WorldWideScience

Sample records for neutron tunneling spectroscopy

  1. Neutron resonance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Gunsing, F

    2005-06-15

    The present document has been written in order to obtain the diploma 'Habilitation a Diriger des Recherches'. Since this diploma is indispensable to supervise thesis students, I had the intention to write a document that can be useful for someone starting in the field of neutron resonance spectroscopy. Although the here described topics are already described elsewhere, and often in more detail, it seemed useful to have most of the relevant information in a single document. A general introduction places the topic of neutron-nucleus interaction in a nuclear physics context. The large variations of several orders of magnitude in neutron-induced reaction cross sections are explained in terms of nuclear level excitations. The random character of the resonances make nuclear model calculation predictions impossible. Then several fields in physics where neutron-induced reactions are important and to which I have contributed in some way or another, are mentioned in a first synthetic chapter. They concern topics like parity nonconservation in certain neutron resonances, stellar nucleosynthesis by neutron capture, and data for nuclear energy applications. The latter item is especially important for the transmutation of nuclear waste and for alternative fuel cycles. Nuclear data libraries are also briefly mentioned. A second chapter details the R-matrix theory. This formalism is the foundation of the description of the neutron-nucleus interaction and is present in all fields of neutron resonance spectroscopy. (author)

  2. Planar Tunneling Spectroscopy of Graphene Nanodevices

    Science.gov (United States)

    Wang, Joel I.-Jan; Bretheau, Landry; Pisoni, Riccardo; Watanabe, Kenji; Taniguchi, Takashi; Jarillo-Herrero, Pablo

    2-D Van-der-Waals mesoscopic physics have seen a rapid development in the last 10 years, with new materials each year added to the toolbox. Stacking them like Lego enables the combination of their individual electronic properties. In particular, hexagonal boron nitride, which is an insulator, gives the possibility to perform planar (2-D to 2-D) tunneling spectroscopy within this type of heterostructures. Unlike standard transport measurements, tunneling spectroscopy enables to probe the electronic properties in the energy domain. Moreover, since planar tunneling probes a large area of the system, global quantum features such as quantum Hall effect, superconducting proximity effect or quantum confinement can be investigated. In this talk, we will present implementation of heterostructures consisting of graphene, hexagonal boron nitride, and graphite, fabricated for planar tunneling spectroscopy. In order to reveal the intrinsic properties of materials, the fabrication scheme aims at preserving the pristine nature of the 2-DEGS as well as minimizing the doping introduced by external probes. As a demonstration, measurements of these devices in normal states, high magnetic field environment, and induced superconducting state will be presented.

  3. Neutron spectroscopy with the Spherical Proportional Counter

    CERN Document Server

    Bougamont, E; Derre, J; Galan, J; Gerbier, G; Giomataris, I; Gros, M; Katsioulas, I; Jourde, D; Magnier, P; Navick, X F; Papaevangelou, T; Savvidis, I; Tsiledakis, G

    2015-01-01

    A novel large volume spherical proportional counter, recently developed, is used for neutron measurements. Gas mixtures of $N_{2}$ with $C_{2}H_{6}$ and pure $N_{2}$ are studied for thermal and fast neutron detection, providing a new way for the neutron spectroscopy. The neutrons are detected via the ${}^{14}N(n, p)C^{14}$ and ${}^{14}N(n, \\alpha)B^{11}$ reactions. Here we provide studies of the optimum gas mixture, the gas pressure and the most appropriate high voltage supply on the sensor of the detector in order to achieve the maximum amplification and better resolution. The detector is tested for thermal and fast neutrons detection with a ${}^{252}Cf$ and a ${}^{241}Am-{}^{9}Be$ neutron source. The atmospheric neutrons are successfully measured from thermal up to several MeV, well separated from the cosmic ray background. A comparison of the spherical proportional counter with the current available neutron counters is also given.

  4. Inelastic Electron Tunneling Spectroscopy for Topological Insulators

    Science.gov (United States)

    She, Jian-Huang; Fransson, Jonas; Bishop, A. R.; Balatsky, Alexander V.

    2013-01-01

    Inelastic electron tunneling spectroscopy is a powerful spectroscopy that allows one to investigate the nature of local excitations and energy transfer in the system of interest. We study inelastic electron tunneling spectroscopy for topological insulators and investigate the role of inelastic scattering on the Dirac node states on the surface of topological insulators. Local inelastic scattering is shown to significantly modify the Dirac node spectrum. In the weak coupling limit, peaks and steps are induced in second derivative d2I/dV2. In the strong coupling limit, the local negative-U centers are formed at impurity sites, and the Dirac cone structure is fully destroyed locally. At intermediate coupling, resonance peaks emerge. We map out the evolution of the resonance peaks from weak to strong coupling, which interpolate nicely between the two limits. There is a sudden qualitative change of behavior at intermediate coupling, indicating the possible existence of a local quantum phase transition. We also find that, even for a simple local phonon mode, the inherent coupling of spin and orbital degrees in topological insulators leads to the spin-polarized texture in inelastic Friedel oscillations induced by the local mode.

  5. Preparation of reliable probes for electrochemical tunneling spectroscopy.

    Science.gov (United States)

    Güell, Aleix G; Díez-Pérez, Ismael; Gorostiza, Pau; Sanz, Fausto

    2004-09-01

    We present a new procedure to prepare Pt/Ir probes for electrochemical scanning tunneling microscopy (STM) and spectroscopy applications. We detail the experimental setup and the improvements over previous methods. The probes have been used successfully for measurements of tunneling spectroscopy under electrochemical control, which requires scanning the potential of the tip at high velocity. Copyright 2004 American Chemical Society

  6. Tunnelling spectroscopy of Andreev states in graphene

    Science.gov (United States)

    Bretheau, Landry; Wang, Joel I.-Jan; Pisoni, Riccardo; Watanabe, Kenji; Taniguchi, Takashi; Jarillo-Herrero, Pablo

    2017-08-01

    A normal conductor placed in good contact with a superconductor can inherit its remarkable electronic properties. This proximity effect microscopically originates from the formation in the conductor of entangled electron-hole states, called Andreev states. Spectroscopic studies of Andreev states have been performed in just a handful of systems. The unique geometry, electronic structure and high mobility of graphene make it a novel platform for studying Andreev physics in two dimensions. Here we use a full van der Waals heterostructure to perform tunnelling spectroscopy measurements of the proximity effect in superconductor-graphene-superconductor junctions. The measured energy spectra, which depend on the phase difference between the superconductors, reveal the presence of a continuum of Andreev bound states. Moreover, our device heterostructure geometry and materials enable us to measure the Andreev spectrum as a function of the graphene Fermi energy, showing a transition between different mesoscopic regimes. Furthermore, by experimentally introducing a novel concept, the supercurrent spectral density, we determine the supercurrent-phase relation in a tunnelling experiment, thus establishing the connection between Andreev physics at finite energy and the Josephson effect. This work opens up new avenues for probing exotic topological phases of matter in hybrid superconducting Dirac materials.

  7. Neutron and X-ray Spectroscopy

    CERN Document Server

    Hippert, Françoise; Hodeau, Jean Louis; Lelièvre-Berna, Eddy; Regnard, Jean-René

    2006-01-01

    Neutron and X-Ray Spectroscopy delivers an up-to-date account of the principles and practice of inelastic and spectroscopic methods available at neutron and synchrotron sources, including recent developments. The chapters are based on a course of lectures and practicals (the HERCULES course) delivered to young scientists who require these methods in their professional careers. Each chapter, written by a leading specialist in the field, introduces the basic concepts of the technique and provides an overview of recent work. This volume, which focuses on spectroscopic techniques in synchrotron radiation and inelastic neutron scattering, will be a primary source of information for physicists, chemists and materials scientists who wish to acquire a basic understanding of these techniques and to discover the possibilities offered by them. Emphasizing the complementarity of the neutron and X-ray methods, this tutorial will also be invaluable to scientists already working in neighboring fields who seek to extend thei...

  8. Scanning tunneling spectroscopy of Pb thin films

    Energy Technology Data Exchange (ETDEWEB)

    Becker, Michael

    2010-12-13

    The present thesis deals with the electronic structure, work function and single-atom contact conductance of Pb thin films, investigated with a low-temperature scanning tunneling microscope. The electronic structure of Pb(111) thin films on Ag(111) surfaces is investigated using scanning tunneling spectroscopy (STS). Quantum size effects, in particular, quantum well states (QWSs), play a crucial role in the electronic and physical properties of these films. Quantitative analysis of the spectra yields the QWS energies as a function of film thickness, the Pb bulk-band dispersion in {gamma}-L direction, scattering phase shifts at the Pb/Ag interface and vacuum barrier as well as the lifetime broadening at anti {gamma}. The work function {phi} is an important property of surfaces, which influences catalytic reactivity and charge injection at interfaces. It controls the availability of charge carriers in front of a surface. Modifying {phi} has been achieved by deposition of metals and molecules. For investigating {phi} at the atomic scale, scanning tunneling microscopy (STM) has become a widely used technique. STM measures an apparent barrier height {phi}{sub a}, which is commonly related to the sample work function {phi}{sub s} by: {phi}{sub a}=({phi}{sub s}+{phi}{sub t}- vertical stroke eV vertical stroke)/2, with {phi}{sub t} the work function of the tunneling tip, V the applied tunneling bias voltage, and -e the electron charge. Hence, the effect of the finite voltage in STM on {phi}{sub a} is assumed to be linear and the comparison of {phi}{sub a} measured at different surface sites is assumed to yield quantitative information about work function differences. Here, the dependence of {phi}{sub a} on the Pb film thickness and applied bias voltage V is investigated. {phi}{sub a} is found to vary significantly with V. This bias dependence leads to drastic changes and even inversion of contrast in spatial maps of {phi}{sub a}, which are related to the QWSs in the Pb

  9. Neutron spectroscopy of magnesium dihydride

    Energy Technology Data Exchange (ETDEWEB)

    Kolesnikov, Alexander I [ORNL; Antonov, Vladimir E. [Institute of Solid State Physics, Russian Ac. Sci., Chernogolovka, Moscow, Russi; Efimchenko, V. S. [Institute of Solid State Physics, Russian Ac. Sci., Chernogolovka, Moscow, Russi; Granroth, Garrett E [ORNL; Klyamkin, S. N. [Moscow State University; Levchenko, A. V. [Institute of Problems of Chemical Physics, Russian Ac. Sci, Chernogolovka, Russia; Sakharov, M. K. [Institute of Solid State Physics, Russian Ac. Sci., Chernogolovka, Moscow, Russi; Ren, Yang [Argonne National Laboratory (ANL)

    2011-01-01

    Inelastic neutron scattering spectra of -MgH2 powder have been measured at T = 7 K with an energy resolution better than 1.5% using the time-of-flight direct geometry spectrometer SEQUOIA. Based on these spectra, the density g(E) of phonon states in -MgH2 has been experimentally constructed for the fist time. Comparing the available experimental data on the heat capacity of -MgH2 with those calculated using the obtained g(E) spectrum confirmed the good accuracy of its determination.

  10. Neutron spectroscopy with scintillation detectors using wavelets

    Science.gov (United States)

    Hartman, Jessica

    The purpose of this research was to study neutron spectroscopy using the EJ-299-33A plastic scintillator. This scintillator material provided a novel means of detection for fast neutrons, without the disadvantages of traditional liquid scintillation materials. EJ-299-33A provided a more durable option to these materials, making it less likely to be damaged during handling. Unlike liquid scintillators, this plastic scintillator was manufactured from a non-toxic material, making it safer to use, as well as easier to design detectors. The material was also manufactured with inherent pulse shape discrimination abilities, making it suitable for use in neutron detection. The neutron spectral unfolding technique was developed in two stages. Initial detector response function modeling was carried out through the use of the MCNPX Monte Carlo code. The response functions were developed for a monoenergetic neutron flux. Wavelets were then applied to smooth the response function. The spectral unfolding technique was applied through polynomial fitting and optimization techniques in MATLAB. Verification of the unfolding technique was carried out through the use of experimentally determined response functions. These were measured on the neutron source based on the Van de Graff accelerator at the University of Kentucky. This machine provided a range of monoenergetic neutron beams between 0.1 MeV and 24 MeV, making it possible to measure the set of response functions of the EJ-299-33A plastic scintillator detector to neutrons of specific energies. The response of a plutonium-beryllium (PuBe) source was measured using the source available at the University of Nevada, Las Vegas. The neutron spectrum reconstruction was carried out using the experimentally measured response functions. Experimental data was collected in the list mode of the waveform digitizer. Post processing of this data focused on the pulse shape discrimination analysis of the recorded response functions to remove the

  11. Challenges in neutron spin echo spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Pappas, C., E-mail: c.pappas@tudelft.n [Helmholtz-Zentrum Berlin for Materials and Energy, Glienicker Str. 100, 14109 Berlin (Germany); Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); Lelievre-Berna, E.; Falus, P.; Farago, B. [Institut Laue Langevin, 6 rue Jules Horowitz, 38042 Grenoble (France); Bentley, P. [Helmholtz-Zentrum Berlin for Materials and Energy, Glienicker Str. 100, 14109 Berlin (Germany); Institut Laue Langevin, 6 rue Jules Horowitz, 38042 Grenoble (France); Moskvin, E. [Helmholtz-Zentrum Berlin for Materials and Energy, Glienicker Str. 100, 14109 Berlin (Germany); PNPI, 188300 Gatchina, Leningrad District (Russian Federation); Krist, Th. [Helmholtz-Zentrum Berlin for Materials and Energy, Glienicker Str. 100, 14109 Berlin (Germany); Grigoriev, S. [PNPI, 188300 Gatchina, Leningrad District (Russian Federation)

    2009-09-01

    With the new brilliant neutron sources and the developments of novel optical elements, neutron spin echo (NSE) spectroscopy evolves to tackle new problems and scientific fields. The new developments pave the way to complex experimental set-ups such as the intensity modulated variant of NSE (IMNSE), a powerful technique which was introduced some 20 years ago but found limited use up to now. With the new compact supermirror or He{sup 3} polarizers IMNSE becomes attractive for a broad range of applications in magnetism, soft matter and biology. A novel development along this line is the polarimetric NSE technique, which combines IMNSE and the zero-field polarimeter Cryopad to access components of the scattered polarization that are transverse to the incoming polarization. Polarimetric NSE is the method of choice for studying chiral fluctuations, as illustrated by new results on the reference helimagnet MnSi.

  12. Scanning tunneling spectroscopy on electron-boson interactions in superconductors

    CERN Document Server

    Schackert, Michael Peter

    2015-01-01

    This work describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end.

  13. Tunneling spectroscopy of carbon nanostructures: A romance in many dimensions

    Science.gov (United States)

    Dirks, Travis Lee

    In this dissertation we present results from various methods of tunneling spectroscopy in carbon nanotubes, which shed light on electron -- electron interaction in carbon nanotubes and low dimensional systems in general. We also apply those methods to two dimensional graphene sheets. We first review the fabrication techniques used to make the devices studied here. Some of the techniques are standard in nanofabrication, and some were developed in-house to make the particular device geometries studied here possible. In particular, we developed recipes for the growth and contact of clean, ultra-long carbon nanotubes as well as for the fabrication of non-invasive top tunnel probes. We then present results on normal metal tunneling spectroscopy of carbon nanotube devices of varying length. We measure the exponent of the conductance power law in the density of states as a function of device length over two orders of magnitude and find unexpected evidence of finite size effects in long devices. Next, we present results from the first measurement of the non-equilibrium electron energy distribution function in carbon nanotubes measured via non-equilibrium superconducting tunneling spectroscopy and find little evidence of scattering at low temperatures, which is consistent with a clean, strongly interacting Luttinger liquid. In addition, we discuss two ways we are working to extend this powerful technique. We also present results of superconducting tunneling spectroscopy of a clean carbon nanotube quantum dot. We are able to characterize the energy spectrum of the quantum dot and distinguish between spin singlet and spin triplet shell filling. We observe elastic and inelastic co-tunneling features which are not visible when the probe is made normal by a magnetic field. These co-tunneling rates have important technological implications for carbon nanotubes as single electron transistors. We also observe an energetically forbidden conductance inside the superconducting gap

  14. Laser spectroscopy of neutron deficient Sn isotopes

    CERN Multimedia

    We propose to study the ground state properties of neutron-deficient Sn isotopes towards the doubly-magic nucleus $^{100}$Sn. Nuclear spins, changes in the rms charge radii and electromagnetic moments of $^{101-121}$Sn will be measured by laser spectroscopy using the CRIS experimental beam line. These ground-state properties will help to clarify the evolution of nuclear structure properties approaching the $\\textit{N = Z =}$ 50 shell closures. The Sn isotopic chain is currently the frontier for the application of state-of-the-art ab-initio calculations. Our knowledge of the nuclear structure of the Sn isotopes will set a benchmark for the advances of many-body methods, and will provide an important test for modern descriptions of the nuclear force.

  15. Chandra Spectroscopy of a Remarkable Neutron Star

    Science.gov (United States)

    Miller, Jon

    2013-09-01

    IGR J17062-6143 is one of only 5 sources that have displayed a super-expansion burst. This requires a special mode of continuous low-level accretion that allows material to accumulate on the stellar surface, without triggering smaller bursts. Swift spectroscopy of a super-expansion burst in IGR J17062-6143 revealed the only strong detections of atomic emission and absorption lines in a burst observed at CCD or gratings resolution. Whereas atomic features from the stellar surface have not been detected in other neutron stars, the accretion mode in IGR J17062-6143 may provide the right conditions. To search for lines from the surface, and to better understand the nature of low-level accretion, we request a 100 ksec HETGS observation of IGR J17062-6143.

  16. Tunneling spectroscopy of a magnetic adatoms on topological insulator surfaces

    Science.gov (United States)

    Misiorny, M.; Bjerngaard, M.; Paaske, J.

    In this communication, we address the question of how the presence of a magnetic impurity on a topological insulator (TI) surface manifests in the inelastic electron tunneling spectroscopy (IETS) when such a system is probed by a STM. For this purpose, we consider a single magnetic adatom with arbitrary spin, whose dynamics is governed by the local magnetic anisotropy. The spin is exchange-coupled to two-dimensional helical surface electrons, corresponding to the surface of a three-dimensional TI like Bi2Se3, with its characteristic hexagonally warped Dirac cone band structure. Employing an effective exchange-tunneling model, we calculate the non-linear differential conductance from a spin-polarized STM tip to the helical substrate, valid in the perturbative regime of weak exchange-tunneling and including the nonequilibrium pumping of the adatom spin states. The interplay between the magnetic anisotropy and the spin-momentum locked surface electrons is shown to give a number of specific imprints in the IETS, which could be investigated by spin-resolved scanning tunneling spectroscopy. M. Misiorny, M. Bjerngaard and J. Paaske, manuscript in preparation Work supported by the Polish Ministry of Science and Education as `Iuventus Plus' project (IP2014 030973) in years 2015-2016.

  17. A note on black hole spectroscopy in the tunneling mechanism

    CERN Document Server

    Jiang, Qing-Quan

    2012-01-01

    There is a long-standing belief that a black hole horizon should be endowed with a quantum area spectrum given by $A_n=\\gamma l_p^2 n$. In recent work, it has been claimed, in the tunneling mechanism, the area spacing parameter is given by $\\gamma=4$. This spacing level is encouraging, since it is not only in full agreement with the Hod's result, but more importantly, is smaller than that given by Bekenstein as well as the one obtained in the context of black hole quasinormal modes. Unfortunately, the Bohr-Sommerfeld quantization rule used in these work is somewhat misleading, so its resulting area spacing seems unconvincing. In this paper, we associate a tunneling process with a large $n$ transition of a quantum black hole to straighten this misunderstanding out. Then, under the new interpretation for a tunneling process, we refine the Hod's idea and Kunstatter's treatment to revisit the black hole spectroscopy in the tunneling mechanism. It is finally found that, in the tunneling mechanism, the area spacing...

  18. High-resolution Josephson spectroscopy with a scanning tunneling microscope

    Science.gov (United States)

    Randeria, Mallika T.; Feldman, Benjamin E.; Drozdov, Ilya K.; Yazdani, Ali

    2015-03-01

    Conventional scanning tunneling microscopy (STM) measurements use a normal metal tip to probe local quasi-particle density of states with atomic resolution. Using a superconducting tip to conduct spectroscopy significantly boosts the energy resolution of the measurements, thus expanding the STM capabilities. Moreover, superconducting tips make it possible to probe superconductivity via the Josephson effect, which provides a direct measure of the local superconducting order parameter. Therefore, scanning Josephson spectroscopy measurements have the potential to characterize of a wide variety of superconducting materials on the atomic scale. I will present superconducting Pb tip measurements performed at temperatures below 250mK in a dilution refrigerator STM. By controlling the junction resistance, we are able to explore a wide range of tunneling regimes. Josephson measurements on Pb samples exhibit features including multiple Andreev reflections, and I will discuss the extension of these techniques to study atomic scale variations in Josephson current.

  19. Capture-Gated Fast Neutron Spectroscopy

    Science.gov (United States)

    Mumm, H. P.; Abdurashitov, J. N.; Beise, E. J.; Breuer, H.; Gavrin, V. N.; Heimbach, C. R.; Langford, T. J.; Mendenhall, M.; Nico, J. S.; Shikhin, A. A.

    2015-10-01

    We present recent developments in fast neutron detection using segmented spectrometers based on the principle of capture-gating. Our approach employs an organic scintillator to detect fast neutrons through their recoil interaction with protons in the scintillator. The neutrons that thermalize and are captured produce a signal indicating that the event was due to a neutron recoil and that the full energy of the neutron was deposited. The delayed neutron capture also serves to discriminate against uncorrelated background events. The segmentation permits reconstruction of the initial neutron energy despite the nonlinear response of the scintillator. We have constructed spectrometers using both He-3 proportional counters and Li-6 doping as capture agents in plastic and liquid organic scintillators. We discuss the operation of the spectrometers for the measurement of low levels of fast neutrons for several applications, including the detection of very low-activity neutron sources and the characterization of the flux and spectrum of fast neutrons at the Earth's surface and in the underground environment.

  20. C7LYC Scintillators and Fast Neutron Spectroscopy

    Science.gov (United States)

    Chowdhury, P.; Brown, T.; Doucet, E.; Lister, C. J.; Wilson, G. L.; D'Olympia, N.; Devlin, M.; Mosby, S.

    2016-09-01

    Cs2 LiYCl6 (CLYC) scintillators detect both gammas and neutrons with excellent pulse shape discrimination. At UML, fast neutron measurements with a 16-element 1''x1'' CLYC array show promise for low energy nuclear science. CLYC detects fast neutrons via the 35Cl (n,p) reaction (resolution UML. Results will be discussed in the context of constructing a C7LYC array at FRIB for reaction and decay spectroscopy of neutron-rich fragments. Supported by the NNSA Stewardship Science Academic Alliance Program under Grant DE-NA00013008.

  1. Scanning tunneling microscopy and spectroscopy studies of graphite edges

    CERN Document Server

    Niimi, Y; Kambara, H; Tagami, K; Tsukada, M; Fukuyama, H; Fukuyama, Hiroshi

    2004-01-01

    We studied experimentally and theoretically the electronic local density of states (LDOS) near single step edges at the surface of exfoliated graphite. In scanning tunneling microscopy measurements, we observed the $(\\sqrt{3} \\times \\sqrt{3}) R 30^{\\circ}$ and honeycomb superstructures both extending over 3$-$4 nm either from the zigzag or armchair edge. Calculations based on a density-functional derived non-orthogonal tight-binding model show that these superstructures can coexist if the two types of edge admix each other in real graphite step edges. Scanning tunneling spectroscopy measurements near the zigzag edge reveal a clear peak in the LDOS at an energy below the Fermi energy by 20 meV. No such a peak was observed near the armchair edge. We concluded that this peak corresponds to the "edge state" theoretically predicted for graphene ribbons, since a similar prominent LDOS peak due to the edge state is obtained by the first principles calculations.

  2. Tunneling spectroscopy of organic monolayers and single molecules.

    Science.gov (United States)

    Hipps, K W

    2012-01-01

    Basic concepts in tunneling spectroscopy applied to molecular systems are presented. Junctions of the form M-A-M, M-I-A-M, and M-I-A-I'-M, where A is an active molecular layer, are considered. Inelastic electron tunneling spectroscopy (IETS) is found to be readily applied to all the above device types. It can provide both vibrational and electron spectroscopic data about the molecules comprising the A layer. In IETS there are no strong selection rules (although there are preferences) so that transitions that are normally IR, Raman, or even photon-forbidden can be observed. In the electronic transition domain, spin and Laporte forbidden transitions may be observed. Both vibrational and electronic IETS can be acquired from single molecules. The negative aspect of this seemingly ideal spectroscopic method is the thermal line width of about 5 k(B)T. This limits the useful measurement of vibrational IETS to temperatures below about 10 K. In the case of most electronic transitions where the intrinsic linewidth is much broader, useful experiments above 100 K are possible. One further limitation of electronic IETS is that it is generally limited to transitions with energy less than about 20,000 cm(-1). IETS can be identified by peaks in d(2) I/dV (2) vs bias voltage plots that occur at the same position (but not necessarily same intensity) in either bias polarity.Elastic tunneling spectroscopy is discussed in the context of processes involving molecular ionization and electron affinity states, a technique we call orbital mediated tunneling spectroscopy, or OMTS. OMTS can be applied readily to M-I-A-M and M-I-A-I'-M systems, but application to M-A-M junctions is problematic. Spectra can be obtained from single molecules. Ionization state results correlate well with UPS spectra obtained from the same systems in the same environment. Both ionization and affinity levels measured by OMTS can usually be correlated with one electron oxidation and reduction potentials for the

  3. Results from Point Contact Tunnelling Spectroscopy and Atomic Layer Deposition

    Energy Technology Data Exchange (ETDEWEB)

    Proslier, Th. [Illinois Institute of Technology; Zasadzinski, J. [Illinois Institute of Technology; Ciovati, Gianluigi [JLAB; Kneisel, Peter K. [JLAB; Elam, J. W. [ANL; Norem, J. [ANL; Pellin, M. J. [ANL

    2009-11-01

    We have shown previously that magnetic niobium oxides can influence the superconducting density of states at the surface of cavity-grade niobium coupons. We will present recent results obtained by Point Contact Tunneling spectroscopy (PCT) on coupons removed from hot and cold spots in a niobium cavity, as well as a comparative study of magnetic oxides on mild baked/unbaked electropolished coupons. We will also describe recent results obtained from coated cavities, ALD films properties and new materials using Atomic Layer Deposition (ALD).

