnetic dipole forbidden transitions in the EPR spectrum of highly mismatched DMS superlattices grown by Molecular Beam Epitaxy (MBE). We investigated ZnTe/MnTe, ZnTe/CdTe:Mn and CdTe/ZnTe:Mn superlattices where the lattice mismatch between layers reaches values as large as 6%. We report the appearance of forbidden transitions even at orientations where strain should not produce any mixing, and interpret them as the onset of three dimensional growth of Quantum Dots (QD)...

  11. Electron Paramagnetic Resonance Imaging and Spectroscopy of Polydopamine Radicals.

    Science.gov (United States)

    Mrówczyński, Radosław; Coy, L Emerson; Scheibe, Błażej; Czechowski, Tomasz; Augustyniak-Jabłokow, Maria; Jurga, Stefan; Tadyszak, Krzysztof

    2015-08-13

    A thorough investigation of biomimetic polydopamine (PDA) by Electron Paramagnetic Resonance (EPR) is shown. In addition, temperature dependent spectroscopic EPR data are presented in the range 3.8-300 K. Small discrepancies in magnetic susceptibility behavior are observed between previously reported melanin samples. These variations were attributed to thermally acitivated processes. More importantly, EPR spatial-spatial 2D imaging of polydopamine radicals on a phantom is presented for the first time. In consequence, a new possible application of polydopamine as EPR imagining marker is addressed.

  12. Electron paramagnetic resonance studies of beta-alumina, a prototype glass

    Energy Technology Data Exchange (ETDEWEB)

    Kurtz, Steven Ross

    1980-01-01

    Electron paramagnetic resonance techniques are used to study single crystal Na, K, and Li beta-alumina. Color centers are introduced into this material by irradiating the samples with electrons at liquid nitrogen temperature. Using electron paramagnetic resonance and electron nuclear double resonance, the color centers generated in this manner are identified, and their location within the material is determined. For one of these centers, an F/sup +/ center, the electron spin relaxation rate is measured over the range 2 to 20/sup 0/K using the pulse saturation and recovery technique. These measurements reveal an exceptionally fast relaxation rate with anomalous temperature and microwave frequency dependence. Beta-alumina is a structurally unique system. It is partially disordered and consists of ordered blocks of aluminum oxide separated by planar disordered regions. Extensive measurements have shown that beta-alumina displays properties identical to those observed for glasses at low temperature as a result of this limited structural disorder. These glass-like properties have been explained by proposing that atomic tunneling occurs in beta-alumina at low temperature producing a system of localized two level states. A model is developed which quantitatively describes the electron spin relaxation data. The proposed relaxation mechanism couples the color center spin to the phonon induced relaxation of a nearby localized two level tunneling state. A detailed comparison shows that this model is in good agreement with earlier heat capacity, thermal conductivity, and dielectric susceptibility measurements in beta-alumina.

  13. Electron paramagnetic resonance in Cu-doped ZnO

    Science.gov (United States)

    Buchheit, R.; Acosta-Humánez, F.; Almanza, O.

    2016-04-01

    In this work, ZnO and Cu-doped ZnO nanoparticles (Zn1-xCuxO, x = 3%), with a calcination temperature of 500∘C were synthesized using the sol-gel method. The particles were analyzed using atomic absorption spectroscopy (AAS), X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) at X-band, measurement in a temperature range from 90 K to room temperature. AAS confirmed a good correspondence between the experimental doping concentration and the theoretical value. XRD reveals the presence of ZnO phase in hexagonal wurtzite structure and a nanoparticle size for the samples synthesized. EPR spectroscopy shows the presence of point defects in both samples with g-values of g = 1.959 for shallow donors and g = 2.004 for ionized vacancies. It is important when these materials are required have been used as catalysts, as suggested that it is not necessary prepare them at higher temperature. A simulation of the Cu EPR signal using an anisotropic spin Hamiltonian was performed and showed good coincidence with the experimental spectra. It was shown that Cu2+ ions enter interstitial octahedral sites of orthorhombic symmetry in the wurtzite crystal structure. Temperature dependence of the EPR linewidth and signal intensity shows a paramagnetic behavior of the sample in the measurement range. A Néel temperature TN = 78 ± 19 K was determined.

  14. Pulsed electron beam precharger

    Energy Technology Data Exchange (ETDEWEB)

    Finney, W.C. (ed.); Shelton, W.N.

    1990-01-01

    Florida State University is investigating the concept of pulsed electron beams for fly ash precipitation. This report describes the results and data on three of the subtasks of this project and preliminary work only on the remaining five subtasks. Described are the modification of precharger for pulsed and DC energization of anode; installation of the Q/A measurement system; and modification and installation of pulsed power supply to provide both pulsed and DC energization of the anode. The other tasks include: measurement of the removal efficiency for monodisperse simulated fly ash particles; measurement of particle charge; optimization of pulse energization schedule for maximum removal efficiency; practical assessment of results; and measurement of the removal efficiency for polydisperse test particles. 15 figs., 1 tab. (CK)

  15. Egyptian limestone for gamma dosimetry: an electron paramagnetic resonance study

    Science.gov (United States)

    Salama, E.

    2014-04-01

    The electron paramagnetic resonance (EPR) properties of limestone from a certain Egyptian site were investigated in order to propose an efficient and low-cost gamma dosimeter. Radiation-induced free radicals were of one type which was produced in the limestone samples at g=2.0066 after exposure to gamma radiation (60Co). EPR spectrum was recorded and analyzed. The microwave power saturation curve and the effect of changing modulation amplitude on peak-to- peak signal height were investigated. The response of limestone to different radiation doses (0.5-20 kGy) was studied. Except for the decrease in signal intensities during the first five hours following irradiation, over the period of two months fair stabilities of signal intensities were noticed. From the current results, it is possible to conclude that natural limestone may be a suitable material for radiation dosimetry in the range of irradiation processing.

  16. Pulsed Electron Holography

    CERN Document Server

    Germann, Matthias; Escher, Conrad; Fink, Hans-Werner

    2013-01-01

    A technique of pulsed low-energy electron holography is introduced that allows for recording highly resolved holograms within reduced exposure times. Therefore, stacks of holograms are accumulated in a pulsed mode with individual acquisition times as short as 50 {\\mu}s. Subsequently, these holograms are aligned and finally superimposed. The resulting holographic record reveals previously latent high-order interference fringes and thereby pushing interference resolution into the sub-nanometer regime. In view of the non-damaging character of low-energy electrons, the method is of particular interest for structural analysis of fragile biomolecules.

  17. Pauli Spin Paramagnetism and Electronic Specific Heat in Generalised d-Dimensions

    Institute of Scientific and Technical Information of China (English)

    Muktish Acharyya

    2011-01-01

    The variations of pauli spin paramagnetic susceptibility and the electronic specific heat of solids, are calculated as functions of temperature following the free electron approximation, in generalised d-dimensions.The results are compared and become consistent with that obtained in three dimensions.Interestingly, the Pauli spin paramagnetic susceptibility becomes independent of temperature only in two dimensions.

  18. Reconstruction of images from radiofrequency electron paramagnetic resonance spectra.

    Science.gov (United States)

    Smith, C M; Stevens, A D

    1994-12-01

    This paper discusses methods for obtaining image reconstructions from electron paramagnetic resonance (EPR) spectra which constitute object projections. An automatic baselining technique is described which treats each spectrum consistently; rotating the non-horizontal baselines which are caused by stray magnetic effects onto the horizontal axis. The convolved backprojection method is described for both two- and three-dimensional reconstruction and the effect of cut-off frequency on the reconstruction is illustrated. A slower, indirect, iterative method, which does a non-linear fit to the projection data, is shown to give a far smoother reconstructed image when the method of maximum entropy is used to determine the value of the final residual sum of squares. Although this requires more computing time than the convolved backprojection method, it is more flexible and overcomes the problem of numerical instability encountered in deconvolution. Images from phantom samples in vitro are discussed. The spectral data for these have been accumulated quickly and have a low signal-to-noise ratio. The results show that as few as 16 spectra can still be processed to give an image. Artifacts in the image due to a small number of projections using the convolved backprojection reconstruction method can be removed by applying a threshold, i.e. only plotting contours higher than a given value. These artifacts are not present in an image which has been reconstructed by the maximum entropy technique. At present these techniques are being applied directly to in vivo studies.

  19. A new electron paramagnetic resonance method to identify irradiated soybean.

    Science.gov (United States)

    Sanyal, Bhaskar; Sharma, Arun

    2009-10-01

    Low-dose gamma irradiation causes minimal changes in food matrix making identification of radiation-processed foods a challenging task. In the present study, soybean samples were irradiated with commercially permitted gamma radiation dose in the 0.25 to 1.0 kGy range for insect disinfestations of food. Immediately after irradiation electron paramagnetic resonance (EPR) spectrum of the skin part of soybean showed a triplet signal (g = 2.0046, hyperfine coupling constant hfcc = 3.0 mT) superimposed on naturally present singlet. These signals were characterized as cellulose and phenoxyl radicals using EPR spectrum simulation technique. Kernel part of the samples exhibited a short-lived, radiation-induced singlet of carbon-centered radical superimposed on naturally present sextet signal of Mn2+. A detailed study on relaxation and thermal behavior of induced radicals in skin part was carried out using EPR spectroscopy. These findings revealed that progressive saturation and thermal characteristics of the induced radicals may be the most suitable parameters to distinguish soybean subjected to radiation dose as low as 0.25 kGy from thermally treated and nonirradiated samples, even after a prolonged period of storage.

  20. Identification of irradiated cashew nut by electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Sanyal, Bhaskar; Sajilata, M G; Chatterjee, Suchandra; Singhal, Rekha S; Variyar, Prasad S; Kamat, M Y; Sharma, Arun

    2008-10-01

    Cashew nut samples were irradiated at gamma-radiation doses of 0.25, 0.5, 0.75, and 1 kGy, the permissible dose range for insect disinfestation of food commodities. A weak and short-lived triplet (g = 2.004 and hfcc = 30 G) along with an anisotropic signal (g perpendicular = 2.0069 and g parallel = 2.000) were produced immediately after irradiation. These signals were assigned to that of cellulose and CO 2 (-) radicals. However, the irradiated samples showed a dose-dependent increase of the central line (g = 2.0045 +/- 0.0002). The nature of the free radicals formed during conventional processing such as thermal treatment was investigated and showed an increase in intensity of the central line (g = 2.0045) similar to that of irradiation. Characteristics of the free radicals were studied by their relaxation and thermal behaviors. The present work explores the possibility to identify irradiated cashew nuts from nonirradiated ones by the thermal behaviors of the radicals beyond the period, when the characteristic electron paramagnetic resonance spectral lines of the cellulose free radicals have essentially disappeared. In addition, this study for the first time reports that relaxation behavior of the radicals could be a useful tool to distinguish between roasted and irradiated cashew nuts.

  1. Uniform spinning sampling gradient electron paramagnetic resonance imaging.

    Science.gov (United States)

    Johnson, David H; Ahmad, Rizwan; Liu, Yangping; Chen, Zhiyu; Samouilov, Alexandre; Zweier, Jay L

    2014-02-01

    To improve the quality and speed of electron paramagnetic resonance imaging (EPRI) acquisition by combining a uniform sampling distribution with spinning gradient acquisition. A uniform sampling distribution was derived for spinning gradient EPRI acquisition (uniform spinning sampling, USS) and compared to the existing (equilinear spinning sampling, ESS) acquisition strategy. Novel corrections were introduced to reduce artifacts in experimental data. Simulations demonstrated that USS puts an equal number of projections near each axis whereas ESS puts excessive projections at one axis, wasting acquisition time. Artifact corrections added to the magnetic gradient waveforms reduced noise and correlation between projections. USS images had higher SNR (85.9 ± 0.8 vs. 56.2 ± 0.8) and lower mean-squared error than ESS images. The quality of the USS images did not vary with the magnetic gradient orientation, in contrast to ESS images. The quality of rat heart images was improved using USS compared to that with ESS or traditional fast-scan acquisitions. A novel EPRI acquisition which combines spinning gradient acquisition with a uniform sampling distribution was developed. This USS spinning gradient acquisition offers superior SNR and reduced artifacts compared to prior methods enabling potential improvements in speed and quality of EPR imaging in biological applications. Copyright © 2013 Wiley Periodicals, Inc.

  2. Pulsed plasma electron sourcesa)

    Science.gov (United States)

    Krasik, Ya. E.; Yarmolich, D.; Gleizer, J. Z.; Vekselman, V.; Hadas, Y.; Gurovich, V. Tz.; Felsteiner, J.

    2009-05-01

    There is a continuous interest in research of electron sources which can be used for generation of uniform electron beams produced at E ≤105 V/cm and duration ≤10-5 s. In this review, several types of plasma electron sources will be considered, namely, passive (metal ceramic, velvet and carbon fiber with and without CsI coating, and multicapillary and multislot cathodes) and active (ferroelectric and hollow anodes) plasma sources. The operation of passive sources is governed by the formation of flashover plasma whose parameters depend on the amplitude and rise time of the accelerating electric field. In the case of ferroelectric and hollow-anode plasma sources the plasma parameters are controlled by the driving pulse and discharge current, respectively. Using different time- and space-resolved electrical, optical, spectroscopical, Thomson scattering and x-ray diagnostics, the parameters of the plasma and generated electron beam were characterized.

  3. Pulsed electron beam precharger

    Energy Technology Data Exchange (ETDEWEB)

    Finney, W.C. (ed.); Shelton, W.N.

    1990-01-01

    Electrostatic collection of a high resistivity aerosol using the Electron Beam Precipitator (EBP) collecting section was demonstrated during this reporting period (Quarter Five). Collection efficiency experiments were designed to confirm and extend some of the work performed under the previous contract. The reason for doing this was to attempt to improve upon the collection efficiency of the precipitator alone when testing with a very high resistivity, moderate-to-high concentration dust load. From the collector shakedown runs, a set of suitable operational parameters were determined for the downstream electrostatic collecting sections of the Electron Beam Precipitator wind tunnel. These parameters, along with those for the MINACC electron beam, will generally be held constant while the numerous precharging parameters are varied to produce an optimum particle charge. The electrostatic collector experiments were part of a larger, comprehensive investigation on electron beam precharging of high resistivity aerosol particles performed during the period covered by Quarters Five, Six, and Seven. This body of work used the same experimental apparatus and procedures and the experimental run period lasted nearly continuously for six months. A summary of the Quarter Five work is presented in the following paragraphs. Section II-A of TPR 5 contains a report on the continuing effort which was expended on the modification and upgrade of the pulsed power supply and the monitoring systems prior to the initiation of the electron beam precharging experimental work.

  4. Using Electron Paramagnetic Resonance Spectroscopy To Facilitate Problem Solving in Pharmaceutical Research and Development.

    Science.gov (United States)

    Mangion, Ian; Liu, Yizhou; Reibarkh, Mikhail; Williamson, R Thomas; Welch, Christopher J

    2016-08-19

    As new chemical methodologies driven by single-electron chemistry emerge, process and analytical chemists must develop approaches to rapidly solve problems in this nontraditional arena. Electron paramagnetic resonance spectroscopy has been long known as a preferred technique for the study of paramagnetic species. However, it is only recently finding application in contemporary pharmaceutical development, both to study reactions and to track the presence of undesired impurities. Several case studies are presented here to illustrate its utility in modern pharmaceutical development efforts.

  5. Electron paramagnetic resonance dosimetry and dating potential of whewellite (calcium oxalate monohydrate)

    Energy Technology Data Exchange (ETDEWEB)

    Thompson, J. [Medical Physics and Applied Radiation Sciences Unit, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4K1 (Canada)], E-mail: thompjw@mcmaster.ca; Schwarcz, H.P. [School of Geography and Earth Sciences, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4K1 (Canada)

    2008-08-15

    We use electron paramagnetic resonance (EPR) to demonstrate the presence of radiation-induced paramagnetic species in synthetic whewellite (CaC{sub 2}O{sub 4}.H{sub 2}O), with the primary EPR signal at g=2.0042. The radiosensitive EPR signal has a lifetime of at least 1 year. Freshly synthesized whewellite also displays a paramagnetic signal that increases in intensity upon exposure to fluorescent light. Although the widespread occurrence of natural whewellite suggests applications in geological or archaeological dating, no corresponding radiosensitive EPR signal has been identified in samples of natural whewellite.

  6. Dosimetry of ionizing radiations by Electron paramagnetic resonance; Dosimetria de radiaciones ionizantes por resonancia paramagnetica electronica

    Energy Technology Data Exchange (ETDEWEB)

    Azorin N, J. [UAM-I, Av. San Rafael Atlixco 186, 09340 Mexico D.F. (Mexico)

    2005-07-01

    In this work, some historical and theoretical aspects about the Electron Paramagnetic Resonance (EPR), its characteristics, the resonance detection, the paramagnetic species, the radiation effects on inorganic and organic materials, the diagrams of the instrumentation for the EPR detection, the performance of an EPR spectrometer, the coherence among EPR and dosimetry and, practical applications as well as in the food science there are presented. (Author)

  7. Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kovács, A.; Duchamp, M.; Boothroyd, C. B.; Dunin-Borkowski, R. E. [Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich (Germany); Ney, A.; Ney, V. [Institut für Halbleiter- und Festkörperphysik, Johannes Kepler Universität, Altenberger Str. 69, 4040 Linz (Austria); Galindo, P. L. [Departamento de Ingeniería Informática, Universidad de Cádiz, 11510 Cádiz (Spain); Kaspar, T. C.; Chambers, S. A. [Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354 (United States)

    2013-12-28

    We study planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al{sub 2}O{sub 3}), as well as the Co:ZnO/Al{sub 2}O{sub 3} interface, using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy. Co:ZnO samples that were deposited using pulsed laser deposition and reactive magnetron sputtering are both found to contain extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3–4 Co:ZnO layers next to the Al{sub 2}O{sub 3} substrate. The stacking fault density is in the range of 10{sup 17} cm{sup −3}. We also measure the local lattice distortions around the stacking faults. It is shown that despite the relatively high density of planar defects, lattice distortions, and small compositional variation, the Co:ZnO films retain paramagnetic properties.

  8. Electron paramagnetic resonance of radicals and metal complexes. 2. international conference of the Polish EPR Association. Warsaw 9-13 September 1996

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1996-12-31

    The conference of Electron Paramagnetic Resonance of Radicals and Metal Complexes has been held in Warsaw from 9 to 13 September 1996. It was the Second International Conference of the Polish EPR Association. The very extensive group of systems containing paramagnetic species has been studied by means of ESR or other magnetic techniques like ENDOR, Spin Echo etc. By radiation or photochemically generated radicals have been stabilized in low temperatures or being detected by means of very fast pulsed techniques. The chemical reactions, reaction kinetics of radicals as well as spin interaction with matrices have been studied and discussed. Over 100 lectures and posters have been presented.

  9. Critical Electron-Paramagnetic-Resonance Spin Dynamics in NiCl2

    DEFF Research Database (Denmark)

    Birgeneau, R.J.; Rupp, L.W.; Guggenheim, H.J.;

    1973-01-01

    We have studied the critical behavior of the electron-paramagnetic-resonance linewidth in the planar XY antiferromagnet NiCl2; it is found that the linewidth diverges like ξ∼(T-TN)-0.7 rather than ξ5/2 predicted by the current random-phase-approximation theory.......We have studied the critical behavior of the electron-paramagnetic-resonance linewidth in the planar XY antiferromagnet NiCl2; it is found that the linewidth diverges like ξ∼(T-TN)-0.7 rather than ξ5/2 predicted by the current random-phase-approximation theory....

  10. Electron paramagnetic resonance and quantitative color investigations of various vacuum heat treated wood species

    Directory of Open Access Journals (Sweden)

    E.I. Kondratyeva, K.R. Safiullin, I.G. Motygullin, A.V. Klochkov, M.S. Tagirov, V.V. Kuzmin

    2015-12-01

    Full Text Available The effect of the heat treatment duration on the electron paramagnetic resonance signal amplitude of free radicals for various wood species was observed. It was found that the amplitude of the electron paramagnetic resonance signal grows linearly with the vacuum heat treatment duration. The quantitative measurements of color changes for various wood species (pine, spruce, larch, birch and small-leaved lime were performed. It is found that results of EPR experiments and color measurements of heat treated samples correlate with each other.

  11. The Effect of Electronic Paramagnetism on Nuclear Magnetic Resonance Frequencies in Metals

    Science.gov (United States)

    Townes, C. H.; Herring, C.; Knight, W. D.

    1950-09-22

    Observations on the shifts of nuclear resonances in metals ( Li{sup 7}, Na{sup 23}, Cu {sup 63}, Be{sup 9}, Pb{sup 207}, Al{sup 27}, and Ca{sup 69} ) due to free electron paramagnetism; comparison with theoretical values.

  12. (Pulsed electron beam precharger)

    Energy Technology Data Exchange (ETDEWEB)

    Finney, W.C. (ed.); Shelton, W.N.

    1990-01-01

    This report discusses the following topics on electron beam guns: Precharger Modification; Installation of Charge vs. Radius Apparatus; High Concentration Aerosol Generation; and Data Acquisition and Analysis System.

  13. Biophysical Characterisation of Globins and Multi-Heme Cytochromes Using Electron Paramagnetic Resonance and Optical Spectroscopy

    Science.gov (United States)

    Desmet, Filip

    Heme proteins of different families were investigated in this work, using a combination of pulsed and continuous-wave electron paramagnetic resonance (EPR) spectroscopy, optical absorption spectroscopy, resonance Raman spectroscopy and laser flash photolysis. The first class of proteins that were investigated, were the globins. The globin-domain of the globin-coupled sensor of the bacterium Geobacter sulfurreducens was studied in detail using different pulsed EPR techniques (HYSCORE and Mims ENDOR). The results of this pulsed EPR study are compared with the results of the optical investigation and the crystal structure of the protein. The second globin, which was studied, is the Protoglobin of Methanosarcina acetivorans, various mutants of this protein were studied using laser flash photolysis and Raman spectroscopy to unravel the link between this protein's unusual structure and its ligand-binding kinetics. In addition to this, the CN -bound form of this protein was investigated using EPR and the influence of the strong deformation of the heme on the unusual low gz values is discussed. Finally, the neuroglobins of three species of fishes, Danio rerio, Dissostichus mawsoni and Chaenocephalus aceratus are studied. The influence of the presence or absence of two cysteine residues in the C-D and D-region of the protein on the EPR spectrum, and the possible formation of a disulfide bond is studied. The second group of proteins that were studied in this thesis belong to the family of the cytochromes. First the Mouse tumor suppressor cytochrome b561 was studied, the results of a Raman and EPR investigation are compared to the Human orthologue of the protein. Secondly, the tonoplast cytochrome b561 of Arabidopsis was investigated in its natural form and in two double-mutant forms, in which the heme at the extravesicular side was removed. The results of this investigation are then compared with two models in literature that predict the localisation of the hemes in this

  14. Pulsed electron beam precharger

    Energy Technology Data Exchange (ETDEWEB)

    Finney, W.C. (ed.); Shelton, W.N.

    1991-01-01

    Electron beam precharging of a high resistivity aerosol was successfully demonstrated during this reporting period (Quarters Five and Six). The initial E-beam particle precharging experiments completed this term were designed to confirm and extend some of the work performed under the previous contract. There are several reasons for doing this: (1) to re-establish a baseline performance criterion for comparison to other runs, (2) to test several recently upgraded or repaired subsystems, and (3) to improve upon the collection efficiency of the electron beam precipitator when testing precharging effectiveness with a very high resistivity, moderate-to-high concentration dust load. In addition, these shakedown runs were used to determine a set of suitable operational parameters for the wind tunnel, the electrostatic collecting sections, and the MINACC E-beam accelerator. These parameters will generally be held constant while the precharging parameters are varied to produce an optimum particle charge.

  15. Pulsed electron beam precharger

    Energy Technology Data Exchange (ETDEWEB)

    Finney, W.C. (ed.); Shelton, W.N.

    1991-01-01

    During the previous reporting period (Quarter Six), the charging and removal of a fine, high resistivity aerosol using the advanced technology of electron beam precipitation was successfully accomplished. Precharging a dust stream circulating through the EBP wind tunnel produced collection efficiency figures of up to 40 times greater than with corona charging and collection alone (Table 1). The increased system collection efficiency attributed to electron beam precharging was determined to be the result of increased particle charge. It was found that as precharger electric field was raised, collection efficiency became greater. In sequence, saturation particle charge varies with the precharger electric field strength, particle migration velocity varies with the precharger and collector electric field, and collection efficiency varies with the migration velocity. Maximizing the system collection efficiency requires both a high charging electric field (provided by the E-beam precharger), and a high collecting electric field (provided by the collector wires and plates). Because increased particle collection efficiency is directly attributable to higher particle charge, the focus of research during Quarter Seven was shifted to learning more about the actual charge magnitude on the aerosol particles. Charge determinations in precipitators have traditionally been made on bulk dust samples collected from the flue gas stream, which gives an overall charge vs. mass (Q/M) ratio measurement. More recently, techniques have been developed which allow the measurement of the charge on individual particles in a rapid and repeatable fashion. One such advanced technique has been developed at FSU for use in characterizing the electron beam precharger.

  16. Handbook of multifrequency electron paramagnetic resonance data and techniques

    CERN Document Server

    Misra, Sushil K

    2014-01-01

    This handbook is aimed to deliver an up-to-date account of some of the recently developed experimental and theoretical methods in EPR, as well as a complete up-to-date listing of the experimentally determined values of multifrequency transition-ion spin Hamiltonian parameters by Sushil Misra, reported in the past 20 years, extending such a listing published by him in the Handbook on Electron Spin Resonance, volume 2. This extensive data tabulation makes up roughly 60% of the book`s content. It is complemented by the first full compilation of hyperfine splittings and g-factors for aminoxyl (nit

  17. Electron paramagnetic resonance and FT-IR spectroscopic studies of glycine anhydride and betaine hydrochloride

    Science.gov (United States)

    Halim Başkan, M.; Kartal, Zeki; Aydın, Murat

    2015-12-01

    Gamma irradiated powders of glycine anhydride and betaine hydrochloride have been investigated at room temperature by electron paramagnetic resonance (EPR). In these compounds, the observed paramagnetic species were attributed to the R1 and R2 radicals, respectively. It was determined that the free electron interacted with environmental protons and 14N nucleus in both radicals. The EPR spectra of gamma irradiated powder samples remained unchanged at room temperature for two weeks after irradiation. Also, the Fourier Transform Infrared (FT-IR), FT-Raman and thermal analyses of both compounds were investigated. The functional groups in the molecular structures of glycine anhydride and betaine hydrochloride were identified by vibrational spectroscopies (FT-IR and FT-Raman).

  18. Thermally stimulated luminescence and electron paramagnetic resonance studies on uranium doped calcium phosphate

    CERN Document Server

    Natarajan, V; Veeraraghavan, R; Sastry, M D

    2003-01-01

    Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies on uranium doped calcium phosphate yielded mechanistic information on the observed glow peaks at 365, 410 and 450 K. TSL spectral studies of the glow peaks showed that UO sub 2 sup 2 sup + acts as the luminescent center. Electron paramagnetic resonance studies on gamma-irradiated samples revealed that the predominant radiation induced centers are H sup 0 , PO sub 4 sup 2 sup - , PO sub 3 sup 2 sup - and O sup - ion. Studies on the temperature dependence studies of the EPR spectra of samples annealed to different temperatures indicate the role of H sup 0 and PO sub 4 sup 2 sup - ions in the main glow peak at 410 K.

  19. Electronic correlations at the alpha-gamma structural phase transition in paramagnetic iron

    OpenAIRE

    Leonov, I.; Poteryaev, A. I.; Anisimov, V. I.; Vollhardt, D.

    2010-01-01

    We compute the equilibrium crystal structure and phase stability of iron at the alpha(bcc)-gamma(fcc) phase transition as a function of temperature, by employing a combination of ab initio methods for calculating electronic band structures and dynamical mean-field theory. The magnetic correlation energy is found to be an essential driving force behind the alpha-gamma structural phase transition in paramagnetic iron.

  20. Scaling craters in carbonates: Electron paramagnetic resonance analysis of shock damage

    OpenAIRE

    Polanskey, Carol A.; Ahrens, Thomas J.

    1994-01-01

    Carbonate samples from the 8.9-Mt nuclear (near-surface explosion) crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance (EPR). Samples from below the OAK apparent crater floor were obtained from six boreholes, as well as ejecta recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to spectra of Solenhofen and Kaibab limestone, which had been...

  1. Determining residual impurities in sapphire by means of electron paramagnetic resonance and nuclear activation analysis

    Science.gov (United States)

    Bletskan, D. I.; Bratus', V. Ya.; Luk'yanchuk, A. R.; Maslyuk, V. T.; Parlag, O. A.

    2008-07-01

    Sapphire (α-Al2O3) single crystals grown using the Verneuil and Kyropoulos methods have been analyzed using electron paramagnetic resonance and γ-ray spectroscopy with 12-MeV bremsstrahlung excitation. It is established that uncontrolled impurities in the final sapphire single crystals grown by the Kyropoulos method in molybdenum-tungsten crucibles are supplied both from the initial materials and from the furnace and crucible materials

  2. Electron spin resonance study of the demagnetization fields of the ferromagnetic and paramagnetic films

    Directory of Open Access Journals (Sweden)

    I.I. Gimazov, Yu.I. Talanov

    2015-12-01

    Full Text Available The results of the electron spin resonance study of the La1-xCaxMnO3 manganite and the diphenyl-picrylhydrazyl thin films for the magnetic field parallel and perpendicular to plane of the films are presented. The temperature dependence of the demagnetizing field is obtained. The parameters of the Curie-Weiss law are estimated for the paramagnetic thin film.

  3. In vivo pO2 imaging of tumors: Oxymetry with very low frequency Electron Paramagnetic Resonance

    Science.gov (United States)

    Epel, Boris; Halpern, Howard J.

    2016-01-01

    For over a century it has been known that tumor hypoxia, regions of a tumor with low levels of oxygenation, are important contributors to tumor resistance to radiation therapy and failure of radiation treatment of cancer. Recently, using novel pulse electron paramagnetic resonance (EPR) oxygen imaging, near absolute images of the partial pressure of oxygen (pO2) in tumors of living animals have been obtained. We discuss here the means by which EPR signals can be obtained in living tissues and tumors. We review development of EPR methods to image the pO2 in tumors and the potential for the pO2 image acquisition in human subjects. PMID:26477263

  4. Electron paramagnetic resonance study on n-type electron-irradiated 3C-SiC

    Energy Technology Data Exchange (ETDEWEB)

    Carlsson, P; Rabia, K; Son, N T; Janzen, E [Department of Physics, Chemistry and Biology, Linkoeping University, SE-581 83 Linkoeping (Sweden); Ohshima, T; Morishita, N; Itoh, H [Japan Atomic Energy Research Institute, Takasaki 370-1292 (Japan); Isoya, J [University of Tsukuba, Tsukuba 305-8550 (Japan)], E-mail: paca@ifm.liu.se

    2008-03-15

    Electron Paramagnetic Resonance (EPR) was used to study defects in n-type 3C-SiC films irradiated by 3-MeV electrons at room temperature with a dose of 2x10{sup 18} cm{sup -2}. After electron irradiation, two new EPR spectra with an effective spin S = 1, labeled L5 and L6, were observed. The L5 center has C{sub 3v} symmetry with g = 2.004 and a fine-structure parameter D = 436.5x10{sup -4} cm{sup -1}. The L5 spectrum was only detected under light illumination and it could not be detected after annealing at {approx}550{sup 0}C. The principal z-axis of the D tensor is parallel to the <111>-directions, indicating the location of spins along the Si-C bonds. Judging from the symmetry and the fact that the signal was detected under illumination in n-type material, the L5 center may be related to the divacancy in the neutral charge state. The L6 center has a C{sub 2v}-symmetry with an isotropic g-value of g = 2.003 and the fine structure parameters D = 547.7x10{sup -4} cm{sup -1} and E = 56.2x10{sup -4} cm{sup -1}. The L6 center disappeared after annealing at a rather low temperature ({approx}200 deg. C), which is substantially lower than the known annealing temperatures for vacancy-related defects in 3C-SiC. This highly mobile defect may be related to carbon interstitials.

  5. Electron paramagnetic resonance: a powerful tool to support magnetic resonance imaging research.

    Science.gov (United States)

    Danhier, Pierre; Gallez, Bernard

    2015-01-01

    The purpose of this paper is to describe some of the areas where electron paramagnetic resonance (EPR) has provided unique information to MRI developments. The field of application mainly encompasses the EPR characterization of MRI paramagnetic contrast agents (gadolinium and manganese chelates, nitroxides) and superparamagnetic agents (iron oxide particles). The combined use of MRI and EPR has also been used to qualify or disqualify sources of contrast in MRI. Illustrative examples are presented with attempts to qualify oxygen sensitive contrast (i.e. T1 - and T2 *-based methods), redox status or melanin content in tissues. Other areas are likely to benefit from the combined EPR/MRI approach, namely cell tracking studies. Finally, the combination of EPR and MRI studies on the same models provides invaluable data regarding tissue oxygenation, hemodynamics and energetics. Our description will be illustrative rather than exhaustive to give to the readers a flavour of 'what EPR can do for MRI'.

  6. Temperature dependence of Q-band electron paramagnetic resonance spectra of nitrosyl heme proteins

    Energy Technology Data Exchange (ETDEWEB)

    Flores, Marco; Wajnberg, Eliane; Bemski, George

    1997-11-01

    The Q-band (35 GHz) electron paramagnetic resonance (EPR) spectra of nitrosyl hemoglobin (Hb N O) and nitrosyl myoglobin (Mb NO) were studied as a function of temperature between 19 K and 200 K. The spectra of both heme proteins show classes of variations as a function of temperature. The first one has previously been associated with the existence of two paramagnetic species, one with rhombic and the other with axial symmetry. The second one manifests itself in changes in the g-factors and linewidths of each species. These changes are correlated with the conformational substates model and associate the variations of g-values with changes in the angle of the N(his)-Fe-N (NO) bond in the rhombic species and with changes in the distance between Fe and N of the proximal (F8) histidine in the axial species. (author) 24 refs., 6 figs.

  7. Paramagnetic defects induced by electron irradiation in barium hollandite ceramics for caesium storage.

    Science.gov (United States)

    Aubin-Chevaldonnet, V; Gourier, D; Caurant, D; Esnouf, S; Charpentier, T; Costantini, J M

    2006-04-26

    We have studied by electron paramagnetic resonance the mechanism of defect production by electron irradiation in barium hollandite, a material used for immobilization of radioactive caesium. The irradiation conditions were the closest possible to those occurring in Cs storage waste forms. Three paramagnetic defects were observed, independently of the irradiation conditions. A hole centre (H centre) is attributed to a superoxide ion O(2)(-) originating from hole trapping by interstitial oxygen produced by electron irradiation. An electron centre (E(1) centre) is attributed to a Ti(3+) ion adjacent to the resulting oxygen vacancy. Another electron centre (E(2) centre) is attributed to a Ti(3+) ion in a cation site adjacent to an extra Ba(2+) ion in a neighbouring tunnel, originating from barium displacement by elastic collisions. Comparison of the effects of external irradiations by electrons with the β-decay of Cs in storage waste forms is discussed. It is concluded that the latter would be dominated by E(1) and H centres rather than E(2) centres.

  8. High field electron paramagnetic resonance spectroscopy under ultrahigh vacuum conditions—A multipurpose machine to study paramagnetic species on well defined single crystal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Rocker, J.; Cornu, D.; Kieseritzky, E.; Hänsel-Ziegler, W.; Freund, H.-J. [Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin (Germany); Seiler, A. [Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin (Germany); Laboratorium für Applikationen der Synchrotronstrahlung, KIT Campus Süd, Kaiserstr. 12, 76131 Karlsruhe (Germany); Bondarchuk, O. [Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin (Germany); CIC energiGUNE, Parque Tecnologico, C/Albert Einstein 48, CP 01510 Minano (Alava) (Spain); Risse, T., E-mail: risse@chemie.fu-berlin.de [Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin (Germany); Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin (Germany)

    2014-08-01

    A new ultrahigh vacuum (UHV) electron paramagnetic resonance (EPR) spectrometer operating at 94 GHz to investigate paramagnetic centers on single crystal surfaces is described. It is particularly designed to study paramagnetic centers on well-defined model catalysts using epitaxial thin oxide films grown on metal single crystals. The EPR setup is based on a commercial Bruker E600 spectrometer, which is adapted to ultrahigh vacuum conditions using a home made Fabry Perot resonator. The key idea of the resonator is to use the planar metal single crystal required to grow the single crystalline oxide films as one of the mirrors of the resonator. EPR spectroscopy is solely sensitive to paramagnetic species, which are typically minority species in such a system. Hence, additional experimental characterization tools are required to allow for a comprehensive investigation of the surface. The apparatus includes a preparation chamber hosting equipment, which is required to prepare supported model catalysts. In addition, surface characterization tools such as low energy electron diffraction (LEED)/Auger spectroscopy, temperature programmed desorption (TPD), and infrared reflection absorption spectroscopy (IRAS) are available to characterize the surfaces. A second chamber used to perform EPR spectroscopy at 94 GHz has a room temperature scanning tunneling microscope attached to it, which allows for real space structural characterization. The heart of the UHV adaptation of the EPR experiment is the sealing of the Fabry-Perot resonator against atmosphere. To this end it is possible to use a thin sapphire window glued to the backside of the coupling orifice of the Fabry Perot resonator. With the help of a variety of stabilization measures reducing vibrations as well as thermal drift it is possible to accumulate data for a time span, which is for low temperature measurements only limited by the amount of liquid helium. Test measurements show that the system can detect paramagnetic

  9. Infrared spectroscopic and electron paramagnetic resonance studies on Dy substituted magnesium ferrite

    Energy Technology Data Exchange (ETDEWEB)

    Bamzai, K.K., E-mail: kkbamz@yahoo.com [Crystal Growth and Materials Research Laboratory, Department of Physics and Electronics, University of Jammu, Jammu (India); Kour, Gurbinder; Kaur, Balwinder [Crystal Growth and Materials Research Laboratory, Department of Physics and Electronics, University of Jammu, Jammu (India); Arora, Manju; Pant, R.P. [National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi (India)

    2013-11-15

    Dysprosium substituted magnesium ferrite with composition MgDy{sub x}Fe{sub 2−x}O{sub 4} with 0.00≤x≤0.07 synthesized by the solid state reaction technique was subjected to Fourier transform infrared spectroscopy and electron paramagnetic resonance studies. Infrared spectrum analysis were carried out to confirm the spinel phase formation and to ascertain the cation distribution in the ferrite phase. The absorption spectra show two significant absorption bands between 400 and 1000 cm{sup −1} which are attributed to tetrahedral (A) and octahedral (B) sites of the spinel phase. The positions of bands were found to be composition dependent. Splitting of bands as well as appearance of shoulders shows the presence of Fe{sup 2+} ions in the system. The force constants for tetrahedral and octahedral sites were calculated and found to vary with Dy{sup 3+} ions content. Electron paramagnetic resonance spectra of these samples exhibit broad, asymmetric resonance signal due to Fe{sup 3+}/Dy{sup 3+} ions present in the host lattice. The spectra become broader with Dy{sup 3+} ions substitution in pure Mg-ferrite and this broadening is attributed to surface spin disorder (spin frustration) possibly coming from mainly antiferromagnetic interactions between the neighbouring spins in the magnetic grains. The weak superexchange interactions results in the broadening of the resonance line width and large g-value as compared to the free electron value. - Highlights: • Absorption bands between 400 and 1000 cm{sup −1} reveal the formation of spinel phase. • The force constant on tetrahedral and octahedral site is used to explain the bond length. • Electron paramagnetic resonance spectra exhibit broad, asymmetric resonance peaks. • Spin frustration in spinel ferrites is explained by the broadening of line width.

  10. Al-doped MgB2 materials studied using electron paramagnetic resonance and Raman spectroscopy

    Science.gov (United States)

    Bateni, Ali; Erdem, Emre; Repp, Sergej; Weber, Stefan; Somer, Mehmet

    2016-05-01

    Undoped and aluminum (Al) doped magnesium diboride (MgB2) samples were synthesized using a high-temperature solid-state synthesis method. The microscopic defect structures of Al-doped MgB2 samples were systematically investigated using X-ray powder diffraction, Raman spectroscopy, and electron paramagnetic resonance. It was found that Mg-vacancies are responsible for defect-induced peculiarities in MgB2. Above a certain level of Al doping, enhanced conductive properties of MgB2 disappear due to filling of vacancies or trapping of Al in Mg-related vacancy sites.

  11. Retrospective dosimetry of nail by Electron Paramagnetic Resonance; Dosimetria retrospectiva de unha por Ressonancia Paramagnetica Eletronica

    Energy Technology Data Exchange (ETDEWEB)

    Giannoni, Ricardo A., E-mail: giannoni@ird.gov.br [Instituto de Radioprotecao e Dosimetria (IRD/CNEN-RJ), Rio de Janeiro, RJ (Brazil); Rodrigues Junior, Orlando, E-mail: rodrijr@ipen.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2015-07-01

    The purpose of this study is to characterize samples of human nails, subjected to irradiation of high doses through Technical Electron Paramagnetic Resonance (EPR). The goal is to establish a dose/response relationship in order to assess dose levels absorbed by individuals exposed in radiation accidents situations, retrospectively. Samples of human nails were irradiated with gamma radiation, and received a dose of 20 Gy. EPR measurements performed on samples before irradiation identified EPR signals associated with defects caused by the mechanical action of the sample collection. After irradiation other species of free radicals, associated with the action of gamma radiation, have been identified.

  12. Ordering of PCDTBT revealed by time-resolved electron paramagnetic resonance spectroscopy of its triplet excitons.

    Science.gov (United States)

    Biskup, Till; Sommer, Michael; Rein, Stephan; Meyer, Deborah L; Kohlstädt, Markus; Würfel, Uli; Weber, Stefan

    2015-06-22

    Time-resolved electron paramagnetic resonance (TREPR) spectroscopy is shown to be a powerful tool to characterize triplet excitons of conjugated polymers. The resulting spectra are highly sensitive to the orientation of the molecule. In thin films cast on PET film, the molecules' orientation with respect to the surface plane can be determined, providing access to sample morphology on a microscopic scale. Surprisingly, the conjugated polymer investigated here, a promising material for organic photovoltaics, exhibits ordering even in bulk samples. Orientation effects may significantly influence the efficiency of solar cells, thus rendering proper control of sample morphology highly important.

  13. Low temperature electron paramagnetic resonance anomalies in Fe-based nanoparticles

    Science.gov (United States)

    Koksharov, Yu. A.; Gubin, S. P.; Kosobudsky, I. D.; Beltran, M.; Khodorkovsky, Y.; Tishin, A. M.

    2000-08-01

    A study of the electron paramagnetic resonance of Fe-based nanoparticles embedded in polyethylene matrix was performed as a function of temperature ranging from 3.5 to 500 K. Nanoparticles with a narrow size distribution were prepared by the high-velocity thermodestruction of iron-containing compounds. A temperature-driven transition from superparamagnetic to ferromagnetic resonance was observed for samples with different Fe content. The unusual behavior of the spectra at about 25 K is considered evidence of a spin-glass state in iron oxide nanoparticles.

  14. Single-ion anisotropy in the gadolinium pyrochlores studied by electron paramagnetic resonance

    Science.gov (United States)

    Glazkov, V. N.; Zhitomirsky, M. E.; Smirnov, A. I.; Krug von Nidda, H.-A.; Loidl, A.; Marin, C.; Sanchez, J.-P.

    2005-07-01

    The electron paramagnetic resonance is used to measure the single-ion anisotropy of Gd3+ ions in the pyrochlore structure of (Y1-xGdx)2Ti2O7 . A rather strong easy-plane-type anisotropy is found. The anisotropy constant D is comparable to the exchange integral J in the prototype Gd2Ti2O7 , D≃0.75J , and exceeds the dipolar energy scale. Physical implications of an easy-plane anisotropy for a pyrochlore antiferromagnet are considered. We calculate the magnetization curves at T=0 and discuss phase transitions in a magnetic field.

  15. Spin Labeling and Characterization of Tau Fibrils Using Electron Paramagnetic Resonance (EPR).

    Science.gov (United States)

    Meyer, Virginia; Margittai, Martin

    2016-01-01

    Template-assisted propagation of Tau fibrils is essential for the spreading of Tau pathology in Alzheimer's disease. In this process, small seeds of fibrils recruit Tau monomers onto their ends. The physical properties of the fibrils play an important role in their propagation. Here, we describe two different electron paramagnetic resonance (EPR) techniques that have provided crucial insights into the structure of Tau fibrils. Both techniques rely on the site-directed introduction of one or two spin labels into the protein monomer. Continuous-wave (CW) EPR provides information on which amino acid residues are contained in the fibril core and how they are stacked along the long fibril axis. Double electron-electron resonance (DEER) determines distances between two spin labels within a single protein and hence provides insights into their spatial arrangement in the fibril cross section. Because of the long distance range accessible to DEER (~2-5 nm) populations of distinct fibril conformers can be differentiated.

  16. Application of electron paramagnetic resonance spectroscopy for validation of the novel (AN+DN) solvent polarity scale.

    Science.gov (United States)

    Malavolta, Luciana; Poletti, Erick F; Silva, Elias H; Schreier, Shirley; Nakaie, Clovis R

    2008-06-01

    Based on solvation studies of polymers, the sum (1:1) of the electron acceptor (AN) and electron donor (DN) values of solvents has been proposed as an alternative polarity scale. To test this, the electron paramagnetic resonance isotropic hyperfine splitting constant, a parameter known to be dependent on the polarity/proticity of the medium, was correlated with the (AN+DN) term using three paramagnetic probes. The linear regression coefficient calculated for 15 different solvents was approximately 0.9, quite similar to those of other well-known polarity parameters, attesting to the validity of the (AN+DN) term as a novel "two-parameter" solvent polarity scale.

  17. Application of electron paramagnetic resonance (EPR) spectroscopy and imaging in drug delivery research - chances and challenges.

    Science.gov (United States)

    Kempe, Sabine; Metz, Hendrik; Mäder, Karsten

    2010-01-01

    Electron Paramagnetic Resonance (EPR) spectroscopy is a powerful technique to study chemical species with unpaired electrons. Since its discovery in 1944, it has been widely used in a number of research fields such as physics, chemistry, biology and material and food science. This review is focused on its application in drug delivery research. EPR permits the direct measurement of microviscosity and micropolarity inside drug delivery systems (DDS), the detection of microacidity, phase transitions and the characterization of colloidal drug carriers. Additional information about the spatial distribution can be obtained by EPR imaging. The chances and also the challenges of in vitro and in vivo EPR spectroscopy and imaging in the field of drug delivery are discussed.

  18. Magnetometry and electron paramagnetic resonance studies of phosphine- and thiol-capped gold nanoparticles

    Science.gov (United States)

    Guerrero, E.; Muñoz-Márquez, M. A.; Fernández, A.; Crespo, P.; Hernando, A.; Lucena, R.; Conesa, J. C.

    2010-03-01

    In the last years, the number of studies performed by wholly independent research groups that confirm the permanent magnetism, first observed in our research lab, for thiol-capped Au nanoparticles (NPs) has rapidly increased. Throughout the years, the initial magnetometry studies have been completed with element-specific magnetization measurements based on, for example, the x-ray magnetic circular dichroism technique that have allowed the identification of gold as the magnetic moment carrier. In the research work here presented, we have focused our efforts in the evaluation of the magnetic behavior and iron impurities content in the synthesized samples by means of superconducting quantum interference device magnetometry and electron paramagnetic resonance spectrometry, respectively. As a result, hysteresis cycles typical of a ferromagnetic material have been measured from nominally iron-free gold NPs protected with thiol, phosphine, and chlorine ligands. It is also observed that for samples containing both, capped gold NPs and highly diluted iron concentrations, the magnetic behavior of the NPs is not affected by the presence of paramagnetic iron impurities. The hysteresis cycles reported for phosphine-chlorine-capped gold NPs confirm that the magnetic behavior is not exclusively for the metal-thiol system.

  19. Electron Paramagnetic Resonance of a Single NV Nanodiamond Attached to an Individual Biomolecule

    Science.gov (United States)

    Teeling-Smith, Richelle M.; Jung, Young Woo; Scozzaro, Nicolas; Cardellino, Jeremy; Rampersaud, Isaac; North, Justin A.; Šimon, Marek; Bhallamudi, Vidya P.; Rampersaud, Arfaan; Johnston-Halperin, Ezekiel; Poirier, Michael G.; Hammel, P. Chris

    2016-05-01

    A key limitation of electron paramagnetic resonance (EPR), an established and powerful tool for studying atomic-scale biomolecular structure and dynamics is its poor sensitivity, samples containing in excess of 10^12 labeled biomolecules are required in typical experiments. In contrast, single molecule measurements provide improved insights into heterogeneous behaviors that can be masked by ensemble measurements and are often essential for illuminating the molecular mechanisms behind the function of a biomolecule. We report EPR measurements of a single labeled biomolecule that merge these two powerful techniques. We selectively label an individual double-stranded DNA molecule with a single nanodiamond containing nitrogen-vacancy (NV) centers, and optically detect the paramagnetic resonance of NV spins in the nanodiamond probe. Analysis of the spectrum reveals that the nanodiamond probe has complete rotational freedom and that the characteristic time scale for reorientation of the nanodiamond probe is slow compared to the transverse spin relaxation time. This demonstration of EPR spectroscopy of a single nanodiamond labeled DNA provides the foundation for the development of single molecule magnetic resonance studies of complex biomolecular systems.

  20. Electron paramagnetic resonance of double perovskite Ba{sub 2}FeMoO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Gomez, Pablo [Dept. Electricidad y Electronica, Universidad de Valladolid, Valladolid (Spain); Almanza, Ovidio [Dept. Fisica, Universidad Nacional de Colombia, Ciudad Universitaria, Bogota D.C. (Colombia)

    2007-07-01

    In this work we present electron paramagnetic resonance (EPR) measurement of double perovskite Ba{sub 2}FeMoO{sub 6}. This type of materials are of great interest due to their simultaneous conducting and ferrimagnetic properties, being them able to use in practical devices for their giant magnetoresistance effect at room temperature The samples have been synthesized with standard ceramic route, with sintering temperature of 1200 C in a reducing He/H{sub 2} atmosphere. EPR measurements have been carried out in a Bruker spectrometer operating in X band, in the temperature range 80 to 400 K. Below Curie temperature the single line becomes asymmetric, broadens and shifts to lower fields with decreasing temperature. In the paramagnetic region the peak-to-peak intensity decreases sharply and the line broadens up to 340 K. The experimental data are compared with similar results of other double perovskites analyzed previously by other authors. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. Electron paramagnetic resonance (EPR) spectroscopy characterization of wheat grains from plants of different water stress tolerance.

    Science.gov (United States)

    Łabanowska, Maria; Filek, Maria; Kurdziel, Magdalena; Bednarska, Elżbieta; Dłubacz, Aleksandra; Hartikainen, Helina

    2012-09-01

    Grains of five genotypes of wheat (four Polish and one Finnish), differing in their tolerance to drought stress were chosen for this investigation. Electron paramagnetic resonance spectroscopy allowed observation of transition metal ions (Mn, Fe, Cu) and different types of stable radicals, including semiquinone centers, present in seed coats, as well as several types of carbohydrate radicals found mainly in the inner parts of grains. The content of paramagnetic metal centers was higher in sensitive genotypes (Radunia, Raweta) than in tolerant ones (Parabola, Nawra), whereas the Finnish genotype (Manu) exhibited intermediate amounts. Similarly, the concentrations of both types of radicals, carbohydrates and semiquinone were significantly higher in the grains originating from more sensitive wheat genotypes. The nature of carbohydrate radicals and their concentrations were confronted with the kinds and amounts of sugars found by the biochemical analyses and microscopy observations. It is suggested that some long lived radicals (semiquinone and starch radicals) occurring in grains could be indicators of stress resistance of wheat plants.

  2. Gd(3+)-Gd(3+) distances exceeding 3 nm determined by very high frequency continuous wave electron paramagnetic resonance.

    Science.gov (United States)

    Clayton, Jessica A; Qi, Mian; Godt, Adelheid; Goldfarb, Daniella; Han, Songi; Sherwin, Mark S

    2017-02-15

    Electron paramagnetic resonance spectroscopy in combination with site-directed spin labeling is a very powerful tool for elucidating the structure and organization of biomolecules. Gd(3+) complexes have recently emerged as a new class of spin labels for distance determination by pulsed EPR spectroscopy at Q- and W-band. We present CW EPR measurements at 240 GHz (8.6 Tesla) on a series of Gd-rulers of the type Gd-PyMTA-spacer-Gd-PyMTA, with Gd-Gd distances ranging from 1.2 nm to 4.3 nm. CW EPR measurements of these Gd-rulers show that significant dipolar broadening of the central |-1/2〉 → |1/2〉 transition occurs at 30 K for Gd-Gd distances up to ∼3.4 nm with Gd-PyMTA as the spin label. This represents a significant extension for distances accessible by CW EPR, as nitroxide-based spin labels at X-band frequencies can typically only access distances up to ∼2 nm. We show that this broadening persists at biologically relevant temperatures above 200 K, and that this method is further extendable up to room temperature by immobilizing the sample in glassy trehalose. We show that the peak-to-peak broadening of the central transition follows the expected 1/r(3) dependence for the electron-electron dipolar interaction, from cryogenic temperatures up to room temperature. A simple procedure for simulating the dependence of the lineshape on interspin distance is presented, in which the broadening of the central transition is modeled as an S = 1/2 spin whose CW EPR lineshape is broadened through electron-electron dipolar interactions with a neighboring S = 7/2 spin.

  3. Distance measurements between paramagnetic centers and a planar object by matrix Mims electron nuclear double resonance

    Science.gov (United States)

    Zänker, Paul-Philipp; Jeschke, Gunnar; Goldfarb, Daniella

    2005-01-01

    Frequency-domain electron nuclear double resonance (ENDOR), two time-domain electron nuclear double resonance techniques, and electron spin echo envelope modulation spectroscopy are compared with respect to their merit in measurements of small hyperfine couplings to nuclei with intermediate gyromagnetic ratio such as 31P. The frequency-domain Mims ENDOR experiment is found to provide the most faithful line shapes. In the limit of long electron-nuclear distances of more than 0.5 nm, sensitivity of this experiment is optimized by matching the first interpulse delay to the transverse relaxation time of the electron spins. In the same limit, Mims ENDOR efficiency scales inversely with the sixth power of distance. Hyperfine splittings as small as 33 kHz can be detected, corresponding to an electron-31P distance of 1 nm. In systems, where a certain kind of nuclei is distributed in a plane, measurements of intermolecular hyperfine couplings can be analyzed in terms of a distance of closest approach of a paramagnetic center to that plane. By applying this technique to spin-labeled lipids in a fully hydrated lipid bilayer it is found that for a fraction of lipids, chain tilt angles can be 25° larger than the mean tilt angle of the lipid chains. This model of all-trans hydrocarbon chains with a broad distribution of tilt angles is also consistent with orientation selection effects in high-field ENDOR spectra.

  4. Time-resolved electron paramagnetic resonance of radical pair intermediates in cryptochromes

    Science.gov (United States)

    Biskup, Till

    2013-12-01

    Electron transfer plays a key role in many biological systems, including core complexes of photosynthesis and respiration. As this involves unpaired electron spins, electron paramagnetic resonance (EPR) is the method of choice to investigate such processes. Systems that show photo-induced charge separation and electron transfer are of particular interest, as here the processes can easily be synchronised to the experiment and therefore followed directly over its time course. One particular class of proteins, the cryptochromes, showing charge separation and in turn spin-correlated radical pairs upon excitation with blue light, have been investigated by time-resolved EPR spectroscopy in great detail and the results obtained so far are summarised in this contribution. Highlights include the first observation of spin-correlated radical pairs in these proteins, a fact with great impact on the proposed role as key part of a magnetic compass of migratory birds, as well as the assignment of the radical-pair partners and the unravelling of alternative and unexpected electron transfer pathways in these proteins, giving new insights into aspects of biological electron transfer itself.

  5. An electron paramagnetic resonance study of PP and PP/SBS blends irradiated with gamma rays

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Pedro E-mail: silva@ivic.ve; Albano, Carmen; Perera, Rosestela; Gonzalez, Jeanette; Ichazo, Miren

    2004-11-01

    Electron paramagnetic resonance (EPR) measurements of Polypropylene (PP) and its blends with a Styrene-Butadiene-Styrene (SBS) copolymer in 10, 20, 30 and 40 wt.% of SBS were carried out. The samples were irradiated in the 0{<=}D{<=}100 kGy range at a dose rate of 4.8 kGy/h. Typical spectra indicative of the formation of peroxy and alkyl radicals were obtained. The dynamics of formation and recombination of radicals in these samples could be explained using a mixed zero and first order generation-recombination fit of the total spin concentration as a function of the integral dose. The time dependence of the spin concentration was studied assuming a mixed first order fit in the decay process. The parameters obtained from the fitting are interpreted in terms of the rate of formation of free radicals at the irradiation time and in terms of the decay time of the total free radical concentration.

  6. Age of an Indonesian Fossil Tooth Determined by Electron Paramagnetic Resonance

    Energy Technology Data Exchange (ETDEWEB)

    Bogard, JS

    2004-04-07

    The first fossil hominid tooth recovered during 1999 excavations from the Cisanca River region in West Java, Indonesia, was associated with a series of bovid teeth from a single individual that was recovered 190 cm beneath the hominid tooth. The age of the fossil bovid teeth was determined using electron paramagnetic resonance (EPR) analysis as part of an effort to bracket the age of the hominid tooth. The EPR-derived age of the bovid teeth is (5.16 {+-} 2.01) x 10{sup 5} years. However, the age estimate reported here is likely an underestimate of the actual age of deposition since evidence of heating was detected in the EPR spectra of the bovid teeth, and the heating may have caused a decrease in the intensity of EPR components on which the age calculation is based.

  7. Imaging thiol redox status in murine tumors in vivo with rapid-scan electron paramagnetic resonance

    Science.gov (United States)

    Epel, Boris; Sundramoorthy, Subramanian V.; Krzykawska-Serda, Martyna; Maggio, Matthew C.; Tseytlin, Mark; Eaton, Gareth R.; Eaton, Sandra S.; Rosen, Gerald M.; Kao, Joseph P. Y.; Halpern, Howard J.

    2017-03-01

    Thiol redox status is an important physiologic parameter that affects the success or failure of cancer treatment. Rapid scan electron paramagnetic resonance (RS EPR) is a novel technique that has shown higher signal-to-noise ratio than conventional continuous-wave EPR in in vitro studies. Here we used RS EPR to acquire rapid three-dimensional images of the thiol redox status of tumors in living mice. This work presents, for the first time, in vivo RS EPR images of the kinetics of the reaction of 2H,15N-substituted disulfide-linked dinitroxide (PxSSPx) spin probe with intracellular glutathione. The cleavage rate is proportional to the intracellular glutathione concentration. Feasibility was demonstrated in a FSa fibrosarcoma tumor model in C3H mice. Similar to other in vivo and cell model studies, decreasing intracellular glutathione concentration by treating mice with L-buthionine sulfoximine (BSO) markedly altered the kinetic images.

  8. Dosimetric evaluation of sodium carbonate (Na2CO3) by electronic paramagnetic resonance

    Science.gov (United States)

    Ureña-Núñez, F.; Dávila Ballesteros, M. R.

    This work presents the possibility to use the electron paramagnetic resonance (EPR) signal of gamma-irradiated sodium carbonate for dosimetric purposes. The dosimeters were irradiated in a 60Co source. The process induced in sodium carbonate by gamma rays results in the formation of carboxil radical anions img style="vertical-align: text-bottom;" class="inlinematheqn" src="/ampp/image?path=/713648881/910447398/grad_a_327316_o_ilm0001.gif" alt="./GRAD_A_327316_O_XML_IMAGES/GRAD_A_327316_O_ILM0001.gif" border="0" /> . This way, the method is based on the evaluation of the EPR signal of these radical anions in the material. The aspects studied were peak-to-peak signal amplitude as a function of received dose, signal fading, signal repeatability, sample homogeneity, zero response and environmental effects. It has been concluded that sodium carbonate can be used as a sensitive material to gamma radiation.

  9. High-Frequency Electron Paramagnetic Resonance Spectroscopy of Nitroxide-Functionalized Nanodiamonds in Aqueous Solution.

    Science.gov (United States)

    Akiel, R D; Stepanov, V; Takahashi, S

    2016-06-21

    Nanodiamond (ND) is an attractive class of nanomaterial for fluorescent labeling, magnetic sensing of biological molecules, and targeted drug delivery. Many of those applications require tethering of target biological molecules on the ND surface. Even though many approaches have been developed to attach macromolecules to the ND surface, it remains challenging to characterize dynamics of tethered molecule. Here, we show high-frequency electron paramagnetic resonance (HF EPR) spectroscopy of nitroxide-functionalized NDs. Nitroxide radical is a commonly used spin label to investigate dynamics of biological molecules. In the investigation, we developed a sample holder to overcome water absorption of HF microwave. Then, we demonstrated HF EPR spectroscopy of nitroxide-functionalized NDs in aqueous solution and showed clear spectral distinction of ND and nitroxide EPR signals. Moreover, through EPR spectral analysis, we investigate dynamics of nitroxide radicals on the ND surface. The demonstration sheds light on the use of HF EPR spectroscopy to investigate biological molecule-functionalized nanoparticles.

  10. Ion exchange in alginate gels--dynamic behaviour revealed by electron paramagnetic resonance.

    Science.gov (United States)

    Ionita, Gabriela; Ariciu, Ana Maria; Smith, David K; Chechik, Victor

    2015-12-14

    The formation of alginate gel from low molecular weight alginate and very low molecular weight alginate in the presence of divalent cations was investigated using Electron Paramagnetic Resonance (EPR) spectroscopy. The transition from sol to gel in the presence of divalent cations was monitored by the changes in the dynamics of spin labelled alginate. The immobilisation of the spin labelled alginate in the gel reflects the strength of interaction between the cation and alginate chain. Diffusion experiments showed that both the cation and alginate polyanion in the gel fibres can exchange with molecules in solution. In particular, we showed that dissolved alginate polyanions can replace alginates in the gel fibres, which can hence diffuse through the bulk of the gel. This illustrates the surprisingly highly dynamic nature of these gels and opens up the possibility of preparing multicomponent alginate gels via polyanion exchange process.

  11. New Experimental Limit on the Electric Dipole Moment of the Electron in a Paramagnetic Insulator

    CERN Document Server

    Kim, Y J; Lamoreaux, S K; Visser, G; Kunkler, B; Matlashov, A V; Kunkler, B

    2011-01-01

    We report results of an experimental search for the intrinsic Electric Dipole Moment (EDM) of the electron using a solid-state technique. The experiment employs a paramagnetic, insulating gadolinium gallium garnet (GGG) that has a large magnetic response at low temperatures. The presence of the eEDM would lead to a small but non-zero magnetization as the GGG sample is subject to a strong electric field. We search for the resulting Stark-induced magnetization with a sensitive magnetometer. Recent progress on the suppression of several sources of background allows the experiment to run free of spurious signals at the level of the statistical uncertainties. We report our first limit on the eEDM of $(-5.57 \\pm 7.98 \\pm 0.12)\\times10^{-25}$e$\\cdot$cm with 5 days of data averaging.

  12. Identification and Quantification of Copper Sites in Zeolites by Electron Paramagnetic Resonance Spectroscopy

    DEFF Research Database (Denmark)

    Godiksen, Anita; Vennestrøm, Peter N. R.; Rasmussen, Søren Birk

    2016-01-01

    Recent quantitative electron paramagnetic resonance spectroscopy (EPR) data on different copper species present in copper exchanged CHA zeolites are presented and put into context with the literature on other copper zeolites. Results presented herein were obtained using ex situ and in situ EPR...... on copper ion exchanged into a CHA zeolite with Si/Al = 14 ± 1 to obtain Cu/Al = 0.46 ± 0.02. The results shed light on the identity of different copper species present after activation in air. Since the EPR signal is quantifiable, the content of the different EPR active species has been elucidated and Cu2...... information about the reactivity and the quantity of some of the otherwise EPR silent species. In this way the [Cu–OH]+ species in copper substituted low-Al zeolites has been indirectly observed and quantified. EPR active Cu2+ species have been followed under reduction and oxidation with gas mixtures relevant...

  13. Growth Kinetics of the S Sub H Center on Magnesium Oxide Using Electron Paramagnetic Resonance

    Science.gov (United States)

    Jayne, J. P.

    1971-01-01

    Electron paramagnetic resonance spectroscopy was used to study the growth of S sub H centers on magnesium oxide powder which had hydrogen adsorbed on its surface. The centers were produced by ultraviolet radiation. The effects of both radiation intensity and hydrogen pressure were also studied. At constant hydrogen pressure and radiation dose, the initial S sub H center growth rate was found to be zero order. Beyond the initial region the growth rate deviated from zero order and finally approached saturation. The results are interpreted in terms of a model which assumes that the S sub H center is a hydrogen atom associated with a surface vacancy. Saturation appears to result from a limited supply of surface vacancies.

  14. Electron paramagnetic resonance spectroscopy in radiation research: Current status and perspectives

    Directory of Open Access Journals (Sweden)

    Sudha Rana

    2010-01-01

    Full Text Available Exposure to radiation leads to a number of health-related malfunctions. Ionizing radiation is more harmful than non-ionizing radiation, as it causes both direct and indirect effects. Irradiation with ionizing radiation results in free radical-induced oxidative stress. Free radical-mediated oxidative stress has been implicated in a plethora of diseased states, including cancer, arthritis, aging, Parkinson′s disease, and so on. Electron Paramagnetic Resonance (EPR spectroscopy has various applications to measure free radicals, in radiation research. Free radicals disintegrate immediately in aqueous environment. Free radicals can be detected indirectly by the EPR spin trapping technique in which these forms stabilize the radical adduct and produce characteristic EPR spectra for specific radicals. Ionizing radiation-induced free radicals in calcified tissues, for example, teeth, bone, and fingernail, can be detected directly by EPR spectroscopy, due to their extended stability. Various applications of EPR in radiation research studies are discussed in this review.

  15. Study of free radicals in gamma irradiated cellulose of cultural heritage materials using Electron Paramagnetic Resonance

    Science.gov (United States)

    Kodama, Yasko; Rodrigues, Orlando, Jr.; Garcia, Rafael Henrique Lazzari; Santos, Paulo de Souza; Vasquez, Pablo A. S.

    2016-07-01

    Main subject of this article was to study room temperature stable radicals in Co-60 gamma irradiated contemporary paper using Electron Paramagnetic Resonance spectrometer (EPR). XRD was used to study the effect of ionizing radiation on the morphology of book paper. SEM images presented regions with cellulose fibers and regions with particles agglomeration on the cellulose fibers. Those agglomerations were rich in calcium, observed by EDS. XRD analysis confirmed presence of calcium carbonate diffraction peaks. The main objective of this study was to propose a method using conventional kinetics chemical reactions for the observed radical formed by ionizing radiation. Therefore, further analyses were made to study the half-life and the kinetics of the free radical created. This method can be suitably applied to study radicals on cultural heritage objects.

  16. Preliminary study for precision dosimetry using electron paramagnetic resonance (EPR) in radiotherapy applications

    Energy Technology Data Exchange (ETDEWEB)

    Shehzadi, N. N.; Kim, I. J.; Yi, C. Y. [Center for Ionizing Radiation, Korea Research for Standards and Science, Daejeon (Korea, Republic of)

    2015-10-15

    EPR (Electron paramagnetic resonance) dosimetry for radiotherapy dose range (1-10 Gy) is still being established.Alanine is an important material for EPR dosimetry because in terms of density and radiation absorption properties, it is water equivalent. High repeatability and high reproducibility of alanine spectrum measurement makes it possible to estimate the irradiation dose accurately. This baseline study has been carried out to establish precision EPR dosimetry in therapeutic photon range. For that purpose, an EPR dosimetry system has been setup and repeatability as well as reproducibility of measurements using alanine dosimeter have been evaluated. Effect of anisotropy of alanine dosimeter in spectrometer cavity has also been observed. EPR dosimetry system is set up at KRISS. It is found that reproducibility of the system at therapeutic photon range is 1.5 % - 6.6 %.

  17. Free radical scavenging activity of erdosteine metabolite I investigated by electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Braga, Pier Carlo; Culici, Maria; Dal Sasso, Monica; Falchi, Mario; Spallino, Alessandra

    2010-01-01

    The aim of this study was to explore the antiradical activity of Met I (an active metabolite of erdosteine) containing a pharmacologically active sulphydryl group, by means of electron paramagnetic resonance (EPR) spectroscopy which has not previously been used to characterize the antiradical activity of Met I. The effects of concentrations of 20, 10, 5, 2.5, 1.25 and 0.625 microg/ml of Met I were tested against: (a) the Fenton reaction model system with EPR detection of HO.; (b) the KO2-crown ether system with EPR detection of O2-.; (c) the EPR assay based on the reduction of the Tempol radical, and (d) the EPR assay based on the reduction of Fremy's salt radical. Our findings show that the intensity of 4 different free radicals was significantly reduced in the presence of Met I, thus indicating the presence of a termination reaction between the free radicals and Met I.

  18. A superheterodyne spectrometer for electronic paramagnetic. Resonance; Spectrometre superheterodyne de resonance paramagnetique electronique

    Energy Technology Data Exchange (ETDEWEB)

    Laffon, J.L. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1963-12-15

    After a few generalities about electron paramagnetic resonance, a consideration of different experimental techniques authorises the choice of a particular type of apparatus. An EPR superheterodyne spectrometer built in the laboratory and having a novel circuit is described in detail. With this apparatus, many experimental results have been obtained and some of these are described as example. (author) [French] Apres quelques generalites sur le phenomene de resonance paramagnetique electronique, une synthese des differentes techniques experimentales, permet de fixer le choix d'un type d'appareillage. Un spectrometre de RPE superheterodyne realise en laboratoire et comportant un circuit original est expose dans le detail. Cet appareil a permis de nombreux resultats experimentaux dont quelques-uns sont decrits a titre d'exemple. (auteur)

  19. Optically detected electron paramagnetic resonance by microwave modulated magnetic circular dichroism

    Science.gov (United States)

    Börger, Birgit; Bingham, Stephen J.; Gutschank, Jörg; Schweika, Marc Oliver; Suter, Dieter; Thomson, Andrew J.

    1999-11-01

    Electron paramagnetic resonance (EPR) can be detected optically, with a laser beam propagating perpendicular to the static magnetic field. As in conventional EPR, excitation uses a resonant microwave field. The detection process can be interpreted as coherent Raman scattering or as a modulation of the laser beam by the circular dichroism of the sample oscillating at the microwave frequency. The latter model suggests that the signal should show the same dependence on the optical wavelength as the MCD signal. We check this for two different samples [cytochrome c-551, a metalloprotein, and ruby (Cr3+:Al2O3)]. In both cases, the observed wavelength dependence is almost identical to that of the MCD signal. A quantitative estimate of the amplitude of the optically detected EPR signal from the MCD also shows good agreement with the experimental results.

  20. Electron paramagnetic resonance (EPR) investigations of lichens - 1: effects of air pollution

    Science.gov (United States)

    Jezierski, Adam; Bylinska, Ewa; Seaward, Mark R. D.

    Electron paramagnetic resonance (EPR) investigations were carried out on more than 800 samples of lichens from Lower Silesia, southwest Poland. A statistically confirmed correlation between annual average concentration of sulphur dioxide in the atmosphere and concentration of semiquinone radicals in Hypogymnia physodes thalli was found. Similar results were obtained for Umbilicaria species from the Karkonosze Mountains. Distribution of semiquinone radicals in lichen thalli was also investigated. The action of nitrogen dioxide on Umbilicaria species resulted in the synthesis of iminoxy radicals in the thalli. The intensification of the semiquinone free radical production in lichen thalli from atmospherically polluted environments and the degradation of lichen acids to β-diketone compounds would appear to be parallel processes. The properties of the iminoxyls derived from β-diketones in the lichen matrix (anisotropic spectra at room temperature) and in organic solutions after extraction procedure were also examined by EPR.

  1. Electron paramagnetic resonance (EPR) investigations of lichens - 1: effects of air pollution

    Energy Technology Data Exchange (ETDEWEB)

    Jezierski, A.; Bylinska, E.; Seaward, M.R.D. [University of Wroclaw, Wroclaw (Poland). Faculty of Chemistry

    1999-07-01

    The paper describes how electron paramagnetic resonance (EPR) investigations were carried out on more than 800 samples of lichens from Lower Silesia, southwest Poland. A statistically confirmed correlation between annual average concentration of sulphur dioxide in the atmosphere and concentration of semiquinone radicals in Hypogymnia physodes thalli was found. Similar results were obtained from Umbilicaria species from the Karkonoszo Mountains. Distribution of semiquinone radicals in lichen thalli was also investigated. the action of nitrogen dioxide on Umbilicaria species resulted in the synthesis of iminoxy radicals in the thalli. The intensification of the semiquinone free radical production in lichen thalli from atmospherically polluted environments and the degradation of lichen acids to beta-diketone compounds appeared to be parallel processes.

  2. Gd$^{3+}$ - Gd$^{3+}$ distances exceeding 3 nm determined by very high frequency continuous wave electron paramagnetic resonance

    CERN Document Server

    Clayton, Jessica A; Godt, Adelheid; Goldfarb, Daniella; Han, Songi; Sherwin, Mark S

    2016-01-01

    Electron paramagnetic resonance spectroscopy in combination with site-directed spin-labeling is a very powerful tool for elucidating the structure and organization of biomolecules. Gd$^{3+}$ complexes have recently emerged as a new class of spin labels for distance determination by pulsed EPR spectroscopy at Q- and W-band. We present CW EPR measurements at 240 GHz (8.6 Tesla) on a series of Gd-rulers of the type Gd-PyMTA---spacer---Gd-PyMTA, with Gd-Gd distances ranging from 1.2 nm to 4.3 nm. CW EPR measurements of these Gd-rulers show that significant dipolar broadening of the central $|-1/2\\rangle\\rightarrow|1/2\\rangle$ transition occurs at 30 K for Gd-Gd distances up to $\\sim$ 3.4 nm with Gd-PyMTA as the spin label. This represents a significant extension for distances accessible by CW EPR, as nitroxide-based spin labels at X-band frequencies can typically only access distances up to $\\sim$ 2 nm. We show that this broadening persists at biologically relevant temperatures above 200 K, and that this method i...

  3. High-frequency (95 GHz) electron paramagnetic resonance study of the photoinduced charge transfer in conjugated polymer-fullerene composites

    NARCIS (Netherlands)

    Ceuster, J. De; Goovaerts, E.; Bouwen, A.; Hummelen, J.C.; Dyakonov, V.

    2001-01-01

    Light-induced electron paramagnetic resonance (LEPR) measurements are reported in composites of poly(2-methoxy-5-(3-,7-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), a soluble derivative of C60. Under illumination of the sample, two

  4. Determination of very rapid molecular rotation by using the central electron paramagnetic resonance line.

    Science.gov (United States)

    Kurban, Mark R

    2013-02-21

    Picosecond rotational correlation times of perdeuterated tempone (PDT) are found in alkane and aromatic liquids by directly using the spectral width of the central electron paramagnetic resonance line. This is done by mathematically eliminating the nonsecular spectral density from the spectral parameter equations, thereby removing the need to assume a particular form for it. This is preferable to fitting a constant correction factor to the spectral density, because such a factor does not fit well in the low picosecond range. The electron-nuclear spin dipolar interaction between the probe and solvent is shown to be negligible for the very rapid rotation of PDT in these liquids at the temperatures of the study. The rotational correlation times obtained with the proposed method generally agree to within experimental uncertainty with those determined by using the traditional parameters. Using the middle line width offers greater precision and smoother trends. Previous work with the central line width is discussed, and past discrepancies are explained as possibly resulting from residual inhomogeneous broadening. The rotational correlation time almost forms a common curve across all of the solvents when plotted with respect to isothermal compressibility, which shows the high dependence of rotation on liquid free volume.

  5. Electron paramagnetic resonance study of a photosynthetic microbial mat and comparison with Archean cherts.

    Science.gov (United States)

    Bourbin, M; Derenne, S; Gourier, D; Rouzaud, J-N; Gautret, P; Westall, F

    2012-12-01

    Organic radicals in artificially carbonized biomass dominated by oxygenic and non-oxygenic photosynthetic bacteria, Microcoleus chthonoplastes-like and Chloroflexus-like bacteria respectively, were studied by Electron Paramagnetic Resonance (EPR) spectroscopy. The two bacteria species were sampled in mats from a hypersaline lake. They underwent accelerated ageing by cumulative thermal treatments to induce progressive carbonization of the biological material, mimicking the natural maturation of carbonaceous material of Archean age. For thermal treatments at temperatures higher than 620 °C, a drastic increase in the EPR linewidth is observed in the carbonaceous matter from oxygenic photosynthetic bacteria and not anoxygenic photosynthetic bacteria. This selective EPR linewidth broadening reflects the presence of a catalytic element inducing formation of radical aggregates, without affecting the molecular structure or the microstructure of the organic matter, as shown by Raman spectroscopy and Transmission Electron Microscopy. For comparison, we carried out an EPR study of organic radicals in silicified carbonaceous rocks (cherts) from various localities, of different ages (0.42 to 3.5 Gyr) and having undergone various degrees of metamorphism, i.e. various degrees of natural carbonization. EPR linewidth dispersion for the most primitive samples was quite significant, pointing to a selective dipolar broadening similar to that observed for carbonized bacteria. This surprising result merits further evaluation in the light of its potential use as a marker of past bacterial metabolisms, in particular oxygenic photosynthesis, in Archean cherts.

  6. Copper Environment in Artificial Metalloproteins Probed by Electron Paramagnetic Resonance Spectroscopy.

    Science.gov (United States)

    Flores, Marco; Olson, Tien L; Wang, Dong; Edwardraja, Selvakumar; Shinde, Sandip; Williams, JoAnn C; Ghirlanda, Giovanna; Allen, James P

    2015-10-29

    The design of binding sites for divalent metals in artificial proteins is a productive platform for examining the characteristics of metal-ligand interactions. In this report, we investigate the spectroscopic properties of small peptides and four-helix bundles that bind Cu(II). Three small peptides, consisting of 15 amino acid residues, were designed to have two arms, each containing a metal-binding site comprised of different combinations of imidazole and carboxylate side chains. Two four-helix bundles each had a binding site for a central dinuclear metal cofactor, with one design incorporating additional potential metal ligands at two identical sites. The small peptides displayed pH-dependent, metal-induced changes in the circular dichroism spectra, consistent with large changes in the secondary structure upon metal binding, while the spectra of the four-helix bundles showed a predominant α-helix content but only small structural changes upon metal binding. Electron paramagnetic resonance spectra were measured at X-band revealing classic Cu(II) axial patterns with hyperfine coupling peaks for the small peptides and four-helix bundles exhibiting a range of values that were related to the specific chemical natures of the ligands. The variety of electronic structures allow us to define the distinctive environment of each metal-binding site in these artificial systems, including the designed additional binding sites in one of the four-helix bundles.

  7. A versatile and modular quasi optics-based 200 GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument

    Science.gov (United States)

    Siaw, Ting Ann; Leavesley, Alisa; Lund, Alicia; Kaminker, Ilia; Han, Songi

    2016-03-01

    Solid-state dynamic nuclear polarization (DNP) at higher magnetic fields (>3 T) and cryogenic temperatures (∼2-90 K) has gained enormous interest and seen major technological advances as an NMR signal enhancing technique. Still, the current state of the art DNP operation is not at a state at which sample and freezing conditions can be rationally chosen and the DNP performance predicted a priori, but relies on purely empirical approaches. An important step towards rational optimization of DNP conditions is to have access to DNP instrumental capabilities to diagnose DNP performance and elucidate DNP mechanisms. The desired diagnoses include the measurement of the "DNP power curve", i.e. the microwave (MW) power dependence of DNP enhancement, the "DNP spectrum", i.e. the MW frequency dependence of DNP enhancement, the electron paramagnetic resonance (EPR) spectrum, and the saturation and spectral diffusion properties of the EPR spectrum upon prolonged MW irradiation typical of continuous wave (CW) DNP, as well as various electron and nuclear spin relaxation parameters. Even basic measurements of these DNP parameters require versatile instrumentation at high magnetic fields not commercially available to date. In this article, we describe the detailed design of such a DNP instrument, powered by a solid-state MW source that is tunable between 193 and 201 GHz and outputs up to 140 mW of MW power. The quality and pathway of the transmitted and reflected MWs is controlled by a quasi-optics (QO) bridge and a corrugated waveguide, where the latter couples the MW from an open-space QO bridge to the sample located inside the superconducting magnet and vice versa. Crucially, the versatility of the solid-state MW source enables the automated acquisition of frequency swept DNP spectra, DNP power curves, the diagnosis of MW power and transmission, and frequency swept continuous wave (CW) and pulsed EPR experiments. The flexibility of the DNP instrument centered around the QO MW

  8. Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kovacs, Andras; Ney, A.; Duchamp, Martial; Ney, V.; Boothroyd, Chris; Galindo, Pedro L.; Kaspar, Tiffany C.; Chambers, Scott A.; Dunin-Borkowski, Rafal

    2013-12-23

    We have studied planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al2O3) and the Co:ZnO/Al2O3 interface structure at atomic resolution using aberration-corrected transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). Comparing Co:ZnO samples deposited by pulsed laser deposition and reactive magnetron sputtering, both exhibit extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3-4 Co:ZnO layers at the interface.. In addition, we have measured the local strain which reveals the lattice distortion around the stacking faults.

  9. Disulfide-Linked Dinitroxides for Monitoring Cellular Thiol Redox Status through Electron Paramagnetic Resonance Spectroscopy.

    Science.gov (United States)

    Legenzov, Eric A; Sims, Stephen J; Dirda, Nathaniel D A; Rosen, Gerald M; Kao, Joseph P Y

    2015-12-01

    Intracellular thiol-disulfide redox balance is crucial to cell health, and may be a key determinant of a cancer's response to chemotherapy and radiation therapy. The ability to assess intracellular thiol-disulfide balance may thus be useful not only in predicting responsiveness of cancers to therapy, but in assessing predisposition to disease. Assays of thiols in biology have relied on colorimetry or fluorimetry, both of which require UV-visible photons, which do not penetrate the body. Low-frequency electron paramagnetic resonance imaging (EPRI) is an emerging magnetic imaging technique that uses radio waves, which penetrate the body well. Therefore, in combination with tailored imaging agents, EPRI affords the opportunity to image physiology within the body. In this study, we have prepared water-soluble and membrane-permeant disulfide-linked dinitroxides, at natural isotopic abundance, and with D,(15)N-substitution. Thiols such as glutathione cleave the disulfides, with simple bimolecular kinetics, to yield the monomeric nitroxide species, with distinctive changes in the EPR spectrum. Using the D,(15)N-substituted disulfide-dinitroxide and EPR spectroscopy, we have obtained quantitative estimates of accessible intracellular thiol in cultured human lymphocytes. Our estimates are in good agreement with published measurements. This suggests that in vivo EPRI of thiol-disulfide balance is feasible. Finally, we discuss the constraints on the design of probe molecules that would be useful for in vivo EPRI of thiol redox status.

  10. Electron paramagnetic resonance study of amphiphiles partitioning behavior in desiccation-tolerant moss during dehydration

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Desiccation tolerance is a crucial characteristic for desert moss surviving in arid regions. Desiccation procedure always induces amphiphiles transferring from the polar cytoplasm into lipid bodies. The behavior of amphiphiles transferring can contribute to the enhancement of desiccation tolerance and the reduction of plasma membrane integrity simultaneously. The effects of amphiphiles partitioning into the lipid phase during water loss has been studied for pollen and seeds using electron paramagnetic resonance (EPR) spectroscopy. However, desiccation-tolerant high plants occur among mosses, several angiosperms and higher plants seeds or pollens. They have different strategies for survival in dehydration and rehydration. A desiccation-tolerant moss Tortula desertorurn was used to investigate the behaviors of amphiphilic molecules during drying by spin label technology. There are small amount of amphiphilic probes partitioning into membrane during moss leaves dehydration, comparing with that in higher plants. Cytoplasm viscosity changed from 1.14 into glass state only dehydration less than 60 min. Moss leaves lost plasma membrane integrity slightly,from 0.115 to 0.237, occurred simultaneously with amphiphiles partition. The results showed the more advantages of mosses than higher plants in adapting fast dehydration. We propose that EPR spin label is feasible for studying the amphiphiles partitioning mechanisms in membrane protection and damage for desiccation-tolerant mosses.(C) 2007 Yan Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

  11. Electron Paramagnetic Resonance and Optical Absorption Studies on Copper Ions in Mixed Alkali Cadmium Phosphate Glasses

    Institute of Scientific and Technical Information of China (English)

    G.Giridhar; M.Rangacharyulu; R.V.S.S.N.Ravikumar; P.Sambasiva Rao

    2009-01-01

    Electron paramagnetic resonance (EPR) and optical absorption studies were carried out at room temperature on copper doped mixed alkali cadmium phosphate (LiNaCdP) glasses to understand the nature and symmetry of dopant. Three samples with varying concentrations of alkali ions have been prepared. The spin Hamiltonian parameters obtained from room temperature EPR spectra are: g||=2.437, g⊥=2.096, A||=117×10-4 cm-1, A⊥=26×10-4 cm-1 for LiNaCdP1, g||=2.441, g⊥=2.088, A||=121×10-4 cm-1, A⊥=25×10-4 cm-1 for LiNaCdP2 and g||=2.433, g⊥=2.096, A||=125×10-4 cm-1, A⊥=32×10-4 cm-1 for LiNaCdP3. These EPR results indicate that the dopant Cu2+ ion enters the glass matrix into a tetragonally elongated octahedral site. The bonding parameters evaluated by correlating optical and EPR data suggest that bonding between the central metal ion and ligands is partially covalent. The mixed alkali effect in cadmium phosphate glasses was reported.

  12. Electron paramagnetic resonance measurements of absorbed dose in teeth from citizens of Ozyorsk

    Energy Technology Data Exchange (ETDEWEB)

    Wieser, A.; Semiochkina, N. [Helmholtz Zentrum Muenchen - German Research Center for Environmental Health, Institute of Radiation Protection, Neuherberg (Germany); Vasilenko, E.; Aladova, E.; Smetanin, M. [Southern Urals Biophysics Institute, Ozyorsk (Russian Federation); Fattibene, P. [Istituto Superiore di Sanita, Rome (Italy)

    2014-05-15

    In 1945, within the frame of the Uranium Project for the production of nuclear weapons, the Mayak nuclear facilities were constructed at the Lake Irtyash in the Southern Urals, Russia. The nuclear workers of the Mayak Production Association (MPA), who lived in the city of Ozyorsk, are the focus of epidemiological studies for the assessment of health risks due to protracted exposure to ionising radiation. Electron paramagnetic resonance measurements of absorbed dose in tooth enamel have already been used in the past, in an effort to validate occupational external doses that were evaluated in the Mayak Worker Dosimetry System. In the present study, 229 teeth of Ozyorsk citizens not employed at MPA were investigated for the assessment of external background exposure in Ozyorsk. The annually absorbed dose in tooth enamel from natural background radiation was estimated to be (0.7 ± 0.3) mGy. For citizens living in Ozyorsk during the time of routine noble gas releases of the MPA, which peaked in 1953, the average excess absorbed dose in enamel above natural background was (36 ± 29) mGy, which is consistent with the gamma dose obtained by model calculations. In addition, there were indications of possible accidental gaseous MPA releases that affected the population of Ozyorsk, during the early and late MPA operation periods, before 1951 and after 1960. (orig.)

  13. Electron Paramagnetic Resonance and Mössbauer Spectra of Iron Ions in Bizen Pottery

    Science.gov (United States)

    Matsuoka, Yuki; Ikeya, Motoji

    1995-11-01

    Electron paramagnetic resonance (EPR) and Mössbauer spectra of Japanese traditional Bizen pottery and its constituent clays have been measured to study the relationship between the color of pottery surface and the relevant states of iron ions ( Fe3+ and Fe2+). Hyperfine signals of Mn2+, presumably in carbonates, and a broad signal at g=2.0 similar to that of hematite ( Fe2O3) were observed for good-quality clay, while a signal at g>9 similar to that of magnetite ( Fe3O4) was observed for poor-quality clay. In pottery, the apparent g-factor of g=4.3 due to a large orthorhombic distortion E(Sx2-Sy2) and g=6 due to a large axial field DSz2 were observed in addition to the broad signal around g=2 due to oxidation of iron into Fe2O3. Subtle change of colors resulted in the change of EPR spectra. Mössbauer spectra indicatcd that almost all of the iron ions at the surface of pottery are strongly oxidized into Fe3+ when the pottery is fired in oxidizing atmosphere, while those inside the pottery and at the surface fired at reducing atmosphere are not strongly oxidized into Fe3+.

  14. Electron paramagnetic resonance parameters and local structure for Gd3+ in KY3F10

    Indian Academy of Sciences (India)

    Shao-Yi Wu; Hua-Ming Zhang; Guang-Duo Lu; Zhi-Hong Zhang

    2007-09-01

    The electron paramagnetic resonance parameters, zero-field splittings (ZFSs) b$_{2}^{0}$, b$_{4}^{0}$, b$_{4}^{4}$, b$_{6}^{0}$, b$_{6}^{4}$ and the factors for Gd3+ on the tetragonal Y3+ site in KY3F10 are theoretically studied from the superposition model for the ZFSs and the approximation formula for the factor containing the admixture of the ground 8S7/2 and the excited 6L7/2 (L=P, D, F, G) states via the spin–orbit coupling interactions, respectively. By analysing the above ZFSs, the local structure information for the impurity Gd3+ is obtained, i.e., the impurity–ligand bonding angles related to the four-fold (C4) axis for the impurity Gd3+ center are found to be about 0.6° larger than those for the host Y3+ site in KY3F10. The calculated ZFSs based on the above angular distortion as well as the factors are in reasonable agreement with the observed values. The present studies on the ZFSs and the local structure would be helpful to understand the optical and magnetic properties of this material with Gd dopants.

  15. Characterization of molecular mobility in seed tissues: an electron paramagnetic resonance spin probe study.

    Science.gov (United States)

    Buitink, J; Hemminga, M A; Hoekstra, F A

    1999-06-01

    The relationship between molecular mobility (tauR) of the polar spin probe 3-carboxy-proxyl and water content and temperature was established in pea axes by electron paramagnetic resonance (EPR) and saturation transfer EPR. At room temperature, tauR increased during drying from 10(-11) s at 2.0 g water/g dry weight to 10(-4) s in the dry state. At water contents below 0.07 g water/g dry weight, tauR remained constant upon further drying. At the glass transition temperature, tauR was constant at approximately 10(-4) s for all water contents studied. Above Tg, isomobility lines were found that were approximately parallel to the Tg curve. The temperature dependence of tauR at all water contents studied followed Arrhenius behavior, with a break at Tg. Above Tg the activation energy for rotational motion was approximately 25 kJ/mol compared to 10 kJ/mol below Tg. The temperature dependence of tauR could also be described by the WLF equation, using constants deviating considerably from the universal constants. The temperature effect on tauR above Tg was much smaller in pea axes, as found previously for sugar and polymer glasses. Thus, although glasses are present in seeds, the melting of the glass by raising the temperature will cause only a moderate increase in molecular mobility in the cytoplasm as compared to a huge increase in amorphous sugars.

  16. Anthocyanin composition of wild Colombian fruits and antioxidant capacity measurement by electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Santacruz, Liliana; Carriazo, José G; Almanza, Ovidio; Osorio, Coralia

    2012-02-15

    The qualitative and quantitative anthocyanin composition of four wild tropical fruits from Colombia was studied. Compounds of "mora pequeña" ( Rubus megalococcus Focke.), "uva de árbol" ( Myrciaria aff. cauliflora O. Berg), coral, and motilón ( Hyeronima macrocarpa Mull. Arg.) fruits were separately extracted with methanol-acetic acid (95:5, v/v). The anthocyanin-rich extracts (AREs) were obtained by selective adsorption on Amberlite XAD-7. Each extract was analyzed by HPLC-PDA and HPLC-HRESI-MS(n) with LCMS-IT-TOF equipment in order to characterize the anthocyanin pigments and the coinjection in HPLC using standards allowed identifying the major constituents in each extract. The antioxidant activity was measured by electron paramagnetic resonance (EPR) and UV-vis spectroscopy, using ABTS and DPPH free radicals. The ARE of motilón ( H. macrocarpa Müll. Arg) exhibited the highest radical scavenging activity in comparison to the other extracts. A second-order kinetic model was followed in all of the cases. These results suggested that the studied fruits are promising not only as source of natural pigments but also as antioxidant materials for food industry.

  17. Temperature dependent electron paramagnetic resonance (EPR) of SrZrO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Santosh K., E-mail: santufrnd@gmail.com [Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai (India); Pathak, Nimai [Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai (India); Ghosh, P.S. [Materials Science Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Rajeshwari, B. [Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai (India); Materials Science Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Natarajan, V. [Materials Science Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Kadam, R.M. [Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai (India)

    2015-10-01

    SrZrO{sub 3} (SZO), a distorted perovskite was synthesized using gel-combustion route employing citric acid as a fuel and ammonium nitrate as oxidizer followed by characterization using X-ray diffraction (XRD) and electron paramagnetic resonance (EPR). Purity of the sample is confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis. Broadening and shift of the resonance field position in EPR spectrum to the lower field was observed as the temperature is lowered; which is the characteristic of ferromagnetic resonance spectra. The value of Curie–Weiss temperature obtained for SZO particles is 8.7 K. The positive sign of the Curie–Weiss temperature indicates that some of the spins are ferromagnetically coupled in this sample. Theoretical investigation using density functional theory (DFT) calculation revealed that Vacancy at zirconium site contribute maximum to the magnetic moment. - Highlights: • Gel-combustion synthesis of SrZrO{sub 3} perovskite at relatively low temperature. • EPR evidence for ferromagnetic resonance. • Positive sign of the Curie–Weiss temperature ~8.7 K. • Defect induced magnetism- Zirconium vacancy induces maximum magnetic moment.

  18. Sensor fusion of electron paramagnetic resonance and magnetorelaxometry data for quantitative magnetic nanoparticle imaging

    Science.gov (United States)

    Coene, A.; Leliaert, J.; Crevecoeur, G.; Dupré, L.

    2017-03-01

    Magnetorelaxometry (MRX) imaging and electron paramagnetic resonance (EPR) are two non-invasive techniques capable of recovering the magnetic nanoparticle (MNP) distribution. Both techniques solve an ill-posed inverse problem in order to find the spatial MNP distribution. A lot of research has been done on increasing the stability of these inverse problems with the main objective to improve the quality of MNP imaging. In this paper a proof of concept is presented in which the sensor data of both techniques is fused into EPR–MRX, with the intention to stabilize the inverse problem. First, both techniques are compared by reconstructing several phantoms with different sizes for various noise levels and calculating stability, sensitivity and reconstruction quality parameters for these cases. This study reveals that both techniques are sensitive to different information from the MNP distributions and generate complementary measurement data. As such, their merging might stabilize the inverse problem. In a next step we investigated how both techniques need to be combined to reduce their respective drawbacks, such as a high number of required measurements and reduced stability, and to improve MNP reconstructions. We were able to stabilize both techniques, increase reconstruction quality by an average of 5% and reduce measurement times by 88%. These improvements could make EPR–MRX a valuable and accurate technique in a clinical environment.

  19. Electron Paramagnetic Resonance Imaging of the Spatial Distribution of Free Radicals in PMR-15 Polyimide Resins

    Science.gov (United States)

    Ahn, Myong K.; Eaton, Sandra S.; Eaton, Gareth R.; Meador, Mary Ann B.

    1997-01-01

    Prior studies have shown that free radicals generated by heating polyimides above 300 C are stable at room temperature and are involved in thermo-oxidative degradation in the presence of oxygen gas. Electron Paramagnetic Resonance Imaging (EPRI) is a technique to determine the spatial distribution of free radicals. X-band (9.5 GHz) EPR images of PMR-15 polyimide were obtained with a spatial resolution of about 0.18 mm along a 2 mm dimension of the sample. In a polyimide sample that was not thermocycled, the radical distribution was uniform along the 2 mm dimension of the sample. For a polyimide sample that was exposed to thermocycling in air for 300 one-hour cycles at 335 C, one-dimensional EPRI showed a higher concentration of free radicals in the surface layers than in the bulk sample. A spectral-spatial two-dimensional image showed that the EPR lineshape of the surface layer remained the same as that of the bulk. These EPRI results suggest that the thermo-oxidative degradation of PMR-15 resin involves free radicals present in the oxygen-rich surface layer.

  20. Electron paramagnetic resonance and low-field microwave absorption in the manganese–gallium oxide

    Energy Technology Data Exchange (ETDEWEB)

    Montiel, H., E-mail: herlinda_m@yahoo.com [Centro de Ciencias Aplicadas y Desarrollo Tecnológico de la Universidad Nacional Autónoma de México, Cd. Universitaria, A.P. 70-186, México DF 04510 (Mexico); Alvarez, G., E-mail: memodin@yahoo.com [Escuela Superior de Física y Matemáticas del Instituto Politécnico Nacional, U.P. Adolfo López Mateos, Edificio 9, Av. Instituto Politécnico Nacional S/N, San Pedro Zacatenco, México DF 07738 (Mexico); Departamento de Física, CINVESTAV-IPN, A.P. 14-740, México DF 07360 (Mexico); Conde-Gallardo, A. [Departamento de Física, CINVESTAV-IPN, A.P. 14-740, México DF 07360 (Mexico); Zamorano, R. [Escuela Superior de Física y Matemáticas del Instituto Politécnico Nacional, U.P. Adolfo López Mateos, Edificio 9, Av. Instituto Politécnico Nacional S/N, San Pedro Zacatenco, México DF 07738 (Mexico)

    2015-07-01

    Microwave absorption measurements in MnGa{sub 2}O{sub 4} powders are carried out at X-band (8.8–9.8 GHz) in 92–296 K temperature range. For all temperatures, the electron paramagnetic resonance (EPR) spectra show a single broad line due to Mn{sup 2+} ions. Temperature dependence of the EPR parameters: the peak-to-peak linewidth (ΔH{sub pp}), the integrated intensity (I{sub EPR}) and the g-factor, suggests the presence of magnetic fluctuations that precede to antiferromagnetic ordering at low temperature. Additionally, the low-field microwave absorption (LFMA) is used to give further information on this material, giving also evidence of these magnetic fluctuations. - Highlights: • We have investigated the microwave absorption in MnGa{sub 2}O{sub 4} powders in 92–296 K temperature range. • EPR spectra suggest the presence of magnetic fluctuations that proceed to antiferromagnetic ordering at low temperature. • LFMA signal give also evidence of these magnetic fluctuations.

  1. An electron spin injection driven, paramagnetic solid-state MASER device

    OpenAIRE

    Watts, S. M.; van Wees, B. J.

    2006-01-01

    In response to an external, microwave-frequency magnetic field, a paramagnetic medium will absorb energy from the field that drives the magnetization dynamics. Here we describe a new process by which an external spin injection source, when combined with the microwave field spin-pumping, can drive the paramagnetic medium from one that absorbs microwave energy to one that emits microwave energy. We derive a simple condition for the crossover from absorptive to emissive behavior. Based on this p...

  2. Coherent excitation with short electron pulses

    Science.gov (United States)

    Guertler, Andreas; Robicheaux, Francis; Noordam, Bart

    2000-06-01

    [1pt] The probability for a transition within an atom to be driven by a collision with a long pulse of electrons is proportional to the electron flux with the proportionality factor being the cross section for this transition. Recently it was shown [1] that for electron pulses shorter than the orbit time of the electron in the atom, a contribution of coherent scattering plays a role, which is proportional to the differential cross section in forward direction and the square of the electron flux. To investigate this effect, we are developing a picosecond electron gun [2]. Collision experiments will be done with Rydberg states in lithium around n=40 with Kepler orbit times in the order of 10 ps. For picosecond electron pulses, a quadratic dependance of the transition probability on the electron flux is expected in contrast to the linear dependance expected for nanosecond electron pulses. [1pt] References [1pt] [1] F. Robicheaux and L. D. Noordam, submitted to Phys. Rev. Lett. [1pt] [2] F. Robicheaux, G. M. Lankhuijzen, and L. D. Noordam, JOSA B 15, 1 (1998)

  3. G-tensors of the flavin adenine dinucleotide radicals in glucose oxidase: a comparative multifrequency electron paramagnetic resonance and electron-nuclear double resonance study.

    Science.gov (United States)

    Okafuji, Asako; Schnegg, Alexander; Schleicher, Erik; Möbius, Klaus; Weber, Stefan

    2008-03-20

    The flavin adenine dinucleotide (FAD) cofactor of Aspergillus niger glucose oxidase (GO) in its anionic (FAD*-) and neutral (FADH*) radical form was investigated by electron paramagnetic resonance (EPR) at high microwave frequencies (93.9 and 360 GHz) and correspondingly high magnetic fields and by pulsed electron-nuclear double resonance (ENDOR) spectroscopy at 9.7 GHz. Because of the high spectral resolution of the frozen-solution continuous-wave EPR spectrum recorded at 360 GHz, the anisotropy of the g-tensor of FAD*- could be fully resolved. By least-squares fittings of spectral simulations to experimental data, the principal values of g have been established with high precision: gX=2.00429(3), gY=2.00389(3), gZ=2.00216(3) (X, Y, and Z are the principal axes of g) yielding giso=2.00345(3). The gY-component of FAD*- from GO is moderately shifted upon deprotonation of FADH*, rendering the g-tensor of FAD*- slightly more axially symmetric as compared to that of FADH*. In contrast, significantly altered proton hyperfine couplings were observed by ENDOR upon transforming the neutral FADH* radical into the anionic FAD*- radical by pH titration of GO. That the g-principal values of both protonation forms remain largely identical demonstrates the robustness of g against local changes in the electron-spin density distribution of flavins. Thus, in flavins, the g-tensor reflects more global changes in the electronic structure and, therefore, appears to be ideally suited to identify chemically different flavin radicals.

  4. Cathodoluminescence, laser ablasion inductively coupled plasma mass spectrometry, electron probe microanalysis and electron paramagnetic resonance analyses of natural sphalerite

    Science.gov (United States)

    Karakus, M.; Hagni, R.D.; Koenig, A.; Ciftc, E.

    2008-01-01

    Natural sphalerite associated with copper, silver, lead-zinc, tin and tungsten deposits from various world-famous mineral deposits have been studied by cathodoluminescence (CL), laser ablasion inductively coupled plasma mass spectrometry (LA-ICP-MS), electron probe microanalysis (EPMA) and electron paramagnetic resonance (EPR) to determine the relationship between trace element type and content and the CL properties of sphalerite. In general, sphalerite produces a spectrum of CL colour under electron bombardment that includes deep blue, turquoise, lime green, yellow-orange, orange-red and dull dark red depending on the type and concentration of trace quantities of activator ions. Sphalerite from most deposits shows a bright yellow-orange CL colour with ??max centred at 585 nm due to Mn2+ ion, and the intensity of CL is strongly dependent primarily on Fe2+ concentration. The blue emission band with ??max centred at 470-490 nm correlates with Ga and Ag at the Tsumeb, Horn Silver, Balmat and Kankoy mines. Colloform sphalerite from older well-known European lead-zinc deposits and late Cretaceous Kuroko-type VMS deposits of Turkey shows intense yellowish CL colour and their CL spectra are characterised by extremely broad emission bands ranging from 450 to 750 nm. These samples are characterised by low Mn (behaviour of sphalerite serves to characterise ore types and help detect technologically important trace elements.

  5. Electron photodetachment by short laser pulse

    NARCIS (Netherlands)

    Golovinski, P. A.; Drobyshev, A. A.

    2012-01-01

    Expressions are derived for calculations of the total probabilities and electron spectra for the photodetachment of electrons from negative ions with filled valence s shells by ultrashort laser pulses. Particular calculations have been performed for two negative ions (H- and Li-) and titanium-sapphi

  6. Electron photodetachment by short laser pulse

    NARCIS (Netherlands)

    Golovinski, P. A.; Drobyshev, A. A.

    2012-01-01

    Expressions are derived for calculations of the total probabilities and electron spectra for the photodetachment of electrons from negative ions with filled valence s shells by ultrashort laser pulses. Particular calculations have been performed for two negative ions (H- and Li-) and titanium-sapphi

  7. Electron paramagnetic resonance spectroscopic study of copper hopping in doped bis(L-histidinato)cadmium dihydrate.

    Science.gov (United States)

    Colaneri, Michael J; Vitali, Jacqueline; Kirschbaum, Kristin

    2013-04-25

    Electron paramagnetic resonance (EPR) spectroscopy was used to study Cu(II) dynamic behavior in a doped biological model crystal, bis(L-histidinato)cadmium dihydrate, in order to gain better insight into copper site stability in metalloproteins. Temperature-dependent changes in the low temperature X-band EPR spectra became visible around 100 K and continued up to room temperature. The measured 298 K g-tensor (principal values: 2.17, 2.16, 2.07) and copper hyperfine coupling tensor (principal values: -260, -190, -37 MHz) were similar to the average of the 77 K tensor values pertaining to two neighboring histidine binding sites. The observed temperature dependence was interpreted using Anderson's theory of motional narrowing, where the magnetic parameters for the different states are averaged as the copper rapidly hops between sites. The EPR pattern was also found to undergo a sharp sigmoidal-shaped, temperature-dependent conversion between two species with a critical temperature T(c) ≈ 160 K. The species below T(c) hops between the two low temperature site patterns, and the one above T(c) represents an average of the molecular spin Hamiltonian coupling tensors of the two 77 K sites. In addition, the low and high temperature species hop between one another, contributing to the dynamic averaging. Spectral simulations using this 4-state model determined a hop rate between the two low temperature sites ν(h4) = 4.5 × 10(8) s(-1) and between the low and high temperature states ν(h2) = 1.7 × 10(8) s(-1) at 160 K. An Arrhenius relationship of hop rate and temperature gave energy barriers of ΔE4 = 389 cm(-1) and ΔE2 = 656 cm(-1) between the two low temperature sites and between the low and high temperature states, respectively.

  8. Electron paramagnetic resonance study of ternary CuII compounds with glycine and phenanthroline

    Indian Academy of Sciences (India)

    Ricardo C Santana; Anderson B C Araújo; Jesiel F Carvalho; Rafael Calvo

    2014-01-01

    We report here electron paramagnetic resonance (EPR) measurements at 9 and 34 GHz, and room temperature (), in powder and single crystal samples of the ternary compounds of copper nitrate or copper chloride with glycine and 1,10-phenanthroline [Cu(Gly)(phen)(H2O)]·NO3·1.5H2O (1) and [Cu(Gly)(phen)Cl]2·7H2O (2). In compound 1, the copper ions are arranged in 1-D chains along one of the crystal axes connected by syn-anti carboxylate ligands, while in 2 the array is nearly 3-D and the connections involve -bonds and stacking interactions. The angular variation of the squared g-factor and the line width were measured as a function of orientation of the magnetic field (0) in three orthogonal crystal planes. In both compounds we observed one resonance without hyperfine structure for any magnetic field orientation which we attribute to the collapse of the hyperfine coupling and of the resonances of two chemically identical but rotated coppers in the unit cell, produced by exchange interactions. We analyse the results in terms of the structures of the compounds and chemical paths connecting neighbour copper ions which support the exchange interactions between neighbour spins in the lattice. Considering the collapse of the EPR signals of rotated sites in the lattices we are able to set lower limits to the exchange interactions, which are supported by weak equatorial-apical carboxylate bridges in 1, and by paths containing hydrogen bonds and aromatic - interactions in 2. Broadening due to dipole-dipole couplings and hyperfine interactions are strongly reduced by these exchange couplings and their role in the EPR line width is more difficult to recognize.

  9. Study of nanostructural organization of ionic liquids by electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Merunka, Dalibor; Peric, Mirna; Peric, Miroslav

    2015-02-19

    The X-band electron paramagnetic resonance spectroscopy (EPR) of a stable, spherical nitroxide spin probe, perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (pDTO) has been used to study the nanostructural organization of a series of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids (ILs) with alkyl chain lengths from two to eight carbons. By employing nonlinear least-squares fitting of the EPR spectra, we have obtained values of the rotational correlation time and hyperfine coupling splitting of pDTO to high precision. The rotational correlation time of pDTO in ILs and squalane, a viscous alkane, can be fit very well to a power law functionality with a singular temperature, which often describes a number of physical quantities measured in supercooled liquids. The viscosity of the ILs and squalane, taken from the literature, can also be fit to the same power law expression, which means that the rotational correlation times and the ionic liquid viscosities have similar functional dependence on temperature. The apparent activation energy of both the rotational correlation time of pDTO and the viscous flow of ILs and squalane increases with decreasing temperature; in other words, they exhibit strong non-Arrhenius behavior. The rotational correlation time of pDTO as a function of η/T, where η is the shear viscosity and T is the temperature, is well described by the Stokes-Einstein-Debye (SED) law, while the hydrodynamic probe radii are solvent dependent and are smaller than the geometric radius of the probe. The temperature dependence of hyperfine coupling splitting is the same in all four ionic liquids. The value of the hyperfine coupling splitting starts decreasing with increasing alkyl chain length in the ionic liquids in which the number of carbons in the alkyl chain is greater than four. This decrease together with the decrease in the hydrodynamic radius of the probe indicates a possible existence of nonpolar nanodomains.

  10. Electron paramagnetic resonance study of chosen gadolinium(III) sandwiched- and encapsulated-polyoxometalate complexes

    Energy Technology Data Exchange (ETDEWEB)

    Szyczewski, A.; Kruczynski, Z.; Pietrzak, J. [Uniwersytet Adama Mickiewicza, Poznan (Poland). Inst. Fizyki; Lis, S.; But, S.; Elbanowski, M. [Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan (Poland)

    1998-07-24

    The gadolinium(III) complexes with polyoxometalates were studied using X-band electron paramagnetic resonance (EPR) spectroscopy. We selected the following sandwiched complexes: Gd(SiW{sub 11}O{sub 39}){sub 2}{sup 13-} [I], GdW{sub 10}O{sub 36}{sup 9-} [II], Gd(P{sub 2}W{sub 17}O{sub 61}){sub 2}{sup 17-} [III], and encrypted [GdSb{sub 9}W{sub 17}O{sub 86}]{sup 16-} [IV], [GdP{sub 5}W{sub 30}O{sub 110}]{sup 12-} [V]. The EPR spectra obtained for the compounds I-III and IV-V differ markedly from the U-spectrum characteristic for Gd(III) in glasses. The values of the zero-field splitting parameter D for both kind of complexes studied have been estimated. Taking into account the spin-hamiltonian calculations, the existence of Gd(III) ion in two different surroundings, in a strong crystal field of rhombic symmetry and in a weak crystal field, is observed. The differences observed between the case I-III and IV-V seems to be related to a various coordination of the Gd(III) ion and its hydration degree. Our study shows a relation between the presence of particular g-values of the spectral lines and the number of the inner-sphere water molecules as well as the type of the Gd(III) complex (sandwiched and/or encrypted) in solid. (orig.) 14 refs.

  11. A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Sidabras, Jason W.; Varanasi, Shiv K.; Hyde, James S. [Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53211 (United States); Mett, Richard R. [Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53211 (United States); Department of Physics and Chemistry, Milwaukee School of Engineering, Milwaukee, Wisconsin 53202 (United States); Swarts, Steven G. [Department of Radiation Oncology, University of Florida, Gainesville, Florida, 32610 (United States); Swartz, Harold M. [Department of Radiology, Geisel Medical School at Dartmouth, Hanover, New Hampshire 03755 (United States)

    2014-10-15

    A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg{sup 2+} doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.

  12. Analysis of Gamma-irradiated Soybean Components by Electron Paramagnetic Resonance

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, M.R. R. de; Quadrado, M.G.O.; Mastro, N.L. del [Center of Radiation Technology, IPEN-CNEN/SP, P. O.BOX 11049, 05422-700 Sao Paulo (Brazil)

    2007-07-01

    Soybean (Glycine max) seeds contain besides oil and protein, important phytochemicals that have been shown in recent years to offer important health benefits. Soybean contains at least six classes of antioxidant compounds: flavonol, isoflavones, anthocyanins, proanthocyanidins, tocopherols, and poly carboxylic acids. An increasing number of studies have documented the significant value of many classes of these compounds, mainly isoflavones, not only as potent antioxidants, but also as antitumor agents and cardio protective compounds. Food irradiation is gaining increasing attention around the world but it is not a worldwide approved treatment yet. Electron paramagnetic resonance, EPR, is considered the most important technique to detect free-radicals on food. Results from a previous work showed that irradiated soybean could be detected by EPR only when higher doses were employed. This study was undertaken to investigate the radiation response of the diverse parts of the soy seed: hull or seed coat, cotyledons, hilum and hypocotyl axis or germ, from different soybean cultivars. Soybean samples were obtained from the National Soybean Research Center (Embrapa-Soja), Londrina, Brazil, separated in their components and gamma-irradiated in a Gamma cell 220 (AECL) with doses of 0.1 and 2.0 kGy at a dose rate of 2.9 kGy/h. EPR measurements were performed on an X-band spectrometer (ER 041 XG Microwave Bridge, Bruker). Both irradiation and EPR measurements were performed at room temperature (20-25 C). The results showed that the EPR signal intensity correlated with the ionizing radiation dose, although different cultivars presented differences in their radiation response. The main EPR peak corresponding to free radical presented differences in shape and intensity. The hull and the hilum presented signals higher and easier to be analyzed than the whole bean, indicating strong differences in radiation sensitivity of soybean components. (Author)

  13. A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces

    Science.gov (United States)

    Sidabras, Jason W.; Varanasi, Shiv K.; Mett, Richard R.; Swarts, Steven G.; Swartz, Harold M.; Hyde, James S.

    2014-10-01

    A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg2+ doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.

  14. A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces.

    Science.gov (United States)

    Sidabras, Jason W; Varanasi, Shiv K; Mett, Richard R; Swarts, Steven G; Swartz, Harold M; Hyde, James S

    2014-10-01

    A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg(2+) doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.

  15. Optimal dielectric and cavity configurations for improving the efficiency of electron paramagnetic resonance probes.

    Science.gov (United States)

    Elnaggar, Sameh Y; Tervo, Richard; Mattar, Saba M

    2014-08-01

    An electron paramagnetic resonance (EPR) spectrometer's lambda efficiency parameter (Λ) is one of the most important parameters that govern its sensitivity. It is studied for an EPR probe consisting of a dielectric resonator (DR) in a cavity (CV). Expressions for Λ are derived in terms of the probe's individual DR and CV components, Λ1 and Λ2 respectively. Two important cases are considered. In the first, a probe consisting of a CV is improved by incorporating a DR. The sensitivity enhancement depends on the relative rather than the absolute values of the individual components. This renders the analysis general. The optimal configuration occurs when the CV and DR modes are nearly degenerate. This configuration guarantees that the probe can be easily coupled to the microwave bridge while maintaining a large Λ. It is shown that for a lossy CV with a small quality factor Q2, one chooses a DR that has the highest filling factor, η1, regardless of its Λ1 and Q1. On the other hand, if the CV has a large Q2, the optimum DR is the one which has the highest Λ1. This is regardless of its η1 and relative dielectric constant, ɛr. When the quality factors of both the CV and DR are comparable, the lambda efficiency is reduced by a factor of 2. Thus the signal intensity for an unsaturated sample is cut in half. The second case is the design of an optimum shield to house a DR. Besides preventing radiation leakage, it is shown that for a high loss DR, the shield can actually boost Λ above the DR value. This can also be very helpful for relatively low efficiency dielectrics as well as lossy samples, such as polar liquids.

  16. The sensitivity of saturation transfer electron paramagnetic resonance spectra to restricted amplitude uniaxial rotational diffusion.

    Science.gov (United States)

    Hustedt, E J; Beth, A H

    2001-12-01

    Computational methods have been developed to model the effects of constrained or restricted amplitude uniaxial rotational diffusion (URD) on saturation transfer electron paramagnetic resonance (ST-EPR) signals observed from nitroxide spin labels. These methods, which have been developed to model the global rotational motion of intrinsic membrane proteins that can interact with the cytoskeleton or other peripheral proteins, are an extension of previous work that described computationally efficient algorithms for calculating ST-EPR spectra for unconstrained URD (Hustedt and Beth, 1995, Biophys. J. 69:1409-1423). Calculations are presented that demonstrate the dependence of the ST-EPR signal (V'(2)) on the width (Delta) of a square-well potential as a function of the microwave frequency, the correlation time for URD, and the orientation of the spin-label with respect to the URD axis. At a correlation time of 10 micros, the V'(2) signal is very sensitive to Delta in the range from 0 to 60 degrees, marginally sensitive from 60 degrees to 90 degrees, and insensitive beyond 90 degrees. Sensitivity to Delta depends on the correlation time for URD with higher sensitivity to large values of Delta at the shorter correlation times, on the microwave frequency, and on the orientation of the spin-label relative to the URD axis. The computational algorithm has been incorporated into a global nonlinear least-squares analysis approach, based upon the Marquardt-Levenberg method (Blackman et al., 2001, Biophys. J. 81:3363-3376). This has permitted determination of the correlation time for URD and the width of the square-well potential by automated fitting of experimental ST-EPR data sets obtained from a spin-labeled membrane protein and provided a new automated method for analysis of data obtained from any system that exhibits restricted amplitude URD.

  17. Electron paramagnetic resonance study of lipid and protein membrane components of erythrocytes oxidized with hydrogen peroxide

    Energy Technology Data Exchange (ETDEWEB)

    Mendanha, S.A.; Anjos, J.L.V.; Silva, A.H.M.; Alonso, A. [Instituto de Física, Universidade Federal de Goiás, Goiânia, GO (Brazil)

    2012-04-05

    Electron paramagnetic resonance (EPR) spectroscopy of spin labels was used to monitor membrane dynamic changes in erythrocytes subjected to oxidative stress with hydrogen peroxide (H{sub 2}O{sub 2}). The lipid spin label, 5-doxyl stearic acid, responded to dramatic reductions in membrane fluidity, which was correlated with increases in the protein content of the membrane. Membrane rigidity, associated with the binding of hemoglobin (Hb) to the erythrocyte membrane, was also indicated by a spin-labeled maleimide, 5-MSL, covalently bound to the sulfhydryl groups of membrane proteins. At 2% hematocrit, these alterations in membrane occurred at very low concentrations of H{sub 2}O{sub 2} (50 µM) after only 5 min of incubation at 37°C in azide phosphate buffer, pH 7.4. Lipid peroxidation, suggested by oxidative hemolysis and malondialdehyde formation, started at 300 µM H{sub 2}O{sub 2} (for incubation of 3 h), which is a concentration about six times higher than those detected with the probes. Ascorbic acid and α-tocopherol protected the membrane against lipoperoxidation, but did not prevent the binding of proteins to the erythrocyte membrane. Moreover, the antioxidant (+)-catechin, which also failed to prevent the cross-linking of cytoskeletal proteins with Hb, was very effective in protecting erythrocyte ghosts from lipid peroxidation induced by the Fenton reaction. This study also showed that EPR spectroscopy can be useful to assess the molecular dynamics of red blood cell membranes in both the lipid and protein domains and examine oxidation processes in a system that is so vulnerable to oxidation.

  18. Synthesis and characterization of a combined fluorescence, phosphorescence, and electron paramagnetic resonance probe

    Science.gov (United States)

    Beth, Albert H.; Cobb, Charles E.; Beechem, Joseph M.

    1992-04-01

    A spin-labeled derivative of eosin was chemically synthesized from 5-aminoeosin and the nitroxide spin label 2,2,5,5-tetramethylpyrrolin-1-oxyl-3-carboxylic acid. Following determination of the chemical identity of the spin-labeled eosin (5-SLE) by FAB mass spectroscopy, its optical and magnetic resonance spectroscopic properties were characterized in aqueous solution and compared to a diamagnetic eosin derivative, 5-acetamido eosin (5- AcE). The visible light absorption maximum of 5-SLE was 518 nm, the same as for 5-AcE. The fluorescence quantum yield of 5-SLE was only reduced by approximately 10% relative to 5-AcE, and the fluorescence lifetime was marginally reduced relative to 5-AcE. The phosphorescence lifetime and yield for 5-SLE were very similar to those for 5-AcE. The phosphorescence yield of 5-SLE bound noncovalently to BSA was reduced by approximately 60% relative to 5-AcE, and the phosphorescence lifetime reduced from approximately 2.4 msec (5-AcE) to 1.6 msec (5-SLE). Reduction of the nitroxide moiety of the 5-SLE with sodium ascorbate resulted in minimal changes in the fluorescence and phosphorescence quantum yields and lifetimes. This indicated that the unpaired electron of the nitroxide spin label did not seriously affect the optical spectroscopic characteristics of the spin-labeled eosin molecule. The quantum yields and lifetimes of 5-SLE were still quite acceptable for time- resolved fluorescence and phosphorescence studies. The electron paramagnetic resonance (EPR) spectrum of 5-SLE in aqueous solution has a lineshape consistent with a molecule the size of 5-SLE undergoing rapid rotational reorientation. When bound to BSA, the EPR spectrum of 5-SLE was broadened to a near slow motion limit for EPR, as expected for the relatively slowly rotating protein-5-SLE complex. Time-resolved phosphorescence anisotropy and saturation transfer EPR (ST-EPR) experiments with samples of 5-SLE bound to BSA in solutions of varying glycerol concentrations at 2

  19. Pulsed EPR and NMR spectroscopy of paramagnetic iron porphyrinates and related iron macrocycles: how to understand patterns of spin delocalization and recognize macrocycle radicals.

    Science.gov (United States)

    Walker, F Ann

    2003-07-28

    Pulsed EPR spectroscopic techniques, including ESEEM (electron spin echo envelope modulation) and pulsed ENDOR (electron-nuclear double resonance), are extremely useful for determining the magnitudes of the hyperfine couplings of macrocycle and axial ligand nuclei to the unpaired electron(s) on the metal as a function of magnetic field orientation relative to the complex. These data can frequently be used to determine the orientation of the g-tensor and the distribution of spin density over the macrocycle, and to determine the metal orbital(s) containing unpaired electrons and the macrocycle orbital(s) involved in spin delocalization. However, these studies cannot be carried out on metal complexes that do not have resolved EPR signals, as in the case of paramagnetic even-electron metal complexes. In addition, the signs of the hyperfine couplings, which are not determined directly in either ESEEM or pulsed ENDOR experiments, are often needed in order to translate hyperfine couplings into spin densities. In these cases, NMR isotropic (hyperfine) shifts are extremely useful in determining the amount and sign of the spin density at each nucleus probed. For metal complexes of aromatic macrocycles such as porphyrins, chlorins, or corroles, simple rules allow prediction of whether spin delocalization occurs through sigma or pi bonds, and whether spin density on the ligands is of the same or opposite sign as that on the metal. In cases where the amount of spin density on the macrocycle and axial ligands is found to be too large for simple metal-ligand spin delocalization, a macrocycle radical may be suspected. Large spin density on the macrocycle that is of the same sign as that on the metal provides clear evidence of either no coupling or weak ferromagnetic coupling of a macrocycle radical to the unpaired electron(s) on the metal, while large spin density on the macrocycle that is of opposite sign to that on the metal provides clear evidence of antiferromagnetic coupling

  20. A solid state paramagnetic maser device driven by electron spin injection

    NARCIS (Netherlands)

    Watts, S. M.; van Wees, B. J.

    2006-01-01

    In response to an external, microwave-frequency magnetic field, a paramagnetic medium will absorb energy from the field that drives the magnetization dynamics. Here we describe a new process by which an external spin-injection source, when combined with the microwave field spin pumping, can drive

  1. A solid state paramagnetic maser device driven by electron spin injection

    NARCIS (Netherlands)

    Watts, S. M.; van Wees, B. J.

    2006-01-01

    In response to an external, microwave-frequency magnetic field, a paramagnetic medium will absorb energy from the field that drives the magnetization dynamics. Here we describe a new process by which an external spin-injection source, when combined with the microwave field spin pumping, can drive th

  2. One nanosecond pulsed electron gun systems

    Energy Technology Data Exchange (ETDEWEB)

    Koontz, R.F.

    1979-02-01

    At SLAC there has been a continuous need for the injection of very short bunches of electrons into the accelerator. Several time-of-flight experiments have used bursts of short pulses during a normal 1.6 micro-second rf acceleration period. Single bunch beam loading experiments made use of a short pulse injection system which included high power transverse beam chopping equipment. Until the equipment described in this paper came on line, the basic grid-controlled gun pulse was limited to a rise time of 7 nanoseconds and a pulse width of 10 nanoseconds. The system described here has a grid-controlled rise time of less than 500 pico-seconds, and a minimum pulse width of less than 1 nanosecond. Pulse burst repetition rate has been demonstrated above 20 MHz during a 1.6 microsecond rf accelerating period. The order-of-magnitude increase in gun grid switching speed comes from a new gun design which minimizes lead inductance and stray capacitance, and also increases gun grid transconductance. These gun improvements coupled with a newly designed fast pulser mounted directly within the gun envelope make possible subnanosecond pulsing of the gun.

  3. Studying lipid-protein interactions with electron paramagnetic resonance spectroscopy of spin-labeled lipids.

    Science.gov (United States)

    Páli, Tibor; Kóta, Zoltán

    2013-01-01

    Spin label electron paramagnetic resonance (EPR) of lipid-protein interactions reveals crucial features of the structure and assembly of integral membrane proteins. Spin label EPR spectroscopy is the technique of choice to characterize the protein-solvating lipid shell in its highly dynamic nature, because the EPR spectra of lipids that are spin labeled close to the terminal methyl end of their acyl chains display two spectral components, those corresponding to lipids directly contacting the protein and those corresponding to lipids in the bulk fluid bilayer regions of the membrane. In this chapter, typical spin label EPR procedures are presented that allow determination of the stoichiometry of interaction of spin-labeled lipids with the intra-membranous region of membrane proteins or polypeptides, as well as the association constant of the spin-labeled lipid with respect to the host lipid. The lipids giving rise to the so-called immobile spectral component in the EPR spectrum of such samples are identified as the motionally restricted first-shell lipids solvating membrane proteins in biomembranes. Stoichiometry and selectivity are directly related to the structure of the intra-membranous sections of membrane-associated proteins or polypeptides and can be used to study the state of assembly of such proteins in the membrane. Since these characteristics of lipid-protein interactions are discussed in detail in the literature [see Marsh (Eur Biophys J 39:513-525, 2010) for a most recent review], here we focus more on how to spin label model and biomembranes and how to measure and analyze the two-component EPR spectra of spin-labeled lipids in phospholipid bilayers that contain proteins or polypeptides. After a description of how to prepare spin-labeled model and native biological membranes, we present the reader with computational procedures for determining the molar fraction of motionally restricted lipids when both, one, or none of the pure isolated-mobile or

  4. Visualization of Distance Distribution from Pulsed Double Electron-Electron Resonance Data

    Energy Technology Data Exchange (ETDEWEB)

    Bowman, Michael K.; Maryasov, Alexander G.; Kim, Nak-Kyoon; DeRose, Victoria J.

    2004-01-01

    Double electron-electron resonance (DEER), also known as pulsed electron-electron double resonance (PELDOR), is a time-domain electron paramagnetic resonance method that can measure the weak dipole-dipole interactions between unpaired electrons. DEER has been applied to discrete pairs of free radicals in biological macromolecules and to clusters containing small numbers of free radicals in polymers and irradiated materials. The goal of such work is to determine the distance or distribution of distances between radicals, which is an underdetermined problem. That is, the spectrum of dipolar interactions can be readily calculated for any distribution of free radicals, but there are many, quite different distributions of radicals that could produce the same experimental dipolar spectrum. This paper describes two methods that are useful for approximating the distance distributions for the large subset of cases in which the mutual orientations of the free radicals are uncorrelated and the width of the distribution is more than a few percent of its mean. The first method relies on a coordinate transformation and is parameter free, while the second is based on iterative least-squares with Tikhonov regularization. Both methods are useful in DEER studies of spin labeled biomolecules containing more than two labels.

  5. Pulsed electron-nuclear-electron triple resonance spectroscopy

    Science.gov (United States)

    Thomann, Hans; Bernardo, Marcelino

    1990-05-01

    A new experimental technique, pulsed electron-nuclear-electron triple resonance spectroscopy, is demonstrated. It is based on a modification of the pulse sequence for electron-nuclear double resonance (ENDOR) in which two EPR and one NMR transition are irradiated. The irradiation of one EPR transition is detected via a second EPR transition. The nuclear hyperfine coupling, which separates these EPR transition frequencies, is the irradiated NMR transition. The major advantages of triple resonance spectroscopy include the ability to resolve overlapping nuclear resonances in the ENDOR spectrum and a more direct quantitative assignment of nuclear hyperfine and quadrupole couplings. The triple resonance experiment is an alternative to the recently proposed method of employing rapid magnetic field jumps between microwave pulses for generating hyperfine selective ENDOR spectra.

  6. Comparative electron paramagnetic resonance investigation of reduced graphene oxide and carbon nanotubes with different chemical functionalities for quantum dot attachment

    Science.gov (United States)

    Pham, Chuyen V.; Krueger, Michael; Eck, Michael; Weber, Stefan; Erdem, Emre

    2014-03-01

    Electron paramagnetic resonance (EPR) spectroscopy has been applied to different chemically treated reduced graphene oxide (rGO) and multiwalled carbon nanotubes (CNTs). A narrow EPR signal is visible at g = 2.0029 in both GO and CNT-Oxide from carbon-related dangling bonds. EPR signals became broader and of lower intensity after oxygen-containing functionalities were reduced and partially transformed into thiol groups to obtain thiol-functionalized reduced GO (TrGO) and thiol-functionalized CNT (CNT-SH), respectively. Additionally, EPR investigation of CdSe quantum dot-TrGO hybrid material reveals complete quenching of the TrGO EPR signal due to direct chemical attachment and electronic coupling. Our work confirms that EPR is a suitable tool to detect spin density changes in different functionalized nanocarbon materials and can contribute to improved understanding of electronic coupling effects in nanocarbon-nanoparticle hybrid nano-composites promising for various electronic and optoelectronic applications.

  7. Electron paramagnetic resonance-based pH mapping using spectral-spatial imaging of sequentially scanned spectra

    OpenAIRE

    Koda, Shunichi; Goodwin, Jonathan; Khramtsov, Valery V.; Fujii, Hirotada; Hirata, Hiroshi

    2012-01-01

    The development of electron paramagnetic resonance (EPR)-based mapping of pH is an important advancement for the field of diagnostic imaging. The ability to accurately quantify pH change in vivo and monitor spatial distribution is desirable for the assessment of a number of pathological conditions in the human body as well as the monitoring of treatment response. In this work we introduce a method for EPR-based pH mapping, utilizing a method of spectral-spatial imaging of sequentially scanned...

  8. Exploring Structure, Dynamics, and Topology of Nitroxide Spin-Labeled Proteins Using Continuous-Wave Electron Paramagnetic Resonance Spectroscopy.

    Science.gov (United States)

    Altenbach, Christian; López, Carlos J; Hideg, Kálmán; Hubbell, Wayne L

    2015-01-01

    Structural and dynamical characterization of proteins is of central importance in understanding the mechanisms underlying their biological functions. Site-directed spin labeling (SDSL) combined with continuous-wave electron paramagnetic resonance (CW EPR) spectroscopy has shown the capability of providing this information with site-specific resolution under physiological conditions for proteins of any degree of complexity, including those associated with membranes. This chapter introduces methods commonly employed for SDSL and describes selected CW EPR-based methods that can be applied to (1) map secondary and tertiary protein structure, (2) determine membrane protein topology, (3) measure protein backbone flexibility, and (4) reveal the existence of conformational exchange at equilibrium.

  9. The influence of oxygen-17 enriched oxygen-donor ligands on the electronic spin relaxation behaviour of paramagnetic metal ions

    Science.gov (United States)

    Wells, Gregg B.; Yim, Moon B.; Makinen, Marvin W.

    Continuous wave microwave power saturation of high-spin paramagnetic metalloprotein complexes of Co2+ and Fe3+ showed that the value of the saturation parameter P1/2 is influenced by the coordination of oxygen-17 enriched water to the metal ion. No change was observed for H218O or 2H2O. Pulse saturation and recovery of paramagnetic high-spin Fe3+ heme proteins identified a fast relaxation component sensitive to isotopic oxygen-17 composition that was assigned to the process of spectral diffusion. It is shown that the change in relaxation time for spectral diffusion can alter the (apparent) spin-lattice relaxation to account for the observed changes in continuous wave microwave power saturation experiments. These changes are shown to correlate with alterations in the extent of covalency between the metal ion and oxygen-donor ligand. The experimental results provide a basis for use of continuous wave microwave saturation to identify the presence of oxygen-donor ligands within the inner coordination shell of high-spin Co2+ or Fe3+ in metalloprotein and small molecule complexes and to qualitatively assess the extent of covalency between the metal ion and the oxygen-donor ligand.

  10. Reactive oxygen species' role in endothelial dysfunction by electron paramagnetic resonance

    Science.gov (United States)

    Wassall, Cynthia D.

    The endothelium is a single layer of cells lining the arteries and is involved in many physiological reactions which are responsible for vascular tone. Free radicals are important participants in these chemical reactions in the endothelium. Here we quantify free radicals, ex vivo, in biological tissue with continuous wave electron paramagnetic resonance (EPR). In all of the experiments in this thesis, we use a novel EPR spin trapping technique that has been developed for tissue segments. EPR spin trapping is often considered the 'gold standard' in reactive oxygen species (ROS) detection because of its sensitivity and non-invasive nature. In all experiments, tissue was placed in physiological saline solution with 190-mM PBN (N-tert -butyl-α-phenylnitrone), 10% by volume dimethyl-sulphoxide (DMSO) for cryopreservation, and incubated in the dark for between 30 minutes up to 2 hours at 37°C while gently being stirred. Tissue and supernatant were then loaded into a syringe and frozen at -80°C until EPR analysis. In our experiments, the EPR spectra were normalized with respect to tissue volume. Conducting experiments at liquid nitrogen temperature leads to some experimental advantages. The freezing of the spin adducts renders them stable over a longer period, which allows ample time to analyze tissue samples for ROS. The dielectric constant of ice is greatly reduced over its liquid counterpart; this property of water enables larger sample volumes to be inserted into the EPR cavity without overloading it and leads to enhanced signal detection. Due to Maxwell-Boltzmann statistics, the population difference goes up as the temperature goes down, so this phenomenon enhances the signal intensity as well. With the 'gold standard' assertion in mind, we investigated whether slicing tissue to assay ROS that is commonly used in fluorescence experiments will show more free radical generation than tissue of a similar volume that remains unsliced. Sliced tissue exhibited a 76

  11. Compression of Electron Pulses for Femtosecond Electron Diffraction

    Science.gov (United States)

    Zandi, Omid; Yang, Jie; Centurion, Martin

    2014-05-01

    Our goal is to improve the temporal resolution in electron diffraction experiments to 100 fs by compressing the electron pulses using a time-varying electric field. The compressed pulse can be used for a better understanding of the dynamics of molecules under study. A bunch of 3 million electrons is generated at a photocathode by femtosecond UV laser pulses and accelerated to 100 keV in a static electric field. Then, the longitudinal component of the electric field of a microwave cavity is employed to compress the bunch. The cavity's frequency and phase are accurately tuned in such a way that the electric field is parallel to the bunch motion at its arrival and antiparallel to it at its exit. Compression in the transverse directions is done by magnetic lenses. Simulations have been done to predict the bunch profile at different positions and times by General Particle Tracer code. A streak camera has been built to measure the duration of the pulses. It uses the electric field of a discharging parallel plate capacitor to rotate the bunch so that angular spreading of the bunch is proportional to its duration. The capacitor is discharged by a laser pulse incident on a photo switch.