  4. Spin-echo spectroscopy with ultracold neutrons

    CERN Document Server

    Afach, S; Ban, G; Bison, G; Bodek, K; Chowdhuri, Z; Daum, M; Fertl, M; Franke, B; Griffith, W C; Grujić, Z D; Harris, P G; Heil, W; Hélaine, V; Kasprzak, M; Kermaidic, Y; Kirch, K; Knowles, P; Koch, H -C; Komposch, S; Kozela, A; Krempel, J; Lauss, B; Lefort, T; Lemière, Y; Mtchedlishvili, A; Musgrave, M; Naviliat-Cunic, O; Pendlebury, J M; Piegsa, F M; Pignol, G; Plonka-Spehr, C; Prashanth, P N; Quéméner, G; Rawlik, M; Rebreyend, D; Ries, D; Roccia, S; Rozpedzik, D; Schmidt-Wellenburg, P; Severijns, N; Thorne, J A; Weis, A; Wursten, E; Wyszynski, G; Zejma, J; Zenner, J; Zsigmond, G

    2015-01-01

    We describe a spin-echo method for ultracold neutrons (UCNs) confined in a precession chamber and exposed to a |B_0 | = 1uT magnetic field. We demonstrate a gravity-dependent spin dephasing by applying small vertical magnetic field gradients. The method gives access to the energy spectrum of stored UCNs, which can be crucial for the assessment of systematic effects in precision experiments such as searches for an electric dipole moment of the neutron.

  5. Enhanced Performance Neutron Scattering Spectroscopy by Use of Correlation Techniques

    CERN Document Server

    Mezei, F; Migliardo, F; Magazù, S

    2016-01-01

    Neutron correlation spectroscopy can exceed direct spectroscopy in the incoming beam intensity by up to two orders of magnitude at the same energy resolution. However, the propagation of the counting noise in the correlation algorithm of data reduction is disadvantageous for the lowest intensity parts of the observed spectrum. To mitigate this effect at pulsed neutron sources we propose two dimensional time-of-flight recording of each neutron detection event: with respect to both the neutron source pulses and to the rotation phase of the pseudo-random beam modulation statistical chopper. We have identified a formulation of the data reduction algorithm by matching the data processing time channel width to the inherent time resolution of this chopper, which makes the reconstruction of the direct time-of-flight spectra exact and independent of all other contributions to instrumental resolution. Two ways are proposed for most flexible choice of intensity vs. resolution without changing the statistical chopper or ...

  6. Fast neutron spectroscopy with tensioned metastable fluid detectors

    Science.gov (United States)

    Grimes, T. F.; Taleyarkhan, R. P.

    2016-09-01

    This paper describes research into development of a rapid-turnaround, neutron-spectroscopy capable (gamma-beta blind), high intrinsic efficiency sensor system utilizing the tensioned metastable fluid detector (TMFD) architecture. The inability of prevailing theoretical models (developed successfully for the classical bubble chamber) to adequately predict detection thresholds for tensioned metastable fluid conditions is described. Techniques are presented to overcome these inherent shortcomings, leading thereafter, to allow successful neutron spectroscopy using TMFDs - via the newly developed Single Atom Spectroscopy (SAS) approach. SAS also allows for a unique means for rapidly determining neutron energy thresholds with TMFDs. This is accomplished by simplifying the problem of determining Cavitation Detection Events (CDEs) arising from neutron interactions with one in which several recoiling atom species contribute to CDEs, to one in which only one dominant recoil atom need be considered. The chosen fluid is Heptane (C7H16) for which only recoiling C atoms contribute to CDEs. Using the SAS approach, the threshold curve for Heptane was derived using isotope neutron source data, and then validated against experiments with mono-energetic (2.45/14 MeV) neutrons from D-D and D-T accelerators. Thereafter the threshold curves were used to produce the response matrix for various geometries. The response matrices were in turn combined with experimental data to recover the continuous spectra of fission (Cf-252) and (α,n) Pu-Be isotopic neutron sources via an unfolding algorithm. A generalized algorithm is also presented for performing neutron spectroscopy using any other TMFD fluid that meets the SAS approach assumptions.

  7. Fast neutron spectroscopy with tensioned metastable fluid detectors

    Energy Technology Data Exchange (ETDEWEB)

    Grimes, T.F.; Taleyarkhan, R.P., E-mail: rusi@purdue.edu

    2016-09-11

    This paper describes research into development of a rapid-turnaround, neutron-spectroscopy capable (gamma-beta blind), high intrinsic efficiency sensor system utilizing the tensioned metastable fluid detector (TMFD) architecture. The inability of prevailing theoretical models (developed successfully for the classical bubble chamber) to adequately predict detection thresholds for tensioned metastable fluid conditions is described. Techniques are presented to overcome these inherent shortcomings, leading thereafter, to allow successful neutron spectroscopy using TMFDs – via the newly developed Single Atom Spectroscopy (SAS) approach. SAS also allows for a unique means for rapidly determining neutron energy thresholds with TMFDs. This is accomplished by simplifying the problem of determining Cavitation Detection Events (CDEs) arising from neutron interactions with one in which several recoiling atom species contribute to CDEs, to one in which only one dominant recoil atom need be considered. The chosen fluid is Heptane (C{sub 7}H{sub 16}) for which only recoiling C atoms contribute to CDEs. Using the SAS approach, the threshold curve for Heptane was derived using isotope neutron source data, and then validated against experiments with mono-energetic (2.45/14 MeV) neutrons from D-D and D-T accelerators. Thereafter the threshold curves were used to produce the response matrix for various geometries. The response matrices were in turn combined with experimental data to recover the continuous spectra of fission (Cf-252) and (α,n) Pu–Be isotopic neutron sources via an unfolding algorithm. A generalized algorithm is also presented for performing neutron spectroscopy using any other TMFD fluid that meets the SAS approach assumptions.

  8. Neutron spectroscopy at the turn of the century

    CERN Document Server

    Popov, Yu P

    2003-01-01

    Neutron spectrometry is a powerful method of investigating atomic nuclei and condensed matter. Such investigations provide necessary data for a very wide spectrum of scientific and technological applications from the fundamental problems of the structure of matter and nucleosynthesis in the Universe to atomic power technologies and the structure of condensed matter. The most frequently utilized is the time-of-flight (TOF) method for powerful pulsed neutron sources. However, in many cases, one can use more effective, simpler and cheaper methods. For example, for astrophysics and radioactive waste transmutation problems, it is sufficient to know an average resonance cross section or "resonance integrals" for capture and fission reactions for neutron spectra specific to neutron fluxes in stars or in the active zone of a transmutation reactor. In these cases, the slow-down neutron spectroscopy (SDNS) methods in lead and graphite moderators will be useful. Compared to the TOF method, the lead SDNS gives a 10/sup 3...

  9. Focusing adaptive-optics for neutron spectroscopy at extreme conditions

    Energy Technology Data Exchange (ETDEWEB)

    Simeoni, G. G., E-mail: ggsimeoni@outlook.com [Heinz Maier-Leibnitz Zentrum (MLZ), FRM II, Technical University of Munich, D-85748 Garching (Germany); Physics Department E13, Technical University of Munich, D-85748 Garching (Germany); Valicu, R. G. [Heinz Maier-Leibnitz Zentrum (MLZ), FRM II, Technical University of Munich, D-85748 Garching (Germany); Physics Department E13, Technical University of Munich, D-85748 Garching (Germany); Physics Department E21, Technical University of Munich, D-85748 Garching (Germany); Borchert, G. [Heinz Maier-Leibnitz Zentrum (MLZ), FRM II, Technical University of Munich, D-85748 Garching (Germany); Böni, P. [Physics Department E21, Technical University of Munich, D-85748 Garching (Germany); Rasmussen, N. G. [Nanoscience Center, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen (Denmark); Yang, F.; Kordel, T.; Holland-Moritz, D.; Kargl, F.; Meyer, A. [Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt, D-51170 Köln (Germany)

    2015-12-14

    Neutron Spectroscopy employing extreme-conditions sample environments is nowadays a crucial tool for the understanding of fundamental scientific questions as well as for the investigation of materials and chemical-physical properties. For all these kinds of studies, an increased neutron flux over a small sample area is needed. The prototype of a focusing neutron guide component, developed and produced completely at the neutron source FRM II in Garching (Germany), has been installed at the time-of-flight (TOF) disc-chopper neutron spectrometer TOFTOF and came into routine-operation. The design is based on the compressed Archimedes' mirror concept for finite-size divergent sources. It represents a unique device combining the supermirror technology with Adaptive Optics, suitable for broad-bandwidth thermal-cold TOF neutron spectroscopy (here optimized for 1.4–10 Å). It is able to squeeze the beam cross section down to a square centimeter, with a more than doubled signal-to-background ratio, increased efficiency at high scattering angles, and improved symmetry of the elastic resolution function. We present a comparison between the simulated and measured beam cross sections, as well as the performance of the instrument within real experiments. This work intends to show the unprecedented opportunities achievable at already existing instruments, along with useful guidelines for the design and construction of next-generation neutron spectrometers.

  10. Disorder effects in pnictides: a tunneling spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Noat, Y; Cren, T; Dubost, V; Lange, S; Debontridder, F; Roditchev, D [Institut des Nanosciences de Paris, CNRS UMR 7588, Universite Pierre et Marie Curie Paris 6, Campus Boucicaut, 140 rue de Lourmel, F-75015 Paris (France); Toulemonde, P; Marcus, J; Sulpice, A [Institut Neel, CNRS et Universite Joseph Fourier, 25 rue des Martyrs, BP 166, F-38042 Grenoble (France); Sacks, W, E-mail: yves.noat@insp.jussieu.f [Institut de Mineralogie et de Physique des Milieux Condenses, CNRS UMR 7590, Campus Boucicaut, 140 rue de Lourmel, F-75015 Paris (France)

    2010-11-24

    We present the synthesis and the tunneling spectroscopy study of superconducting FeSe{sub 0.5}Te{sub 0.5} (T{sub c} = 14 K), SmFeAsO{sub 0.85} (T{sub c} = 54 K) and SmFeAsO{sub 0.9}F{sub 0.1} (T{sub c} = 45 K). The samples were characterized by Rietveld refinement of x-ray diffraction patterns and transport as well as temperature-dependent magnetic measurements. Tunneling experiments on FeSe{sub 0.5}Te{sub 0.5} revealed a single superconducting gap {approx} 1 meV in BCS-like tunneling conductance spectra. In SmFeAsO{sub 0.85} and SmFeAsO{sub 0.9}F{sub 0.1}, however, more complex spectra were observed, characterized by two gap-like structures at {approx} 4 and {approx} 10 meV. These spectra are qualitatively understood assuming a two-band superconductor with a 's {+-}' order parameter. We show that, depending on the sign relation between the pairing amplitudes in the two bands, the interband quasiparticle scattering has a crucial effect on the shape of the tunneling spectra. On the other hand, single-gap spectra found in FeSe{sub 0.5}Te{sub 0.5} are more compatible with a disorder-induced 's '-wave gap, due to the Se-Te substitution.

  11. Scanning Tunnelling Spectroscopy of Vortices with Normal and Superconducting tips

    Science.gov (United States)

    Rodrigo, J. G.; Suderow, H.; Vieira, S.

    Scanning tunnelling microscopy and spectroscopy (STM/S) has proved to be a powerful tool to study superconductivity down to atomic level. Vortex lattice studies require characterizing areas of enough size to contain a large number of vortices. On the other hand, it is necessary to combine this capability with high spectroscopic and microscopic resolution. This is a fundamental aspect to measure and detect the subtle changes appearing inside and around a single vortex. We report in this chapter our approach to the use of STM/S, using normal and superconducting tips, to observe the lattice of vortices in several compounds, and the information acquired inside these fascinating entities. The combination of superconducting tips and scanning tunneling spectroscopy, (ST)2S, presents advantages for the study of superconducting samples. It allows to distinguish relevant features of the sample density of states, which manifest itself as small changes in the Josephson coupling between sample and tip condensates, and it has also shown to be very efficient in the study of the ferromagnetic-superconductor transition in the re-entrant superconductor ErRh4B4.

  12. Multidimensional vibrational spectroscopy for tunneling processes in a dissipative environment.

    Science.gov (United States)

    Ishizaki, Akihito; Tanimura, Yoshitaka

    2005-07-01

    Simulating tunneling processes as well as their observation are challenging problems for many areas. In this study, we consider a double-well potential system coupled to a heat bath with a linear-linear (LL) and square-linear (SL) system-bath interactions. The LL interaction leads to longitudinal (T1) and transversal (T2) homogeneous relaxations, whereas the SL interaction leads to the inhomogeneous dephasing (T2*) relaxation in the white noise limit with a rotating wave approximation. We discuss the dynamics of the double-well system under infrared (IR) laser excitations from a Gaussian-Markovian quantum Fokker-Planck equation approach, which was developed by generalizing Kubo's stochastic Liouville equation. Analytical expression of the Green function is obtained for a case of two-state-jump modulation by performing the Fourier-Laplace transformation. We then calculate a two-dimensional infrared signal, which is defined by the four-body correlation function of optical dipole, for various noise correlation time, system-bath coupling parameters, and temperatures. It is shown that the bath-induced vibrational excitation and relaxation dynamics between the tunneling splitting levels can be detected as the isolated off-diagonal peaks in the third-order two-dimensional infrared (2D-IR) spectroscopy for a specific phase matching condition. Furthermore, this spectroscopy also allows us to directly evaluate the rate constants for tunneling reactions, which relates to the coherence between the splitting levels; it can be regarded as a novel technique for measuring chemical reaction rates. We depict the change of reaction rates as a function of system-bath coupling strength and a temperature through the 2D-IR signal.

  13. A proton recoil telescope for neutron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Donzella, A., E-mail: antonietta.donzella@ing.unibs.i [Universita di Brescia, 38 Via Branze, I-25123 Brescia (Italy); INFN Sezione di Pavia, 6 Via Bassi, I-27100 Pavia (Italy); Barbui, M. [INFN Laboratori Nazionali di Legnaro, 2 Viale dell' Universita, I-35020 Legnaro, Padova (Italy); Bocci, F. [INFN and Universita di Pavia, 6 Via Bassi, I-27100 Pavia (Italy); Bonomi, G. [Universita di Brescia, 38 Via Branze, I-25123 Brescia (Italy); INFN Sezione di Pavia, 6 Via Bassi, I-27100 Pavia (Italy); Cinausero, M. [INFN Laboratori Nazionali di Legnaro, 2 Viale dell' Universita, I-35020 Legnaro, Padova (Italy); Fabris, D. [INFN and Universita di Padova, 8 Via Marzolo, I-35131 Padova (Italy); Fontana, A. [INFN Sezione di Pavia, 6 Via Bassi, I-27100 Pavia (Italy); Giroletti, E. [INFN and Universita di Pavia, 6 Via Bassi, I-27100 Pavia (Italy); Lunardon, M.; Moretto, S.; Nebbia, G. [INFN and Universita di Padova, 8 Via Marzolo, I-35131 Padova (Italy); Necchi, M.M. [Universita di Brescia, 38 Via Branze, I-25123 Brescia (Italy); Pesente, S. [INFN and Universita di Padova, 8 Via Marzolo, I-35131 Padova (Italy); Prete, G.; Rizzi, V. [INFN Laboratori Nazionali di Legnaro, 2 Viale dell' Universita, I-35020 Legnaro, Padova (Italy); Viesti, G. [INFN and Universita di Padova, 8 Via Marzolo, I-35131 Padova (Italy); Zenoni, A. [Universita di Brescia, 38 Via Branze, I-25123 Brescia (Italy); INFN Sezione di Pavia, 6 Via Bassi, I-27100 Pavia (Italy)

    2010-01-21

    A new proton recoil telescope (PRT) detector is presented: it is composed by an active multilayer of segmented plastic scintillators as neutron to proton converter, by two silicon strip detectors and by a final thick CsI(Tl) scintillator. The PRT can be used to measure neutron spectra in the range 2-160 MeV. The detector characteristics have been studied in detail with the help of Monte Carlo simulations. The overall energy resolution of the system ranges from about 20% at the lowest neutron energy to about 2% at 160 MeV. The global efficiency is about 3x10{sup -5}. Experimental tests have been performed by using the reaction {sup 13}C(d,n) at 40 MeV deuteron energy.

  14. Decay-Assisted Laser Spectroscopy of Neutron-Deficient Francium

    CERN Document Server

    Lynch, K M; Bissell, M L; Budincevic, I; Cocolios, T E; De Groote, R P; De Schepper, S; Fedosseev, V N; Flanagan, K T; Franchoo, S; Garcia Ruiz, R F; Heylen, H; Marsh, B A; Neyens, G; Procter, T J; Rossel, R E; Rothe, S; Strashnov, I; Stroke, H H; Wendt, K D A

    2014-01-01

    This paper reports on the hyperfine-structure and radioactive-decay studies of the neutron-deficient francium isotopes $^{202-206}$Fr performed with the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at the ISOLDE facility, CERN. The high resolution innate to collinear laser spectroscopy is combined with the high efficiency of ion detection to provide a highly-sensitive technique to probe the hyperfine structure of exotic isotopes. The technique of decay-assisted laser spectroscopy is presented, whereby the isomeric ion beam is deflected to a decay spectroscopy station for alpha-decay tagging of the hyperfine components. Here, we present the first hyperfine-structure measurements of the neutron-deficient francium isotopes $^{202-206}$Fr, in addition to the identification of the low-lying states of $^{202,204}$Fr performed at the CRIS experiment.

  15. Recent results on neutron rich tin isotopes by laser spectroscopy

    CERN Document Server

    Roussière, B; Crawford, J E; Essabaa, S; Fedosseev, V; Geithner, W; Genevey, J; Girod, M; Huber, G; Horn, R; Kappertz, S; Lassen, J; Le Blanc, F; Lee, J K P; Le Scornet, G; Lettry, Jacques; Mishin, V I; Neugart, R; Obert, J; Oms, J; Ouchrif, A; Peru, S; Pinard, J; Ravn, H L; Sauvage, J; Verney, D

    2001-01-01

    Laser spectroscopy measurements have been performed on neutron rich tin isotopes using the COMPLIS experimental setup. The nuclear charge radii of the even-even isotopes from A=108 to 132 are compared to the results of macroscopic and microscopic calculations. The improvements and optimizations needed to perform the isotope shift measurement on $^{134}$Sn are presented.

  16. Gamma spectroscopy of neutron rich actinide nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Birkenbach, Benedikt; Geibel, Kerstin; Vogt, Andreas; Hess, Herbert; Reiter, Peter; Steinbach, Tim; Schneiders, David [Koeln Univ. (Germany). IKP; Collaboration: AGATA-Collaboration

    2013-07-01

    Excited states in neutron-rich actinide Th and U nuclei were investigated after multi nucleon transfer reactions employing the AGATA demonstrator and PRISMA setup at LNL (INFN, Italy). A primary {sup 136}Xe beam of 1 GeV hitting a {sup 238}U target was used to produce the nuclei of interest. Beam-like reaction products of Xe- and Ba isotopes after neutron transfer were selected by the PRISMA spectrometer. The recoil like particles were registered by a MCP detector inside the scattering chamber. Coincident γ-rays from excited states in beam and target like particles were measured with the position sensitive AGATA HPGe detectors. Improved Doppler correction and quality of the γ-spectra is based on the novel γ-ray tracking technique which was successfully exploited. First results on the collective properties of various Th and U isotopes are discussed.

  17. Beta-delayed neutron spectroscopy using ion traps

    Science.gov (United States)

    Wang, Barbara; Czeszumska, A.; Siegl, K.; Caldwell, S.; Aprahamian, A.; Burkey, M.; Clark, J.; Levand, A.; Marley, S.; Morgan, G.; Norman, E.; Nystrom, A.; Orford, R.; Padgett, S.; Perez Galvan, A.; Savard, G.; Scielzo, N.; Sharma, K.; Strauss, S.

    2017-01-01

    Trapped radioactive ions suspended in vacuum allow for a new way to perform beta-delayed neutron spectroscopy. Decay branching ratios and energy spectra of the emitted neutrons are inferred from a measurement of the nuclear recoil, thereby circumventing the many limitations associated with direct neutron detection. Beta-delayed neutron measurements were carried out for 137-138,140I, 134-136Sb, and 144-145Cs at the Californium Rare Isotope Breeder Upgrade (CARIBU) facility at Argonne National Laboratory. The data collected are needed in many fields of basic and applied science such as nuclear energy, nuclear astrophysics, and stockpile stewardship. Results for the isotopes 135-136Sb and 140I will be presented. Supported by NSF under PHY-1419765, and U.S. DOE under NEUP 13-5485, DE-AC02-06CH11357 (ANL), DE-AC52-07NA27344 (LLNL), and DE-NA0000979 (NNSA).

  18. Recent progress in vortex studies by tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kohen, A. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France)]. E-mail: Amir.Kohen@insp.jussieu.fr; Cren, T. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Noat, Y. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Proslier, T. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Giubileo, F. [Physics Department and INFM-SUPERMAT Laboratory, University of Salerno, via S. Allende, 84081 Baronissi (SA) (Italy); Bobba, F. [Physics Department and INFM-SUPERMAT Laboratory, University of Salerno, via S. Allende, 84081 Baronissi (SA) (Italy); Cucolo, A.M. [Physics Department and INFM-SUPERMAT Laboratory, University of Salerno, via S. Allende, 84081 Baronissi (SA) (Italy); Zhigadlo, N. [Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich (Switzerland); Kazakov, S.M. [Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich (Switzerland); Karpinski, J. [Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich (Switzerland); Sacks, W. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France); Roditchev, D. [Institut des NanoSciences de Paris, UMR7588 au CNRS, Universite Paris 6 and Paris 7, 140 rue de Lourmel, 75015 Paris (France)

    2006-05-15

    Among the methods used to study the vortex state in superconductors, scanning tunneling spectroscopy (STS), is unique in its ability to measure in real space the variations in the local quasiparticle density of states. Thus, as opposed to magnetic imaging, STS gives direct access to the coherence length rather than to the penetration length. Here we discuss two novel methods which enhance the capabilities of STS as a tool for the study of the vortex state. In the first one, called Lazy Fisherman [A. Kohen et al., Appl. Phys. Lett. 86 (2005) 212503], the scanning tunneling microscope's tip is kept fixed at a selected location while the vortices are being moved by varying the applied magnetic field. By continuously acquiring the local tunneling conductance spectra, dI/dV(V), we detect the changes in the local density of states under the tip due to the vortex motion. With no need for scanning, the method permits one to extend the study of vortices to samples in which scanning is difficult or even impossible due to surface non-uniformity and allows one to detect faster vortex dynamics. To illustrate the approach we study single crystal samples of MgB{sub 2}. In the second STS method, we replace the commonly used normal metal STM tip by a superconducting (SC) tip which we produce either by mechanically breaking a Nb wire under vacuum in the STM chamber [A. Kohen et al., Physica C 49 (2005) 18] or by gluing a piece of a crystal of MgB{sub 2} [F. Giubileo et al., Phys. Rev. Lett. 87 (2001) 177008]. The use of a SC tip enhances the energy resolution of STS in comparison to that obtained with a normal metal tip. The method is illustrated by using Nb and MgB{sub 2} tips to perform a simultaneous topographic and spectroscopic imaging on 2H-NbSe{sub 2}.

  19. Neutrons and numerical methods. A new look at rotational tunneling

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, M.R.; Kearley, G.J. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

    1997-04-01

    Molecular modelling techniques are easily adapted to calculate rotational potentials in crystals of simple molecular compounds. A comparison with the potentials obtained from the tunnelling spectra provides a stringent means for validating current methods of calculating Van der Waals, Coulomb and covalent terms. (author). 5 refs.

  20. A cryogen-free low temperature scanning tunneling microscope capable of inelastic electron tunneling spectroscopy.

    Science.gov (United States)

    Zhang, Shuai; Huang, Di; Wu, Shiwei

    2016-06-01

    The design and performance of a cryogen-free low temperature scanning tunneling microscope (STM) housed in ultrahigh vacuum (UHV) are reported. The cryogen-free design was done by directly integrating a Gifford-McMahon cycle cryocooler to a Besocke-type STM, and the vibration isolation was achieved by using a two-stage rubber bellow between the cryocooler and a UHV-STM interface with helium exchange gas cooling. A base temperature of 15 K at the STM was achieved, with a possibility to further decrease by using a cryocooler with higher cooling power and adding additional low temperature stage under the exchange gas interface. Atomically sharp STM images and high resolution dI/dV spectra on various samples were demonstrated. Furthermore, we reported the inelastic tunneling spectroscopy on a single carbon monoxide molecule adsorbed on Ag(110) surface with a cryogen-free STM for the first time. Being totally cryogen-free, the system not only saves the running cost significantly but also enables uninterrupted data acquisitions and variable temperature measurements with much ease. In addition, the system is capable of coupling light to the STM junction by a pair of lens inside the UHV chamber. We expect that these enhanced capabilities could further broaden our views to the atomic-scale world.