  12. Inter-spin distance determination using L-band (1-2 GHz) non-adiabatic rapid sweep electron paramagnetic resonance (NARS EPR)

    Science.gov (United States)

    Kittell, Aaron W.; Hustedt, Eric J.; Hyde, James S.

    2012-08-01

    Site-directed spin-labeling electron paramagnetic resonance (SDSL EPR) provides insight into the local structure and motion of a spin probe strategically attached to a molecule. When a second spin is introduced to the system, macromolecular information can be obtained through measurement of inter-spin distances either by continuous wave (CW) or pulsed electron double resonance (ELDOR) techniques. If both methodologies are considered, inter-spin distances of 8-80 Å can be experimentally determined. However, there exists a region at the upper limit of the conventional X-band (9.5 GHz) CW technique and the lower limit of the four-pulse double electron-electron resonance (DEER) experiment where neither method is particularly reliable. The work presented here utilizes L-band (1.9 GHz) in combination with non-adiabatic rapid sweep (NARS) EPR to address this opportunity by increasing the upper limit of the CW technique. Because L-band linewidths are three to seven times narrower than those at X-band, dipolar broadenings that are small relative to the X-band inhomogeneous linewidth become observable, but the signal loss, due to the frequency dependence of the Boltzmann factor, has made L-band especially challenging. NARS has been shown to increase sensitivity by a factor of five, and overcomes much of this loss, making L-band distance determination more feasible [1]. Two different systems are presented, and distances of 18-30 Å have been experimentally determined at physiologically relevant temperatures. Measurements are in excellent agreement with a helical model and values determined by DEER.

  13. Slow-Motion Theory of Nuclear Spin Relaxation in Paramagnetic Low-Symmetry Complexes: A Generalization to High Electron Spin

    Science.gov (United States)

    Nilsson, T.; Kowalewski, J.

    2000-10-01

    The slow-motion theory of nuclear spin relaxation in paramagnetic low-symmetry complexes is generalized to comprise arbitrary values of S. We describe the effects of rhombic symmetry in the static zero-field splitting (ZFS) and allow the principal axis system of the static ZFS tensor to deviate from the molecule-fixed frame of the nuclear-electron dipole-dipole tensor. We show nuclear magnetic relaxation dispersion (NMRD) profiles for different illustrative cases, ranging from within the Redfield limit into the slow-motion regime with respect to the electron spin dynamics. We focus on S = 3/2 and compare the effects of symmetry-breaking properties on the paramagnetic relaxation enhancement (PRE) in this case with that of S = 1, which we have treated in a previous paper. We also discuss cases of S = 2, 5/2, 3, and 7/2. One of the main objectives of this investigation, together with the previous papers, is to provide a set of standard calculations using the general slow-motion theory, against which simplified models may be tested.

  14. Applications of electron paramagnetic resonance spectroscopy to study interactions of iron proteins in cells with nitric oxide

    Science.gov (United States)

    Cammack, R.; Shergill, J. K.; Ananda Inalsingh, V.; Hughes, Martin N.

    1998-12-01

    Nitric oxide and species derived from it have a wide range of biological functions. Some applications of electron paramagnetic resonance (EPR) spectroscopy are reviewed, for observing nitrosyl species in biological systems. Nitrite has long been used as a food preservative owing to its bacteriostatic effect on spoilage bacteria. Nitrosyl complexes such as sodium nitroprusside, which are added experimentally as NO-generators, themselves produce paramagnetic nitrosyl species, which may be seen by EPR. We have used this to observe the effects of nitroprusside on clostridial cells. After growth in the presence of sublethal concentrations of nitroprusside, the cells show they have been converted into other, presumably less toxic, nitrosyl complexes such as (RS) 2Fe(NO) 2. Nitric oxide is cytotoxic, partly due to its effects on mitochondria. This is exploited in the destruction of cancer cells by the immune system. The targets include iron-sulfur proteins. It appears that species derived from nitric oxide such as peroxynitrite may be responsible. Addition of peroxynitrite to mitochondria led to depletion of the EPR-detectable iron-sulfur clusters. Paramagnetic complexes are formed in vivo from hemoglobin, in conditions such as experimental endotoxic shock. This has been used to follow the course of production of NO by macrophages. We have examined the effects of suppression of NO synthase using biopterin antagonists. Another method is to use an injected NO-trapping agent, Fe-diethyldithiocarbamate (Fe-DETC) to detect accumulated NO by EPR. In this way we have observed the effects of depletion of serum arginine by arginase. In brains from victims of Parkinson's disease, a nitrosyl species, identified as nitrosyl hemoglobin, has been observed in substantia nigra. This is an indication for the involvement of nitric oxide or a derived species in the damage to this organ.

  15. Microwave absorption in the singlet paramagnet HoVO 4 in high pulsed magnetic fields up to 40 T

    Science.gov (United States)

    Goiran, M.; Klingeler, R.; Kazei, Z. A.; Snegirev, V. V.

    2007-11-01

    Microwave absorption of the rare-earth (RE) oxide compound HoVO 4 (tetragonal-zircon structure) is investigated in pulsed magnetic fields up to 40 T in the low-temperature range. For a magnetic field along the tetragonal crystal axis a few resonance absorption lines are observed at the wavelengths 871, 406 and 305 μm corresponding to electron transitions from the ground and low-lying energy levels of the Ho 3+ ion. In addition, broad non-resonance absorption is observed at 871 and 406 μm in fields up to 15 T. The positions and intensities of the observed resonance lines are described quite well within the crystal field formalism with the known crystal field parameters. The effects of the small orthorhombic component of the crystal field, magnetic field misorientation out the symmetry axis and various pair interactions on the absorption spectra in HoVO 4 are analyzed and discussed.

  16. Electron paramagnetic resonance and photoluminescence investigation of europium local structure in oxyfluoride glass ceramics containing SrF2 nanocrystals

    Science.gov (United States)

    Antuzevics, A.; Kemere, M.; Krieke, G.; Ignatans, R.

    2017-10-01

    Different compositions of europium doped aluminosilicate oxyfluoride glass ceramics prepared in air atmosphere have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy methods. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements show presence of homogenously distributed SrF2 nanocrystals after the heat treatment of the precursor glass. Efficient Eu3+ incorporation in the high symmetry environment of glass ceramics is observed from the photoluminescence spectra. EPR spectra indicate Eu3+ → Eu2+ reduction upon precipitation of crystalline phases in the glass matrix. For composition abundant with Eu2+ in the glassy state such behaviour is not detected. Local structure around europium ions is discussed based on differences in chemical compositions.

  17. A Mononuclear Mn(II) Pseudoclathrochelate Complex Studied by Multi-Frequency Electron-Paramagnetic-Resonance Spectroscopy.

    Science.gov (United States)

    Azarkh, Mykhailo; Penkova, Larysa V; Kats, Svitlana V; Varzatskii, Oleg A; Voloshin, Yan Z; Groenen, Edgar J J

    2014-03-06

    Knowledge of the correlation between structural and spectroscopic properties of transition-metal complexes is essential to deepen the understanding of their role in catalysis, molecular magnetism, and biological inorganic chemistry. It provides topological and, sometimes, functional insight with respect to the active site properties of metalloproteins. The electronic structure of a high-spin mononuclear Mn(II) pseudoclathrochelate complex has been investigated by electron-paramagnetic-resonance (EPR) spectroscopy at 9.5 and 275.7 GHz. A substantial, virtually axial zero-field splitting with D = -9.7 GHz (-0.32 cm(-1)) is found, which is the largest one reported to date for a Mn(II) complex with six nitrogen atoms in the first coordination sphere.

  18. Breakdown behavior of electronics at variable pulse repetition rates

    OpenAIRE

    Korte, S.; H. Garbe

    2006-01-01

    The breakdown behavior of electronics exposed to single transient electromagnetic pulses is subject of investigations for several years. State-of-the-art pulse generators additionally provide the possibility to generate pulse sequences with variable pulse repetition rate. In this article the influence of this repetition rate variation on the breakdown behavior of electronic systems is described. For this purpose microcontroller systems are examined during line-led exposure to pulses with repe...

  19. Comparison of neutron and gamma irradiation effects on KU1 fused silica monitored by electron paramagnetic resonance

    Energy Technology Data Exchange (ETDEWEB)

    Bravo, D. [Department Fisica de Materiales, Universidad Autonoma de Madrid, E-28049 Madrid (Spain)], E-mail: david.bravo@uam.es; Lagomacini, J.C. [Department Fisica de Materiales, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Leon, M.; Martin, P. [Materiales para Fusion, CIEMAT, Avda. Complutense 22, E-28040 Madrid (Spain); Martin, A. [Department Fisica e Instalaciones, ETS Arquitectura UPM, E-28040 Madrid (Spain); Lopez, F.J. [Department Fisica de Materiales, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Ibarra, A. [Materiales para Fusion, CIEMAT, Avda. Complutense 22, E-28040 Madrid (Spain)

    2009-06-15

    Electron paramagnetic resonance (EPR) studies have been carried out on KU1 fused silica irradiated with neutrons at fluences 10{sup 21} and 10{sup 22} n/m{sup 2}, and gamma-ray doses up to 12 MGy. The effects of post-irradiation thermal annealing treatments, up to 850 deg. C, have also been investigated. Paramagnetic oxygen-related defects (POR and NBOHC) and E'-type defects have been identified and their concentration has been measured as a function of neutron fluence, gamma dose and post-irradiation annealing temperature. It is found that neutrons at the highest fluence generate a much higher concentration of defects (mainly E' and POR, both at concentrations about 5 x 10{sup 18} spins/cm{sup 3}) than gamma irradiations at the highest dose (mainly E' at a concentration about 4 x 10{sup 17} spins/cm{sup 3}). Moreover, for gamma-irradiated samples a lower treatment temperature (about 400 deg. C) is required to annihilate most of the observed defects than for neutron-irradiated ones (about 600 deg. C)

  20. Prebunching and electron pulse phase stability in FELIX

    Science.gov (United States)

    Oepts, D.; Weits, H. H.

    1997-06-01

    The importance of coherent spontaneous emission in a free-electron laser operating with short electron pulses is discussed. A coherent enhancement by many orders of magnitude has been observed in the far infrared with the FELIX device. The associated coherence between independent optical micropulses is used to determine the phase stability of the electron pulses. It is found that the pulse-to-pulse jitter is not more than some tens of femtoseconds on a timescale of nanoseconds.

  1. Two-dimensional electron paramagnetic resonance spectroscopy of nitroxides: Elucidation of restricted molecular motions in glassy solids

    Science.gov (United States)

    Dubinskii, Alexander A.; Maresch, Günter G.; Spiess, Hans-Wolfgang

    1994-02-01

    The combination of concepts of two-dimensional (2D) spectroscopy with the well-known field step electron-electron double resonance (ELDOR) method offers a practical route to recording 2D ELDOR spectra covering the full spectral range needed for electron paramagnetic resonance (EPR) of nitroxide spin labels in the solid state. The 2D ELDOR pattern provides information about molecular reorientation measured in real time, the anisotropies of electron phase, and electron spin-lattice relaxation as well as nuclear spin-lattice relaxation all of which are connected with the detailed geometry of the molecular reorientation. Thus, in 2D ELDOR the same electron spin probes the motional behavior over a wide range of correlation times from 10-4 to 10-12 s. An efficient algorithm for simulating 2D ELDOR spectra is derived, based on analytical solutions of the spin relaxation behavior for small-angle fluctuations and offers a means of quantitatively analyzing experimental data. As an example, the motion of nitroxide spin labels in a liquid-crystalline side-group polymer well below its glass transition is determined as a β-relaxation process with a mean angular amplitude of 5° and a distribution of correlation times with a mean correlation time of 0.9×10-10 s and a width of 2.5 decades.

  2. 76 FR 67200 - Prospective Grant of Exclusive License: Electron Paramagnetic Resonance Devices and Systems for...

    Science.gov (United States)

    2011-10-31

    .......... Pending. to Resonance Research, Inc., a company incorporated under the laws of the Commonwealth of... pulse sequence well-known in MRI where the images are obtained by the filtered back-projection after...

  3. Superoxide Anion Radical Production in the Tardigrade Paramacrobiotus richtersi, the First Electron Paramagnetic Resonance Spin-Trapping Study.

    Science.gov (United States)

    Savic, Aleksandar G; Guidetti, Roberto; Turi, Ana; Pavicevic, Aleksandra; Giovannini, Ilaria; Rebecchi, Lorena; Mojovic, Milos

    2015-01-01

    Anhydrobiosis is an adaptive strategy that allows withstanding almost complete body water loss. It has been developed independently by many organisms belonging to different evolutionary lines, including tardigrades. The loss of water during anhydrobiotic processes leads to oxidative stress. To date, the metabolism of free radicals in tardigrades remained unclear. We present a method for in vivo monitoring of free radical production in tardigrades, based on electron paramagnetic resonance and spin-trap DEPMPO, which provides simultaneous identification of various spin adducts (i.e., different types of free radicals). The spin trap can be easily absorbed in animals, and tardigrades stay alive during the measurements and during 24-h monitoring after the treatment. The results show that hydrated specimens of the tardigrade Paramacrobiotus richtersi produce the pure superoxide anion radical ((•)O2(-)). This is an unexpected result, as all previously examined animals and plants produce both superoxide anion radical and hydroxyl radical ((•)OH) or exclusively hydroxyl radical.

  4. A quantitative method to monitor reactive oxygen species production by electron paramagnetic resonance in physiological and pathological conditions.

    Science.gov (United States)

    Mrakic-Sposta, Simona; Gussoni, Maristella; Montorsi, Michela; Porcelli, Simone; Vezzoli, Alessandra

    2014-01-01

    The growing interest in the role of Reactive Oxygen Species (ROS) and in the assessment of oxidative stress in health and disease clashes with the lack of consensus on reliable quantitative noninvasive methods applicable. The study aimed at demonstrating that a recently developed Electron Paramagnetic Resonance microinvasive method provides direct evidence of the "instantaneous" presence of ROS returning absolute concentration levels that correlate with "a posteriori" assays of ROS-induced damage by means of biomarkers. The reliability of the choice to measure ROS production rate in human capillary blood rather than in plasma was tested (step I). A significant (P condition, were found significantly different (range 0.0001-0.05 P level). The comparison of the results with antioxidant capacity and oxidative damage biomarkers concentrations showed that all changes indicating increased oxidative stress are directly related to ROS production increase. Therefore, the adopted method may be an automated technique for a lot of routine in clinical trials.

  5. Localization of dexamethasone within dendritic core-multishell (CMS) nanoparticles and skin penetration properties studied by multi-frequency electron paramagnetic resonance (EPR) spectroscopy.

    Science.gov (United States)

    Saeidpour, S; Lohan, S B; Anske, M; Unbehauen, M; Fleige, E; Haag, R; Meinke, M C; Bittl, R; Teutloff, C

    2016-10-15

    The skin and especially the stratum corneum (SC) act as a barrier and protect epidermal cells and thus the whole body against xenobiotica of the external environment. Topical skin treatment requires an efficient drug delivery system (DDS). Polymer-based nanocarriers represent novel transport vehicles for dermal application of drugs. In this study dendritic core-multishell (CMS) nanoparticles were investigated as promising candidates. CMS nanoparticles were loaded with a drug (analogue) and were applied to penetration studies of skin. We determined by dual-frequency electron paramagnetic resonance (EPR) how dexamethasone (Dx) labelled with 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PCA) is associated with the CMS. The micro-environment of the drug loaded to CMS nanoparticles was investigated by pulsed high-field EPR at cryogenic temperature, making use of the fact that magnetic parameters (g-, A-matrices, and spin-lattice relaxation time) represent specific probes for the micro-environment. Additionally, the rotational correlation time of spin-labelled Dx was probed by continuous wave EPR at ambient temperature, which provides independent information on the drug environment. Furthermore, the penetration depth of Dx into the stratum corneum of porcine skin after different topical applications was investigated. The location of Dx in the CMS nanoparticles is revealed and the function of CMS as penetration enhancers for topical application is shown.

  6. AgInS{sub 2}-ZnS nanocrystals: Evidence of bistable states using light-induced electron paramagnetic resonance and photoluminescence

    Energy Technology Data Exchange (ETDEWEB)

    Nobre, Sonia S.; Renard, Olivier; Chevallier, Theo; Le Blevennec, Gilles [Laboratoire d' Innovation pour les Technologies des Energies Nouvelles et les Nanomateriaux, Departement de Technologie des Nano-Materiaux, Service d' Elaboration de Nanomateriaux, Laboratoire de Synthese et Integration des Nanomateriaux, CEA-Grenoble (France); Lombard, Christian; Pepin-Donat, Brigitte [Laboratoire Structure et Proprietes d' Architecture Moleculaire (UMR 5819) CEA-CNRS - UJF/INAC/CEA-Grenoble (France)

    2014-04-15

    The precursor (AgIn){sub x} Zn{sub 2(1-x)}(S{sub 2}CN(C{sub 2}H{sub 5}){sub 2}){sub 4} was used to prepared AgInS{sub 2}-ZnS nanocrystals with different compositions (x = 0.4 and x = 0.7) and with different time of reaction (10 min and 75 min). The photoluminescence features of the nanocrystals were addressed by combining steady-state spectroscopy and light-induced electron paramagnetic resonance. Both techniques showed the contribution of at least two components for the emission, previously assigned to surface and intrinsic states. Light-induced electron paramagnetic resonance allowed detection of the photocreation both of irreversible paramagnetic species that are likely responsible for the nano-crystals degradation assigned to surface states and of reversible paramagnetic species assigned to intrinsic states. Moreover, reversible bistable paramagnetic states were observed. This Letter provides a scheme that might be useful in addressing the well-known problem of aging of the nanocrystals. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Comparative electron paramagnetic resonance investigation of reduced graphene oxide and carbon nanotubes with different chemical functionalities for quantum dot attachment

    Energy Technology Data Exchange (ETDEWEB)

    Pham, Chuyen V.; Krueger, Michael, E-mail: michael.krueger@fmf.uni-freiburg.de, E-mail: emre.erdem@physchem.uni-freiburg.de; Eck, Michael [Freiburg Materials Research Center (FMF), University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg (Germany); Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Köhler-Allee 103, 79110 Freiburg (Germany); Weber, Stefan; Erdem, Emre, E-mail: michael.krueger@fmf.uni-freiburg.de, E-mail: emre.erdem@physchem.uni-freiburg.de [Institute of Physical Chemistry, University of Freiburg, Albertstr. 21, 79104 Freiburg (Germany)

    2014-03-31

    Electron paramagnetic resonance (EPR) spectroscopy has been applied to different chemically treated reduced graphene oxide (rGO) and multiwalled carbon nanotubes (CNTs). A narrow EPR signal is visible at g = 2.0029 in both GO and CNT-Oxide from carbon-related dangling bonds. EPR signals became broader and of lower intensity after oxygen-containing functionalities were reduced and partially transformed into thiol groups to obtain thiol-functionalized reduced GO (TrGO) and thiol-functionalized CNT (CNT-SH), respectively. Additionally, EPR investigation of CdSe quantum dot-TrGO hybrid material reveals complete quenching of the TrGO EPR signal due to direct chemical attachment and electronic coupling. Our work confirms that EPR is a suitable tool to detect spin density changes in different functionalized nanocarbon materials and can contribute to improved understanding of electronic coupling effects in nanocarbon-nanoparticle hybrid nano-composites promising for various electronic and optoelectronic applications.

  8. Electron paramagnetic resonance and electron-nuclear double resonance study of the neutral copper acceptor in ZnGeP sub 2 crystals

    CERN Document Server

    Stevens, K T; Setzler, S D; Schünemann, P G; Pollak, T M

    2003-01-01

    Electron paramagnetic resonance (EPR) and electron-nuclear double resonance have been used to characterize the neutral copper acceptor in ZnGeP sub 2 crystals. The copper substitutes for zinc and behaves as a conventional acceptor (i.e. the 3d electrons do not play a dominant role). Because of a high degree of compensation from native donors, the copper acceptors in our samples were initially in the nonparamagnetic singly ionized state (Cu sub Z sub n sup -). The paramagnetic neutral state (Cu sub Z sub n sup 0) was observed when the crystals were exposed to 632.8 nm or 1064 nm laser light while being held at a temperature below 50 K. The g matrix of the neutral copper acceptor is axial g sub p sub a sub r = 2.049 and g sub p sub e sub r sub p = 2.030), with the unique principal direction parallel to the tetragonal c axis of the crystal. The hyperfine and nuclear quadrupole matrices also exhibit c-axis symmetry (A sub p sub a sub r = 87.6 MHz, A sub p sub e sub r sub p = 34.8 MHz and P = 0.87 MHz for sup 6 su...

  9. Pyrazoles and imidazoles as ligands. X. electron paramagnetic resonance spectra of MnII in a tetragonal environment of four pyrazoles and two anions

    NARCIS (Netherlands)

    Dowsing, R.D.; Nieuwenhuijse, B.; Reedijk, J.

    1971-01-01

    Electron Paramagnetic Resonance Spectra have been recorded for some compounds of the type Mn(ligand)4- (anion)2, with pyrazole and 3(5)-methyl pyrazole as the ligands, and Cl−, Br−, I−, and NO3−, as the anions. The spectra show absorptions far from geff=2 for all compounds at both X- and Q-band fre

  10. Electron paramagnetic resonance spectroscopic investigation of the inhibition of the phosphoroclastic system of Clostridium sporogenes by nitrite.

    Science.gov (United States)

    Payne, M J; Woods, L F; Gibbs, P; Cammack, R

    1990-10-01

    The proposal that nitrite exerts its inhibitory effect on anaerobic bacteria by direct interaction with the iron-sulphur proteins of the phosphoroclastic system was investigated. The effects of nitrate, nitrite with or without ascorbate, and nitric oxide on the growth of Clostridium sporogenes in liquid cultures at pH 7.4, on the rates of hydrogen production, and on the activities of the enzymes pyruvate-ferredoxin oxidoreductase and hydrogenase, and of ferredoxin were investigated. In agreement with previous studies, nitrate was the least effective inhibitor of cell growth, and nitric oxide the most effective. Nitrite reductase activity was very low in C. sporogenes, indicating that the presence of external reducing agents would be necessary for the reduction of nitrite to nitric oxide. Inhibition by nitrite was enhanced by ascorbate; 0.5 mM-nitrite with 10 mM-ascorbate stopped growth completely. In partially-purified preparations 4.1 mM-NaNO2 and equimolar ascorbate caused complete inactivation of hydrogenase activity but only partial (up to 78%) inactivation of pyruvate-ferredoxin oxidoreductase. This agreed with the loss of hydrogen production observed with nitrite in vivo. Inhibition occurred within 5 min, and was irreversible in each case. Electron paramagnetic resonance (EPR) spectroscopy showed that paramagnetic [Fe(NO)2(SR)2] species were formed during growth in the presence of nitrite, and were associated with cells. However, the intensity of these EPR signals did not correlate with the inhibition of cell growth. The [4Fe-4S] clusters in ferredoxin were shown by EPR spectroscopy to be resistant to treatment with 3.6 mM-NaNO2 and 3.6 mM-ascorbate. It is concluded that the effects of nitrite on pre-formed iron-sulphur proteins are not convincing as a basis for the lethal effects on bacterial cells.

  11. New roles of flavoproteins in molecular cell biology: blue-light active flavoproteins studied by electron paramagnetic resonance.

    Science.gov (United States)

    Schleicher, Erik; Bittl, Robert; Weber, Stefan

    2009-08-01

    Exploring enzymatic mechanisms at a molecular level is one of the major challenges in modern biophysics. Based on enzyme structure data, as obtained by X-ray crystallography or NMR spectroscopy, one can suggest how substrates and products bind for catalysis. However, from the 3D structure alone it is very rarely possible to identify how intermediates are formed and how they are interconverted. Molecular spectroscopy can provide such information and thus supplement our knowledge on the specific enzymatic reaction under consideration. In the case of enzymatic processes in which paramagnetic molecules play a role, EPR and related methods such as electron-nuclear double resonance (ENDOR) are powerful techniques to unravel important details, e.g. the electronic structure or the protonation state of the intermediate(s) carrying (the) unpaired electron spin(s). Here, we review recent EPR/ENDOR studies of blue-light active flavoproteins with emphasis on photolyases that catalyze the enzymatic repair of UV damaged DNA, and on cryptochrome blue-light photoreceptors that act in several species as central components of the circadian clock.

  12. The effect of spin polarization on zero field splitting parameters in paramagnetic pi-electron molecules.

    Science.gov (United States)

    van Gastel, Maurice

    2009-09-28

    Spin polarization effects play an important role in the theory of isotropic hyperfine interactions for aromatic protons. The spin polarization gives rise to significant isotropic proton hyperfine interactions--spin-dependent one-electron properties--smaller than 0 MHz and the effect has been theoretically described [H. M. McConnell and D. B. J. Chesnut, Chem. Phys. 28, 107 (1958)]. The influence of spin polarization on the zero field splitting parameters, which are spin-dependent two-electron properties, has not been clearly identified yet. A phenomenological equation is proposed here for the contribution of spin polarization to the zero field splitting parameter D in analogy to McConnell's equation for hyperfine interactions. The presence of the effect is demonstrated in a series of calculations on polyacenes in the triplet state and turns out to be responsible for up to 50% of the D parameter in the case of naphthalene! It is found that spin-unrestricted single-determinant methods, including the widely used density functional theory methods, do not accurately reproduce the two-electron reduced electron density required for the evaluation of two-electron spin-dependent properties. For the accurate calculation of zero field splitting parameters by quantum chemical methods, it thus seems necessary to resort to correlated ab initio methods which do not give rise to spin contamination and which do provide an accurate description of the two-electron reduced electron density.

  13. All-optical three-dimensional electron pulse compression

    CERN Document Server

    Wong, Liang Jie; Rohwer, Timm; Gedik, Nuh; Johnson, Steven G

    2014-01-01

    We propose an all-optical, three-dimensional electron pulse compression scheme in which Hermite-Gaussian optical modes are used to fashion a three-dimensional optical trap in the electron pulse's rest frame. We show that the correct choices of optical incidence angles are necessary for optimal compression. We obtain analytical expressions for the net impulse imparted by Hermite-Gaussian free-space modes of arbitrary order. Although we focus on electrons, our theory applies to any charged particle and any particle with non-zero polarizability in the Rayleigh regime. We verify our theory numerically using exact solutions to Maxwell's equations for first-order Hermite-Gaussian beams, demonstrating single-electron pulse compression factors of $>10^{2}$ in both longitudinal and transverse dimensions with experimentally realizable optical pulses. The proposed scheme is useful in ultrafast electron imaging for both single- and multi-electron pulse compression, and as a means of circumventing temporal distortions in ...

  14. The Electron Trajectory in a Relativistic Femtosecond Laser Pulse

    Institute of Scientific and Technical Information of China (English)

    He Feng; Yu Wei; Lu Peixiang; Xu Han; Shen Baifei; Li Ruxin; Xu Zhizhan

    2005-01-01

    In this report, we start from Lagrange equation and analyze theoretically the electron dynamics in electromagnetic field. By solving the relativistic government equations of electron,the trajectories of an electron in plane laser pulse, focused laser pulse have been given for different initial conditions. The electron trajectory is determined by its initial momentum, the amplitude,spot size and polarization of the laser pulse. The optimum initial momentum of the electron for LSS (laser synchrotron source) is obtained. Linear polarized laser is more advantaged than circular polarized laser for generating harmonic radiation.

  15. Axially uniform magnetic field-modulation excitation for electron paramagnetic resonance in rectangular and cylindrical cavities by slot cutting

    Science.gov (United States)

    Sidabras, Jason W.; Richie, James E.; Hyde, James S.

    2017-01-01

    In continuous-wave (CW) Electron Paramagnetic Resonance (EPR) a low-frequency time-harmonic magnetic field, called field modulation, is applied parallel to the static magnetic field and incident on the sample. Varying amplitude of the field modulation incident on the sample has consequences on spectral line-shape and line-height over the axis of the sample. Here we present a method of coupling magnetic field into the cavity using slots perpendicular to the sample axis where the slot depths are designed in such a way to produce an axially uniform magnetic field along the sample. Previous literature typically assumes a uniform cross-section and axial excitation due to the wavelength of the field modulation being much larger than the cavity. Through numerical analysis and insights obtained from the eigenfunction expansion of dyadic Green's functions, it is shown that evanescent standing-wave modes with complex cross-sections are formed within the cavity. From this analysis, a W-band (94 GHz) cylindrical cavity is designed where modulation slots are optimized to present a uniform 100 kHz field modulation over the length of the sample.

  16. Characterizing the conformational dynamics of metal-free PsaA using molecular dynamics simulations and electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Deplazes, Evelyne; Begg, Stephanie L; van Wonderen, Jessica H; Campbell, Rebecca; Kobe, Bostjan; Paton, James C; MacMillan, Fraser; McDevitt, Christopher A; O'Mara, Megan L

    2015-12-01

    Prokaryotic metal-ion receptor proteins, or solute-binding proteins, facilitate the acquisition of metal ions from the extracellular environment. Pneumococcal surface antigen A (PsaA) is the primary Mn(2+)-recruiting protein of the human pathogen Streptococcus pneumoniae and is essential for its in vivo colonization and virulence. The recently reported high-resolution structures of metal-free and metal-bound PsaA have provided the first insights into the mechanism of PsaA-facilitated metal binding. However, the conformational dynamics of metal-free PsaA in solution remain unknown. Here, we use continuous wave electron paramagnetic resonance (EPR) spectroscopy and molecular dynamics (MD) simulations to study the relative flexibility of the structural domains in metal-free PsaA and its distribution of conformations in solution. The results show that the crystal structure of metal-free PsaA is a good representation of the dominant conformation in solution, but the protein also samples structurally distinct conformations that are not captured by the crystal structure. Further, these results suggest that the metal binding site is both larger and more solvent exposed than indicated by the metal-free crystal structure. Collectively, this study provides atomic-resolution insight into the conformational dynamics of PsaA prior to metal binding and lays the groundwork for future EPR and MD based studies of PsaA in solution.

  17. Combustion Synthesized Cr3+-doped-BaMgAl10O17 Phosphor: An Electron Paramagnetic Resonance and Optical Study

    Science.gov (United States)

    Singh, Vijay; Sivaramaiah, G.; Rao, J. L.; Srivastava, Anoop K.; Ravikumar, R. V. S. S. N.; Dhoble, S. J.; Singh, P. K.; Mohapatra, Manoj

    2016-01-01

    BaMgAl10O17 phosphors doped with Cr3+ ions were prepared by a combustion route at a furnace temperature of 773 K. The X-ray diffraction pattern revealed that the BaMgAl10O17 phosphor was in a hexagonal phase. Energy-dispersive X-ray mapping images demonstrated the presence of the dopant ion in the BaMgAl10O17 matrix. The bands observed in the optical absorption spectrum were characteristic of Cr3+ ions in octahedral geometry. Upon 555-nm excitation, an intense narrow red emission line centred at 690 nm due to the 2Eg → 4A2g transition of Cr3+ ions was observed. The electron paramagnetic resonance (EPR) spectrum of Cr3+ ions in BaMgAl10O17 phosphor showed multiple absorption bands having at least 6 g values. Based on the EPR data, various parameters such as the absolute number of spins, Gibbs potential, magnetic susceptibility and magnetic moments, Curie constant, etc., for the system were evaluated.

  18. Spin-label electron paramagnetic resonance studies on the interaction of avidin with dimyristoyl-phosphatidylglycerol membranes.

    Science.gov (United States)

    Swamy, M J; Marsh, D

    2001-08-06

    The interaction of avidin--a basic protein from hen egg-white--with dimyristoyl-phosphatidylglycerol membranes was investigated by spin-label electron paramagnetic resonance spectroscopy. Phosphatidylcholines, bearing the nitroxide spin label at different positions along the sn-2 acyl chain of the lipid were used to investigate the effect of protein binding on the lipid chain-melting phase transition and acyl chain dynamics. Binding of the protein at saturating levels results in abolition of the chain-melting phase transition of the lipid and accompanying perturbation of the lipid acyl chain mobility. In the fluid phase region, the outer hyperfine splitting increases for all phosphatidylcholine spin-label positional isomers, indicating that the chain mobility is decreased by binding avidin. However, there was no evidence for direct interaction of the protein with the lipid acyl chains, clearly indicating that the protein does not penetrate the hydrophobic interior of the membrane. Selectivity experiments with different spin-labelled lipid probes indicate that avidin exhibits a preference for negatively charged lipid species, although all spin-labelled lipid species indirectly sense the protein binding. The interaction with negatively charged lipids is relevant to the use of avidin in applications such as the ultrastructural localization of biotinylated lipids in histochemical studies.

  19. Electron paramagnetic resonance studies of the soluble CuA protein from the cytochrome ba3 of Thermus thermophilus.

    Science.gov (United States)

    Karpefors, M; Slutter, C E; Fee, J A; Aasa, R; Källebring, B; Larsson, S; Vänngård, T

    1996-11-01

    The electron paramagnetic resonance (EPR) spectrum of the binuclear CuA center in the water-soluble subunit II fragment from cytochrome ba3 of Thermus thermophilus was recorded at 3.93, 9.45, and 34.03 GHz, and the EPR parameters were determined by computer simulations. The frequency and M1 dependence of the linewidth was discussed in terms of g strain superimposed on a correlation between the A and g values. The g values were found to be gx = 1.996, gy = 2.011, gz = 2.187, and the two Cu ions contribute nearly equally to the hyperfine structure, with magnitude of Ax magnitude of approximately 15 G, magnitude of Ay magnitude = 29 G, and magnitude of Az magnitude of = 28.5 G (65Cu). Theoretical CNDO/S calculations, based on the x-ray structure of the Paracoccus denitrificans enzyme, yield a singly occupied antibonding orbital in which each Cu is pi*-bonded to one S and sigma*-bonded to the other. In contrast to the equal spin distribution suggested by the EPR simulations, the calculated contributions from the Cu ions differ by a factor of 2. However, only small changes in the ligand geometry are needed to reproduce the experimental results.

  20. Decoupling of automatic control systems in a continuous-wave electron paramagnetic resonance spectrometer for biomedical applications.

    Science.gov (United States)

    Hirata, Hiroshi; Watanabe, Hiroyuki; Kumada, Masaharu; Itoh, Kouichi; Fujii, Hirotada

    2004-08-01

    This article describes a systematic approach to decoupling automatic tuning control (ATC) and automatic matching control (AMC) systems in continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy for animal experiments. This technique enables us to improve the stability of CW-EPR spectroscopy even if the animal is moving during the data acquisition of EPR spectra. The control systems are formulated to allow the behavior of interference between them to be investigated, since they are generally coupled due to the characteristics of the microwave resonator. The stability of the entire control system in a 1.1 GHz CW-EPR spectrometer is evaluated with the generalized Nyquist stability criterion. We compare the EPR spectra of a triarylmethyl (TAM) radical that is dosed in anesthetized mice in terms of the signal-to-noise ratio (SNR) to test the precompensator for decoupling the ATC and AMC systems. The experimental findings suggest that the present technique is useful for improving the SNR of EPR spectra in animal experiments. The SNR of the measured EPR spectra was improved by about 50% with the precompensator.

  1. An electron paramagnetic resonance study of the behaviour of copper (II) in ageing catechin-based model wines

    Energy Technology Data Exchange (ETDEWEB)

    Mitri, M.; Scollary, G.R. [The University of Melbourne, Parkville, VIC (Australia). School of Chemistry; Troup, G.J.; Hutton, D.R.; Hunter, C.A.; Hewitt, D.G. [Monash University, Clayton, VIC (Australia). Depts of Physics, Anatomy and Chemistry

    1996-12-31

    This poster reports an electron paramagnetic resonance (EPR) study of copper in a model white wine. The model consists of a saturated 12% ethanol solution of potassium hydrogen tartrate solution (the `wine base`) containing copper and catechin as the oxidizable substrate. Ascorbic acid, as a supposed anti-oxidant, was added to some solutions. A Varian E-12 EPR spectrometer ({approx}9.1 GHz frequency) with quartz sample tubes was used and spectra were recorded at liquid nitrogen temperature to avoid polar water losses. Solutions were examined on four successive days whilst kept at room temperature and subsequently every third day when stored at 45 degree C. Variations in signal intensity, linewidth and form will be shown and the changes related to the degree of browning, as measured by visible absorption spectroscopy at 440 nm. The ESP spectra of the brown deposits reveal that the copper (II) ion is in a low symmetry site and a well defined free radical signal was also observed. No free radical signal was found in solutions containing copper and catechin, indicating that a high degree of polymerization of the oxidized catechin is required to stabilize the free radical species Truncated abstract. 1 fig.

  2. Use of Fe(3+) ion probe to study the stability of urea-intercalated kaolinite by electron paramagnetic resonance.

    Science.gov (United States)

    Budziak Fukamachi, Cristiane Regina; Wypych, Fernando; Mangrich, Antonio Salvio

    2007-09-15

    The effect of mechanical and chemical activation in processes of urea intercalation in the interlayer spacing of kaolinite and the effect of varying the temperature of the intercalation product between 100 and 200 degrees C were studied using Fe(3+) ions as a probe in electron paramagnetic resonance (EPR) spectroscopy. Other techniques were also used to characterize the samples. Monitoring the heating of urea-intercalated kaolinite, FTIR, and XRD revealed that the product obtained was stable up to a temperature of 150-160 degrees C. The EPR data indicated that the intercalation process promoted an approximation and increase of the magnetic interactions among the Fe(3+) ions. The DRUV-vis analysis of the product before heating showed an absorption band at 680 nm that was absent in the raw kaolinite. This band was attributed to the transition A(1)6-->T(2)4(G4) in the adjacent Fe(3+) ions, intensified by magnetic coupling among these ions. We suggest that intercalated urea forms hydrogen bonds between the carbonyl's oxygen and the hydroxyls bound to the Fe(3+) ions of the kaolinite structure. This would cause the approximation of the Fe(3+) ions, maximizing magnetic couplings and intensifying concentrated centers of Fe(3+), as was visible by EPR spectroscopy.

  3. 2-Mercaptobenzoxazole pentacyanoferrate(II/III complexes: UV-Visible, Mössbauer, electron paramagnetic resonance, electrochemistry and molecular modeling

    Directory of Open Access Journals (Sweden)

    Luiz Juciane B

    2004-01-01

    Full Text Available 2-Mercaptobenzoxazole pentacyanoferrate(II/III complexes, [FeII/III(CN5(bzoxs]3-/2- , were prepared in MeOH/H2O 75:25% solutions and characterized by spectroscopic UV-Vis, Mössbauer, electron paramagnetic resonance (epr and electrochemical-cyclic voltammetry- techniques. UV-Vis and epr spectra along with the electrochemical behavior suggested the coordination of the multi-functional N,S,O- donor ligand, bzoxs, to iron(III through the sulfur atom. The crystal field parameters, DqL and Dt, calculated for the iron(II complex, in addition to the reversible redox process FeIII-bzoxs + e- -> FeII-bzoxs also pointed to coordination via the sulfur atom. The results were compared with the chemical properties of pentacyanoferrate complexes containing other monodentate N-, S- and O-donor ligands. Ab initio calculations revealed the composition of the frontier orbitals of bzoxs and are in agreement with the mode of coordination proposed from the experimental data.

  4. Electron paramagnetic resonance evidence of hydroxyl radical generation and oxidative damage induced by tetrabromobisphenol A in Carassius auratus

    Energy Technology Data Exchange (ETDEWEB)

    Shi Huahong [State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, Nanjing 210093 (China)]. E-mail: huahongshi@tom.com; Wang Xiaorong [State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, Nanjing 210093 (China); Luo Yi [State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, Nanjing 210093 (China); Su Yan [State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, Nanjing 210093 (China)

    2005-09-30

    Tetrabromobisphenol A (TBBPA) is one of the most widely used brominated flame retardants (BFRs). To confirm its putative oxidative stress-inducing activity, freshwater fish Carassius auratus were injected intraperitoneally with TBBPA. One experiment lasted 3 h to 28 days after a single injection of 100 mg/kg TBBPA, and the other lasted 24 h after a single injection of 0-300 mg/kg TBBPA. Reactive oxygen species (ROS) were trapped by phenyl-tert-butyl nitrone (PBN) and detected by electron paramagnetic resonance (EPR). Protein carbonyl (PCO) and lipid peroxidation product (LPO) content were also determined. A six-line EPR spectrum was detected in the sample prepared in air, and a multiple one was obtained in nitrogen. The observed spectrum in nitrogen fits the simulation one with PBN/{center_dot}OCH{sub 3} and PBN/{center_dot}CH{sub 3} quite well. As compared to the control group, TBBPA significantly induced ROS production marked by the intensity of the prominent spectra in liver and bile. TBBPA (100 mg/kg) also significantly increased PCO content in liver starting 24 h and LPO content 3 days after injection. Either PCO or LPO content showed significant relation with ROS production. Based on the hyperfine constants and shape of the spectrum, ROS induced by TBBPA was determined as {center_dot}OH. The results clearly indicated that TBBPA could induce {center_dot}OH generation and result in oxidative damage in liver of C. auratus.

  5. Electron paramagnetic resonance spectroscopy of lactoperoxidase complexes: clarification of hyperfine splitting for the NO adduct of lactoperoxidase

    Energy Technology Data Exchange (ETDEWEB)

    Lukat, G.S.; Rodgers, K.R.; Goff, H.M.

    1987-11-03

    Electron paramagnetic resonance (EPR) studies of the nitrosyl adduct of ferrous lactoperoxidase (LPO) confirm that the fifth axial ligand in LPO is bound to the iron via a nitrogen atom. Complete reduction of the ferric LPO sample is required in order to observe the nine-line hyperfine splitting in the ferrous LPO/NO EPR spectrum. The ferrous LPO/NO complex does not exhibit a pH or buffer system dependence when examined by EPR. Interconversion of the ferrous LPO/NO complex and the ferric LPO/NO/sub 2//sup -/ complex is achieved by addition of the appropriate oxidizing or reducing agent. Characterization of the low-spin LPO/NO/sub 2//sup -/ complex by EPR and visible spectroscopy is reported. The pH dependence of the EPR spectra of ferric LPO and ferric LPO/CN/sup -/ suggests that a high-spin anisotrophic LPO complex is formed at high pH and an acid-alkaline transition of the protein conformation near the heme site does occur in LPO/CN/sup -/. The effect of tris(hydroxymethyl)aminomethane buffer on the LPO EPR spectrum is also examined.

  6. Investigation of Antioxidant Activity of Pomegranate Juices by Means of Electron Paramagnetic Resonance and UV-Vis Spectroscopy.

    Science.gov (United States)

    Kozik, Violetta; Jarzembek, Krystyna; Jędrzejowska, Agnieszka; Bąk, Andrzej; Polak, Justyna; Bartoszek, Mariola; Pytlakowska, Katarzyna

    2015-01-01

    Pomegranate fruit (Punica granatum L.) is a source of numerous phenolic compounds, and it contains flavonoids such as anthocyanins, anthocyanidins, cyanidins, catechins and other complexes of flavonoids, ellagitannins, and hydrolyzed tannins. Pomegranate juice shows antioxidant, antiproliferative, and anti-atherosclerotic properties. The antioxidant capacity (TEAC) of the pomegranate juices was measured using electron paramagnetic resonance (EPR) spectroscopy and 1,1-diphenyl-2-picrylhydrazyl (DPPH•) as a source of free radicals, and the total phenolic (TP) content was measured using UV-Vis spectroscopy. All the examined pomegranate juices exhibited relatively high antioxidant properties. The TEAC values determined by means of EPR spectroscopy using Trolox (TE) as a free radical scavenger were in the range of 463.12 to 1911.91 μmol TE/100 mL juice. The TP content measured by the Folin-Ciocalteu method, using gallic acid (GA) as a free radical scavenger, widely varied in the investigated pomegranate juice samples and ranged from 1673.62 to 5263.87 mg GA/1 L juice. The strongest antioxidant properties were observed with the fresh pomegranate juices obtained from the fruits originating from Israel, Lebanon, and Azerbaijan. Correlation analysis of numerical data obtained by means of EPR spectroscopy (TEAC) and UV-Vis spectroscopy (TP) gave correlation coefficient (r)=0.90 and determination coefficient (r2)=0.81 (P<0.05).

  7. Retrospective assessment of radiation exposure using biological dosimetry: chromosome painting, electron paramagnetic resonance and the glycophorin a mutation assay.

    Science.gov (United States)

    Kleinerman, R A; Romanyukha, A A; Schauer, D A; Tucker, J D

    2006-07-01

    Biological monitoring of dose can contribute important, independent estimates of cumulative radiation exposure in epidemiological studies, especially in studies in which the physical dosimetry is lacking. Three biodosimeters that have been used in epidemiological studies to estimate past radiation exposure from external sources will be highlighted: chromosome painting or FISH (fluorescence in situ hybridization), the glycophorin A somatic mutation assay (GPA), and electron paramagnetic resonance (EPR) with teeth. All three biodosimeters have been applied to A-bomb survivors, Chernobyl clean-up workers, and radiation workers. Each biodosimeter has unique advantages and limitations depending upon the level and type of radiation exposure. Chromosome painting has been the most widely applied biodosimeter in epidemiological studies of past radiation exposure, and results of these studies provide evidence that dose-related translocations persist for decades. EPR tooth dosimetry has been used to validate dose models of acute and chronic radiation exposure, although the present requirement of extracted teeth has been a disadvantage. GPA has been correlated with physically based radiation dose after high-dose, acute exposures but not after low-dose, chronic exposures. Interindividual variability appears to be a limitation for both chromosome painting and GPA. Both of these techniques can be used to estimate the level of past radiation exposure to a population, whereas EPR can provide individual dose estimates of past exposure. This paper will review each of these three biodosimeters and compare their application in selected epidemiological studies.

  8. Ultrafast imprinting of topologically protected magnetic textures via pulsed electrons

    Science.gov (United States)

    Schäffer, A. F.; Dürr, H. A.; Berakdar, J.

    2017-07-01

    Short electron pulses are demonstrated to trigger and control magnetic excitations, even at low electron current densities. We show that the tangential magnetic field surrounding a picosecond electron pulse can imprint topologically protected magnetic textures such as skyrmions in a sample with a residual Dzyaloshinskii-Moriya spin-orbital coupling. Characteristics of the created excitations such as the topological charge can be steered via the duration and the strength of the electron pulses. The study points to a possible way for a spatiotemporally controlled generation of skyrmionic excitations.

  9. Deficiencies of active electronic radiation protection dosimeters in pulsed fields.

    Science.gov (United States)

    Ankerhold, U; Hupe, O; Ambrosi, P

    2009-07-01

    Nowadays nearly all radiation fields used for X-ray diagnostics are pulsed. These fields are characterised by a high dose rate during the pulse and a short pulse duration in the range of a few milliseconds. The use of active electronic dosimeters has increased in the past few years, but these types of dosimeters might possibly not measure reliably in pulsed radiation fields. Not only personal dosimeters but also area dosimeters that are used mainly for dose rate measurements are concerned. These cannot be substituted by using passive dosimeter types. The characteristics of active electronic dosimeters determined in a continuous radiation field cannot be transferred to those in pulsed fields. Some provisional measurements with typical electronic dosimeters in pulsed radiation fields are presented to reveal this basic problem.

  10. Patterning molecular scale paramagnets at Au Surface: A root to Magneto-Molecular-Electronics

    CERN Document Server

    Messina, Paul C; Sorace, L; Rovai, D; Caneschi, A; Gatteschi, Dante; Messina, Paolo; Mannini, Matteo; Sorace, Lorenzo; Rovai, Donella; Caneschi, Andrea; Gatteschi, Dante

    2004-01-01

    Few examples of the exploitation of molecular magnetic properties in molecular electronics are known to date. Here we propose the realization of Self assembled monolayers (SAM) of a particular stable organic radical. This radical is meant to be used as a standard molecule on which to prove the validity of a single spin reading procedure known as ESR-STM. We demonstrate here that the radical is chemically anchored at the surface, preserves its magnetic functionality and can be imaged by STM. STM and ESR investigations of the molecular film is reported. We also discuss a range of possible applications, further than ESR-STM, of magnetic monolayers of simple purely organic magnetic molecule.

  11. Initial deposition and electron paramagnetic resonance defects characterization of TiO{sub 2} films prepared using successive ionic layer adsorption and reaction method

    Energy Technology Data Exchange (ETDEWEB)

    Wu Yiyong, E-mail: wuyiyong2001@yahoo.com.cn [National Key Laboratory of Materials Behaviors and Evaluation Technology in Space Environments, Harbin Institute of Technology, P.O. 432, Nan gang District, Harbin, 150080 (China); Shi Yaping [National Key Laboratory of Materials Behaviors and Evaluation Technology in Space Environments, Harbin Institute of Technology, P.O. 432, Nan gang District, Harbin, 150080 (China); Harbin University of Commerce, P.O. 493, Song bei District, Harbin, 150028 (China); Xu Xianbin; Sun Chengyue [National Key Laboratory of Materials Behaviors and Evaluation Technology in Space Environments, Harbin Institute of Technology, P.O. 432, Nan gang District, Harbin, 150080 (China)

    2012-06-01

    Successive ionic layer adsorption and reaction (SILAR) technique was considered promisingly to deposit ultra thin titanium dioxide (TiO{sub 2}) films under ambient condition. In this paper, the growth process, structures and paramagnetic defects of the films were characterized by complementary techniques of atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and electron paramagnetic resonance spectroscopy. The results indicate that on glass substrate the SILAR TiO{sub 2} film nucleates in an island mode within the initial five deposition cycles but grows in a layer-by-layer mode afterwards. The growth rate was measured as 4.6 A/cycle. In the as-deposited films, a kind of paramagnetic defects is detected at g (2.0029) and it can be attributed to oxygen vacancies. These as-received oxygen vacancies could be annealed out at 473 K. Ultraviolet irradiation on the as-deposited films can also decrease the density of the defects. The relative mechanisms on the phenomenon were discussed in this paper. - Highlights: Black-Right-Pointing-Pointer TiO{sub 2} films are deposited on glass at 25 Degree-Sign C by successive ionic layer adsorption and reaction method with a rate of 4.6 A/cycle. Black-Right-Pointing-Pointer The films nucleate in an island mode initially but grow in a layer mode afterwards. Black-Right-Pointing-Pointer The SILAR TiO{sub 2} films nucleation period is five cycles. Black-Right-Pointing-Pointer Electron paramagnetic resonance spectroscopy shows that TiO{sub 2} films paramagnetic defects are attributed to oxygen vacancies. Black-Right-Pointing-Pointer They will decrease by anneal or ultraviolet radiation and form hydroxyl or superoxide radicals.

  12. Electron paramagnetic resonance and electron-nuclear double-resonance study of Ti sup 3 sup + centres in KTiOPO sub 4

    CERN Document Server

    Setzler, S D; Fernelius, N C; Scripsick, M P; Edwards, G J; Halliburton, L E

    2003-01-01

    Electron paramagnetic resonance and electron-nuclear double resonance have been used to characterize four Ti sup 3 sup + centres in undoped crystals of potassium titanyl phosphate (KTiOPO sub 4 or KTP). These 3d sup 1 defects (S = 1/2) are produced by ionizing radiation (either 60 kV x-rays or 355 nm photons from a tripled Nd:YAG laser), and form when the regular Ti sup 4 sup + ions in the crystal trap an electron. Two of these trapped-electron centres are only observed in hydrothermally grown KTP and the other two are dominant in flux-grown KTP. Both of the Ti sup 3 sup + centres in hydrothermally grown crystals have a neighbouring proton (i.e. an OH sup - molecule). In the flux-grown crystals, one of the Ti sup 3 sup + centres is adjacent to an oxygen vacancy and the other centre is tentatively attributed to a self-trapped electron (i.e. a Ti sup 3 sup + centre with no stabilizing entity nearby). The g matrix and phosphorus hyperfine matrices are determined for all four Ti sup 3 sup + centres, and the proto...

  13. Flue gas dry scrubbing using pulsed electron beams

    Energy Technology Data Exchange (ETDEWEB)

    Penetrante, B.M.

    1996-02-20

    Electron beam dry scrubbing is a technique for removing in a single step both nitrogen oxides (NO{sub x}) and sulfur dioxide (SO{sub 2}) from the off-gas generated by utilities burning high sulfur coal. The use of pulsed electron beams may provide the most cost-effective solution to the implementation of this technique. This paper presents the results of plasma chemistry calculations to study the effect of dose rate, pulse length and pulse repetition rate on pulsed electron beam processing of NO{sub x} and SO{sub 2} in flue gases. The main objective is to determine if the proposed combinations of dose rate, pulse length and pulse repetition rate would have any deleterious effect on the utilization of radicals for pollutant removal. For a dose rate of 2x10{sup 5} megarads per second and a pulse length of 30 nanoseconds, the average dose per pulse is sufficiently low to prevent any deleterious effect on process efficiency because of radical-radical recombination reactions. During each post-pulse period, the radicals are utilized in the oxidation of NO{sub x} and SO{sub 2} in a timescale of around 200 microseconds; thus, with pulse frequencies of around 5 kilohertz or less, the radical concentrations remain sufficiently low to prevent any significant competition between radical-pollutant and radical-radical reactions. The main conclusion is that a pulsed electron beam reactor, operating with a dose rate of 2x10{sup 5} megarads per second, pulse length of 30 ns and pulse repetition rate of up to around 5 kHz, will have the same plasma chemistry efficiency as an electron beam reactor operating with a very low dose rate in continuous mode.

  14. Structural characterization of titania by X-ray diffraction, photoacoustic, Raman spectroscopy and electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Kadam, R M; Rajeswari, B; Sengupta, Arijit; Achary, S N; Kshirsagar, R J; Natarajan, V

    2015-02-25

    A titania mineral (obtained from East coast, Orissa, India) was investigated by X-ray diffraction (XRD), photoacoustic spectroscopy (PAS), Raman and Electron Paramagnetic Resonance (EPR) studies. XRD studies indicated the presence of rutile (91%) and anatase (9%) phases in the mineral. Raman investigation supported this information. Both rutile and anatase phases have tetragonal structure (rutile: space group P4(2)/mnm, a=4.5946(1) Å, c=2.9597(1) Å, V=62.48(1) (Å)(3), Z=2; anatase: space group I4(1)/amd, 3.7848(2) Å, 9.5098(11) Å, V=136.22(2) (Å)(3), Z=4). The deconvoluted PAS spectrum showed nine peaks around 335, 370, 415,485, 555, 605, 659, 690,730 and 785 nm and according to the ligand field theory, these peaks were attributed to the presence of V(4+), Cr(3+), Mn(4+) and Fe(3+) species. EPR studies revealed the presence of transition metal ions V(4+)(d(1)), Cr(3+)(d(3)), Mn(4+)(d(3)) and Fe(3+)(d(5)) at Ti(4+) sites. The EPR spectra are characterized by very large crystal filed splitting (D term) and orthorhombic distortion term (E term) for multiple electron system (s>1) suggesting that the transition metal ions substitute the Ti(4+) in the lattice which is situated in distorted octahedral coordination of oxygen. The possible reasons for observation of unusually large D and E term in the EPR spectra of transition metal ions (S=3/2 and 5/2) are discussed.

  15. Phospholipid bilayer relaxation dynamics as revealed by the pulsed electron-electron double resonance of spin labels

    Science.gov (United States)

    Syryamina, V. N.; Dzuba, S. A.

    2012-10-01

    Electron paramagnetic resonance (EPR) spectroscopy in the form of pulsed electron-electron double resonance (ELDOR) was applied to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) phospholipid bilayers containing lipids that were spin-labeled at different carbon positions along the lipid acyl chain. Pulsed ELDOR detects motionally induced spin flips of nitrogen nuclei in the nitroxide spin labels, which manifests itself as magnetization transfer (MT) in the nitroxide EPR spectrum. The MT effect was observed over a wide temperature range (100-225 K) on a microsecond time scale. In line with a previous study on molecular glasses [N. P. Isaev and S. A. Dzuba, J. Chem. Phys. 135, 094508 (2011), 10.1063/1.3633241], the motions that induce MT effect were suggested to have the same nature as those in dielectric secondary (β) Johari-Goldstein fast relaxation. The results were compared with literature dielectric relaxation data for POPC bilayers, revealing some common features. Molecular motions resulting in MT are faster for deeper spin labels in the membrane interior. The addition of cholesterol to the bilayer suppresses the lipid motions near the steroid nucleus and accelerates the lipid motions beyond the steroid nucleus, in the bilayer interior. This finding was attributed to the lipid acyl chains being more ordered near the steroid nucleus and less ordered in the bilayer interior. The motions are absent in dry lipids, indicating that the motions are determined by intermolecular interactions in the bilayer.

  16. A pulse radiolysis study on electron affinity of piperonal

    Institute of Scientific and Technical Information of China (English)

    MA; Jianhua; LIN; Weizhen; WANG; Wenfeng; YAO; Side

    2005-01-01

    The piperonal electron affinity was studied using pulse radiolysis technique. The electron transfer reaction process between piperonal and anthraquinone-2-sulfate was observed in the pH 7 phosphoric acid salt buffer. The transient absorption spectra of electron transfer reaction between piperonal and anthraquinone-2-sulfate were obtained, and the initial proof of the electron transfer between electron donor and acceptor was provided directly. The one-electron reduction potential of piperonal was determined to be -0.457 V.

  17. [Electron paramagnetic resonance study of the interactions between steroid hormones and binding proteins].

    Science.gov (United States)

    Basset, M; Chambaz, E M; Defaye, G; Metz, B

    1978-01-01

    Interaction of a spin labeled corticosteroid (desoxycorticosterone nitroxyde: DOC -NO) with three purified proteins (albumin, transcortin, progesterone binding protein: PBG) was studied by electron spin resonance (ESR) spectroscopy. DOC-NO was competitive with natural corticosteroids and therefore bound at the same site to specific binding proteins. ESR spectra in the presence of each of the proteins showed an immobilized (bound) form of the spin labeled steroid and allowed the calculation of the corresponding association constant (Ka) at equilibrium. The three binding proteins could be characterized by the ESR parameters of the DOC-NO bound form. The thermodynamic parameters (deltaH, deltaS) of the steroid-protein interactions were calculated from the ESR data obtained within a wide temperature range (3--40 degrees C). The ESR spectra width (2T) was used to evaluate the polarity of the spin label environment within the steroid binding site: a hydrophobic character was observed for transcortin whereas PBG exhibited a more hydrophilic steroid binding sits. The rotational correlation time of the three protein DOC-NO complexes at equilibrium were calculated from ESR data; the results were correlated with the protein molecular size and suggested a non spherical shape for the binding macromolecule in solution. Spin labelling of biologically active steroids thus provides a novel approach for the study of the interaction of these hormones with their binding protein. Providing a suitable spin label, the ESR parameters may allow the characterization of several types of binding sites of different biological significance for the same hormone, in biological fluids as well as in target tissues.

  18. Uses of pulsed electron beam to solid-states studies

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, Noriaki; Nakayama, Takeyoshi; Tanimura, Katsumi; Chong, Taisu; Saidoh, Masahiro

    1982-03-01

    A survey is given on the use of the pulsed electron beams to studies of solid states. Even though main emphasis is placed on the studies carried out at the Faculty of Engineering, Nagoya University, using the Pulsed Electron Facilities installed in 1970, the works carried out at other institutes are also included. Only the studies of crystalline solids with simple structures, such as alkali halides and aromatic hydrocarbons are covered. In the first place several instrumentations which have extended utilities of pulsed-electron beams are presented. Then we discuss the studies of the dynamic of excitons, emphasizing the advantages and disadvantages of the usage of the electron pulses. Then usages of the pulsed-electron beam for the studies of the excited states of the quasi-stable defects are described. Application of the electron pulse for studies of the excitation spectroscopy of the photochemistry is described. The dynamic studies of defects introduced by electron-pulse bombardment is discussed finally. A summary is given, which includes also the possible future experiments.

  19. Application of electron paramagnetic resonance spectroscopy to comparative examination of different groups of free radicals in thermal injuries treated with propolis and silver sulphadiazine.

    Science.gov (United States)

    Olczyk, Pawel; Ramos, Pawel; Bernas, Marcin; Komosinska-Vassev, Katarzyna; Stojko, Jerzy; Pilawa, Barbara

    2013-01-01

    Different groups of free radicals expressed in burn wounds treated with propolis and silver sulphadiazine were examined. The thermal effect forms major types of free radicals in a wound because of the breaking of chemical bonds. Free radicals, located in the heated skin, were tested after 21 days of treating by these two substances. The aim of this work was to find the method for determination of types and concentrations of different groups of free radicals in wound after high temperature impact during burning. The effects of the therapy by propolis and silver sulphadiazine on free radicals were studied. Since the chemical methods of free radicals studies are destructive, the usefulness of the electron paramagnetic resonance spectroscopy was tested in this work. The electron paramagnetic resonance spectra measured with the microwave power of 2.2 mW were numerically fitted by theoretical curves of Gaussian and Lorentzian shapes. The experimental electron paramagnetic resonance spectra of tissue samples are best fitted by the sum of one Gauss and two Lorentz lines. An innovatory numerical procedure of spectroscopic skin analysis was presented. It is very useful in the alternative medicine studies.

  20. Manganese binding properties of human calprotectin under conditions of high and low calcium: X-ray crystallographic and advanced electron paramagnetic resonance spectroscopic analysis.

    Science.gov (United States)

    Gagnon, Derek M; Brophy, Megan Brunjes; Bowman, Sarah E J; Stich, Troy A; Drennan, Catherine L; Britt, R David; Nolan, Elizabeth M

    2015-03-04

    The antimicrobial protein calprotectin (CP), a hetero-oligomer of the S100 family members S100A8 and S100A9, is the only identified mammalian Mn(II)-sequestering protein. Human CP uses Ca(II) ions to tune its Mn(II) affinity at a biologically unprecedented hexahistidine site that forms at the S100A8/S100A9 interface, and the molecular basis for this phenomenon requires elucidation. Herein, we investigate the remarkable Mn(II) coordination chemistry of human CP using X-ray crystallography as well as continuous-wave (CW) and pulse electron paramagnetic resonance (EPR) spectroscopies. An X-ray crystallographic structure of Mn(II)-CP containing one Mn(II), two Ca(II), and two Na(I) ions per CP heterodimer is reported. The CW EPR spectrum of Ca(II)- and Mn(II)-bound CP prepared with a 10:0.9:1 Ca(II):Mn(II):CP ratio is characterized by an unusually low zero-field splitting of 485 MHz (E/D = 0.30) for the S = 5/2 Mn(II) ion, consistent with the high symmetry of the His6 binding site observed crystallographically. Results from electron spin-echo envelope modulation and electron-nuclear double resonance experiments reveal that the six Mn(II)-coordinating histidine residues of Ca(II)- and Mn(II)-bound CP are spectroscopically equivalent. The observed (15)N (I = 1/2) hyperfine couplings (A) arise from two distinct classes of nitrogen atoms: the coordinating ε-nitrogen of the imidazole ring of each histidine ligand (A = [3.45, 3.71, 5.91] MHz) and the distal δ-nitrogen (A = [0.11, 0.18, 0.42] MHz). In the absence of Ca(II), the binding affinity of CP for Mn(II) drops by two to three orders of magnitude and coincides with Mn(II) binding at the His6 site as well as other sites. This study demonstrates the role of Ca(II) in enabling high-affinity and specific binding of Mn(II) to the His6 site of human calprotectin.

  1. Models for Copper Dynamic Behavior in Doped Cadmium dl-Histidine Crystals: Electron Paramagnetic Resonance and Crystallographic Analysis.

    Science.gov (United States)

    Colaneri, Michael J; Teat, Simon J; Vitali, Jacqueline

    2015-11-12

    Electron paramagnetic resonance and crystallographic studies of copper-doped cadmium dl-histidine, abbreviated as CdDLHis, were undertaken to gain further understanding on the relationship between site structure and dynamic behavior in biological model complexes. X-ray diffraction measurements determined the crystal structure of CdDLHis at 100 and 298 K. CdDLHis crystallizes in the monoclinic space group P21/c with two cadmium complexes per asymmetric unit. In each complex, the Cd is hexacoordinated to two histidine molecules. Both histidines are l in one complex and d in the other. Additionally, each complex contains multiple waters of varying disorder. Single crystal EPR spectroscopic splitting (g) and copper hyperfine (A(Cu)) tensors at room temperature (principal values: g = 2.249, 2.089, 2.050; A(Cu) = -453, -30.5, -0.08 MHz) were determined from rotational experiments. Alignments of the tensor directions with the host structure were used to position the copper unpaired dx(2)-y(2) orbital in an approximate plane made by four proposed ligand atoms: the N-imidazole and N-amino of one histidine, and the N-amino and O-carboxyl of the other. Each complex has two such planes related by noncrystallographic symmetry, which make an angle of 65° and have a 1.56 Å distance between their midpoints. These findings are consistent with three interpretations that can adequately explain previous temperature-dependent EPR powder spectra of this system: (1) a local structural distortion (static strain) at the copper site has a temperature dependence significant enough to affect the EPR pattern, (2) the copper can hop between the two sites in each complex at high temperature, and (3) there exists a dynamic Jahn-Teller effect involving the copper ligands.

  2. An Electron Paramagnetic Resonance Spectroscopic Study of Copper Hopping in Doped Bis(L-histidinato)cadmium Dihydrate

    Science.gov (United States)

    Colaneri, Michael J.; Vitali, Jacqueline; Kirschbaum, Kristin

    2013-01-01

    Electron Paramagnetic Resonance (EPR) spectroscopy was used to study Cu(II) dynamic behavior in a doped biological model crystal; bis(L-histidinato)cadmium dihydrate, in order to gain better insight into copper site stability in metalloproteins. Temperature dependent changes in the low temperature X-band EPR spectra became visible around 100 K and continued up to room temperature. The measured 298 K g-tensor (principal values: 2.17, 2.16, 2.07) and copper hyperfine coupling tensor (principal values: −260, − 190, −37 MHz) were similar to the average of the 77 K tensor values pertaining to two neighboring histidine binding sites. The observed temperature dependence was interpreted using Anderson’s theory of motional narrowing, where the magnetic parameters for the different states are averaged as the copper rapidly hops between sites. The EPR pattern was also found to undergo a sharp sigmoidal-shaped, temperature dependent conversion between two species with a critical temperature Tc ≈ 160 K. The species below Tc hops between the two low temperature site patterns, and the one above Tc represents an average of the molecular spin Hamiltonian coupling tensors of the two 77 K sites. In addition, the low and high temperature species hop between one another, contributing to the dynamic averaging. Spectral simulations using this 4-state model determined a hop rate between the two low temperature sites νh4 = 4.5 × 108 s−1 and between the low and high temperature states νh2 = 1.7 × 108 s−1 at 160 K. An Arrhenius relationship of hop rate and temperature gave energy barriers of ΔE4 = 389 cm−1 and ΔE2 = 656 cm−1 between the two low temperature sites, and between the low and high temperature states, respectively. PMID:23530765

  3. Antioxidant activity of Calendula officinalis extract: inhibitory effects on chemiluminescence of human neutrophil bursts and electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Braga, Pier Carlo; Dal Sasso, Monica; Culici, Maria; Spallino, Alessandra; Falchi, Mario; Bertelli, Aldo; Morelli, Roberto; Lo Scalzo, Roberto

    2009-01-01

    There is growing interest in natural chemical compounds from aromatic, spicy, medicinal and other plants with antioxidant properties in order to find new sources of compounds inactivating free radicals generated by metabolic pathways within body tissue and cells, mainly polymorphonuclear leukocytes (PMNs) whose overregulated recruitment and activation generate a large amount of reactive oxygen species (ROS) and reactive nitrogen species (RNS), leading to an imbalance of redox homeostasis and oxidative stress. The aim of this study was to examine whether a propylene glycol extract of Calendula officinalis interferes with ROS and RNS during the PMN respiratory bursts, and to establish the lowest concentration at which it still exerts antioxidant activity by means of luminol-amplified chemiluminescence. Electron paramagnetic resonance (EPR) spectroscopy was also used in order to confirm the activity of the C. officinalis extract. The C. officinalis extract exerted its anti-ROS and anti-RNS activity in a concentration-dependent manner, with significant effects being observed at even very low concentrations: 0.20 microg/ml without L-arginine, 0.10 microg/ml when L-arginine was added to the test with phorbol 12-myristate 13-acetate and 0.05 microg/ml when it was added to the test with N-formyl-methionyl-leucyl-phenylalanine. The EPR study confirmed these findings, 0.20 microg/ml being the lowest concentration of C. officinalis extract that significantly reduced 2,2-diphenyl-1-picrylhydrazyl. These findings are interesting for improving the antioxidant network and restoring the redox balance in human cells with plant-derived molecules as well as extending the possibility of antagonizing the oxidative stress generated in living organisms when the balance is in favor of free radicals as a result of the depletion of cell antioxidants.

  4. Effects of pre-irradiation annealing at high temperature on optical absorption and electron paramagnetic resonance of natural pumpellyite mineral

    Energy Technology Data Exchange (ETDEWEB)

    Javier-Ccallata, Henry, E-mail: henrysjc@gmail.com [Escuela de Ingeniería Electrónica y Telecomunicaciones, Universidad Alas Peruanas Filial Arequipa, Urb. D. A. Carrión G-14, J. L. Bustamante y Rivero, Arequipa (Peru); Laboratório de Sistemas Nanoestruturados, Departamento de Física, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina (Brazil); Filho, Luiz Tomaz [Departamento de Física Nuclear, Instituto de Física, Universidade de São Paulo, Rua do Matão, travessa R, 187, CEP 05508-900 São Paulo, SP (Brazil); Faculdade de Tecnologia e Ciências Exatas, Universidade São Judas Tadeu, Rua Taquari 546, São Paulo, SP (Brazil); Sartorelli, Maria L. [Laboratório de Sistemas Nanoestruturados, Departamento de Física, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina (Brazil); Watanabe, Shigueo [Departamento de Física Nuclear, Instituto de Física, Universidade de São Paulo, Rua do Matão, travessa R, 187, CEP 05508-900 São Paulo, SP (Brazil)

    2013-09-15

    Highlights: •Natural pumpellyite mineral presents superposition bands around 900 and 1060 nm due Fe{sup 2+}and Fe{sup 3+}. •High temperature annealing influences the EPR and OA spectra. •The behavior of EPR line for 800 and 900 °C can be attributed to forbidden dd transitions due the Fe{sup 3+}. -- Abstract: Natural silicate mineral of pumpellyite, Ca{sub 2}MgAl{sub 2}(SiO{sub 4})(Si{sub 2}O{sub 7})(OH){sub 2}·(H{sub 2}O), point group A2/m, has been studied concerning high temperature annealing and γ-radiation effects on Optical Absorption (OA) and Electron Paramagnetic Resonance (EPR) properties. Chemical analysis revealed that besides Si, Al, Ca and Mg, other oxides i.e., Fe, Mn, Na, K, Ti and P are present in the structure as impurities. OA measurements of natural and annealed pumpellyite revealed several bands in the visible region due to spin forbidden transitions of Fe{sup 2+} and Fe{sup 3+}. The behaviour of bands around 900 and 1060 nm, with pre-annealing and γ radiation dose, indicating a transition Fe{sup 2+} → e{sup −} + Fe{sup 3+}. On the other hand, EPR measurements reveal six lines of Mn{sup 2+}, and satellites due to hyperfine interaction, superimposed on the signal of Fe{sup 3+} around of g = 2. For heat treatment from 800 °C the signal grows significantly and for 900 °C a strong signal of Fe{sup 3+} hides all Mn{sup 2+} lines. The strong growth of this signal indicates that the transitions are due to Fe{sup 3+} dipole–dipole interactions.

  5. In Vivo Formation of Electron Paramagnetic Resonance-Detectable Nitric Oxide and of Nitrotyrosine Is Not Impaired during Murine Leishmaniasis

    Science.gov (United States)

    Giorgio, Selma; Linares, Edlaine; Ischiropoulos, Harry; Von Zuben, Fernando José; Yamada, Aureo; Augusto, Ohara

    1998-01-01

    Recent studies have provided evidence for a dual role of nitric oxide (NO) during murine leishmaniasis. To explore this problem, we monitored the formation of NO and its derived oxidants during the course of Leishmania amazonensis infection in tissues of susceptible (BALB/c) and relatively resistant (C57BL/6) mice. NO production was detected directly by low-temperature electron paramagnetic resonance spectra of animal tissues. Both mouse strains presented detectable levels of hemoglobin nitrosyl (HbNO) complexes and of heme nitrosyl and iron-dithiol-dinitrosyl complexes in the blood and footpad lesions, respectively. Estimation of the nitrosyl complex levels demonstrated that most of the NO is synthesized in the footpad lesions. In agreement, immunohistochemical analysis of the lesions demonstrated the presence of nitrotyrosine in proteins of macrophage vacuoles and parasites. Since macrophages lack myeloperoxidase, peroxynitrite is likely to be the nitrating NO metabolite produced during the infection. The levels of HbNO complexes in the blood reflected changes occurring during the infection such as those in parasite burden and lesion size. The maximum levels of HbNO complexes detected in the blood of susceptible mice were higher than those of C57BL/6 mice but occurred at late stages of infection and were accompanied by the presence of bacteria in the cutaneous lesions. The results indicate that the local production of NO is an important mechanism for the elimination of parasites if it occurs before the parasite burden becomes too high. From then on, elevated production of NO and derived oxidants aggravates the inflammatory process with the occurrence of a hypoxic environment that may favor secondary infections. PMID:9453645

  6. Role of leptin as antioxidant in obstructive sleep apnea: an in vitro study using electron paramagnetic resonance method.

    Science.gov (United States)

    Macrea, Madalina; Martin, Thomas; Zagrean, Leon; Jia, Zhenquan; Misra, Hara

    2013-03-01

    As in obstructive sleep apnea (OSA), the chronic cycles of hypoxia and reoxygenation are thought to be conducive of oxidative stress (OS) with generation of reactive oxygen species, identifying effective mechanisms of protection against oxidant-mediated tissue damage becomes of outmost importance. Leptin's role had been recently extended into that of participant to OS; while its exact role in this process is yet to be defined, elevated leptin levels correlate significantly with several indices of OSA disease severity such as nocturnal hypoxemia, possibly acting as a counteractive mechanism against the chronic intermittent hypoxia-related OS and serving as a marker of future risk of atherosclerotic disease. We therefore investigated leptin's antioxidant mechanism on superoxide (O (2) (-•) ) anions using spectrophotometry and electron paramagnetic resonance (EPR). The O (2) (-•) was generated by oxidation of xanthine (XAN) by xanthine oxidase (XO) in the presence of spin trap 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide with various concentrations of leptin (0.001, 0.01, 0.1, and 1 mg/ml) and without leptin. Signal intensity between 3,440 and 3,540 G was expressed as standard means ± SD. The activity of leptin on XO was determined by monitoring the conversion of XAN to uric acid at 293 nm using a Beckman DU 800 UV-visible spectrophotometer. Leptin added to aqueous solutions at 0.1 and 1 mg/ml concentrations was associated with a statistically significant decrease in the EPR signal due to leptin's direct scavenging activity towards the O (2) (-•) . Leptin is an antioxidant agent of possible use as a marker of OS and future risk of atherosclerotic disease in OSA.

  7. Preliminary study on electron paramagnetic resonance (EPR) signal properties of mobile phone components for dose estimation in radiation accident

    Energy Technology Data Exchange (ETDEWEB)

    Park, Byeong Ryong; Ha, Wi Ho; Park, Sun Hoo; Lee, Jin Kyeong; Lee, Seung Sook [Korea Institute of Radiological and Medical Sciences, Seoul (Korea, Republic of)

    2015-12-15

    We have investigated the EPR signal properties in 12 components of two mobile phones (LCD, OLED) using electron paramagnetic resonance (EPR) spectrometer in this study.EPR measurements were performed at normal atmospheric conditions using Bruker EXEXSYS-II E500 spectrometer with X-band bridge, and samples were irradiated by {sup 137}C{sub s} gamma-ray source. To identify the presence of radiation-induced signal (RIS), the EPR spectra of each sample were measured unirradiated and irradiated at 50 Gy. Then, dose-response curve and signal intensity variating by time after irradiation were measured. As a result, the signal intensity increased after irradiation in all samples except the USIM plastic and IC chip. Among the samples, cover glass(CG), lens, light guide plate(LGP) and diffusion sheet have shown fine linearity (R{sup 2} > 0.99). Especially, the LGP had ideal characteristics for dosimetry because there were no signal in 0 Gy and high rate of increase in RIS. However, this sample showed weakness in fading. Signal intensity of LGP and Diffusion Sheet decreased by 50% within 72 hours after irradiation, while signals of Cover Glass and Lens were stably preserved during the short period of time. In order to apply rapidly EPR dosimetry using mobile phone components in large-scale radiation accidents, further studies on signal differences for same components of the different mobile phone, fading, pretreatment of samples and processing of background signal are needed. However, it will be possible to do dosimetry by dose-additive method or comparative method using unirradiated same product in small-scale accident.

  8. In vivo tumour extracellular pH monitoring using electron paramagnetic resonance: the effect of X-ray irradiation.

    Science.gov (United States)

    Goodwin, Jonathan; Yachi, Katsuya; Nagane, Masaki; Yasui, Hironobu; Miyake, Yusuke; Inanami, Osamu; Bobko, Andrey A; Khramtsov, Valery V; Hirata, Hiroshi

    2014-04-01

    The in vivo quantification of extracellular pH (pHe ) in tumours may provide a useful biomarker for tumour cell metabolism. In this study, we assessed the viability of continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopy with a pH-sensitive nitroxide for the measurement of extracellular tumour pH in a mouse model. CW-EPR spectroscopy (750 MHz) of C3H HeJ mice hind leg squamous cell tumour was performed after intravenous tail vein injection of pH-sensitive nitroxide (R-SG, 2-(4-((2-(4-amino-4-carboxybutanamido)-3-(carboxymethylamino)-3-oxoproylthio)methyl)phenyl)-4-pyrrolidino-2,5,5-triethyl-2,5-dihydro-1Н-imidazol-1-oxyl) during stages of normal tumour growth and in response to a single 10-Gy dose of X-ray irradiation. An inverse relationship was observed between tumour volume and pHe value, whereby, during normal tumour growth, a constant reduction in pHe was observed. This relationship was disrupted by X-ray irradiation and, from 2-3 days post-exposure, a transitory increase in pHe was observed. In this study, we demonstrated the viability of CW-EPR spectroscopy using R-SG nitroxide to obtain high-sensitivity pH measurements in a mouse tumour model with an accuracy of <0.1 pH units. In addition, the measured changes in pHe in response to X-ray irradiation suggest that this may offer a useful method for the assessment of the physiological change in response to existing and novel cancer therapies. Copyright © 2014 John Wiley & Sons, Ltd.

  9. Time-Resolved Electron Paramagnetic Resonance Study of Photoinduced Electron Transfer in Pd Porphyrin-Quinone and Zn Porphyrin-Quinone Dyads with a Cyclohexylene Spacer.

    Science.gov (United States)

    Perchanova, Maya; Kurreck, Harry; Berg, Alexander

    2015-07-23

    Peculiarities of the light induced intramolecular electron transfer processes in two ensembles where Pd porphyrin and Zn porphyrin donors with similar peripheral substituents are covalently linked via cyclohexylene spacer with a quinone acceptor, were studied by time-resolved electron paramagnetic resonance spectroscopy in different phases of the magnetically oriented nematic liquid crystal E-7. In the photoexcited PdP-Q the net absorptive signal was observed and ascribed to the thermally equilibrated spectrum of (3)*(PdP(•+)-Q(•-)). In ZnP-Q photoinduced intramolecular electron transfer was also found. It was demonstrated that the multiplet spectrum of the charge-separated state (3)*(ZnP(•+)-Q(•-)) consists of two signals with different widths and decay times. The signals were assigned to two spin-polarized triplets of the radical pairs formed in "stretched" and "folded" ensemble conformers, corresponding to different configurations of the cyclohexylene spacer. These findings were discussed in terms of differences in the properties of the porphyrin metal cores, macrocycle peripheral substituents and geometry of the donor-acceptor cyclohexylene spacer.

  10. Electron pulse shaping in the FELIX RF accelerator

    NARCIS (Netherlands)

    Weits, H. H.; van der Geer, C. A. J.; Oepts, D.; van der Meer, A. F. G.

    1999-01-01

    The FELIX free-electron laser uses short pulses of relativistic electrons produced by an RF accelerator. The design target for the duration of these electron bunches was around 3 ps. In experiments we observed that the bunches emit coherently enhanced spontaneous emission (CSE) when they travel thro

  11. Two-pulse laser control of nuclear and electronic motion

    DEFF Research Database (Denmark)

    Grønager, Michael; Henriksen, Niels Engholm

    1997-01-01

    We discuss an explicitly time-dependent two-pulse laser scheme for controlling where nuclei and electrons are going in unimolecular reactions. We focus on electronic motion and show, with HD+ as an example, that one can find non-stationary states where the electron (with some probability) oscilla...

  12. Electron pulse shaping in the FELIX RF accelerator

    NARCIS (Netherlands)

    Weits, H. H.; van der Geer, C. A. J.; Oepts, D.; van der Meer, A. F. G.

    1999-01-01

    The FELIX free-electron laser uses short pulses of relativistic electrons produced by an RF accelerator. The design target for the duration of these electron bunches was around 3 ps. In experiments we observed that the bunches emit coherently enhanced spontaneous emission (CSE) when they travel

  13. Transient of power pulse and its sequence in power electronics

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Various failures and destructions occur in the applications of the power electronic converter. The real practice shows that these failures are connected with the con-centration of the transient power pulse. In allusion to the physical characteristics of power electronic converters,this paper proposed that the power pulse and its se-quence are the basis for power electronics in the perspective of electromagnetic energy. The authors analyzed the transient processes in the power semiconductors,electric conduction loops and controller system and illustrated the power pulse phenomena in high voltage and high power inverters. This investigation on the power pulse sequence is very meaningful for the failure analysis and device pro-tection and has become an important topic in power electronics.

  14. Transient of power pulse and its sequence in power electronics

    Institute of Scientific and Technical Information of China (English)

    ZHAO ZhengMing; BAI Hua; YUAN LiQiang

    2007-01-01

    Various failures and destructions occur in the applications of the power electronic converter, The real practice shows that these failures are connected with the concentration of the transient power pulse. In allusion to the physical characteristics of power electronic converters, this paper proposed that the power pulse and its sequence are the basis for power electronics in the perspective of electromagnetic energy. The authors analyzed the transient processes in the power semiconductors,electric conduction loops and controller system and illustrated the power pulse phenomena in high voltage and high power inverters. This investigation on the power pulse sequence is very meaningful for the failure analysis and device protection and has become an important topic in power electronics.

  15. Characterization of endothelial nitric-oxide synthase and its reaction with ligand by electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Tsai, A L; Berka, V; Chen, P F; Palmer, G

    1996-12-20

    Electron paramagnetic resonance was used to characterize the heme structure of resting endothelial nitric-oxide synthase (eNOS), eNOS devoid of its myristoylation site (G2A mutant), and their heme complexes formed with 16 different ligands. Resting eNOS and the G2A mutant have a mixture of low spin and high spin P450-heme with widely different relaxation behavior and a stable flavin semiquinone radical identified by EPR as a neutral radical. This flavin radical showed efficient electron spin relaxation as a consequence of dipolar interaction with the heme center; P1/2 is independent of Ca2+-calmodulin and tetrahydrobiopterin. Seven of the 16 ligands led to the formation of low spin heme complexes. In order of increasing rhombicity they are pyrimidine, pyridine, thiazole, L-lysine, cyanide, imidazole, and 4-methylimidazole. These seven low spin eNOS complexes fell in a region between the P and O zones on the "truth diagram" originally derived by Blumberg and Peisach (Blumberg, W. E., and Peisach, J. (1971) in Probes and Structure and Function of Macromolecules and Membranes (Chance, B., Yonetani, T., and Mildvan, A. S., eds) Vol. 2, pp. 215-229, Academic Press, New York) and had significant overlap with complexes of chloroperoxidase. A re-definition of the P and O zones is proposed. As eNOS and chloroperoxidase lie closer than do eNOS and P450cam on the truth diagram, it implies that the distal heme environment in eNOS resembles chloroperoxidase more than P450cam. In contrast, 4-ethylpyridine, 4-methylpyrimidine, acetylguanidine, ethylguanidine, 2-aminothiazole, 2amino-4,5-dimethylthiazole, L-histidine, and 7-nitroindazole resulted in high spin heme complexes of eNOS, similar to that observed with L-arginine. This contrasting EPR behavior caused by families of ligands such as imidazole/L-histidine or thiazole/2-aminothiazole confirms the conclusion derived from parallel optical and kinetic studies. The ligands resulting in the low spin complexes bind directly to the

  16. Application of the Electron paramagnetic resonance to the ionizing radiation dosimetry; Aplicacion de la Resonancia paramagnetica electronica a la dosimetria de las radiaciones ionizantes

    Energy Technology Data Exchange (ETDEWEB)

    Urena N, F. [Instituto Nacional de Investigaciones Nucleares, Km. 36.5 Carretera Mexico-Toluca, 52045 Salazar, Estado de Mexico (Mexico)

    2000-07-01

    The Electron Paramagnetic Resonance (EPR) is defined as the resonant absorption of electromagnetic energy in paramagnetic substances by the spin transition of a non-pairing electron between different energy levels in presence of a magnetic field. (Slighter, 1989). One of the more important characteristic of EPR is that the electron spin levels are subdivided by the electron interaction with the magnetic dipoles of the nearby nucleus giving occasion for a spectral structure called hyperfine structure. In this kind of interactions two limit cases are distinguished: 1. when the non-pairing electron is located in a central ion surrounded of atoms belonging to coordinate molecules. 2. When a non-pairing electron interactioning in the same form with a number of equivalent nucleus, which is common in organic radicals, these will give as result spectra. Some EPR spectrometer can be used to dosimetric purposes by free radicals via. In this work, it is presented the application of EPR to dosimetry of ionizing radiations by free radicals via which allows to determinations of high doses. (Author)

  17. Effects of MnO doping on the electronic properties of zinc oxide: 406 GHz electron paramagnetic resonance spectroscopy and Newman superposition model analysis

    Energy Technology Data Exchange (ETDEWEB)

    Yüksel Price, Berat, E-mail: berat@istanbul.edu.tr, E-mail: muhammed.acikgoz@eng.bahcesehir.edu.tr, E-mail: emre.erdem@physchem.uni-freiburg.de; Hardal, Gökhan [Engineering Faculty, Metallurgical and Materials Engineering Department, Istanbul University, Avcılar, 34320 Istanbul (Turkey); Açıkgöz, Muhammed, E-mail: berat@istanbul.edu.tr, E-mail: muhammed.acikgoz@eng.bahcesehir.edu.tr, E-mail: emre.erdem@physchem.uni-freiburg.de [Faculty of Arts and Sciences, Bahcesehir University, Besiktas, 34349 Istanbul (Turkey); Repp, Sergej; Erdem, Emre, E-mail: berat@istanbul.edu.tr, E-mail: muhammed.acikgoz@eng.bahcesehir.edu.tr, E-mail: emre.erdem@physchem.uni-freiburg.de [Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg (Germany)

    2015-11-07

    MnO-doped ZnO ceramics have been synthesized through the conventional ceramic processing route. Mn{sup 2+} ions have been incorporated into the ZnO lattice within the limits of solid solubility. By using X-band-frequency and high-field electron paramagnetic resonance (EPR), we have resolved some of the main electronic transitions for the S = 5/2, I = 5/2 high-spin system and have determined accurately the EPR spin-Hamiltonian parameters. By combining data from crystallographic X-ray diffraction and EPR with the semi-empirical Newman superposition model, we have found the local configurational position of Mn{sup 2+} and have confirmed the symmetry of the lattice. The results presented in this contribution indicate that Mn ions substitute at Zn sites in ZnO. The effect of Mn{sup 2+} ions on the intrinsic defects becomes remarkable, thus the vacancy related intrinsic defect signals cannot be visible in the EPR spectrum. MnO doping affects the band gap energy of ZnO system which was confirmed via UV-Vis spectroscopy.

  18. Effects of MnO doping on the electronic properties of zinc oxide: 406 GHz electron paramagnetic resonance spectroscopy and Newman superposition model analysis

    Science.gov (United States)

    Yüksel Price, Berat; Hardal, Gökhan; Açıkgöz, Muhammed; Repp, Sergej; Erdem, Emre

    2015-11-01

    MnO-doped ZnO ceramics have been synthesized through the conventional ceramic processing route. Mn2+ ions have been incorporated into the ZnO lattice within the limits of solid solubility. By using X-band-frequency and high-field electron paramagnetic resonance (EPR), we have resolved some of the main electronic transitions for the S = 5/2, I = 5/2 high-spin system and have determined accurately the EPR spin-Hamiltonian parameters. By combining data from crystallographic X-ray diffraction and EPR with the semi-empirical Newman superposition model, we have found the local configurational position of Mn2+ and have confirmed the symmetry of the lattice. The results presented in this contribution indicate that Mn ions substitute at Zn sites in ZnO. The effect of Mn2+ ions on the intrinsic defects becomes remarkable, thus the vacancy related intrinsic defect signals cannot be visible in the EPR spectrum. MnO doping affects the band gap energy of ZnO system which was confirmed via UV-Vis spectroscopy.

  19. Intramolecular electron transfer versus substrate oxidation in lactoperoxidase: investigation of radical intermediates by stopped-flow absorption spectrophotometry and (9-285 GHz) electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Fielding, Alistair J; Singh, Rahul; Boscolo, Barbara; Loewen, Peter C; Ghibaudi, Elena M; Ivancich, Anabella

    2008-09-16

    We have combined the information obtained from rapid-scan electronic absorption spectrophotometry and multifrequency (9-295 GHz) electron paramagnetic resonance (EPR) spectroscopy to unequivocally determine the electronic nature of the intermediates in milk lactoperoxidase as a function of pH and to monitor their reactivity with organic substrates selected by their different accessibilities to the heme site. The aim was to address the question of the putative catalytic role of the protein-based radicals. This experimental approach allowed us to discriminate between the protein-based radical intermediates and [Fe(IV)=O] species, as well as to directly detect the oxidation products by EPR. The advantageous resolution of the g anisotropy of the Tyr (*) EPR spectrum at high fields showed that the tyrosine of the [Fe(IV)=O Tyr (*)] intermediate has an electropositive and pH-dependent microenvironment [g(x) value of 2.0077(0) at pH >or= 8.0 and 2.0066(2) at 4.0 electron transfer (favored at pH 8) not involving the tyrosyl radical, the formation of which competed with the substrate oxidation at pH 5. In contrast, the very efficient reaction with ABTS at pH 5 is consistent with [Fe(IV)=O Tyr (*)] being the oxidizing species. Accordingly, the identification of the ABTS binding site by X-ray crystallography may be a valuable tool in rational drug design.

  20. SU-C-BRD-05: Non-Invasive in Vivo Biodosimetry in Radiotherapy Patients Using Electron Paramagnetic Resonance (EPR) Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Bahar, N; Roberts, K; Stabile, F; Mongillo, N; Decker, RD; Wilson, LD; Husain, Z; Contessa, J; Carlson, DJ [Yale University School of Medicine, New Haven, Connecticut (United States); Williams, BB; Flood, AB; Swartz, HM [Geisel Medical School at Dartmouth University, Hanover, New Hampshire (United States)

    2015-06-15

    Purpose: Medical intervention following a major, unplanned radiation event can elevate the human whole body exposure LD50 from 3 to 7 Gy. On a large scale, intervention cannot be achieved effectively without accurate and efficient triage. Current methods of retrospective biodosimetry are restricted in capability and applicability; published human data is limited. We aim to further develop, validate, and optimize an automated field-deployable in vivo electron paramagnetic resonance (EPR) instrument that can fill this need. Methods: Ionizing radiation creates highly-stable, carbonate-based free radicals within tooth enamel. Using a process similar to nuclear magnetic resonance, EPR directly measures the presence of radiation-induced free radicals. We performed baseline EPR measurements on one of the upper central incisors of total body irradiation (TBI) and head and neck (H&N) radiotherapy patients before their first treatment. Additional measurements were performed between subsequent fractions to examine the EPR response with increasing radiation dose. Independent dosimetry measurements were performed with optically-stimulated luminescent dosimeters (OSLDs) and diodes to more accurately establish the relationship between EPR signal and delivered radiation dose. Results: 36 EPR measurements were performed over the course of four months on two TBI and four H & N radiotherapy patients. We observe a linear increase in EPR signal with increasing dose across the entirety of the tested range. A linear least squares-weighted fit of delivered dose versus measured signal amplitude yields an adjusted R-square of 0.966. The standard error of inverse prediction (SEIP) is 1.77 Gy. For doses up to 7 Gy, the range most relevant to triage, we calculate an SEIP of 1.29 Gy. Conclusion: EPR spectroscopy provides a promising method of retrospective, non-invasive, in vivo biodosimetry. Our preliminary data show an excellent correlation between predicted signal amplitude and delivered

  1. Electron paramagnetic resonance and AC susceptibility studies of Mn and Gd doped 1:2:3 superconductors

    Energy Technology Data Exchange (ETDEWEB)

    La Robina, M.A. [Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW (Australia)

    1997-12-31

    For many years superconductivity was considered to be a low temperature phenomenon occurring below {approx} 25K. All this changed in April 1986 when J. G. Bednorz and K. A. Muller showed that the oxide La{sub 2-x}Ba{sub x}CuO{sub 4} becomes a superconductor at {approx} 30K. Later in December 1986 the oxides La{sub 2-x} Sr{sub x} CuO{sub 4} and La{sub 2-x}Ba{sub x}CuO{sub 4} synthesised under high pressure, were shown to superconduct at {approx} 40K and {approx} 50K, respectively. Finally in February 1987, Chu synthesised the classic superconductor YBa{sub 2}Cu{sub 3}O{sub 6.8}, the so-called 1:2:3 material, which has a critical temperature circa 92K. In this thesis, electron paramagnetic resonance (EPR) and susceptibility measurements are reported on various superconductors. In 1987 Bowden et al., showed that pure phase 1:2:3 samples are characterised by an absence of Cu EPR signals. This contrasts sharply with the Green phase material, Y{sub 2}Ba{sub 1}Cu{sub 1}O{sub 5}, which shows a very large EPR signal with a g{sub eff} of 2.08. In an attempt to induce EPR signals, Mn doped 1:2:3 samples have been synthesised and characterised with EPR , AC susceptibility, XRD and SEM measurements. It is shown that Mn EPR signals are not evident in the Mn doped samples with a g{sub eff} of 2.09. Also, below T{sub c} the EPR signals of the lightly doped Mn samples vanish. It is argued that this is due to fluxoids motion within the superconductor, which gives rise to very large non-reproducible signals. It is suggested that the signals originate from Cu, impurity contaminants and multiple phases produced when the 1:2:3 superconductor is doped with Manganese (author) refs., figs.

  2. Linearity of photoconductive GaAs detectors to pulsed electrons

    Energy Technology Data Exchange (ETDEWEB)

    Ziegler, L.H.

    1995-12-31

    The response of neutron damaged GaAs photoconductor detectors to intense, fast (50 psec fwhm) pulses of 16 MeV electrons has been measured. Detectors made from neutron damaged GaAs are known to have reduced gain, but significantly improved bandwidth. An empirical relationship between the observed signal and the incident electron fluence has been determined.

  3. A high current, high gradient, laser excited, pulsed electron gun

    Energy Technology Data Exchange (ETDEWEB)

    Batchelor, K.; Farrell, J.P.; Dudnikova, G. [Brookhaven Technology Group, Inc., Stony Brook, NY (United States); Ben-Zvi, I.; Srinivasan-Rao, T.; Smedley, J.; Yakimenko, V. [Brookhaven National Lab., Upton, NY (United States)

    1998-06-01

    This paper describes a pulsed electron gun that can be used as an FEL, as an injector for electron linear accelerators or for rf power generation. It comprises a 1 to 5 MeV, 1 to 2 ns pulsed power supply feeding a single diode, photoexcited acceleration gap. Beam quality of a {approximately}1nC charge in {approximately}1 GV/m field was studied. Computations of the beam parameters as a function of electrode configuration and peak electron current are presented together with descriptions of the power supply, laser and beam diagnostics systems.

  4. Shutterless ion mobility spectrometer with fast pulsed electron source

    Science.gov (United States)

    Bunert, E.; Heptner, A.; Reinecke, T.; Kirk, A. T.; Zimmermann, S.

    2017-02-01

    Ion mobility spectrometers (IMS) are devices for fast and very sensitive trace gas analysis. The measuring principle is based on an initial ionization process of the target analyte. Most IMS employ radioactive electron sources, such as 63Ni or 3H. These radioactive materials have the disadvantage of legal restrictions and the electron emission has a predetermined intensity and cannot be controlled or disabled. In this work, we replaced the 3H source of our IMS with 100 mm drift tube length with our nonradioactive electron source, which generates comparable spectra to the 3H source. An advantage of our emission current controlled nonradioactive electron source is that it can operate in a fast pulsed mode with high electron intensities. By optimizing the geometric parameters and developing fast control electronics, we can achieve very short electron emission pulses for ionization with high intensities and an adjustable pulse width of down to a few nanoseconds. This results in small ion packets at simultaneously high ion densities, which are subsequently separated in the drift tube. Normally, the required small ion packet is generated by a complex ion shutter mechanism. By omitting the additional reaction chamber, the ion packet can be generated directly at the beginning of the drift tube by our pulsed nonradioactive electron source with only slight reduction in resolving power. Thus, the complex and costly shutter mechanism and its electronics can also be omitted, which leads to a simple low-cost IMS-system with a pulsed nonradioactive electron source and a resolving power of 90.

  5. Pulsed Power for a Dynamic Transmission Electron Microscope

    Energy Technology Data Exchange (ETDEWEB)

    dehope, w j; browning, n; campbell, g; cook, e; king, w; lagrange, t; reed, b; stuart, b; Shuttlesworth, R; Pyke, B

    2009-06-25

    Lawrence Livermore National Laboratory (LLNL) has converted a commercial 200kV transmission electron microscope (TEM) into an ultrafast, nanoscale diagnostic tool for material science studies. The resulting Dynamic Transmission Electron Microscope (DTEM) has provided a unique tool for the study of material phase transitions, reaction front analyses, and other studies in the fields of chemistry, materials science, and biology. The TEM's thermionic electron emission source was replaced with a fast photocathode and a laser beam path was provided for ultraviolet surface illumination. The resulting photoelectron beam gives downstream images of 2 and 20 ns exposure times at 100 and 10 nm spatial resolution. A separate laser, used as a pump pulse, is used to heat, ignite, or shock samples while the photocathode electron pulses, carefully time-synchronized with the pump, function as probe in fast transient studies. The device functions in both imaging and diffraction modes. A laser upgrade is underway to make arbitrary cathode pulse trains of variable pulse width of 10-1000 ns. Along with a fast e-beam deflection scheme, a 'movie mode' capability will be added to this unique diagnostic tool. This talk will review conventional electron microscopy and its limitations, discuss the development and capabilities of DTEM, in particularly addressing the prime and pulsed power considerations in the design and fabrication of the DTEM, and conclude with the presentation of a deflector and solid-state pulser design for Movie-Mode DTEM.

  6. Spectrotemporal shaping of seeded free-electron laser pulses.

    Science.gov (United States)

    Gauthier, David; Ribič, Primož Rebernik; De Ninno, Giovanni; Allaria, Enrico; Cinquegrana, Paolo; Danailov, Miltcho Bojanov; Demidovich, Alexander; Ferrari, Eugenio; Giannessi, Luca; Mahieu, Benoît; Penco, Giuseppe

    2015-09-11

    We demonstrate the ability to control and shape the spectrotemporal content of extreme-ultraviolet (XUV) pulses produced by a seeded free-electron laser (FEL). The control over the spectrotemporal properties of XUV light was achieved by precisely manipulating the linear frequency chirp of the seed laser. Our results agree with existing theory, which allows us to retrieve the temporal properties (amplitude and phase) of the FEL pulse from measurements of the spectra as a function of the FEL operating parameters. Furthermore, we show the first direct evidence of the full temporal coherence of FEL light and generate Fourier limited pulses by fine-tuning the FEL temporal phase. The possibility of tailoring the spectrotemporal content of intense short-wavelength pulses represents the first step towards efficient nonlinear optics in the XUV to x-ray spectral region and will enable precise manipulation of core-electron excitations using the methods of coherent quantum control.

  7. Electronic paramagnetic resonance (EPR) of spices treated by gamma irradiation; Ressonancia paramagnetica eletronica (RPE) aplicada a analise de especiarias irradiadas (com radiacao gama)

    Energy Technology Data Exchange (ETDEWEB)

    Leal, Alexandre Soares; Rodrigues, Rogerio Rivail, E-mail: asleal@cdtn.b [Centro de Desenvolvimento de Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil). Serv. de Reator e Irradiacoes; Krambrock, Klaus; Guedes, Kassilio [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil)

    2004-07-15

    The treatment of food by ionizing radiation is a method that has been increased in many countries in substitution for the use of chemical products. The knowledge of safe and reliable techniques of detection of irradiated food is a factor that can contribute to the largest acceptance for the consuming market. This work presents the electron paramagnetic resonance (EPR) as method of detection of the irradiated spices rosemary and cilantro. The obtained results indicate that EPR can be used satisfactorily for that group of victuals in the identification of irradiated species and in the determination of the received dose. (author)

  8. Experimental Model for Retrospective Assessment of X-Ray Exposures in Dento-Maxillary Radiology Measured by Electron Paramagnetic Resonance in Tooth Enamel

    Directory of Open Access Journals (Sweden)

    Ioana Costina DÂNŞOREANU

    2009-12-01

    Full Text Available Electron paramagnetic resonance (EPR dosimetry of human tooth enamel has been widely used in measuring radiation doses in various scenarios. For experimental purposes in X-ray diagnostic or therapy human persons can not be involved. For such cases we have developed an EPR dosimetry technique making use of enamel of molars extracted from pigs. The method can evaluate doses and dose-profiles of irradiated teeth at low level as 50 – 100 mGy (in air. EPR-spectra acquisition, data processing and dose assessment were done using non-dedicated equipment, devices and software.

  9. Electron Paramagnetic Resonance: Elementary Theory and Practical Applications, Second Edition (John A. Weil and James R. Bolton)

    Science.gov (United States)

    Williams, Ffrancon

    2009-01-01

    The detection of electron magnetic resonance by Zavoiskii in the mid 1940s (1) ushered in a golden age of physical and chemical applications. Perhaps no single book did more to stimulate this development of EPR spectroscopy than the classic text by Wertz and Bolton (2) , which appeared in 1972. A revised version, with John A. Weil added as a co-author, was published by Wiley in 1994. This 2007 text is formally described as the second edition of the 1994 version. Wertz died shortly after the publication of the 1994 edition leaving Weil and Bolton as authors. In noting that the senior author (JAW) takes most of the responsibility for the content of this 2007 version, the Preface refers to it at one point as the "third edition", which of course is precisely how older readers will regard it. The main thrust of the book is decidedly on the physical aspects of EPR, so that it nicely complements the more chemical emphasis provided in the recent comprehensive text by Gerson and Hüber (3) . As the authors remark, the 2007 edition does not differ dramatically from the 1994 version. The titles of the 13 chapters remain the same except for chapter 11, which now refers to the "Noncontinuous" instead of the "Time-Dependent" Excitation of Spins. Recent developments are generally accommodated by a few extra pages in each chapter. Thus, chapter 1 on Basic Principles of Paramagnetic Resonance has been expanded from 31 to 36 pages to introduce the topics of parallel-field EPR, time-resolved EPR, "computerology", and EPR imaging. Chapter 2 on Magnetic Interactions is essentially unchanged while chapter 3 on Isotropic Hyperfine Effects has been expanded to include new sections on Deviations from the Simple Multinomial Scheme (3.7) and Some Interesting π-Type Free Radicals (3.9). Section 3.9 provides a useful corrective to the notion that the EPR method can detect and characterize almost any type of radical species. This welcome touch of realism is nicely illustrated by mentioning

  10. Vibrationally-induced electronic population inversion with strong femtosecond pulses

    CERN Document Server

    Sampedro, Pablo; Sola, Ignacio R

    2016-01-01

    We discover a new mechanism of electronic population inversion using strong femtosecond pulses, where the transfer is mediated by vibrational motion on a light-induced potential. The process can be achieved with a single pulse tuning its frequency to the red of the Franck-Condon window. We show the determinant role that the sign of the slope of the transition dipole moment can play on the dynamics, and extend the method to multiphoton processes with odd number of pulses. As an example, we show how the scheme can be applied to population inversion in Na2.

  11. Spatially modulated laser pulses for printing electronics.

    Science.gov (United States)

    Auyeung, Raymond C Y; Kim, Heungsoo; Mathews, Scott; Piqué, Alberto

    2015-11-01

    The use of a digital micromirror device (DMD) in laser-induced forward transfer (LIFT) is reviewed. Combining this technique with high-viscosity donor ink (silver nanopaste) results in laser-printed features that are highly congruent in shape and size to the incident laser beam spatial profile. The DMD empowers LIFT to become a highly parallel, rapidly reconfigurable direct-write technology. By adapting half-toning techniques to the DMD bitmap image, the laser transfer threshold fluence for 10 μm features can be reduced using an edge-enhanced beam profile. The integration of LIFT with this beam-shaping technique allows the printing of complex large-area patterns with a single laser pulse.

  12. Location of Trapped Electron Centers in the Bulk of Epitaxial MgO(001) Films Grown on Mo(001) Using in situ W-band Electron Paramagnetic Resonance Spectroscopy.

    Science.gov (United States)

    Cornu, Damien; Rocker, Jan; Gonchar, Anastasia; Risse, Thomas; Freund, Hans-Joachim

    2016-07-01

    We present the first in situ W-band (94-GHz) electron paramagnetic resonance (EPR) study of a trapped electron center in thin MgO(001) films. The improved resolution of the high-field EPR experiments proves that the signal originate from a well-defined species present in the bulk of the films, whose projection of the principal g-tensor components onto the (001) plane are oriented along the [110] direction of the MgO lattice. Based on a comparison between the structural properties of the films, knowledge of the ability of bulk defects to trap electrons, and the properties of the EPR signal, it is possible to propose that the paramagnetic species are located at the origin of a screw dislocation in the bulk of the film.

  13. CTS and CZTS for solar cells made by pulsed laser deposition and pulsed electron deposition

    DEFF Research Database (Denmark)

    Ettlinger, Rebecca Bolt

    , which make them promising alternatives to the commercially successful solar cell material copper indium gallium diselenide (CIGS). Complementing our group's work on pulsed laser deposition of CZTS, we collaborated with IMEM-CNR in Parma, Italy, to deposit CZTS by pulsed electron deposition for the first...... time. We compared the results of CZTS deposition by PLD at DTU in Denmark to CZTS made by PED at IMEM-CNR, where CIGS solar cells have successfully been fabricated at very low processing temperatures. The main results of this work were as follows: Monoclinic-phase CTS films were made by pulsed laser...

  14. Synchronization of Sub-Picosecond Electron and Laser Pulses

    Energy Technology Data Exchange (ETDEWEB)

    Rosenzweig, J.B.; Le Sage G.P.

    2000-08-15

    Sub-picosecond laser-electron synchronization is required to take full advantage of the experimental possibilities arising from the marriage of modern high intensity lasers and high brightness electron beams in the same laboratory. Two particular scenarios stand out in this regard, injection of ultra-short electron pulses in short wavelength laser-driven plasma accelerators, and Compton scattering of laser photons from short electron pulses. Both of these applications demand synchronization, which is subpicosecond, with tens of femtosecond synchronization implied for next-generation experiments. Typically, an RF electron accelerator is synchronized to a short pulse laser system by detecting the repetition signal of a laser oscillator, adjusted to an exact subharmonic of the linac RF frequency, and multiplying or phase locking this signal to produce the master RF clock. Pulse-to-pulse jitter characteristic of self-mode-locked laser oscillators represents a direct contribution to the ultimate timing jitter between a high intensity laser focus and electron beam at the interaction point, or a photocathode drive laser in an RF photoinjector. This timing jitter problem has been addressed most seriously in the context of the RF photoinjector, where the electron beam properties are sensitive functions of relative timing jitter. The timing jitter achieved in synchronized photocathode drive laser systems is near, or slightly below one picosecond. The ultimate time of arrival jitter of the beam at the photoinjector exit is typically a bit smaller than the photocathode drive-laser jitter due to velocity compression effects in the first RF cell of the gun. This tendency of the timing of the electron beam arrival at a given spatial point to lock to the RF lock is strongly reinforced by use of magnetic compression.

  15. Adsorption and collective paramagnetism

    CERN Document Server

    Selwood, Pierce W

    1962-01-01

    Adsorption and Collective Paramagnetism describes a novel method for studying chemisorption. The method is based on the change in the number of unpaired electrons in the adsorbent as chemisorption occurs. The method is applicable to almost all adsorbates, but it is restricted to ferromagnetic adsorbents such as nickel, which may be obtained in the form of very small particles, that is to say, to ferromagnetic adsorbents with a high specific surface. While almost all the data used illustratively have been published elsewhere this is the first complete review of the subject. The book is addresse

  16. Two-electron quantum ring in short pulses

    Institute of Scientific and Technical Information of China (English)

    Poonam Silotia; Rakesh Kumar Meena; Vinod Prasad

    2015-01-01

    The response of two-electron quantum ring system to the short laser pulses of different shapes in the presence of external static electric field is studied. The variation of transition probabilities of the two-electron quatum ring from ground state to excited states with a number of parameters is shown and explained. The energy levels and wavefunctions of the system in the presence of static electric field are found by solving the time-independent Schr ¨odinger equation numerically by finite difference method. The shape of the pulse plays a dominant role on the dynamics.

  17. Native and induced triplet nitrogen-vacancy centers in nano- and micro-diamonds: Half-field electron paramagnetic resonance fingerprint

    Science.gov (United States)

    Shames, A. I.; Osipov, V. Yu.; von Bardeleben, H.-J.; Boudou, J.-P.; Treussart, F.; Vul', A. Ya.

    2014-02-01

    Multiple frequency electron paramagnetic resonance (EPR) study of small (4-25 nm) nanodiamonds obtained by various dynamic synthesis techniques reveals systematic presence in the half-field (HF) region a distinctive doublet fingerprint consisting of resolved gHF1 = 4.26 and gHF2 = 4.00 signals. This feature is attributed to "forbidden" ΔMS = 2 transitions in EPR spectra of two native paramagnetic centers of triplet (S = 1) origin designated as TR1 and TR2, characterized by zero field splitting values D1 = 0.0950 ± 0.002 cm-1 and D2 = 0.030 ± 0.005 cm-1. Nanodiamonds of ˜50 nm particle size, obtained by crushing of Ib type nitrogen rich synthetic diamonds, show only HF TR2 signal whereas the same sample undergone high energy (20 MeV) electron irradiation and thermal annealing demonstrates rise of HF TR1 signal. The same HF TR1 signals appear in the process of fabrication of fluorescent nanodiamonds from micron-size synthetic diamond precursors. Results obtained allow unambiguous attribution of the half-field TR1 EPR signals with gHF1 = 4.26, observed in nano- and micron-diamond powders, to triplet negatively charged nitrogen-vacancy centers. These signals are proposed as reliable and convenient fingerprints in both qualitative and quantitative study of fluorescent nano- and micron-diamonds.

  18. Experimental investigation of electron beam wave interactions utilising short pulses

    CERN Document Server

    Wiggins, S M

    2000-01-01

    Experiments have investigated the production of ultra-short electromagnetic pulses and their interaction with electrons in various resonant structures. Diagnostic systems used in the measurements included large bandwidth detection systems for capturing the short pulses. Deconvolution techniques have been applied to account for bandwidth limitation of the detection systems and to extract the actual pulse amplitudes and durations from the data. A Martin-Puplett interferometer has been constructed for use as a Fourier transform spectrometer. The growth of superradiant electromagnetic spikes from short duration (0.5-1.0 ns), high current (0.6-2.0 kA) electron pulses has been investigated in a Ka-band Cherenkov maser and Ka- and W-band backward wave oscillators (BWO). In the Cherenkov maser, radiation spikes were produced with a peak power = 70 ps and a bandwidth <= 19 %. It is shown that coherent spontaneous emission from the leading edge of the electron pulse drives these interactions, giving rise to self-amp...

  19. Detection of pulsed neutrons with solid-state electronics

    Science.gov (United States)

    Chatzakis, J.; Rigakis, I.; Hassan, S. M.; Clark, E. L.; Lee, P.

    2016-09-01

    Measurements of the spatial and time-resolved characteristics of pulsed neutron sources require large area detection materials and fast circuitry that can process the electronic pulses readout from the active region of the detector. In this paper, we present a solid-state detector based on the nuclear activation of materials by neutrons, and the detection of the secondary particle emission of the generated radionuclides’ decay. The detector utilizes a microcontroller that communicates using a modified SPI protocol. A solid-state, pulse shaping filter follows a charge amplifier, and it is designed as an inexpensive, low-noise solution for measuring pulses measured by a digital counter. An imaging detector can also be made by using an array of these detectors. The system can communicate with an interface unit and pass an image to a personal computer.

  20. The envelope Hamiltonian for electron interaction with ultrashort pulses

    CERN Document Server

    Toyota, Koudai; Rost, Jan M

    2014-01-01

    For ultrashort VUV pulses with a pulse length comparable to the orbital time of the bound electrons they couple to we propose a simplified envelope Hamiltonian. It is based on the Kramers-Henneberger representation in connection with a Floquet expansion of the strong-field dynamics but keeps the time dependence of the pulse envelope explicit. Thereby, the envelope Hamiltonian captures the essence of the physics, -- light-induced shifts of bound states, single-photon absorption, and non-adiabatic electronic transitions. It delivers quantitatively accurate ionization dynamics and allows for physical insight into the processes occurring. Its minimal requirements for construction in terms of laser parameters make it ideally suited for a large class of atomic and molecular problems.

  1. Electron rescattering at metal nanotips induced by ultrashort laser pulses

    Science.gov (United States)

    Wachter, G.; Lemell, C.; Burgdörfer, J.

    2014-04-01

    We theoretically investigate the interaction of moderate intensity near-infrared few cycle laser pulses with nano-scale metal tips. Local field enhancement in a nanometric region around the tip apex triggers coherent electron emission on the nanometer length and femtosecond time scale. The quantum dynamics at the surface are simulated with time-dependent density functional theory (TDDFT) and interpreted based on the simple man's model. We investigate the dependence of the emitted electron spectra on the laser wavelength.

  2. Accurate Extraction of Nanometer Distances in Multimers by Pulse EPR

    Science.gov (United States)

    Valera, Silvia; Ackermann, Katrin; Pliotas, Christos; Huang, Hexian; Naismith, James H.

    2016-01-01

    Abstract Pulse electron paramagnetic resonance (EPR) is gaining increasing importance in structural biology. The PELDOR (pulsed electron–electron double resonance) method allows extracting distance information on the nanometer scale. Here, we demonstrate the efficient extraction of distances from multimeric systems such as membrane‐embedded ion channels where data analysis is commonly hindered by multi‐spin effects. PMID:26865468

  3. Magic angle spinning NMR of paramagnetic proteins.

    Science.gov (United States)

    Knight, Michael J; Felli, Isabella C; Pierattelli, Roberta; Emsley, Lyndon; Pintacuda, Guido

    2013-09-17

    Metal ions are ubiquitous in biochemical and cellular processes. Since many metal ions are paramagnetic due to the presence of unpaired electrons, paramagnetic molecules are an important class of targets for research in structural biology and related fields. Today, NMR spectroscopy plays a central role in the investigation of the structure and chemical properties of paramagnetic metalloproteins, linking the observed paramagnetic phenomena directly to electronic and molecular structure. A major step forward in the study of proteins by solid-state NMR came with the advent of ultrafast magic angle spinning (MAS) and the ability to use (1)H detection. Combined, these techniques have allowed investigators to observe nuclei that previously were invisible in highly paramagnetic metalloproteins. In addition, these techniques have enabled quantitative site-specific measurement of a variety of long-range paramagnetic effects. Instead of limiting solid-state NMR studies of biological systems, paramagnetism provides an information-rich phenomenon that can be exploited in these studies. This Account emphasizes state-of-the-art methods and applications of solid-state NMR in paramagnetic systems in biological chemistry. In particular, we discuss the use of ultrafast MAS and (1)H-detection in perdeuterated paramagnetic metalloproteins. Current methodology allows us to determine the structure and dynamics of metalloenzymes, and, as an example, we describe solid-state NMR studies of microcrystalline superoxide dismutase, a 32 kDa dimer. Data were acquired with remarkably short times, and these experiments required only a few milligrams of sample.

  4. Pulse radiolysis of liquid water using picosecond electron pulses produced by a table-top terawatt laser system

    Energy Technology Data Exchange (ETDEWEB)

    Saleh, Ned [Center for Ultrafast Optical Science, University of Michigan, 2200 Bonisteel Boulevard, Ann Arbor, Michigan 48109-2099 (United States); Flippo, Kirk [Center for Ultrafast Optical Science, University of Michigan, 2200 Bonisteel Boulevard, Ann Arbor, Michigan 48109-2099 (United States); Nemoto, Koshichi [Center for Ultrafast Optical Science, University of Michigan, 2200 Bonisteel Boulevard, Ann Arbor, Michigan 48109-2099 (United States); Umstadter, Donald [Center for Ultrafast Optical Science, University of Michigan, 2200 Bonisteel Boulevard, Ann Arbor, Michigan 48109-2099 (United States); Crowell, Robert A. [Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Jonah, Charles D. [Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Trifunac, Alexander D. [Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

    2000-06-01

    A laser based electron generator is shown, for the first time, to produce sufficient charge to conduct time resolved investigations of radiation induced chemical events. Electron pulses generated by focussing terawatt laser pulses into a supersonic helium gas jet are used to ionize liquid water. The decay of the hydrated electrons produced by the ionizing electron pulses is monitored with 0.3 {mu}s time resolution. Hydrated electron concentrations as high as 22 {mu}M were generated. The results show that terawatt lasers offer both an alternative to linear accelerators and a means to achieve subpicosecond time resolution for pulse radiolysis studies. (c) 2000 American Institute of Physics.

  5. Cooling of relativistic electron beams in chirped laser pulses

    CERN Document Server

    Yoffe, Samuel R; Kravets, Yevgen; Jaroszynski, Dino A

    2015-01-01

    The next few years will see next-generation high-power laser facilities (such as the Extreme Light Infrastructure) become operational, for which it is important to understand how interaction with intense laser pulses affects the bulk properties of a relativistic electron beam. At such high field intensities, we expect both radiation reaction and quantum effects to play a significant role in the beam dynamics. The resulting reduction in relative energy spread (beam cooling) at the expense of mean beam energy predicted by classical theories of radiation reaction depends only on the energy of the laser pulse. Quantum effects suppress this cooling, with the dynamics additionally sensitive to the distribution of energy within the pulse. Since chirps occur in both the production of high-intensity pulses (CPA) and the propagation of pulses in media, the effect of using chirps to modify the pulse shape has been investigated using a semi-classical extension to the Landau--Lifshitz theory. Results indicate that even la...

  6. Kinetics study of the solvated electron decay in THF using laser-synchronised picosecond electron pulse

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Picosecond pulse radiolysis of neat tetrahydrofuran (THF) shows a fast decay of the solvated electron within 2.5ns. The decay of the solvated electron observed at 790nm is because of spur reaction. A numerical simulation using time dependent Smoluchowski equation containing a sink term with a distance dependent reaction rate is used to fit the pulse-probe data and shows that the geminate reaction can proceed at long distance in this low polar solvent.

  7. Electron density and electron temperature measurements in nanosecond pulse discharges over liquid water surface

    Science.gov (United States)

    Simeni Simeni, M.; Roettgen, A.; Petrishchev, V.; Frederickson, K.; Adamovich, I. V.

    2016-12-01

    Time-resolved electron density, electron temperature, and gas temperature in nanosecond pulse discharges in helium and O2-He mixtures near liquid water surface are measured using Thomson/pure rotational Raman scattering, in two different geometries, (a) ‘diffuse filament’ discharge between a spherical high-voltage electrode and a grounded pin electrode placed in a reservoir filled with distilled water, with the tip exposed, and (b) dielectric barrier discharge between the high-voltage electrode and the liquid water surface. A diffuse plasma filament generated between the electrodes in helium during the primary discharge pulse exhibits noticeable constriction during the secondary discharge pulse several hundred ns later. Adding oxygen to the mixture reduces the plasma filament diameter and enhances constriction during the secondary pulse. In the dielectric barrier discharge, diffuse volumetric plasma occupies nearly the entire space between the high voltage electrode and the liquid surface, and extends radially along the surface. In the filament discharge in helium, adding water to the container results in considerable reduction of plasma lifetime compared to the discharge in dry helium, by about an order of magnitude, indicating rapid electron recombination with water cluster ions. Peak electron density during the pulse is also reduced, by about a factor of two, likely due to dissociative attachment to water vapor during the discharge pulse. These trends become more pronounced as oxygen is added to the mixture, which increases net rate of dissociative attachment. Gas temperature during the primary discharge pulse remains near room temperature, after which it increases up to T ~ 500 K over 5 µs and decays back to near room temperature before the next discharge pulse several tens of ms later. As expected, electron density and electron temperature in diffuse DBD plasmas are considerably lower compared to peak values in the filament discharge. Use of Thomson

  8. Shaping the electron beams with submicrosecond pulse duration in sources and electron accelerators with plasma emitters

    CERN Document Server

    Gushenets, V I

    2001-01-01

    One studies the techniques in use to shape submicrosecond electron beams and the physical processes associated with extraction of electrons from plasma in plasma emitters. Plasma emitter base sources and accelerators enable to generate pulse beams with currents varying from tens of amperes up to 10 sup 3 A, with current densities up to several amperes per a square centimeter, with pulse duration constituting hundreds of nanoseconds and with high frequencies of repetition

  9. Superradiance of short electron pulses in regular and corrugated waveguides

    Energy Technology Data Exchange (ETDEWEB)

    Ginzburg, N.S.; Konoplev, I.V.; Sergeev, A.S. [Institute of Applied Physics, Nizhny Novgorod (Russian Federation)] [and others

    1995-12-31

    The report is devoted to theoretical and experimental study of superradiance of short electron pulses moving through waveguide systems. It is suggested that electrons oscillate or in undulator field (undulator SR) or in homogeneous magnetic field (cyclotron SR). We studied specific regimes of SR which may occur due to peculiarities of waveguide dispersion. Among them there are regimes of radiation near cut-off frequency as well as regimes of group synchronism. At the last operating regimes an electron bunch longitudinal velocity coincide with group velocity of e.m. wave. It is found the increasing of the SR instability grows rate and energy extraction efficiency in such regimes. It is also possible to observe the same enhancement using external feedback in periodically corrugated waveguide when Bragg resonance condition with forward propagated e.m. wave is fulfill. For experimental observation of cyclotron SR we intend to use compact subnanosecond accelerator RADAN 303B on the base of the high voltage generator with special subnansecond transformer. Accelerator generates short 0.3ns electron pulses with current about 1kA and particles energy 200keV. Design of magnetic confound system provide possibility to install an active locker to impose to electrons cyclotron rotation with pitch-factor about 1-1.5. According to numerical simulation at the mm and submm wavebands it is possible to achieve radiation pick power about 5-10MW with pulse duration less than 1ns.

  10. High current precision long pulse electron beam position monitor

    CERN Document Server

    Nelson, S D; Fessenden, T J; Holmes, C

    2000-01-01

    Precision high current long pulse electron beam position monitoring has typically experienced problems with high Q sensors, sensors damped to the point of lack of precision, or sensors that interact substantially with any beam halo thus obscuring the desired signal. As part of the effort to develop a multi-axis electron beam transport system using transverse electromagnetic stripline kicker technology, it is necessary to precisely determine the position and extent of long high energy beams for accurate beam position control (6 - 40 MeV, 1 - 4 kA, 2 μs beam pulse, sub millimeter beam position accuracy.) The kicker positioning system utilizes shot-to-shot adjustments for reduction of relatively slow (< 20 MHz) motion of the beam centroid. The electron beams passing through the diagnostic systems have the potential for large halo effects that tend to corrupt position measurements.

  11. Electron paramagnetic resonance study on the ionizing radiation induced defects of the tooth enamel hydroxyapatite; Estudo por ressonancia paramagnetica eletronica de defeitos induzidos pelas radiacoes ionizantes na hidroxiapatita do esmalte dentario

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Liana Macedo de

    1995-01-01

    Hydroxyapatite is the main constituent of calcified tissues. Defects induced by ionizing radiations in this biomineral can present high stability and then, these are used as biological markers in radiological accidents, irradiated food identifying and geological and archaeological dating. In this work, paramagnetic centers induced on the enamel of the teeth by environmental ionizing radiation, are investigated by electron paramagnetic resonance (EPR). Decay thermal kinetic presents high complexity and shows the formation of different electron ligation energy centers and structures 65 refs., 40 figs., 5 tabs.

  12. Progressive and resonant wave helices application to electron paramagnetic resonance; Helices a ondes progressives et resonnantes application a la resonance paramagnetique electronique

    Energy Technology Data Exchange (ETDEWEB)

    Volino, F. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1969-07-01

    We show that helices can be used as resonant systems. Their properties are theoretically and experimentally studied. We describe resonant helices for electron paramagnetic resonance in X-band and develop a comparison between their sensitivity and the sensitivity of a normal resonant cavity. For cylindrical samples less than 3 mm diameter, the helix is more sensitive and can produce more intense microwave magnetic fields. (author) [French] Il est montre que les helices peuvent etre utilisees comme systeme resonnant. Leurs proprietes sont discutees theoriquement et experimentalement. Des helices resonnantes en bande X pour la resonance paramagnetique electronique sont decrites et leur sensibilite est comparee a celle des cavites resonnantes. Pour des echantillons cylindriques de moins de 3 mm de diametre, l'helice est plus sensible et peut produire des champs magnetiques hyper fins plus intenses. (auteur)

  13. Theoretical study of the electron paramagnetic resonance parameters and local structure for the tetragonal Ir2+ centre in NaCl

    Indian Academy of Sciences (India)

    Y-X Hu; S-Y Wu; X-F Wang; P Xu

    2010-04-01

    The electron paramagnetic resonance (EPR) parameters (the factors, hyperfine structure constants and the superhyperfine parameters) for the tetragonal Ir2+ centre in NaCl are theoretically investigated from the perturbation formulas of these parameters for a 5d7 ion in tetragonally elongated octahedra. This impurity centre is attributed to the substitutional [IrCl6]4- cluster on host Na+ site, associated with the 4% relative elongation along the 4-axis due to the Jahn–Teller effect. Despite the ionicity of host NaCl, the [IrCl6]4- cluster still exhibits moderate covalency and then the ligand orbital and spin-orbit coupling contributions should be taken into account. In addition, the theoretical EPR parameters based on the Jahn–Teller elongation show good agreement with the observed values.

  14. Characterization of vanadium compounds in selected crudes. II. Electron paramagnetic resonance studies of the first coordination spheres in porphyrin and non-porphyrin fractions

    Energy Technology Data Exchange (ETDEWEB)

    Reynolds, J.G.; Biggs, W.R.; Fetzer, J.C.

    1985-11-01

    The authors applied electron paramagnetic resonance spectroscopy (EPR) to heavy petroleum fractions to characterize the first coordination sphere around the vanadyl +2 ion. The fractions were generated using a modified porphyrin extraction procedure. For the residual oil from the extraction, which contains the non-porphyrin metals, the first coordination sphere was dominated by 4N and N O 2S for Boscan, Beta, Morichal, and Arabian Heavy crudes. Maya had distinctively different parameters. These findings are significant for determining the overall structure of metal-containing compounds in heavy crude oils. They discuss the difference between the porphyrin and non-porphyrin behavior, possible biogenic precursors, and some process implications. 59 references, 1 figure, 2 tables.

  15. Electronic Paramagnetic Resonance of irradiated nails: challenges for a dosimetry in radiation accidents; Ressonancia Paramagnetica Eletronica de unhas irradiadas: desafios para uma dosimetria em acidentes radiologicos

    Energy Technology Data Exchange (ETDEWEB)

    Giannoni, Ricardo A., E-mail: giannoni@ird.gov.br [Instituto de Radioprotecao e Dosimetria, (IRD/CNEN-RJ), Rio de Janeiro, RJ (Brazil); Rodrigues Junior, Orlando [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2014-07-01

    The purpose of this work is to characterize samples of human nails exposed to high doses of radiation, applying the technique of Electron Paramagnetic Resonance (EPR). The objective is to establish a dose response study that allow determine the absorbed dose by exposed individuals in situations of radiological accidents, in a retrospective form. Samples of human nails were collected and afterward irradiated with gamma radiation, and received dose of 20 Gy. The EPR measurement performed on the samples, before irradiation, permitted the signal identification of the components associated with effects caused by the mechanical stress during the fingernail cutting, the so-called mechanically induced signal (MIS). After the irradiation, different species of free radicals were identified, the so-called radiation induced signal (RIS). (author)

  16. Hyperbolic decay of photo-created Sb2+ ions in Sn2P2S6:Sb crystals detected with electron paramagnetic resonance

    Science.gov (United States)

    Basun, S. A.; Halliburton, L. E.; Evans, D. R.

    2017-01-01

    In this paper, we employed a method that overcomes the known limitations of electron paramagnetic resonance (EPR) to monitor charge trap dynamics over a broad temperature range not normally accessible due to the lifetime broadening of the EPR lines at higher temperatures. This was achieved by measuring the decay of the EPR intensity after thermal annealing by rapid cycling back to low temperatures for the EPR measurement. This technique was used to experimentally demonstrate interesting physics in the form of a direct measurement of the hyperbolic decay 1/(1+t) of a charge trap population, which previously was only considered theoretically. The nontrivial effects of bimolecular recombination are demonstrated in the Sn2S2P6:Sb crystals, providing an explanation of the optical sensitization process observed in photorefractive Sn2P2S6:Sb used for dynamic holography.

  17. Electron paramagnetic resonance spectral study of [Mn(acs){sub 2}(2–pic){sub 2}(H{sub 2}O){sub 2}] single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Kocakoç, Mehpeyker, E-mail: mkocakoc@cu.edu.tr [Çukurova University (Turkey); Tapramaz, Recep, E-mail: recept@omu.edu.tr [Ondokuz Mayıs University (Turkey)

    2016-03-25

    Acesulfame potassium salt is a synthetic and non-caloric sweetener. It is also important chemically for its capability of being ligand in coordination compounds, because it can bind over Nitrogen and Oxygen atoms of carbonyl and sulfonyl groups and ring oxygen. Some acesulfame containing transition metal ion complexes with mixed ligands exhibit solvato and thermo chromic properties and these properties make them physically important. In this work single crystals of Mn{sup +2} ion complex with mixed ligand, [Mn(acs){sub 2}(2-pic){sub 2}(H{sub 2}O){sub 2}], was studied with electron paramagnetic resonance (EPR) spectroscopy. EPR parameters were determined. Zero field splitting parameters indicated that the complex was highly symmetric. Variable temperature studies showed no detectable chance in spectra.

  18. Use of electron paramagnetic resonance dosimetry with tooth enamel for retrospective dose assessment. Report of a co-ordinated research project

    CERN Document Server

    2002-01-01

    Electron paramagnetic resonance (EPR) dosimetry is a physical method for the assessment of absorbed dose from ionising radiation. It is based on the measurement of stable radiation induced radicals in human calcified tissues (primarily in tooth enamel). EPR dosimetry with teeth is now firmly established in retrospective dosimetry. It is a powerful method for providing information on exposure to ionising radiation many years after the event, since the 'signal' is 'stored' in the tooth or the bone. This technique is of particular relevance to relatively low dose exposures or when the results of conventional dosimetry are not available (e.g. in accidental circumstances). The use of EPR dosimetry, as an essential tool for retrospective assessment of radiation exposure is an important part of radioepidemiological studies and also provides data to select appropriate countermeasures based on retrospective evaluation of individual doses. Despite well established regulations and protocols for maintaining radiation pro...

  19. Electron detachment from negative ions in a short laser pulse

    Energy Technology Data Exchange (ETDEWEB)

    Shearer, S. F. C.; Smyth, M. C.; Gribakin, G. F. [School of Mathematics and Physics, Queen' s University Belfast, Belfast, BT7 1NN (United Kingdom)

    2011-09-15

    We present an efficient and accurate method to study electron detachment from negative ions by a few-cycle linearly polarized laser pulse. The adiabatic saddle-point method of Gribakin and Kuchiev [Phys. Rev. A 55, 3760 (1997)] is adapted to calculate the transition amplitude for a short laser pulse. Its application to a pulse with N optical cycles produces 2(N+1) saddle points in complex time, which form a characteristic 'smile.' Numerical calculations are performed for H{sup -} in a 5-cycle pulse with frequency 0.0043 a.u. and intensities of 10{sup 10}, 5x10{sup 10}, and 10{sup 11} W/cm{sup 2}, and for various carrier-envelope phases. We determine the spectrum of the photoelectrons as a function of both energy and emission angle, as well as the angle-integrated energy spectra and total detachment probabilities. Our calculations show that the dominant contribution to the transition amplitude is given by 5-6 central saddle points, which correspond to the strongest part of the pulse. We examine the dependence of the photoelectron angular distributions on the carrier-envelope phase and show that measuring such distributions can provide a way of determining this phase.

  20. Theoretical studies of the local structure and electron paramagnetic resonance parameters for tetragonal VO{sup 2+} in C{sub 6}H{sub 7}KO{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Ping [Chongqing Jiaotong Univ. (China). School of Science; Li, Ling [Sichuan University of Arts and Science, Dazhou (China). Dept. of Maths and Finance-Economics

    2015-07-01

    The optical spectra, electron paramagnetic resonance parameters (i.e., the spin Hamiltonian parameters, including paramagnetic g factors and the hyperfine structure constants A{sub i}) and the local distortion structure for the tetragonal VO{sup 2+} in C{sub 6}H{sub 7}KO{sub 7} are theoretically studied based on the crystal-field theory and three-order perturbation formulas of a 3d{sup 1} centre in tetragonal site. The magnitude of orbital reduction factor, core polarisation constant κ, and local structure parameters are obtained by fitting the calculated optical spectra and electron paramagnetic resonance parameters to the experimental values. The theoretical results are in reasonable agreement with the experimental values.

  1. Application of electron paramagnetic resonance imaging to the characterization of the Ultem(R) exposed to 1 MeV electrons. Correlation of radical density data to tiger code calculations

    Science.gov (United States)

    Suleman, Naushadalli K.

    1994-12-01

    A major long-term goal of the Materials Division at the NASA Langley Research Center is the characterization of new high-performance materials that have potential applications in the aircraft industry, and in space. The materials used for space applications are often subjected to a harsh and potentially damaging radiation environment. The present study constitutes the application of a novel technique to obtain reliable data for ascertaining the molecular basis for the resilience and durability of materials that have been exposed to simulated space radiations. The radiations of greatest concern are energetic electrons and protons, as well as galactic cosmic rays. Presently, the effects of such radiation on matter are not understood in their entirety. It is clear however, that electron radiation causes ionization and homolytic bond rupture, resulting in the formation of paramagnetic spin centers in the polymer matrices of the structural materials. Since the detection and structure elucidation of paramagnetic species are most readily accomplished using Electron Paramagnetic Resonance (EPR) Spectroscopy, the NASA LaRC EPR system was brought back on-line during the 1991 ASEE term. The subsequent 1992 ASEE term was devoted to the adaptation of the EPR core system to meet the requirements for EPR Imaging (EPRI), which provides detailed information on the spatial distribution of paramagnetic species in bulk media. The present (1994) ASEE term was devoted to the calibration of this EPR Imaging system, as well as to the application of this technology to study the effects of electron irradiation on Ultem(exp R), a high performance polymer which is a candidate for applications in aerospace. The Ultem was exposed to a dose of 2.4 x 10(exp 9) Rads (1-MeV energy/electron) at the LaRC electron accelerator facility. Subsequently, the exposed specimens were stored in liquid nitrogen, until immediately prior to analyses by EPRI. The intensity and dimensions of the EPR Images that

  2. Application of electron paramagnetic resonance imaging to the characterization of the Ultem(R) exposed to 1 MeV electrons. Correlation of radical density data to tiger code calculations

    Science.gov (United States)

    Suleman, Naushadalli K.