  1. A cryogen-free variable temperature scanning tunneling microscope capable for inelastic electron tunneling spectroscopy

    Science.gov (United States)

    Zhang, Shuai; Huang, Di; Wu, Shiwei

    While low temperature scanning tunneling microscope (STM) has become an indispensable research tool in surface science, its versatility is yet limited by the shortage or high cost of liquid helium. The makeshifts include the use of alternative cryogen (such as liquid nitrogen) at higher temperature or the development of helium liquefier system usually at departmental or campus wide. The ultimate solution would be the direct integration of a cryogen-free cryocooler based on GM or pulse tube closed cycle in the STM itself. However, the nasty mechanical vibration at low frequency intrinsic to cryocoolers has set the biggest obstacle because of the known challenges in vibration isolation required to high performance of STM. In this talk, we will present the design and performance of our home-built cryogen-free variable temperature STM at Fudan University. This system can obtain atomically sharp STM images and high resolution dI/dV spectra comparable to state-of-the-art low temperature STMs, but with no limitation on running hours. Moreover, we demonstrated the inelastic tunneling spectroscopy (STM-IETS) on a single CO molecule with a cryogen-free STM for the first time.

  2. Laser Spectroscopy of Neutron Rich Bismuth Isotopes

    CERN Multimedia

    2002-01-01

    %IS344 :\\\\ \\\\ The aim of the experiment is to measure the optical isotope shifts and hyperfine structures of bismuth isotopes across the N=126 shell closure in order to extract the change in mean square charge radii ($\\delta\\langle r^{2}\\rangle$) and static moments. These include the first isotones of lead to be measured directly above the shell closure and will provide new information on the systematics of the kink ($\\delta\\langle r^{2}\\rangle)$ seen in the lead isotopic chain. After two very successful runs the programme has been extended to include the neutron deficient isotopes below $^{201}$Bi to study the systematics across the $i_{13/2}$ neutron sub-shell closure at N=118.\\\\ \\\\ During the initial 2 runs (9 shifts) the isotope shifts and hyperfine structures of three new isotopes, $ ^{210,212,213}$Bi and the 9$^{-}$ isomer of $^{210}$Bi have been measured. The accuracy of the previous measurements of $^{205,206,208}$Bi have been greatly improved. The samples of $ ^{208,210,210^{m}}$Bi were prepared by c...

  3. Deuterated scintillators and their application to neutron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Febbraro, M., E-mail: febbraro@umich.edu [Department of Physics, University of Michigan, Ann Arbor, MI 48109 (United States); Lawrence, C.C. [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Zhu, H. [Department of Physics, University of Michigan, Ann Arbor, MI 48109 (United States); Pierson, B. [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Torres-Isea, R.O; Becchetti, F.D. [Department of Physics, University of Michigan, Ann Arbor, MI 48109 (United States); Kolata, J.J. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Riggins, J. [Department of Physics, University of Michigan, Ann Arbor, MI 48109 (United States)

    2015-06-01

    Deuterated scintillators have been used as a tool for neutron spectroscopy without Neutron Time-of-Flight (n-ToF) for more than 30 years. This article will provide a brief historical overview of the technique and current uses of deuterated scintillators in the UM-DSA and DESCANT arrays. Pulse-shape discrimination and spectrum unfolding with the maximum-likelihood expectation maximization algorithm will be discussed. Experimental unfolding and cross section results from measurements of (d,n), ({sup 3}He,n) and (α,n) reactions are shown.

  4. Quantum tunneling, adiabatic invariance and black hole spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Li, Guo-Ping; Zu, Xiao-Tao [University of Electronic Science and Technology of China, School of Physical Electronics, Chengdu (China); Pu, Jin [University of Electronic Science and Technology of China, School of Physical Electronics, Chengdu (China); China West Normal University, College of Physics and Space Science, Nanchong (China); Jiang, Qing-Quan [China West Normal University, College of Physics and Space Science, Nanchong (China)

    2017-05-15

    In the tunneling framework, one of us, Jiang, together with Han has studied the black hole spectroscopy via adiabatic invariance, where the adiabatic invariant quantity has been intriguingly obtained by investigating the oscillating velocity of the black hole horizon. In this paper, we attempt to improve Jiang-Han's proposal in two ways. Firstly, we once again examine the fact that, in different types (Schwarzschild and Painleve) of coordinates as well as in different gravity frames, the adiabatic invariant I{sub adia} = circular integral p{sub i}dq{sub i} introduced by Jiang and Han is canonically invariant. Secondly, we attempt to confirm Jiang-Han's proposal reasonably in more general gravity frames (including Einstein's gravity, EGB gravity and HL gravity). Concurrently, for improving this proposal, we interestingly find in more general gravity theories that the entropy of the black hole is an adiabatic invariant action variable, but the horizon area is only an adiabatic invariant. In this sense, we emphasize the concept that the quantum of the black hole entropy is more natural than that of the horizon area. (orig.)

  5. Tunneling spectroscopy of a p-i-n diode interface

    Energy Technology Data Exchange (ETDEWEB)

    Loth, Sebastian; Wenderoth, Martin; Teichmann, Karen; Homoth, Jan; Loeser, Karolin; Ulbrich, Rainer G. [IV. Physikalisches Institut, Georg-August-Universitaet Goettingen (Germany); Malzer, Stefan; Doehler, Gottfried H. [Universitaet Erlangen-Nuernberg (Germany). Max-Planck-Research Group, Institute of Optics, Information, and Photonics

    2008-07-01

    The performance of modern semiconductor devices is largely influenced by the spatial distribution of dopants in the device's active region on the nanoscale. Since the late 80's Scanning Tunneling Microscopy (STM) was employed to study the local properties of p-n interfaces. Most studies were carried out on p-n superlattices allowing the investigation of intrinsic features accessible without applied bias across the diode. Here, a single GaAs p-i-n diode heterostructure is investigated with cross-sectional STM (X-STM) in a three-terminal configuration. External source and drain contacts control the electric field across the junction. Then, the diode's active region is mapped with atomic resolution. Local I(V)-spectroscopy (STS) directly resolves the band edge alignment from p to n for different diode bias conditions. The effect of the external electric field on the spatial and spectral images of individual dopant atoms in the active layer is discussed.

  6. An apparatus for studying spallation neutrons in the Aberdeen Tunnel laboratory

    CERN Document Server

    Blyth, S C; Chen, X C; Chu, M C; Hahn, R L; Ho, T H; Hsiung, Y B; Hu, B Z; Kwan, K K; Kwok, M W; Kwok, T; Lau, Y P; Lee, K P; Leung, J K C; Leung, K Y; Lin, G L; Lin, Y C; Luk, K B; Luk, W H; Ngai, H Y; Ngan, S Y; Pun, C S J; Shih, K; Tam, Y H; Tsang, R H M; Wang, C H; Wong, C M; Wong, H L; Wong, H H C; Wong, K K; Yeh, M

    2013-01-01

    In this paper, we describe the design, construction and performance of an apparatus installed in the Aberdeen Tunnel laboratory in Hong Kong for studying spallation neutrons induced by cosmic-ray muons under a vertical rock overburden of 611 meter water equivalent (m.w.e.). The apparatus comprises of six horizontal layers of plastic-scintillator hodoscopes for determining the direction and position of the incident cosmic-ray muons. Sandwiched between the hodoscope planes is a neutron detector filled with 650 kg of liquid scintillator doped with about 0.06% of Gadolinium by weight for improving the e?ciency of detecting the spallation neutrons. Performance of the apparatus is also presented.

  7. Neutron spectroscopy with the Spherical Proportional Counter based on nitrogen gas

    Science.gov (United States)

    Bougamont, E.; Dastgheibi, A.; Derre, J.; Galan, J.; Gerbier, G.; Giomataris, I.; Gros, M.; Katsioulas, I.; Jourde, D.; Magnier, P.; Navick, X. F.; Papaevangelou, T.; Savvidis, I.; Tsiledakis, G.

    2017-03-01

    A novel large volume spherical proportional counter, recently developed, is used for neutron measurements. The pure N2 gas is studied for thermal and fast neutron detection, providing a new way for neutron spectroscopy. The neutrons are detected via the 14N (n , p)C14 and 14N (n , α)B11 reactions. The detector is tested for thermal and fast neutrons detection with 252Cf and 241Am -9Be neutron sources. The atmospheric neutrons are successfully measured from thermal up to several MeV, well separated from the cosmic ray background. A comparison of the spherical proportional counter with the current available neutron counters is also presented.

  8. DSP Algorithms for Fission Fragment and Prompt Fission Neutron Spectroscopy

    Science.gov (United States)

    Zeynalova, O.; Zeynalov, Sh.; Hambsch, F.-J.; Oberstedt, S.; Fabry, I.

    2009-10-01

    Digital signal processing (DSP) algorithms are in high demand for modern nuclear fission investigation due to importance of increase the accuracy of fissile nuclear data for new generation of nuclear power stations. DSP algorithms for fission fragment (FF) and prompt fission neutron (PFN) spectroscopy are described in the present work. The twin Frisch-grid ionization chamber (GTIC) is used to measure the kinetic energy-, mass- and angular distributions of the FF in the 252Cf(SF) reaction. Along with the neutron time-of-flight (TOF) measurement the correlation between neutron emission and FF mass and energy is investigated. The TOF is measured between common cathode of the GTIC and the neutron detector (ND) pulses. Waveform digitizers (WFD) having 12 bit amplitude resolution and 100 MHz sampling frequency are used for the detector pulse sampling. DSP algorithms are developed as recursive procedures to perform the signal processing, similar to those available in various nuclear electronics modules, such as constant fraction discriminator (CFD), pulse shape discriminator (PSD), peak-sensitive analogue-to-digital converter (pADC) and pulse shaping amplifier (PSA). To measure the angle between FF and the cathode plane normal to the GTIC a new algorithm is developed having advantage over the traditional analogue pulse processing schemes. Algorithms are tested by comparing the numerical simulation of the data analysis of the 252Cf(SF) reaction with data available from literature.

  9. Inelastic electron tunneling spectroscopy: A route to the identification of the tip-apex structure

    Science.gov (United States)

    Vitali, Lucia; Borisova, Svetlana D.; Rusina, Galina G.; Chulkov, Evgueni V.; Kern, Klaus

    2010-04-01

    The vibrational spectrum of a tunneling junction on a clean Cu(111) surface has been characterized by vibrational density of states calculations and inelastic electron tunneling spectroscopy technique. We demonstrate that the achieved spectrum consists not only of vibrational modes excited by the tunneling electrons on the clean surface but also of modes characteristic of the structure of the tip apex. This allows to identify unequivocally the atomic structure of the tip, which is still the largest unknown parameter in a scanning tunneling microscope. This opens a new perspective in the interpretation of the measurements of vibrational modes with a scanning tunneling microscope. Additionally, it might have implications in the measurements of electron conductance through single atom or molecules contacted by the tip of scanning tunneling microscope.

  10. Development of positron annihilation spectroscopy for characterizing neutron irradiated tungsten

    Energy Technology Data Exchange (ETDEWEB)

    C.N. Taylor; M. Shimada; D.W. Akers; M.W. Drigert; B.J. Merrill; Y. Hatano

    2013-05-01

    Tungsten samples (6 mm diameter, 0.2 mm thick) were irradiated to 0.025 and 0.3 dpa with neutrons in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Samples were then exposed to deuterium plasma in the tritium plasma experiment (TPE) at 100, 200 and 500ºC to a total fluence of 1 x 1026 m-2. Nuclear reaction analysis (NRA) and Doppler broadening positron annihilation spectroscopy (DB-PAS) were performed at various stages to characterize damage and retention. We present the first known results of neutron damaged tungsten characterized by DB-PAS in order to study defect concentration. Two positron sources, 22Na and 68Ge, probe ~58 µm and through the entire 200 µm thick samples, respectively. DB-PAS results reveal clear differences between the various irradiated samples. These results, and the calibration of DB-PAS to NRA data are presented.

  11. Macromolecular Dynamics in Red Blood Cells Investigated Using Neutron Spectroscopy

    CERN Document Server

    Stadler, Andreas Maximilian; Demmel, Franz; Artmann, Gerhard; 10.1098/rsif.2010.0306

    2011-01-01

    We present neutron scattering measurements on the dynamics of hemoglobin (Hb) in human red blood cells in vivo. Global and internal Hb dynamics were measured in the ps to ns time- and {\\AA} length-scale using quasielastic neutron backscattering spectroscopy. We observed the cross-over from global Hb short-time to long-time self-diffusion. Both short- and long-time diffusion coefficients agree quantitatively with predicted values from hydrodynamic theory of non-charged hard-sphere suspensions when a bound water fraction of around 0.23g H2O/ g Hb is taken into account. The higher amount of water in the cells facilitates internal protein fluctuations in the ps time-scale when compared to fully hydrated Hb powder. Slower internal dynamics of Hb in red blood cells in the ns time-range were found to be rather similar to results obtained with fully hydrated protein powders, solutions and E. coli cells.

  12. High-resolution tunnelling spectroscopy of a graphene quartet.

    Science.gov (United States)

    Song, Young Jae; Otte, Alexander F; Kuk, Young; Hu, Yike; Torrance, David B; First, Phillip N; de Heer, Walt A; Min, Hongki; Adam, Shaffique; Stiles, Mark D; MacDonald, Allan H; Stroscio, Joseph A

    2010-09-01

    Electrons in a single sheet of graphene behave quite differently from those in traditional two-dimensional electron systems. Like massless relativistic particles, they have linear dispersion and chiral eigenstates. Furthermore, two sets of electrons centred at different points in reciprocal space ('valleys') have this dispersion, giving rise to valley degeneracy. The symmetry between valleys, together with spin symmetry, leads to a fourfold quartet degeneracy of the Landau levels, observed as peaks in the density of states produced by an applied magnetic field. Recent electron transport measurements have observed the lifting of the fourfold degeneracy in very large applied magnetic fields, separating the quartet into integer and, more recently, fractional levels. The exact nature of the broken-symmetry states that form within the Landau levels and lift these degeneracies is unclear at present and is a topic of intense theoretical debate. Here we study the detailed features of the four quantum states that make up a degenerate graphene Landau level. We use high-resolution scanning tunnelling spectroscopy at temperatures as low as 10 mK in an applied magnetic field to study the top layer of multilayer epitaxial graphene. When the Fermi level lies inside the fourfold Landau manifold, significant electron correlation effects result in an enhanced valley splitting for even filling factors, and an enhanced electron spin splitting for odd filling factors. Most unexpectedly, we observe states with Landau level filling factors of 7/2, 9/2 and 11/2, suggestive of new many-body states in graphene.

  13. Collinear Resonance Ionization Spectroscopy of Neutron-Deficient Francium Isotopes

    CERN Document Server

    Flanagan, K T; Ruiz, R F Garcia; Budincevic, I; Procter, T J; Fedosseev, V N; Lynch, K M; Cocolios, T E; Marsh, B A; Neyens, G; Strashnov, I; Stroke, H H; Rossel, R E; Heylen, H; Billowes, J; Rothe, S; Bissell, M L; Wendt, K D A; de Groote, R P; De Schepper, S

    2013-01-01

    The magnetic moments and isotope shifts of the neutron-deficient francium isotopes Fr202-205 were measured at ISOLDE-CERN with use of collinear resonance ionization spectroscopy. A production-to-detection efficiency of 1\\% was measured for Fr-202. The background from nonresonant and collisional ionization was maintained below one ion in 10(5) beam particles. Through a comparison of the measured charge radii with predictions from the spherical droplet model, it is concluded that the ground-state wave function remains spherical down to Fr-205, with a departure observed in Fr-203 (N = 116).

  14. Thin liquid sample fabrication for neutron resonance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Noguere, G. [CEA Cadarache, F-13108 Saint Paul les Durance (France)], E-mail: gilles.noguere@cea.fr; Brusegan, A. [EC-JRC-IRMM, B-2440 Geel (Belgium); Lepretre, A. [CEA Saclay, F-91191 Gif sur Yvette (France); Lombard, T.; Lupo, J. [EC-JRC-IRMM, B-2440 Geel (Belgium)

    2008-03-11

    In neutron resonance spectroscopy, preparation of thin cylindrical samples of large diameter containing 10{sup -4}-10{sup -5} atoms per barn of raw materials in powder form make pressing a uniform thickness sample difficult. The use of liquid samples is a suitable alternative to overcome the technical limits inherent to the fabrication of pressed solid samples by compaction methods. This paper presents the fabrication of a 2 mm thick cylindrical sample, with a inner diameter of 65 mm, filled with an aqueous solution of lithium iodide. The sample was designed to measure the low neutron energy range of the {sup 127}I total cross-section by means of the neutron resonance transmission technique. The resonance shape analysis provided results consistent with those obtained by measuring a 17.5 mm thick lead iodine sample under the same experimental conditions as for LiI sample. Such liquid sample could be used to repeat similar measurements on a large variety of stable isotopes and low radioactive materials.

  15. Tunneling and Tunneling Switching Dynamics in Phenol and Ortho-D FTIR Spectroscopy with Synchrotron Radiation and Theory

    Science.gov (United States)

    Albert, S.; Prentner, R.; Quack, M.; Lerch, Ph.

    2013-06-01

    The understanding of tunneling in chemical reactions is of fundamental interest. A particularly intriguing recent development is the theoretical prediction of tunneling switching in ortho-D-phenol (C_6H_4DOH) as opposed to phenol (C_6H_5OH) where only tunneling dominates the dynamics. For ortho-D-phenol at low energy, tunneling is completely suppressed due to isotopic substitution, which introduces an asymmetry in the effective potential including zero point energy. This localizes the molecular wavefunction in either the syn or the anti structure of ortho-D-phenol. At higher torsional states of ortho-D-phenol, tunneling becomes dominant, thus switching the dynamics to a delocalized quantum wavefunction. Therefore, we have investigated the rotationally resolved THz and IR spectra of phenol and ortho-D-phenol measured with our FTIR setup at the Swiss Light Source (SLS) using synchrotron radiation. We have been able to analyse the torsional fundamentals, the first and second overtones of both isotopomers. A comparison of the spectra of phenol and ortho-D-phenol indicates the theoretically predicted behavior of tunneling switching upon excitation of the torsional mode. In detail, we shall discuss the splitting of the torsional fundamental, of its first and second overtones of phenol as well as the fundamentals of syn- and anti- ortho-D-phenol and the possible tunneling switching in the torsional overtone region of ortho-D-phenol. The results shall be also discussed in relation to the quasiadiabatic channel Reaction Path Hamiltonian approach. We shall also discuss the comparison with results for meta-D-phenol. M. Quack, Fundamental symmetries and symmetry violations in Handbook of High Resolution Spectroscopy, Vol. 1(Eds. M. Quack and F. Merkt), Wiley, Chicester (2011), 659-722. S. Albert, Ph. Lerch, R. Prentner, M. Quack, Angew. Chem. Int. Ed. 2013, 52, 346-349. S. Albert and M. Quack, ChemPhysChem, 2007, 8, 1271-1281, S. Albert, K. Keppler Albert and M. Quack, High

  16. New approach towards imaging -DNA using scanning tunneling microscopy/spectroscopy (STM/STS)

    Indian Academy of Sciences (India)

    Shirshendu Dey; Sushama Pethkar; Suguna D Adyanthaya; Murali Sastry; C V Dharmadhikari

    2008-06-01

    A new methodology to anchor -DNA to silanized -Si(111) surface using Langmuir Blodget trough was developed. The -Si (111) was silanized by treating it with low molecular weight octyltrichlorosilane in toluene. Scanning tunneling microscopy (STM) image of -DNA on octyltrichlorosilane deposited Si substrate shows areas exhibiting arrayed structures of 700 nm length and 40 nm spacing. Scanning tunneling spectroscopy (STS) at different stages depict a broad distribution of defect states in the bandgap region of -Si(111) which presumably facilitates tunneling through otherwise insulating DNA layer.

  17. Modeling of tunneling spectroscopy in high-TC superconductors

    Science.gov (United States)

    Shukrinov, Yu. M.; Namiranian, A.; Najafi, A.

    2001-01-01

    The tunneling density of states of high-Tc superconductors is calculated taking into account the tight-binding band structure, group velocity, and tunneling directionality for s-wave and d-wave gap symmetry. The characteristic density of states has asymmetry of the quasiparticle peaks, flat s-wave and cusplike d-wave subgap behavior, and an asymmetric background. It is assumed that the underlying asymmetry of the conductance peaks is primarily due to the features of the quasiparticle energy spectrum and that the d-wave symmetry enhances the degree of asymmetry of the peaks. Increasing the lifetime broadening factor changes the degree of asymmetry of the tunneling conductance peaks and leads to confluence of the quasiparticle and van Hove singularity peaks.

  18. Laser Spectroscopy Studies in the Neutron-Rich Sn Region

    CERN Multimedia

    Obert, J

    2002-01-01

    We propose to use the powerful laser spectroscopy method to determine the magnetic moment $\\mu$ and the variation of the mean square charge radius ($\\delta\\,\\langle$r$_{c}^{2}\\,\\rangle$) for ground and long-lived isomeric states of the Sn isotopes from A=125 to the doubly-magic $^{132}$Sn isotope and beyond. For these neutron-rich Sn nuclei, numerous $\\delta\\,\\langle$r$^{2}_{c}\\,\\rangle$ curves have already been calculated and the predictions depend upon the effective interactions used. Therefore, a study of the effect of the shell closure N=82 on the $\\delta\\,\\langle$r$^{2}_{c}\\,\\rangle$ values in the Z=50 magic nuclei is of great interest, especially because $^{132}$Sn is located far from the stability valley. It will help to improve the parameters of the effective interactions and make them more suitable to predict the properties of exotic nuclei. \\\\ \\\\The neutron-rich Sn isotopes produced with an uranium carbide target, are ionized using either a hot plasma ion source or the resonant ionization laser ion ...

  19. Characterization of Mars' seasonal caps using neutron spectroscopy

    Science.gov (United States)

    Prettyman, T.H.; Feldman, W.C.; Titus, T.N.

    2009-01-01

    Mars' seasonal caps are characterized during Mars years 26 and 27 (April 2002 to January 2006) using data acquired by the 2001 Mars Odyssey Neutron Spectrometer. Time-dependent maps of the column abundance of seasonal CO 2 surface ice poleward of 60?? latitude in both hemispheres are determined from spatially deconvolved, epithermal neutron counting data. Sources of systematic error are analyzed, including spatial blurring by the spectrometer's broad footprint and the seasonal variations in the abundance of noncondensable gas at high southern latitudes, which are found to be consistent with results reported by Sprague et al. (2004, 2007). Corrections for spatial blurring are found to be important during the recession, when the column abundance of seasonal CO2 ice has the largest latitude gradient. The measured distribution and inventory of seasonal CO2 ice is compared to simulations by a general circulation model (GCM) calibrated using Viking lander pressure data, cap edge functions determined by thermal emission spectroscopy, and other nuclear spectroscopy data sets. On the basis of the amount of CO2 cycled through the caps during years 26 and 27, the gross polar energy balance has not changed significantly since Viking. The distribution of seasonal CO2 ice is longitudinally asymmetric: in the north, deposition rates of CO2 ice are elevated in Acidalia, which is exposed to katabatic winds from Chasma Borealis; in the south, CO2 deposition is highest near the residual cap. During southern recession, CO 2 ice is present longer than calculated by the GCM, which has implications for the local polar energy balance. Copyright 2009 by the American Geophysical Union.

  20. Rabi noise spectroscopy of individual two-level tunneling defects

    Science.gov (United States)

    Matityahu, Shlomi; Lisenfeld, Jürgen; Bilmes, Alexander; Shnirman, Alexander; Weiss, Georg; Ustinov, Alexey V.; Schechter, Moshe

    2017-06-01

    Understanding the nature of two-level tunneling defects is important for minimizing their disruptive effects in various nanodevices. By exploiting the resonant coupling of these defects to a superconducting qubit, one can probe and coherently manipulate them individually. In this work, we utilize a phase qubit to induce Rabi oscillations of single tunneling defects and measure their dephasing rates as a function of the defect's asymmetry energy, which is tuned by an applied strain. The dephasing rates scale quadratically with the external strain and are inversely proportional to the Rabi frequency. These results are analyzed and explained within a model of interacting defects, in which pure dephasing of coherent high-frequency (gigahertz) defects is caused by interaction with incoherent low-frequency thermally excited defects. Our analysis sets an upper bound for the relaxation rates of thermally excited defects interacting strongly with strain fields.

  1. Thermal Emissivity-Based Chemical Spectroscopy through Evanescent Tunneling.

    Science.gov (United States)

    Poole, Zsolt L; Ohodnicki, Paul R

    2016-04-01

    A new spectroscopic technique is presented, with which environmentalchemistry-induced thermal emissivity changes of thin films are extracted with high isolation through evanescent tunneling. With this method the hydrogen-induced emissivity changes of films of TiO2 , Pd-TiO2 , and Au-TiO2 , with properties of high conductivity, hydrogen chemisorption, and plasmonic activity, are characterized in the UV-vis and NIR wavelength ranges, at 1073 K.