    1994-01-01

    A major long-term goal of the Materials Division at the NASA Langley Research Center is the characterization of new high-performance materials that have potential applications in the aircraft industry, and in space. The materials used for space applications are often subjected to a harsh and potentially damaging radiation environment. The present study constitutes the application of a novel technique to obtain reliable data for ascertaining the molecular basis for the resilience and durability of materials that have been exposed to simulated space radiations. The radiations of greatest concern are energetic electrons and protons, as well as galactic cosmic rays. Presently, the effects of such radiation on matter are not understood in their entirety. It is clear however, that electron radiation causes ionization and homolytic bond rupture, resulting in the formation of paramagnetic spin centers in the polymer matrices of the structural materials. Since the detection and structure elucidation of paramagnetic species are most readily accomplished using Electron Paramagnetic Resonance (EPR) Spectroscopy, the NASA LaRC EPR system was brought back on-line during the 1991 ASEE term. The subsequent 1992 ASEE term was devoted to the adaptation of the EPR core system to meet the requirements for EPR Imaging (EPRI), which provides detailed information on the spatial distribution of paramagnetic species in bulk media. The present (1994) ASEE term was devoted to the calibration of this EPR Imaging system, as well as to the application of this technology to study the effects of electron irradiation on Ultem(exp R), a high performance polymer which is a candidate for applications in aerospace. The Ultem was exposed to a dose of 2.4 x 10(exp 9) Rads (1-MeV energy/electron) at the LaRC electron accelerator facility. Subsequently, the exposed specimens were stored in liquid nitrogen, until immediately prior to analyses by EPRI. The intensity and dimensions of the EPR Images that

  3. Native and induced triplet nitrogen-vacancy centers in nano- and micro-diamonds: Half-field electron paramagnetic resonance fingerprint

    Energy Technology Data Exchange (ETDEWEB)

    Shames, A. I., E-mail: sham@bgu.ac.il [Department of Physics, Ben-Gurion University of the Negev, Be' er-Sheva 84105 (Israel); Osipov, V. Yu.; Vul’, A. Ya. [Ioffe Physical-Technical Institute, Polytechnicheskaya 26, 194021 St. Petersburg (Russian Federation); Bardeleben, H.-J. von [Institut des Nano Sciences de Paris-INSP, Université Pierre et Marie Curie/UMR 7588 au CNRS, 7500 Paris (France); Boudou, J.-P.; Treussart, F. [Laboratoire Aimé Cotton, CNRS, Université Paris-Sud and ENS Cachan, 91405 Orsay (France)

    2014-02-10

    Multiple frequency electron paramagnetic resonance (EPR) study of small (4–25 nm) nanodiamonds obtained by various dynamic synthesis techniques reveals systematic presence in the half-field (HF) region a distinctive doublet fingerprint consisting of resolved g{sub HF1} = 4.26 and g{sub HF2} = 4.00 signals. This feature is attributed to “forbidden” ΔM{sub S} = 2 transitions in EPR spectra of two native paramagnetic centers of triplet (S = 1) origin designated as TR1 and TR2, characterized by zero field splitting values D{sub 1} = 0.0950 ± 0.002 cm{sup −1} and D{sub 2} = 0.030 ± 0.005 cm{sup −1}. Nanodiamonds of ∼50 nm particle size, obtained by crushing of Ib type nitrogen rich synthetic diamonds, show only HF TR2 signal whereas the same sample undergone high energy (20 MeV) electron irradiation and thermal annealing demonstrates rise of HF TR1 signal. The same HF TR1 signals appear in the process of fabrication of fluorescent nanodiamonds from micron-size synthetic diamond precursors. Results obtained allow unambiguous attribution of the half-field TR1 EPR signals with g{sub HF1} = 4.26, observed in nano- and micron-diamond powders, to triplet negatively charged nitrogen-vacancy centers. These signals are proposed as reliable and convenient fingerprints in both qualitative and quantitative study of fluorescent nano- and micron-diamonds.

  4. A pulsed electron gun for the Plane Wave Transformer Linac

    CERN Document Server

    Mahadevan, S; Nandedkar, R V

    2003-01-01

    A pulsed diode electron gun delivering 500 mA current at 40 kV is described. The gun geometry is optimized using the Electron Trajectory Program EGUN at higher scaling factors by choosing the closest converging starting surface. The effect of an annular gap between cathode and focusing electrode on beam behaviour is compensated by using a suitable focusing electrode. The estimated perveance is 0.065 mu perv and the normalized emittance is within 5 pi mm mrad. The variation in current density at the cathode has been limited to within 10% across the face of the cathode. Salient features of the pulsed power supply and an insight of its interconnection with the gun are presented. The current measured at the Faraday cup is in agreement with the designed perveance.

  5. Pulsed electron source characterization with the modified three gradient method

    CERN Document Server

    Marghitu, S; Dinca, C; Marghitu, O

    2001-01-01

    Results from the Modified Three Gradient Method (MTGM), applied to a pulsed high intensity electron source, are presented. The MTGM makes possible the non-destructive determination of beam emittance in the space charge presence [1]. We apply the MTGM to an experimental system equipped with a Pierce convergent diode, working in pulse mode, and having a directly heated cathode as electron source. This choice was mainly motivated by the availability of an analytical characterization of this source type [2], as well as the extended use of the Pierce type sources in linear accelerators. The experimental data are processed with a numerical matching program, based on the K-V equation for an axially symmetric configuration [3], to determine the emittance and object cross-over position and diameter. The variation of these parameters is further investigated with respect to both electrical and constructive characteristics of the source: cathode heating current, extraction voltage, and cathode-anode distance.

  6. Surface modification of pure titanium by pulsed electron beam

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, X.D. [Key Laboratory of Materials Modification and School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Laboratoired' Etude des Microstructures et de Mecanique des Materiaux (LEM3), CNRS UMR 7239, Universite Paul Verlaine - Metz, Ile du Saulcy, 57045 Metz (France); Hao, S.Z., E-mail: ebeam@dlut.edu.cn [Key Laboratory of Materials Modification and School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Li, X.N. [Key Laboratory of Materials Modification and School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Dong, C., E-mail: dong@dlut.edu.cn [Key Laboratory of Materials Modification and School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Grosdidier, T., E-mail: Thierry.grosdidier@univ-metz.fr [Laboratoired' Etude des Microstructures et de Mecanique des Materiaux (LEM3), CNRS UMR 7239, Universite Paul Verlaine - Metz, Ile du Saulcy, 57045 Metz (France)

    2011-04-15

    The microstructure, hardness and corrosion resistance of commercially pure Ti treated by low energy high current pulsed electron beam (LEHCPEB) have been investigated. The thin near-surface melted layer rapidly solidified into {beta} and subsequently transformed into ultrafine {alpha}' martensite. This has led to a drastic improvement of the corrosion properties and a significant increase (more than 60%) in hardness of the top surface.

  7. Electronic structure description of a [Co(III)3Co(IV)O4] cluster: a model for the paramagnetic intermediate in cobalt-catalyzed water oxidation.

    Science.gov (United States)

    McAlpin, J Gregory; Stich, Troy A; Ohlin, C André; Surendranath, Yogesh; Nocera, Daniel G; Casey, William H; Britt, R David

    2011-10-01

    Multifrequency electron paramagnetic resonace (EPR) spectroscopy and electronic structure calculations were performed on [Co(4)O(4)(C(5)H(5)N)(4)(CH(3)CO(2))(4)](+) (1(+)), a cobalt tetramer with total electron spin S = 1/2 and formal cobalt oxidation states III, III, III, and IV. The cuboidal arrangement of its cobalt and oxygen atoms is similar to that of proposed structures for the molecular cobaltate clusters of the cobalt-phosphate (Co-Pi) water-oxidizing catalyst. The Davies electron-nuclear double resonance (ENDOR) spectrum is well-modeled using a single class of hyperfine-coupled (59)Co nuclei with a modestly strong interaction (principal elements of the hyperfine tensor are equal to [-20(±2), 77(±1), -5(±15)] MHz). Mims (1)H ENDOR spectra of 1(+) with selectively deuterated pyridine ligands confirm that the amount of unpaired spin on the cobalt-bonding partner is significantly reduced from unity. Multifrequency (14)N ESEEM spectra (acquired at 9.5 and 34.0 GHz) indicate that four nearly equivalent nitrogen nuclei are coupled to the electron spin. Cumulatively, our EPR spectroscopic findings indicate that the unpaired spin is delocalized almost equally across the eight core atoms, a finding corroborated by results from DFT calculations. Each octahedrally coordinated cobalt ion is forced into a low-spin electron configuration by the anionic oxo and carboxylato ligands, and a fractional electron hole is localized on each metal center in a Co 3d(xz,yz)-based molecular orbital for this essentially [Co(+3.125)(4)O(4)] system. Comparing the EPR spectrum of 1(+) with that of the catalyst film allows us to draw conclusions about the electronic structure of this water-oxidation catalyst.

  8. Effects of the Electronic Spin-Orbit Interaction on the Anomalous Asymmetric Scattering of the Spin-Polarized 4He+ Beam with Paramagnetic Target Materials

    Science.gov (United States)

    Sakai, Osamu; Suzuki, Taku T.

    2017-06-01

    The scattering of the electron-spin-polarized 4He+ beam on paramagnetic materials has an anomalously large asymmetric scattering component (ASC) around 5%, which is 104 of that expected from the spin-orbit coupling (SOC) for the potential of the target nucleus. In addition, the ASC of some materials (for example, Au and Pt) changes sign near the scattering angle (θ) of 90° unlike the result predicted by using the potential scattering theory. When the 4He+ approaches the target, virtual electron-transfer (ET) excitations between them occur. The effects of the SOC of electrons (SOEs) on the target atom in the ET intermediate state are studied within the frame of the lowest-order perturbation theory about the ET process. The ASC is caused through the combination of the quantum development of electron orbital states under the SOEs and the He nucleus motion in the intermediate state because the preferred orbital states for the ET depend on the position of the He nucleus. It is shown by a numerical calculation that the present process has the possibility of producing the ASC with a magnitude of around 0.1. In the present process, the ASC shows a θ dependence of cos θ sin θ, which changes sign at θ = 90° when the excited orbital in the ET state has the d-character like the Au and Pt cases.

  9. Ultrafast electron dynamics in phenylalanine initiated by attosecond pulses

    Science.gov (United States)

    Calegari, F.; Ayuso, D.; Trabattoni, A.; Belshaw, L.; De Camillis, S.; Anumula, S.; Frassetto, F.; Poletto, L.; Palacios, A.; Decleva, P.; Greenwood, J. B.; Martín, F.; Nisoli, M.

    2014-10-01

    In the past decade, attosecond technology has opened up the investigation of ultrafast electronic processes in atoms, simple molecules, and solids. Here, we report the application of isolated attosecond pulses to prompt ionization of the amino acid phenylalanine and the subsequent detection of ultrafast dynamics on a sub-4.5-femtosecond temporal scale, which is shorter than the vibrational response of the molecule. The ability to initiate and observe such electronic dynamics in polyatomic molecules represents a crucial step forward in attosecond science, which is progressively moving toward the investigation of more and more complex systems.

  10. Powderspec, a program for the efficient simulation of spectra of electron paramagnetic resonance of powders with orthorhombic symmetry; Powderspec, un programa para la simulacion eficiente de espectros de resonancia paramagnetica electronica de polvos con simetria ortorrombica

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez T, L.; Beltran L, V

    1991-09-15

    In this report a FORTRAN source program which simulates the second order powder pattern and spectrum of electron paramagnetic resonance (EPR) in crystal fields with orthorhombic symmetry using Gauss-Legendre quadratures is given. Also the commentaries which describe each step in detail are presented. (Author)

  11. Electron heating enhancement by frequency-chirped laser pulses

    Science.gov (United States)

    Yazdani, E.; Sadighi-Bonabi, R.; Afarideh, H.; Riazi, Z.; Hora, H.

    2014-09-01

    Propagation of a chirped laser pulse with a circular polarization through an uprising plasma density profile is studied by using 1D-3V particle-in-cell simulation. The laser penetration depth is increased in an overdense plasma compared to an unchirped pulse. The induced transparency due to the laser frequency chirp results in an enhanced heating of hot electrons as well as increased maximum longitudinal electrostatic field at the back side of the solid target, which is very essential in target normal sheath acceleration regime of proton acceleration. For an applied chirp parameter between 0.008 and 0.01, the maximum amount of the electrostatic field is improved by a factor of 2. Furthermore, it is noticed that for a chirped laser pulse with a0 = 5, because of increasing the plasma transparency length, the laser pulse can penetrate up to about ne ≈ 6nc, where nc is plasma critical density. It shows 63% increase in the effective critical density compared to the relativistic induced transparency regime for an unchirped condition.

  12. Electron heating enhancement by frequency-chirped laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Yazdani, E.; Afarideh, H., E-mail: hafarideh@aut.ac.ir [Department of Energy Engineering and Physics, Amirkabir University of Technology, P.O. Box 15875-4413, Tehran (Iran, Islamic Republic of); Sadighi-Bonabi, R., E-mail: Sadighi@sharif.ir [Department of Physics, Sharif University of Technology, P.O. Box 11365-9567, Tehran (Iran, Islamic Republic of); Riazi, Z. [Physics and Accelerator School, Tehran (Iran, Islamic Republic of); Hora, H. [Department of Theoretical Physics, University of New South Wales, Sydney 2052 (Australia)

    2014-09-14

    Propagation of a chirped laser pulse with a circular polarization through an uprising plasma density profile is studied by using 1D-3V particle-in-cell simulation. The laser penetration depth is increased in an overdense plasma compared to an unchirped pulse. The induced transparency due to the laser frequency chirp results in an enhanced heating of hot electrons as well as increased maximum longitudinal electrostatic field at the back side of the solid target, which is very essential in target normal sheath acceleration regime of proton acceleration. For an applied chirp parameter between 0.008 and 0.01, the maximum amount of the electrostatic field is improved by a factor of 2. Furthermore, it is noticed that for a chirped laser pulse with a₀=5, because of increasing the plasma transparency length, the laser pulse can penetrate up to about n{sub e}≈6n{sub c}, where n{sub c} is plasma critical density. It shows 63% increase in the effective critical density compared to the relativistic induced transparency regime for an unchirped condition.

  13. Magnetically insulated electron flows in pulsed power systems

    Science.gov (United States)

    Lawconnell, Robert I.

    1989-08-01

    Magnetic insulation is crucial in the operation of large pulsed power systems. Particular attention will be paid to describing magnetic insulation in realistic pulsed power systems. A theoretical model is developed that allows the production of self consistent magnetically insulated laminar flows in perturbed cylindrical systems given only the electron density profile. The theory is checked and justified by detailed comparisons with results from a 2-dimensional electromagnetic code, MASK. The procedure followed in the theoretical development is to use the relativistic Vlasov equation, Ampere's law and Gauss' law, to obtain a relation between the density profile and the velocity profile for insulated flows. Given the density profile and the corresponding derived velocity profile, a self consistent flow solution is obtained by means of Maxwell's equations. It is checked by taking a special case (corresponding to no perturbations) which results in the well known Brillouin flow theory. Emphasis is placed on determining the magnetic insulation threshold of a pulsed power system employing a plasma erosion opening switch. The procedure employed in the computational study is to vary critical aspects of the pulsed power system and then note whether magnetic insulation breaks down. The point at which magnetic insulation breaks down (as a function of geometry, load impedance, and applied voltage) is the magnetic insulation threshold for the system.

  14. Light-induced electron paramagnetic resonance evidence of charge transfer in electrospun fibers containing conjugated polymer/fullerene and conjugated polymer/fullerene/carbon nanotube blends

    Science.gov (United States)

    Shames, Alexander I.; Bounioux, Céline; Katz, Eugene A.; Yerushalmi-Rozen, Rachel; Zussman, Eyal

    2012-03-01

    Electrospun sub-micron fibers containing conjugated polymer (poly(3-hexylthiophene), P3HT) with a fullerene derivative, phenyl-C61-butyric acid methylester (PCBM) or a mixture of PCBM and single-walled carbon nanotubes (SWCNTs) were studied by light-induced electron paramagnetic resonance spectroscopy. The results provide experimental evidence of electron transfer between PCBM and P3HT components in both fiber systems and suggest that the presence of a dispersing block-copolymer, which acts via physical adsorption onto the PCBM and SWCNT moieties, does not prevent electron transfer at the P3HT-PCBM interface. These findings suggest a research perspective towards utilization of fibers of functional nanocomposites in fiber-based organic optoelectronic and photovoltaic devices. The latter can be developed in the textile-type large area photovoltaics or individual fiber-based solar cells that will broaden energy applications from macro-power tools to micro-nanoscale power conversion devices and smart textiles.

  15. The impact of adsorption on the localization of spins in graphene oxide and reduced graphene oxide, observed with electron paramagnetic resonance

    Science.gov (United States)

    Kempiński, Mateusz; Florczak, Patryk; Jurga, Stefan; Śliwińska-Bartkowiak, Małgorzata; Kempiński, Wojciech

    2017-08-01

    We report the observations of electronic properties of graphene oxide and reduced graphene oxide, performed with electron paramagnetic resonance technique in a broad temperature range. Both materials were examined in pure form and saturated with air, helium, and heavy water molecules. We show that spin localization strongly depends on the type and amount of molecules adsorbed at the graphene layer edges (and possible in-plane defects). Physical and chemical states of edges play crucial role in electrical transport within graphene-based materials, with hopping as the leading mechanism of charge carrier transport. Presented results are a good basis to understand the electronic properties of other carbon structures made of graphene-like building blocks. Most active carbons show some degree of functionalization and are known of having good adsorptive properties; thus, controlling both phenomena is important for many applications. Sample treatment with temperature, vacuum, and various adsorbents allowed for the observation of a possible metal-insulator transition and sorption pumping effects. The influence of adsorption on the localization phenomena in graphene would be very important if to consider the graphene-based material as possible candidates for the future spintronics that works in ambient conditions.

  16. Infrared imaging diagnostics for intense pulsed electron beam

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Xiao; Shen, Jie; Liu, Wenbin; Zhong, Haowen; Zhang, Jie; Zhang, Gaolong; Le, Xiaoyun, E-mail: xyle@buaa.edu.cn [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); International Research Center for Nuclei and Particles in the Cosmos, Beihang University, Beijing 100191 (China); Qu, Miao; Yan, Sha [Institute of Heavy Ion Physics, Peking University, Beijing 100871 (China)

    2015-08-15

    Infrared imaging diagnostic method for two-dimensional calorimetric diagnostics has been developed for intense pulsed electron beam (IPEB). By using a 100-μm-thick tungsten film as the infrared heat sink for IPEB, the emitting uniformity of the electron source can be analyzed to evaluate the efficiency and stability of the diode system. Two-dimensional axisymmetric finite element method heat transfer simulation, combined with Monte Carlo calculation, was performed for error estimation and optimization of the method. The test of the method was finished with IPEB generated by explosive emission electron diode with pulse duration (FWHM) of 80 ns, electron energy up to 450 keV, and a total beam current of over 1 kA. The results showed that it is possible to measure the cross-sectional energy density distribution of IPEB with energy sensitivity of 0.1 J/cm{sup 2} and spatial resolution of 1 mm. The technical details, such as irradiation protection of bremsstrahlung γ photons and the functional extensibility of the method were discussed in this work.

  17. Infrared imaging diagnostics for intense pulsed electron beam.

    Science.gov (United States)

    Yu, Xiao; Shen, Jie; Qu, Miao; Liu, Wenbin; Zhong, Haowen; Zhang, Jie; Yan, Sha; Zhang, Gaolong; Le, Xiaoyun

    2015-08-01

    Infrared imaging diagnostic method for two-dimensional calorimetric diagnostics has been developed for intense pulsed electron beam (IPEB). By using a 100-μm-thick tungsten film as the infrared heat sink for IPEB, the emitting uniformity of the electron source can be analyzed to evaluate the efficiency and stability of the diode system. Two-dimensional axisymmetric finite element method heat transfer simulation, combined with Monte Carlo calculation, was performed for error estimation and optimization of the method. The test of the method was finished with IPEB generated by explosive emission electron diode with pulse duration (FWHM) of 80 ns, electron energy up to 450 keV, and a total beam current of over 1 kA. The results showed that it is possible to measure the cross-sectional energy density distribution of IPEB with energy sensitivity of 0.1 J/cm(2) and spatial resolution of 1 mm. The technical details, such as irradiation protection of bremsstrahlung γ photons and the functional extensibility of the method were discussed in this work.

  18. Chirped pulse inverse free-electron laser vacuum accelerator

    Science.gov (United States)

    Hartemann, Frederic V.; Baldis, Hector A.; Landahl, Eric C.

    2002-01-01

    A chirped pulse inverse free-electron laser (IFEL) vacuum accelerator for high gradient laser acceleration in vacuum. By the use of an ultrashort (femtosecond), ultrahigh intensity chirped laser pulse both the IFEL interaction bandwidth and accelerating gradient are increased, thus yielding large gains in a compact system. In addition, the IFEL resonance condition can be maintained throughout the interaction region by using a chirped drive laser wave. In addition, diffraction can be alleviated by taking advantage of the laser optical bandwidth with negative dispersion focusing optics to produce a chromatic line focus. The combination of these features results in a compact, efficient vacuum laser accelerator which finds many applications including high energy physics, compact table-top laser accelerator for medical imaging and therapy, material science, and basic physics.

  19. Electronics for the pulsed rubidium clock: design and characterization.

    Science.gov (United States)

    Calosso, Claudio E; Micalizio, Salvatore; Godone, Aldo; Bertacco, Elio K; Levi, Filippo

    2007-09-01

    Pulsing the different operation phases of a vapor-cell clock (optical pumping, interrogation, and detection) has been recognized as one of the most effective techniques to reduce light shift and then to improve the stability perspectives of vapor cell clocks. However, in order to take full advantage of the pulsed scheme, a fast-gated electronics is required, the times involved being of the order of milliseconds. In this paper we describe the design and the implementation of the electronics that synchronizes the different phases of the clock operation, as well as of the electronics that is mainly devoted to the thermal stabilization of the clock physics package. We also report some characterization measurements, including a measurement of the clock frequency stability. In particular, in terms of Allan deviation, we measured a frequency stability of 1.2 x 10(-12) tao(-1/2) for averaging times up to tao = 10(5) s, a very interesting result by itself and also for a possible space application of such a clock.

  20. Application of Numerical Analysis of the Shape of Electron Paramagnetic Resonance Spectra for Determination of the Number of Different Groups of Radicals in the Burn Wounds

    Directory of Open Access Journals (Sweden)

    Paweł Olczyk

    2017-01-01

    Full Text Available Background. The evidence exists that radicals are crucial agents necessary for the wound regeneration helping to enhance the repair process. Materials and methods. The lineshape of the electron paramagnetic resonance (EPR spectra of the burn wounds measured with the low microwave power (2.2 mW was numerically analyzed. The experimental spectra were fitted by the sum of two and three lines. Results. The number of the lines in the EPR spectrum corresponded to the number of different groups of radicals in the natural samples after thermal treatment. The component lines were described by Gaussian and Lorentzian functions. The spectra of the burn wounds were superposition of three lines different in shape and in linewidths. The best fitting was obtained for the sum of broad Gaussian, broad Lorentzian, and narrow Lorentzian lines. Dipolar interactions between the unpaired electrons widened the broad Gaussian and broad Lorentzian lines. Radicals with the narrow Lorentzian lines existed mainly in the tested samples. Conclusions. The spectral shape analysis may be proposed as a useful method for determining the number of different groups of radicals in the burn wounds.

  1. The g-tensor of the flavin cofactor in (6-4) photolyase: a 360 GHz/12.8 T electron paramagnetic resonance study

    Science.gov (United States)

    Schnegg, A.; Kay, C. W. M.; Schleicher, E.; Hitomi, K.; Todo, T.; Möbius, K.; Weber, S.

    2006-05-01

    The g-tensor of the neutral radical form of the flavin adenine dinucleotide cofactor FADH• of (6-4) photolyase from Xenopus laevis has been determined by very high-magnetic-field/high-microwave-frequency electron-paramagnetic resonance (EPR) performed at 360 GHz/12.8 T. Due to the high spectral resolution the anisotropy of the g-tensor could be fully resolved in the frozen-solution continuous-wave EPR spectrum. By least square fittings of spectral simulations to experimental data, the principal values of the g-tensor have been established: gX = 2.00433(5), gY = 2.00368(5), gZ = 2.00218(7). A comparison of very high-field EPR data and proton and deuteron electron-nuclear double resonance measurements yielded precise information concerning the orientation of the g-tensor with respect to the molecular frame. This data allowed a comparison to be made between the principal values of the g-tensors of the FADH• cofactors of photolyases involved in the repair of two different DNA lesions: the cyclobutane pyrimidine dimer (CPD) and the (6-4) photoproduct. It was found that gX and gZ are similar in both enzymes, whereas the gY component is slightly larger in (6-4) photolyase. This result clearly shows the sensitivity of the g-tensor to subtle differences in the protein environment experienced by the flavin.

  2. Time-resolved electron density and electron temperature measurements in nanosecond pulse discharges in helium

    Science.gov (United States)

    Roettgen, A.; Shkurenkov, I.; Simeni Simeni, M.; Petrishchev, V.; Adamovich, I. V.; Lempert, W. R.

    2016-10-01

    Thomson scattering is used to study temporal evolution of electron density and electron temperature in nanosecond pulse discharges in helium sustained in two different configurations, (i) diffuse filament discharge between two spherical electrodes, and (ii) surface discharge over plane quartz surface. In the diffuse filament discharge, the experimental results are compared with the predictions of a 2D plasma fluid model. Electron densities are put on an absolute scale using pure rotational Raman spectra in nitrogen, taken without the plasma, for calibration. In the diffuse filament discharge, electron density and electron temperature increase rapidly after breakdown, peaking at n e  ≈  3.5 · 1015 cm-3 and T e  ≈  4.0 eV. After the primary discharge pulse, both electron density and electron temperature decrease (to n e ~ 1014 cm-3 over ~1 µs and to T e ~ 0.5 eV over ~200 ns), with a brief transient rise produced by the secondary discharge pulse. At the present conditions, the dominant recombination mechanism is dissociative recombination of electrons with molecular ions, \\text{He}2+ . In the afterglow, the electron temperature does not relax to gas temperature, due to superelastic collisions. Electron energy distribution functions (EEDFs) inferred from the Thomson scattering spectra are nearly Maxwellian, which is expected at high ionization fractions, when the shape of EEDF is controlled primarily by electron-electron collisions. The kinetic model predictions agree well with the temporal trends detected in the experiment, although peak electron temperature and electron density are overpredicted. Heavy species temperature predicted during the discharge and the early afterglow remains low and does not exceed T  =  400 K, due to relatively slow quenching of metastable He* atoms in two-body and three-body processes. In the surface discharge, peak electron density and electron temperature are n e  ≈  3 · 1014 cm3 and T e

  3. Electron rescattering at metal nanotips induced by ultrashort laser pulses

    CERN Document Server

    Wachter, Georg; Burgdörfer, Joachim; Schenk, Markus; Krüger, Michael; Hommelhoff, Peter

    2012-01-01

    We report on the first investigation of plateau and cut-off structures in photoelectron spectra from nano-scale metal tips interacting with few-cycle near-infrared laser pulses. These hallmarks of electron rescattering, well-known from atom-laser interaction in the strong-field regime, appear at remarkably low laser intensities with nominal Keldysh parameters of the order of $\\gtrsim 10$. Quantum and quasi-classical simulations reveal that a large field enhancement near the tip and the increased backscattering probability at a solid-state target play a key role. Plateau electrons are by an order of magnitude more abundant than in comparable atomic spectra, reflecting the high density of target atoms at the surface. The position of the cut-off serves as an in-situ probe for the locally enhanced electric field at the tip apex.

  4. Influence of pulse polarity on electron emission property of antiferroelectric ceramic

    Institute of Scientific and Technical Information of China (English)

    SHENG ZhaoXuan; FENG YuJun; OUI Jie; HUANG Xuan; XU Zhuo; SUN XinLi

    2008-01-01

    The electron emission property of a novel antiferroelectric cathode material lanthanum-doped lead zirconate stannate titanate (PLZST) on the application of positive or negative triggering voltage pulses has been investigated. All experiments were performed in a vacuum of 10-5 Torr and at room tempera-ture. It was discovered that there were two electron emission pulses when low positive triggering voltage was applied to the rear electrode, and three electron emission pulses when high positive trig-gering voltage was applied. However there were always two electron emission pulses when negative triggering pulses were applied. This phenomenon is proposed to be a result of both field electron emission at triple junctions and electron emission caused by polarization reversal. The experimental observations indicate that domain movement in the vicinity close to the triple junction under applica-tion of the triggering voltage pulse may be a primary origin of electron emission from PLZST.

  5. Identification of irradiated wheat using paramagnetic electronic resonance and germination test; Identificacao de trigo irradiado utilizando ressonancia paramagnetica eletronica e teste de germinacao

    Energy Technology Data Exchange (ETDEWEB)

    Barros, Adilson C.; Arthur, Valter [Centro de Energia Nuclear na Agricultura (CENA), Piracicaba, SP (Brazil); Freund, Maria Teresa L. [Sao Paulo Univ., SP (Brazil). Inst. de Fisica; Villavicenzio, Ana Lucia C.H. [Instituto de Pesquisas Energeticas e Nucleares (IPEN), Sao Paulo, SP (Brazil)

    2000-07-01

    The objective of this research was to verify the possibility of detection of irradiated wheat by electron spin resonance spectroscopy, because ionizing radiation cause paramagnetic free radicals in materials and the germination test that established in radiobiological effects of inhibition of root-shoot lengths and germination percentages in seeds due radiation. For ESR spectroscopy, grains and shell have been irradiated with doses as follows: 0 kGy ; 1,0 kGy and 10,0 kGy at a dose rate of 6,20 kGy/h. For germination test only grains have been irradiated with 0 kGy; 0,10 kGy; 0,25 kGy; 0,50 kGy; 0,75 kGy; 1,0 kGy and 2,0 kGy at a dose rate of 1,724 kGy/h and stored by 90 days before germination. The ESR signal decay fast with time but shell have free radicals ten times more than grains by mass unit. As we can observe in germination test, occurs a reduction in development of root-shoot and germination percentages with dose increase. The results indicated that the ESR and germination test may be used for detection of irradiated wheat. (author)

  6. Structural, optical and electron paramagnetic resonance studies on Cu-doped ZnO nanoparticles synthesized using a novel auto-combustion method

    Science.gov (United States)

    Elilarassi, R.; Chandrasekaran, G.

    2013-06-01

    Nanocrystalline Zn1 - x Cu x O ( x = 0, 0.02, 0.04, 0.06, 0.08) samples were synthesized by a novel auto-combustion method using glycine as the fuel material. The structural, optical and magnetic properties of the samples were characterized using XRD, SEM, photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies. The XRD spectra of samples reveal the hexagonal wurtzite structures of ZnO. As the copper content increases, a diffraction peak at 2 θ = 39° corresponding to secondary phase of CuO ([111] crystalline face) appears when x ⩽ 6 mol.%. PL spectra of the samples show a strong ultraviolet (UV) emission and defect related visible emissions. Cu-doping in ZnO can effectively adjust the energy level in ZnO, which leads to red shift in the emission peak position in UV region. The EPR spectra of Cu-doped ZnO nanoparticles show a distinct and broad signal at room temperature, suggesting that it may be attributed to the exchange interactions within Cu2+ ions.

  7. Association of resistin with impaired membrane fluidity of red blood cells in hypertensive and normotensive men: an electron paramagnetic resonance study.

    Science.gov (United States)

    Tsuda, Kazushi

    2016-10-01

    Abnormalities in physical properties of the cell membranes may strongly be linked to hypertension. Recent evidence indicates that resistin may actively participate in the pathophysiology of insulin resistance, diabetes mellitus, hypertension and other circulatory disorders. The present study was undertaken to investigate the possible relationships among plasma resistin, oxidative stress and membrane fluidity (a reciprocal value of membrane microviscosity) in hypertension. We measured the membrane fluidity of red blood cells (RBCs) in hypertensive and normotensive men using an electron paramagnetic resonance (EPR) and spin-labeling method. The order parameter (S) for the spin-label agents (5-nitroxide stearate) in EPR spectra of red blood cell (RBC) membranes was significantly higher in hypertensive men than in normotensive men, indicating that membrane fluidity was decreased in hypertension. Plasma resistin levels were correlated with systolic blood pressure and 8-iso-prostaglandin F2α levels (an index of oxidative stress). Furthermore, the order parameter (S) of RBCs significantly correlated with plasma resistin and plasma 8-isoPG F2α, suggesting that reduced membrane fluidity of RBCs might be associated with hyperresistinemia and increased oxidative stress. Multivariate regression analysis showed that, after adjustment for confounding factors, plasma resistin might be an independent determinant of membrane fluidity of RBCs. The EPR study suggests that resistin might have a close correlation with impaired rheologic behavior of RBCs and microcirculatory dysfunction in hypertension, at least in part, via an oxidative stress-dependent mechanism.

  8. Physical, Optical and Electron paramagnetic resonance studies of PbBr2-PbO-B2O3 glasses containing Cu2+ ions

    Science.gov (United States)

    Sekhar, K. Chandra; Hameed, Abdul; Chary, M. Narasimha; Shareefuddin, Md

    2016-09-01

    The glasses with the composition PbBr2-PbO-B2O3 glasses containing Cu2+ ions were prepared by melt quenching technique. X-ray diffractograms revealed the amorphous nature of the glasses. Density and molar volume were determined. Density is found to decrease while the molar volume increases with increase of PbBr2 content. The optical absorption spectra exhibited a broad band corresponding to the d- d transition of Cu2+ ion. From optical absorption spectra Eopt and Urbach energies were determined. Electron Paramagnetic Resonance (EPR) studies were carried out by introducing Cu2+ as the spin probe. Glasses containing transition metal(TM) ions such as Cu2+ give the information about the structure and the site symmetry around the TM ions. EPR spectra of all the glass samples were recorded at X-band frequencies. From the EPR spectra spin-Hamiltonian parameters were evaluated. It was observed that g∥ >g±>ge (2.0023) and A∥>A±. From this values it is concluded that the ground state of Cu2+ is dx2-y2 (2B1g) and the site symmetry around Cu2+ ion is tetragonally distorted octahedral. From the EPR and Optical data bonding coefficients were evaluated. The in plane o-bonding(α2) is moderately ionic while out of plane 7t-bonding(β2) and in plane 7t-bonding(β1 2) are ionic nature

  9. Signature of ferro–paraelectric transition in biferroic LuCrO{sub 3} from electron paramagnetic resonance and non-resonant microwave absorption

    Energy Technology Data Exchange (ETDEWEB)

    Alvarez, G., E-mail: memodin@yahoo.com [Escuela Superior de Física y Matemáticas del Instituto Politécnico Nacional, U.P.A.L.M, Edificio 9, Av. Instituto Politécnico Nacional S/N, San Pedro Zacatenco, México DF 07738 (Mexico); Montiel, H. [Centro de Ciencias Aplicadas y Desarrollo Tecnológico de la Universidad Nacional Autónoma de México, Cd. Universitaria, A.P. 70-186, México DF 04510 (Mexico); Durán, A. [Centro de Nanociencias y Nanotecnología de la Universidad Nacional Autónoma de México, Km. 107, Carretera Tijuana-Ensenada, Apartado Postal 14, C.P. 22800 Ensenada, B.C. México (Mexico); Conde-Gallardo, A. [Departamento de Física, CINVESTAV-IPN, A.P. 14-740, México DF 07360 (Mexico); Zamorano, R. [Escuela Superior de Física y Matemáticas del Instituto Politécnico Nacional, U.P.A.L.M, Edificio 9, Av. Instituto Politécnico Nacional S/N, San Pedro Zacatenco, México DF 07738 (Mexico)

    2014-12-15

    An electron paramagnetic resonance (EPR) study in the polycrystalline biferroic LuCrO{sub 3} is carried out at X-band (8.8–9.8 GHz) in the 295–510 K temperature range. For all the temperatures, the EPR spectra show a single broad line attributable to Cr{sup 3+} (S = 3/2) ions. The onset of a ferro–paraelectric transition has been determined from the temperature dependence of the parameters deduced from EPR spectra: the peak-to-peak linewidth (ΔH{sub pp}), the g-factor and the integral intensity (I{sub EPR}). Magnetically modulated microwave absorption spectroscopy (MAMMAS) and low-field microwave absorption (LFMA) are used to give further information on this material, where these techniques give also evidence of the ferro–paraelectric transition; indicating a behavior in agreement with a diffuse phase transition. - Highlights: • LuCrO{sub 3} powders are obtained via auto-ignition synthesis. • EPR is employed to study the onset of the ferro–paraelectric transition. • MAMMAS and LFMA techniques are used to give further information on this material.

  10. Electron paramagnetic resonance study of hydrogen peroxide/ascorbic acid ratio as initiator redox pair in the inulin-gallic acid molecular grafting reaction.

    Science.gov (United States)

    Arizmendi-Cotero, Daniel; Gómez-Espinosa, Rosa María; Dublán García, Octavio; Gómez-Vidales, Virginia; Dominguez-Lopez, Aurelio

    2016-01-20

    Gallic acid (GA) was grafted onto inulin using the free radicals method, generated by the hydrogen peroxide/ascorbic acid (H2O2/AA) redox pair. Molar ratios of H2O2/AA at 9, 20, 39 and 49 were evaluated by Electron Paramagnetic Resonance in order to find the effect of the oxidation of the inulin and the efficiency in the inulin-gallic acid grafting (IGA). The highest concentration of the inulin macro-radical was obtained with H2O2/AA molar ratios of 20 and 49 with the removal of a hydrogen atom from a methyl group of the inulin fructose monomers. The highest grafting ratio (30.4 mg GA eq/g IGA) was obtained at 9 M of H2O2/AA. UV-Vis, FT-IR-ATR and XDR results confirmed a successful IGA grafting. The efficiency of the grafting reaction depends on the concentration of the macro-radical, it depends on the molar ratio of H2O2/AA, being affected by simultaneous reactions between components of the mixture (H2O2, AA, inulin, GA and eventually atmospheric oxygen) as well.

  11. Dose-dependent vitamin C uptake and radical scavenging activity in human skin measured with in vivo electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Lauer, Anna-Christina; Groth, Norbert; Haag, Stefan F; Darvin, Maxim E; Lademann, Jürgen; Meinke, Martina C

    2013-01-01

    Vitamin C is a potent radical scavenger and a physiological part of the antioxidant system in human skin. The aim of this study was to measure changes in the radical-scavenging activity of human skin in vivo due to supplementation with different doses of vitamin C and at different time points. Therefore, 33 volunteers were supplemented with vitamin C or placebo for 4 weeks. The skin radical-scavenging activity was measured with electron paramagnetic resonance spectroscopy. After 4 weeks, the intake of 100 mg vitamin C/day resulted in a significant increase in the radical-scavenging activity by 22%. Intake of 180 mg/day even resulted in a significant increase of 37%. No changes were found in the placebo group. A part of the study population was additionally measured after 2 weeks: in this group radical scavenging had already reached maximal activity after 2 weeks. In conclusion, orally administered vitamin C increases the radical-scavenging activity of the skin. The effect occurs fast and is enhanced with higher doses of vitamin C.

  12. Temperature-Dependent Electron Paramagnetic Resonance Studies of Docosahexaenoic Acid and Gamma Linolenic Acid Effects on Phospholipid Membranes With and Without Cholesterol

    Science.gov (United States)

    Yonar, D.; Horasanb, N.; Sünnetçioğlu, M. Maral

    2016-07-01

    Free docosahexaenoic acid (DHAn-3) and gamma linolenic acid (GLAn-6) effects on dimyristoyl phosphatidylcholine (DMPC) membranes were studied as a function of temperature by electron paramagnetic resonance (EPR) spectroscopy. 5- and 16-doxyl stearic acid (5-, 16-DS) spin labels were utilized to obtain information from the interfacial and alkyl chain region, respectively. In the studied temperature range, the presence of DHAn-3 or GLAn-6 caused decreases in maximum hyperfi ne splitting values and correlation times of DMPC membranes. Both in the interfacial region and depths of membrane, changes were more pronounced for DHAn-3 in pure DMPC. In the presence of cholesterol (CH), DHAn-3 and GLAn-6 effects were similar and more pronounced in the depths of the membrane. The changes in the structure and dynamics of samples were obtained from simulations of spectra, which indicated some changes in the number of spectral components by incorporation of DHAn-3 and GLAn-6. In the interfacial region and below the main phase transition temperature of DMPC, there was an increase in heterogeneity. For temperatures above the phase transition, a more homogeneous environment for spin label was obtained in the presence of fatty acids.

  13. Electron paramagnetic resonance investigations of alpha-Al sub 2 O sub 3 powders doped with Fe sup 3 sup + ions: experiments and simulations

    CERN Document Server

    Buzare, J Y; Klein, J; Scholz, G; Stoesser, R; Nofz, M

    2002-01-01

    Electron paramagnetic resonance (EPR) of Fe sup 3 sup + ions in Al sub 2 O sub 3 is studied in powder samples prepared by different routes and/or modified by thermal or mechanical treatments, with different doping levels and grain sizes. The measurements are performed in various frequency bands (S, X, K, Q and W) and with bimodal detection in X-band. Simulations of the spectra are achieved with a code designed for computing EPR powder spectra described by any spin Hamiltonian including second-, fourth-and sixth-order ZFS terms (S <= 7/2). The linewidths, intensities and lineshapes are accounted for. The lineshape is Gaussian at low Fe sup 3 sup + concentration whereas it is Lorentzian for higher concentration. The linewidths are interpreted as the superimposition of three main contributions: intrinsic linewidth, dipolar broadening and broadening due to lattice imperfections. The latter is tentatively interpreted in terms of quadrupolar spin Hamiltonian parameter distributions treated using first-order pert...

  14. Substitution mechanisms and location of Co2+ ions in congruent and stoichiometric lithium niobate crystals derived from electron paramagnetic resonance data

    Science.gov (United States)

    Grachev, V. G.; Hansen, K.; Meyer, M.; Kokanyan, E. P.; Malovichko, G. I.

    2017-03-01

    Electron paramagnetic resonance (EPR) spectra and their angular dependencies were measured for Co2+ trace impurities in stoichiometric samples of lithium niobate doped with rhodium. It was found that Co2+ substitutes for Li+ in the dominant axial center (CoLi) and that the principal substitution mechanism in stoichiometric lithium niobate is 4Co2+ ↔ 3Li+  +  Nb5+. The four Co2+ ions can occupy the nearest possible cation sites by occupying a Nb site and its three nearest-neighbor Li sites, creating a trigonal pyramid with C3 symmetry, as well as non-neighboring sites (e.g. a CoNb-CoLi pair at the nearest sites on the C3 axis with two nearby isolated single Co2+ ions substituted for Li+). In congruent crystals and samples with Li content enriched by vapor transport equilibrium treatment the excess charge of the Co2+ centers is compensated by lithium vacancies located rather far from the Co2+ ions for the dominant axial center or in the nearest neighborhood for low-symmetry satellite centers (the Co2+ ↔ 2Li+ substitution mechanism). The use of exact numerical diagonalization of the spin-Hamiltonian matrices explains all the details of the EPR spectra and gives a value for hyperfine interaction A || that is several times smaller than that obtained using perturbation formulae. The refined values of A and g-tensor components can be used as reliable cornerstones for ab initio and cluster calculations.

  15. Characterization of complexes metal-polymer by electron paramagnetic resonance (EPR); Caracterizacao de complexos polimero-metal por ressonancia paramagnetica eletronica (RPE)

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Venina dos; Crespo, Janaina S.; Zeni, Mara [Universidade de Caxias do Sul, RS (Brazil). Centro de Ciencias Exatas e Tecnologia. Dept. de Fisica e Quimica]. E-mail: vsantos2@ucs.br; Mangrich, Antonio S. [Parana Univ., Curitiba, PR (Brazil). Dept. de Quimica

    2003-07-01

    In this work polymeric films of the polyvinyl alcohol (Pva) containing manganese ions (II) were investigated and analysed with enzymes were immobilized from photochemical process. The coordination and structural analysis of the compounds (Pva, Pva-Mn{sup 2+} and Pva-Mn{sup 2+}-enzyme) were all characterized by Electron Paramagnetic Resonance (EPR) and Infrared Spectroscopy (IR). The results EPR shows that the Pva is diamagnetic, films Pva-Mn{sup 2+} present specters complex of external sphere (g=2; A=96G). The commercial enzyme (DeniLite{sup TM} II S) presents a state triplet where two Cu{sup 2+} interact ferromagnetically. The enzyme when immobilized in the Pva-Mn{sup 2+} it causes to only one small widening of the line due the presence of the Cu{sup 2+}. The Pva-Mn{sup 2+} films present in the IR spectra an absorption at 715 cm{sup -1} attributed at the deformation in the PVA-Mn{sup 2+} complex in plane and out of plane. (author)

  16. Microstructure evaluation of dermally applicable liquid crystals as a function of water content and temperature: Can electron paramagnetic resonance provide complementary data?

    Science.gov (United States)

    Matjaž, Mirjam Gosenca; Mravljak, Janez; Rogač, Marija Bešter; Šentjurc, Marjeta; Gašperlin, Mirjana; Pobirk, Alenka Zvonar

    2017-05-18

    Insight into the microstructure of lyotropic liquid crystals (LCs) is of crucial importance for development of novel dermal delivery systems. Our aim was to evaluate the phase behaviour of dermally applicable LCs composed of isopropyl myristate/Tween 80/lecithin/water, along the dilution line, where phase transitions are predominantly driven by increased water content. Additionally, identification of LC temperature dependence is of great importance for skin application. Selected LCs were evaluated using electron paramagnetic resonance (EPR) plus conventionally used methods of polarization microscopy, small-angle X-ray scattering, differential scanning calorimetry, and rheological measurements. Depending on water content, LCs formed diverse microstructures, from (pseudo)hexagonal (LC1) and lamellar (LC2-LC7) liquid crystalline phases that possibly co-exist with rod-like micelles (LC4-LC7), to a transitional micellar phase (LC8). Furthermore, the LCs microstructure remained unaltered within the tested temperature range. EPR was shown to detect microstructural transitions of LCs and to provide complementary data to other techniques. These data thus confirm the applicability of EPR as a complementary technique for better understanding of LC microstructural transitions that are expected to contribute greatly to studies oriented towards the drug release characteristics from such systems. Copyright © 2017 Elsevier B.V. All rights reserved.

  17. The lead acceptor in p-type natural 2H-polytype MoS2 crystals evidenced by electron paramagnetic resonance

    Science.gov (United States)

    Iacovo, S.; Stesmans, A.; Houssa, M.; Afanas'ev, V. V.

    2017-03-01

    A low-temperature (T  =  1.5-8 K) electron paramagnetic resonance study of p-type 2H-polytype natural MoS2 crystals reveals a previously unreported anisotropic signal of corresponding defect density (spin S  =  ½) ~5  ×  1014 cm-3. For the applied magnetic field B//c-axis, the response is comprised of a single central asymmetric Zeeman peak at zero-crossing g  =  2.102(1), amid a symmetrically positioned hyperfine doublet of splitting 6.6(2) G. Field angular observations reveal a two-branch g pattern, indicative of a defect of lower than axial symmetry, likely orthorhombic (C 2v). Based on the signal specifics, it is ascribed to a system of decoupled Pb impurities substituting for Mo, the defect operating as an acceptor, with estimated thermal activation energy  >10 meV. Supporting theoretical anticipation, the results pinpoint the conduct of the Pb impurity in layered MoS2.

  18. Bond-order wave phase of the extended Hubbard model: Electronic solitons, paramagnetism, and coupling to Peierls and Holstein phonons

    Science.gov (United States)

    Kumar, Manoranjan; Soos, Zoltán G.

    2010-10-01

    The bond-order wave (BOW) phase of the extended Hubbard model (EHM) in one dimension (1D) is characterized at intermediate correlation U=4t by exact treatment of N -site systems. Linear coupling to lattice (Peierls) phonons and molecular (Holstein) vibrations are treated in the adiabatic approximation. The molar magnetic susceptibility χM(T) is obtained directly up to N=10 . The goal is to find the consequences of a doubly degenerate ground state (gs) and finite magnetic gap Em in a regular array. Degenerate gs with broken inversion symmetry are constructed for finite N for a range of V near the charge-density-wave boundary at V≈2.18t where Em≈0.5t is large. The electronic amplitude B(V) of the BOW in the regular array is shown to mimic a tight-binding band with small effective dimerization δeff . Electronic spin and charge solitons are elementary excitations of the BOW phase and also resemble topological solitons with small δeff . Strong infrared intensity of coupled molecular vibrations in dimerized 1D systems is shown to extend to the regular BOW phase while its temperature dependence is related to spin solitons. The Peierls instability to dimerization has novel aspects for degenerate gs and substantial Em that suppresses thermal excitations. Finite Em implies exponentially small χM(T) at low temperature followed by an almost linear increase with T . The EHM with U=4t is representative of intermediate correlations in quasi-1D systems such as conjugated polymers or organic ion-radical and charge-transfer salts. The vibronic and thermal properties of correlated models with BOW phases are needed to identify possible physical realizations.

  19. Measurement of Hot Electron Spectrum During the Interaction of Ultrashort Pulse UV Laser With Solid Target

    Institute of Scientific and Technical Information of China (English)

    LIYe-jun; SHANYu-sheng; ZHANGJi; ZHANGHai-feng; TANGXiu-zhang; WANGLei-jian

    2003-01-01

    The hot electron spectrum was measured using electron magnetic spectrometer through the irradiation of solid Cu target by an intense, UV (248 nm) femtosecond (440 fs) laser pulse with free pre-pulse, and the intensity of laser is 1017 W/cm2. We find the electron spectrum presents two temperatures Maxwellian distribution.

  20. Photoluminescence, thermally stimulated luminescence and electron paramagnetic resonance studies of U6+ doped BaSO4

    Indian Academy of Sciences (India)

    M K Bhide; T K Seshagiri; Sashikala Ojha; S V Godbole

    2014-02-01

    U6+ doped BaSO4 samples were synthesized by precipitation route. PL, TL and EPR investigations of and self irradiated samples were carried out. PL spectra of these samples give structured broad band peaking around 518 nm with five vibronic bands centred around 498.4, 516.0, 533.7, 554.0 and 575.1 nm, respectively and the average frequency of symmetric stretching of O=U=O in the ground electronic state was found to be 674 cm−1. Trap level spectroscopic studies of U doped BaSO4 give glow peaks at 411, 488 and 512 K, respectively and their spectral characteristics are typical of UO$_{2}^{2+}$ emission. EPR studies of -irradiated U6+:BaSO4 sample have shown the presence of sulphoxy centred radicals like SO$_{4}^{−}$ and SO$_{3}^{−}$ in addition to OH$^{\\bullet}$, O$_{3}^{−}$ and SH2−. TSL peaks at 411 and 488 K were correlated with thermal destruction of SO$_{4}^{−}$ and SO$_{3}^{−}$ radicals.

  1. Pyroelectric materials as electronic pulse detectors of ultraheavy nuclei

    Science.gov (United States)

    Simpson, J. A.; Tuzzolino, A. J.

    1984-01-01

    The design and testing of ultraheavy-nucleus pulse detectors based on pyroelectric materials are reported, extending the preliminary findings of Tuzzolino (1983) and Simpson and Tuzzolino (1983). Uranium-ion beams of about 240 MeV/u are detected by a 39.5-micron-thick Si detector, degraded to about 175 MeV/u by Al absorbers, and then strike 700-micron-thick polyvinylidene fluoride or 1000-micron-thick LiTaO3 pyroelectric samples. Both detector systems are connected to a coincidence circuit via charge-sensitive preamplifiers, shaping amplifiers with 30-microsec effective time constants, and electronic discriminators. Sample spectra are shown, and the pulse heights measured are found to agree with theoretical calculations to within a factor of about 2. The response of the pyroelectric materials is found to be unaffected by exposure to about 10 Mrad of 2-7-MeV/u heavy ion radiation. With further study and improvement of the detection sensitivity, devices of this type could be applied to large-area space measurements of low ultraheavy-ion fluxes.

  2. Fast pulsed operation of a small non-radioactive electron source with continuous emission current control.

    Science.gov (United States)

    Cochems, P; Kirk, A T; Bunert, E; Runge, M; Goncalves, P; Zimmermann, S

    2015-06-01

    Non-radioactive electron sources are of great interest in any application requiring the emission of electrons at atmospheric pressure, as they offer better control over emission parameters than radioactive electron sources and are not subject to legal restrictions. Recently, we published a simple electron source consisting only of a vacuum housing, a filament, and a single control grid. In this paper, we present improved control electronics that utilize this control grid in order to focus and defocus the electron beam, thus pulsing the electron emission at atmospheric pressure. This allows short emission pulses and excellent stability of the emitted electron current due to continuous control, both during pulsed and continuous operations. As an application example, this electron source is coupled to an ion mobility spectrometer. Here, the pulsed electron source allows experiments on gas phase ion chemistry (e.g., ion generation and recombination kinetics) and can even remove the need for a traditional ion shutter.

  3. Intense pulsed light sintering of copper nanoink for printed electronics

    Science.gov (United States)

    Kim, Hak-Sung; Dhage, Sanjay R.; Shim, Dong-Eun; Hahn, H. Thomas

    2009-12-01

    An intense pulsed light (IPL) from a xenon flash lamp was used to sinter copper nanoink printed on low-temperature polymer substrates at room temperature in ambient condition. The IPL can sinter the copper nanoink without damaging the polymer substrates in extremely short time (2 ms). The microstructure of the sintered copper film was investigated using X-ray powder diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), X-ray micro tomography, and atomic force microscopy (AFM). The sintered copper film has a grainy structure with neck-like junctions. The resulting resistivity was 5 μΩ cm of electrical resistivity which is only 3 times as high as that of bulk copper. The IPL sintering technique allows copper nanoparticles to be used in inkjet printing on low-temperature substrates such as polymers in ambient conditions.

  4. Intense pulsed light sintering of copper nanoink for printed electronics

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hak-Sung; Dhage, Sanjay R.; Shim, Dong-Eun [University of California, Mechanical and Aerospace Engineering Department, Los Angeles, CA (United States); Hahn, H.T. [University of California, Mechanical and Aerospace Engineering Department, Los Angeles, CA (United States); University of California, Material Science and Engineering Department, California NanoSystems Institute, Los Angeles, CA (United States)

    2009-12-15

    An intense pulsed light (IPL) from a xenon flash lamp was used to sinter copper nanoink printed on low-temperature polymer substrates at room temperature in ambient condition. The IPL can sinter the copper nanoink without damaging the polymer substrates in extremely short time (2 ms). The microstructure of the sintered copper film was investigated using X-ray powder diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), X-ray micro tomography, and atomic force microscopy (AFM). The sintered copper film has a grainy structure with neck-like junctions. The resulting resistivity was 5{mu}{omega} cm of electrical resistivity which is only 3 times as high as that of bulk copper. The IPL sintering technique allows copper nanoparticles to be used in inkjet printing on low-temperature substrates such as polymers in ambient conditions. (orig.)

  5. Femtosecond electron pulse generation and measurement for diffractive imaging of isolated molecules

    Science.gov (United States)

    Zandi, Omid; Wilkin, Kyle J.; DeSimone, Alice J.; Yang, Jie; Centurion, Martin

    2016-09-01

    We have constructed an electron gun that delivers highly charged femtosecond electron pulses to a target with kHz repetition rate. Electron pulses are generated by femtosecond laser pulses in a photoemission process and are accelerated up to 100 kV and compressed to sub-picosecond duration. Compression is essential to compensate for the space charge effect that increases the size of electron pulses in all directions significantly. The pulses are compressed transversely by magnetic lenses and longitudinally by the longitudinal electric field of a radio-frequency cavity. The longitudinal compression is achieved by decelerating the electrons in the leading edge of the pulse, and accelerating the electrons in the trailing edge of the pulse. This results in the pulse compressing and reaching the minimum pulse duration at a known distance from the compression cavity. The short pulse duration and high repetition rate will be essential to observe subpicosecond dynamic processes in molecules in gas phase with a good signal to noise ratio. A streak camera, consisting of a millimeter-sized parallel plate capacitor, was used to measure the pulse duration in situ.

  6. Optimization and control of electron beams from laser wakefield accelerations using asymmetric laser pulses

    Science.gov (United States)

    Gopal, K.; Gupta, D. N.

    2017-10-01

    Optimization and control of electron beam quality in laser wakefield acceleration are explored by using a temporally asymmetric laser pulse of the sharp rising front portion. The temporally asymmetric laser pulse imparts stronger ponderomotive force on the ambient plasma electrons. The stronger ponderomotive force associated with the asymmetric pulse significantly affects the injection of electrons into the wakefield and consequently the quality of the injected bunch in terms of injected charge, mean energy, and emittance. Based on particle-in-cell simulations, we report to generate a monoenergetic electron beam with reduced emittance and enhanced charge in laser wakefield acceleration using an asymmetric pulse of duration 30 fs.

  7. Externally Controlled Injection of Electrons by a Laser Pulse in a Laser Wakefield Electron Accelerator

    CERN Document Server

    Chen Szu Yuan; Chen Wei Ting; Chien, Ting-Yei; Lee, Chau-Hwang; Lin, Jiunn-Yuan; Wang, Jyhpyng

    2005-01-01

    Spatially and temporally localized injection of electrons is a key element for development of plasma-wave electron accelerator. Here we report the demonstration of two different schemes for electron injection in a self-modulated laser wakefield accelerator (SM-LWFA) by using a laser pulse. In the first scheme, by implementing a copropagating laser prepulse with proper timing, we are able to control the growth of Raman forward scattering and the production of accelerated electrons. We found that the stimulated Raman backward scattering of the prepulse plays the essential role of injecting hot electrons into the fast plasma wave driven by the pump pulse. In the second scheme, by using a transient density ramp we achieve self-injection of electrons in a SM-LWFA with spatial localization. The transient density ramp is produced by a prepulse propagating transversely to drill a density depression channel via ionization and expansion. The same mechanism of injection with comparable efficiency is also demonstrated wi...

  8. Pulsed electron-electron double resonance (PELDOR) as EPR spectroscopy in nanometre range

    Energy Technology Data Exchange (ETDEWEB)

    Tsvetkov, Yu D; Milov, A D; Maryasov, A G [Institute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)

    2008-06-30

    The results of development of pulsed electron-electron double resonance (PELDOR) method and its applications in structural studies are generalised and described systematically. The foundations of the theory of the method are outlined, some methodological features and applications are considered, in particular, determination of the distances between spin labels in the nanometre range for iminoxyl biradicals, spin-labelled biomacromolecules, radical ion pairs and peptide-membrane complexes. The attention is focussed on radical systems that form upon self-assembly of nanosized complexes (in particular, peptide complexes), spatial effects, and radical pairs in photolysis and photosynthesis. The position of PELDOR among other structural EPR techniques is analysed.

  9. An electron paramagnetic resonance spectroscopy investigation of the retention mechanisms of Mn and Cu in the nanopore channels of three zeolite minerals

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira, Daniel R.; Schulthess, Cristian P.; Amonette, James E.; Walter, Eric D.

    2012-12-01

    The adsorption mechanisms of divalent cations in zeolite nanopore channels can vary as a function of their pore dimensions. The nanopore inner-sphere enhancement (NISE) theory predicts that ions may dehydrate inside small nanopore channels in order to adsorb more closely to the mineral surface if the nanopore channel is sufficiently small. The results of an electron paramagnetic resonance (EPR) spectroscopy study of Mn and Cu adsorption on the zeolite minerals zeolite Y (large nanopores), ZSM-5 (intermediate nanopores), and mordenite (small nanopores) are presented. The Cu and Mn cations both adsorbed via an outer-sphere mechanism on zeolite Y based on the similarity between the adsorbed spectra and the aqueous spectra. Conversely, Mn and Cu adsorbed via an inner-sphere mechanism on mordenite based on spectrum asymmetry and peak broadening of the adsorbed spectra. However, Mn adsorbed via an outer-sphere mechanism on ZSM-5, whereas Cu adsorbed on ZSM-5 shows a high degree of surface interaction that indicates that it is adsorbed closer to the mineral surface. Evidence of dehydration and immobility was more readily evident in the spectrum of mordenite than ZSM-5, indicating that Cu was not as close to the surface on ZSM-5 as it was when adsorbed on mordenite. Divalent Mn cations are strongly hydrated and are held strongly only in zeolites with small nanopore channels. Divalent Cu cations are also strongly hydrated, but can dehydrate more easily, presumably due to the Jahn-Teller effect, and are held strongly in zeolites with medium sized nanopore channels or smaller.

  10. Experimental determination of the radial dose distribution in high gradient regions around {sup 192}Ir wires: Comparison of electron paramagnetic resonance imaging, films, and Monte Carlo simulations

    Energy Technology Data Exchange (ETDEWEB)

    Kolbun, N.; Leveque, Ph.; Abboud, F.; Bol, A.; Vynckier, S.; Gallez, B. [Biomedical Magnetic Resonance Unit, Louvain Drug Research Institute, Universite catholique de Louvain, Avenue Mounier 73.40, B-1200 Brussels (Belgium); Molecular Imaging and Experimental Radiotherapy Unit, Institute of Experimental and Clinical Research, Universite catholique de Louvain, Avenue Hippocrate 55, B-1200 Brussels (Belgium); Biomedical Magnetic Resonance Unit, Louvain Drug Research Institute, Universite catholique de Louvain, Avenue Mounier 73.40, B-1200 Brussels (Belgium)

    2010-10-15

    Purpose: The experimental determination of doses at proximal distances from radioactive sources is difficult because of the steepness of the dose gradient. The goal of this study was to determine the relative radial dose distribution for a low dose rate {sup 192}Ir wire source using electron paramagnetic resonance imaging (EPRI) and to compare the results to those obtained using Gafchromic EBT film dosimetry and Monte Carlo (MC) simulations. Methods: Lithium formate and ammonium formate were chosen as the EPR dosimetric materials and were used to form cylindrical phantoms. The dose distribution of the stable radiation-induced free radicals in the lithium formate and ammonium formate phantoms was assessed by EPRI. EBT films were also inserted inside in ammonium formate phantoms for comparison. MC simulation was performed using the MCNP4C2 software code. Results: The radical signal in irradiated ammonium formate is contained in a single narrow EPR line, with an EPR peak-to-peak linewidth narrower than that of lithium formate ({approx}0.64 and 1.4 mT, respectively). The spatial resolution of EPR images was enhanced by a factor of 2.3 using ammonium formate compared to lithium formate because its linewidth is about 0.75 mT narrower than that of lithium formate. The EPRI results were consistent to within 1% with those of Gafchromic EBT films and MC simulations at distances from 1.0 to 2.9 mm. The radial dose values obtained by EPRI were about 4% lower at distances from 2.9 to 4.0 mm than those determined by MC simulation and EBT film dosimetry. Conclusions: Ammonium formate is a suitable material under certain conditions for use in brachytherapy dosimetry using EPRI. In this study, the authors demonstrated that the EPRI technique allows the estimation of the relative radial dose distribution at short distances for a {sup 192}Ir wire source.

  11. Resonance Raman, electron paramagnetic resonance, and density functional theory calculations of a phenolate-bound iron porphyrin complex: electrostatic versus covalent contribution to bonding.

    Science.gov (United States)

    Das, Pradip Kumar; Dey, Abhishek

    2014-07-21

    Resonance Raman (rR), electron paramagnetic resonance (EPR), and density functional theory (DFT) calculations of a phenolate-bound iron porphyrin complex are reported. The complex is found to exist in a five-coordinate high-spin state in a noncoordinating solvent and in a six-coordinate low-spin state in a coordinating solvent. The vibrations originating from the iron phenolate-bound chromophores reproduced those reported for heme tyrosine active sites in nature. The EPR parameters and iron-pyrrole (Fe-Npyr) vibrations of phenolate, thiolate, and imidazole ligated iron porphyrin complexes indicate that the phenolate axial ligand acts as a π anisotropic ligand, which is more covalent than a neutral imidazole ligand but less covalent than a thiolate axial ligand. While the Fe(III/II) potential of the phenolate compound in a noncoordinating solvent is 500 mV more negative than that of the imidazole-bound complex, it is also 110 mV more negative than that of the thiolate-bound complex. DFT calculations reproduce the geometry and vibrational frequencies and show that while both phenolate and thiolate axial ligands bear π and σ interaction with the ferric center, the former is significantly less covalent than the thiolate. The higher covalency of the thiolate ligand is responsible for the lower Fe-Npyr vibration and higher V/λ (from EPR) of the thiolate-bound complexes relative to those of the phenolate-bound complex, whereas the greater electrostatic stabilization of the Fe(III)-OPh bond is responsible for lowering the Fe(III/II) E° of the phenolate-bound complex relative to that of the thiolate-bound complex in a medium having a reasonable dielectric constant.

  12. Multiple structural states exist throughout the helical nucleation sequence of the intrinsically disordered protein stathmin, as reported by electron paramagnetic resonance spectroscopy.

    Science.gov (United States)

    Chui, Ashley J; López, Carlos J; Brooks, Evan K; Chua, Katherina C; Doupey, Tonia G; Foltz, Gretchen N; Kamel, Joseph G; Larrosa, Estefania; Sadiki, Amissi; Bridges, Michael D

    2015-03-10

    The intrinsically disordered protein (IDP) stathmin plays an important regulatory role in cytoskeletal maintenance through its helical binding to tubulin and microtubules. However, it lacks a stable fold in the absence of its binding partner. Although stathmin has been a focus of research over the past two decades, the solution-phase conformational dynamics of this IDP are poorly understood. It has been reported that stathmin is purely monomeric in solution and that it bears a short helical region of persistent foldedness, which may act to nucleate helical folding in the C-terminal direction. Here we report a comprehensive study of the structural equilibria local to this region in stathmin that contradicts these two claims. Using the technique of electron paramagnetic resonance (EPR) spectroscopy on spin-labeled stathmin mutants in the solution-phase and when immobilized on Sepharose solid support, we show that all sites in the helical nucleation region of stathmin exhibit multiple spectral components that correspond to dynamic states of differing mobilities and stabilities. Importantly, a state with relatively low mobility dominates each spectrum with an average population greater than 50%, which we suggest corresponds to an oligomerized state of the protein. This is in contrast to a less populated, more mobile state, which likely represents a helically folded monomeric state of stathmin, and a highly mobile state, which we propose is the random coil conformer of the protein. Our interpretation of the EPR data is confirmed by further characterization of the protein using the techniques of native and SDS PAGE, gel filtration chromatography, and multiangle and dynamic light scattering, all of which show the presence of oligomeric stathmin in solution. Collectively, these data suggest that stathmin exists in a diverse equilibrium of states throughout the purported helical nucleation region and that this IDP exhibits a propensity toward oligomerization.

  13. Brain redox imaging in the pentylenetetrazole (PTZ)-induced kindling model of epilepsy by using in vivo electron paramagnetic resonance and a nitroxide imaging probe.

    Science.gov (United States)

    Emoto, Miho C; Yamato, Mayumi; Sato-Akaba, Hideo; Yamada, Ken-ichi; Fujii, Hirotada G

    2015-11-01

    Much evidence supports the idea that oxidative stress is involved in the pathogenesis of epilepsy, and therapeutic interventions with antioxidants are expected as adjunct antiepileptic therapy. The aims of this study were to non-invasively obtain spatially resolved redox data from control and pentylenetetrazole (PTZ)-induced kindled mouse brains by electron paramagnetic resonance (EPR) imaging and to visualize the brain regions that are sensitive to oxidative damage. After infusion of the redox-sensitive imaging probe 3-methoxycarbonyl-2,2,5,5-tetramethyl-piperidine-1-oxyl (MCP), a series of EPR images of PTZ-induced mouse heads were measured. Based on the pharmacokinetics of the reduction reaction of MCP in the mouse heads, the pixel-based rate constant of its reduction reaction was calculated as an index of redox status in vivo and mapped as a redox map. The obtained redox map showed heterogeneity in the redox status in PTZ-induced mouse brains compared with control. The co-registered image of the redox map and magnetic resonance imaging (MRI) for both control and PTZ-induced mice showed a clear change in the redox status around the hippocampus after PTZ. To examine the role of antioxidants on the brain redox status, the levels of antioxidants were measured in brain tissues of control and PTZ-induced mice. Significantly lower concentrations of glutathione in the hippocampus of PTZ-kindled mice were detected compared with control. From the results of both EPR imaging and the biochemical assay, the hippocampus was found to be susceptible to oxidative damage in the PTZ-induced animal model of epilepsy.

  14. Electron paramagnetic resonance study of the multisite character of Yb{sup 3+} ions in LuVO{sub 4} single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Guillot-Noel, O [Ecole Nationale Superieure de Chimie de Paris (ENSCP), Laboratoire de Chimie Appliquee de l' Etat Solide, UMR-CNRS 7574, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05 (France); Goldner, Ph [Ecole Nationale Superieure de Chimie de Paris (ENSCP), Laboratoire de Chimie Appliquee de l' Etat Solide, UMR-CNRS 7574, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05 (France); Bettinelli, M [Dipartimento Scientifico e Tecnologico and INSTM, Universita di Verona, Ca' Vignal, Strada Le Grazie 15, 37134 Verona (Italy); Cavalli, E [Instituto Nazionale per la Fisica della Materia e Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica e Chimica Fisica, Universita di Parma, Viale delle Scienze, 43100 Parma (Italy)

    2005-05-18

    Electron paramagnetic resonance?(EPR) is used to identify the different substitution sites of Yb{sup 3+} ions in the LuVO{sub 4} host. Three different types of sites are observed. One site, referred to as Yb{sub I}, with tetragonal D{sub 2d} symmetry characterized by g-values of vertical bar g{sub perp} vertical bar=0.59(7) and vertical bar g{sub parallel} vertical bar=6.464(9), corresponds to 80% (50%) of the total number of Yb{sup 3+} ions for the 1% (5%) doped compound. Two other tetragonal sites, referred to as Yb{sub IIa,IIb}, with the same D{sub 2d} symmetry and characterized by g-values of vertical bar g{sub perp} vertical bar=0.89(3) , vertical bar g{sub parallel} vertical bar=2.75(1) and vertical bar g{sub perp} vertical bar=0.89(3), vertical bar g{sub parallel} vertical bar=2.84(1), represent 20% (50%) of the total number of ytterbium ions for the 1% (5%) compound. One minor site, referred to as Yb{sub III}, corresponding to less than 1% of the Yb{sup 3+} ions, with a lower C{sub 2v} or D{sub 2} symmetry, is also seen in the EPR spectra. The temperature dependence of the EPR linewidth is studied and shows for all the sites a dominant Orbach process for the spin-lattice relaxation time T{sub 1} for T>12K.

  15. Structural and dynamic study of the tetramerization region of non-erythroid alpha-spectrin: a frayed helix revealed by site-directed spin labeling electron paramagnetic resonance.

    Science.gov (United States)

    Li, Qufei; Fung, L W-M

    2009-01-13

    The N-terminal region of alpha-spectrin is responsible for its association with beta-spectrin in a heterodimer, forming functional tetramers. Non-erythroid alpha-spectrin (alphaII-spectrin) has a significantly higher association affinity for beta-spectrin than the homologous erythroid alpha-spectrin (alphaI-spectrin). We have previously determined the solution structure of the N-terminal region of alphaI-spectrin by NMR methods, but currently no structural information is available for alphaII-spectrin. We have used cysteine scanning, spin labeling electron paramagnetic resonance (EPR), and isothermal titration calorimetry (ITC) methods to study the tetramerization region of alphaII-spectrin. EPR data clearly show that, in alphaII-spectrin, the first nine N-terminal residues were unstructured, followed by an irregular helix (helix C'), frayed at the N-terminal end, but rigid at the C-terminal end, which merges into the putative triple-helical structural domain. The region corresponding to the important unstructured junction region linking helix C' to the first structural domain in alphaI-spectrin was clearly structured. On the basis of the published model for aligning helices A', B', and C', important interactions among residues in helix C' of alphaI- and alphaII-spectrin and helices A' and B' of betaI- and betaII-spectrin are identified, suggesting similar coiled coil helical bundling for spectrin I and II in forming tetramers. The differences in affinity are likely due to the differences in the conformation of the junction regions. Equilibrium dissociation constants of spin-labeled alphaII and betaI complexes from ITC measurements indicate that residues 15, 19, 37, and 40 are functionally important residues in alphaII-spectrin. Interestingly, all four corresponding homologous residues in alphaI-spectrin (residues 24, 28, 46, and 49) have been reported to be clinically significant residues involved in hematological diseases.

  16. Solution-state dynamics of sugar-connected spin probes in sucrose solution as studied by multiband (L-, X-, and W-band) electron paramagnetic resonance.

    Science.gov (United States)

    Fukui, Kôichi; Ito, Tomohiro; Tada, Mika; Aoyama, Masaaki; Sato, Shingo; Onodera, Jun ichi; Ohya, Hiroaki

    2003-07-01

    A multiband (L-band, 0.7GHz; X-band, 9.4GHz; and W-band, 94GHz) electron paramagnetic resonance (EPR) study was performed for two glycosidated spin probes, 4-(alpha,beta-D-glucopyranosyloxy)-TEMPO (Glc-TEMPO) and 4-(alpha,beta-D-lactopyranosyloxy)-TEMPO (Lac-TEMPO), and one non-glycosylated spin probe, 4-hydroxy-TEMPO (TEMPOL), where TEMPO=2,2,6,6-tetramethyl-1-piperidinyloxyl, to characterize fundamental hydrodynamic properties of sugar-connected spin probes. The linewidths of these spin probes were investigated in various concentrations of sucrose solutions (0-50wt%). The multiband approach has allowed full characterization of the linewidth parameters, providing insights into the molecular shapes of the spin probes in sucrose solution. The analysis based on the fast-motional linewidth theory has yielded anisotropy parameters of rho(x) approximately 2.6 and rho(y) approximately 0.9 for Glc-TEMPO, and rho(x) approximately 4.2 and rho(y) approximately 0.9 for Lac-TEMPO. These values indicate that the glycosidated spin probes have a prolate-type molecular shape elongated along the x-axis (NO(rad) axis) with Lac-TEMPO elongated more remarkably, consistent with their molecular structures. The interaction parameters k (the ratios of the effective hydrodynamic volumes to the real ones) corrected for the difference in molecular shape have been estimated and found to have the relation k(TEMPOL)spin probes can have stronger hydrogen bonding to water. Glycosidated spin probes are expected to be useful for probing sugar-involving interactions, which commonly occur in biological systems. Thus this study will provide an indispensable basis for such spin-probe studies.

  17. Electron paramagnetic resonance and optical properties of Cr{sup 3+} doped YAl{sub 3}(BO{sub 3}){sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Wells, Jon-Paul R [Department of Physics and Astronomy, University of Sheffield, Sheffield (United Kingdom); Yamaga, Mitsuo [Department of Mathematical and Design Engineering, Gifu University, Gifu (Japan); Han, Thomas P J [Department of Physics, University of Strathclyde, Glasgow (United Kingdom); Honda, Makoto [Faculty of Science, Naruto University of Education, Naruto (Japan)

    2003-01-29

    We report on the electron paramagnetic resonance (EPR) and optical absorption and fluorescence spectroscopy of YAl{sub 3}(BO{sub 3}){sub 4} single crystals doped with 0.2 mol% of trivalent chromium. From EPR we determine that the Cr{sup 3+} ions reside in sites of essentially octahedral symmetry with an orthorhombic distortion. The ground state {sup 4}A{sub 2} splitting is determined to be 2{radical}D{sup 2} + 3E{sup 2} {approx} 1.05 {+-} 0.04 cm{sup -1}, where D and E are fine-structure parameters, and we can attribute this splitting to the combined effect of a low-symmetry distortion and spin-orbit coupling. The g-values and fine-structure parameters D and E of the ground state {sup 4}A{sub 2} are measured to be g{sub x} {approx} g{sub y} {approx} g{sub z} = 1.978 {+-} 0.005, vertical bar D vertical bar = 0.52 {+-} 0.02 cm{sup -1} and vertical bar E vertical bar 0.010 {+-} 0.005 cm{sup -1} respectively. From 10 K optical absorption we have measured the position and crystal-field splittings of the {sup 2}E, {sup 2}T{sub 1}, {sup 4}T{sub 2}, {sup 2}T{sub 2} and {sup 4}T{sub 1} states with the {sup 4}T{sub 2} and {sup 4}T{sub 1} levels appearing as vibronically broadened bands.

  18. An electron paramagnetic resonance study on Sm{sup 3+} and Yb{sup 3+} in KY{sub 3}F{sub 10} crystals

    Energy Technology Data Exchange (ETDEWEB)

    Yamaga, M. [Department of Electrical and Electronic Engineering, Faculty of Engineering, Gifu University, Gifu (Japan); Honda, M. [Faculty of Science, Naruto University of Education, Naruto, Tokushima (Japan); Wells, J.P.R. [FELIX Free Electron Laser Facility, FOM-Institute for Plasma Physics, Rijnhuizen, Nieuwegein (Netherlands); Han, T.P.J.; Gallagher, H.G. [Department of Physics and Applied Physics, University of Strathclyde, Glasgow (United Kingdom)

    2000-10-09

    Electron paramagnetic resonance (EPR) spectra of Sm{sup 3+} and Yb{sup 3+} ions in KY{sub 3}F{sub 10} single crystals have been measured at X-band microwave frequencies and low temperatures. The EPR lines have been fitted to a tetragonal spin Hamiltonian to determine effective g-values (g{sub parallel},g{sub perpendicular}). The observed g-values, (g{sub parallel} = 0.714(2),g{sub perpendicular} = 0.11(1)), for Sm{sup 3+} are in agreement with those calculated via crystal-field J-mixing of the first excited-state multiplet {sup 6}H{sub 7/2} into the groundstate multiplet {sup 6}H{sub 5/2} of Sm{sup 3+} as the second-order perturbation. On the other hand, the observed g-values, (g{sub parallel}=5.363(5), g{sub perpendicular}=1.306(2)) for Yb{sup 3+} are coincident with those calculated via mixing in only the groundstate multiplet {sup 2}F{sub 7/2} as the first-order perturbation because the first excited-state multiplet {sup 2}F{sub 5/2} lies above {approx}10,000 cm{sup -1} from the groundstate. The groundstate eigenfunctions of Sm{sup 3+} and Yb{sup 3+} obtained from the EPR results are close to those calculated from a C{sub 4v} symmetry crystal-field analysis applied to their optical transitions. The distortions of the Sm{sup 3+} and Yb{sup 3+} complexes in KY{sub 3}F{sub 10} are discussed in the term of the crystal-field Hamiltonian in comparison with LiYF{sub 4}. (author)

  19. Copper doping of ZnO crystals by transmutation of {sup 64}Zn to {sup 65}Cu: An electron paramagnetic resonance and gamma spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Recker, M. C.; McClory, J. W., E-mail: John.McClory@afit.edu; Holston, M. S.; Golden, E. M.; Giles, N. C. [Department of Engineering Physics, Air Force Institute of Technology, Wright-Patterson Air Force Base, Ohio 45433 (United States); Halliburton, L. E. [Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506 (United States)

    2014-06-28

    Transmutation of {sup 64}Zn to {sup 65}Cu has been observed in a ZnO crystal irradiated with neutrons. The crystal was characterized with electron paramagnetic resonance (EPR) before and after the irradiation and with gamma spectroscopy after the irradiation. Major features in the gamma spectrum of the neutron-irradiated crystal included the primary 1115.5 keV gamma ray from the {sup 65}Zn decay and the positron annihilation peak at 511 keV. Their presence confirmed the successful transmutation of {sup 64}Zn nuclei to {sup 65}Cu. Additional direct evidence for transmutation was obtained from the EPR of Cu{sup 2+} ions (where {sup 63}Cu and {sup 65}Cu hyperfine lines are easily resolved). A spectrum from isolated Cu{sup 2+} (3d{sup 9}) ions acquired after the neutron irradiation showed only hyperfine lines from {sup 65}Cu nuclei. The absence of {sup 63}Cu lines in this Cu{sup 2+} spectrum left no doubt that the observed {sup 65}Cu signals were due to transmuted {sup 65}Cu nuclei created as a result of the neutron irradiation. Small concentrations of copper, in the form of Cu{sup +}-H complexes, were inadvertently present in our as-grown ZnO crystal. These Cu{sup +}-H complexes are not affected by the neutron irradiation, but they dissociate when a crystal is heated to 900 °C. This behavior allowed EPR to distinguish between the copper initially in the crystal and the copper subsequently produced by the neutron irradiation. In addition to transmutation, a second major effect of the neutron irradiation was the formation of zinc and oxygen vacancies by displacement. These vacancies were observed with EPR.

  20. Structural and dielectric properties, electron paramagnetic resonance, and defect chemistry of Pr-doped BaTiO{sub 3} ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Lu, D.-Y., E-mail: cninjp11232000@yahoo.com [Research Center for Materials Science and Engineering, Jilin Institute of Chemical Technology, Jilin 132022 (China); Sun, X.-Y. [Research Center for Materials Science and Engineering, Jilin Institute of Chemical Technology, Jilin 132022 (China); Liu, B. [Research Center for Materials Science and Engineering, Jilin Institute of Chemical Technology, Jilin 132022 (China); College of Chemistry, Jilin University, Changchun 130021 (China); Zhang, J.-L. [Research Center for Materials Science and Engineering, Jilin Institute of Chemical Technology, Jilin 132022 (China); Ogata, T. [Graduate School of Science and Engineering, Yamagata University, Yonezawa 992-8510 (Japan)

    2014-12-05

    Highlights: • Structure, dielectric, EPR and defect chemistry of (Ba{sub 1−x}Pr{sub x})Ti{sub 1−x/4}O{sub 3} were studied. • The dielectric-peak temperature decreases rapidly at a rate of −22 °C/at.% Pr. • Pr doping in BaTiO{sub 3} can suppress grain growth and form a fine-grained ceramic. • A thermally accessible signal at g = 3.77 provides the evidence for Pr{sup 4+} ions. • A new Raman band at 837 cm{sup −1} is indicative of the amount of Ba-site Pr{sup 3+} ions. - Abstract: Fine-grained Pr-doped BaTiO{sub 3} ceramics (BPT) were prepared according to the nominal formula (Ba{sub 1−x}Pr{sub x})Ti{sub 1−x/4}O{sub 3} (0.02 ⩽ x ⩽ 0.05) using a mixed oxide method. Structure, microstructure, dielectric properties, and defect chemistry were investigated by X-ray diffraction (XRD), Raman spectroscopy, electron paramagnetic resonance (EPR), scanning electron microscopy (SEM), and dielectric measurements. Crystal structure changed from tetragonal (0.02 ⩽ x ⩽ 0.04) to cubic (x = 0.05), accompanied by a linear decline of the c/a axial ratio with x. BPT exhibited a slight diffuse phase transition behavior and its dielectric-peak temperature (T{sub m}) decreased rapidly at a rate of −22 °C/at.% Pr. Pr ions were substituted predominantly for Ba sites as Pr{sup 3+} and induced Ti-vacancy defects, which are evidenced by a change in unit cell volume, a rapid T{sub m} – shifting rate, a new Raman band at ∼837 cm{sup −1}, and an EPR signal at g = 2.002. A very small number of Pr ions inevitably entered Ti sites as Pr{sup 4+}, which is evidenced by a thermally accessible signal at g = 3.77 related to the preservation history of the x = 0.05 sample. The effect of electron free radicals on EPR signal is discussed. Another thermally accessible EPR signal associated with a rhombic g-tensor of the stronger g = 2.002 signal was observed. This signal is also related to the preservation history of the sample.

  1. Structure of the P700(+ )A1(-) radical pair intermediate in photosystem I by high time resolution multifrequency electron paramagnetic resonance: analysis of quantum beat oscillations.

    Science.gov (United States)

    Link, G; Berthold, T; Bechtold, M; Weidner, J U; Ohmes, E; Tang, J; Poluektov, O; Utschig, L; Schlesselman, S L; Thurnauer, M C; Kothe, G

    2001-05-01

    The geometry of the secondary radical pair P700(+)A1(-), in photosystem I (PSI) from the deuterated and 15N-substituted cyanobacterium Synechococcus lividus, has been determined by high time resolution electron paramagnetic resonance (EPR), performed at three different microwave frequencies. Structural information is extracted from light-induced quantum beats observed in the transverse magnetization of P700(+)A1(-) at early times after laser excitation. A computer analysis of the two-dimensional Q-band experiment provides the orientation of the various magnetic tensors of with respect to a magnetic reference frame. The orientation of the cofactors of the primary donor in the g-tensor system of is then evaluated by analyzing time-dependent X-band EPR spectra, extracted from a two-dimensional data set. Finally, the cofactor arrangement of P700(+)A1(-) in the photosynthetic membrane is deduced from angular-dependent W-band spectra, observed for a magnetically aligned sample. Thus, the orientation of the g-tensor of P700(+) with respect to a chlorophyll based reference system could be determined. The angle between the g1(z) axis and the chlorophyll plane normal is found to be 29 +/- 7 degrees, while the g1(y) axis lies in the chlorophyll plane. In addition, a complete structural model for the reduced quinone acceptor, A1(-), is evaluated. In this model, the quinone plane of is found to be inclined by 68 +/- 7 degrees relative to the membrane plane, while the P700(+)-A1(-) axis makes an angle of 35 +/- 6 degrees with the membrane normal. All of these values refer to the charge separated state, observed at low temperatures, where forward electron transfer to the iron-sulfur centers is partially blocked. Preliminary room temperature studies of P700(+)A1(-), employing X-band quantum beat oscillations, indicate a different orientation of A1(-) in its binding pocket. A comparison with crystallographic data provides information on the electron-transfer pathway in PSI. It

  2. Constraints on photon pulse duration from longitudinal electron beam diagnostics at a soft x-ray free-electron laser

    Directory of Open Access Journals (Sweden)

    C. Behrens

    2012-03-01

    Full Text Available The successful operation of x-ray free-electron lasers (FELs, like the Linac Coherent Light Source or the Free-Electron Laser in Hamburg (FLASH, makes unprecedented research on matter at atomic length and ultrafast time scales possible. However, in order to take advantage of these unique light sources and to meet the strict requirements of many experiments in photon science, FEL photon pulse durations need to be known and tunable. This can be achieved by controlling the FEL driving electron beams, and high-resolution longitudinal electron beam diagnostics can be utilized to provide constraints on the expected FEL photon pulse durations. In this paper, we present comparative measurements of soft x-ray pulse durations and electron bunch lengths at FLASH. The soft x-ray pulse durations were measured by FEL radiation pulse energy statistics and compared to electron bunch lengths determined by frequency-domain spectroscopy of coherent transition radiation in the terahertz range and time-domain longitudinal phase space measurements. The experimental results, theoretical considerations, and simulations show that high-resolution longitudinal electron beam diagnostics provide reasonable constraints on the expected FEL photon pulse durations. In addition, we demonstrated the generation of soft x-ray pulses with durations below 50 fs (FWHM after the implementation of the new uniform electron bunch compression scheme used at FLASH.

  3. Consequences of short electron-beam pulses in the FELIX project

    Science.gov (United States)

    Jaroszynski, D. A.; Oepts, D.; Van Der Meer, A. F. G.; Van Amersfoort, P. W.; Colson, W. B.

    1990-10-01

    We discuss the consequences of short micropulses on the output of infrared and far-infrared free electron lasers with special reference to the FELIX project which operates with 3 ps long electron pulses.

  4. Determination of g-tensors of low-symmetry Nd{sup 3+} centers in LiNbO{sub 3} by rectification of angular dependence of electron paramagnetic resonance spectra

    Energy Technology Data Exchange (ETDEWEB)

    Grachev, V., E-mail: grachev@physics.montana.edu; Malovichko, G. [Physics Department, Montana State University, Bozeman, Montana 59717 (United States); Munro, M. [Quantel Laser, Bozeman, Montana 59715 (United States); Kokanyan, E. [Institute of Physical Researches, Ashtarak (Armenia)

    2015-07-28

    Two procedures for facilitation of line tracing and deciphering of complicated spectra of electron paramagnetic resonance (EPR) were developed: a correction of microwave frequencies for every orientation of external magnetic field on the base of known values of g-tensor components for a reference paramagnetic center and followed rectification of measured angular dependences using plots of effective deviation of g{sup 2}-factors of observed lines from effective g{sup 2}-factors of the reference center versus angles or squared cosines of angles describing magnetic field orientations. Their application to EPR spectra of nearly stoichiometric lithium niobate crystals doped with neodymium allowed identifying two axial and six different low-symmetry Nd{sup 3+} centers, to determine all components of their g-tensors, and to propose common divacancy models for a whole family of Nd{sup 3+} centers.

  5. Two-electron time-delay interference in atomic double ionization by attosecond pulses

    Energy Technology Data Exchange (ETDEWEB)

    Rescigno, Thomas N

    2009-10-04

    A two-color two-photon atomic double ionization experiment using subfemtosecond UV pulses can be designed such that the sequential two-color process dominates and one electron is ejected by each pulse. Nonetheless, ab initio calculations show that, for sufficiently short pulses, a prominent interference pattern in the joint energy distribution of the sequentially ejected electrons can be observed that is due to their indistinguishability and the exchange symmetry of the wave function.

  6. A 20 kV, 5 A, 1 ns Risetime Pulsed Electron Beam Source

    Institute of Scientific and Technical Information of China (English)

    Chen Yulan; Zeng Zhengzhong; Wang Haiyang; Ma Lianying

    2005-01-01

    A 20 kV, 1 ns risetime pulsed electron beam source was developed using an extremely small gap (0.1 mm) diode driven by a sub-nanosecond risetime, 10 kV rectangular pulse generator. A beam current of 5 A was detected by using a fast response Faraday cup at a distance of 2 cm away from a grid anode. The shot to shot variation of the electron beam pulse was less than 10%.

  7. Pulse height measurements and electron attachment in drift chambers operated with Xe,CO2 mixtures

    CERN Document Server

    Andronic, A

    2003-01-01

    We present pulse height measurements in drift chambers operated with Xe,CO2 gas mixtures. We investigate the attachment of primary electrons on oxygen and SF6 contaminants in the detection gas. The measurements are compared with simulations of properties of drifting electrons. We present two methods to check the gas quality: gas chromatography and Fe55 pulse height measurements using monitor detectors.

  8. Electron paramagnetic resonance and Mössbauer spectroscopy and density functional theory analysis of a high-spin Fe(IV)-oxo complex.

    Science.gov (United States)

    Gupta, Rupal; Lacy, David C; Bominaar, Emile L; Borovik, A S; Hendrich, Michael P

    2012-06-13

    High-spin Fe(IV)-oxo species are known to be kinetically competent oxidants in non-heme iron enzymes. The properties of these oxidants are not as well understood as the corresponding intermediate-spin oxidants of heme complexes. The present work gives a detailed characterization of the structurally similar complexes [Fe(IV)H(3)buea(O)](-), [Fe(III)H(3)buea(O)](2-), and [Fe(III)H(3)buea(OH)](-) (H(3)buea = tris[(N'-tert-butylureaylato)-N-ethylene]aminato) using Mössbauer and dual-frequency/dual-mode electron paramagnetic resonance (EPR) spectroscopies. The [Fe(IV)H(3)buea(O)](-) complex has a high-spin (S = 2) configuration imposed by the C(3)-symmetric ligand. The EPR spectra of the [Fe(IV)H(3)buea(O)](-) complex presented here represent the first documented examples of an EPR signal from an Fe(IV)-oxo complex, demonstrating the ability to detect and quantify Fe(IV) species with EPR spectroscopy. Quantitative simulations allowed the determination of the zero-field parameter, D = +4.7 cm(-1), and the species concentration. Density functional theory (DFT) calculations of the zero-field parameter were found to be in agreement with the experimental value and indicated that the major contribution to the D value is from spin-orbit coupling of the ground state with an excited S = 1 electronic configuration at 1.2 eV. (17)O isotope enrichment experiments allowed the determination of the hyperfine constants ((17)O)A(z) = 10 MHz for [Fe(IV)H(3)buea(O)](-) and ((17)O)A(y) = 8 MHz, ((17)O)A(z) = 12 MHz for [Fe(III)H(3)buea(OH)](-). The isotropic hyperfine constant (((17)O)A(iso) = -16.8 MHz) was derived from the experimental value to allow a quantitative determination of the spin polarization (ρ(p) = 0.56) of the oxo p orbitals of the Fe-oxo bond in [Fe(IV)H(3)buea(O)](-). This is the first experimental determination for non-heme complexes and indicates significant covalency in the Fe-oxo bond. High-field Mössbauer spectroscopy gave an (57)Fe A(dip) tensor of (+5.6, +5

  9. Paramagnetic Spin Seebeck Effect

    Science.gov (United States)

    Wu, Stephen M.; Pearson, John E.; Bhattacharya, Anand

    2015-05-01

    We report the observation of the longitudinal spin Seebeck effect in paramagnetic insulators. By using a microscale on-chip local heater, we generate a large thermal gradient confined to the chip surface without a large increase in the total sample temperature. Using this technique at low temperatures (<20 K ), we resolve the paramagnetic spin Seebeck effect in the insulating paramagnets Gd3Ga5O12 (gadolinium gallium garnet) and DyScO3 (DSO), using either W or Pt as the spin detector layer. By taking advantage of the strong magnetocrystalline anisotropy of DSO, we eliminate contributions from the Nernst effect in W or Pt, which produces a phenomenologically similar signal.

  10. PERCEPTION LEVEL EVALUATION OF RADIO ELECTRONIC MEANS TO A PULSE OF ELECTROMAGNETIC RADIATION

    Directory of Open Access Journals (Sweden)

    2016-01-01

    Full Text Available The method for evaluating the perception level of electronic means to pulsed electromagnetic radiation is consid- ered in this article. The electromagnetic wave penetration mechanism towards the elements of electronic systems and the impact on them are determined by the intensity of the radiation field on the elements of electronic systems. The impact of electromagnetic radiation pulses to the electronic systems refers to physical and analytical parameters of the relationship between exposure to pulses of electromagnetic radiation and the sample parameters of electronic systems. A physical and mathematical model of evaluating the perception level of electronic means to pulsed electromagnetic radiation is given. The developed model was based on the physics of electronics means failure which represents the description of electro- magnetic, electric and thermal processes that lead to the degradation of the original structure of the apparatus elements. The conditions that lead to the total equation electronic systems functional destruction when exposed to electromagnetic radia- tion pulses are described. The internal characteristics of the component elements that respond to the damaging effects are considered. The ratio for the power failure is determined. A thermal breakdown temperature versus pulse duration of expo- sure at various power levels is obtained. The way of evaluation the reliability of electronic systems when exposed to pulses of electromagnetic radiation as a destructive factor is obtained.

  11. A high current, short pulse electron source for wakefield accelerators

    Energy Technology Data Exchange (ETDEWEB)

    Ho, Ching-Hung

    1992-12-31

    Design studies for the generation of a high current, short pulse electron source for the Argonne Wakefield Accelerator are presented. An L-band laser photocathode rf gun cavity is designed using the computer code URMEL to maximize the electric field on the cathode surface for fixed frequency and rf input power. A new technique using a curved incoming laser wavefront to minimize the space charge effect near the photocathode is studied. A preaccelerator with large iris to minimize wakefield effects is used to boost the drive beam to a useful energy of around 20 MeV for wakefield acceleration experiments. Focusing in the photocathode gun and the preaccelerator is accomplished with solenoids. Beam dynamics simulations throughout the preaccelerator are performed using particle simulation codes TBCI-SF and PARMELA. An example providing a useful set of operation parameters for the Argonne Wakefield Accelerator is given. The effects of the sagitta of the curved beam and laser amplitude and timing jitter effects are discussed. Measurement results of low rf power level bench tests and a high power test for the gun cavity are presented and discussed.

  12. A high current, short pulse electron source for wakefield accelerators

    Energy Technology Data Exchange (ETDEWEB)

    Ho, Ching-Hung.

    1992-01-01

    Design studies for the generation of a high current, short pulse electron source for the Argonne Wakefield Accelerator are presented. An L-band laser photocathode rf gun cavity is designed using the computer code URMEL to maximize the electric field on the cathode surface for fixed frequency and rf input power. A new technique using a curved incoming laser wavefront to minimize the space charge effect near the photocathode is studied. A preaccelerator with large iris to minimize wakefield effects is used to boost the drive beam to a useful energy of around 20 MeV for wakefield acceleration experiments. Focusing in the photocathode gun and the preaccelerator is accomplished with solenoids. Beam dynamics simulations throughout the preaccelerator are performed using particle simulation codes TBCI-SF and PARMELA. An example providing a useful set of operation parameters for the Argonne Wakefield Accelerator is given. The effects of the sagitta of the curved beam and laser amplitude and timing jitter effects are discussed. Measurement results of low rf power level bench tests and a high power test for the gun cavity are presented and discussed.

  13. A study of ultrafast electron diffusion kinetics in ultrashort-pulse laser ablation of metals

    Institute of Scientific and Technical Information of China (English)

    Yang Jian-Jun; Liu Wei-Wei; Zhu Xiao-Nong

    2007-01-01

    Temperature dependence of the electron diffusion in metallic targets, where the electron-electron collision is the dominant process, is investigated with the help of an extended two-temperature model. In sharp contrast to the low electron temperature case, where only the electron-phonon collisions are commonly considered, the electron diffusion process underlying the high electron temperatures evolves dramatically different in both temporal and spatial domains.Calculated results of the ablation yield at different pulse durations are presented for a copper plate impinged by ultrashort laser pulses with energy fluences ranging from 0.1 J/cm2 to 10 J/cm2. The excellent agreement between the simulation results and the experimental data indicates the significant role of electron-electron collisions in material ablations using intense ultrashort laser pulses.

  14. Evidence of secondary electron emission during PIII pulses as measured by calorimetric probe

    Science.gov (United States)

    Haase, Fabian; Manova, Darina; Mändl, Stephan; Kersten, Holger

    2016-09-01

    Secondary electrons are an ubiquitous nuisance during plasma immersion ion implantation (PIII) necessitating excessive current supplies and shielding for X-rays generated by them. However, additional effects - especially at low pulse voltages - can include interactions with the plasma and transient increases in the plasma density. Here, it is shown that the transient thermal flux associated with secondary electrons emitted from the pulsed substrate can be directly measured using a passive calorimetric probe mounted near the chamber wall away from the pulsed substrate holder. A small increase of a directed energy flux from the substrate towards the probe is consistently observed on top of the isotropic flux from the plasma surrounding the probe, scaling with pulse frequency, pulse voltage, pulse length - as well as depending on gas and substrate material. A strong correlation between voltage and substrate-probe distance is observed, which should allow further investigation of low energy electrons with the plasma itself.

  15. Temporal and lateral electron pulse compression by a compact spherical electrostatic capacitor

    Energy Technology Data Exchange (ETDEWEB)

    Grzelakowski, Krzysztof P., E-mail: kgrzelakowski@op.pl [OPTICON Nanotechnology, Muchoborska 18, PL54-424 Wrocław (Poland); Tromp, Rudolf M. [IBM Research Division, T.J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States)

    2013-07-15

    A novel solution for high intensity electron pulse compression in both space and time is proposed in this paper. Based on the unique properties of the central-force electrostatic field of a spherical electrostatic capacitor, the newly developed α-Spherical Deflector Analyzer (α-SDA) with 2π total deflection is utilized for the practical realization of femtosecond electron pulse compression. The mirror symmetry of the system at π deflection causes not only the cancellation of the geometrical and chromatic aberrations at 2π, but also leads to aberration-free time reversal of the electron pulse in the exit plane. As a consequence, the time-divergent electrons at the input are transformed to a time-convergent pulse at the output. In the symmetric case with the first time compression exactly at π, the shortest electron pulse behind the α-SDA analyzer is a mirror symmetric to the original electron pulse at the photocathode. It results in extremely short final electron pulses that are limited only by the duration of the laser pulse, the emittance of the electron bunch, and by imperfections of the real system. - Highlights: • We propose a new method for spatial and temporal compression of ultrafast electron pulses. • Compact in-line construction is based on the idea of the spherical electrostatic capacitor (α-SDA). • It is free of chromatic, geometrical and temporal aberrations after 2π deflection. • Contrary to other methods it enables time reversal of the pulse with static electric fields only. • Spatial and temporal focus can be independently fine-adjusted at the target position.

  16. Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization

    Energy Technology Data Exchange (ETDEWEB)

    Sidabras, Jason W.; Anderson, James R.; Mainali, Laxman; Hyde, James S. [Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226 (United States); Strangeway, Robert A. [Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226 (United States); Department of Electrical Engineering and Computer Science, Milwaukee School of Engineering, Milwaukee, Wisconsin 53201 (United States); Mett, Richard R. [Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226 (United States); Department of Chemistry and Physics, Milwaukee School of Engineering, Milwaukee, Wisconsin 53201 (United States)

    2016-03-15

    Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R. Mett et al., Rev. Sci. Instrum. 82, 074704 (2011)]. The oversize section reduces broadband insertion loss for an Electron Paramagnetic Resonance (EPR) probe placed in a 3.36 T magnet. Hyperbolic-cosine tapers minimize reflection of the main mode and the excitation of unwanted propagating waveguide modes. Oversize waveguide is distinguished from corrugated waveguide, overmoded waveguide, or quasi-optic techniques by minimal coupling to higher-order modes. Only the TE{sub 10} mode of the parent WR10 waveguide is propagated. In the present work, a new oversize assembly with a gradual 90° twist was implemented. Microwave power measurements show that the twisted oversize waveguide assembly reduces the power loss in the observe and pump arms of a W-band bridge by an average of 2.35 dB and 2.41 dB, respectively, over a measured 1.25 GHz bandwidth relative to a straight length of WR10 waveguide. Network analyzer measurements confirm a decrease in insertion loss of 2.37 dB over a 4 GHz bandwidth and show minimal amplitude distortion of approximately 0.15 dB. Continuous wave EPR experiments confirm these results. The measured phase variations of the twisted oversize waveguide assembly, relative to an ideal distortionless transmission line, are reduced by a factor of two compared to a straight length of WR10 waveguide. Oversize waveguide with proper transitions is demonstrated as an effective way to increase incident power and the return signal for broadband EPR experiments. Detailed performance characteristics, including continuous wave experiment using 1 μM 2,2,6,6-tetramethylpiperidine-1-oxyl in aqueous solution, provided here serve as a benchmark for other broadband low-loss probes in

  17. Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization.

    Science.gov (United States)

    Sidabras, Jason W; Strangeway, Robert A; Mett, Richard R; Anderson, James R; Mainali, Laxman; Hyde, James S

    2016-03-01

    Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R. Mett et al., Rev. Sci. Instrum. 82, 074704 (2011)]. The oversize section reduces broadband insertion loss for an Electron Paramagnetic Resonance (EPR) probe placed in a 3.36 T magnet. Hyperbolic-cosine tapers minimize reflection of the main mode and the excitation of unwanted propagating waveguide modes. Oversize waveguide is distinguished from corrugated waveguide, overmoded waveguide, or quasi-optic techniques by minimal coupling to higher-order modes. Only the TE10 mode of the parent WR10 waveguide is propagated. In the present work, a new oversize assembly with a gradual 90° twist was implemented. Microwave power measurements show that the twisted oversize waveguide assembly reduces the power loss in the observe and pump arms of a W-band bridge by an average of 2.35 dB and 2.41 dB, respectively, over a measured 1.25 GHz bandwidth relative to a straight length of WR10 waveguide. Network analyzer measurements confirm a decrease in insertion loss of 2.37 dB over a 4 GHz bandwidth and show minimal amplitude distortion of approximately 0.15 dB. Continuous wave EPR experiments confirm these results. The measured phase variations of the twisted oversize waveguide assembly, relative to an ideal distortionless transmission line, are reduced by a factor of two compared to a straight length of WR10 waveguide. Oversize waveguide with proper transitions is demonstrated as an effective way to increase incident power and the return signal for broadband EPR experiments. Detailed performance characteristics, including continuous wave experiment using 1 μM 2,2,6,6-tetramethylpiperidine-1-oxyl in aqueous solution, provided here serve as a benchmark for other broadband low-loss probes in

  18. Large Mn25 single-molecule magnet with spin S = 51/2: magnetic and high-frequency electron paramagnetic resonance spectroscopic characterization of a giant spin state.

    Science.gov (United States)

    Murugesu, Muralee; Takahashi, Susumu; Wilson, Anthony; Abboud, Khalil A; Wernsdorfer, Wolfgang; Hill, Stephen; Christou, George

    2008-10-20

    The synthesis and structural, spectroscopic, and magnetic characterization of a Mn25 coordination cluster with a large ground-state spin of S = 51/2 are reported. Reaction of MnCl2 with pyridine-2,6-dimethanol (pdmH2) and NaN3 in MeCN/MeOH gives the mixed valence cluster [Mn25O18(OH)2(N3)12(pdm)6(pdmH)6]Cl2 (1; 6Mn(II), 18Mn(III), Mn(IV)), which has a barrel-like cage structure. Variable temperature direct current (dc) magnetic susceptibility data were collected in the 1.8-300 K temperature range in a 0.1 T field. Variable-temperature and -field magnetization (M) data were collected in the 1.8-4.0 K and 0.1-7 T ranges and fit by matrix diagonalization assuming only the ground state is occupied at these temperatures. The fit parameters were S = 51/2, D = -0.020(2) cm(-1), and g = 1.87(3), where D is the axial zero-field splitting parameter. Alternating current (ac) susceptibility measurements in the 1.8-8.0 K range and a 3.5 G ac field oscillating at frequencies in the 50-1500 Hz range revealed a frequency-dependent out-of-phase (chi(M)'') signal below 3 K, suggesting 1 to be a single-molecule magnet (SMM). This was confirmed by magnetization vs dc field sweeps, which exhibited hysteresis loops but with no clear steps characteristic of resonant quantum tunneling of magnetization (QTM). However, magnetization decay data below 1 K were collected and used to construct an Arrhenius plot, and the fit of the thermally activated region above approximately 0.5 K gave U(eff)/k = 12 K, where U(eff) is the effective relaxation barrier. The g value and the magnitude and sign of the D value were independently confirmed by detailed high-frequency electron paramagnetic resonance (HFEPR) spectroscopy on polycrystalline samples. The combined studies confirm both the high ground-state spin S = 51/2 of complex 1 and that it is a SMM that, in addition, exhibits QTM.

  19. Probing Structural Dynamics and Topology of the KCNE1 Membrane Protein in Lipid Bilayers via Site-Directed Spin Labeling and Electron Paramagnetic Resonance Spectroscopy.

    Science.gov (United States)

    Sahu, Indra D; Craig, Andrew F; Dunagan, Megan M; Troxel, Kaylee R; Zhang, Rongfu; Meiberg, Andrew G; Harmon, Corrinne N; McCarrick, Robert M; Kroncke, Brett M; Sanders, Charles R; Lorigan, Gary A

    2015-10-20

    KCNE1 is a single transmembrane protein that modulates the function of voltage-gated potassium channels, including KCNQ1. Hereditary mutations in the genes encoding either protein can result in diseases such as congenital deafness, long QT syndrome, ventricular tachyarrhythmia, syncope, and sudden cardiac death. Despite the biological significance of KCNE1, the structure and dynamic properties of its physiologically relevant native membrane-bound state are not fully understood. In this study, the structural dynamics and topology of KCNE1 in bilayered lipid vesicles was investigated using site-directed spin labeling (SDSL) and electron paramagnetic resonance (EPR) spectroscopy. A 53-residue nitroxide EPR scan of the KCNE1 protein sequence including all 27 residues of the transmembrane domain (45-71) and 26 residues of the N- and C-termini of KCNE1 in lipid bilayered vesicles was analyzed in terms of nitroxide side-chain motion. Continuous wave-EPR spectral line shape analysis indicated the nitroxide spin label side-chains located in the KCNE1 TMD are less mobile when compared to the extracellular region of KCNE1. The EPR data also revealed that the C-terminus of KCNE1 is more mobile when compared to the N-terminus. EPR power saturation experiments were performed on 41 sites including 18 residues previously proposed to reside in the transmembrane domain (TMD) and 23 residues of the N- and C-termini to determine the topology of KCNE1 with respect to the 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPG) lipid bilayers. The results indicated that the transmembrane domain is indeed buried within the membrane, spanning the width of the lipid bilayer. Power saturation data also revealed that the extracellular region of KCNE1 is solvent-exposed with some of the portions partially or weakly interacting with the membrane surface. These results are consistent with the previously published solution NMR

  20. A comparative study by electron paramagnetic resonance of free radical species in the mainstream and sidestream smoke of cigarettes with conventional acetate filters and 'bio-filters'.

    Science.gov (United States)

    Valavanidis, A; Haralambous, E

    2001-01-01

    Tobacco smoking is the most important extrinsic cause, after the diet, for increasing morbidity and mortality in humans. Unless current tobacco smoking patterns in industrialised and non-industrialised countries change, cigarettes will kill prematurely 10 million people a year by 2025. Greece is at the top of the list of European countries in cigarette consumption. In 1997, a Greek tobacco company introduced a new 'bio-filter' (BF) claiming that it reduces substantially the risks of smoking. In a recent publication [Deliconstantinos G, Villiotou V, Stavrides J. Scavenging effects of hemoglobin and related heme containing compounds on nitric oxide, reactive oxidants and carcinogenic volatile nitrosocompounds of cigarette smoke. A new method for protection against the dangerous cigarette constituents. Anticancer Res 1994; 14: 2717-2726] it was claimed that the new 'bio-filter' (activated carbon impregnated with dry hemoglobin) reduces certain toxic substances and oxidants (like NO, CO, NOx, H2O2, aldehydes, trace elements and nitroso-compounds) in the gas-phase of the mainstream smoke. We have investigated by electron paramagnetic resonance (EPR) the mainstream and sidestream smoke of the BF cigarette, in comparison with three other cigarettes with similar tar and nicotine contents, that have conventional acetate filters. We found that BF cigarette smoke has similar tar radical species with the same intensity EPR signals to those of the other cigarettes. The ability of the aqueous cigarette tar extracts to produce hydroxyl radicals (HO*), which were spin trapped by DMPO, was very similar to, or even higher than, the other 3 brands. The gas-phase of the mainstream smoke of the BF cigarette showed a 30-35% reduction in the production of oxygen-centered radicals (spin trapped with PBN). In the case of the sidestream smoke, BF cigarettes produced substantially higher concentrations of gas-phase radicals, compared to the other brands. These results suggest that BF is

  1. Magnetization oscillations induced by spin current in a paramagnetic disc

    NARCIS (Netherlands)

    Slachter, Abraham; van Wees, Bart Jan

    2011-01-01

    When electron spins are injected uniformly into a paramagnetic disk, they can precess along the demagnetizing field induced by the resulting magnetic moment. Normally this precession damps out by virtue of the spin relaxation, which is present in paramagnetic materials. We propose a mechanism to exc

  2. Evidence of emerging Griffiths singularity in La{sub 0.5} Sr{sub 0.5} MnO{sub 3} nanocrystalline probed by magnetization and electron paramagnetic resonance

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiyuan [Department of Applied Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Fan, Jiyu, E-mail: jiyufan@nuaa.edu.cn [Department of Applied Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Xu, Lisa [Department of Applied Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Tong, Wei [High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031 (China); Hu, Dazhi [Department of Applied Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); He, Xun [College of Environmental Science and Engineering, Hunan University, Changsha 410082 (China); Zhang, Lei; Pi, Li; Zhang, Yuheng [High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031 (China)

    2016-06-01

    We present an investigation of Griffiths singularity in La{sub 0.5} Sr{sub 0.5} MnO{sub 3} nanocrystalline by means of magnetic susceptibility and electron paramagnetic resonance (EPR). An unusual platform was found in paramagnetic region. Based on the analysis of EPR spectrum and magnetization variation across the whole temperature range of phase transition, we confirm it is due to the presence of Griffiths singularity rather than a superparamagnetic state in the nanocrystalline system. Such a singularity phase is constituted with some correlated ferromagnetic clusters which embed in paramagnetic matrix. Although they form ferromagnetic spin correlation, the system do not yield any spontaneous magnetization. According to core–shell model, the emergence of Griffiths singularity can be considered due to the presence of local ferromagnetic fluctuations originated from surface spin disorder as the sample size is confined to nanoscale. - Highlights: • Griffiths singularity rather than superparamagnetism occurs in La{sub 0.5}Sr{sub 0.5}MnO{sub 3} nanoparticals. • The sample’s size reduced to nanoscale results in the short-range ferromagnetic interaction. • The core-shell model is used to understand the formation of Griffiths phase in nanometer La{sub 0.5}Sr{sub 0.5}MnO{sub 3}.

  3. Hot electrons generated by ultra-short pulse laser interacting with solid targets

    Institute of Scientific and Technical Information of China (English)

    陈黎明; 张杰; 李玉同; 梁天骄; 王龙; 魏志义; 江文勉

    2000-01-01

    Hot electrons produced by ultra-short pulse laser interacting with solid targets were studied systematically. When 800 nm, 8 × 1015 W/cm2 laser pulses interacted with solid targets, hot electron e-mission was found to be collimated in certain directions and the angular distribution of hot electrons depended on the energy absorption. The angular divergence of outgoing hot electrons was inversely proportional to the hot electron energy. The energy spectrum of hot electrons was found to be in a bi-Maxwellian distribution and the maximum energy was over 500 keV.

  4. Hot electrons generated by ultra-short pulse laser interacting with solid targets

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Hot electrons produced by ultra-short pulse laser interacting with solid targets were studied systematically. When 800 nm, 8×1015 W/cm2 laser pulses interacted with solid targets, hot electron emission was found to be collimated in certain directions and the angular distribution of hot electrons depended on the energy absorption. The angular divergence of outgoing hot electrons was inversely proportional to the hot electron energy. The energy spectrum of hot electrons was found to be in a bi-Maxwellian distribution and the maximum energy was over 500 keV.

  5. Acceleration of injected electron beam by ultra-intense laser pulses with phase disturbances

    CERN Document Server

    Nakamura, T; Kato, S; Tanimoto, M; Koyama, K; Koga, J

    2003-01-01

    Acceleration of an injected electron beam by ultra-intense laser pulses with phase disturbances is investigated. The energy gain of the beam electrons depends on the initial energy of the injected electrons in the stochastic acceleration process. The effect is larger for electrons with some injection energy as opposed to electrons with no initial energy. The corresponding accelerating field for electrons having certain amounts of initial energy becomes larger than that of the standard wakefield. (author)

  6. Pulse-periodic generation of supershort avalanche electron beams and X-ray emission

    Science.gov (United States)

    Baksht, E. Kh.; Burachenko, A. G.; Erofeev, M. V.; Tarasenko, V. F.

    2014-05-01

    Pulse-periodic generation of supershort avalanche electron beams (SAEBs) and X-ray emission in nitrogen, as well as the transition from a single-pulse mode to a pulse-periodic mode with a high repetition frequency, was studied experimentally. It is shown that, in the pulse-periodic mode, the full width at halfmaximum of the SAEB is larger and the decrease rate of the gap voltage is lower than those in the single-pulse mode. It is found that, when the front duration of the voltage pulse at a nitrogen pressure of 90 Torr decreases from 2.5 to 0.3 ns, the X-ray exposure dose in the pulse-periodic mode increases by more than one order of magnitude and the number of SAEB electrons also increases. It is shown that, in the pulse-periodic mode of a diffuse discharge, gas heating in the discharge gap results in a severalfold increase in the SAEB amplitude (the number of electrons in the beam). At a generator voltage of 25 kV, nitrogen pressure of 90 Torr, and pulse repetition frequency of 3.5 kHz, a runaway electron beam was detected behind the anode foil.

  7. Nonlinear reflection of high-amplitude laser pulses from relativistic electron mirrors

    Science.gov (United States)

    Kulagin, V. V.; Kornienko, V. N.; Cherepenin, V. A.

    2016-04-01

    A coherent X-ray pulse of attosecond duration can be formed in the reflection of a counterpropagating laser pulse from a relativistic electron mirror. The reflection of a high-amplitude laser pulse from the relativistic electron mirror located in the field of an accelerating laser pulse is investigated by means of two-dimensional (2D) numerical simulation. It is shown that provided the amplitude of the counterpropagating laser pulse is several times greater than the amplitude of the accelerating laser pulse, the reflection process is highly nonlinear, which causes a significant change in the X-ray pulse shape and its shortening up to generation of quasi-unipolar pulses and single-cycle pulses. A physical mechanism responsible for this nonlinearity of the reflection process is explained, and the parameters of the reflected X-ray pulses are determined. It is shown that the duration of these pulses may constitute 50 - 60 as, while their amplitude may be sub-relativistic.

  8. Injection of electrons by colliding laser pulses in a laser wakefield accelerator

    Science.gov (United States)

    Hansson, M.; Aurand, B.; Ekerfelt, H.; Persson, A.; Lundh, O.

    2016-09-01

    To improve the stability and reproducibility of laser wakefield accelerators and to allow for future applications, controlling the injection of electrons is of great importance. This allows us to control the amount of charge in the beams of accelerated electrons and final energy of the electrons. Results are presented from a recent experiment on controlled injection using the scheme of colliding pulses and performed using the Lund multi-terawatt laser. Each laser pulse is split into two parts close to the interaction point. The main pulse is focused on a 2 mm diameter gas jet to drive a nonlinear plasma wave below threshold for self-trapping. The second pulse, containing only a fraction of the total laser energy, is focused to collide with the main pulse in the gas jet under an angle of 150°. Beams of accelerated electrons with low divergence and small energy spread are produced using this set-up. Control over the amount of accelerated charge is achieved by rotating the plane of polarization of the second pulse in relation to the main pulse. Furthermore, the peak energy of the electrons in the beams is controlled by moving the collision point along the optical axis of the main pulse, and thereby changing the acceleration length in the plasma.

  9. Electron spin dynamics of Ce3 + ions in YAG crystals studied by pulse-EPR and pump-probe Faraday rotation

    Science.gov (United States)

    Azamat, D. V.; Belykh, V. V.; Yakovlev, D. R.; Fobbe, F.; Feng, D. H.; Evers, E.; Jastrabik, L.; Dejneka, A.; Bayer, M.

    2017-08-01

    The spin relaxation dynamics of Ce3 + ions in heavily cerium-doped YAG crystals is studied using pulse-electron paramagnetic resonance and time-resolved pump-probe Faraday rotation. Both techniques address the 4 f ground state, while pump-probe Faraday rotation also provides access to the excited 5 d state. We measure a millisecond spin-lattice relaxation time T1, a microsecond spin coherence time T2, and a ˜10 ns inhomogeneous spin dephasing time T2* for the Ce3 + ground state at low temperatures. The spin-lattice relaxation of Ce3 + ions is due to modified Raman processes involving the optical phonon mode at ˜125 cm-1 . The relaxation at higher temperature goes through a first excited level of the 5/2 2F term at about ℏ ω ≈228 cm-1 . Effects provided by the hyperfine interaction of the Ce3 + with the 27Al nuclei are observed.

  10. An Electronic Patch for Wearable Health Monitoring by Reflectance Pulse Oximetry

    DEFF Research Database (Denmark)

    Haahr, Rasmus Grønbek; Duun, Sune Bro; Toft, Mette H.;

    2012-01-01

    We report the development of an Electronic Patch for wearable health monitoring. The Electronic Patch is a new health monitoring system incorporating biomedical sensors, microelectronics, radio frequency (RF) communication, and a battery embedded in a 3-dimensional hydrocolloid polymer...... photodiode to enable low power consumption by the light emitting components. The Electronic Patch has a disposable part of soft adhesive hydrocolloid polymer and a reusable part of hard polylaurinlactam. The disposable part contains the battery. The reusable part contains the reflectance pulse oximetry....... In this paper the Electronic Patch is demonstrated with a new optical biomedical sensor for reflectance pulse oximetry so that the Electronic Patch in this case can measure the pulse and the oxygen saturation. The reflectance pulse oximetry solution is based on a recently developed annular backside silicon...

  11. Evolution of electron beam pulses of short duration in the solar corona

    Science.gov (United States)

    Casillas-Pérez, G. A.; Jeyakumar, S.; Pérez-Enríquez, H. R.; Trinidad, M. A.

    2016-11-01

    Narrowband radio bursts with durations of the order of milliseconds, called spikes, are known to be associated with solar flares. In order to understand the particle beams responsible for the radio spike phenomena, evolution of electron beam pulses injected from a solar flare region into the corona is studied. Numerical integration of the Fokker-Planck (FP) equation is used to follow the evolution of the electron beam pulse. The simulations show that the short duration pulses lose most of their energy within a second of propagation into the corona. Electron beam with a small low energy cut off is thermalized faster than that with a high low energy cut off.

  12. Generation of Phase-Locked Pulses from a Seeded Free-Electron Laser.

    Science.gov (United States)

    Gauthier, David; Ribič, Primož Rebernik; De Ninno, Giovanni; Allaria, Enrico; Cinquegrana, Paolo; Danailov, Miltcho Bojanov; Demidovich, Alexander; Ferrari, Eugenio; Giannessi, Luca

    2016-01-15

    In a coherent control experiment, light pulses are used to guide the real-time evolution of a quantum system. This requires the coherence and the control of the pulses' electric-field carrier waves. In this work, we use frequency-domain interferometry to demonstrate the mutual coherence of time-delayed pulses generated by an extreme ultraviolet seeded free-electron laser. Furthermore, we use the driving seed laser to lock and precisely control the relative phase between the two free-electron laser pulses. This new capability opens the way to a multitude of coherent control experiments, which will take advantage of the high intensity, short wavelength, and short duration of the pulses generated by seeded free-electron lasers.

  13. Forward acceleration and generation of femtosecond, megaelectronvolt electron beams by an ultrafast intense laser pulse

    Institute of Scientific and Technical Information of China (English)

    Xiaofang wang(王晓方); Quandong Wang(汪权东); Baifei Shen(沈百飞)

    2003-01-01

    We present a new mechanism of energy gain of electrons accelerated by a laser pulse. It is shown that when the intensity of an ultrafast intense laser pulse decreases rapidly along the direction of propagation, electrons leaving the pulse experience an action of ponderomotive deceleration at the descending part of a lower-intensity laser field than acceleration at the ascending part of a high-intensity field, thus gain net energy from the pulse and move directly forward. By means of such a mechanism, a megaelectronvolt electron beam with a bunch length shorter than 100 fs could be realized with an ultrafast (≤30 fs),intense (>1019 W/cm2) laser pulse.

  14. Solid-state pulse modulator using Marx generator for a medical linac electron-gun

    Science.gov (United States)

    Lim, Heuijin; Hyeok Jeong, Dong; Lee, Manwoo; Lee, Mujin; Yi, Jungyu; Yang, Kwangmo; Ro, Sung Chae

    2016-04-01

    A medical linac is used for the cancer treatment and consists of an accelerating column, waveguide components, a magnetron, an electron-gun, a pulse modulator, and an irradiation system. The pulse modulator based on hydrogen thyratron-switched pulse-forming network is commonly used in linac. As the improvement of the high power semiconductors in switching speed, voltage rating, and current rating, an insulated gate bipolar transistor has become the more popular device used for pulsed power systems. We propose a solid-state pulse modulator to generator high voltage by multi-stacked storage-switch stages based on the Marx generator. The advantage of our modulator comes from the use of two semiconductors to control charging and discharging of the storage capacitor at each stage and it allows to generate the pulse with various amplitudes, widths, and shapes. In addition, a gate driver for two semiconductors is designed to reduce the control channels and to protect the circuits. It is developed for providing the pulsed power to a medical linac electron-gun that requires 25 kV and 1 A as the first application. In order to improve the power efficiency and achieve the compactness modulator, a capacitor charging power supply, a Marx pulse generator, and an electron-gun heater isolated transformer are constructed and integrated. This technology is also being developed to extend the high power pulsed system with > 1 MW and also other applications such as a plasma immersed ion implantation and a micro pulse electrostatic precipitator which especially require variable pulse shape and high repetition rate > 1 kHz. The paper describes the design features and the construction of this solid-state pulse modulator. Also shown are the performance results into the linac electron-gun.

  15. Study of the nature and of the properties of paramagnetic centers observed by electron spin resonance in conjugated polymers; Etude de la nature des propriete des centres paramagnetiques observes par resonance paramagnetique electronique dans les polymeres conjugues

    Energy Technology Data Exchange (ETDEWEB)

    Nechtschein, M. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1967-06-15

    Conjugated polymers contain paramagnetic centers. It is established that these centers are free radicals and a model which defines their electronic structure is proposed. The interactions between these centers are studied, notably by dynamic polarisation experiments. Finally it is shown that the centers have catalytic properties. (author) [French] Les polymeres conjugues contiennent des centres paramagnetiques. L'origine radicalaire de ces centres est etablie et un modele precisant leur structure electronique est propose. Les interactions entre ces centres sont etudiees, notamment a l'aide d'experiences de polarisation dynamique. Des proprietes catalytiques sont mises en evidence. (auteur)

  16. Simulations and Measurement of Electron Energy and Effective Electron Temperature of Nanosecond Pulsed Argon Plasma%Simulations and Measurement of Electron Energy and Effective Electron Temperature of Nanosecond Pulsed Argon Plasma

    Institute of Scientific and Technical Information of China (English)

    闻雪晴; 信裕; 冯春雷; 丁洪斌

    2012-01-01

    The behavior of argon plasma driven by nanosecond pulsed plasma in a low-pressure plasma reactor is investigated using a global model, and the results are compared with the experimental measurements. The time evolution of plasma density and the electron energy probability function are calculated by solving the energy balance and Boltzmann equations. During and shortly after the discharge pulse, the electron energy probability function can be represented by a bi-Maxwellian distribution, indicating two energy groups of electrons. According to the effective electron temperature calculation, we find that there are more high-energy electrons that play an important role in the excitation and ionization processes than low-energy electrons. The effective electron temperature is also measured via optical emission spectroscopy to evaluate the simulation model. In the comparison, the simulation results are found to be in agreement with the measure- ments. Furthermore, variations of the effective electron temperature are presented versus other discharge parameters, such as pulse width time, pulse rise time and gas pressure.

  17. Quenching Plasma Waves in Two Dimensional Electron Gas by a Femtosecond Laser Pulse

    Science.gov (United States)

    Shur, Michael; Rudin, Sergey; Greg Rupper Collaboration; Andrey Muraviev Collaboration

    Plasmonic detectors of terahertz (THz) radiation using the plasma wave excitation in 2D electron gas are capable of detecting ultra short THz pulses. To study the plasma wave propagation and decay, we used femtosecond laser pulses to quench the plasma waves excited by a short THz pulse. The femtosecond laser pulse generates a large concentration of the electron-hole pairs effectively shorting the 2D electron gas channel and dramatically increasing the channel conductance. Immediately after the application of the femtosecond laser pulse, the equivalent circuit of the device reduces to the source and drain contact resistances connected by a short. The total response charge is equal to the integral of the current induced by the THz pulse from the moment of the THz pulse application to the moment of the femtosecond laser pulse application. This current is determined by the plasma wave rectification. Registering the charge as a function of the time delay between the THz and laser pulses allowed us to follow the plasmonic wave decay. We observed the decaying oscillations in a sample with a partially gated channel. The decay depends on the gate bias and reflects the interplay between the gated and ungated plasmons in the device channel. Army Research Office.

  18. Pulse-by-pulse multi-beam-line operation for x-ray free-electron lasers

    Directory of Open Access Journals (Sweden)

    Toru Hara

    2016-02-01

    Full Text Available The parallel operation of plural undulator beam lines is an important means of improving the efficiency and usability of x-ray free-electron laser facilities. After the installation of a second undulator beam line (BL2 at SPring-8 Angstrom compact free-electron laser (SACLA, pulse-by-pulse switching between two beam lines was tested using kicker and dc twin-septum magnets. To maintain a compact size, all undulator beam lines at SACLA are designed to be placed within the same undulator hall located downstream of the accelerator. In order to ensure broad tunability of the laser wavelength, the electron bunches are accelerated to different beam energies optimized for the wavelengths of each beam line. In the demonstration, the 30 Hz electron beam was alternately deflected to two beam lines and simultaneous lasing was achieved with 15 Hz at each beam line. Since the electron beam was deflected twice by 3° in a dogleg to BL2, the coherent synchrotron radiation (CSR effects became non-negligible. Currently in a wavelength range of 4–10 keV, a laser pulse energy of 100–150  μJ can be obtained with a reduced peak current of around 1 kA by alleviating the CSR effects. This paper reports the results and operational issues related to the multi-beam-line operation of SACLA.

  19. High energy electron generation by the 15 mJ ultrashort pulse laser

    Energy Technology Data Exchange (ETDEWEB)

    Takano, K; Hotta, E; Nemoto, K [Department of Energy Sciences Tokyo Institute of Technology 4259 Nagatsuta-cho Midori-ku Yokohama 226-8502 (Japan); Nayuki, T; Oishi, Y; Fujii, T; Zhidkov, A [Central Research Institute of Electric Power Industry 2-6-1 Nagasaka, Yokosuka, Kanagawa, 240-0196 (Japan); Todoriki, M; Hasegawa, S [University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-8654 (Japan)], E-mail: k-tn@plasma.es.titech.ac.jp

    2008-05-01

    We propose a small size high energy X-ray source utilizing ultrashort pulse lasers, and a new scheme for generating quasi-monoenergetic electrons. In this paper, we developed a compact laser electron generator and performed experiment that generated energetic electrons over 1 MeV electrons with only 15 mJ laser energy. The temperatures of emitted electrons were measured to be 0.2 MeV and 0.25 MeV without and with prepulse, respectively.

  20. Quantum control of electron wave packets in bound molecules by trains of half-cycle pulses

    Energy Technology Data Exchange (ETDEWEB)

    Persson, Emil; Pichler, Markus; Wachter, Georg; Hisch, Thomas; Burgdoerfer, Joachim; Graefe, Stefanie [Institute for Theoretical Physics, Vienna University of Technology, Wiedner Hauptstr. 8-10, A-1040 Vienna (Austria); Jakubetz, Werner [Institute for Theoretical Chemistry, University of Vienna, Waehringerstr. 38, A-1090 Vienna (Austria)

    2011-10-15

    We investigate protocols for transient localization of electrons in homodiatomic molecules, as well as permanent localization via population inversion in polar molecules. By examining three different model systems with one electronic and one nuclear degree of freedom, we identify mechanisms leading to control over the localization of the electronic wave packets. We show that electronic states dressed by the quasi-dc component of the train of half-cycle pulses steer the combined electronic and nuclear motion toward the targeted state.

  1. Thermal conductivity and electron-phonon relaxation in a metal heated by a subpicosecond laser pulse

    Science.gov (United States)

    Petrov, Yu. V.; Anisimov, S. I.

    2006-06-01

    This paper discusses the initial stages of the interaction of subpicosecond laser pulses with metallic targets: the absorption of light, energy transport by electronic thermal conductivity, and electron-phonon relaxation. It is shown that, with moderate surface energy density, hydrodynamic motion begins after the electronic and lattice temperatures equalize. A connection is established between the energy exchange rate between the electrons and the lattice and the electronic thermal conductivity (an analog of the Wiedemann-Franz law).

  2. Electronic structure of p-type La{sub 1-x}M{sub x}{sup 2+}MnO{sub 3} manganites in the ferromagnetic and paramagnetic phases in the LDA + GTB approach

    Energy Technology Data Exchange (ETDEWEB)

    Gavrichkov, V. A., E-mail: gav@iph.krasn.ru; Ovchinnikov, S. G. [Russian Academy of Sciences, Kirensky Institute of Physics, Siberian Branch (Russian Federation); Nekrasov, I. A. [Russian Academy of Sciences, Institute of Electrophysics, Ural Branch (Russian Federation); Pchelkina, Z. V. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)

    2011-05-15

    The band structure, spectral intensity, and position of the Fermi level in doped p-type La{sub 1-x}M{sub x/2+}MnO{sub 3} manganites (M = Sr, Ca, Ba) is analyzed using the LDA + GBT method for calculating the electronic structure of systems with strong electron correlations, taking into account antiferro-orbital ordering and using the Kugel-Khomskii ideas and real spin S = 2. The results of the ferromagnetic phase reproduce the state of a spin half-metal with 100% spin polarization at T = 0, when the spectrum is of the metal type for a quasiparticle with one spin projection and of the dielectric type for the other. It is found that the valence band becomes approximately three times narrower upon a transition to the paramagnetic phase. For the paramagnetic phase, metal properties are observed because the Fermi level is located in the valence band for any nonzero x. The dielectrization effect at the Curie temperature is possible and must be accompanied by filling of d{sub x} orbitals upon doping. The effect itself is associated with strong electron correlations, and a complex structure of the top of the valence band is due to the Jahn-Teller effect in cubic materials.

  3. Electronically driven adsorbate excitation mechanism in femtosecond-pulse laser desorption

    DEFF Research Database (Denmark)

    Brandbyge, Mads; Hedegård, Per; Heinz, T. F.

    1995-01-01

    Femtosecond-pulse laser desorption is a process in which desorption is driven by a subpicosecond temperature pulse of order 5000 K in the substrate-adsorbate electron system, whose energy is transferred into the adsorbate center-of-mass degrees of freedom by a direct coupling mechanism. We presen...

  4. H- extraction from electron-cyclotron-resonance-driven multicusp volume source operated in pulsed mode

    Science.gov (United States)

    Svarnas, P.; Bacal, M.; Auvray, P.; Béchu, S.; Pelletier, J.

    2006-03-01

    H2 microwave (2.45GHz) pulsed plasma is produced from seven elementary electron cyclotron resonance sources installed into the magnetic multipole chamber "Camembert III" (École Polytechnique—Palaiseau) from which H- extraction takes place. The negative-ion and electron extracted currents are studied through electrical measurements and the plasma parameters by means of electrostatic probe under various experimental conditions. The role of the plasma electrode bias and the discharge duty cycle in the extraction process is emphasized. The gas breakdown at the beginning of every pulse gives rise to variations of the plasma characteristic parameters in comparison with those established at the later time of the pulse, where the electron temperature, the plasma potential, and the floating potential converge to the values obtained for a continuous plasma. The electron density is significantly enhanced in the pulsed mode.

  5. Surface electronic and structural properties of nanostructured titanium oxide grown by pulsed laser deposition

    NARCIS (Netherlands)

    Fusi, M.; Maccallini, E.; Caruso, T.; Casari, C. S.; Bassi, A. Li; Bottani, C. E.; Rudolf, P.; Prince, K. C.; Agostino, R. G.

    2011-01-01

    Titanium oxide nanostructured thin films synthesized by pulsed laser deposition (PLD) were here characterized with a multi-technique approach to investigate the relation between surface electronic, structural and morphological properties. Depending on the growth parameters, these films present chara

  6. Electron correlation in two-photon double ionization of helium from attosecond to FEL pulses

    Energy Technology Data Exchange (ETDEWEB)

    Collins, Lee [Los Alamos National Laboratory

    2009-01-01

    We investigate the role of electron correlation in the two-photon double ionization of helium for ultrashort pulses in the extreme ultraviolet (XUV) regime with durations ranging from a hundred attoseconds to a few femtoseconds. We perform time-dependent ab initio calculations for pulses with mean frequencies in the so-called 'sequential' regime ({Dirac_h}{omega} > 54.4 eV). Electron correlation induced by the time correlation between emission events manifests itself in the angular distribution of the ejected electrons, which strongly depends on the energy sharing between them. We show that for ultrashort pulses two-photon double ionization probabilities scale non-uniformly with pulse duration depending on the energy sharing between the electrons. Most interestingly we find evidence for an interference between direct ('nonsequential') and indirect ('sequential') double photoionization with intermediate shake-up states, the strength of which is controlled by the pulse duration. This observation may provide a route towards measuring the pulse duration of x-ray free-electron laser (XFEL) pulses.