  2. Neutron resonance transmission spectroscopy with high spatial and energy resolution at the J-PARC pulsed neutron source

    Energy Technology Data Exchange (ETDEWEB)

    Tremsin, A.S., E-mail: ast@ssl.berkeley.edu [University of California at Berkeley, 7 Gauss Way, Berkeley, CA 94720 (United States); Shinohara, T.; Kai, T.; Ooi, M. [Japan Atomic Energy Agency, 2–4 Shirakata-shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan); Kamiyama, T.; Kiyanagi, Y.; Shiota, Y. [Hokkaido University, Kita 13 Nishi 8 Kita-ku, Sapporo-shi, Hokkaido 060-8628 (Japan); McPhate, J.B.; Vallerga, J.V.; Siegmund, O.H.W. [University of California at Berkeley, 7 Gauss Way, Berkeley, CA 94720 (United States); Feller, W.B. [NOVA Scientific, Inc., 10 Picker Rd., Sturbridge, MA 01566 (United States)

    2014-05-11

    The sharp variation of neutron attenuation at certain energies specific to particular nuclides (the lower range being from ∼1 eV up to ∼1 keV), can be exploited for the remote mapping of element and/or isotope distributions, as well as temperature probing, within relatively thick samples. Intense pulsed neutron beam-lines at spallation sources combined with a high spatial, high-timing resolution neutron counting detector, provide a unique opportunity to measure neutron transmission spectra through the time-of-flight technique. We present the results of experiments where spatially resolved neutron resonances were measured, at energies up to 50 keV. These experiments were performed with the intense flux low background NOBORU neutron beamline at the J-PARC neutron source and the high timing resolution (∼20 ns at epithermal neutron energies) and spatial resolution (∼55 µm) neutron counting detector using microchannel plates coupled to a Timepix electronic readout. Simultaneous element-specific imaging was carried out for several materials, at a spatial resolution of ∼150 µm. The high timing resolution of our detector combined with the low background beamline, also enabled characterization of the neutron pulse itself – specifically its pulse width, which varies with neutron energy. The results of our measurements are in good agreement with the predicted results for the double pulse structure of the J-PARC facility, which provides two 100 ns-wide proton pulses separated by 600 ns, broadened by the neutron energy moderation process. Thermal neutron radiography can be conducted simultaneously with resonance transmission spectroscopy, and can reveal the internal structure of the samples. The transmission spectra measured in our experiments demonstrate the feasibility of mapping elemental distributions using this non-destructive technique, for those elements (and in certain cases, specific isotopes), which have resonance energies below a few keV, and with lower

  3. Spectroscopy of neutron rich nuclei using cold neutron induced fission of actinide targets at the ILL: the EXILL campaign

    Directory of Open Access Journals (Sweden)

    de France G.

    2014-03-01

    Full Text Available A combination of germanium detectors has been installed at the PF1B neutron guide of the ILL to perform the prompt spectroscopy of neutron-rich nuclei produced in the neutron-capture induced-fission of 235U and 241Pu. In addition LaBr3 detectors from the FATIMA collaboration have been installed in complement with the EXOGAM clovers to measure lifetimes of low-lying excited states. The measured characteristics and online spectra indicate very good performances of the overall setup.

  4. Superconducting LiFeAs as seen by scanning tunneling microscopy/spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Pohle, Rico; Scheffler, Martha; Schlegel, Ronny; Haenke, Torben; Baumann, Danny; Bachmann, Anne; Bombor, Dirk; Sykora, Steffen; Harnagea, Luminita; Wurmehl, Sabine; Hess, Christian; Buechner, Bernd [Institut fuer Festkoerperforschung IFW Dresden (Germany)

    2012-07-01

    Among the entire class of iron-based superconductors the material LiFeAs is of particular interest since an absence of nesting between electron and hole pockets suggests an unconventional type of pairing in this material. Using Scanning Tunnelling Microscopy (STM) and Spectroscopy (STS) we investigate topographic properties of the surface as well as the temperature dependency of the superconducting gap. The good agreement of our results with model calculations for the tunnelling conductance allows us to draw conclusions about the low energy properties of the superconducting system. Furthermore, we compare our results with Transport- and NMR-measurements.

  5. Strong overtones modes in inelastic electron tunneling spectroscopy with cross-conjugated molecules

    DEFF Research Database (Denmark)

    Jørgensen, Jacob Lykkebo; Gagliardi, Alessio; Pecchia, Alessandro

    2013-01-01

    . With this in mind, we investigate a spectroscopic method capable of providing insight into these junctions for cross-conjugated molecules: inelastic electron tunneling spectroscopy (IETS). IETS has the advantage that the molecule interface is probed directly by the tunneling current. Previously, it has been thought...... of the transmission channels of the π system only, and consequently, in the vicinity of the interference feature, the transmission channels of the σ system and the π system become equally transmissive. This allows for scattering between the different transmission channels, which serves as a pathway to bypass...

  6. Scanning tunneling spectroscopy of CdSe nanocrystals covalently bound to GaAs

    DEFF Research Database (Denmark)

    Walzer, K.; Marx, E.; Greenham, N.C.;

    2003-01-01

    We present scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of CdSe nanocrystals covalently attached to doped GaAs substrates using monolayers of 1,6-hexanedithiol. STM measurements showed the formation of stable, densely packed, homogeneous monolayers of...... Elsevier Science B.V. All rights reserved....... and the bands in the substrate which are bent under the influence of the strong electric field between the closely separated semiconductor substrate and STM tip. The polarity of the forward bias direction is determined by the alignment of the CdSe electronic states with the semiconductor bands. (C) 2003...

  7. Scanning tunneling spectroscopy in MgB2.

    Science.gov (United States)

    Karapetrov, G; Iavarone, M; Kwok, W K; Crabtree, G W; Hinks, D G

    2001-05-01

    We present scanning tunneling microscopy measurements of the surface of superconducting MgB2 with a critical temperature of 39 K. In zero magnetic field the conductance spectra can be analyzed in terms of the standard BCS theory with a smearing parameter gamma. The value of the superconducting gap is 5 meV at 4.2 K, with no experimentally significant variation across the surface of the sample. The temperature dependence of the gap follows the BCS form, fully consistent with phonon-mediated superconductivity in this novel superconductor. The application of a magnetic field induces strong pair breaking as seen in the conductance spectra in fields up to 6 T.

  8. Characterization of defect accumulation in neutron-irradiated Mo by positron annihilation spectroscopy

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Li, Meimei; Snead, L.L.

    2008-01-01

    Positron annihilation lifetime spectroscopy measurements were performed on neutron-irradiated low carbon arc cast Mo. Irradiation took place in the high flux isotope reactor, Oak Ridge National Laboratory, at a temperature of 80 +/- 10 degrees C. Neutron fluences ranged from 2 x 10(21) to 8 x 10...

  9. A comparison of different neutron spectroscopy systems at the reactor facility VENUS

    Energy Technology Data Exchange (ETDEWEB)

    Vanhavere, F. E-mail: fvanhave@sckcen.be; Vermeersch, F.; Chartier, J.L.; Itie, C.; Rosenstock, W.; Koeble, T.; D' Errico, F

    2002-01-01

    The VENUS facility is a zero-power research reactor mainly devoted to studies on LWR fuels. Localised high-neutron rates were found around the reactor, with a neutron/gamma dose equivalent rate ratio as high as three. Therefore, a study of the neutron dosimetry around the reactor was started some years ago. During this study, several methods of neutron spectroscopy were employed and a study of individual and ambient dosemeters was performed. A first spectrometric measurement was done with the IPSN multisphere spectrometer in three positions around the reactor. Secondly, the ROSPEC spectrometer from the Fraunhofer Institut was used. The spectra were also measured with the bubble interactive neutron spectrometer. These measurements were compared with a numerical simulation of the neutron field made with the code TRIPOLI-3. Dosimetric measurements were made with three types of personal neutron dosemeters: an albedo type, a track etch detector and a bubble detector.

  10. Strong Asymmetric Charge Carrier Dependence in Inelastic Electron Tunneling Spectroscopy of Graphene Phonons.

    Science.gov (United States)

    Natterer, Fabian D; Zhao, Yue; Wyrick, Jonathan; Chan, Yang-Hao; Ruan, Wen-Ying; Chou, Mei-Yin; Watanabe, Kenji; Taniguchi, Takashi; Zhitenev, Nikolai B; Stroscio, Joseph A

    2015-06-19

    The observation of phonons in graphene by inelastic electron tunneling spectroscopy has been met with limited success in previous measurements arising from weak signals and other spectral features which inhibit a clear distinction between phonons and miscellaneous excitations. Utilizing a back-gated graphene device that allows adjusting the global charge carrier density, we introduce an averaging method where individual tunneling spectra at varying charge carrier density are combined into one representative spectrum. This method improves the signal for inelastic transitions while it suppresses dispersive spectral features. We thereby map the total graphene phonon density of states, in good agreement with density functional calculations. Unexpectedly, an abrupt change in the phonon intensity is observed when the graphene charge carrier type is switched through a variation of the back-gate electrode potential. This sudden variation in phonon intensity is asymmetric in the carrier type, depending on the sign of the tunneling bias.

  11. Studying the universality of field induced tunnel ionization times via high-order harmonic spectroscopy

    CERN Document Server

    Soifer, Hadas; Negro, Matteo; Devetta, Michele; Faccialà, Davide; Vozzi, Caterina; de Silvestri, Sandro; Stagira, Salvatore; Dudovich, Nirit

    2014-01-01

    High-harmonics generation spectroscopy is a promising tool for resolving electron dynamics and structure in atomic and molecular systems. This scheme, commonly described by the strong field approximation, requires a deep insight into the basic mechanism that leads to the harmonics generation. Recently, we have demonstrated the ability to resolve the first stage of the process -- field induced tunnel ionization -- by adding a weak perturbation to the strong fundamental field. Here we generalize this approach and show that the assumptions behind the strong field approximation are valid over a wide range of tunnel ionization conditions. Performing a systematic study -- modifying the fundamental wavelength, intensity and atomic system -- we observed a good agreement with quantum path analysis over a range of Keldysh parameters. The generality of this scheme opens new perspectives in high harmonics spectroscopy, holding the potential of probing large, complex molecular systems.

  12. MONSTER: a TOF Spectrometer for β-delayed Neutron Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Martínez, T., E-mail: trino.martinez@ciemat.es [Centro de Investigaciones Energéticas, MedioAmbientales y Tecnológicas, CIEMAT, Madrid 28040 (Spain); Cano-Ott, D.; Castilla, J.; Garcia, A.R.; Marin, J.; Martinez, G.; Mendoza, E.; Santos, C.; Tera, F.J.; Villamarin, D. [Centro de Investigaciones Energéticas, MedioAmbientales y Tecnológicas, CIEMAT, Madrid 28040 (Spain); Agramunt, J.; Algora, A.; Domingo, C.; Jordan, M.D.; Rubio, B.; Taín, J.L. [Instituto de Física Corpuscular, CSIC-Universidad de Valencia (Spain); Bhattacharya, C.; Banerjee, K.; Bhattacharya, S.; Roy, P. [Variable Energy Cyclotron Centre (VECC), Kolkata (India); and others

    2014-06-15

    β-delayed neutron (DN) data, including emission probabilities, Pn, and energy spectrum, play an important role in our understanding of nuclear structure, nuclear astrophysics and nuclear technologies. A MOdular Neutron time-of-flight SpectromeTER (MONSTER) is being built for the measurement of the neutron energy spectra and branching ratios. The TOF spectrometer will consist of one hundred liquid scintillator cells covering a significant solid angle. The MONSTER design has been optimized by using Monte Carlo (MC) techniques. The response function of the MONSTER cell has been characterized with mono-energetic neutron beams and compared to dedicated MC simulations.

  13. MONSTER: a TOF Spectrometer for β-delayed Neutron Spectroscopy

    Science.gov (United States)

    Martínez, T.; Cano-Ott, D.; Castilla, J.; Garcia, A. R.; Marin, J.; Martinez, G.; Mendoza, E.; Santos, C.; Tera, F. J.; Villamarin, D.; Agramunt, J.; Algora, A.; Domingo, C.; Jordan, M. D.; Rubio, B.; Taín, J. L.; Bhattacharya, C.; Banerjee, K.; Bhattacharya, S.; Roy, P.; Meena, J. K.; Kundu, S.; Mukherjee, G.; Ghosh, T. K.; Rana, T. K.; Pandey, R.; Saxena, A.; Behera, B.; Penttilä, H.; Jokinen, A.; Rinta-Antila, S.; Guerrero, C.; Ovejero, M. C.

    2014-06-01

    β-delayed neutron (DN) data, including emission probabilities, Pn, and energy spectrum, play an important role in our understanding of nuclear structure, nuclear astrophysics and nuclear technologies. A MOdular Neutron time-of-flight SpectromeTER (MONSTER) is being built for the measurement of the neutron energy spectra and branching ratios. The TOF spectrometer will consist of one hundred liquid scintillator cells covering a significant solid angle. The MONSTER design has been optimized by using Monte Carlo (MC) techniques. The response function of the MONSTER cell has been characterized with mono-energetic neutron beams and compared to dedicated MC simulations.

  14. Scanning tunneling spectroscopy on heavy-fermion systems; Rastertunnelspektroskopie an Schwere-Fermionen-Systemen

    Energy Technology Data Exchange (ETDEWEB)

    Ernst, Stefan

    2011-06-24

    in the framework of this thesis different heavy-fermion systems were studied by means of scanning tunneling microscopy and spectroscopy. In the experiment two main topics existed. On the one hand the heavy-fermion superconductivity in the compounds CeCu{sub 2}Si{sub 2}, CeCoIn{sub 5}, and on the other hand the Kondo effect in the Kondo-lattice system YbRh{sub 2}Si{sub 2}.

  15. Characterization of thin film semiconductors by scanning probe microscopy and tunneling spectroscopy

    Science.gov (United States)

    Gichuhi, Anthony

    We have used scanning tunneling microscopy, atomic force microscopy, tunneling spectroscopy, resonance Raman spectroscopy and electrochemistry to study the electrosynthesis of II-VI compound semiconductors with special emphasis on ZnS, CdS, and HgS. This dissertation will focus mainly on the electrochemical and scanning probe (STM and AFM) applications to these compounds, in addition to novel materials such as CoSb. We hope to understand the structural, as well optical properties of these materials. Finally, we hope to develop a recipe for the electrosynthesis of high quality semiconductor films. In Chapter 2, we report an electrochemical, scanning probe microscopic and Raman spectroscopic investigation of thin US films grown by electrochemical atomic layer epitaxy (EC-ALE) aimed at understanding the role played by the order of deposition on film quality. In Chapter 3, we report a study of electrosynthesized CdS-HgS heterojunctions using scanning tunneling microscopy (STM), photoluminescence spectroscopy (PL), and electrochemistry. US thin films were grown by electrochemical atomic layer epitaxy onto Au(111) substrates and were terminated with a single HgS monolayer. In Chapter 4, the structure and chemical composition of electrosynthesized ZnS thin films on Au(111) substrates grown by alternating underpotential deposition and oxidative adsorption cycles of S and Zn from solution precursors was studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). In Chapter 5, conditions for the growth of. stable mercury sulfide (HgS) monolayers on Au(111) surfaces using electrochemical atomic layer epitaxy have been investigated. HgS thin films were characterized by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Chapter 6: This chapter describes the use of resonance Raman spectroscopy to characterize thin films of the II-VI compound semiconductors electrosynthesized on metal surfaces. We describe how resonance

  16. Broad Energy Range Neutron Spectroscopy using a Liquid Scintillator and a Proportional Counter: Application to a Neutron Spectrum Similar to that from an Improvised Nuclear Device.

    Science.gov (United States)

    Xu, Yanping; Randers-Pehrson, Gerhard; Marino, Stephen A; Garty, Guy; Harken, Andrew; Brenner, David J

    2015-09-11

    A novel neutron irradiation facility at the Radiological Research Accelerator Facility (RARAF) has been developed to mimic the neutron radiation from an Improvised Nuclear Device (IND) at relevant distances (e.g. 1.5 km) from the epicenter. The neutron spectrum of this IND-like neutron irradiator was designed according to estimations of the Hiroshima neutron spectrum at 1.5 km. It is significantly different from a standard reactor fission spectrum, because the spectrum changes as the neutrons are transported through air, and it is dominated by neutron energies from 100 keV up to 9 MeV. To verify such wide energy range neutron spectrum, detailed here is the development of a combined spectroscopy system. Both a liquid scintillator detector and a gas proportional counter were used for the recoil spectra measurements, with the individual response functions estimated from a series of Monte Carlo simulations. These normalized individual response functions were formed into a single response matrix for the unfolding process. Several accelerator-based quasi-monoenergetic neutron source spectra were measured and unfolded to test this spectroscopy system. These reference neutrons were produced from two reactions: T(p,n)(3)He and D(d,n)(3)He, generating neutron energies in the range between 0.2 and 8 MeV. The unfolded quasi-monoenergetic neutron spectra indicated that the detection system can provide good neutron spectroscopy results in this energy range. A broad-energy neutron spectrum from the (9)Be(d,n) reaction using a 5 MeV deuteron beam, measured at 60 degrees to the incident beam was measured and unfolded with the evaluated response matrix. The unfolded broad neutron spectrum is comparable with published time-of-flight results. Finally, the pair of detectors were used to measure the neutron spectrum generated at the RARAF IND-like neutron facility and a comparison is made to the neutron spectrum of Hiroshima.

  17. Probing Nanoscale Electronic and Magnetic Interaction with Scanning Tunneling Spectroscopy

    DEFF Research Database (Denmark)

    Bork, Jakob

    This thesis is concerned with fundamental research into electronic and magnetic interaction on the nanoscale. From small metallic and magnetic islands and layers to single atoms. The research revolves around magnetic interaction probed through the spectroscopic capabilities of the scanning....... This is related to research in correlated electron materials such as studies of phase transitions in heavy fermion compounds and magnetic interaction in spintronic research. The capping of cobalt islands on Cu(111) with silver is investigated with STM and photoemission spectroscopy. It is shown that at low...... coverage the silver preferably nucleates on top of the bilayer high cobalt islands compared to directly on the Cu(111) substrate. Furthermore, the silver forms a combination of a reconstruction and a Moire pattern which is investigated with low-energy electron diraction and spectroscopic STM mapping at 6...

  18. Spin measurement and neutron resonance spectroscopy for ^155Gd

    Science.gov (United States)

    Baramsai, Bayarbadrakh; Mitchell, G. E.; Chyzh, A.; Dashdorj, D.; Walker, C.; Bredeweg, T. A.; Couture, A.; Haight, R. C.; Jandel, M.; Keksis, A. L.; O'Donnell, J. M.; Rundberg, R. S.; Wouters, J. M.; Ullmann, J. L.; Viera, D. J.; Agvaanluvsan, U.; Becvar, F.; Krticka, M.

    2009-05-01

    The ^155Gd(n,γ) reaction has been measured with the DANCE calorimeter at Los Alamos Neutron Science Center. The highly segmented calorimeter provided detailed multiplicity distributions of the capture γ - rays. With this information the spins of the neutron capture resonances have been determined. The improved sensitivity of this method allowed the determination of the spins of even weak and unresolved resonances. With these new spin assignments as well as previously determined resonance parameters, level spacings and neutron strength functions are determined separately for s-wave resonances with J = 1 and 2.

  19. Theory of scanning tunneling spectroscopy: from Kondo impurities to heavy fermion materials

    Science.gov (United States)

    Morr, Dirk K.

    2017-01-01

    Kondo systems ranging from the single Kondo impurity to heavy fermion materials present us with a plethora of unconventional properties whose theoretical understanding is still one of the major open problems in condensed matter physics. Over the last few years, groundbreaking scanning tunneling spectroscopy (STS) experiments have provided unprecedented new insight into the electronic structure of Kondo systems. Interpreting the results of these experiments—the differential conductance and the quasi-particle interference spectrum—however, has been complicated by the fact that electrons tunneling from the STS tip into the system can tunnel either into the heavy magnetic moment or the light conduction band states. In this article, we briefly review the theoretical progress made in understanding how quantum interference between these two tunneling paths affects the experimental STS results. We show how this theoretical insight has allowed us to interpret the results of STS experiments on a series of heavy fermion materials providing detailed knowledge of their complex electronic structure. It is this knowledge that is a conditio sine qua non for developing a deeper understanding of the fascinating properties exhibited by heavy fermion materials, ranging from unconventional superconductivity to non-Fermi-liquid behavior in the vicinity of quantum critical points.

  20. Scanning tunneling microscopy/spectroscopy of vortices in LiFeAs

    Science.gov (United States)

    Hanaguri, T.; Kitagawa, K.; Matsubayashi, K.; Mazaki, Y.; Uwatoko, Y.; Takagi, H.

    2012-06-01

    We investigate vortices in LiFeAs using scanning tunneling microscopy/spectroscopy. Zero-field tunneling spectra show two superconducting gaps without detectable spectral weight near the Fermi energy, evidencing fully gapped multiband superconductivity. We image vortices in a wide field range from 0.1 T to 11 T by mapping the tunneling conductance at the Fermi energy. A quasihexagonal vortex lattice at low field contains domain boundaries which consist of alternating vortices with unusual coordination numbers of 5 and 7. With increasing field, the domain boundaries become ill defined, resulting in a uniformly disordered vortex matter. Tunneling spectra taken at the vortex center are characterized by a sharp peak just below the Fermi energy, apparently violating particle-hole symmetry. The image of each vortex shows energy-dependent 4-fold anisotropy which may be associated with the anisotropy of the Fermi surface. The vortex radius shrinks with decreasing temperature and becomes smaller than the coherence length estimated from the upper critical field. This is direct evidence of the Kramer-Pesch effect expected in a clean superconductor.

  1. Neutron Spectroscopy Using LiF Thin-Film Detectors

    Science.gov (United States)

    2013-03-01

    with an effective mass (mn or mp, respectively) different from elementary electrons not embedded in the lattice. The occupation probability for an...Below is a brief explanation of neutron kinematics. The formulas are quite elementary , however, they accurately describe the motion of a neutron as it...domains including: high energy physics, astrophysics and space science, medical physics and radiation protection. Figure 29. Flow chart representation of a

  2. First neutron spectroscopy measurements with a pixelated diamond detector at JET

    Energy Technology Data Exchange (ETDEWEB)

    Muraro, A., E-mail: muraro@ifp.cnr.it; Giacomelli, L.; Grosso, G.; Tardocchi, M. [Istituto di Fisica del Plasma “P. Caldirola,” CNR, Milano (Italy); Nocente, M.; Rebai, M.; Rigamonti, D.; Gorini, G. [Istituto di Fisica del Plasma “P. Caldirola,” CNR, Milano (Italy); University of Milano Bicocca, Piazza della Scienza 3, 20126 Milano (Italy); Belli, F. [Centro Ricerca ENEA-Frascati, Via E.Fermi 45, Frascati, Rome (Italy); Calvani, P.; Girolami, M.; Trucchi, D. M. [CNR—Istituto di Struttura della Materia (ISM), Via Salaria km 29.300, 00015 Monterotondo Scalo, Rome (Italy); Figueiredo, J. [Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisbon (Portugal); EUROfusion Programme Management Unit, Culham Science Centre, Abingdon (United Kingdom); Murari, A. [Culham Centre for Fusion Energy, Culham (United Kingdom); Consorzio RFX (CNR, ENEA, INFN, Università di Padova, Acciaierie Venete SpA), Padova (Italy); Popovichev, S. [Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisbon (Portugal); Collaboration: EUROfusion Consortium, JET, Culham Science Centre, Abingdon OX14 3DB (United Kingdom)

    2016-11-15

    A prototype Single crystal Diamond Detector (SDD) was installed at the Joint European Torus (JET) in 2013 along an oblique line of sight and demonstrated the possibility to carry out neutron spectroscopy measurements with good energy resolution and detector stability in discharges heated by neutral beam injection and radio-frequency waves. Starting from these positive results, within the Vertical Neutron Spectrometer project of the Joint European Torus, we have developed a pixelated instrument consisting of a matrix of 12 independent SDDs, called the Diamond Vertical Neutron Spectrometer (DVNS), which boosts the detection efficiency of a single SDD by an order of magnitude. In this paper we describe the main features of the DVNS, including the detector design, energy resolution, and data acquisition system for on-line processing. Preliminary spectroscopy measurements of 2.5 MeV neutrons from the present deuterium plasma at JET are finally presented.

  3. First neutron spectroscopy measurements with a pixelated diamond detector at JET

    Science.gov (United States)

    Muraro, A.; Giacomelli, L.; Nocente, M.; Rebai, M.; Rigamonti, D.; Belli, F.; Calvani, P.; Figueiredo, J.; Girolami, M.; Gorini, G.; Grosso, G.; Murari, A.; Popovichev, S.; Trucchi, D. M.; Tardocchi, M.

    2016-11-01

    A prototype Single crystal Diamond Detector (SDD) was installed at the Joint European Torus (JET) in 2013 along an oblique line of sight and demonstrated the possibility to carry out neutron spectroscopy measurements with good energy resolution and detector stability in discharges heated by neutral beam injection and radio-frequency waves. Starting from these positive results, within the Vertical Neutron Spectrometer project of the Joint European Torus, we have developed a pixelated instrument consisting of a matrix of 12 independent SDDs, called the Diamond Vertical Neutron Spectrometer (DVNS), which boosts the detection efficiency of a single SDD by an order of magnitude. In this paper we describe the main features of the DVNS, including the detector design, energy resolution, and data acquisition system for on-line processing. Preliminary spectroscopy measurements of 2.5 MeV neutrons from the present deuterium plasma at JET are finally presented.

  4. Spectroscopy of neutron rich nuclei using cold neutron induced fission of actinide targets at the ILL: The EXILL campaign

    Directory of Open Access Journals (Sweden)

    Blanc A.

    2013-12-01

    Full Text Available One way to explore exotic nuclei is to study their structure by performing γ-ray spectroscopy. At the ILL, we exploit a high neutron flux reactor to induce the cold fission of actinide targets. In this process, fission products that cannot be accessed using standard spontaneous fission sources are produced with a yield allowing their detailed study using high resolution γ-ray spectroscopy. This is what was pursued at the ILL with the EXILL (for EXOGAM at the ILL campaign. In the present work, the EXILL setup and performance will be presented.

  5. Scanning Tunneling Spectroscopy of Metal Phthalocyanines on a Au(111) Surface with a Ni Tip

    Institute of Scientific and Technical Information of China (English)

    JIA Zhi-Chun; HU Zhen-Peng; ZHAO Ai-Di; LI Zhen-Yu; LI Bin

    2011-01-01

    Scanning tunneling spectroscopy of metal phthalocyanines (MPc) adsorbed on a A u(111) surface with a Ni(111) scanning tunneling microscopy tip is simulated on the basis of first-principles calculations and a modified Bardeen approximation.Local d orbital symmetry matching between the molecule and the Ni tip brings obvious negative differential resistance (NDR) phenomena,of which,bias voltage and resonant orbitals can be tuned sensitively by the central ion of the molecule.Different dependences of the NDR peak on the tip-molecule distance at two bias polarities and rectifying phenomena are also interpreted in terms of specific structures of 3d orbitals of the adsorbed MPc and Ni tip.

  6. Conductance maps by electrochemical tunneling spectroscopy to fingerprint the electrode electronic structure.

    Science.gov (United States)

    Díez-Pérez, Ismael; Güell, Aleix G; Sanz, Fausto; Gorostiza, Pau

    2006-10-15

    We describe a methodology to perform reliable tunneling spectroscopy in electrochemical media. Sequential in situ tunneling spectra are recorded while the electrochemical potential of the electrode is scanned. Spectroscopic data are presented as conductance maps or conductograms that show the in situ electronic structure of an electrode surface while it undergoes an electrochemical reaction. The conductance map or conductogram represents the redox fingerprint of an electrode/liquid interface in a specific medium and can serve to predict its electrochemical behavior in a quantitative energy scale. The methodology is validated studying the reversible oxidation and passivity of an iron electrode in borate buffer, and we describe the main quantitative information that can be extracted concerning the semiconducting properties of the Fe passive film. This methodology is useful to study heterogeneous catalysis, electrochemical sensing and bioelectronic systems.

  7. Estimation of neutron spectrum in the low-level gamma spectroscopy system using unfolding procedure

    Science.gov (United States)

    Knežević, D.; Jovančević, N.; Krmar, M.

    2016-03-01

    The radiation resulting from neutron interactions with Ge nuclei in active volume of HPGe detectors is one of the main concerns in low-level gamma spectroscopy measurements [1,2]. It is usually not possible to measure directly spectrum of neutrons which strike detector. This paper explore the possibility of estimation of neutron spectrum using measured activities of certain Ge(n,γ) and Ge(n,n') reactions (obtained from low-level gamma measurements), available ENDF cross section data and unfolding procedures. In this work HPGe detector with passive shield made from commercial low background lead was used for the measurement. The most important objective of this study was to reconstruct muon induced neutron spectrum created in the shield of the HPGe detector. MAXED [3] and GRAVEL [4] algorithms for neutron spectra unfolding were used. The results of those two algorithms were compared and we analyzed the sensitivity of the unfolding procedure to the various input parameters.

  8. Neutron counting and gamma spectroscopy with PVT detectors.

    Energy Technology Data Exchange (ETDEWEB)

    Mitchell, Dean James; Brusseau, Charles A.

    2011-06-01

    Radiation portals normally incorporate a dedicated neutron counter and a gamma-ray detector with at least some spectroscopic capability. This paper describes the design and presents characterization data for a detection system called PVT-NG, which uses large polyvinyl toluene (PVT) detectors to monitor both types of radiation. The detector material is surrounded by polyvinyl chloride (PVC), which emits high-energy gamma rays following neutron capture reactions. Assessments based on high-energy gamma rays are well suited for the detection of neutron sources, particularly in border security applications, because few isotopes in the normal stream of commerce have significant gamma ray yields above 3 MeV. Therefore, an increased count rate for high-energy gamma rays is a strong indicator for the presence of a neutron source. The sensitivity of the PVT-NG sensor to bare {sup 252}Cf is 1.9 counts per second per nanogram (cps/ng) and the sensitivity for {sup 252}Cf surrounded by 2.5 cm of polyethylene is 2.3 cps/ng. The PVT-NG sensor is a proof-of-principal sensor that was not fully optimized. The neutron detector sensitivity could be improved, for instance, by using additional moderator. The PVT-NG detectors and associated electronics are designed to provide improved resolution, gain stability, and performance at high-count rates relative to PVT detectors in typical radiation portals. As well as addressing the needs for neutron detection, these characteristics are also desirable for analysis of the gamma-ray spectra. Accurate isotope identification results were obtained despite the common impression that the absence of photopeaks makes data collected by PVT detectors unsuitable for spectroscopic analysis. The PVT detectors in the PVT-NG unit are used for both gamma-ray and neutron detection, so the sensitive volume exceeds the volume of the detection elements in portals that use dedicated components to detect each type of radiation.

  9. Analysis of Neutron Induced Gamma Activity in Lowbackground Ge - Spectroscopy Systems

    Science.gov (United States)

    Jovančević, Nikola; Krmar, Midrag

    Neutron interactions with materials of Ge-spectroscopy systems are one of the main sources of background radiation in low-level gamma spectroscopy measurements. Because of that detailed analysis of neutron induced gamma activity in low-background Ge-spectroscopy systems was done. Two HPGe detectors which were located in two different passive shields: one in pre-WW II made iron and the second in commercial low background lead were used in the experiment. Gamma lines emitted after neutron capture, as well as after inelastic scattering on the germanium crystal and shield materials (lead, iron, hydrogen, NaI) were detected and then analyzed. The thermal and fast neutron fluxes were calculated and their values were compared for the two different kinds of detector shield. The relative intensities of several gamma lines emitted after the inelastic scattering of neutrons (created by cosmic muons) in 56Fe were report. These relative intensities of detected gamma lines of 56Fe are compared with the results collected in the same iron shield by the use of the 252Cf neutrons.

  10. Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy

    Directory of Open Access Journals (Sweden)

    Mingsen Deng

    2015-01-01

    Full Text Available The probe of flexible molecular conformation is crucial for the electric application of molecular systems. We have developed a theoretical procedure to analyze the couplings of molecular local vibrations with the electron transportation process, which enables us to evaluate the structural fingerprints of some vibrational modes in the inelastic electron tunneling spectroscopy (IETS. Based on a model molecule of Bis-(4-mercaptophenyl-ether with a flexible center angle, we have revealed and validated a simple mathematical relationship between IETS signals and molecular angles. Our results might open a route to quantitatively measure key geometrical parameters of molecular junctions, which helps to achieve precise control of molecular devices.

  11. First-Principles Simulations of Inelastic Electron Tunneling Spectroscopy of Molecular Electronic Devices

    Science.gov (United States)

    Jiang, Jun; Kula, Mathias; Lu, Wei; Luo, Yi

    2005-08-01

    A generalized Green's function theory is developed to simulate the inelastic electron tunneling spectroscopy (IETS) of molecular junctions. It has been applied to a realistic molecular junction with an octanedithiolate embedded between two gold contacts in combination with the hybrid density functional theory calculations. The calculated spectra are in excellent agreement with recent experimental results. Strong temperature dependence of the experimental IETS spectra is also reproduced. It is shown that the IETS is extremely sensitive to the intra-molecular conformation and to the molecule-metal contact geometry.

  12. Adsorbate-induced quantum Hall system probed by scanning tunneling spectroscopy combined with transport measurements

    Energy Technology Data Exchange (ETDEWEB)

    Masutomi, Ryuichi, E-mail: masutomi@phys.s.u-tokyo.ac.jp; Okamoto, Tohru [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2015-06-22

    An adsorbate-induced quantum Hall system at the cleaved InSb surfaces is investigated in magnetic fields up to 14 T using low-temperature scanning tunneling microscopy and spectroscopy combined with transport measurements. We show that an enhanced Zeeman splitting in the Shubnikov-de Haas oscillations is explained by an exchange enhancement of spin splitting and potential disorder, both of which are obtained from the spatially averaged density of states (DOS). Moreover, the Altshuler–Aronov correlation gap is observed in the spatially averaged DOS at 0 T.

  13. Statistical Spectroscopy for Neutron-rich sd-Shell Nuclei

    CERN Document Server

    Kar, Kamales

    2012-01-01

    Statistical spectroscopic results using the spectral distribution theory are obtained for the structure of neutron-rich light nuclei going towards the drip line and compared to experimental values available. These results will be useful for nuclear astrophysics problems where often averaged nuclear properties are adequate.

  14. Beta-delayed neutron spectroscopy of spherical and deformed neutron emitters with VANDLE

    Science.gov (United States)

    King, Thomas; Gross, C. J.; Grzywacz, R. K.; Paulauskas, S. V.; Rykaczewski, K. P.; Stracener, D. W.,; Taylor, S. Z.; Vandle Collaboration

    2016-09-01

    For many neutron-rich isotopes, the main decay mode is through beta-delayed neutron and gamma emission. Neutron and gamma coincidences provide information necessary to extract the beta-strength distribution. These distributions are inputs to test nuclear models needed for r-process modeling. The detailed data on beta decay feeding to neutron-unbound states are used to calculate reactor decay heat and understand the antineutrino spectrum. A series of measurements with selective ion sources was performed at the On-Line Test Facility (OLTF) at Oak Ridge National Laboratory with the Versatile Array of Neutron Detectors at Low Energy (VANDLE). These experiments revisited decays of spherical and deformed isotopes produced in proton induced fission of 238U, which included beta delayed precursors of bromine, rubidium, cesium, and iodine. Unique data sets with neutron and gamma ray coincidences were collected. Achieving high coincidence efficiency required the addition of high-efficiency gamma-ray detectors consisting of 16 LaBr3 crystals (HAGRiD) and a large volume set of NaI detectors to VANDLE. Preliminary results will be presented. This research was sponsored by DOE under Contracts DE-FG52-08NA2855, DE-AC05-00OR22725 and DE-FG02-96ER40983.

  15. Revisiting the inelastic electron tunneling spectroscopy of single hydrogen atom adsorbed on the Cu(100) surface

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Zhuoling; Wang, Hao [Centre for Nanoscale Science and Technology, Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing 100871 (China); Sanvito, Stefano [School of Physics, AMBER and CRANN Institute, Trinity College, Dublin 2 (Ireland); Hou, Shimin, E-mail: smhou@pku.edu.cn [Centre for Nanoscale Science and Technology, Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing 100871 (China); Beida Information Research (BIR), Tianjin 300457 (China)

    2015-12-21

    Inelastic electron tunneling spectroscopy (IETS) of a single hydrogen atom on the Cu(100) surface in a scanning tunneling microscopy (STM) configuration has been investigated by employing the non-equilibrium Green’s function formalism combined with density functional theory. The electron-vibration interaction is treated at the level of lowest order expansion. Our calculations show that the single peak observed in the previous STM-IETS experiments is dominated by the perpendicular mode of the adsorbed H atom, while the parallel one only makes a negligible contribution even when the STM tip is laterally displaced from the top position of the H atom. This propensity of the IETS is deeply rooted in the symmetry of the vibrational modes and the characteristics of the conduction channel of the Cu-H-Cu tunneling junction, which is mainly composed of the 4s and 4p{sub z} atomic orbitals of the Cu apex atom and the 1s orbital of the adsorbed H atom. These findings are helpful for deepening our understanding of the propensity rules for IETS and promoting IETS as a more popular spectroscopic tool for molecular devices.

  16. Revisiting the inelastic electron tunneling spectroscopy of single hydrogen atom adsorbed on the Cu(100) surface.

    Science.gov (United States)

    Jiang, Zhuoling; Wang, Hao; Sanvito, Stefano; Hou, Shimin

    2015-12-21

    Inelastic electron tunneling spectroscopy (IETS) of a single hydrogen atom on the Cu(100) surface in a scanning tunneling microscopy (STM) configuration has been investigated by employing the non-equilibrium Green's function formalism combined with density functional theory. The electron-vibration interaction is treated at the level of lowest order expansion. Our calculations show that the single peak observed in the previous STM-IETS experiments is dominated by the perpendicular mode of the adsorbed H atom, while the parallel one only makes a negligible contribution even when the STM tip is laterally displaced from the top position of the H atom. This propensity of the IETS is deeply rooted in the symmetry of the vibrational modes and the characteristics of the conduction channel of the Cu-H-Cu tunneling junction, which is mainly composed of the 4s and 4pz atomic orbitals of the Cu apex atom and the 1s orbital of the adsorbed H atom. These findings are helpful for deepening our understanding of the propensity rules for IETS and promoting IETS as a more popular spectroscopic tool for molecular devices.

  17. Temperature dependence of the superconducting proximity effect quantified by scanning tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Stępniak, A.; Caminale, M.; Leon Vanegas, A. A.; Oka, H.; Sander, D., E-mail: sander@mpi-halle.mpg.de [Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle (Saale) (Germany); Kirschner, J. [Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle (Saale) (Germany); Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06120 Halle (Saale) (Germany)

    2015-01-15

    Here, we present the first systematic study on the temperature dependence of the extension of the superconducting proximity effect in a 1–2 atomic layer thin metallic film, surrounding a superconducting Pb island. Scanning tunneling microscopy/spectroscopy (STM/STS) measurements reveal the spatial variation of the local density of state on the film from 0.38 up to 1.8 K. In this temperature range the superconductivity of the island is almost unaffected and shows a constant gap of a 1.20 ± 0.03 meV. Using a superconducting Nb-tip a constant value of the proximity length of 17 ± 3 nm at 0.38 and 1.8 K is found. In contrast, experiments with a normal conductive W-tip indicate an apparent decrease of the proximity length with increasing temperature. This result is ascribed to the thermal broadening of the occupation of states of the tip, and it does not reflect an intrinsic temperature dependence of the proximity length. Our tunneling spectroscopy experiments shed fresh light on the fundamental issue of the temperature dependence of the proximity effect for atomic monolayers, where the intrinsic temperature dependence of the proximity effect is comparably weak.

  18. Temperature dependence of the superconducting proximity effect quantified by scanning tunneling spectroscopy

    Directory of Open Access Journals (Sweden)

    A. Stępniak

    2015-01-01

    Full Text Available Here, we present the first systematic study on the temperature dependence of the extension of the superconducting proximity effect in a 1–2 atomic layer thin metallic film, surrounding a superconducting Pb island. Scanning tunneling microscopy/spectroscopy (STM/STS measurements reveal the spatial variation of the local density of state on the film from 0.38 up to 1.8 K. In this temperature range the superconductivity of the island is almost unaffected and shows a constant gap of a 1.20 ± 0.03 meV. Using a superconducting Nb-tip a constant value of the proximity length of 17 ± 3 nm at 0.38 and 1.8 K is found. In contrast, experiments with a normal conductive W-tip indicate an apparent decrease of the proximity length with increasing temperature. This result is ascribed to the thermal broadening of the occupation of states of the tip, and it does not reflect an intrinsic temperature dependence of the proximity length. Our tunneling spectroscopy experiments shed fresh light on the fundamental issue of the temperature dependence of the proximity effect for atomic monolayers, where the intrinsic temperature dependence of the proximity effect is comparably weak.

  19. Spectroscopy of low-lying states in neutron-deficient astatine and francium nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Jakobsson, U., E-mail: ulrjak@kth.se; Cederwall, B. [KTH, The Division of Nuclear Physics, AlbaNova University Center, SE-10691 Stockholm (Sweden); Uusitalo, J.; Auranen, K.; Badran, H.; Cox, D. M.; Grahn, T.; Greenlees, P. T.; Julin, R.; Juutinen, S.; Herzáň, A.; Konki, J.; Leino, M.; Mallaburn, M.; Pakarinen, J.; Papadakis, P.; Partanen, J.; Rahkila, P.; Sandzelius, M.; Sarén, J. [University of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla (Finland); and others

    2015-10-15

    Low-lying states in neutron-deficient astatine and francium nuclei have been studied by means of in-beam and delayed spectroscopy. The 13/2{sup +} state has been observed in francium nuclei with a similar down-sloping trend as in neighbouring astatine and bismuth isotopes, as a function of decreasing neutron number. A systematic trend can also now be seen for the 1/2{sup +} state both in astatine and francium nuclei, where the level energy decreases steeply as a function of neutron number when moving further away from the neutron shell closure. This trend is very similar between astatine nuclei and their francium isotones. Moreover, shape coexistence has been observed between the 13/2{sup +} state and the spherical 9/2{sup −} ground state in {sup 203}Fr and {sup 205}Fr.

  20. Dynamic measurement of temperature using neutron resonance spectroscopy (NRS)

    Energy Technology Data Exchange (ETDEWEB)

    Funk, D.J.; Asay, B.W.; Bennett, B.I.; Bowman, J.D.; Boat, R.M.; Dickson, P.M.; Henson, B.F.; Hull, L.M.; Idar, D.J.; Laabs, G.W.; London, R.K.; Mace, J.L.; Morgan, G.L.; Murk, D.M.; Rabie, R.L.; Ragan, C.E.; Stacy, H.L.; Yuan, V.W. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    1998-07-01

    Accurate temperature measurements in dynamic systems have been pursued for decades and have usually relied on optical techniques. These approaches are generally hampered by insufficient information regarding the emissivity of the system under study. We are developing NRS techniques to measure temperature in dynamic systems and overcome these limitations. Many neutron resonances have narrow intrinsic Breit-Wigner widths such that the resonance is substantially broadened by the atomic motion even at room temperature. Thus, accurate measurement of the Doppler contribution allows one to infer the material temperature, and for the conditions achieved using standard high explosives, the probe itself is not perturbed by the high temperature and pressure. Experiments are conducted using a pulsed spallation source at LANSCE with time-of-flight measurement of the neutron spectra. In initial experiments, we have demonstrated that measurements with ten percent accuracy are possible. We have fielded dynamic tests, most of which were neutron-flux limited. An overview of the approach and the status of our experimental campaign are discussed. {copyright} {ital 1998 American Institute of Physics.}

  1. Band structure of Heusler compounds studied by photoemission and tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Arbelo Jorge, Elena

    2011-07-01

    Heusler compounds are key materials for spintronic applications. They have attracted a lot of interest due to their half-metallic properties predicted by band structure calculations. The aim of this work is to evaluate experimentally the validity of the predictions of half metallicity by band structure calculations for two specific Heusler compounds, Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa. Two different spectroscopy methods for the analysis of the electronic properties were used: Angular Resolved Ultraviolet Photoemission Spectroscopy (ARUPS) and Tunneling Spectroscopy. Heusler compounds are prepared as thin films by RF-sputtering in an ultra high vacuum system. For the characterization of the samples, bulk and surface crystallographic and magnetic properties of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa are studied. X-ray and electron diffraction reveal a bulk and surface crossover between two different types of sublattice order (from B2 to L2{sub 1}) with increasing annealing temperature. X-ray magnetic circular dichroism results show that the magnetic properties in the surface and bulk are identical, although the magnetic moments obtained are 5 % below from the theoretically predicted. By ARUPS evidence for the validity of the predicted total bulk density of states (DOS) was demonstrated for both Heusler compounds. Additional ARUPS intensity contributions close to the Fermi energy indicates the presence of a specific surface DOS. Moreover, it is demonstrated that the crystallographic order, controlled by annealing, plays an important role on broadening effects of DOS features. Improving order resulted in better defined ARUPS features. Tunneling magnetoresistance measurements of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa based MTJ's result in a Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} spin polarization of 44 %, which is the highest experimentally obtained value for this compound, although it is lower than the 100 % predicted. For Co

  2. Inelastic electron tunneling spectroscopy of CoFeB/ MgO/ CoFeB based magnetic tunnel junctions in high magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Walter, Marvin; Zbarskyy, Vladyslav; Muenzenberg, Markus [I. Phys. Inst., Georg-August-Universitaet Goettingen, 37077 Goettingen (Germany); Seibt, Michael [IV. Phys. Inst., Georg-August-Universitaet Goettingen, 37077 Goettingen (Germany); Drewello, Volker; Schaefers, Markus; Reiss, Guenter; Thomas, Andy [Bielefeld University, Physics Department, 33501 Bielefeld (Germany)

    2010-07-01

    Magnetic tunnel junctions (MTJs) showing a high tunnel magnetoresistance (TMR) are important for the fabrication of MRAM devices when combined with current induced switching. We discuss inelastic electron tunneling spectroscopy (IETS) measurements on CoFeB/MgO/CoFeB magnetic tunnel junctions. The junctions are prepared by means of magnetron sputtering of CoFeB and e-beam evaporation of stoichiometric MgO. Structuring of the multilayer is done using a photolithography process and Argon ion-milling. The IETS measurements are carried out at low temperatures down to 4.2 K, high magnetic fields up to 9 T and in parallel as well as antiparallel electrode configuration in order to distinguish between different kind of excitations such as e.g. magnons and phonons. Furthermore, oxygen vacancies in the MgO barrier are controlled through variation of the sample temperature during e-beam growth to investigate the influences of these vacancies on the tunneling spectra of MTJs.

  3. Spectroscopy of neutron-unbound $^{27,28}$F

    CERN Document Server

    Christian, G; Ash, S; Baumann, T; DeYoung, P A; Finck, J E; Gade, A; Grinyer, G F; Luther, B; Mosby, M; Mosby, S; Smith, J K; Snyder, J; Spyrou, A; Strongman, M J; Thoennessen, M; Warren, M; Weisshaar, D; Wersal, A

    2012-01-01

    The ground state of $^{28}$F has been observed as an unbound resonance $2\\underline{2}0$ keV above the ground state of $^{27}$F. Comparison of this result with USDA/USDB shell model predictions leads to the conclusion that the $^{28}$F ground state is primarily dominated by $sd$-shell configurations. Here we present a detailed report on the experiment in which the ground state resonance of $^{28}$F was first observed. Additionally, we report the first observation of a neutron-unbound excited state in $^{27}$F at an excitation energy of $25\\underline{0}0 (2\\underline{2}0)$ keV.

  4. Back-exchange of deuterium in neutron crystallography: characterization by IR spectroscopy

    Science.gov (United States)

    Yee, Ai Woon; Moulin, Martine; Haertlein, Michael; Mitchell, Edward; Forsyth, V. Trevor

    2017-01-01

    The application of IR spectroscopy to the characterization and quality control of samples used in neutron crystallography is described. While neutron crystallography is a growing field, the limited availability of neutron beamtime means that there may be a delay between crystallogenesis and data collection. Since essentially all neutron crystallographic work is carried out using D2O-based solvent buffers, a particular concern for these experiments is the possibility of H2O back-exchange across reservoir or capillary sealants. This may limit the quality of neutron scattering length density maps and of the associated analysis. Given the expense of central facility beamtime and the effort that goes into the production of suitably sized (usually perdeuterated) crystals, a systematic method of exploiting IR spectroscopy for the analysis of back-exchange phenomena in the reservoirs used for crystal growth is valuable. Examples are given in which the characterization of D2O/H2O back-exchange in transthyretin crystals is described. PMID:28381984

  5. Combining X-ray and neutron crystallography with spectroscopy

    Science.gov (United States)

    Smith, Oliver

    2017-01-01

    X-ray protein crystallography has, through the determination of the three-dimensional structures of enzymes and their complexes, been essential to the understanding of biological chemistry. However, as X-rays are scattered by electrons, the technique has difficulty locating the presence and position of H atoms (and cannot locate H+ ions), knowledge of which is often crucially important for the understanding of enzyme mechanism. Furthermore, X-ray irradiation, through photoelectronic effects, will perturb the redox state in the crystal. By using single-crystal spectrophotometry, reactions taking place in the crystal can be monitored, either to trap intermediates or follow photoreduction during X-ray data collection. By using neutron crystallography, the positions of H atoms can be located, as it is the nuclei rather than the electrons that scatter neutrons, and the scattering length is not determined by the atomic number. Combining the two techniques allows much greater insight into both reaction mechanism and X-ray-induced photoreduction. PMID:28177310

  6. Decay spectroscopy of neutron-rich rare-earth isotopes and collectivity around double midshell

    Energy Technology Data Exchange (ETDEWEB)

    Watanabe, Hiroshi, E-mail: hiroshi@ribf.riken.jp [IRCNPC, School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)

    2015-10-15

    Neutron-rich rare-earth isotopes with A ≈ 170, which locate near the middle of the major shells for both proton and neutron between the doubly magic nuclei {sup 132}Sn and {sup 208}Pb, have been investigated by means of decay spectroscopy techniques at the RIBF facility at RIKEN. The nuclei of interest were produced by in-flight fission of a high-intensity {sup 238}U beam at 345 MeV/u. In this contribution, scientific motivations, the details of experimental procedures, and some prospects of the data analysis are reported.