  7. Effect of electron emission on solids heating by femtosecond laser pulse

    Science.gov (United States)

    Svirina, V. V.; Sergaeva, O. N.; Yakovlev, E. B.

    2011-02-01

    Ultrashort laser pulse interaction with material involves a number of specialities as compared to longer irradiations. We study laser heating of metal by femtosecond pulse with taking into account electron photo- and thermionic emission leading to accumulation of a high positive charge on the target surface and, thus, to the generation of the electric field which causes Coulomb explosion (an electronic mechanism of ablation). Also emission slightly influences the thermal and optical properties of solids.

  8. Injection of electrons by colliding laser pulses in a laser wakefield accelerator

    Energy Technology Data Exchange (ETDEWEB)

    Hansson, M., E-mail: martin.hansson@fysik.lth.se; Aurand, B.; Ekerfelt, H.; Persson, A.; Lundh, O.

    2016-09-01

    To improve the stability and reproducibility of laser wakefield accelerators and to allow for future applications, controlling the injection of electrons is of great importance. This allows us to control the amount of charge in the beams of accelerated electrons and final energy of the electrons. Results are presented from a recent experiment on controlled injection using the scheme of colliding pulses and performed using the Lund multi-terawatt laser. Each laser pulse is split into two parts close to the interaction point. The main pulse is focused on a 2 mm diameter gas jet to drive a nonlinear plasma wave below threshold for self-trapping. The second pulse, containing only a fraction of the total laser energy, is focused to collide with the main pulse in the gas jet under an angle of 150°. Beams of accelerated electrons with low divergence and small energy spread are produced using this set-up. Control over the amount of accelerated charge is achieved by rotating the plane of polarization of the second pulse in relation to the main pulse. Furthermore, the peak energy of the electrons in the beams is controlled by moving the collision point along the optical axis of the main pulse, and thereby changing the acceleration length in the plasma. - Highlights: • Compact colliding pulse injection set-up used to produce low energy spread e-beams. • Beam charge controlled by rotating the polarization of injection pulse. • Peak energy controlled by point of collision to vary the acceleration length.

  9. On the response of electronic personal dosimeters in constant potential and pulsed X-ray beams

    Energy Technology Data Exchange (ETDEWEB)

    Guimaraes, Margarete C.; Silva, Teogenes; Silva, Claudete R.E., E-mail: margaretecristinag@gmail.com [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil); Oliveira, Paulo Marcio C. de [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Departamento de Anatomia e Imagem

    2015-07-01

    Electronic personal dosimeters (EPDs) based on solid state detectors have widely been used but some deficiencies in their response in pulsed radiation beams have been reported. Nowadays, there is not an international standard for pulsed X-ray beams for calibration or type testing of dosimeters. Irradiation conditions for testing the response of EPDs in both the constant potential and pulsed X-ray beams were established in CDTN. Three different types of EPDs were tested in different conditions in similar ISO and IEC X-ray qualities. Results stressed the need of performing additional checks before using EPDs in constant potential or pulsed X-rays. (author)

  10. On the response of electronic personal dosimeters in constant potential and pulsed x- ray beams

    Science.gov (United States)

    Guimarães, M. C.; Silva, C. R. E.; Oliveira, P. M. C.; da Silva, T. A.

    2016-07-01

    Electronic personal dosimeters (EPDs) based on solid state detectors have widely been used but some deficiencies in their response in pulsed radiation beams have been reported. Nowadays, there is not an international standard for pulsed x-ray beams for calibration or type testing of dosimeters. Irradiation conditions for testing the response of EPDs in both the constant potential and pulsed x-ray beams were established in CDTN. Three different types of EPDs were tested in different conditions in similar ISO and IEC x-ray qualities. Results stressed the need of performing additional checks before using EPDs in constant potential or pulsed x-rays.

  11. Intense ultrashort pulse generation using the JAERI far-infrared free electron laser

    CERN Document Server

    Nagai, R; Nishimori, N; Kikuzawa, N; Sawamura, M; Minehara, E J

    2002-01-01

    An intense ultrashort optical pulse has been quasi-continuously generated using a superconducting RF linac-based free-electron laser at a wavelength of 22.5 mu m. The pulse shape and width are measured by second-order optical autocorrelation with a birefringent Te crystal. At synchronism of the optical resonator, the pulse shape is a smooth single pulse with an FWHM width of 255 fs and energy of 74 mu J. A train of subpulses is developed by increasing the desynchronism of the optical resonator. The measured results are in good agreement with numerical simulation.

  12. Pulsed Electron Beam Spectroscopy for Temperature Measurements in Hypersonic Flows

    Science.gov (United States)

    2010-01-01

    as rotational-level dependent, so the proper modeling of k i can be important as temperature changes and if tem perature measurements based on the...through a hy drogen thyratron switch into the primary of a step-up transformer. A limited number of off-th e-shelf prod ucts perfor ming the function...of a thyratron drive for pulse switching were identifie d, but none met the specialize d power a nd switchin g wavefor m requirements of the pulsed

  13. Transient thermal and nonthermal electron and phonon relaxation after short-pulsed laser heating of metals

    Energy Technology Data Exchange (ETDEWEB)

    Giri, Ashutosh; Hopkins, Patrick E., E-mail: phopkins@virginia.edu [Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States)

    2015-12-07

    Several dynamic thermal and nonthermal scattering processes affect ultrafast heat transfer in metals after short-pulsed laser heating. Even with decades of measurements of electron-phonon relaxation, the role of thermal vs. nonthermal electron and phonon scattering on overall electron energy transfer to the phonons remains unclear. In this work, we derive an analytical expression for the electron-phonon coupling factor in a metal that includes contributions from equilibrium and nonequilibrium distributions of electrons. While the contribution from the nonthermal electrons to electron-phonon coupling is non-negligible, the increase in the electron relaxation rates with increasing laser fluence measured by thermoreflectance techniques cannot be accounted for by only considering electron-phonon relaxations. We conclude that electron-electron scattering along with electron-phonon scattering have to be considered simultaneously to correctly predict the transient nature of electron relaxation during and after short-pulsed heating of metals at elevated electron temperatures. Furthermore, for high electron temperature perturbations achieved at high absorbed laser fluences, we show good agreement between our model, which accounts for d-band excitations, and previous experimental data. Our model can be extended to other free electron metals with the knowledge of the density of states of electrons in the metals and considering electronic excitations from non-Fermi surface states.

  14. Transient thermal and nonthermal electron and phonon relaxation after short-pulsed laser heating of metals

    Science.gov (United States)

    Giri, Ashutosh; Hopkins, Patrick E.

    2015-12-01

    Several dynamic thermal and nonthermal scattering processes affect ultrafast heat transfer in metals after short-pulsed laser heating. Even with decades of measurements of electron-phonon relaxation, the role of thermal vs. nonthermal electron and phonon scattering on overall electron energy transfer to the phonons remains unclear. In this work, we derive an analytical expression for the electron-phonon coupling factor in a metal that includes contributions from equilibrium and nonequilibrium distributions of electrons. While the contribution from the nonthermal electrons to electron-phonon coupling is non-negligible, the increase in the electron relaxation rates with increasing laser fluence measured by thermoreflectance techniques cannot be accounted for by only considering electron-phonon relaxations. We conclude that electron-electron scattering along with electron-phonon scattering have to be considered simultaneously to correctly predict the transient nature of electron relaxation during and after short-pulsed heating of metals at elevated electron temperatures. Furthermore, for high electron temperature perturbations achieved at high absorbed laser fluences, we show good agreement between our model, which accounts for d-band excitations, and previous experimental data. Our model can be extended to other free electron metals with the knowledge of the density of states of electrons in the metals and considering electronic excitations from non-Fermi surface states.

  15. Role of electron-nuclear coupled dynamics on charge migration induced by attosecond pulses in glycine

    Science.gov (United States)

    Lara-Astiaso, Manuel; Palacios, Alicia; Decleva, Piero; Tavernelli, Ivano; Martín, Fernando

    2017-09-01

    We present a theoretical study of charge dynamics initiated by an attosecond XUV pulse in the glycine molecule, which consists in delocalized charge fluctuations all over the molecular skeleton. For this, we have explicitly used the actual electron wave packet created by such a broadband pulse. We show that, for the chosen pulse, charge dynamics in glycine is barely affected by nuclear motion or non adiabatic effects during the first 8 fs, and that the initial electronic coherences do not dissipate during the first 20 fs. In contrast, small variations in the initial nuclear positions, compatible with the geometries expected in the Franck-Condon region, lead to noticeable changes in this dynamics.

  16. Electron-Positron Pair Production in Structured Pulses of Electric Fields

    CERN Document Server

    Kohlfürst, Christian

    2012-01-01

    The non-perturbative electron-positron pair production in time-dependent electric fields is investigated. The quantum kinetic formalism is employed in order to calculate the electron density for various field configurations. The corresponding set of first order, ordinary differential equations is analyzed and numerically solved. The focus of this study lies on the dynamically assisted Schwinger effect in pulsed electric fields with at least two different time scales. Furthermore, interference effects arising in setups with multiple pulses are examined and first results for an optimization of the particle number yield by pulse-shaping are given.

  17. Wakefield evolution and electron acceleration in interaction of frequency-chirped laser pulse with inhomogeneous plasma

    Science.gov (United States)

    Rezaei-Pandari, M.; Niknam, A. R.; Massudi, R.; Jahangiri, F.; Hassaninejad, H.; Khorashadizadeh, S. M.

    2017-02-01

    The nonlinear interaction of an ultra-short intense frequency-chirped laser pulse with an underdense plasma is studied. The effects of plasma inhomogeneity and laser parameters such as chirp, pulse duration, and intensity on plasma density and wakefield evolutions, and electron acceleration are examined. It is found that a properly chirped laser pulse could induce a stronger laser wakefield in an inhomogeneous plasma and result in higher electron acceleration energy. It is also shown that the wakefield amplitude is enhanced by increasing the slope of density in the inhomogeneous plasma.

  18. Simulation of the relativistic electron dynamics and acceleration in a linearly-chirped laser pulse

    CERN Document Server

    Jisrawi, Najeh M; Salamin, Yousef I

    2014-01-01

    Theoretical investigations are presented, and their results are discussed, of the laser acceleration of a single electron by a chirped pulse. Fields of the pulse are modeled by simple plane-wave oscillations and a $\\cos^2$ envelope. The dynamics emerge from analytic and numerical solutions to the relativistic Lorentz-Newton equations of motion of the electron in the fields of the pulse. All simulations have been carried out by independent Mathematica and Python codes, with identical results. Configurations of acceleration from a position of rest as well as from injection, axially and sideways, at initial relativistic speeds are studied.

  19. Energy gain of an electron by a laser pulse in the presence of radiation reaction.

    Science.gov (United States)

    Lehmann, G; Spatschek, K H

    2011-10-01

    A well-known no-energy-gain theorem states that an electron cannot gain energy when being overrun by a plane (transverse) laser pulse of finite length. The theorem is based on symmetries which are broken when radiation reaction (RR) is included. It is shown here that an electron, e.g., being initially at rest, will gain a positive velocity component in the laser propagation direction after being overrun by an intense laser pulse (of finite duration and with intensity of order 5×10(22) W/cm(2) or larger). The velocity increment is due to RR effects. The latter are incorporated in the Landau-Lifshitz form. Both linear as well as circular polarization of the laser pulse are considered. It is demonstrated that the velocity gain is proportional to the pulse length and the square of the peak amplitude of the laser pulse. The results of numerical simulations are supported by analytical estimates.

  20. Electron paramagnetic resonance and optical spectroscopy of Yb sup 3 sup + ions in SrF sub 2 and BaF sub 2; an analysis of distortions of the crystal lattice near Yb sup 3 sup +

    CERN Document Server

    Falin, M L; Latypov, V A; Leushin, A M

    2003-01-01

    SrF sub 2 and BaF sub 2 crystals, doped with the Yb sup 3 sup + ions, have been investigated by electron paramagnetic resonance and optical spectroscopy. As-grown crystals of SrF sub 2 and BaF sub 2 show the two paramagnetic centres for the cubic (T sub c) and trigonal (T sub 4) symmetries of the Yb sup 3 sup + ions. Empirical diagrams of the energy levels were established and the potentials of the crystal field were determined. Information was obtained on the SrF sub 2 and BaF sub 2 phonon spectra from the electron-vibrational structure of the optical spectra. The crystal field parameters were used to analyse the crystal lattice distortions in the vicinity of the impurity ion and the F sup - ion compensating for the excess positive charge in T sub 4. Within the frames of a superposition model, it is shown that three F sup - ions from the nearest surrounding cube, located symmetrically with respect to the C sub 3 axis from the side of the ion-compensator, approach the impurity ion and cling to the axis of the...

  1. Pulse energy control through dual loop electronic feedback

    CSIR Research Space (South Africa)

    Jacobs, Cobus

    2006-07-01

    Full Text Available surgery • Better accuracy in laser-based scientific measurements Pulse Energy Control handptright Cobus Jacobs et al. head2righthead2rightPump/Gain • Duration & intensity of pump determine energy stored in laser medium barb2rightbarb2right Problem...

  2. Electron and phonon dynamics in laser short pulses-heated metals

    Science.gov (United States)

    Pietanza, L. D.; Colonna, G.; Capitelli, M.

    2005-07-01

    The simultaneous electron and phonon relaxation dynamic in a metal film subjected to a laser pulse has been theoretically investigated. A system of two coupled time- and energy-dependent Boltzmann equations describing the electron and phonon dynamics has been numerically solved. The collision processes considered are electron-electron (e-e) and electron-phonon (e-p) collisions. Our results show the non-equilibrium electron distribution and the electron and phonon relaxation dynamics both after a femtosecond and a picosecond laser perturbations.

  3. Multiple quasi-monoenergetic electron beams from laser-wakefield acceleration with spatially structured laser pulse

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Y.; Li, M. H.; Li, Y. F.; Wang, J. G.; Tao, M. Z.; Han, Y. J.; Zhao, J. R.; Huang, K.; Yan, W. C.; Ma, J. L.; Li, Y. T. [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100080 (China); Chen, L. M., E-mail: lmchen@iphy.ac.cn [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100080 (China); Department of Physics and Astronomy and IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240 (China); Li, D. Z. [Institute of High Energy Physics, CAS, Beijing 100049 (China); Chen, Z. Y. [Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, Sichuan 621999 (China); Sheng, Z. M. [Department of Physics and Astronomy and IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240 (China); Department of Physics, Scottish Universities Physics Alliance, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Zhang, J. [Department of Physics and Astronomy and IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240 (China)

    2015-08-15

    By adjusting the focus geometry of a spatially structured laser pulse, single, double, and treble quasi-monoenergetic electron beams were generated, respectively, in laser-wakefield acceleration. Single electron beam was produced as focusing the laser pulse to a single spot. While focusing the laser pulse to two spots that are approximately equal in energy and size and intense enough to form their own filaments, two electron beams were produced. Moreover, with a proper distance between those two focal spots, three electron beams emerged with a certain probability owing to the superposition of the diffractions of those two spots. The energy spectra of the multiple electron beams are quasi-monoenergetic, which are different from that of the large energy spread beams produced due to the longitudinal multiple-injection in the single bubble.

  4. Obtaining attosecond x-ray pulses using a self-amplified spontaneous emission free electron laser

    Directory of Open Access Journals (Sweden)

    A. A. Zholents

    2005-05-01

    Full Text Available We describe a technique for the generation of a solitary attosecond x-ray pulse in a free-electron laser (FEL, via a process of self-amplified spontaneous emission. In this method, electrons experience an energy modulation upon interacting with laser pulses having a duration of a few cycles within single-period wiggler magnets. Two consecutive modulation sections, followed by compression in a dispersive section, are used to obtain a single, subfemtosecond spike in the electron peak current. This region of the electron beam experiences an enhanced growth rate for FEL amplification. After propagation through a long undulator, this current spike emits a ∼250   attosecond x-ray pulse whose intensity dominates the x-ray emission from the rest of the electron bunch.

  5. Quantum Computing Using Pulse-Based Electron-Nuclear Double Resonance (endor):. Molecular Spin-Qubits

    Science.gov (United States)

    Sato, Kazuo; Nakazawa, Shigeki; Rahimi, Robabeh D.; Nishida, Shinsuke; Ise, Tomoaki; Shimoi, Daisuke; Toyota, Kazuo; Morita, Yasushi; Kitagawa, Masahiro; Carl, Parick; Höfner, Peter; Takui, Takeji

    2009-06-01

    Electrons with the spin quantum number 1/2, as physical qubits, have naturally been anticipated for implementing quantum computing and information processing (QC/QIP). Recently, electron spin-qubit systems in organic molecular frames have emerged as a hybrid spin-qubit system along with a nuclear spin-1/2 qubit. Among promising candidates for QC/QIP from the materials science side, the reasons for why electron spin-qubits such as molecular spin systems, i.e., unpaired electron spins in molecular frames, have potentialities for serving for QC/QIP will be given in the lecture (Chapter), emphasizing what their advantages or disadvantages are entertained and what technical and intrinsic issues should be dealt with for the implementation of molecular-spin quantum computers in terms of currently available spin manipulation technology such as pulse-based electron-nuclear double resonance (pulsed or pulse ENDOR) devoted to QC/QIP. Firstly, a general introduction and introductory remarks to pulsed ENDOR spectroscopy as electron-nuclear spin manipulation technology is given. Super dense coding (SDC) experiments by the use of pulsed ENDOR are also introduced to understand differentiating QC ENDOR from QC NMR based on modern nuclear spin technology. Direct observation of the spinor inherent in an electron spin, detected for the first time, will be shown in connection with the entanglement of an electron-nuclear hybrid system. Novel microwave spin manipulation technology enabling us to deal with genuine electron-electron spin-qubit systems in the molecular frame will be introduced, illustrating, from the synthetic strategy of matter spin-qubits, a key-role of the molecular design of g-tensor/hyperfine-(A-)tensor molecular engineering for QC/QIP. Finally, important technological achievements of recently-emerging CD ELDOR (Coherent-Dual ELectron-electron DOuble Resonance) spin technology enabling us to manipulate electron spin-qubits are described.

  6. Intense terahertz pulses from SLAC electron beams using coherent transition radiation.

    Science.gov (United States)

    Wu, Ziran; Fisher, Alan S; Goodfellow, John; Fuchs, Matthias; Daranciang, Dan; Hogan, Mark; Loos, Henrik; Lindenberg, Aaron

    2013-02-01

    SLAC has two electron accelerators, the Linac Coherent Light Source (LCLS) and the Facility for Advanced Accelerator Experimental Tests (FACET), providing high-charge, high-peak-current, femtosecond electron bunches. These characteristics are ideal for generating intense broadband terahertz (THz) pulses via coherent transition radiation. For LCLS and FACET respectively, the THz pulse duration is typically 20 and 80 fs RMS and can be tuned via the electron bunch duration; emission spectra span 3-30 THz and 0.5 THz-5 THz; and the energy in a quasi-half-cycle THz pulse is 0.2 and 0.6 mJ. The peak electric field at a THz focus has reached 4.4 GV/m (0.44 V/Å) at LCLS. This paper presents measurements of the terahertz pulses and preliminary observations of nonlinear materials response.

  7. Magnetic resonance force microscopy with a paramagnetic probe

    Science.gov (United States)

    Berman, G. P.; Gorshkov, V. N.; Tsifrinovich, V. I.

    2017-04-01

    We consider theoretically extension of magnetic resonance force microscopy (MRFM) replacing a ferromagnetic probe on a cantilever tip (CT) with a paramagnetic one (PMRFM). The dynamics of the interaction between the paramagnetic probe and a local magnetic moment in a sample is analyzed, using a quasi-classical approach. We show that the application of a proper sequence of electromagnetic pulses provides a significant deflection of the CT from the initial equilibrium position. Periodic application of these sequences of pulses results in quasi-periodic CT deflections from the equilibrium, which can be used for detection of the magnetic moment in a sample.

  8. Electron Acceleration by a Focused Gaussian Laser Pulse in Vacuum

    Institute of Scientific and Technical Information of China (English)

    何峰; 余玮; 陆培祥; 徐涵

    2004-01-01

    By numerically solving the relativistic equations of motion of a single electron in laser fields modeled by a Gaussian laser beam, we get the trajectory and energy of the electron. When the drifting distance is comparable to or even longer than the corresponding Rayleigh length, the evolution of the beam waist cannot be neglected. The asymmetry of intensity in acceleration and deceleration leads to the conclusion that the electron can be accelerated effectively and extracted by the longitudinal ponderomotive force. For intensities above, an electron's energy gain about MeV can be realized, and the energetic electron is parallel with the propagation axis.

  9. Laser Activated Streak Camera for Measurement of Electron Pulses with Femtosecond Resolution

    Science.gov (United States)

    Zandi, Omid; Desimone, Alice; Wilkin, Kyle; Yang, Jie; Centurion, Martin

    2015-05-01

    The duration of femtosecond electron pulses used in time-resolved diffraction and microscopy experiments is challenging to measure in-situ. To overcome this problem, we have fabricated a streak camera that uses the time-varying electric field of a discharging parallel plate capacitor. The capacitor is discharged using a laser-activated GaAs photoswitch, resulting in a damped oscillation of the electric field. The delay time between the laser pulse and electron pulse is set so that the front and back halves of the bunch encounter opposite electric fields of the capacitor and are deflected in opposite directions. Thus, the electron bunch appears streaked on the detector with a length proportional to its duration. The temporal resolution of the streak camera is proportional to the maximum value of the electric field and the frequency of the discharge oscillation. The capacitor is charged by high voltage short pulses to achieve a high electric field and prevent breakdown. We have achieved an oscillation frequency in the GHz range by reducing the circuit size and hence its inductance. The camera was used to measure 100 keV electron pulses with up to a million electrons that are compressed transversely by magnetic lenses and longitudinally by an RF cavity. This work was supported mainly by the Air Force Office of Scientific Research, Ultrashort Pulse Laser Matter Interaction program, under grant # FA9550-12-1-0149.

  10. Global Remote Sensing of Precipitating Electron Energies: A Comparison of Substorms and Pressure Pulse Related Intensifications

    Science.gov (United States)

    Chua, D.; Parks, G. K.; Brittnacher, M. J.; Germany, G. A.; Spann, J. F.

    2000-01-01

    The Polar Ultraviolet Imager (UVI) observes aurora responses to incident solar wind pressure pulses and interplanetary shocks such its those associated with coronal mass ejections. Previous observations have demonstrated that the arrival of it pressure pulse at the front of the magnetosphere results in highly disturbed geomagnetic conditions and a substantial increase in both dayside and nightside aurora precipitations. Our observations show it simultaneous brightening over bread areas of the dayside and nightside auroral in response to a pressure pulse, indicating that more magnetospheric regions participate as sources for auroral precipitation than during isolate substorm. We estimate the characteristic energies of incident auroral electrons using Polar UVI images and compare the precipitation energies during pressure pulse associated event to those during isolated substorms. We estimate the characteristic energies of incident auroral electrons using Polar UVI images and compare the precipitation energies during pressure pulse associated events to those during isolated auroral substorms. Electron precipitation during substorms has characteristic energies greater than 10 KeV and is structured both in local time and in magnetic latitude. For auroral intensifications following the arrival of'a pressure pulse or interplanetary shock. Electron precipitation is less spatially structured and has greater flux of lower characteristic energy electrons (Echar less than 7 KeV) than during isolated substorm onsets. These observations quantify the differences between global and local auroral precipitation processes and will provide a valuable experimental check for models of sudden storm commencements and magnetospheric response to perturbations in the solar wind.

  11. On Cu(II) Cu(II) distance measurements using pulsed electron electron double resonance

    Science.gov (United States)

    Yang, Zhongyu; Becker, James; Saxena, Sunil

    2007-10-01

    The effects of orientational selectivity on the 4-pulse electron electron double resonance (PELDOR) ESR spectra of coupled Cu(II)-Cu(II) spins are presented. The data were collected at four magnetic fields on a poly-proline peptide containing two Cu(II) centers. The Cu(II)-PELDOR spectra of this peptide do not change appreciably with magnetic field at X-band. The data were analyzed by adapting the theory of Maryasov, Tsvetkov, and Raap [A.G. Maryasov, Y.D. Tsvetkov, J. Raap, Weakly coupled radical pairs in solids:ELDOR in ESE structure studies, Appl. Magn. Reson. 14 (1998) 101-113]. Simulations indicate that orientational effects are important for Cu(II)-PELDOR. Based on simulations, the field-independence of the PELDOR data for this peptide is likely due to two effects. First, for this peptide, the Cu(II) g-tensor(s) are in a very specific orientation with respect to the interspin vector. Second, the flexibility of the peptide washes out the orientation effects. These effects reduce the suitability of the poly-proline based peptide as a good model system to experimentally probe orientational effects in such experiments. An average Cu(II)-Cu(II) distance of 2.1-2.2 nm was determined, which is consistent with earlier double quantum coherence ESR results.

  12. Pulse

    Science.gov (United States)

    ... resting for at least 10 minutes. Take the exercise heart rate while you are exercising. ... pulse rate can help determine if the person's heart is pumping. Pulse ... rate gives information about your fitness level and health.

  13. Electron - nuclear recoil discrimination by pulse shape analysis

    CERN Document Server

    Elbs, J; Collin, E; Godfrin, H; Suvorova, O

    2007-01-01

    In the framework of the ``ULTIMA'' project, we use ultra cold superfluid 3He bolometers for the direct detection of single particle events, aimed for a future use as a dark matter detector. One parameter of the pulse shape observed after such an event is the thermalization time constant. Until now it was believed that this parameter only depends on geometrical factors and superfluid 3He properties, and that it is independent of the nature of the incident particles. In this report we show new results which demonstrate that a difference for muon- and neutron events, as well as events simulated by heater pulses exist. The possibility to use this difference for event discrimination in a future dark matter detector will be discussed.

  14. Chirped pulse amplification in an extreme-ultraviolet free-electron laser

    Science.gov (United States)

    Gauthier, David; Allaria, Enrico; Coreno, Marcello; Cudin, Ivan; Dacasa, Hugo; Danailov, Miltcho Boyanov; Demidovich, Alexander; di Mitri, Simone; Diviacco, Bruno; Ferrari, Eugenio; Finetti, Paola; Frassetto, Fabio; Garzella, David; Künzel, Swen; Leroux, Vincent; Mahieu, Benoît; Mahne, Nicola; Meyer, Michael; Mazza, Tommaso; Miotti, Paolo; Penco, Giuseppe; Raimondi, Lorenzo; Ribič, Primož Rebernik; Richter, Robert; Roussel, Eléonore; Schulz, Sebastian; Sturari, Luca; Svetina, Cristian; Trovò, Mauro; Walker, Paul Andreas; Zangrando, Marco; Callegari, Carlo; Fajardo, Marta; Poletto, Luca; Zeitoun, Philippe; Giannessi, Luca; de Ninno, Giovanni

    2016-12-01

    Chirped pulse amplification in optical lasers is a revolutionary technique, which allows the generation of extremely powerful femtosecond pulses in the infrared and visible spectral ranges. Such pulses are nowadays an indispensable tool for a myriad of applications, both in fundamental and applied research. In recent years, a strong need emerged for light sources producing ultra-short and intense laser-like X-ray pulses, to be used for experiments in a variety of disciplines, ranging from physics and chemistry to biology and material sciences. This demand was satisfied by the advent of short-wavelength free-electron lasers. However, for any given free-electron laser setup, a limit presently exists in the generation of ultra-short pulses carrying substantial energy. Here we present the experimental implementation of chirped pulse amplification on a seeded free-electron laser in the extreme-ultraviolet, paving the way to the generation of fully coherent sub-femtosecond gigawatt pulses in the water window (2.3-4.4 nm).

  15. Chirped pulse amplification in an extreme-ultraviolet free-electron laser.

    Science.gov (United States)

    Gauthier, David; Allaria, Enrico; Coreno, Marcello; Cudin, Ivan; Dacasa, Hugo; Danailov, Miltcho Boyanov; Demidovich, Alexander; Di Mitri, Simone; Diviacco, Bruno; Ferrari, Eugenio; Finetti, Paola; Frassetto, Fabio; Garzella, David; Künzel, Swen; Leroux, Vincent; Mahieu, Benoît; Mahne, Nicola; Meyer, Michael; Mazza, Tommaso; Miotti, Paolo; Penco, Giuseppe; Raimondi, Lorenzo; Ribič, Primož Rebernik; Richter, Robert; Roussel, Eléonore; Schulz, Sebastian; Sturari, Luca; Svetina, Cristian; Trovò, Mauro; Walker, Paul Andreas; Zangrando, Marco; Callegari, Carlo; Fajardo, Marta; Poletto, Luca; Zeitoun, Philippe; Giannessi, Luca; De Ninno, Giovanni

    2016-12-01

    Chirped pulse amplification in optical lasers is a revolutionary technique, which allows the generation of extremely powerful femtosecond pulses in the infrared and visible spectral ranges. Such pulses are nowadays an indispensable tool for a myriad of applications, both in fundamental and applied research. In recent years, a strong need emerged for light sources producing ultra-short and intense laser-like X-ray pulses, to be used for experiments in a variety of disciplines, ranging from physics and chemistry to biology and material sciences. This demand was satisfied by the advent of short-wavelength free-electron lasers. However, for any given free-electron laser setup, a limit presently exists in the generation of ultra-short pulses carrying substantial energy. Here we present the experimental implementation of chirped pulse amplification on a seeded free-electron laser in the extreme-ultraviolet, paving the way to the generation of fully coherent sub-femtosecond gigawatt pulses in the water window (2.3-4.4 nm).

  16. Low-field theory of nuclear spin relaxation in paramagnetic low-symmetry complexes for electron spin systems of S = 1, 3/2, 2, 5/2, 3 and 7/2

    Science.gov (United States)

    Nilsson, T.; Kowalewski, J.

    A low-field theory of nuclear spin relaxation in paramagnetic systems is developed, resulting in closed analytical expressions. We use the same approach as Westlund, who derived the lowfield expression in the case of S = 1 for a rhombic static zero-field splitting (ZFS). In the present paper we extend the derivation to include S = 3/2, 2, 5/2, 3 and 7/2 for the case of an axial static ZFS, whereas only S = 3/2 is considered for a rhombic static ZFS. The slowmotion theory of nuclear spin relaxation in paramagnetic systems was recently generalized to account for arbitrary electron spin S and the calculations showed some unexpected features. Thus, one objective of the derivation of closed analytical low-field expressions is to provide a framework for physical explanation of slow-motion calculations. We find that the results of the low-field theory are, indeed, in good agreement with the slow-motion calculations in the case of slowly rotating complexes (e.g. metalloproteins). It is evident that the static ZFS influences the electron spin relaxation more markedly for higher spin systems than for S = 1. In fact, systems of S = 2 and S = 3 show more similarities in the electron spin-lattice relaxation properties to half-integer spin systems than to S = 1 in the case of an axially symmetric static ZFS. These findings show the shortcomings of using Bloembergen-Morgan theory for the description of electron spin relaxation in the low-field limit and provide improved tools for the interpretation of experimental variable-field relaxation data.

  17. Photon-echo spectroscopy of the hydrated electron with 5-fs pulses

    NARCIS (Netherlands)

    Pshenichnikov, MS; Baltuska, A; Emde, MF; Wiersma, DA; Elsaesser, T; Mukamel, S; Murnane, MM; Scherer, NF

    2001-01-01

    Employing photon-echo techniques with extremely short laser pulses that consist of only few optical cycles, we investigate the dynamics of the equilibrated hydrated electron. The pure dephasing time of the hydrated electron deduced from the measurements is similar to1.6 fs. The shape of the absorpti

  18. Instantaneous nonvertical electronic transitions with shaped femtosecond laser pulses: Is it possible?

    DEFF Research Database (Denmark)

    Henriksen, Niels Engholm; Møller, Klaus Braagaard

    2003-01-01

    In molecular electronic transitions, a vertical transition can be induced by an ultrashort laser pulse. That is, a replica of the initial nuclear state-times the transition dipole moment of the electronic transition-can be created instantaneously (on the time scale of nuclear motion) in the excited...

  19. Quantum computers based on electron spins controlled by ultrafast off-resonant single optical pulses.

    Science.gov (United States)

    Clark, Susan M; Fu, Kai-Mei C; Ladd, Thaddeus D; Yamamoto, Yoshihisa

    2007-07-27

    We describe a fast quantum computer based on optically controlled electron spins in charged quantum dots that are coupled to microcavities. This scheme uses broadband optical pulses to rotate electron spins and provide the clock signal to the system. Nonlocal two-qubit gates are performed by phase shifts induced by electron spins on laser pulses propagating along a shared waveguide. Numerical simulations of this scheme demonstrate high-fidelity single-qubit and two-qubit gates with operation times comparable to the inverse Zeeman frequency.

  20. Radiation Reaction Effects in Cascade Scattering of Intense, Tightly Focused Laser Pulses by Relativistic Electrons

    CERN Document Server

    Zhidkov, A; Bulanov, S S; Hosokai, T; Koga, J; Kodama, R

    2013-01-01

    Non-linear cascade scattering of intense, tightly focused laser pulses by relativistic electrons is studied numerically in the classical approximation including the radiation damping for the quantum parameter hwx-ray/E<1 and an arbitrary radiation parameter Kai. The electron energy loss, along with its side scattering by the ponderomotive force, makes the scattering in the vicinity of high laser field nearly impossible at high electron energies. The use of a second, co-propagating laser pulse as a booster is shown to solve this problem.

  1. Energy-spread measurement of triple-pulse electron beams based on the magnetic dispersion principle

    CERN Document Server

    Wang, Yi; Yang, Zhiyong; Zhang, Huang; Ding, Hengsong; Yang, Anmin; Wang, Minhong

    2016-01-01

    The energy-spread of the triple-pulse electron beam generated by the Dragon-II linear induction accelerator is measured using the method of energy dispersion in the magnetic field. A sector magnet is applied for energy analyzing of the electron beam, which has a bending radius of 300 mm and a deflection angle of 90 degrees. For each pulse, both the time-resolved and the integral images of the electron position at the output port of the bending beam line are recorded by a streak camera and a CCD camera, respectively. Experimental results demonstrate an energy-spread of less than +-2.0% for the electron pulses. The cavity voltage waveforms obtained by different detectors are also analyzed for comparison.

  2. Investigating Pulsed Discharge Polarity Employing Solid-State Pulsed Power Electronics

    DEFF Research Database (Denmark)

    Davari, Pooya; Zare, Firuz; Blaabjerg, Frede

    2015-01-01

    . In this paper, effects of applied voltage polarity on plasma discharge have been investigated in different mediums at atmospheric pressure. The experiments have been conducted based on high voltage DC power supply and high voltage pulse generator for point-to-point and point-to-plane geometries. Furthermore......, the influence of electric field distribution is analyzed using Finite Element simulations for the employed geometries and mediums. The experimental and simulation results have verified the important role of the applied voltage polarity, employed geometry and medium of the system on plasma generation....... condition plays an important role in maintaining the desired performance. Investigating the system parameters contributed to the generated pulses is an effective way in improving the system performance further ahead. One of these parameters is discharge polarity which has received less attention...

  3. Electron paramagnetic resonance study of alinement induced by magnetic fields in two smectic-A liquid crystals not exhibiting nematic phases

    Science.gov (United States)

    Fryburg, G. C.; Gelerinter, E.

    1972-01-01

    Using vanadyl acetylacetonate (VAAC) as a paramagnetic probe, the molecular ordering in two smectic-A liquid crystals that do not display nematic phases were studied. Reproducible alinement was attained by slow cooling throughout the isotropic smectic-A transition in dc magnetic fields of 1.1 and 2.15 teslas. The degree of order attained is small for a smectic-A liquid crystal. Measurements were made of the variation of the average hyperfine splitting of the alined samples as a function of orientation relative to the dc magnetic field of the spectrometer. This functional dependence is in agreement with the theoretical prediction except where the viscosity of the liquid crystal becomes large enough to slow the tumbling of the VAAC, as indicated by asymmetry in the end lines of the spectrum.

  4. Detection of the magnetic and electric transitions by electron paramagnetic resonance and low-field microwave absorption in the magnetoelectric Pb(Fe{sub 0.5}Ta{sub 0.5})O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Alvarez, G., E-mail: memodin@yahoo.co [Departamento de Fisica, ESFM-IPN, U.P. Adolfo Lopez Mateos Edificio 9, Av. Instituto Politecnico Nacional S/N, San Pedro Zacatenco, Mexico DF 07738 (Mexico); Montiel, H. [Departamento de Tecnociencias, Centro de Ciencias Aplicadas y Desarrollo Tecnologico de la Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, Mexico DF 04510 (Mexico); Pena, J.A.; Castellanos, M.A. [Facultad de Quimica, Universidad Nacional Autonoma de Mexico, Cd. Universitaria, Mexico DF 04510 (Mexico); Zamorano, R. [Departamento de Fisica, ESFM-IPN, U.P. Adolfo Lopez Mateos Edificio 9, Av. Instituto Politecnico Nacional S/N, San Pedro Zacatenco, Mexico DF 07738 (Mexico)

    2010-10-22

    Graphical abstract: Display Omitted Research highlights: {yields} LFMA spectra showed straight lines with positive slope and non-hysteretic traces. {yields} The spectral changes for the plot of the slope vs. temperature give evidence of magnetic and electric orderings, with a very high detection sensibility. - Abstract: An electron paramagnetic resonance (EPR) study of Pb(Fe{sub 0.5}Ta{sub 0.5})O{sub 3} powder samples in perovskite-type structure at X-band (8.8-9.8 GHz), in the 120-300 K temperature range, is presented. For all the temperatures, the EPR spectra show a single broad line attributable to Fe{sup 3+} ions. The onset of the ferro-paraelectric and antiferro-paramagnetic transitions has been determined from the temperature dependence of parameters deduced from the EPR spectra: the peak-to-peak linewidth ({Delta}H{sub pp}), the resonance field (H{sub res}) and the integrated intensity (I{sub EPR}). Low-field microwave absorption (LFMA) is used to give further knowledge on this material; where this technique also gives evidence of the magnetic and electric orders.

  5. One-electron oxidations of ferrocenes: a pulse radiolysis study

    Energy Technology Data Exchange (ETDEWEB)

    Faraggi, Moshe; Weinraub, Dany; Broitman, Federico; DeFelippis, M.R.; Klapper, M.H.

    1988-01-01

    Using the pulse radiolysis technique we have studied the oxidation by various inorganic radicals of four water soluble ferrocene derivatives, hydroxyethyl, dimethylaminomethyl, monocarboxylic acid and dicarboxylic acid. We report the second order rate constants for these reactions, the stabilities and spectral properties of the ferrocinium products, and the electrochemically determined ferrocinium/ferrocene redox potentials. We also present preliminary estimates of tyrosine and tryptophan radical redox potentials obtained with the dicarboxylic acid ferrocene derivative as reference, and we discuss the relationship between redox potential differences and the reactivities of the ferrocenes with the inorganic radicals.

  6. One-electron oxidations of ferrocenes: A pulse radiolysis study

    Science.gov (United States)

    Faraggi, Moshe; Weinraub, Dany; Broitman, Federico; DeFelippis, Michael R.; Klapper, Michael H.

    Using the pulse radiolysis technique we have studied the oxidation by various inorganic radicals of four water soluble ferrocene derivatives, hydroxyethyl, dimethylaminomethyl, monocarboxylic acid and dicarboxylic acid. We report the second order rate constants for these reactions, the stabilities and spectral properties of the ferrocinium products, and the electrochemically determined ferrocinium/ferrocene redox potentials. We also present preliminary estimates of tyrosine and tryptophan radical redox potentials obtained with the dicarboxylic acid ferrocene derivative as reference, and we discuss the relationship between redox potential differences and the reactivities of the ferrocenes with the inorganic radicals.

  7. Double ionization effect in electron accelerations by high-intensity laser pulse interaction with a neutral gas

    Science.gov (United States)

    Nandan Gupta, Devki

    2013-11-01

    We study the effect of laser-induced double-ionization of a helium gas (with inhomogeneous density profile) on vacuum electron acceleration. For enough laser intensity, helium gas can be found doubly ionized and it strengthens the divergence of the pulse. The double ionization of helium gas can defocus the laser pulse significantly, and electrons are accelerated by the front of the laser pulse in vacuum and then decelerated by the defocused trail part of the laser pulse. It is observed that the electrons experience a very low laser-intensity at the trailing part of the laser pulse. Hence, there is not much electron deceleration at the trailing part of the pulse. We found that the inhomogeneity of the neutral gas reduced the rate of tunnel ionization causing less defocusing of the laser pulse and thus the electron energy gain is reduced.

  8. Double ionization effect in electron accelerations by high-intensity laser pulse interaction with a neutral gas

    Directory of Open Access Journals (Sweden)

    Gupta Devki Nandan

    2013-11-01

    Full Text Available We study the effect of laser-induced double-ionization of a helium gas (with inhomogeneous density profile on vacuum electron acceleration. For enough laser intensity, helium gas can be found doubly ionized and it strengthens the divergence of the pulse. The double ionization of helium gas can defocus the laser pulse significantly, and electrons are accelerated by the front of the laser pulse in vacuum and then decelerated by the defocused trail part of the laser pulse. It is observed that the electrons experience a very low laser-intensity at the trailing part of the laser pulse. Hence, there is not much electron deceleration at the trailing part of the pulse. We found that the inhomogeneity of the neutral gas reduced the rate of tunnel ionization causing less defocusing of the laser pulse and thus the electron energy gain is reduced.

  9. Electromagnetic cascade in high energy electron, positron, and photon interactions with intense laser pulses

    CERN Document Server

    Bulanov, S S; Esarey, E; Leemans, W P

    2013-01-01

    The interaction of high energy electrons, positrons, and photons with intense laser pulses is studied in head-on collision geometry. It is shown that electrons and/or positrons undergo a cascade-type process involving multiple emissions of photons. These photons can consequently convert into electron-positron pairs. As a result charged particles quickly lose their energy developing an exponentially decaying energy distribution, which suppresses the emission of high energy photons, thus reducing the number of electron-positron pairs being generated. Therefore, this type of interaction suppresses the development of the electromagnetic avalanche-type discharge, i.e., the exponential growth of the number of electrons, positrons, and photons does not occur in the course of interaction. The suppression will occur when 3D effects can be neglected in the transverse particle orbits, i.e., for sufficiently broad laser pulses with intensities that are not too extreme. The final distributions of electrons, positrons, and...

  10. Ultrashort x-ray pulse generation by electron beam slicing in storage rings

    Directory of Open Access Journals (Sweden)

    A. He

    2014-04-01

    Full Text Available We propose a new method to generate ultrashort x-ray pulses using focused short low energy (∼20  MeV electron bunches to create short slices of electrons from the circulating electron bunches in a synchrotron radiation storage ring. When a low energy electron bunch crosses from the top of a high energy storage ring electron bunch, its Coulomb force will kick a short slice from the core of the storage ring electron bunch. The separated slices, when passing through an undulator, will radiate ultrashort x-ray pulses at about 160 fs. We discuss the advantages, challenges, and provide data which confirm the feasibility of this new method.

  11. Electron-lattice kinetics of metals heated by ultrashort laser pulses

    Science.gov (United States)

    Falkovsky, L. A.; Mishchenko, E. G.

    1999-01-01

    We propose a kinetic model of transient nonequilibrium phenomena in metals exposed to ultrashort laser pulses when heated electrons affect the lattice through direct electron-phonon interaction. This model describes the destruction of a metal under intense laser pumping. We derive the system of equations for the metal, which consists of hot electrons and a cold lattice. Hot electrons are described with the help of the Boltzmann equation and equation of thermoconductivity. We use the equations of motion for lattice displacements with the electron force included. The lattice deformation is estimated immediately after the laser pulse up to the time of electron temperature relaxation. An estimate shows that the ablation regime can be achieved.

  12. Spectrum of fast electrons in a dense gas in the presence of a nonuniform pulsed field

    Science.gov (United States)

    Tkachev, A. N.; Yakovlenko, S. I.

    2007-01-01

    The problems of gas preionization in discharges related to laser physics are considered. The propagation of fast electrons injected from the cathode in the presence of a nonuniform nonstationary field and the motion of multiplying electrons at the edge of the avalanche in the presence of a nonuniform nonstationary field are simulated. The effect of the voltage pulse steepness and the field nonuniformity on the mean propagation velocity of fast electrons and their energy distribution is demonstrated. At certain combinations of the voltage pulse rise time and amplitude and at a certain time interval, the center of gravity of the electron cloud can move in the opposite direction relative to the direction of force acting upon electrons. It is also demonstrated that the number of hard particles (and, hence, the hard component of the x-ray bremsstrahlung) increases with both an increase in the voltage amplitude and a decrease in the pulse rise time. For nonoptimal conditions of the picosecond voltage pulse, an assumption is formulated: an electron beam in gas is formed due to the electrons at the edge of the avalanche rather than the background multiplication wave approaching the anode.

  13. Spectro-temporal shaping of seeded free-electron laser pulses

    CERN Document Server

    Gauthier, David; De Ninno, Giovanni; Allaria, Enrico; Cinquegrana, Paolo; Danailov, Miltcho Boyanov; Demidovich, Alexander; Ferrari, Eugenio; Giannessi, Luca; Mahieu, Benoît; Penco, Giuseppe

    2015-01-01

    We demonstrate the ability to control and shape the spectro-temporal content of extreme-ultraviolet (XUV) pulses produced by a seeded free-electron laser (FEL). The control over the spectro-temporal properties of XUV light was achieved by precisely manipulating the linear frequency chirp of the seed laser. Our results agree with existing theory, which allows retrieving the temporal properties (amplitude and phase) of the FEL pulse from measurements of the spectra as a function of the FEL operating parameters. Furthermore, we show the first direct evidence of the full temporal coherence of FEL light and generate Fourier limited pulses by fine-tuning the FEL temporal phase. The possibility to tailor the spectro-temporal content of intense short-wavelength pulses represents the first step towards efficient nonlinear optics in the XUV to X-ray spectral region and will enable precise manipulation of core-electron excitations using the methods of coherent quantum control.

  14. Multichannel computerized control system of current pulses in LIU-30 electron accelerator

    CERN Document Server

    Gerasimov, A I; Kulgavchuk, V V; Pluzhnikov, A V

    2002-01-01

    In LIU-30 power linear pulsed induction electron accelerator (40 MeV, 10 kA, 25 ns) 288 radial lines with water insulation serve as energy accumulators and shapers of accelerating voltage pulses. The lines are charged simultaneously up to 500 kV using a system comprising 72 Arkadiev-Marx screened generators. To control parameter of synchronous pulses of charging current with up to 60 kA amplitude and 0.85 mu s duration in every of 72 charging circuits one applies a computer-aided system. Current pulse is recorded at output of every generator using the Rogowski coil signal from which via a cable line is transmitted to an analog-digital converter, is processed with 50 ns sampling and is recorded to a memory unit. Upon actuation of accelerator the signals are sequentially or selectively displayed and are compared with pulse typical shape

  15. Half-period optical pulse generation using a free-electron laser

    Energy Technology Data Exchange (ETDEWEB)

    Jaroszynski, D.A.; Chaix, P.; Piovella, N. [Commissariat a l`Energie Atomique, Bruycres-le-Chatel (France)

    1995-12-31

    Recently there has been growth, in interest in non-equilibrium interaction of half-period long optical pulses with matter. To date the optical pulses have been produced by chopping out a half-period long segment from a longer pulse using a semiconductor switch driven by a femtosecond laser. In this paper we present new methods for producing tunable ultra-short optical pulses as short as half an optical period using a free-electron laser driven by electron bunches with a duration a fraction of an optical period. Two different methods relying on the production of coherent spontaneous emission will be described. In the first method we show that when a train of ultra-short optical pulses as short as one half period. We present calculations which show that the small signal gain is unimportant in the early stages of radiation build up in the cavity when the startup process is dominated by coherent spontaneous emission. To support our proposed method we present encouraging experimental results from the FELIX experiment in the Netherlands which show that interference effects between the coherent spontaneous optical pulses at start-up are very important. The second proposed method relies on the fact that coherent spontaneous emission mimics the undulations of electrons as they pass through the undulator. We show that ultra-short optical pulses are produced by coherent spontaneous emission when ultra-short electron bunches pass through an ultra-short undulator. We discuss the interesting case of such undulator radiation in the presence of an optical cavity and show that the optical pulse can be {open_quotes}taylored{close_quotes} by simply adjusting the optical cavity desynchronism. The proposed methods may be realisable using existing rf driven FELs in the far-infrared.

  16. Electron Dynamics During High-Power, Short-Pulsed Laser Interactions with Solids and Interfaces

    Science.gov (United States)

    2016-06-28

    PAPER ALSO RECEIVED EXTERNAL MEDIA COVERENCE FROM SIGNAL MAGAZINE : http://www.afcea.org/content/?q=Article-scientists-harness- energy -heat Edited...AFRL-AFOSR-VA-TR-2016-0234 Electron Dynamics During High- Power , Short-Pulsed Laser Interactions with Solids and Interfaces Patrick Hopkins...Dynamics During High- Power , Short-Pulsed Laser Interactions with Solids and Interfaces 5a. CONTRACT NUMBER FA9550-13-1-0067 5b. GRANT NUMBER 5c

  17. Damage threshold and focusability of mid-infrared free-electron laser pulses gated by a plasma mirror with nanosecond switching pulses

    CERN Document Server

    Wang, Xiaolong; Zen, Heishun; Kii, Toshiteru; Ohgaki, Hideaki

    2013-01-01

    The presence of a pulse train structure of an oscillator-type free-electron laser (FEL) results in the immediate damage of a solid target upon focusing. We demonstrate that the laser-induced damage threshold can be significantly improved by gating the mid-infrared (MIR) FEL pulses with a plasma mirror. Although the switching pulses we employ have a nanosecond duration which does not guarantee the clean wavefront of the gated FEL pulses, the high focusablity is experimentally confirmed through the observation of spectral broadening by a factor of 2.1 when we tightly focus the gated FEL pulses onto the Ge plate.

  18. Solid-state pulsed microwave bridge for electron spin echo spectrometers of 8-mm wavelength range

    Directory of Open Access Journals (Sweden)

    Kalabukhova E. N.

    2012-12-01

    Full Text Available The article presents a construction of a coherent pulsed microwave bridge with an output power up to 10 Wt with a time resolution of 10–8 seconds at a pulse repetition rate of 1 kHz designed for electron spin echo spectrometers. The bridge is built on a homodyne scheme based on IMPATT diodes, which are used for modulation and amplification of microwave power coming from the reference Gunn diode oscillator. The advantages of the bridge are optimal power and minimum pulse width, simple operation, low cost.

  19. Production and application of pulsed slow-positron beam using an electron LINAC

    Energy Technology Data Exchange (ETDEWEB)

    Yamazaki, Tetsuo; Suzuki, Ryoichi; Ohdaira, Toshiyuki; Mikado, Tomohisa [Electrotechnical Lab., Tsukuba, Ibaraki (Japan); Kobayashi, Yoshinori

    1997-03-01

    Slow-positron beam is quite useful for non-destructive material research. At the Electrotechnical Laboratory (ETL), an intense slow positron beam line by exploiting an electron linac has been constructed in order to carry out various experiments on material analysis. The beam line can generates pulsed positron beams of variable energy and of variable pulse period. Many experiments have been carried out so far with the beam line. In this paper, various capability of the intense pulsed positron beam is presented, based on the experience at the ETL, and the prospect for the future is discussed. (author)

  20. Femtosecond x-ray free electron laser pulse duration measurement from spectral correlation function

    Directory of Open Access Journals (Sweden)

    A. A. Lutman

    2012-03-01

    Full Text Available We present a novel method for measuring the duration of femtosecond x-ray pulses from self-amplified spontaneous emission free electron lasers by performing statistical analysis in the spectral domain. Analytical expressions of the spectral correlation function were derived in the linear regime to extract both the pulse duration and the spectrometer resolution. Numerical simulations confirmed that the method can be also used in the nonlinear regime. The method was demonstrated experimentally at the Linac Coherent Light Source by measuring pulse durations down to 13 fs FWHM.

  1. Tip-based source of femtosecond electron pulses at 30 keV

    Energy Technology Data Exchange (ETDEWEB)

    Hoffrogge, Johannes; Paul Stein, Jan [Max Planck Institute of Quantum Optics, Hans-Kopfermann-Str. 1, 85748 Garching (Germany); Krüger, Michael; Förster, Michael; Hammer, Jakob; Ehberger, Dominik; Hommelhoff, Peter, E-mail: peter.hommelhoff@fau.de [Max Planck Institute of Quantum Optics, Hans-Kopfermann-Str. 1, 85748 Garching (Germany); Department für Physik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 1, 91058 Erlangen (Germany); Baum, Peter [Max Planck Institute of Quantum Optics, Hans-Kopfermann-Str. 1, 85748 Garching (Germany); Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748 Garching (Germany)

    2014-03-07

    We present a nano-scale photoelectron source, optimized for ultrashort pulse durations and well-suited for time-resolved diffraction and advanced laser acceleration experiments. A tungsten tip of several-ten-nanometers diameter mounted in a suppressor-extractor electrode configuration allows the generation of 30 keV electron pulses with an estimated pulse duration of 9 fs (standard deviation; 21 fs full width at half maximum) at the gun exit. We infer the pulse duration from particle tracking simulations, which are in excellent agreement with experimental measurements of the electron-optical properties of the source in the spatial domain. We also demonstrate femtosecond-laser triggered operation of the apparatus. The temporal broadening of the pulse upon propagation to a diffraction sample can be greatly reduced by collimating the beam. Besides the short electron pulse duration, a tip-based source is expected to feature a large transverse coherence and a nanometric emittance.

  2. Electron energy distributions and electron impact source functions in Ar/N{sub 2} inductively coupled plasmas using pulsed power

    Energy Technology Data Exchange (ETDEWEB)

    Logue, Michael D., E-mail: mdlogue@umich.edu; Kushner, Mark J., E-mail: mjkush@umich.edu [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109-2122 (United States)

    2015-01-28

    In plasma materials processing, such as plasma etching, control of the time-averaged electron energy distributions (EEDs) in the plasma allows for control of the time-averaged electron impact source functions of reactive species in the plasma and their fluxes to surfaces. One potential method for refining the control of EEDs is through the use of pulsed power. Inductively coupled plasmas (ICPs) are attractive for using pulsed power in this manner because the EEDs are dominantly controlled by the ICP power as opposed to the bias power applied to the substrate. In this paper, we discuss results from a computational investigation of EEDs and electron impact source functions in low pressure (5–50 mTorr) ICPs sustained in Ar/N{sub 2} for various duty cycles. We find there is an ability to control EEDs, and thus source functions, by pulsing the ICP power, with the greatest variability of the EEDs located within the skin depth of the electromagnetic field. The transit time of hot electrons produced in the skin depth at the onset of pulse power produces a delay in the response of the EEDs as a function of distance from the coils. The choice of ICP pressure has a large impact on the dynamics of the EEDs, whereas duty cycle has a small influence on time-averaged EEDs and source functions.

  3. Nanosecond pulse-width electron diode based on dielectric wall accelerator technology

    Science.gov (United States)

    Zhao, Quantang; Zhang, Z. M.; Yuan, P.; Cao, S. C.; Shen, X. K.; Jing, Y.; Yu, C. S.; Li, Z. P.; Liu, M.; Xiao, R. Q.; Zong, Y.; Wang, Y. R.; Zhao, H. W.

    2013-11-01

    An electron diode using a short section of dielectric wall accelerator (DWA) has been under development at the Institute of Modern Physics (IMP), Chinese Academy of Sciences. Tests have been carried out with spark gap switches triggered by lasers. The stack voltage efficiency of a four-layer of Blumleins reached about 60-70% with gas filled spark gap switching. The generated pulse voltage of peak amplitude of 23 kV and pulse width of 5 ns is used to extract and accelerate an electron beam of 320 mA, measured by a fast current transformer. A nanosecond pulse width electron diode was achieved successfully. Furthermore, the principle of a DWA is well proven and the development details and discussions are presented in this article.

  4. Effect of pulsed hollow electron-lens operation on the proton beam core in LHC

    CERN Document Server

    Fitterer, Miriam; Valishev, Alexander

    2016-01-01

    Collimation with hollow electron beams is currently one of the most promising concepts for active halo control in the HL-LHC. In order to further increase the diffusion rates for a fast halo removal as e.g. desired before the squeeze, the electron lens (e-lens) can be operated in pulsed mode. In case of profile imperfections in the electron beam the pulsing of the e-lens induces noise on the proton beam which can, depending on the frequency content and strength, lead to emittance growth. In order to study the sensitivity to the pulsing pattern and the amplitude, a beam study (machine development MD) at the LHC has been proposed for August 2016 and we present in this note the preparatory simulations and estimates.

  5. Selective triggering of phase change in dielectrics by femtosecond pulse trains based on electron dynamics control

    Institute of Scientific and Technical Information of China (English)

    Xu Chuan-Cai; Jiang Lan; Leng Ni; Liu Peng-Jun

    2013-01-01

    In this study we experimentally reveal that the phase change mechanism can be selectively triggered by shaping femtosecond pulse trains based on electron dynamics control (EDC),including manipulation of excitations,ionizations,densities,and temperatures of electrons.By designing the pulse energy distribution to adjust the absorptions,excitations,ionizations,and recombinations of electrons,the dominant phase change mechanism experiences transition from nonthermal to thermal process.This phenomenon is observed in quadruple,triple,and double pulses per train ablation of fused silica separately.This opens up possibilities for controlling phase change mechanisms by EDC,which is of great significance in laser processing of dielectrics and fabrication of integrated nano-and micro-optical devices.

  6. Generation of large-bandwidth x-ray free-electron-laser pulses

    Directory of Open Access Journals (Sweden)

    Angela Saa Hernandez

    2016-09-01

    Full Text Available X-ray free-electron lasers (XFELs are modern research tools in disciplines such as biology, material science, chemistry, and physics. Besides the standard operation that aims at minimizing the bandwidth of the produced XFEL radiation, there is a strong scientific demand to produce large-bandwidth XFEL pulses for several applications such as nanocrystallography, stimulated Raman spectroscopy, and multiwavelength anomalous diffraction. We present a self-consistent method that maximizes the XFEL pulse bandwidth by systematically maximizing the energy chirp of the electron beam at the undulator entrance. This is achieved by optimizing the compression scheme and the electron distribution at the source in an iterative back-and-forward tracking. Start-to-end numerical simulations show that a relative bandwidth of 3.25% full-width can be achieved for the hard x-ray pulses in the SwissFEL case.

  7. Optical control of electron phase space in plasma accelerators with incoherently stacked laser pulses

    Energy Technology Data Exchange (ETDEWEB)

    Kalmykov, S. Y., E-mail: skalmykov2@unl.edu; Shadwick, B. A. [Department of Physics and Astronomy, University of Nebraska – Lincoln, Lincoln, Nebraska 68588-0299 (United States); Davoine, X. [CEA, DAM, DIF, Arpajon F-91297 (France); Lehe, R.; Lifschitz, A. F. [Laboratoire d' Optique Appliquée, ENSTA-CNRS-École Polytechnique UMR 7639, Palaiseau F-91761 (France)

    2015-05-15

    It is demonstrated that synthesizing an ultrahigh-bandwidth, negatively chirped laser pulse by incoherently stacking pulses of different wavelengths makes it possible to optimize the process of electron self-injection in a dense, highly dispersive plasma (n{sub 0}∼10{sup 19} cm{sup −3}). Avoiding transformation of the driving pulse into a relativistic optical shock maintains a quasi-monoenergetic electron spectrum through electron dephasing and boosts electron energy far beyond the limits suggested by existing scaling laws. In addition, evolution of the accelerating bucket in a plasma channel is shown to produce a background-free, tunable train of femtosecond-duration, 35–100 kA, time-synchronized quasi-monoenergetic electron bunches. The combination of the negative chirp and the channel permits acceleration of electrons beyond 1 GeV in a 3 mm plasma with 1.4 J of laser pulse energy, thus offering the opportunity of high-repetition-rate operation at manageable average laser power.

  8. Channeling of relativistic laser pulses in underdense plasmas and subsequent electron acceleration

    Directory of Open Access Journals (Sweden)

    Naseri N.

    2013-11-01

    Full Text Available This contribution is concerned with the nonlinear behavior of a relativistic laser pulse focused in an underdense plasma and with the subsequent generation of fast electrons. Specifically, we study the interaction of laser pulses having their intensity Iλ2 in the range [1019, 1020]  W/cm2  μm2, focused in a plasma of electron density n0 such that the ratio n0/nc lies in the interval [10−3, 2 × 10−2], nc denoting the critical density; the laser pulse power PL exceeds the critical power for laser channeling Pch. The laser-plasma interaction in such conditions is investigated by means of 3D Particle in Cell (PIC simulations. It is observed that the laser front gives rise to the excitation of a surface wave which propagates along the sharp boundaries of the electron free channel created by the laser pulse. The mechanism responsible for the generation of the fast electrons observed in the PIC simulations is then analyzed by means of a test particles code. It is thus found that the fast electrons are generated by the combination of the betatron process and of the acceleration by the surface wave. The maximum electron energy observed in the simulations with Iλ2 = 1020  W/cm2  μm2 and n0/nc = 2 × 10−2 is 350 MeV.

  9. Electron Beam Energy Compensation by Controlling RF Pulse Shape

    CERN Document Server

    Kii, T; Kusukame, K; Masuda, K; Nakai, Y; Ohgaki, H; Yamazaki, T; Yoshikawa, K; Zen, H

    2005-01-01

    We have studied on improvement of electron beam macropulse properties from a thermionic RF gun. Though a thermionic RF gun has many salient features, there is a serious problem that back-bombardment effect worsens quality of the beam. To reduce beam energy degradation by this effect, we tried to feed non-flat RF power into the gun. As a result, we successfully obtained about 1.5 times longer macropulse and two times larger total charge per macropulse. On the other hand, we calculated transient evolution of RF power considering non-constant beam loading. The beam loading is evaluated from time evolution of cathode temperature, by use of one dimensional heat conduction model and electron trajectories' calculations by a particle simulation code. Then we found good agreement between the experimental and calculation results. Furthermore, with the same way, we studied the electron beam output dependence on the cathode radius.

  10. Nanosecond pulse-width electron diode based on dielectric wall accelerator technology

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Quantang, E-mail: zhaoquantang@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zhang, Z.M.; Yuan, P.; Cao, S.C.; Shen, X.K.; Jing, Y. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Yu, C.S. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Li, Z.P.; Liu, M.; Xiao, R.Q. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Zong, Y.; Wang, Y.R. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zhao, H.W. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)

    2013-11-21

    An electron diode using a short section of dielectric wall accelerator (DWA) has been under development at the Institute of Modern Physics (IMP), Chinese Academy of Sciences. Tests have been carried out with spark gap switches triggered by lasers. The stack voltage efficiency of a four-layer of Blumleins reached about 60–70% with gas filled spark gap switching. The generated pulse voltage of peak amplitude of 23 kV and pulse width of 5 ns is used to extract and accelerate an electron beam of 320 mA, measured by a fast current transformer. A nanosecond pulse width electron diode was achieved successfully. Furthermore, the principle of a DWA is well proven and the development details and discussions are presented in this article. -- Highlights: •The key technology of DWA, including switches and pulse forming lines were studied. •The SiC PCSS obtained from Shanghai Institute were tested. •Two layers ZIP lines (new structure) and four layers Blumlein lines were studied with laser triggered spark gap switches. •A nanosecond pulse-width electron diode based on DWA technologies is achieved and studied experimentally. •The principle of DWA is also proved by the diode.

  11. Injection of electrons by colliding laser pulses in a laser wakefield accelerator

    CERN Document Server

    Hansson, Martin; Ekerfelt, Henrik; Persson, Anna; Lundh, Olle

    2016-01-01

    To improve the stability and reproducibility of laser wakefield accelerators and to allow for future applications, controlling the injection of electrons is of great importance. This allows us to control the amount of charge in the beams of accelerated electrons and final energy of the electrons. Results are presented from a recent experiment on controlled injection using the scheme of colliding pulses and performed using the Lund multi-terawatt laser. Each laser pulse is split into two parts close to the interaction point. The main pulse is focused on a 2 mm diameter gas jet to drive a nonlinear plasma wave below threshold for self-trapping. The second pulse, containing only a fraction of the total laser energy, is focused to collide with the main pulse in the gas jet under an angle of 150°. Beams of accelerated electrons with low divergence and small energy spread are produced using this set-up. Control over the amount of accelerated charge is achieved by rotating the plane of polarization of the second p...

  12. Controlling the fast electron divergence in a solid target with multiple laser pulses

    Science.gov (United States)

    Volpe, L.; Feugeas, J.-L.; Nicolai, Ph.; Santos, J. J.; Touati, M.; Breil, J.; Batani, D.; Tikhonchuk, V.

    2014-12-01

    Controlling the divergence of laser-driven fast electrons is compulsory to meet the ignition requirements in the fast ignition inertial fusion scheme. It was shown recently that using two consecutive laser pulses one can improve the electron-beam collimation. In this paper we propose an extension of this method by using a sequence of several laser pulses with a gradually increasing intensity. Profiling the laser-pulse intensity opens a possibility to transfer to the electron beam a larger energy while keeping its divergence under control. We present numerical simulations performed with a radiation hydrodynamic code coupled to a reduced kinetic module. Simulation with a sequence of three laser pulses shows that the proposed method allows one to improve the efficiency of the double pulse scheme at least by a factor of 2. This promises to provide an efficient energy transport in a dense matter by a collimated beam of fast electrons, which is relevant for many applications such as ion-beam sources and could present also an interest for fast ignition inertial fusion.

  13. Experimental Study of Diamond Like Carbon (DLC) Coated Electrodes for Pulsed High Gradient Electron Gun

    CERN Document Server

    Paraliev, M; Ivkovic, S; Le Pimpec, F

    2010-01-01

    For the SwissFEL Free Electron Laser project at the Paul Scherrer Institute, a pulsed High Gradient (HG) electron gun was used to study low emittance electron sources. Different metals and surface treatments for the cathode and anode were studied for their HG suitability. Diamond Like Carbon (DLC) coatings are found to perform exceptionally well for vacuum gap insulation. A set of DLC coated electrodes with different coating parameters were tested for both vacuum breakdown and photo electron emission. Surface electric fields over 250MV/m (350 - 400kV, pulsed) were achieved without breakdown. From the same surface, it was possible to photo-emit an electron beam at gradients up to 150MV/m. The test setup and the experimental results are presented

  14. Evaluation by electronic paramagnetic resonance of the number of free radicals produced in irradiated rat bone; Evaluation par resonance paramagnetique electronique du nombre de radicaux libres produits dans l'os de rat irradie

    Energy Technology Data Exchange (ETDEWEB)

    Marble, G.; Valderas, R. [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires

    1966-07-01

    The number of long half-life free radicals created by gamma irradiation in the bones of the rat has been determined from the electrons paramagnetic resonance spectrum. This number decreases slowly with time (calculated half life: 24 days). It is proportional to the dose of gamma radiation given to the rat. The method could find interesting applications in the field of biological dosimetry. (authors) [French] Le nombre de radicaux libres a vie longue crees par irradiation gamma dans l'os de rat a ete determine a partir du spectre de resonance paramagnetique electronique. Ce nombre decroit lentement avec le temps (demi-vie calculee {approx_equal} 24 jours). IL est proportionnel a la dose de rayonnement gamma delivree au rat. La methode pourra trouver en dosimetrie biologique des applications interessantes. (auteurs)

  15. Effects of finite laser pulse width on two-dimensional electronic spectroscopy

    Science.gov (United States)

    Leng, Xuan; Yue, Shuai; Weng, Yu-Xiang; Song, Kai; Shi, Qiang

    2017-01-01

    We combine the hierarchical equations of motion method and the equation-of-motion phase-matching approach to calculate two-dimensional electronic spectra of model systems. When the laser pulse is short enough, the current method reproduces the results based on third-order response function calculations in the impulsive limit. Finite laser pulse width is found to affect both the peak positions and shapes, as well as the time evolution of diagonal and cross peaks. Simulations of the two-color two-dimensional electronic spectra also show that, to observe quantum beats in the diagonal and cross peaks, it is necessary to excite the related excitonic states simultaneously.