  7. Neutron activation analysis via nuclear decay kinetics using gamma-ray spectroscopy at SFU

    Science.gov (United States)

    Domingo, Thomas; Chester, Aaron; Starosta, Krzysztof; Williams, Jonathan

    2016-09-01

    Gamma-ray spectroscopy is a powerful tool used in a variety of fields including nuclear and analytical chemistry, environmental science, and health risk management. At SFU, the Germanium detector for Elemental Analysis and Radiation Studies (GEARS), a low-background shielded high-purity germanium gamma-ray detector, has been used recently in all of the above fields. The current project aims to expand upon the number of applications for which GEARS can be used while enhancing its current functionality. A recent addition to the SFU Nuclear Science laboratory is the Thermo Scientific P 385 neutron generator. This device provides a nominal yield of 3 ×108 neutrons/s providing the capacity for neutron activation analysis, opening a major avenue of research at SFU which was previously unavailable. The isotopes created via neutron activation have a wide range of half-lives. To measure and study isotopes with half-lives above a second, a new analogue data acquisition system has been installed on GEARS allowing accurate measurements of decay kinetics. This new functionality enables identification and quantification of the products of neutron activation. Results from the neutron activation analysis of pure metals will be presented.

  8. Identification of the Atomic Scale Structures of the Gold-Thiol Interfaces of Molecular Nanowires by Inelastic Tunneling Spectroscopy

    CERN Document Server

    Demir, Firuz

    2012-01-01

    We examine theoretically the effects of the bonding geometries at the gold-thiol interfaces on the inelastic tunneling spectra of propanedithiolate (PDT) molecules bridging gold electrodes and show that inelastic tunneling spectroscopy combined with theory can be used to determine these bonding geometries experimentally. With the help of density functional theory, we calculate the relaxed geometries and vibrational modes of extended molecules each consisting of one or two PDT molecules connecting two gold nanoclusters. We formulate a perturbative theory of inelastic tunneling through molecules bridging metal contacts in terms of elastic transmission amplitudes, and use this theory to calculate the inelastic tunneling spectra of the gold-PDT-gold extended molecules. We consider PDT molecules with both trans and gauche conformations bound to the gold clusters at top, bridge and hollow bonding sites. Comparing our results with the experimental data of Hihath et al. [Nano Lett. 8, 1673 (2008)], we identify the mo...

  9. Analysis of accelerator based neutron spectra for BNCT using proton recoil spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Wielopolski, L.; Ludewig, H.; Powell, J.R.; Raparia, D.; Alessi, J.G.; Lowenstein, D.I.

    1999-03-01

    Boron Neutron Capture Therapy (BNCT) is a promising binary treatment modality for high-grade primary brain tumors (glioblastoma multiforme, GM) and other cancers. BNCT employs a boron-10 containing compound that preferentially accumulates in the cancer cells in the brain. Upon neutron capture by {sup 10}B energetic alpha particles and triton released at the absorption site kill the cancer cell. In order to gain penetration depth in the brain Fairchild proposed, for this purpose, the use of energetic epithermal neutrons at about 10 keV. Phase 1/2 clinical trials of BNCT for GM are underway at the Brookhaven Medical Research Reactor (BMRR) and at the MIT Reactor, using these nuclear reactors as the source for epithermal neutrons. In light of the limitations of new reactor installations, e.g. cost, safety and licensing, and limited capability for modulating the reactor based neutron beam energy spectra, alternative neutron sources are being contemplated for wider implementation of this modality in a hospital environment. For example, accelerator based neutron sources offer the possibility of tailoring the neutron beams, in terms of improved depth-dose distributions, to the individual and offer, with relative ease, the capability of modifying the neutron beam energy and port size. In previous work new concepts for compact accelerator/target configuration were published. In this work, using the Van de Graaff accelerator the authors have explored different materials for filtering and reflecting neutron beams produced by irradiating a thick Li target with 1.8 to 2.5 MeV proton beams. However, since the yield and the maximum neutron energy emerging from the Li-7(p,n)Be-7 reaction increase with increase in the proton beam energy, there is a need for optimization of the proton energy versus filter and shielding requirements to obtain the desired epithermal neutron beam. The MCNP-4A computer code was used for the initial design studies that were verified with benchmark

  10. ANALYSIS OF ACCELERATOR BASED NEUTRON SPECTRA FOR BNCT USING PROTON RECOIL SPECTROSCOPY

    Energy Technology Data Exchange (ETDEWEB)

    WIELOPOLSKI,L.; LUDEWIG,H.; POWELL,J.R.; RAPARIA,D.; ALESSI,J.G.; LOWENSTEIN,D.I.

    1998-11-06

    Boron Neutron Capture Therapy (BNCT) is a promising binary treatment modality for high-grade primary brain tumors (glioblastoma multiforme, GM) and other cancers. BNCT employs a boron-10 containing compound that preferentially accumulates in the cancer cells in the brain. Upon neutron capture by {sup 10}B energetic alpha particles and triton released at the absorption site kill the cancer cell. In order to gain penetration depth in the brain Fairchild proposed, for this purpose, the use of energetic epithermal neutrons at about 10 keV. Phase I/II clinical trials of BNCT for GM are underway at the Brookhaven Medical Research Reactor (BMRR) and at the MIT Reactor, using these nuclear reactors as the source for epithermal neutrons. In light of the limitations of new reactor installations, e.g. cost, safety and licensing, and limited capability for modulating the reactor based neutron beam energy spectra alternative neutron sources are being contemplated for wider implementation of this modality in a hospital environment. For example, accelerator based neutron sources offer the possibility of tailoring the neutron beams, in terms of improved depth-dose distributions, to the individual and offer, with relative ease, the capability of modifying the neutron beam energy and port size. In previous work new concepts for compact accelerator/target configuration were published. In this work, using the Van de Graaff accelerator the authors have explored different materials for filtering and reflecting neutron beams produced by irradiating a thick Li target with 1.8 to 2.5 MeV proton beams. However, since the yield and the maximum neutron energy emerging from the Li-7(p,n)Be-7 reaction increase with increase in the proton beam energy, there is a need for optimization of the proton energy versus filter and shielding requirements to obtain the desired epithermal neutron beam. The MCNP-4A computer code was used for the initial design studies that were verified with benchmark

  11. Voltage-controlled magnetic anisotropy in Fe|MgO tunnel junctions studied by x-ray absorption spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Miwa, Shinji, E-mail: miwa@mp.es.osaka-u.ac.jp; Matsuda, Kensho; Tanaka, Kazuhito; Goto, Minori; Suzuki, Yoshishige [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Kotani, Yoshinori; Nakamura, Tetsuya [Japan Synchrotron Radiation Research Institute/SPring-8, Sayo, Hyogo 679-5198 (Japan)

    2015-10-19

    In this study, voltage-controlled magnetic anisotropy (VCMA) in Fe|MgO tunnel junctions was investigated via the magneto-optical Kerr effect, soft x-ray absorption spectroscopy, and magnetic circular dichroism spectroscopy. The Fe|MgO tunnel junctions showed enhanced perpendicular magnetic anisotropy under external negative voltage, which induced charge depletion at the Fe|MgO interface. Despite the application of voltages of opposite polarity, no trace of chemical reaction such as a redox reaction attributed to O{sup 2−} migration was detected in the x-ray absorption spectra of the Fe. The VCMA reported in the Fe|MgO-based magnetic tunnel junctions must therefore originate from phenomena associated with the purely electric effect, that is, surface electron doping and/or redistribution induced by an external electric field.

  12. Contribution to the spectroscopy of 50 neutron isotones; Contribution a la spectroscopie des isotones a 50 neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Picard, J. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1969-05-01

    Proton states in the isotones N = 50 have been studied through the reaction ({sup 3}He,d) on {sup 88}Sr, {sup 90}Zr and {sup 92}Mo target nuclei with 18 MeV {sup 3}He projectiles and also neutron hole states using the ({sup 3}He,{alpha}) reaction on the same target. The information thus obtained on independent quasi-particle or hole states completes the set of experimental data required for a microscopic description of the collective properties of the even isotones {sup 88}Sr, {sup 90}Zr and {sup 92}Mo in the framework of BCS(IGE) + RPA theories. The results of this calculation are compared to experimental data and, more particularly, the results of 20 MeV proton inelastic scattering on {sup 88}Sr are analysed using anti-symmetrized DWBA with the microscopic wave functions calculated previously. (author) [French] Les etats de proton des isotones a 50 neutrons sont etudies par la reaction directe ({sup 3}He,d) sur les noyaux {sup 88}Sr, {sup 90}Zr et {sup 92}Mo avec des projectiles {sup 3}He de 18 MeV d'energie; ainsi que les etats de trou de neutron au moyen de la reaction directe ({sup 3}He,{alpha}) sur les memes cibles. L'information ainsi obtenue sur ces etats de trou ou de quasiparticule independante complete l'ensemble des donnees necessaire pour une description microscopique des proprietes collectives des isotones pairs {sup 88}Sr, {sup 90}Zr et {sup 92}Mo dans le cadre des modeles BCS(IGE) + RPA. Les resultats de ce calcul sont compares a l'experience et, en particulier, les resultats de la diffusion inelastique {sup 88}Sr(p,p'){sup 88}Sr{sup *} avec des protons de 20 MeV sont analyses dans un formalisme antisymetrise de la DWBA utilisant les fonctions d'onde microscopiques calculees precedemment. (auteur)

  13. Molecular structure and ring tunneling of phenyl formate as observed by microwave spectroscopy and quantum chemistry

    Science.gov (United States)

    Ferres, Lynn; Mouhib, Halima; Stahl, Wolfgang; Schwell, Martin; Nguyen, Ha Vinh Lam

    2017-07-01

    Phenyl formate has been investigated by molecular jet Fourier-transform microwave spectroscopy in the frequency range from 2 to 26.5 GHz. Quantum chemical calculations at the MP2/6-311++G(d,p) level of theory indicate that this molecule does not have a plane of symmetry at equilibrium, and that the phenyl ring performs a large amplitude tunneling motion from one side of the Cs configuration to the other. The tilt angle of the ring out of the Hsbnd (Cdbnd O)O plane is ±70° and the calculated tunneling barrier is only 28 cm-1. The two lowest torsional states vt = 0 and 1 are assigned in the experimental spectrum and fitted using the program SPFIT/SPCAT. The Coriolis splitting ΔE between these states is 46.2231(25) GHz, very close to the value of 48.24 GHz calculated using a simple two-top torsional Hamiltonian of the formate group and the phenyl ring.

  14. Plasma Wind Tunnel Investigation of European Ablators in Nitrogen/Methane Using Emission Spectroscopy

    Directory of Open Access Journals (Sweden)

    Ricarda Wernitz

    2013-01-01

    Full Text Available For atmospheric reentries at high enthalpies ablative heat shield materials are used, such as those for probes entering the atmosphere of Saturn’s moon Titan, such as Cassini-Huygens in December, 2004. The characterization of such materials in a nitrogen/methane atmosphere is of interest. A European ablative material, AQ60, has been investigated in plasma wind tunnel tests at the IRS plasma wind tunnel PWK1 using the magnetoplasma dynamic generator RD5 as plasma source in a nitrogen/methane atmosphere. The dimensions of the samples are 45 mm in length with a diameter of 39 mm. The actual ablator has a thickness of 40 mm. The ablator is mounted on an aluminium substructure. The experiments were conducted at two different heat flux regimes, 1.4 MW/m2 and 0.3 MW/m2. In this paper, results of emission spectroscopy at these plasma conditions in terms of plasma species’ temperatures will be presented, including the investigation of the free-stream species, N2 and N2+, and the major erosion product C2, at a wavelength range around 500 nm–600 nm.

  15. Two-gap interplay in MgB{sub 2}: a tunneling spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Roditchev, D.; Giubileo, F.; Bobba, F.; Lamy, R.; Choi, E.-M.; Kim, H.-J.; Kang, W.N.; Miraglia, S.; Marcus, J.; Sacks, W.; Klein, J.; Cucolo, A.M.; Lee, S.-I.; Fruchart, D

    2004-08-01

    Tunneling spectroscopy on various samples of MgB{sub 2} was performed. The first direct evidence for the two-gap superconductivity was given with an inverted junction setup, in which a small crystal of MgB{sub 2} was used as the STM tip and 2H-NbSe{sub 2} as the sample. This technique allowed to show that both gaps close at the critical temperature of the bulk material and thus are intimately related to the superconductivity. The experiments performed in the standard N-I-S geometry evidenced for two strongly coupled gaps {delta}{sub L}=7.0{+-}1.0 meV and {delta}{sub S}=3.0{+-}1.0 meV at 4.2 K. STS on as-grown c-axis oriented thin films yielded only small gap which confirmed the identification of this gap as originating from 3D-like {pi}-band and, by exclusion, that of the large gap from 2D-like {sigma}-band. The low gap values {delta}{sub S}=2.2{+-}0.3 meV were attributed to the degraded film surface. After chemical etching, the gap increased to {delta}{sub S}=2.8{+-}0.3 meV. The c-axis tunneling spectra are better fitted considering anisotropic superconductivity inside the {pi}-band. The issues of our findings are discussed in terms of two-band superconductivity.

  16. Spatially resolved scanning tunneling spectroscopy of single-layer steps on Si(100) surfaces

    Science.gov (United States)

    Wang, Xiqiao; Namboodiri, Pradeep; Li, Kai; Deng, Xiao; Silver, Richard

    2016-09-01

    Single-layer steps at Si(100) surfaces/interfaces present significant challenges to the quantitative characterization of buried dopant devices as well as the accurate imaging and relocation of fabricated quantum structures. We demonstrate the detailed spatially resolved scanning tunneling spectroscopy study across monolayer step edges on Si(100) surfaces and quantitative determination of the local density of state distributions and behavior of the band gap at step edges. The influence on the local electrostatic environment due to step edge states has been quantified while accounting for the effects of scanning tunneling measurement conditions. The dangling bond states on Si(100) surfaces are utilized as a fingerprint to quantify the local band bending landscape and to make corrections to the experimentally observed surface state energy levels and band gap values at the step edge regions. We observe a significant band gap narrowing behavior along a rebonded single-layer type B step edge on a degenerately boron-doped p -type Si substrate.

  17. Double deuterated acetylacetone in neon matrices: infrared spectroscopy, photoreactivity and the tunneling process.

    Science.gov (United States)

    Gutiérrez-Quintanilla, Alejandro; Chevalier, Michèle; Crépin, Claudine

    2016-07-27

    The effect of deuteration of acetylacetone (C5O2H8) is explored by means of IR spectroscopy of its single and double deuterated isotopologues trapped in neon matrices. The whole vibrational spectra of chelated enols are very sensitive to the H-D exchange of the hydrogen atom involved in the internal hydrogen bond. UV excitation of double deuterated acetylacetone isolated in neon matrices induces the formation of four open enol isomers which can be divided into two groups of two conformers, depending on their formation kinetics. Within each group, one conformer is more stable than the other: slow conformer interconversion due to a tunneling process is observed in the dark at low temperature. Moreover, IR laser irradiation at the OD stretching overtone frequency is used to induce interconversion either from the most stable to the less stable conformer or the opposite, depending on the excitation wavelength. The interconversion process is of great help to assign conformers which are definitively identified by comparison between experimental and calculated IR spectra. Kinetic constants of the tunneling process at play are theoretically estimated and agree perfectly with experiments, including previous experiments with the totally hydrogenated acetylacetone [Lozada García et al., Phys. Chem. Chem. Phys., 2012, 14, 3450].

  18. Scanning tunneling microscopy and spectroscopy measurements of superconductor/ferromagnet hybrids

    Science.gov (United States)

    Moore, Steven A.

    The focus of this thesis work is the study of the nanoscale electronic properties of magnetically coupled superconductor/ferromagnet hybrid structures using low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) under ultra-high vacuum conditions. There are a number of novel effects that can occur due to the non-homogenous magnetic field from the ferromagnet, which directly influence the global and local superconducting properties. These effects include the generation of vortices/anti-vortices by the non-uniform magnetic stray field, local modulations in the critical temperature, filamentary superconductivity close to the transition temperature, and superconducting channels that can be controlled by external magnetic fields. Prior to this dissertation the subject of superconductor/ferromagnet hybrid structures has been mainly studied using global measurements (such as transport and magnetization) or scanning probe techniques that are sensitive to the magnetic field. Scanning tunneling microscopy probes the local electronic density of states with atomic resolution, and therefore is the only technique that can study the emergence of superconductivity on the length scale of the coherence length. The novel results presented in this dissertation show that magnetically coupled superconductor/ferromagnet heterostructures offer the possibility to control and tune the strength and location of superconductivity and superconducting vortices, which has potential for promising technological breakthroughs in computing and power applications.

  19. Point contact tunneling spectroscopy apparatus for large scale mapping of surface superconducting properties

    Energy Technology Data Exchange (ETDEWEB)

    Groll, Nickolas; Pellin, Michael J. [Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439 (United States); Zasadzinksi, John F. [Illinois Institute of Technology, Chicago, Illinois 60616 (United States); Proslier, Thomas, E-mail: prolier@anl.gov [Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439 (United States); High Energy Physics Division, Argonne National Laboratory, Lemont, Illinois 60439 (United States)

    2015-09-15

    We describe the design and testing of a point contact tunneling spectroscopy device that can measure material surface superconducting properties (i.e., the superconducting gap Δ and the critical temperature T{sub C}) and density of states over large surface areas with size up to mm{sup 2}. The tip lateral (X,Y) motion, mounted on a (X,Y,Z) piezo-stage, was calibrated on a patterned substrate consisting of Nb lines sputtered on a gold film using both normal (Al) and superconducting (PbSn) tips at 1.5 K. The tip vertical (Z) motion control enables some adjustment of the tip-sample junction resistance that can be measured over 7 orders of magnitudes from a quasi-ohmic regime (few hundred Ω) to the tunnel regime (from tens of kΩ up to few GΩ). The low noise electronic and LabVIEW program interface are also presented. The point contact regime and the large-scale motion capabilities are of particular interest for mapping and testing the superconducting properties of macroscopic scale superconductor-based devices.

  20. Compressed Sensing in Scanning Tunneling Microscopy/Spectroscopy for Observation of Quasi-Particle Interference

    Science.gov (United States)

    Nakanishi-Ohno, Yoshinori; Haze, Masahiro; Yoshida, Yasuo; Hukushima, Koji; Hasegawa, Yukio; Okada, Masato

    2016-09-01

    We applied a method of compressed sensing to the observation of quasi-particle interference (QPI) by scanning tunneling microscopy/spectroscopy to improve efficiency and save measurement time. To solve an ill-posed problem owing to the scarcity of data, the compressed sensing utilizes the sparseness of QPI patterns in momentum space. We examined the performance of a sparsity-inducing algorithm called least absolute shrinkage and selection operator (LASSO), and demonstrated that LASSO enables us to recover a double-circle QPI pattern of the Ag(111) surface from a dataset whose size is less than that necessary for the conventional Fourier transformation method. In addition, the smallest number of data required for the recovery is discussed on the basis of cross validation.

  1. Scanning tunneling spectroscopy of van der Waals graphene/semiconductor interfaces: absence of Fermi level pinning

    Science.gov (United States)

    Le Quang, T.; Cherkez, V.; Nogajewski, K.; Potemski, M.; Dau, M. T.; Jamet, M.; Mallet, P.; Veuillen, J.-Y.

    2017-09-01

    We have investigated the electronic properties of two-dimensional (2D) transition metal dichalcogenides (TMDs), namely trilayer WSe2 and monolayer MoSe2, deposited on epitaxial graphene on silicon carbide, by using scanning tunneling microscopy and spectroscopy (STM/STS) in ultra-high vacuum. Depending on the number of graphene layers below the TMD flakes, we identified variations in the electronic dI/dV(V) spectra measured by the STM tip: the most salient feature is a rigid shift of the TMD spectra (i.e. of the different band onset positions) towards occupied states by about 120 mV when passing from bilayer to monolayer underlying graphene. Since both graphene phases are metallic and present a work function difference in the same energy range, our measurements point towards the absence of Fermi-level pinning for such van der Waals 2D TMD/Metal heterojunctions, following the prediction of the Schottky-Mott model.

  2. Renormalization of the graphene dispersion velocity determined from scanning tunneling spectroscopy.

    Science.gov (United States)

    Chae, Jungseok; Jung, Suyong; Young, Andrea F; Dean, Cory R; Wang, Lei; Gao, Yuanda; Watanabe, Kenji; Taniguchi, Takashi; Hone, James; Shepard, Kenneth L; Kim, Phillip; Zhitenev, Nikolai B; Stroscio, Joseph A

    2012-09-14

    In graphene, as in most metals, electron-electron interactions renormalize the properties of electrons but leave them behaving like noninteracting quasiparticles. Many measurements probe the renormalized properties of electrons right at the Fermi energy. Uniquely for graphene, the accessibility of the electrons at the surface offers the opportunity to use scanned probe techniques to examine the effect of interactions at energies away from the Fermi energy, over a broad range of densities, and on a local scale. Using scanning tunneling spectroscopy, we show that electron interactions leave the graphene energy dispersion linear as a function of excitation energy for energies within ±200  meV of the Fermi energy. However, the measured dispersion velocity depends on density and increases strongly as the density approaches zero near the charge neutrality point, revealing a squeezing of the Dirac cone due to interactions.

  3. How the vortex lattice of a superconductor becomes disordered: a study by scanning tunneling spectroscopy.

    Science.gov (United States)

    Zehetmayer, M

    2015-01-01

    Order-disorder transitions take place in many physical systems, but observing them in detail in real materials is difficult. In two- or quasi-two-dimensional systems, the transition has been studied by computer simulations and experimentally in electron sheets, dusty plasmas, colloidal and other systems. Here I show the different stages of defect formation in the vortex lattice of a superconductor while it undergoes an order-disorder transition by presenting real-space images of the lattice from scanning tunneling spectroscopy. When the system evolves from the ordered to the disordered state, the predominant kind of defect changes from dislocation pairs to single dislocations, and finally to defect clusters forming grain boundaries. Correlation functions indicate a hexatic-like state preceding the disordered state. The transition in the microscopic vortex distribution is mirrored by the well-known spectacular second peak effect observed in the macroscopic current density of the superconductor.

  4. Neutron spectroscopy of gamma-MgH2

    Science.gov (United States)

    Kolesnikov, Alexander; Antonov, Vladimir; Efimchenko, Vadim; Granroth, Garrett; Klyamkin, S. N.; Levchenko, A. V.; Sakharov, Michael; Ren, Yang; Ramirez-Cuesta, Timmy

    2011-03-01

    Under ambient conditions, magnesium dihydride exists in two forms, alpha-MgH2 (the most stable modification) and gamma-MgH2 (a less stable modification). The alpha-phase partly transforms to gamma-MgH2 in the course of ball-milling and under high pressure and temperature. Due to the high hydrogen content of 7.6 wt.%, MgH2 has been intensively studied as a prospective material for hydrogen storage. By exposing of alpha-MgH2 to a pressure of 5 GPa and temperature 840 K, we prepared a sample, in which about 60% of the alpha-MgH2 was transformed to gamma-MgH2. We have measured inelastic neutron scattering (INS) spectra of both the high pressure treated MgH2 and starting alpha-MgH2, and extracted the spectrum for gamma-MgH2. The differences between the INS spectra and their agreement with the first-principles calculations for these compounds will be discussed.

  5. Form fluctuations of polymer loaded spherical microemulsions studied by neutron scattering and dielectric spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kuttich, B., E-mail: B.Kuttich@fkp.physik.tu-darmstadt.de; Stühn, B. [Institute for Condensed Matter Physics, Technische Universität Darmstadt, Darmstadt (Germany); Falus, P.; Grillo, I. [Institut Laue-Langevin, Grenoble (France)

    2014-08-28

    We investigate the structure and shell dynamics of the droplet phase in water/AOT/octane microemulsions with polyethyleneglycol (M{sub W} = 1500) molecules loaded in the droplets. Size and polydispersity of the droplets is determined with small angle X-ray scattering and small angle neutron scattering experiments. Shell fluctuations are measured with neutron spin echo spectroscopy and related to the dynamic percolation seen in dielectric spectroscopy. Shell fluctuations are found to be well described by the bending modulus of the shell and the viscosities inside and outside the droplets. Addition of the polymer decreases the modulus for small droplets. For large droplets the opposite is found as percolation temperature shifts to higher values.

  6. High-resolution photoinduced transient spectroscopy of neutron irradiated bulk silicon

    CERN Document Server

    Kozlowski, R; Nossarzhevska, E

    2002-01-01

    High-resolution photoinduced transient spectroscopy has been employed in a study on the formation of defects in bulk silicon due to 1 MeV neutron irradiation. Apart from divacancies in various charge states, complexes involving interstitial carbon and oxygen were revealed. The defect structure of float zone and Czochralski-grown material exposed to fluences of 2x10 sup 1 sup 4 and 6.75x10 sup 1 sup 4 cm sup - sup 2 is compared.

  7. Event based neutron activation spectroscopy and analysis algorithm using MLE and metaheuristics

    OpenAIRE

    Wallace Barton

    2014-01-01

    Techniques used in neutron activation analysis are often dependent on the experimental setup. In the context of developing a portable and high efficiency detection array, good energy resolution and half-life discrimination are difficult to obtain with traditional methods [1] given the logistic and financial constraints. An approach different from that of spectrum addition and standard spectroscopy analysis [2] was needed. The use of multiple detectors prompts the need for a flexible storage o...

  8. A novel fast-neutron detector concept for energy-selective imaging and imaging spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Cortesi, M.; Prasser, H.-M. [Nuclear Energy and Safety Research Department, Paul Scherrer Institut, Villigen PSI 5234 (Switzerland); Mechanical Engineering Department, Swiss Federal Institute of Technology, Zurich 8092 (Switzerland); Dangendorf, V. [Ion and Neutron Radiation Department, Physikalisch-Technische Bundesanstalt, Braunschweig 38116 (Germany); Zboray, R. [Mechanical Engineering Department, Swiss Federal Institute of Technology, Zurich 8092 (Switzerland)

    2014-07-15

    We present and discuss the operational principle of a new fast-neutron detector concept suitable for either energy-selective imaging or for imaging spectroscopy. The detector is comprised of a series of energy-selective stacks of converter foils immersed in a noble-gas based mixture, coupled to a position-sensitive charge readout. Each foil in the various stacks is made of two layers of different thicknesses, fastened together: a hydrogen-rich (plastic) layer for neutron-to-proton conversion, and a hydrogen-free coating to selectively stop/absorb the recoil protons below a certain energy cut-off. The neutron-induced recoil protons, that escape the converter foils, release ionization electrons in the gas gaps between consecutive foils. The electrons are then drifted towards and localized by a position-sensitive charge amplification and readout stage. Comparison of the images detected by stacks with different energy cut-offs allows energy-selective imaging. Neutron energy spectrometry is realized by analyzing the responses of a sufficient large number of stacks of different energy response and unfolding techniques. In this paper, we present the results of computer simulation studies and discuss the expected performance of the new detector concept. Potential applications in various fields are also briefly discussed, in particularly, the application of energy-selective fast-neutron imaging for nuclear safeguards application, with the aim of determining the plutonium content in Mixed Oxide (MOX) fuels.

  9. Neutron time-of-flight spectroscopy measurement using a waveform digitizer

    Science.gov (United States)

    Liu, Long-Xiang; Wang, Hong-Wei; Ma, Yu-Gang; Cao, Xi-Guang; Cai, Xiang-Zhou; Chen, Jin-Gen; Zhang, Gui-Lin; Han, Jian-Long; Zhang, Guo-Qiang; Hu, Ji-Feng; Wang, Xiao-He

    2016-05-01

    The photoneutron source (PNS, phase 1), an electron linear accelerator (linac)-based pulsed neutron facility that uses the time-of-flight (TOF) technique, was constructed for the acquisition of nuclear data from the Thorium Molten Salt Reactor (TMSR) at the Shanghai Institute of Applied Physics (SINAP). The neutron detector signal used for TOF calculation, with information on the pulse arrival time, pulse shape, and pulse height, was recorded by using a waveform digitizer (WFD). By using the pulse height and pulse-shape discrimination (PSD) analysis to identify neutrons and γ-rays, the neutron TOF spectrum was obtained by employing a simple electronic design, and a new WFD-based DAQ system was developed and tested in this commissioning experiment. The DAQ system developed is characterized by a very high efficiency with respect to millisecond neutron TOF spectroscopy. Supported by Strategic Priority Research Program of the Chinese Academy of Science(TMSR) (XDA02010100), National Natural Science Foundation of China(NSFC)(11475245,No.11305239), Shanghai Key Laboratory of Particle Physics and Cosmology (11DZ2260700)

  10. Recovery of nanomolecular electronic states from tunneling spectroscopy: LDOS of low-dimensional phthalocyanine molecular structures on Cu(111).

    Science.gov (United States)

    Yamagishi, Y; Nakashima, S; Oiso, K; Yamada, T K

    2013-10-04

    Organic nanomolecules have become one of the most attractive materials for new nanoelectronics devices. Understanding of the electronic density of states around the Fermi energy of low-dimensional molecules is crucial in designing the electronic properties of molecular devices. The low dimensionality of nanomolecules results in new electronic properties owing to their unique symmetry. Scanning tunneling spectroscopy is one of the most effective techniques for studying the electronic states of nanomolecules, particularly near the Fermi energy (±1.5 eV), whereas these molecular electronic states are frequently buried by the tunneling probability background in tunneling spectroscopy, resulting in incorrect determination of the molecular electronic states. Here, we demonstrate how to recover nanomolecular electronic states from dI/dV curves obtained by tunneling spectroscopy. Precise local density of states (LDOS) peaks for low-dimensional nanostructures (monolayer ultrathin films, one-dimensional chains, and single molecules) of phthalocyanine (H2Pc) molecules grown on noble fcc-Cu(111) were obtained.

  11. Interfacial scanning tunneling spectroscopy (STS) of chalcogenide/metal hybrid nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Saad, Mahmoud M.; Abdallah, Tamer [Physics Department, Faculty of Science, Ain Shams University, Abbassia, Cairo (Egypt); Easawi, Khalid; Negm, Sohair [Department of Physics and Mathematics, Faculty of Engineering (Shoubra), Benha University (Egypt); Talaat, Hassan, E-mail: hassantalaat@hotmail.com [Physics Department, Faculty of Science, Ain Shams University, Abbassia, Cairo (Egypt)

    2015-05-15

    Graphical abstract: - Highlights: • Comparing band gaps values obtained optically with STS. • Comparing direct imaging with calculated dimensions. • STS determination of the interfacial band bending of metal/chalcogenide. - Abstract: The electronic structure at the interface of chalcogenide/metal hybrid nanostructure (CdSe–Au tipped) had been studied by UHV scanning tunneling spectroscopy (STS) technique at room temperature. This nanostructure was synthesized by a phase transfer chemical method. The optical absorption of this hybrid nanostructure was recorded, and the application of the effective mass approximation (EMA) model gave dimensions that were confirmed by the direct measurements using the scanning tunneling microscopy (STM) as well as the high-resolution transmission electron microscope (HRTEM). The energy band gap obtained by STS agrees with the values obtained from the optical absorption. Moreover, the STS at the interface of CdSe–Au tipped hybrid nanostructure between CdSe of size about 4.1 ± 0.19 nm and Au tip of size about 3.5 ± 0.29 nm shows a band bending about 0.18 ± 0.03 eV in CdSe down in the direction of the interface. Such a result gives a direct observation of the electron accumulation at the interface of CdSe–Au tipped hybrid nanostructure, consistent with its energy band diagram. The presence of the electron accumulation at the interface of chalcogenides with metals has an important implication for hybrid nanoelectronic devices and the newly developed plasmon/chalcogenide photovoltaic solar energy conversion.

  12. Detection of renal cell carcinoma using neutron time of flight spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Viana, Rodrigo S.; Yoriyaz, Helio, E-mail: rodrigossviana@gmail.com [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil); Lakshmanan, Manu N.; Agasthya, Greeshma A.; Kapadia, Anuj J. [Duke University Medical Center, Durham, NC, (United States). Ravin Advanced Imaging Labs, Radiology

    2013-07-01

    The diagnosis of renal cell carcinoma (RCC) is challenging because the symptoms accompanying it are not unique to the disease, and can therefore be misdiagnosed as other diseases. Due to this characteristic, detection of renal cancer is incidental most of time, occurring via abdominal radiographic examinations unrelated to the disease. Presently, biopsy, which is invasive and an unpleasant procedure for the patient, is the most commonly used technique to diagnose RCC. In this study, we demonstrate the application of a novel noninvasive technique for detecting and imaging RCC in vivo. The elemental composition of biological tissues including kidneys has been investigated using a new technique called Neutron Stimulated Emission Computed Tomography (NSECT). This technique is based on detecting the energy signature emitted by the stable isotopes of elements in the body, which are stimulated to emit gamma radiation via inelastic neutron scattering. Methods for improving detection sensitivity and reducing dose, such as time-of-flight neutron spectroscopy have been explored. MCNP5 simulations were used to model the NSECT scanning of the human kidney where the energy and time of arrival of gamma photons were recorded in an ideal detector placed around the human torso. A 5 MeV collimated neutron beam was used to irradiate the kidney containing an RCC lesion. The resulting spectra were resolved in 100 picosecond and 1 keV time and energy bins, respectively. The preliminary results demonstrate the ability to localize the lesion through neutron time of flight spectroscopy and generate a tomographic image at a low dose to the patient. (author)

  13. Elastic Scattering Spectroscopy (ESS): an Instrument-Concept for Dynamics of Complex (Bio-) Systems From Elastic Neutron Scattering

    Science.gov (United States)

    Benedetto, Antonio; Kearley, Gordon J.

    2016-10-01

    A new type of neutron-scattering spectroscopy is presented that is designed specifically to measure dynamics in bio-systems that are difficult to obtain in any other way. The temporal information is largely model-free and is analogous to relaxation processes measured with dielectric spectroscopy, but provides additional spacial and geometric aspects of the underlying dynamics. Numerical simulations of the basic instrument design show the neutron beam can be highly focussed, giving efficiency gains that enable the use of small samples. Although we concentrate on continuous neutron sources, the extension to pulsed neutron sources is proposed, both requiring minimal data-treatment and being broadly analogous with dielectric spectroscopy, they will open the study of dynamics to new areas of biophysics.

  14. Elastic Scattering Spectroscopy (ESS): an Instrument-Concept for Dynamics of Complex (Bio-) Systems From Elastic Neutron Scattering

    Science.gov (United States)

    Benedetto, Antonio; Kearley, Gordon J.

    2016-01-01

    A new type of neutron-scattering spectroscopy is presented that is designed specifically to measure dynamics in bio-systems that are difficult to obtain in any other way. The temporal information is largely model-free and is analogous to relaxation processes measured with dielectric spectroscopy, but provides additional spacial and geometric aspects of the underlying dynamics. Numerical simulations of the basic instrument design show the neutron beam can be highly focussed, giving efficiency gains that enable the use of small samples. Although we concentrate on continuous neutron sources, the extension to pulsed neutron sources is proposed, both requiring minimal data-treatment and being broadly analogous with dielectric spectroscopy, they will open the study of dynamics to new areas of biophysics. PMID:27703184

  15. Direct Neutron Spectroscopy Observation of Cerium Hydride Species on a Cerium Oxide Catalyst.

    Science.gov (United States)

    Wu, Zili; Cheng, Yongqiang; Tao, Franklin; Daemen, Luke; Foo, Guo Shiou; Nguyen, Luan; Zhang, Xiaoyan; Beste, Ariana; Ramirez-Cuesta, Anibal J

    2017-07-19

    Ceria has recently shown intriguing hydrogenation reactivity in catalyzing alkyne selectively to alkenes. However, the mechanism of the hydrogenation reaction, especially the activation of H2, remains experimentally elusive. In this work, we report the first direct spectroscopy evidence for the presence of both surface and bulk Ce-H species upon H2 dissociation over ceria via in situ inelastic neutron scattering spectroscopy. Combined with in situ ambient-pressure X-ray photoelectron spectroscopy, IR, and Raman spectroscopic studies, the results together point to a heterolytic dissociation mechanism of H2 over ceria, leading to either homolytic products (surface OHs) on a close-to-stoichiometric ceria surface or heterolytic products (Ce-H and OH) with the presence of induced oxygen vacancies in ceria. The finding of this work has significant implications for understanding catalysis by ceria in both hydrogenation and redox reactions where hydrogen is involved.

  16. Laser Spectroscopy Study on the Neutron-Rich and Neutron-Deficient Te Isotopes

    CERN Multimedia

    2002-01-01

    We propose to perform laser spectroscopy measurements on the Te isotopes. This will give access to fundamental properties of the ground and rather long-lived isomeric states such as the change in the mean square charge radius ($\\delta\\langle$r$^2_c\\rangle$) and the nuclear moments. For these medium-mass isotopes, at this moment the optical resolution obtained with RILIS is not high enough to perform isotope shift measurements. Thus we will use the COMPLIS experimental setup which allows Resonant Ionization Spectroscopy (RIS) on laser desorbed atoms. The 5p$^{4}$ $^{3}$P$_{2} \\rightarrow$ 5p$^{3}$ 6s $^{3}$S$_{1}$ and 5p$^{4}$ $^{3}$P$_{2} \\rightarrow$ 5p$^{3}$ 6s $^{5}$S$_{2}$ optical transitions have been used to perform, on the stable Te isotopes, the tests required by the INTC committee. For this purpose stable-ion sources have been built and Te isotopes have been delivered as stable beams by the injector coupled to the COMPLIS setup. ISOLDE offers the opportunity for studying the Te isotope series over a ...

  17. Invariant mass spectroscopy of 17C via one-neutron knockout reaction from 18C

    Science.gov (United States)

    Kim, Sunji; Samurai Collaboration

    2014-09-01

    The nuclei away from the β-stability line are expected to have exotic nuclear structures. For example, the ground states of neutron-rich carbon isotopes, 15C, 17C, and 19C, have been predicted to be 5/2+ states in the naive shell model. However, they were identified as 1/2+, 3/2+, and 1/2+, respectively, due to the halo structure and/or nuclear deformation. To understand the properties of the valence orbit relative to the inner orbit in those neutron-rich carbon isotopes, the study of the negative parity states is decisive. The present study focuses on the low-lying negative parity states in 17C above the neutron decay threshold. The experiment was performed for the C(18C,17C*) one-neutron knockout reaction channel at 250 MeV/nucleon using the SAMURAI spectrometer at RIKEN-RIBF, during the first physics runs of the apparatus. The nucleon knockout reaction utilizing the secondary beams in inverse kinematics has become recognized as a sensitive tool for spectroscopy of the nuclei far from the β-stability line. In the presentation, details of the measurement and analysis will be reported together with new results on the low-lying negative parity states in 17C.

  18. Probing the dynamics of high-viscosity entangled polymers under shear using Neutron Spin Echo spectroscopy

    Science.gov (United States)

    Kawecki, M.; Gutfreund, P.; Adlmann, F. A.; Lindholm, E.; Longeville, S.; Lapp, A.; Wolff, M.

    2016-09-01

    Neutron Spin Echo spectroscopy provides unique insight into molecular and submolecular dynamics as well as intra- and inter-molecular interactions in soft matter. These dynamics may change drastically under shear flow. In particular in polymer physics a stress plateau is observed, which might be explained by an entanglement-disentanglement transition. However, such a transition is difficult to identify directly by experiments. Neutron Spin Echo has been proven to provide information about entanglement length and degree by probing the local dynamics of the polymer chains. Combining shear experiments and neutron spin echo is challenging since, first the beam polarisation has to be preserved during scattering and second, Doppler scattered neutrons may cause inelastic scattering. In this paper we present a new shear device adapted for these needs. We demonstrate that a high beam polarisation can be preserved and present first data on an entangled polymer solution under shear. To complement the experiments on the dynamics we present novel SANS data revealing shear- induced conformational changes in highly entangled polymers.

  19. Oxygen vacancies on SrO-terminated SrTi O3(001 ) surfaces studied by scanning tunneling spectroscopy

    Science.gov (United States)

    Sitaputra, Wattaka; Sivadas, Nikhil; Skowronski, Marek; Xiao, Di; Feenstra, Randall M.

    2015-05-01

    The electronic structure of SrTi O3(001 ) surfaces was studied using scanning tunneling spectroscopy and density-functional theory. With high dynamic range measurements, an in-gap transition level was observed on SrO-terminated surfaces, at 2.7 eV above the valence band maximum. The density of centers responsible for this level was found to increase with surface segregation of oxygen vacancies and decrease with exposure to molecular oxygen. Based on these findings, the level is attributed to surface O vacancies. A level at a similar energy is predicted theoretically on SrO-terminated surfaces. For Ti O2 -terminated surfaces, no discrete in-gap state was observed, although one is predicted theoretically. This lack of signal is believed to be due to the nature of the defect wave function involved, as well as the possible influence of transport limitations in the tunneling spectroscopy measurements.

  20. Fast neutron tolerance of the perpendicular-anisotropy CoFeB-MgO magnetic tunnel junctions with junction diameters between 46 and 64 nm

    Science.gov (United States)

    Narita, Yuzuru; Takahashi, Yutaka; Harada, Masahide; Oikawa, Kenichi; Kobayashi, Daisuke; Hirose, Kazuyuki; Sato, Hideo; Ikeda, Shoji; Endoh, Tetsuo; Ohno, Hideo

    2017-08-01

    This work represents the first-ever investigation of the effects of fast neutron exposure on the perpendicular-anisotropy CoFeB-MgO magnetic tunnel junctions (p-MTJs) with practical junction diameters (D) between 46 and 64 nm. In this study, 461 p-MTJs, each with a tunnel magnetoresistance (TMR) ratio above 90%, were irradiated with fast neutrons at a total 1 MeV equivalent fluence of 3.79 × 1012 cm-2, corresponding to 1.90 × 1011 h irradiation with fast atmospheric neutrons (20 cm-2 h-1), without applying a bias voltage. Following irradiation, there were no changes in the properties of these devices, such as their resistance versus magnetic field curves, resistance values in the parallel and anti-parallel states, or TMR ratios, regardless of the neutron fluence. On the basis of these data, the nuclear reactions that occur under the specific experimental neutron irradiation conditions employed in this work are discussed.

  1. Scanning Tunneling Spectroscopy Study of Single Layer Step Edges on Si (100) Surfaces

    Science.gov (United States)

    Wang, Xiqiao; Namboodiri, Pradeep; Li, Kai; Deng, Xiao; Silver, Richard

    Advanced Hydrogen lithography enables the fabrication of atomically precise donor-based quantum devices on Si(100) surfaces. Understanding the defect and step edge interaction with local electronic and geometric structures is needed to properly interpret device measurement results. Low temperature Si epitaxy, used to encapsulate devices, introduces island growth and step edges near/above buried donor nanostructures, presenting a real challenge in relocating and characterizing buried donor devices using Scanning Tunneling Microscopy/Spectroscopy (STM/STS). We present spatially resolved STS results across single layer steps on Si(100) surfaces. While the electronic properties across SA steps were found to be very similar to that on flat terraces, we observed an edge induced gap state on rebonded SB step edges, which was assigned to the unpaired dangling bond state at the lower edge atom of the rebonded SB steps. In addition, we used computational simulation within Bardeen's formalism to probe the influence of subsurface doping density profiles on the observed STS features over step edges and other defects. This study will help to elucidate the role played by surface step edges and subsurface doping densities in characterizing surface and subsurface nanostructures using STS/STM.

  2. Scanning tunnelling spectroscopy as a probe of multi-Q magnetic states of itinerant magnets

    Science.gov (United States)

    Gastiasoro, Maria N.; Eremin, Ilya; Fernandes, Rafael M.; Andersen, Brian M.

    2017-02-01

    The combination of electronic correlations and Fermi surfaces with multiple nesting vectors can lead to the appearance of complex multi-Q magnetic ground states, hosting unusual states such as chiral density waves and quantum Hall insulators. Distinguishing single-Q and multi-Q magnetic phases is however a notoriously difficult experimental problem. Here we propose theoretically that the local density of states (LDOS) near a magnetic impurity, whose orientation may be controlled by an external magnetic field, can be used to map out the detailed magnetic configuration of an itinerant system and distinguish unambiguously between single-Q and multi-Q phases. We demonstrate this concept by computing and contrasting the LDOS near a magnetic impurity embedded in three different magnetic ground states relevant to iron-based superconductors--one single-Q and two double-Q phases. Our results open a promising avenue to investigate the complex magnetic configurations in itinerant systems via standard scanning tunnelling spectroscopy, without requiring spin-resolved capability.

  3. Scanning tunnelling spectroscopy as a probe of multi-Q magnetic states of itinerant magnets

    Science.gov (United States)

    Gastiasoro, Maria N.; Eremin, Ilya; Fernandes, Rafael M.; Andersen, Brian M.

    2017-01-01

    The combination of electronic correlations and Fermi surfaces with multiple nesting vectors can lead to the appearance of complex multi-Q magnetic ground states, hosting unusual states such as chiral density waves and quantum Hall insulators. Distinguishing single-Q and multi-Q magnetic phases is however a notoriously difficult experimental problem. Here we propose theoretically that the local density of states (LDOS) near a magnetic impurity, whose orientation may be controlled by an external magnetic field, can be used to map out the detailed magnetic configuration of an itinerant system and distinguish unambiguously between single-Q and multi-Q phases. We demonstrate this concept by computing and contrasting the LDOS near a magnetic impurity embedded in three different magnetic ground states relevant to iron-based superconductors—one single-Q and two double-Q phases. Our results open a promising avenue to investigate the complex magnetic configurations in itinerant systems via standard scanning tunnelling spectroscopy, without requiring spin-resolved capability. PMID:28176779

  4. Position-sensitive detection of ultracold neutrons with an imaging camera and its implications to spectroscopy

    CERN Document Server

    Wei, Wanchun; Hoffbauer, M A; Makela, M; Morris, C L; Tang, Z; Adamek, E R; Callahan, N B; Clayton, S M; Cude-Woods, C; Currie, S; Dees, E B; Ding, X; Geltenbort, P; Hickerson, K P; Holley, A T; Ito, T M; Leung, K K; Liu, C -Y; Morley, D J; Ramsey, J C; Pattie,, R W; Salvat, D J; Saunders, A; Seestrom, S J; Sharapov, E I; Sjue, S K; Wexler, J; Womack, T L; Young, A R; Zeck, B A; Wang, Zhehui

    2016-01-01

    Position-sensitive detection of ultracold neutrons (UCNs) is demonstrated using an imaging charge-coupled device (CCD) camera. A spatial resolution less than 15 $\\mu$m has been achieved, which through the relation $\\delta E = m_0g \\delta x$, converts to UCN energy resolution below 2 pico-electron volts. The symbols $\\delta E$, $\\delta x$, $m_0$ and $g$ are for energy resolution, spatial resolution, the neutron rest mass and gravitational acceleration respectively. A multilayer surface convertor described previously is used to capture UCNs and emits visible light for CCD imaging. Particle identification and noise rejection are discussed through light intensity profile analysis. This method allows new types of UCN spectroscopy and various applications.

  5. Perspectives for neutron and gamma spectroscopy in high power laser driven experiments at ELI-NP

    Science.gov (United States)

    Negoita, F.; Gugiu, M.; Petrascu, H.; Petrone, C.; Pietreanu, D.; Fuchs, J.; Chen, S.; Higginson, D.; Vassura, L.; Hannachi, F.; Tarisien, M.; Versteegen, M.; Antici, P.; Balabanski, D.; Balascuta, S.; Cernaianu, M.; Dancus, I.; Gales, S.; Neagu, L.; Petcu, C.; Risca, M.; Toma, M.; Turcu, E.; Ursescu, D.

    2015-02-01

    The measurement of energy spectra of neutrons and gamma rays emitted by nuclei, together with charge particles spectroscopy, are the main tools for understanding nuclear phenomena occurring also in high power laser driven experiments. However, the large number of particles emitted in a very short time, in particular the strong X-rays flash produced in laser-target interaction, impose adaptation of technique currently used in nuclear physics experiment at accelerator based facilities. These aspects are discussed (Section 1) in the context of proposed studies at high power laser system of ELI-NP. Preliminary results from two experiments performed at Titan (LLNL) and ELFIE (LULI) facilities using plastic scintillators for neutron detection (Section 2) and LaBr3(Ce) scintillators for gamma detection (Section 3) are presented demonstrating the capabilities and the limitations of the employed methods. Possible improvements of these spectroscopic methods and their proposed implementation at ELI-NP will be discussed as well in the last section.

  6. Penning trap assisted decay spectroscopy of neutron-rich {sup 115}Ru

    Energy Technology Data Exchange (ETDEWEB)

    Kurpeta, J.; Plochocki, A.; Urban, W. [Warsaw University, Faculty of Physics, Warsaw (Poland); Elomaa, V.V.; Eronen, T.; Hakala, J.; Jokinen, A.; Karvonen, P.; Moore, I.; Penttilae, H.; Rahaman, S.; Rinta-Antila, S.; Rissanen, J.; Ronkainen, J.; Saastamoinen, A.; Sonoda, T.; Weber, C.; Aeystoe, J. [University of Jyvaeskylae, Department of Physics (Finland)

    2007-03-15

    Exotic, neutron-rich {sup 111}Mo and {sup 115}Ru nuclei, produced in proton-induced fission of {sup 238}U target, were separated with the IGISOL mass separator. The separator was coupled to the JYFLTRAP Penning trap to select the ions of a single, desired element out of the isobaric IGISOL beam. Monoisotopic samples of {sup 115}Ru and {sup 111}Mo ions were observed with a microchannel plate detector after the trap or were implanted on a catcher foil for gamma- and beta-ray coincidence spectroscopy. In spite of short data taking time new gamma transitions were identified in the beta decay of very neutron-rich {sup 115}Ru. (orig.)

  7. Neutron spectroscopy as a fuel ion ratio diagnostic: lessons from JET and prospects for ITER.

    Science.gov (United States)

    Ericsson, G; Conroy, S; Gatu Johnson, M; Andersson Sundén, E; Cecconello, M; Eriksson, J; Hellesen, C; Sangaroon, S; Weiszflog, M

    2010-10-01

    The determination of the fuel ion ratio n(t)/n(d) in ITER is required at a precision of 20%, time resolution of 100 ms, spatial resolution of a/10, and over a range of 0.01ITER to assess the possibility to use neutron emission spectroscopy (NES) for such measurements. We show that NES meets the requirements for ion temperatures T(i)>6 keV and for n(T)/n(D)ITER due to beam-thermal and tritium-tritium reactions can further enhance the prospects for NES.