  16. Paired-pulse facilitation achieved in protonic/electronic hybrid indium gallium zinc oxide synaptic transistors

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Li Qiang, E-mail: guoliqiang@ujs.edu.cn; Ding, Jian Ning; Huang, Yu Kai [Micro/Nano Science & Technology Center, Jiangsu University, Zhenjiang, 212013 (China); Zhu, Li Qiang, E-mail: lqzhu@nimte.ac.cn [Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China)

    2015-08-15

    Neuromorphic devices with paired pulse facilitation emulating that of biological synapses are the key to develop artificial neural networks. Here, phosphorus-doped nanogranular SiO{sub 2} electrolyte is used as gate dielectric for protonic/electronic hybrid indium gallium zinc oxide (IGZO) synaptic transistor. In such synaptic transistors, protons within the SiO{sub 2} electrolyte are deemed as neurotransmitters of biological synapses. Paired-pulse facilitation (PPF) behaviors for the analogous information were mimicked. The temperature dependent PPF behaviors were also investigated systematically. The results indicate that the protonic/electronic hybrid IGZO synaptic transistors would be promising candidates for inorganic synapses in artificial neural network applications.

  17. Application of strongly focused pulsed electron beam for the reaction wheels balancing

    Science.gov (United States)

    Borduleva, A. O.; Bleykher, G. A.; Solovev, V. V.; Krivobokov, V. P.; Babihina, M. N.

    2016-11-01

    In the given work the material removing possibility by the strongly focused pulsed electron beam was investigated. The optimal mode of flywheels balancing was found. At this mode the power density is 1.6 MW/cm2 and pulse duration is 0.65 s. At such parameters the evaporation rate is equal to 11 g/scm2. It is possible to vary the amount of remote material from 1 to 100 mg, that is sufficient to balance flywheel. It is found that treatment by an electron beam does not change the material structure.

  18. Laser sources for polarized electron beams in cw and pulsed accelerators

    CERN Document Server

    Hatziefremidis, A; Fraser, D; Avramopoulos, H

    1999-01-01

    We report the characterization of a high power, high repetition rate, mode-locked laser system to be used in continuous wave and pulsed electron accelerators for the generation of polarized electron beams. The system comprises of an external cavity diode laser and a harmonically mode-locked Ti:Sapphire oscillator and it can provide up to 3.4 W average power, with a corresponding pulse energy exceeding 1 nJ at 2856 MHz repetition rate. The system is tunable between 770-785 and 815-835 nm with two sets of diodes for the external cavity diode laser. (author)

  19. Intrinsic electric dipole moments of paramagnetic atoms : Rubidium and cesium

    NARCIS (Netherlands)

    Nataraj, H. S.; Sahoo, B. K.; Das, B. P.; Mukherjee, D.

    2008-01-01

    The electric dipole moment (EDM) of paramagnetic atoms is sensitive to the intrinsic EDM contribution from that of its constituent electrons and a scalar-pseudoscalar (S-PS) electron-nucleus interaction. The electron EDM and the S-PS contributions to the EDMs of these atoms scale as approximate to Z

  20. Dynamics of photoionization from molecular electronic wavepacket states in intense pulse laser fields: A nonadiabatic electron wavepacket study

    Science.gov (United States)

    Matsuoka, Takahide; Takatsuka, Kazuo

    2017-04-01

    A theory for dynamics of molecular photoionization from nonadiabatic electron wavepackets driven by intense pulse lasers is proposed. Time evolution of photoelectron distribution is evaluated in terms of out-going electron flux (current of the probability density of electrons) that has kinetic energy high enough to recede from the molecular system. The relevant electron flux is in turn evaluated with the complex-valued electronic wavefunctions that are time evolved in nonadiabatic electron wavepacket dynamics in laser fields. To uniquely rebuild such wavefunctions with its electronic population being lost by ionization, we adopt the complex-valued natural orbitals emerging from the electron density as building blocks of the total wavefunction. The method has been implemented into a quantum chemistry code, which is based on configuration state mixing for polyatomic molecules. Some of the practical aspects needed for its application will be presented. As a first illustrative example, we show the results of hydrogen molecule and its isotope substitutes (HD and DD), which are photoionized by a two-cycle pulse laser. Photon emission spectrum associated with above threshold ionization is also shown. Another example is taken from photoionization dynamics from an excited state of a water molecule. Qualitatively significant effects of nonadiabatic interaction on the photoelectron spectrum are demonstrated.

  1. Ionization-injected electron acceleration with sub-terawatt laser pulses

    Science.gov (United States)

    Feder, Linus; Goers, Andy; Hine, George; Miao, Bo; Salehi, Fatholah; Woodbury, Daniel; Milchberg, Howard

    2016-10-01

    The vast majority of laser wakefield acceleration (LWFA) experiments use drive lasers with peak powers >10 TW and repetition rates from 10 Hz to less than once an hour. However, it was recently demonstrated that by using a thin, high density gas target, LWFA can be driven by laser pulses well below a TW and with high repetition rates. We present experiments and particle-in-cell (PIC) simulations of the effect of doping the high density gas jet with higher Z molecules (here nitrogen). Our earlier experiments with low-Z gas relied on self-injection of electrons into the accelerating wake through wave-breaking. In ionization injection, the relativistically self-focused laser pulse ionizes the inner shell of the dopant inside the plasma wake. High energy electrons are then trapped by the wakefield in the earliest potential buckets, which overlap with the laser pulse. PIC simulations show acceleration of these electrons by LWFA and directly by the laser pulse, with the direct contribution significantly increasing the electron energy beyond the LWFA contribution alone. Additionally, ionization injection can be controlled to prevent dephasing of the electron beam, resulting in a narrower energy spectrum and lower spatial divergence. This research is supported by the Department of Energy and the National Science Foundation.

  2. Transient Self-Amplified Cerenkov Radiation with a Short Pulse Electron Beam

    Energy Technology Data Exchange (ETDEWEB)

    Poole, B R; Blackfield, D T; Camacho, J F

    2009-01-22

    An analytic and numerical examination of the slow wave Cerenkov free electron maser is presented. We consider the steady state amplifier configuration as well as operation in the selfamplified spontaneous emission (SASE) regime. The linear theory is extended to include electron beams that have a parabolic radial density inhomogeneity. Closed form solutions for the dispersion relation and modal structure of the electromagnetic field are determined in this inhomogeneous case. To determine the steady state response, a macro-particle approach is used to develop a set of coupled nonlinear ordinary differential equations for the amplitude and phase of the electromagnetic wave, which are solved in conjunction with the particle dynamical equations to determine the response when the system is driven as an amplifier with a time harmonic source. We then consider the case in which a fast rise time electron beam is injected into a dielectric loaded waveguide. In this case, radiation is generated by SASE, with the instability seeded by the leading edge of the electron beam. A pulse of radiation is produced, slipping behind the leading edge of the beam due to the disparity between the group velocity of the radiation and the beam velocity. Short pulses of microwave radiation are generated in the SASE regime and are investigated using particle-in-cell (PIC) simulations. The nonlinear dynamics are significantly more complicated in the transient SASE regime when compared with the steady state amplifier model due to the slippage of the radiation with respect to the beam. As strong self-bunching of the electron beam develops due to SASE, short pulses of superradiant emission develop with peak powers significantly larger than the predicted saturated power based on the steady state amplifier model. As these superradiant pulses grow, their pulse length decreases and forms a series of soliton-like pulses. Comparisons between the linear theory, macro-particle model, and PIC simulations are

  3. Pulse radiolytic studies of electron transfer processes and applications to solar photochemistry. Progress report

    Energy Technology Data Exchange (ETDEWEB)

    Neta, P.

    1995-02-01

    The pulse radiolysis technique is applied to the study of electron transfer processes in a variety of chemical systems. Reactive intermediates are produced in solution by electron pulse irradiation and the kinetics of their reactions are followed by time resolved absorption spectrophotometry. Complementary experiments are carried out with excimer laser flash photolysis. These studies are concerned with mechanisms, kinetics, and thermodynamics of reactions of organic and inorganic radicals and unstable oxidation states of metal ions. Reactions are studied in both aqueous and non-aqueous solutions. The studies focus on the unique ability of pulse radiolysis to provide absolute rate constants for reactions of many inorganic radicals and organic peroxyl radicals, species that are key intermediates in many chemical processes. A special concern of this work is the study of electron transfer reactions of metalloporphyrins, which permits evaluation of these molecules as intermediates in solar energy conversion. Metalloporphyrins react with free radicals via electron transfer, involving the ligand or the metal center, or via bonding to the metal, leading to a variety of chemical species whose behavior is also investigated. The highlights of the results during the past three years are summarized below under the following sections: (a) electron transfer reactions of peroxyl radicals, concentrating on the characterization of new peroxyl radicals derived from vinyl, phenyl, other aryl, and pyridyl; (b) solvent effects on electron transfer reactions of inorganic and organic peroxyl radicals, including reactions with porphyrins, and (c) electron transfer and alkylation reactions of metalloporphyrins and other complexes.

  4. Generation of Frequency-Chirped Pulses in the Far-Infrared by Means of a Subpicosecond Free-Electron Laser and an External Pulse Shaper

    NARCIS (Netherlands)

    Knippels, G.M.H.; van der Meer, A. F. G.; Mols, Rfxam; van Amersfoort, P. W.; Vrijen, R. B.; Maas, D. J.; Noordam, L. D.

    1995-01-01

    The generation of frequency-chirped optical pulses in the far-infrared is reported. The pulses are produced by the free-electron laser FELIX. The chirp is induced by means of an external shaping device consisting of a grating and a telescope. The shaper is based on reflective optics to permit operat

  5. Electron Acceleration in Wakefield and Supra-Bubble Regimes by Ultraintense Laser with Asvmmetric Pulse*

    Institute of Scientific and Technical Information of China (English)

    BAKE Maimaitiaili; XIE Bai-Song; DULAT Sayipjamal; AIMIDULA Aimierding

    2011-01-01

    Electron acceleration in plasma driven by circular polarized ultraintense laser with asymmetric pulse are investigated analytically and numerically in terms of oscillation-center Hamiltonian formalism.Studies include wakefield acceleration, which dominates in blow-out or bubble regime and snow-plow acceleration which dominates in supra-bubble regime.By a comparison with each other it is found that snow-plow acceleration has lower acceleration capability.In wakefield acceleration, there exists an obvious optimum pulse asymmetry or/and pulse lengths that leads to the high net energy gain while in snow-plow acceleration it is insensitive to the pulse lengths.Power and linear scaling laws for wakefield and snow-plow acceleration respetively are observed from the net energy gain depending on laser field amplitude.Moreover, there exists also an upper and lower limit on plasma density for an effective acceleration in both of regimes.

  6. Electron-Beam Switches For A High Peak Power Sled-II Pulse Compressor

    Energy Technology Data Exchange (ETDEWEB)

    Hirshfield, Jay, L. [Yale Univ., New Haven, CT (United States)

    2015-12-02

    Omega-P demonstrated triggered electron-beam switches on the L=2 m dual-delay-line X-band pulse compressor at Naval Research Laboratory (NRL). In those experiments, with input pulses of up to 9 MW from the Omega-P/NRL X-band magnicon, output pulses having peak powers of 140-165 MW and durations of 16-20 ns were produced, with record peak power gains M of 18-20. Switch designs are described based on the successful results that should be suitable for use with the existing SLAC SLED-II delay line system, to demonstrate C=9, M=7, and n>>78%, yielding 173ns compressed pulses with peak powers up to 350MW with input of a single 50-MW.

  7. 基于电子顺磁共振的锶铁氧体磁特性研究∗%Study on magnetic prop erties of strontium ferrite based on the technology of electron paramagnetic resonance

    Institute of Scientific and Technical Information of China (English)

    李少波; 殷春浩; 徐振坤; 李佩欣; 吴彩平; 冯铭扬

    2015-01-01

    为了研究配料、温度、氧环境和掺杂等条件对锶铁氧体的磁性能的影响问题,利用溶胶-凝胶法制备了锶铁氧体粉末,建立了一种基于电子顺磁共振技术研究锶铁氧体粉末的磁特性的方法.用电子顺磁共振波谱仪对烧结后的产物进行测试发现:400◦C预烧下,锶铁摩尔比为1:9时,中间产物顺磁相α-Fe2 O3含量最多,高于400◦C时其含量减少,亚铁磁相增加,并确定最佳煅烧温度介于800—900◦C.这是由于外磁场和其他磁场综合作用产生亚铁磁相,进而产生较强的磁矩相互作用所致.结合工业实际应用,发现缺氧退火环境下,顺磁相α-Fe2O3含量较大,不利于亚铁磁相生成; X-射线衍射(XRD)表征结果表明:除了少量杂相,其余均为顺磁相和亚铁磁相;电子顺磁共振谱和XRD 谱检测结果综合表明,锶铁摩尔比为1:9时,最终产物的顺磁相含量最少,亚铁磁相含量最多,磁性最强;毫特斯拉计的剩磁检测结果也证实了上述结果.掺杂实验发现镧离子占锶镧总摩尔数的20%至30%时,能够有效降低顺磁相的产生,增强最终产物的亚铁磁性.%In order to study how the ingredient, sintering temperature, oxygen, doping and other conditions affect magnetic properties of strontium ferrite powder, a strontium ferrite powder is prepared by sol-gel method, and a new method of studying magnetic properties of strontium ferrite powder based on an electron paramagnetic resonance (EPR) is established in this paper. The sintered samples are tested by electron paramagnetic resonance spectrometer. Results show thatα-Fe2O3, a paramagnetic intermediate, is most compared with other ratios under calcined at 400 ◦C and the strontium iron mole ratio of 1 : 9; while at the other temperatures it decreases and the ferromagnetic phase increases;the optimum calcination temperature is between 800 ◦C and 900 ◦C. These facts are

  8. The Reduction of NOx Using Pulsed Electron Beams

    Science.gov (United States)

    2015-12-30

    instantly with oxygen to form the brown gas NO2. Nitrogen dioxide is toxic. Dinitrogen trioxide (N2O3) exists as a deep blue solid (-21°C), but is...equilibrium constant for this reaction is plotted in Figure 2 (solid blue line) as a function of temperature in degrees Centigrade. The temperature range on...Swanekamp, D. Weidenheimer, D. Welch, D.V. Rose , and S. Searles, “Electron Beam Pumped KrF Lasers for Fusion Energy,” Phys. Plasmas 10, 2142 (2003

  9. Electron emission properties of gated silicon field emitter arrays driven by laser pulses

    Science.gov (United States)

    Shimawaki, Hidetaka; Nagao, Masayoshi; Neo, Yoichiro; Mimura, Hidenori; Wakaya, Fujio; Takai, Mikio

    2016-10-01

    We report optically modulated electron emission from gated p-type silicon field emitter arrays (Si-FEAs). The device's "volcano" structure is designed to control the photoexcitation of electrons by transmitting light through the small gate aperture, thereby minimizing the photogeneration of slow diffusion carriers outside the depletion region in the tip. Compared to that in the dark, the emission current was enhanced by more than three orders of magnitude in the high field region when irradiated with blue laser pulses. Results from the time-resolved measurements of photoassisted electron emission showed that these possess the same response as the laser pulse with no discernible delay. These results indicate that the volcano device structure is effective at eliminating the generation of diffusion carriers and that a fully optimized FEA is promising as a photocathode for producing high-speed modulated electron beams.

  10. Electron thermalization and attachment in pulse-irradiated oxygen studied by time-resolved microwave conductivity

    Science.gov (United States)

    Warman, John M.; Cooper, Ronald

    The microwave conductivity of oxygen gas following nanosecond pulsed irradiation has been studied for pressures from 5 to 50 torr. The conductivity is found to decrease by a factor of approx. 20 in the early stages ( tN < 2 x 10 11 s cm -3) following the pulse. This is attributed to a decrease in the electron collision frequency as the initial excess energy of the electrons becomes degraded. A further decrease found at longer times is due to the three-body attachment of electrons to O 2 with a rate constant of 2.4 x 10 -30 cm 6s -1. Above a pressure of approx. 30 torr significant attachment begins to occur while electrons are still superthermal. The time at which the microwave signal is within 10% of the value corresponding to thermal energies is given by τ thP ≈ 15 μs.torr.

  11. Anomalous isotopic effect on electron-directed reactivity by a 3-{\\mu}m midinfrared pulse

    CERN Document Server

    Liu, Kunlong; Lan, Pengfei; Lu, Peixiang

    2012-01-01

    We have theoretically studied the effect of nuclear mass on electron localization in dissociating H_2^+ and its isotopes subjected to a few-cycle 3-{\\mu}m laser pulse. Compared to the isotopic trend in the near-infrared regime, our results reveal an inverse isotopic effect in which the degree of electron-directed reactivity is even higher for heavier isotopes. With the semi-classical analysis, we find, for the first time, the pronounced electron localization is established by the interferences through different channels of one- and, more importantly, higher-order photon coupling. Interestingly, due to the enhanced high-order above-threshold dissociation of heavier isotopes, the interference maxima gradually become in phase with growing mass and ultimately lead to the anomalous isotopic behavior of the electron localization. This indicates that the multi-photon coupling channels will play an important role in controlling the dissociation of larger molecules with midinfrared pulses.

  12. Strong-field ionization inducing multi-electron-hole coherence probed by attosecond pulses

    CERN Document Server

    Zhao, Jing; Zhao, Zengxiu

    2015-01-01

    We propose a new scenario to apply IR-pump-XUV-probe schemes to resolving strong field ionization induced and attosecond pulse driven electron-hole dynamics and coherence in real time. The coherent driving of both the infrared laser and the attoscond pulse correlates the dynamics of the core-hole and the valence-hole which leads to the otherwise forbidden absorption and emission of XUV photon. An analytical model is developed based on the strong-field approximation by taking into account of the essential multielectron configurations. The emission spectra from the core-valence transition and the core-hole recombination are found modulating strongly as functions of the time delay between the two pulses, which provides a unique insight into the instantaneous ionization and the interplay of the multi-electron-hole coherence.

  13. Electron-beam pulse annealed Ti-implanted GaP

    Science.gov (United States)

    Werner, Z.; Barlak, M.; Ratajczak, R.; Konarski, P.; Markov, A. M.; Heller, R.

    2016-08-01

    Gallium phosphide heavily doped with substitutional titanium is a prospective material for intermediate band solar cells. To manufacture such a material, single crystals of GaP were implanted with 120 keV Ti ions to doses between 5 × 1014 cm-2 and 5 × 1015 cm-2. They were next pulse annealed with 2 μs electron-beam pulses of electron energy of about 13 keV and pulse energy density between 1 and 2 Jcm-2. The samples were studied by channeled Rutherford Backscattering, particle induced X-ray emission, and SIMS. The results show full recovery of crystal structure damaged by implantation and good retention of the implanted titanium without, however, its significant substitution at crystal sites.

  14. Understanding the ATLAS electromagnetic barrel pulse shapes and the absolute electronic calibration

    CERN Document Server

    Neukermans, L; Zitoun, R

    2001-01-01

    We present an original method to undestand the calibration and physics pulse shapes collected in the 2000 barrel test beam runs with the prototype module. It is based on an electrical description of the calorimeter and its electronics. It allows an understanding of the physics pulse shapes and its absolute calibration (in microA/ADC) to a very good level of accuracy with a small number of parameters (capacitances and inductances). The electrical parameters found by this method agree with the direct measurements independantly performed on the prototype module. Optimal filtering coefficients can then be derived from these physics pulse shape predictions, and more crucial, an absolute electronic calibration. These coefficients are released in the official test beam software EMTB.

  15. A Technique for Temperature and Ultimate Load Calculations of Thin Targets in a Pulsed Electron Beam

    DEFF Research Database (Denmark)

    Hansen, Jørgen-Walther; Lundsager, Per

    1979-01-01

    A technique is presented for the calculation of transient temperature distributions and ultimate load of rotationally symmetric thin membranes with uniform lateral load and exposed to a pulsed electron beam from a linear accelerator. Heat transfer by conduction is considered the only transfer...

  16. Low energy high current pulsed electron beam treatment for improving surface microstructure and properties

    Energy Technology Data Exchange (ETDEWEB)

    Wu, J; Allain-Bonasso, N; Zhang, X D; Hao, S Z; Grosdider, T; Dong, C [Laboratoire d' Etude des Textures et Applications aux Materiaux (LETAM, UMR-CNRS 3143), Universite Paul Verlaine-Metz, Ile du Saulcy, 57045 Metz (France); Zou, J X, E-mail: jiang.wu@univ-metz.fr, E-mail: thierry.grosdidier@univ-metz.fr [National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiao Tong University, Shanghai 200240 (China)

    2010-06-15

    Low energy high current pulsed electron beam (LEHCPEB) is a fairly new technique for surface modifications authorizing improvement in wear and corrosion properties as well as texture changes and hardening. This contribution highlights some microstructure modifications encountered at the surface of HCPEB treated steels and bulk metallic glasses taking into account the effects of surface melting and the effects of the induced stress.

  17. Enhanced Electron Attachment to Highly-Excited Molecules and Its Applications in Pulsed Plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Ding, W.X.; Ma, C.Y.; McCorkle, D.L.; Pinnaduwage, L.A.

    1999-06-27

    Studies conducted over the past several years have shown that electron attachment to highly-excited states of molecules have extremely large cross sections. We will discuss the implications of this for pulsed discharges used for H- generation, material processing, and plasma remediation.

  18. Multiple Ionization of Free Ubiquitin Molecular Ions in Extreme Ultraviolet Free-Electron Laser Pulses

    NARCIS (Netherlands)

    Schlathölter, Thomas; Reitsma, Geert; Egorov, Dmitrii; Gonzalez-Magaña, Olmo; Bari, Sadia; Boschman, Leon; Bodewits, Erwin; Schnorr, Kirsten; Schmid, Georg; Schröter, Claus Dieter; Moshammer, Robert; Hoekstra, Ronnie

    2016-01-01

    The fragmentation of free tenfold protonated ubiquitin in intense 70 femtosecond pulses of 90 eV photons from the FLASH facility was investigated. Mass spectrometric investigation of the fragment cations produced after removal of many electrons revealed fragmentation predominantly into immonium ions

  19. Observation of coherent transition radiation using relativistic pico second electron pulse

    Energy Technology Data Exchange (ETDEWEB)

    Jones, C.R.; Kosai, H.; Dutt, J.M. [North Carolina Central Univ., Durham, NC (United States)

    1995-12-31

    When an electron beams passes through boundaries of two different media with different dielectric constants, it generates radiation. The radiation emitted by the prebunched electron beam becomes coherent if the size of the bunch is smaller than the wavelength. Therefore, transition radiation can be considered as a possible broad band radiation source as well as a probe to the pico second and sub picosecond electron beam profiles. Using 1.2 MeV, 200 mA, macropulse electron beam, transition radiation was generated. The electron gun consists of 2.856 GHz Klystron, thermionic cathode. The emitted electron beam was bunched by passing through an alpha magnet. As a result of the combination, a pico second pulse (1.2 MeV, up to 80 A micropulse) was obtained. Experimental results, comparisons with the theory, and simulated electron beam profiles will be presented.

  20. Electromagnetic cascade in high-energy electron, positron, and photon interactions with intense laser pulses

    Science.gov (United States)

    Bulanov, S. S.; Schroeder, C. B.; Esarey, E.; Leemans, W. P.

    2013-06-01

    The interaction of high-energy electrons, positrons, and photons with intense laser pulses is studied in head-on collision geometry. It is shown that electrons and/or positrons undergo a cascade-type process involving multiple emissions of photons. These photons can consequently convert into electron-positron pairs. As a result charged particles quickly lose their energy developing an exponentially decaying energy distribution, which suppresses the emission of high-energy photons, thus reducing the number of electron-positron pairs being generated. Therefore, this type of interaction suppresses the development of the electromagnetic avalanche-type discharge, i.e., the exponential growth of the number of electrons, positrons, and photons does not occur in the course of interaction. The suppression will occur when three-dimensional effects can be neglected in the transverse particle orbits, i.e., for sufficiently broad laser pulses with intensities that are not too extreme. The final distributions of electrons, positrons, and photons are calculated for the case of a high-energy e-beam interacting with a counterstreaming, short intense laser pulse. The energy loss of the e-beam, which requires a self-consistent quantum description, plays an important role in this process, as well as provides a clear experimental observable for the transition from the classical to quantum regime of interaction.

  1. Communication: The electronic structure of matter probed with a single femtosecond hard x-ray pulse

    Directory of Open Access Journals (Sweden)

    J. Szlachetko

    2014-03-01

    Full Text Available Physical, biological, and chemical transformations are initiated by changes in the electronic configuration of the species involved. These electronic changes occur on the timescales of attoseconds (10−18 s to femtoseconds (10−15 s and drive all subsequent electronic reorganization as the system moves to a new equilibrium or quasi-equilibrium state. The ability to detect the dynamics of these electronic changes is crucial for understanding the potential energy surfaces upon which chemical and biological reactions take place. Here, we report on the determination of the electronic structure of matter using a single self-seeded femtosecond x-ray pulse from the Linac Coherent Light Source hard x-ray free electron laser. By measuring the high energy resolution off-resonant spectrum (HEROS, we were able to obtain information about the electronic density of states with a single femtosecond x-ray pulse. We show that the unoccupied electronic states of the scattering atom may be determined on a shot-to-shot basis and that the measured spectral shape is independent of the large intensity fluctuations of the incoming x-ray beam. Moreover, we demonstrate the chemical sensitivity and single-shot capability and limitations of HEROS, which enables the technique to track the electronic structural dynamics in matter on femtosecond time scales, making it an ideal probe technique for time-resolved X-ray experiments.

  2. Electron-phonon nonequilibrium during ultrashort pulsed laser heating of metals

    Science.gov (United States)

    Smith, Andrew Neil

    2001-10-01

    Ultrashort pulsed lasers have repeatedly been demonstrated as an effective tool for the observation of transport properties on atomistic time and length scales. Accordingly, the number of applications of these types of lasers as diagnostic tools is rapidly increasing. To effectively use these tools, precise knowledge of the energy deposition mechanism is absolutely necessary. The accepted model for ultrashort pulsed laser heating is the ``Two Temperature Model'' which assumes equilibrium electron and phonon distributions that are not in equilibrium with each other. Recently the applicability of the ``Two Temperature Model'' has received some scrutiny for very low and very high intensity application. This model gave rise to the electron-phonon coupling factor, which, when combined with the temperature difference between the two systems, represents the rate of energy transfer for small perturbations in temperature. However, numerous applications use moderate to high intensity ultrashort pulses, which create far more than small perturbations in temperature. In this investigation the temperature dependence of the electron-phonon coupling factor, electron heat capacity, and thermal conductivity are examined for significant changes in the electron temperature. Experimental results are presented for transient thermoreflectance data taken at moderate fluences. A significant discrepancy is apparent between the two temperature model and the experimental data taken on Au. This problem was originally thought to arise from increased electron- phonon coupling for moderate changes in the electron temperature. Investigation into the temperature dependence of the electron-phonon coupling factor did not support this hypothesis. It was discovered that the discrepancy was due to a nonlinear relationship between changes in the electron temperature and changes in reflectance. The incident probe energy used when taking the experimental data was 1.5 eV, which is significantly less than

  3. Characterization of electrons and x-rays produced using chirped laser pulses in a laser wakefield accelerator

    Science.gov (United States)

    Zhao, T. Z.; Behm, K.; He, Z.-H.; Maksimchuk, A.; Nees, J. A.; Yanovsky, V.; Thomas, A. G. R.; Krushelnick, K.

    2016-11-01

    The electron injection process into a plasma-based laser wakefield accelerator can be influenced by modifying the parameters of the driver pulse. We present an experimental study on the combined effect of the laser pulse duration, pulse shape, and frequency chirp on the electron injection and acceleration process and the associated radiation emission for two different gas types—a 97.5% He and 2.5% N2 mixture and pure He. In general, the shortest pulse duration with minimal frequency chirp produced the highest energy electrons and the most charge. Pulses on the positive chirp side sustained electron injection and produced higher charge, but lower peak energy electrons, compared with negatively chirped pulses. A similar trend was observed for the radiant energy. The relationship between the radiant energy and the electron charge remained linear over a threefold change in the electron density and was independent of the drive pulse characteristics. X-ray spectra showed that ionization injection of electrons into the wakefield generally produced more photons than self-injection for all pulse durations/frequency chirp and had less of a spread in the number of photons around the peak x-ray energy.

  4. Investigation of Vortex Structures in Gas-Discharge Nonneutral Electron Plasma: III. Pulse Ejection of Electrons at the Formation and Radial Oscillations of Vortex Structure

    CERN Document Server

    Kervalishvili, N A

    2015-01-01

    The results of experimental investigations of electron ejection from gas-discharge nonneutral electron plasma at the formation and radial oscillations of vortex structure have been presented. The electrons are injected from the vortex structure and the adjacent region of electron sheath in the form of pulses the duration and periodicity of which are determined by the processes of evolution and dynamics of this structure. The possible mechanisms of pulse ejection of electrons are considered. The influence of electron ejection on other processes in discharge electron sheath is analyzed.

  5. Electron self-injection during interaction of tightly focused few-cycle laser pulses with underdense plasma

    Science.gov (United States)

    Zhidkov, Alexei; Fujii, Takashi; Nemoto, Koshichi

    2008-09-01

    We study the interaction of short laser pulses tightly focused in a tiny volume proportional to the cube of the pulse wavelength (λ3) with underdense plasma by means of real-geometry particle-in-cell simulations. Underdense plasma irradiated by relatively low-energy λ3 (and λ2 ) laser pulses is shown to be an efficient source of multi-MeV electrons, ˜50nC/J , and coherent hard x rays, despite a strong pulse diffraction. Transverse wave breaking in the vicinity of the laser focus is found to give rise to an immense electron charge loading to the acceleration phase of a laser wake field. A strong blowout regime provoked by the injected electrons resulting in the distribution of accelerated electrons is found for λ3 pulses (further electron acceleration driving by λ2 pulses runs in the usual way). With an increase of pulse energy, wiggling and electron-hose instabilities in the λ3 pulse wake are recognized in the blowout regime. For higher-energy λ3 pulses, the injected beams are well modulated and may serve as a good source of coherent x rays.

  6. James Webb Space Telescope Mid Infra-Red Instrument Pulse-Tube Cryocooler Electronics

    Science.gov (United States)

    Harvey, D.; Flowers, T.; Liu, N.; Moore, K.; Tran, D.; Valenzuela, P.; Franklin, B.; Michaels, D.

    2013-01-01

    The latest generation of long life, space pulse-tube cryocoolers require electronics capable of controlling self-induced vibration down to a fraction of a newton and coldhead temperature with high accuracy down to a few kelvin. Other functions include engineering diagnostics, heater and valve control, telemetry and safety protection of the cryocooler subsystem against extreme environments and operational anomalies. The electronics are designed to survive the thermal, vibration, shock and radiation environment of launch and orbit, while providing a design life in excess of 10 years on-orbit. A number of our current generation high reliability radiation-hardened electronics units are in various stages of integration on several space flight payloads. This paper describes the features and performance of our latest flight electronics designed for the pulse-tube cryocooler that is the pre-cooler for a closed cycle Joule-Thomson cooler providing 6K cooling for the James Webb Space Telescope (JWST) Mid Infra-Red Instrument (MIRI). The electronics is capable of highly accurate temperature control over the temperature range from 4K to 15K. Self-induced vibration is controlled to low levels on all harmonics up to the 16th. A unique active power filter controls peak-to-peak reflected ripple current on the primary power bus to a very low level. The 9 kg unit is capable of delivering 360W continuous power to NGAS's 3-stage pulse-tube High-Capacity Cryocooler (HCC).

  7. Pulse-mode measurement of electron beam halo using diamond-based detector

    Science.gov (United States)

    Aoyagi, Hideki; Asano, Yoshihiro; Itoga, Toshiro; Nariyama, Nobuteru; Bizen, Teruhiko; Tanaka, Takashi; Kitamura, Hideo

    2012-02-01

    Using a diamond-based detector, the electron beam halo in a high-energy accelerator can be measured with a lower detection limit than that using other instruments, such as a core monitor, a dose meter, or an optical fiber. We have successfully measured an electron beam halo using diamond-based detectors operating in the ionization mode, which were installed in the beam duct to measure the intensity of the beam halo directly. Pulse-by-pulse measurements were adopted to suppress the background noise efficiently. Feasibility tests on the diamond-based detector and beam halo monitor were performed in the beam dump area of the 8 GeV SPring-8 synchrotron booster and at the 250 MeV SPring-8 Compact SASE Source test accelerator for the SPring-8 Angstrom Compact free electron LAser (SACLA), respectively. We achieved a lower detection limit of 2×103electrons/pulse for single-shot measurement, which corresponds to a ratio of about 10-6 relative to the typical charge of the beam core of 0.3 pC. We also confirmed the feasibility of the electron beam halo monitor for use as an interlock sensor to protect undulator permanent magnets used in SACLA from radiation damage.

  8. James Webb Space Telescope Mid Infra-Red Instrument Pulse-Tube Cryocooler Electronics

    Science.gov (United States)

    Harvey, D.; Flowers, T.; Liu, N.; Moore, K.; Tran, D.; Valenzuela, P.; Franklin, B.; Michaels, D.

    2013-01-01

    The latest generation of long life, space pulse-tube cryocoolers require electronics capable of controlling self-induced vibration down to a fraction of a newton and coldhead temperature with high accuracy down to a few kelvin. Other functions include engineering diagnostics, heater and valve control, telemetry and safety protection of the cryocooler subsystem against extreme environments and operational anomalies. The electronics are designed to survive the thermal, vibration, shock and radiation environment of launch and orbit, while providing a design life in excess of 10 years on-orbit. A number of our current generation high reliability radiation-hardened electronics units are in various stages of integration on several space flight payloads. This paper describes the features and performance of our latest flight electronics designed for the pulse-tube cryocooler that is the pre-cooler for a closed cycle Joule-Thomson cooler providing 6K cooling for the James Webb Space Telescope (JWST) Mid Infra-Red Instrument (MIRI). The electronics is capable of highly accurate temperature control over the temperature range from 4K to 15K. Self-induced vibration is controlled to low levels on all harmonics up to the 16th. A unique active power filter controls peak-to-peak reflected ripple current on the primary power bus to a very low level. The 9 kg unit is capable of delivering 360W continuous power to NGAS's 3-stage pulse-tube High-Capacity Cryocooler (HCC).

  9. Strong-field ionization inducing multi-electron-hole coherence probed by attosecond pulses

    Science.gov (United States)

    Zhao, Jing; Yuan, Jianmin; Zhao, Zengxiu

    2016-05-01

    Recent advances in attosecond spectroscopy has enabled resolving electron-hole dynamics in real time. The correlated electron-hole dynamics and the resulted coherence are directly related to how fast the ionization is completed. How the laser-induced electron-hole coherence evolves and whether it can be utilized to probe the core dynamics are among the key questions in attosecond physics or even attosecond chemistry. In this work, we propose a new scenario to apply IR-pump-XUV-probe schemes to resolving strong field ionization induced and attosecond pulse driven electron-hole dynamics and coherence in real time. The coherent driving of both the infrared laser and the attosecond pulse correlates the dynamics of the core-hole and the valence-hole which leads to the otherwise forbidden absorption and emission of XUV photon. An analytical model is developed based on the strong-field approximation by taking into account of the essential multielectron configurations. The emission spectra from the core-valence transition and the core-hole recombination are found modulating strongly as functions of the time delay between the two pulses, which provides a unique insight into the instantaneous ionization and the interplay of the multi-electron-hole coherence.

  10. Pulse-mode measurement of electron beam halo using diamond-based detector

    Directory of Open Access Journals (Sweden)

    Hideki Aoyagi

    2012-02-01

    Full Text Available Using a diamond-based detector, the electron beam halo in a high-energy accelerator can be measured with a lower detection limit than that using other instruments, such as a core monitor, a dose meter, or an optical fiber. We have successfully measured an electron beam halo using diamond-based detectors operating in the ionization mode, which were installed in the beam duct to measure the intensity of the beam halo directly. Pulse-by-pulse measurements were adopted to suppress the background noise efficiently. Feasibility tests on the diamond-based detector and beam halo monitor were performed in the beam dump area of the 8 GeV SPring-8 synchrotron booster and at the 250 MeV SPring-8 Compact SASE Source test accelerator for the SPring-8 Angstrom Compact free electron LAser (SACLA, respectively. We achieved a lower detection limit of 2×10^{3}  electrons/pulse for single-shot measurement, which corresponds to a ratio of about 10^{-6} relative to the typical charge of the beam core of 0.3 pC. We also confirmed the feasibility of the electron beam halo monitor for use as an interlock sensor to protect undulator permanent magnets used in SACLA from radiation damage.

  11. Microsecond resolved electron density measurements with a hairpin resonator probe in a pulsed ICP discharge

    CERN Document Server

    Peterson, David; Larson, Lynda; Shannon, Steven

    2016-01-01

    Time resolved electron density measurements in pulsed RF discharges are shown using a hairpin resonance probe using low cost electronics, on par with normal Langmuir probe boxcar mode operation. Time resolution of less than one microsecond has been demonstrated. A signal generator produces the applied microwave frequency; the reflected waveform is passed through a directional coupler and filtered to remove the RF component. The signal is heterodyned with a frequency mixer and read by an oscilloscope. At certain points during the pulse, the plasma density is such that the applied frequency is the same as the resonance frequency of the probe/plasma system, creating a dip in the reflected signal. The applied microwave frequency is shifted in small increments in a frequency boxcar routine to determine the density as a function of time. The system uses a grounded probe to produce low cost, high fidelity, and highly reproducible electron density measurements that can work in harsh chemical environments. Measurement...

  12. Comparison of short pulse generation schemes for a soft x-ray free electron laser

    Science.gov (United States)

    Martin, I. P. S.; Bartolini, R.

    2011-03-01

    In this paper we study the performance of two complementary short pulse generation schemes as applied to a soft x-ray free electron laser. The first scheme, recently proposed by Saldin et al., makes use of a laser pulse consisting of only a few optical cycles to give an energy chirp to a short section of an electron bunch and tapers the main radiator undulator in order to compensate the chirped region. The second scheme investigated takes a low-charge, high brightness electron bunch and compresses it to ˜1fs in order to operate in the so-called “single-spike” regime. We perform start-to-end simulations of both these schemes, assess the sensitivity of each scheme to realistic jitter sources, and provide a direct comparison of the respective strengths and drawbacks.

  13. Comparison of short pulse generation schemes for a soft x-ray free electron laser

    Directory of Open Access Journals (Sweden)

    I. P. S. Martin

    2011-03-01

    Full Text Available In this paper we study the performance of two complementary short pulse generation schemes as applied to a soft x-ray free electron laser. The first scheme, recently proposed by Saldin et al., makes use of a laser pulse consisting of only a few optical cycles to give an energy chirp to a short section of an electron bunch and tapers the main radiator undulator in order to compensate the chirped region. The second scheme investigated takes a low-charge, high brightness electron bunch and compresses it to ∼1  fs in order to operate in the so-called “single-spike” regime. We perform start-to-end simulations of both these schemes, assess the sensitivity of each scheme to realistic jitter sources, and provide a direct comparison of the respective strengths and drawbacks.

  14. Lateral resolution in focused electron beam-induced deposition: scaling laws for pulsed and static exposure

    Energy Technology Data Exchange (ETDEWEB)

    Szkudlarek, Aleksandra [Empa, Laboratory for Mechanics of Materials and Nanostructures, Thun (Switzerland); AGH University of Science and Technology, Department of Solid State Physics, Faculty of Physics and Applied Computer Science, Krakow (Poland); Szmyt, Wojciech; Kapusta, Czeslaw [AGH University of Science and Technology, Department of Solid State Physics, Faculty of Physics and Applied Computer Science, Krakow (Poland); Utke, Ivo [Empa, Laboratory for Mechanics of Materials and Nanostructures, Thun (Switzerland)

    2014-12-15

    In this work, we review the single-adsorbate time-dependent continuum model for focused electron beam-induced deposition (FEBID). The differential equation for the adsorption rate will be expressed by dimensionless parameters describing the contributions of adsorption, desorption, dissociation, and the surface diffusion of the precursor adsorbates. The contributions are individually presented in order to elucidate their influence during variations in the electron beam exposure time. The findings are condensed into three new scaling laws for pulsed exposure FEBID (or FEB-induced etching) relating the lateral resolution of deposits or etch pits to surface diffusion and electron beam exposure dwell time for a given adsorbate depletion state. (orig.)

  15. Desorption of H atoms from graphite (0001) using XUV free electron laser pulses

    DEFF Research Database (Denmark)

    Siemer, B.; Olsen, Thomas; Hoger, T.;

    2010-01-01

    , and identifies the highest vibrational state in the adsorbate potential as a major source for the slow atoms. It is evident that multiple electron scattering processes are required for this desorption. A direct electronic excitation of a repulsive hydrogen-carbon bond seems not to be important.......The desorption of neutral H atoms from graphite with femtosecond XUV pulses is reported. The velocity distribution of the atoms peaks at extremely low kinetic energies. A DFT-based electron scattering calculation traces this distribution to desorption out of specific adsorption sites on graphite...

  16. A new method for detecting pulse gamma ray with scattered electrons

    Institute of Scientific and Technical Information of China (English)

    Xia Liang-Bin; Ouyang Xiao-Ping; Wang Oun-Shu; Zang Ke-Jun; Tan Xin-Jian

    2008-01-01

    This paper describes a newly designed gamma pulse detector of current mode that uses the scattered electron method. Tungsten is used as the scattering target, an organic thin film scintillator ST401 is used to collect the scattered electrons. The spatial distribution of the electronic energy-flux density is studied by using the MCNP code. The optimization of the target and the thickness of the scintillator are also discussed. The results indicate that the energy response is relatively flat in the range of 0.4 to 5 MeV.

  17. Dissociative multiple ionization of diatomic molecules by extreme-ultraviolet free-electron-laser pulses

    DEFF Research Database (Denmark)

    Madsen, Lars Bojer; Leth, Henriette Astrup

    2011-01-01

    Nuclear dynamics in dissociative multiple ionization processes of diatomic molecules exposed to extreme-ultraviolet free-electron-laser pulses is studied theoretically using the Monte Carlo wave packet approach. By simulated detection of the emitted electrons, the model reduces a full propagation...... of the system to propagations of the nuclear wave packet in one specific electronic charge state at a time. Suggested ionization channels can be examined, and kinetic energy release spectra for the nuclei can be calculated and compared with experiments. Double ionization of O2 is studied as an example, and good...

  18. Practical method and device for enhancing pulse contrast ratio for lasers and electron accelerators

    Science.gov (United States)

    Zhang, Shukui; Wilson, Guy

    2014-09-23

    An apparatus and method for enhancing pulse contrast ratios for drive lasers and electron accelerators. The invention comprises a mechanical dual-shutter system wherein the shutters are placed sequentially in series in a laser beam path. Each shutter of the dual shutter system has an individually operated trigger for opening and closing the shutter. As the triggers are operated individually, the delay between opening and closing first shutter and opening and closing the second shutter is variable providing for variable differential time windows and enhancement of pulse contrast ratio.

  19. Electron Acceleration by a Bichromatic Chirped Laser Pulse in Underdense Plasmas

    CERN Document Server

    Pocsai, Mihály András; Varró, Sándor

    2015-01-01

    A theoretical study of laser and plasma based electron acceleration is presented. An effective model has been used, in which the presence of an underdense plasma has been taken account via its index of refraction $n_{m}$. In the confines of this model, the basic phenomena can be studied by numerically solving the classical relativistic equations of motion. The key idea of this paper is the application of chirped, bichromatic laser fields. We investigated the advantages and disadvantages of mixing the second harmonic to the original $\\lambda = 800 \\, \\mathrm{nm}$ wavelength pulse. We performed calculations both for plane wave and Gaussian pulses.

  20. Pulse laser induced graphite-to-diamond phase transition: the role of quantum electronic stress

    Science.gov (United States)

    Wang, ZhengFei; Liu, Feng

    2017-02-01

    First-principles calculations show that the pulse laser induced graphite-to-diamond phase transition is related to the lattice stress generated by the excited carriers, termed as "quantum electronic stress (QES)". We found that the excited carriers in graphite generate a large anisotropic QES that increases linearly with the increasing carrier density. Using the QES as a guiding parameter, structural relaxation spontaneously transforms the graphite phase into the diamond phase, as the QES is reduced and minimized. Our results suggest that the concept of QES can be generally applied as a good measure to characterize the pulse laser induced phase transitions, in analogy to pressure induced phase transitions.

  1. Electron acceleration by tightly focused radially polarized few-cycle laser pulses

    Institute of Scientific and Technical Information of China (English)

    Liu Jin-Lu; Sheng Zheng-Ming; Zheng Jun

    2012-01-01

    Within the framework of plane-wave angular spectrum analysis of the electromagnetic field structure,a solution valid for tightly focused radially polarized few-cycle laser pulses propagating in vacuum is presented.The resulting field distribution is significantly different from that based on the paraxial approximation for pulses with either small or large beam diameters.We compare the electron accelerations obtained with the two solutions and find that the energy gain obtained with our new solution is usually much larger than that with the paraxial approximation solution.

  2. Space charge calculations of elliptical cross-section electron pulses in PARMELA

    CERN Document Server

    Koltenbah, B E C

    1999-01-01

    The Boeing version of the PARMELA code has been modified to compute the space charge effects for electron pulses with highly elliptical transverse cross-sections. A dynamic gridding routine has been added to allow good resolution for pulses as they evolve in time. The results from calculations for the chicane buncher in the 1 kW visible FEL beam line at Boeing indicate that the old circular algorithm of the SCHEFF subroutine overestimates the emittance growth in the bend plane by 30-40%.

  3. Effect of pulse electron beam characteristics on internal friction and structural alterations in epoxy

    Energy Technology Data Exchange (ETDEWEB)

    Zaikin, Yu.A. [Al Farabi Kazakh National University, Almaty (Kazakhstan)]. E-mail: drzaykin@mail.ru; Ismailova, G.A. [Al Farabi Kazakh National University, Almaty (Kazakhstan); Al-Sheikhly, M. [University of Maryland, College Park (United States)

    2007-08-15

    Temperature dependence of internal friction is experimentally studied in epoxy irradiated by 2.5 MeV pulse electron beam to different doses. Time dependence of internal friction characteristics associated with radiation-induced processes of polymer scission and cross-linking is analyzed and discussed. Experimental data on kinetics of structural transformations in epoxy are interpreted on the base of analytical solutions of differential equations for free radical accumulation during and after irradiation subject to the pulse irradiation mode and an arbitrary effective order of radical recombination.

  4. Plasma electron source for the generation of wide-aperture pulsed beam at forevacuum pressures

    Energy Technology Data Exchange (ETDEWEB)

    Oks, E.; Burdovitsin, V.; Medovnik, A.; Yushkov, Yu. [Tomsk State University of Control Systems and Radioelectronics, Tomsk 634050 (Russian Federation)

    2013-02-15

    This article reports on design and application of wide-aperture pulsed beam source, based on hollow cathode discharge. The source is intended for electron beam generation in pressure range 2-15 Pa. Multi-aperture extraction system, used in a source, provided beam cross-section uniformity of 10% on diameter 40 mm. The limiting values of the current density, pulse duration, and accelerating voltage are 350 mA/cm{sup 2}, 250 {mu}s, and 10 kV, respectively. These parameters are sufficient for surface modification of various materials, including non-conducting matters.

  5. EPR in characterization of seeds paramagnetic species

    Energy Technology Data Exchange (ETDEWEB)

    Luiz, A.P.C.; Mauro, M.F.F.L.; Portugal, K.O.; Barbana, V.M.; Guedes, C.L.B.; Mauro, E. di; Carneiro, C.E.A.; Zaia, D.A.M.; Prete, C.E.C. [Universidade Estadual de Londrina (UEL), PR (Brazil)

    2011-07-01

    Full text. In Brazil, since 1970s, renewable fuel programs has been developed in order to replace petroleum. Today a program that has been discussed is the bio diesel, which intend to replace diesel fuel, fossil oil, to bio diesel, renewal fuel. As seeds are the basis for production of oil and consequently processed into bio diesel, the goal of this work is to characterize and compare paramagnetic species present in the seeds by Electron Paramagnetic Resonance (EPR). Samples used in this study were seeds of sorghum, barley, corn, peanuts, soy beans, cotton, wheat, oats, mustard, rice, sunflower and turnip. Some paramagnetic species present in soil was also investigated as goethite (FeOOH), hematite (Fe{sub 2}O{sub 3}), magnetite (Fe{sub 3}O{sub 4}), and ferrihydrite (Fe{sub 5}HO{sub 8} {center_dot} 4H{sub 2}O), since, these species present in appreciable quantities in the soil can be present in the seeds and analyzed for comparison. The characterization of these species is essential to understand the EPR seeds spectra. Each sample is placed in a thin quartz tube 4 mm in diameter, and it is inserted into the cavity of the spectrometer at room temperature, at low temperature (77 K) and variable temperature using liquid nitrogen flow and hot flow through a compressor air. It was used as standard Mg O:Mn{sup 2+}, which is also inserted into the cavity. Shortly after the potency is regulated, frequency, amplitude and sweep the field. The spectroscopic analysis by EPR X-band ({approx} 9:5GHz), were performed at the Fluorescence and Electron Paramagnetic Resonance Laboratory, Exact Sciences Center, State University of Londrina, Parana state, Brazil, through an EPR spectrometer JEOL brand (JES-PE-3X). In the EPR spectra, spectroscopic factor or g factor and line width were determined in paramagnetic species. Studies from several seeds with EPR technique detected in all of them presence of same complex of Fe{sup 3+} present in the goethite at g {approx} 2, and in the seeds

  6. The effect of PVP on morphology, optical properties and electron paramagnetic resonance of Zn0.5Co0.5Fe2-xPrxO4 nanoparticles

    Science.gov (United States)

    Bitar, Z.; El-Said Bakeer, D.; Awad, R.

    2017-07-01

    Zinc Cobalt nano ferrite doped with Praseodymium, Zn0.5Co0.5Fe2-xPrxO4 (0 ≤ x ≤ 0.2), were prepared by co-precipitation method from an aqueous solution containing metal chlorides and two concentrations of poly(vinylpyrrolidone) (PVP) 0 and 30g/L as capping agent. The samples were characterized using X-ray powder diffraction (XRD), Transmission Electron Microscope (TEM), UV-visible optical spectroscopy, Fourier transform infrared (FTIR) and Electron Paramagnetic Resonance (EPR). XRD results display the formation of cubic spinel structure with space group Fd3m and the lattice parameter (a) is slightly decreased for PVP capping samples. The particle size that determined by TEM, decreases for PVP capping samples. The optical band energy Eg increases for PVP capping samples, confirming the variation of energy gap with the particle size. The FTIR results indicate that the metal oxide bands were shifted for the PVP capping samples. EPR data shows that the PVP addition increases the magnetic resonance field and hence decreases the g-factor.

  7. Laser-driven electron beam generation for secondary photon sources with few terawatt laser pulses

    Science.gov (United States)

    Bohacek, K.; Chaulagain, U.; Horny, V.; Kozlova, M.; Krus, M.; Nejdl, J.

    2017-05-01

    Relativistic electron beams accelerated by laser wakefield have the ability to serve as sources of collimated, point-like and femtosecond X-ray radiation. Experimental conditions for generation of stable quasi-monoenergetic electron bunches using a femtosecond few-terawatt laser pulse (600 mJ, 50 fs) were investigated as they are crucial for generation of stable betatron radiation and X-ray pulses from inverse Compton scattering. A mixture of helium with argon, and helium with an admixture of synthetic air were tested for this purpose using different backing pressures and the obtained results are compared. The approach to use synthetic air was previously proven to stabilize the energy and energy spread of the generated electron beams at the given laser power. The accelerator was operated in nonlinear regime with forced self-injection and resulted in the generation of stable relativistic electron beams with an energy of tens of MeV and betatron X-ray radiation was generated in the keV range. A razor blade was tested to create a steep density gradient in order to improve the stability of electron injection and to increase the total electron bunch charge. It was proven that the stable electron and X-ray source can be built at small-scale facilities, which readily opens possibilities for various applications due to availability of such few-terawatt laser systems in many laboratories around the world.

  8. Water diffusion-exchange effect on the paramagnetic relaxation enhancement in off-resonance rotating frame

    Science.gov (United States)

    Zhang, Huiming; Xie, Yang; Ji, Tongyu

    2007-06-01

    The off-resonance rotating frame technique based on the spin relaxation properties of off-resonance T1 ρ can significantly increase the sensitivity of detecting paramagnetic labeling at high magnetic fields by MRI. However, the in vivo detectable dimension for labeled cell clusters/tissues in T1 ρ-weighted images is limited by the water diffusion-exchange between mesoscopic scale compartments. An experimental investigation of the effect of water diffusion-exchange between compartments on the paramagnetic relaxation enhancement of paramagnetic agent compartment is presented for in vitro/ in vivo models. In these models, the size of paramagnetic agent compartment is comparable to the mean diffusion displacement of water molecules during the long RF pulses that are used to generate the off-resonance rotating frame. The three main objectives of this study were: (1) to qualitatively correlate the effect of water diffusion-exchange with the RF parameters of the long pulse and the rates of water diffusion, (2) to explore the effect of water diffusion-exchange on the paramagnetic relaxation enhancement in vitro, and (3) to demonstrate the paramagnetic relaxation enhancement in vivo. The in vitro models include the water permeable dialysis tubes or water permeable hollow fibers embedded in cross-linked proteins gels. The MWCO of the dialysis tubes was chosen from 0.1 to 15 kDa to control the water diffusion rate. Thin hollow fibers were chosen to provide sub-millimeter scale compartments for the paramagnetic agents. The in vivo model utilized the rat cerebral vasculatures as a paramagnetic agent compartment, and intravascular agents (Gd-DTPA) 30-BSA were administrated into the compartment via bolus injections. Both in vitro and in vivo results demonstrate that the paramagnetic relaxation enhancement is predominant in the T1 ρ-weighted image in the presence of water diffusion-exchange. The T1 ρ contrast has substantially higher sensitivity than the conventional T1

  9. Spatial and temporal coherence properties of single free-electron laser pulses

    CERN Document Server

    Singer, A; Mancuso, A P; Gerasimova, N; Yefanov, O M; Gulden, J; Gorniak, T; Senkbeil, T; Sakdinawat, A; Liu, Y; Attwood, D; Dziarzhytski, S; Mai, D D; Treusch, R; Weckert, E; Salditt, T; Rosenhahn, A; Wurth, W; Vartanyants, I A

    2015-01-01

    The experimental characterization of the spatial and temporal coherence properties of the free-electron laser in Hamburg (FLASH) at a wavelength of 8.0 nm is presented. Double pinhole diffraction patterns of single femtosecond pulses focused to a size of about 10 microns by 10 microns were measured. A transverse coherence length of 6.2 microns in the horizontal and 8.7 microns in the vertical direction was determined from the most coherent pulses. Using a split and delay unit the coherence time of the pulses produced in the same operation conditions of FLASH was measured to be 1.75 fs. From our experiment we estimated the degeneracy parameter of the FLASH beam to be on the order of $10^{10}$ to $10^{11}$, which exceeds the values of this parameter at any other source in the same energy range by many orders of magnitude.

  10. Electron Acceleration and the Propagation of Ultrashort High-Intensity Laser Pulses in Plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xiaofang; Krishnan, Mohan; Saleh, Ned; Wang, Haiwen; Umstadter, Donald

    2000-06-05

    Reported are interactions of high-intensity laser pulses ({lambda}=810 nm and I{<=}3x10{sup 18} W /cm{sup 2} ) with plasmas in a new parameter regime, in which the pulse duration ({tau}=29 fs ) corresponds to 0.6-2.6 plasma periods. Relativistic filamentation is observed to cause laser-beam breakup and scattering of the beam out of the vacuum propagation angle. A beam of megaelectronvolt electrons with divergence angle as small as 1 degree sign is generated in the forward direction, which is correlated to the growth of the relativistic filamentation. Raman scattering, however, is found to be much less than previous long-pulse results. (c) 2000 The American Physical Society.

  11. Laser and Pulsed Power Electron Density Imaging Through Talbot-Lau X-ray Deflectometry

    Science.gov (United States)

    Valdivia Leiva, Maria Pia; Stutman, Dan; Stoeckl, Christian; Mileham, Chad; Begischev, Ildar; Theobald, Wolfgang; Bromage, Jake; Regan, Sean; Klein, Salee; Muñoz-Cordovez, Gonzalo; Vescovi, Milenko; Valenzuela-Villaseca, Vicente; Veloso, Felipe

    2016-10-01

    A Talbot-Lau X-ray Deflectometer was deployed using laser driven and x-pinch x-ray backlighters. The Talbot-Lau X-ray Deflectometer is an ideal electron density diagnostic for High Energy Density plasmas with the potential to simultaneously deliver x-ray refraction, attenuation, elemental composition, and scatter information from a single image with source limited resolution. Grating survival and electron density mapping was demonstrated for 10-29 J, 8-30 ps laser pulses using Cu foil targets at the Multi-TeraWatt facility. An areal electron density of 0.050 g/cm2 was obtained at the center of a fluoro-nylon fiber of 300 mm diameter with a source FWHM of 80 µm and resolution of 50 µm. Grating survival and Moiré pattern formation was demonstrated using a Cu x-pinch plasma of FWHM 27 µm, driven by the 350 kA, 350 ns Llampudken pulsed power generator. These results closely match simulations and laboratory results. It was demonstrated that the technique can detect both sharp and smooth density gradients in the range of 2x1023 to 2x1025 cm-3, thus allowing implementation of the electron density technique as a HED plasma diagnostic in both laser and pulsed power experiments U.S. DoE/NNSA and DE-NA0002955.

  12. Experimental evidence of nonthermal acceleration of relativistic electrons by an intensive laser pulse.

    Science.gov (United States)

    Kuramitsu, Y; Nakanii, N; Kondo, K; Sakawa, Y; Mori, Y; Miura, E; Tsuji, K; Kimura, K; Fukumochi, S; Kashihara, M; Tanimoto, T; Nakamura, H; Ishikura, T; Takeda, K; Tampo, M; Kodama, R; Kitagawa, Y; Mima, K; Tanaka, K A; Hoshino, M; Takabe, H

    2011-02-01

    Nonthermal acceleration of relativistic electrons is investigated with an intensive laser pulse. An energy distribution function of energetic particles in the universe or cosmic rays is well represented by a power-law spectrum, therefore, nonthermal acceleration is essential to understand the origin of cosmic rays. A possible candidate for the origin of cosmic rays is wakefield acceleration at relativistic astrophysical perpendicular shocks. The wakefield is considered to be excited by large-amplitude precursor light waves in the upstream of the shocks. Substituting an intensive laser pulse for the large amplitude light waves, we performed a model experiment of the shock environments in a laboratory plasma. An intensive laser pulse was propagated in a plasma tube created by imploding a hollow polystyrene cylinder, as the large amplitude light waves propagated in the upstream plasma at an astrophysical shock. Nonthermal electrons were generated, and the energy distribution functions of the electrons have a power-law component with an index of ~2. We described the detailed procedures to obtain the nonthermal components from data obtained by an electron spectrometer.

  13. Modeling of beam-target interaction during pulsed electron beam ablation of graphite: Case of melting

    Science.gov (United States)

    Ali, Muddassir; Henda, Redhouane

    2017-02-01

    A one-dimensional thermal model based on a two-stage heat conduction equation is employed to investigate the ablation of graphite target during nanosecond pulsed electron beam ablation. This comprehensive model accounts for the complex physical phenomena comprised of target heating, melting and vaporization upon irradiation with a polyenergetic electron beam. Melting and vaporization effects induced during ablation are taken into account by introducing moving phase boundaries. Phase transition induced during ablation is considered through the temperature dependent thermodynamic properties of graphite. The effect of electron beam efficiency, power density, and accelerating voltage on ablation is analyzed. For an electron beam operating at an accelerating voltage of 15 kV and efficiency of 0.6, the model findings show that the target surface temperature can reach up to 7500 K at the end of the pulse. The surface begins to melt within 25 ns from the pulse start. For the same process conditions, the estimated ablation depth and ablated mass per unit area are about 0.60 μm and 1.05 μg/mm2, respectively. Model results indicate that ablation takes place primarily in the regime of normal vaporization from the surface. The results obtained at an accelerating voltage of 15 kV and efficiency factor of 0.6 are satisfactorily in good accordance with available experimental data in the literature.

  14. Time-resolved microplasma electron dynamics in a pulsed microwave discharge

    Science.gov (United States)

    Monfared, S. K.; Hoskinson, A. R.; Hopwood, J.

    2013-10-01

    Microwave-driven microplasmas are typically operated in a steady-state mode in which the electron temperature is constant in time. Transient measurements of excitation temperature and helium emission lines, however, suggest that short microwave pulses can be used to increase the electron energy by 20-30%. Time-resolved optical emission spectrometry reveals an initial burst of light emission from the igniting microplasma. This emission overshoot is also correlated with a measured increase in excitation temperature. Excimer emission lags atomic emission, however, and does not overshoot. A simple model shows that an increase in electron temperature is responsible for the overshoot of atomic optical emission at the beginning of each microwave pulse. The formation of dimers and subsequent excimer emission requires slower three-body collisions with the excited rare gas atoms, which is why excimer emission does not overshoot the steady-state values. Similar results are observed in argon gas. The overshoot in electron temperature may be used to manipulate the collisional production of species in microplasmas using short, low-duty cycle microwave pulses.

  15. Synthesis of substituted lithium ferrites under the pulsed and continuous electron beam heating

    Science.gov (United States)

    Lysenko, Elena N.; Surzhikov, Anatoliy P.; Vlasov, Vitaliy A.; Nikolaev, Evgeniy V.; Malyshev, Andrey V.; Bryazgin, Alexandr A.; Korobeynikov, Mikhail V.; Mikhailenko, Mikhail A.

    2017-02-01

    Synthesis of substituted lithium ferrites with chemical formulas Li0.6Fe2.2Ti0.2O4 and Li0.649Fe1.598Ti0.5Zn0.2Mn0.051O4 under the pulsed and continuous electron beam heating was investigated by X-ray diffraction and thermomagnetometric analysis. The electron beams heating of Li2CO3-Fe2O3-TiO2 or Li2CO3-ZnO-Fe2O3-TiO2-MnO mixtures was carried out at a temperature of 750 °C during 60 min using two types of electron accelerators: ELV accelerator generating continuous electron beam or ILU-6 accelerator generating pulse electron beam. It was established that a high energy electron beam heating of initial reagents mixtures allows obtaining the substituted lithium ferrites with final composition at significantly lower temperatures (at least 200 °C lower than in the case of using traditional thermal synthesis) and times of synthesis. That statement is in agreement with results obtained by XRD analysis, showing single phase formation; by magnetic measurements, showing high values of specific magnetization; by DTG measurements showing the certain Curie temperatures of the synthesized samples.

  16. Acceleration of electrons under the action of petawatt-class laser pulses onto foam targets

    Science.gov (United States)

    Pugachev, L. P.; Andreev, N. E.; Levashov, P. R.; Rosmej, O. N.

    2016-09-01

    Optimization study for future experiments on interaction of petawatt laser pulses with foam targets was done by 3D PIC simulations. Densities in the range 0.5nc-nc and thicknesses in the range 100 - 500 μm of the targets were considered corresponding to those which are currently available. It is shown that heating of electrons mainly occurs under the action of the ponderomotive force of a laser pulse in which amplitude increases up to three times because of self-focusing effect in underdense plasma. Accelerated electrons gain additional energy directly from the high-frequency laser field at the betatron resonance in the emerging plasma density channels. For thicker targets a higher number of electrons with higher energies are obtained. The narrowing of the angular distribution of electrons for thicker targets is explained by acceleration in multiple narrow filaments. Obtained energies of accelerated electrons can be approximated by Maxwell distribution with the temperature 8.5 MeV. The charge carried by electrons with energies higher than 30 MeV is about 30 nC, that is 3-4 order of magnitude higher than the charge predicted by the ponderomotive scaling for the incident laser amplitude.

  17. Reflection of femtosecond pulses from soft X-ray free-electron laser by periodical multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Ksenzov, D.; Grigorian, S.; Pietsch, U. [Faculty of Physics, University of Siegen (Germany); Hendel, S.; Bienert, F.; Sacher, M.D.; Heinzmann, U. [Faculty of Physics, University of Bielefeld (Germany)

    2009-08-15

    Recent experiments on a soft X-ray free-electron laser (FEL) source (FLASH in Hamburg) have shown that multilayers (MLs) can be used as optical elements for highly intense X-ray irradiation. An effort to find most appropriate MLs has to consider the femtosecond time structure and the particular photon energy of the FEL. In this paper we have analysed the time response of 'low absorbing' MLs (e.g. such as La/B{sub 4}C) as a function of the number of periods. Interaction of a pulse train of Gaussian shaped sub-pulses using a realistic ML grown by electron-beam evaporation technique has been analysed in the soft-X-ray range. The structural parameters of the MLs were obtained by reflectivity measurements at BESSY II and subsequent profile fittings. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  18. Power pulsing scheme for analog and digital electronics of the vertex detectors at CLIC

    CERN Document Server

    Blanchot, Georges

    2015-01-01

    The precision requirements of the vertex detector at CLIC impose strong limitations on the mass of such a detector (< 0.2% of a radiation length, Xo, per layer). To achieve such a low material budget, ultra-thin hybrid pixel detectors are foreseen, while the mass for cooling and services will be reduced by implementing a power pulsing scheme that takes advantage of the low duty cycle of the accelerator. The principal aim is to achieve significant power reduction without compromising the power integrity supplied to the front-end electronics. This report summarises the study of a power pulsing scheme to power the vertex barrel electronics of the future CLIC experiment. Its main goal is to describe in more detail what has been already presented in TWEPP conferences and other presentations. The report can therefore serve as an operator manual for future use and development of the system

  19. Simulation study of electron injection into plasma wake fields by colliding laser pulses using OOPIC

    Institute of Scientific and Technical Information of China (English)

    HE An; GAO Jie; ZHU Xiong-Wei; LI Da-Zhang; XU Hong-Liang

    2009-01-01

    An electron injector concept for a laser-plasma accelerator has been developed which relies on the use of counter propagating ultrashort laser pulses.In this paper,we use OOPIC the fully self-consistent,twodimensional.particle-in-cell code to make a parameter study to determine the bunches that can be obtained through collisions of two collinear laser pulses in uniform plasma.A series of simulations show that one can obtain a short(<10fs)bunch with its charge of about 15pC,and energy spread of about 15%.We also discussed the variation of the transverse spot size of the electron bunch and found the bunch would undergo the betatron oscillations.

  20. Enhancement of ultrafast electron photoemission from metallic nano antennas excited by a femtosecond laser pulse

    CERN Document Server

    Gubko, M A; Ionin, A A; Kudryashov, S I; Makarov, S V; Nathala, C S R; Rudenko, A A; Seleznev, L V; Sinitsyn, D V; Treshin, I V

    2013-01-01

    We have demonstrated for the first time that an array of nanoantennas (central nanotips inside sub-micron pits) on an aluminum surface, fabricated using a specific double-pulse femtosecond laser irradiation scheme, results in a 28-fold enhancement of the non-linear (three-photon) electron photoemission yield, driven by a third intense IR femtosecond laser pulse. The supporting numerical electrodynamic modeling indicates that the electron emission is increased not owing to a larger effective aluminum surface, but due to instant local electromagnetic field enhancement near the nanoantenna, contributed by both the tip's lightning rod effect and the focusing effect of the pit as a microreflector and annular edge as a plasmonic lens.