  8. A fission-fragment-sensitive target for X-ray spectroscopy in neutron-induced fission

    CERN Document Server

    Ethvignot, T; Giot, L; Casoli, P; Nelson, R O

    2002-01-01

    A fission-fragment-sensitive detector built for low-energy photon spectroscopy applications at the WNR 'white' neutron source at Los Alamos is described. The detector consists of eight layers of thin photovoltaic cells, onto which 1 mg/cm sup 2 of pure sup 2 sup 3 sup 8 U is deposited. The detector serves as an active target to select fission events from background and other reaction channels. The fairly small thickness of the detector with respect to transmission of 20-50 keV photons permits the measurement of prompt fission-fragment X-rays. Results with the GEANIE photon spectrometer are presented.

  9. Secondary relaxation in two engineering thermoplastics by neutron scattering and dielectric spectroscopy

    CERN Document Server

    Arrese, S; Alegria, A; Colmenero, J; Frick, B

    2002-01-01

    We present a preliminary investigation of the dynamics of glassy polycarbonate (PC) and polysulfone (PSF) by means of quasielastic neutron scattering and dielectric spectroscopy. Whereas the consideration of pure phenylene ring pi-flips is enough to explain the momentum-transfer (Q) dependence of the inelastic intensity measured for PSF, in the case of PC the Q dependence of both the coherent and the incoherent scattering functions reveal the existence in this polymer of some more complex motion of the phenylene ring. On the other hand, the similarity of the energy landscapes deduced from the different techniques points to a closely related molecular origin for all the relaxation/motions observed. (orig.)

  10. Prompt γ-ray spectroscopy of the neutron-rich 124Cd

    Directory of Open Access Journals (Sweden)

    Vancraeyenest A.

    2013-12-01

    Full Text Available Prompt γ-ray spectroscopy of neutron-rich cadmium isotopes has been performed. The nuclei of interest have been populated via a 25-MeV, proton-induced fission of the 238U thick target and prompt γ-rays measured using the multi-detector HPGe array JUROGAM II. New high-spin decays have been observed and placed in the level scheme using triple coincidence gates. The experimental results are compared to shell-model calculations and show good agreement.

  11. Neutron activation analysis and Mossbauer spectroscopy research on coloring mechanism of Chinese Ru porcelain

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The characteristic spectrum and its main wavelength of Ru porcelain glaze are measured by color difference instrument to determine the relations between glaze color and its main wavelength. The content of the 30 coloring elements in Ru porcelain is determined by neutron activation analysis (NAA), which showed that iron is the major coloring element. M?ssbauer spectroscopy analysis shows that the iron element in the glaze exists in the form of structural iron (Fe2+, Fe3+). The quantitative relationship between the main wavelength of glaze in various colors and the relative content of structural iron (Fe2+/Fe3+) is determined. Thus the coloring mechanism of Ru porcelain is investigated entirely.

  12. Direct measurement of electron transfer distance decay constants of single redox proteins by electrochemical tunneling spectroscopy.

    Science.gov (United States)

    Artés, Juan M; Díez-Pérez, Ismael; Sanz, Fausto; Gorostiza, Pau

    2011-03-22

    We present a method to measure directly and at the single-molecule level the distance decay constant that characterizes the rate of electron transfer (ET) in redox proteins. Using an electrochemical tunneling microscope under bipotentiostatic control, we obtained current−distance spectroscopic recordings of individual redox proteins confined within a nanometric tunneling gap at a well-defined molecular orientation. The tunneling current decays exponentially, and the corresponding decay constant (β) strongly supports a two-step tunneling ET mechanism. Statistical analysis of decay constant measurements reveals differences between the reduced and oxidized states that may be relevant to the control of ET rates in enzymes and biological electron transport chains.

  13. Co on Pt(111) studied by spin-polarized scanning tunneling microscopy and spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Meier, F.K.

    2006-07-01

    In this thesis the electronic properties of the bare Pt(111) surface, the structural, electronic, and magnetic properties of monolayer and double-layer high Co nanostructures as well as the spin-averaged electronic structure of single Co atoms on Pt(111) were studied by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS). The experiments on the bare Pt(111) surface and on single Co atoms have been performed in an STM facility operating at temperatures of down to 0.3 K and at magnetic fields of up to 14 T under ultra-high vacuum conditions. The facility has been taken into operation within the time period of this thesis and its specifications were tested by STS measurements. These characterization measurements show a very high stability of the tunneling junction and an energy resolution of about 100 {mu}eV, which is close to the thermal limit. The investigation of the electronic structure of the bare Pt(111) surface reveals the existence of an unoccupied surface state. By a comparison of the measured dispersion to first-principles electronic structure calculations the state is assigned to an sp-derived surface band at the lower boundary of the projected bulk band gap. The surface state exhibits a strong spin-orbit coupling induced spin splitting. The close vicinity to the bulk bands leads to a strong linear contribution to the dispersion and thus to a deviant appearance in the density of states in comparison to the surface states of the (111) surfaces of noble metals. A detailed study of Co monolayer and double-layer nanostructures on the Pt(111) surface shows that both kinds of nanostructures exhibit a highly inhomogeneous electronic structure which changes at the scale of only a few Aa due to a strong stacking dependence with respect to the Pt(111) substrate. With the help of first principles calculations the different spectroscopic appearance for Co atoms within the Co monolayer is assigned to a stacking dependent hybridization of Co states

  14. Liquid 1-propanol studied by neutron scattering, near-infrared, and dielectric spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sillrén, P.; Matic, A.; Karlsson, M. [Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg (Sweden); Koza, M.; Maccarini, M.; Fouquet, P. [Institut Laue Langevin, 6, rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9 (France); Götz, M.; Bauer, Th.; Gulich, R.; Lunkenheimer, P.; Loidl, A. [Experimental Physics V, University of Augsburg, 86135 Augsburg (Germany); Mattsson, J. [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom); Gainaru, C.; Vynokur, E.; Schildmann, S.; Bauer, S.; Böhmer, R. [Fakultät für Physik, Technische Universität Dortmund, 44221 Dortmund (Germany)

    2014-03-28

    Liquid monohydroxy alcohols exhibit unusual dynamics related to their hydrogen bonding induced structures. The connection between structure and dynamics is studied for liquid 1-propanol using quasi-elastic neutron scattering, combining time-of-flight and neutron spin-echo techniques, with a focus on the dynamics at length scales corresponding to the main peak and the pre-peak of the structure factor. At the main peak, the structural relaxation times are probed. These correspond well to mechanical relaxation times calculated from literature data. At the pre-peak, corresponding to length scales related to H-bonded structures, the relaxation times are almost an order of magnitude longer. According to previous work [C. Gainaru, R. Meier, S. Schildmann, C. Lederle, W. Hiller, E. Rössler, and R. Böhmer, Phys. Rev. Lett. 105, 258303 (2010)] this time scale difference is connected to the average size of H-bonded clusters. The relation between the relaxation times from neutron scattering and those determined from dielectric spectroscopy is discussed on the basis of broad-band permittivity data of 1-propanol. Moreover, in 1-propanol the dielectric relaxation strength as well as the near-infrared absorbance reveal anomalous behavior below ambient temperature. A corresponding feature could not be found in the polyalcohols propylene glycol and glycerol.

  15. Is spin transport through molecules really occurring in organic spin valves? A combined magnetoresistance and inelastic electron tunnelling spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Galbiati, Marta; Tatay, Sergio; Delprat, Sophie; Khanh, Hung Le; Deranlot, Cyrile; Collin, Sophie; Seneor, Pierre, E-mail: pierre.seneor@thalesgroup.com; Mattana, Richard, E-mail: richard.mattana@thalesgroup.com; Petroff, Frédéric [Unité Mixte de Physique CNRS/Thales, 1 Av. A. Fresnel, 91767 Palaiseau, France and Université Paris-Sud, 91405 Orsay (France); Servet, Bernard [Thales Research and Technology, 1 Av. A. Fresnel, 91767 Palaiseau (France)

    2015-02-23

    Molecular and organic spintronics is an emerging research field which combines the versatility of chemistry with the non-volatility of spintronics. Organic materials have already proved their potential as tunnel barriers (TBs) or spacers in spintronics devices showing sizable spin valve like magnetoresistance effects. In the last years, a large effort has been focused on the optimization of these organic spintronics devices. Insertion of a thin inorganic tunnel barrier (Al{sub 2}O{sub 3} or MgO) at the bottom ferromagnetic metal (FM)/organic interface seems to improve the spin transport efficiency. However, during the top FM electrode deposition, metal atoms are prone to diffuse through the organic layer and potentially short-circuit it. This may lead to the formation of a working but undesired FM/TB/FM magnetic tunnel junction where the organic plays no role. Indeed, establishing a protocol to demonstrate the effective spin dependent transport through the organic layer remains a key issue. Here, we focus on Co/Al{sub 2}O{sub 3}/Alq{sub 3}/Co junctions and show that combining magnetoresistance and inelastic electron tunnelling spectroscopy measurements one can sort out working “organic” and short-circuited junctions fabricated on the same wafer.

  16. Preliminary approach to neutron instrument selection at ESS-Bilbao based on experience at ISIS molecular spectroscopy group

    Energy Technology Data Exchange (ETDEWEB)

    Vicente Bueno, J. P. de

    2014-07-01

    Collaborative efforts between the Neutronics and Target Design Group at the Instituto de Fusion Nuclear and the Molecular Spectroscopy Group at the ISIS Pulsed Neutron and Muon Source date back to 2012 in the context of the ESS-Bilbao project. The rationale for these joint activities was twofold, namely: to assess the realm of applicability of the low-energy neutron source proposed by ESS-Bilbao; and to explore instrument capabilities for pulsed-neutron techniques in the range 0.05-3 ms, a time range where ESS-Bilbao and ISIS could offer a significant degree of synergy and complementarity. As part of this collaboration, J.P. de Vicente has spent a three-month period within the ISIS Molecular Spectroscopy Group, to gain hands-on experience on the practical aspects of neutron-instrument design and the requisite neutron-transport simulations. Building upon these previous works, the primary aim of this report is to provide a self contained discussion of general criteria for instrument selection at ESS-Bilbao, the first accelerator-driven, low-energy neutron source designed in Spain. (Author)

  17. Using Neutron Spectroscopy to Constrain the Composition and Provenance of Phobos and Deimos

    Science.gov (United States)

    Elphic, Richard C.

    2015-01-01

    The origin of the Martian moons Phobos and Deimos is obscure and enigmatic. Hypotheses include the capture of asteroids originally from the outer main belt or beyond, residual material left over from Mars' formation, and accreted ejecta from a large impact on Mars, among others. Measurements of reflectance spectra indicate a similarity to dark, red D-type asteroids, but could indicate a highly space-weathered veneer. Here we suggest a way of constraining the near-surface composition of the two moons, for comparison to known meteoritic compositions. Neutron spectroscopy, particularly the thermal and epithermal neutron flux, distinguishes clearly between various classes of meteorites and varying hydrogen (water) abundances. Perhaps most surprising of all, a rendezvous with Phobos or Deimos is not necessary to achieve this. A low-cost mission based on the LADEE spacecraft design in an eccentric orbit around Mars can encounter Phobos every 2 weeks. As few as five flyby encounters at speeds of 2.3 kilometers per second and closest-approach distance of 3 kilometers provide sufficient data to distinguish between ordinary chondrite, water-bearing carbonaceous chondrite, ureilite, Mars surface, and aubrite compositions. A one-Earth year mission design includes many more flybys at lower speeds and closer approach distances, as well as similar multiple flybys at Deimos in the second mission phase, as described in the Phobos And Deimos Mars Environment (PADME) mission concept. This presentation will describe the expected thermal and epithermal neutron fluxes based on MCNP6 (Monte Carlo N (i.e. Neutron)-Particle transport code (version 6) simulations of different meteorite compositions and their uncertainties.

  18. Sensitizers in inelastic electron tunneling spectroscopy: a first-principles study of functional aromatics on Cu(111)

    Science.gov (United States)

    Burema, S. R.; Bocquet, M.-L.

    2012-08-01

    Low sensitivity is a key problem in inelastic electron tunneling spectroscopy (IETS) with the scanning tunneling microscope. Using first-principles simulations, we predict different means to tune the IETS sensitivity of symmetrical functional aromatics on a Cu(111) surface. We show how the IET-spectra of phenyl-NO2 compounds can be greatly enhanced as compared to pristine phenyl. More precisely, the NO2 substituent qualifies as a sensitizer of low-frequency wagging modes, but also as a quencher of high-frequency stretching modes. At variance, the CO2 substituent is found to suppress the whole IET-activity. The head-up (non-anchoring) and head-down (anchoring) configurations of the functional group lead to minor changes in the signals, nevertheless allowing access to discriminate configurational features. It is shown how to disentangle the electronic and steric effects of the substituent in the STM junction.

  19. Bimetallic Catalysts and Platinum Surfaces Studied by X-ray Absorption Spectroscopy and Scanning Tunnelling Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Roenning, Magnus

    2000-07-01

    Bimetallic catalyst systems used in Fischer-Tropsch synthesis (Co-Re/Al{sub 2}O{sub 3}) and in the naphtha reforming process (Pt-Re/Al{sub 2}O{sub 3}) have been studied in situ using X-ray absorption spectroscopy (EXAFS). Additionally, the adsorption of ethene on platinum single crystal surfaces has been investigated using scanning tunnelling microscopy. In situ EXAFS at the cobalt K absorption edge have been carried out at 450{sup o}C on the hydrogen reduction of a rhenium-promoted Co{sub 3}O{sub 4}/Al{sub 2}O{sub 3} catalyst. Reductions carried out using 100% hydrogen and 5% hydrogen in helium gave different results. Whereas the reduction using dilute hydrogen leads to bulk-like metallic cobalt particles (hcp or fcc), reaction with pure hydrogen yields a more dispersed system with smaller cobalt metal particles (< 40 A). The results are rationalised in terms of different degrees of reoxidation of cobalt by the higher and lower concentrations of water generated during the reduction of cobalt oxide by 100% and 5% hydrogen, respectively. Additionally, in both reduction protocols a small fraction (3 -4 wt%) of the cobalt content is randomly dispersed over the tetrahedral vacancies of the alumina support. This dispersion occurs during reduction and not calcination. The cobalt in these sites cannot be reduced at 450 {sup o}C. The local environments about the rhenium atoms in Co-Re/{gamma}-A1{sub 2}O{sub 3} catalyst after different reduction periods have been studied by X-ray absorption spectroscopy. A bimetallic catalyst containing 4.6 wt% cobalt and 2 wt% rhenium has been compared with a corresponding monometallic sample with 2 wt% rhenium on the same support. The rhenium L{sub III} EXAFS analysis shows that bimetallic particles are formed after reduction at 450{sup o}C with the average particle size being 10-15 A. Rhenium is shown to be reduced at a later stage than cobalt. The fraction of cobalt atoms entering the support obstructs the access to the support for the

  20. Bimetallic Catalysts and Platinum Surfaces Studied by X-ray Absorption Spectroscopy and Scanning Tunnelling Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Roenning, Magnus

    2000-07-01

    Bimetallic catalyst systems used in Fischer-Tropsch synthesis (Co-Re/Al{sub 2}O{sub 3}) and in the naphtha reforming process (Pt-Re/Al{sub 2}O{sub 3}) have been studied in situ using X-ray absorption spectroscopy (EXAFS). Additionally, the adsorption of ethene on platinum single crystal surfaces has been investigated using scanning tunnelling microscopy. In situ EXAFS at the cobalt K absorption edge have been carried out at 450{sup o}C on the hydrogen reduction of a rhenium-promoted Co{sub 3}O{sub 4}/Al{sub 2}O{sub 3} catalyst. Reductions carried out using 100% hydrogen and 5% hydrogen in helium gave different results. Whereas the reduction using dilute hydrogen leads to bulk-like metallic cobalt particles (hcp or fcc), reaction with pure hydrogen yields a more dispersed system with smaller cobalt metal particles (< 40 A). The results are rationalised in terms of different degrees of reoxidation of cobalt by the higher and lower concentrations of water generated during the reduction of cobalt oxide by 100% and 5% hydrogen, respectively. Additionally, in both reduction protocols a small fraction (3 -4 wt%) of the cobalt content is randomly dispersed over the tetrahedral vacancies of the alumina support. This dispersion occurs during reduction and not calcination. The cobalt in these sites cannot be reduced at 450 {sup o}C. The local environments about the rhenium atoms in Co-Re/{gamma}-A1{sub 2}O{sub 3} catalyst after different reduction periods have been studied by X-ray absorption spectroscopy. A bimetallic catalyst containing 4.6 wt% cobalt and 2 wt% rhenium has been compared with a corresponding monometallic sample with 2 wt% rhenium on the same support. The rhenium L{sub III} EXAFS analysis shows that bimetallic particles are formed after reduction at 450{sup o}C with the average particle size being 10-15 A. Rhenium is shown to be reduced at a later stage than cobalt. The fraction of cobalt atoms entering the support obstructs the access to the support for the

  1. Discretization of Electronic States in Large InAsP/InP Multilevel Quantum Dots Probed by Scanning Tunneling Spectroscopy

    Science.gov (United States)

    Fain, B.; Robert-Philip, I.; Beveratos, A.; David, C.; Wang, Z. Z.; Sagnes, I.; Girard, J. C.

    2012-03-01

    The topography and the electronic structure of InAsP/InP quantum dots are probed by cross-sectional scanning tunneling microscopy and spectroscopy. The study of the local density of states in such large quantum dots confirms the discrete nature of the electronic levels whose wave functions are measured by differential conductivity mapping. Because of their large dimensions, the energy separation between the discrete electronic levels is low, allowing for quantization in both the lateral and growth directions as well as the observation of the harmonicity of the dot lateral potential.

  2. Study of the Neutron Deficient Pb and Bi Isotopes by Simultaneous Atomic- and Nuclear-Spectroscopy

    CERN Multimedia

    Kessler, T

    2002-01-01

    We propose to study systematically nuclear properties of the neutron deficient lead $^{183-189}$Pb, $^{191g}$Pb, $^{193g}$Pb and bismuth isotopes $^{188-200}$Bi by atomic spectroscopy with the ISOLDE resonance ionisation laser ion source (RILIS) combined with simultaneous nuclear spectroscopy at the detection set-up. The main focus is the determination of the mean square charge radii of $^{183-190}$Pb and $^{188-193}$Bi from which the influence of low-lying intruder states should become obvious. Also the nuclear spin and magnetic moments of ground-states and long-lived isomers will be determined unambiguously through evaluation of the hyperfine structure, and new isomers could be discovered. The decay properties of these nuclei can be measured by $\\alpha$-$\\gamma$ and $\\beta$-$\\gamma$ spectroscopy. With this data at hand, possible shape transitions around mid-shell at N$\\sim$104 will be studied. This data is crucial for the direct test of nuclear theory in the context of intruder state influence (e.g. energy ...

  3. Study of neutron deficient iridium isotopes by using laser spectroscopy; Etude des noyaux d'iridium deficients en neutrons par spectroscopie laser

    Energy Technology Data Exchange (ETDEWEB)

    Verney, D

    2000-12-19

    Resonance ionization spectroscopy was performed on neutron deficient iridium isotopes {sup 182-189}Ir, {sup 186}Ir{sup m} and stable isotopes {sup 191,193}Ir. Hyperfine spectra were recorded from the optical transition at 351,7 nm between the 5d{sup 7}6s{sup 2} {sup 4}F{sub 9/2} ground state and the 5d{sup 7}6s6p {sup 6}F{sub 11/2} excited state. Radioactive iridium isotopes were obtained from {beta}{sup +}/EC decay of radioactive mercury nuclei deposited on a graphite substrate. The radioactive mercury nuclei were produced at the ISOLDE facility at CERN through spallation reactions, by bombarding a molten lead target with the 1 GeV proton beam delivered by the PS-Booster. Magnetic dipole moments and spectroscopic quadrupole moments were extracted from the hyperfine spectra. The mean square charge radius variations, as deduced from the measured isotopic shift, show a sharp change between {sup 187}Ir and {sup 186}Ir{sup g}, accompanied by a sudden increase in deformation: from {beta}2 {approx} 0,16 to {beta}2 > 0, 2. These results were analysed in the framework of an axial rotor plus one or two quasiparticles. The wave functions of the osmium and platinum cores which are used in order to describe the iridium nuclei were calculated from the HF+BCS method with the Skyrme SIII effective interaction. The cores were constrained to take the deformation parameters extracted from the isotopic shift measurements. One shows then that this sudden deformation change corresponds also to a change in the proton state that describes the odd nuclei ground state or that participates in the coupling with the neutron in odd-odd nuclei. This state is identified with the {pi}3/2{sup +}[402] orbital for the smaller deformations nuclei and with the {pi}1/2{sup -}[541] orbital stemming from the h{sub 9/2} subshell for bigger deformations nuclei. (author)

  4. Laser spectroscopy of cadmium isotopes: probing the nuclear structure between the neutron 50 and 82 shell closures

    CERN Multimedia

    Blaum, K; Stroke, H H; Krieger, A R

    We propose to study the isotopic chain of cadmium with high-resolution laser spectroscopy for the first time. Our goal is to determine nuclear spins, moments and root-mean-square charge radii of ground and isomeric states between the neutron 50 and 82 shell closures, contributing decisively to a better understanding of the nuclear structure in the vicinity of the doubly-magic $^{100}$Sn and $^{132}$Sn. On the neutron-rich side this is expected to shed light on a shell-quenching hypothesis and consequently on the duration of the r-process along the waiting-point nuclei below $^{130}$Cd. On the neutron-deficient side it may elucidate the role of the cadmium isotopes in the rp-process for rapidly accreting neutron stars.

  5. Polymorphic drugs examined with neutron spectroscopy: Is making more stable forms really that simple?

    Energy Technology Data Exchange (ETDEWEB)

    Tsapatsaris, Nikolaos [European Spallation Source ESS AB, P.O. Box 176, SE-221 00 Lund (Sweden); Landsgesell, Sven [Helmholtz Zentrum Berlin, Hahn-Meitner Platz, 1, 14109 Berlin (Germany); Koza, Michael M.; Frick, Bernhard [Institut Laue-Langevin, BP 156 38042, Grenoble Cedex 9 (France); Boldyreva, Elena V. [Novosibirsk State University, ul. Pirogova 2, Novosibirsk 630090 (Russian Federation); Institute of Solid State Chemistry and Mechanochemistry, ul. Kutateladze 18, Novosibirsk 630128 (Russian Federation); Bordallo, Heloisa N., E-mail: bordallo@nbi.ku.dk [Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen (Denmark)

    2013-12-12

    Highlights: • Pressure induced transition in the denser polymorphic form. • Weak strength of hydrogen bonds driving new stable packing. • Lattice anisotropy versus charge transfer. - Abstract: Understanding polymorphism in pharmaceutical ingredients is a long-standing challenge in formulation science. A well-known example is paracetamol, C{sub 8}H{sub 9}NO{sub 2}. The marketed stable form I crystallizes with corrugated molecular layers. In contrast, form II, which is thermodynamically favorable at high pressures, has relatively planar layers that can slip over each other without difficulty, but is metastable at ambient conditions. By means of inelastic neutron scattering we demonstrated that the lattice modes of form II exhibit a sudden 1 meV energy shift at 300 K under a pressure of ca 0.4 GPa. Moreover, evidence of an increase of the vibrational energy in both polymorphs was found, which was accompanied, in form I, by an unexpectedly weak increase of the tunnel splitting. These results indicate an anisotropy of the potential surface probed by the methyl rotor, and are discussed in relation to the differences of the strength of the hydrogen bond environment for each polymorph.

  6. Insights into Solid-State Electron Transport through Proteins from Inelastic Tunneling Spectroscopy: The Case of Azurin.

    Science.gov (United States)

    Yu, Xi; Lovrincic, Robert; Sepunaru, Lior; Li, Wenjie; Vilan, Ayelet; Pecht, Israel; Sheves, Mordechai; Cahen, David

    2015-10-27

    Surprisingly efficient solid-state electron transport has recently been demonstrated through "dry" proteins (with only structural, tightly bound H2O left), suggesting proteins as promising candidates for molecular (bio)electronics. Using inelastic electron tunneling spectroscopy (IETS), we explored electron-phonon interaction in metal/protein/metal junctions, to help understand solid-state electronic transport across the redox protein azurin. To that end an oriented azurin monolayer on Au is contacted by soft Au electrodes. Characteristic vibrational modes of amide and amino acid side groups as well as of the azurin-electrode contact were observed, revealing the azurin native conformation in the junction and the critical role of side groups in the charge transport. The lack of abrupt changes in the conductance and the line shape of IETS point to far off-resonance tunneling as the dominant transport mechanism across azurin, in line with previously reported (and herein confirmed) azurin junctions. The inelastic current and hence electron-phonon interaction appear to be rather weak and comparable in magnitude with the inelastic fraction of tunneling current via alkyl chains, which may reflect the known structural rigidity of azurin.

  7. Spectroscopy of neutron-rich hypernucleus, $^{7}_{\\Lambda}$He by electron beam

    CERN Document Server

    Gogami, T; Kawama, D; Achenbach, P; Ahmidouch, A; Albayrak, I; Androic, D; Asaturyan, A; Asaturyan, R; Ates, O; Baturin, P; Badui, R; Boeglin, W; Bono, J; Brash, E; Carter, P; Chiba, A; Christy, E; Danagoulian, S; De Leo, R; Doi, D; Elaasar, M; Ent, R; Fujii, Y; Fujita, M; Furic, M; Gabrielyan, M; Gan, L; Garibaldi, F; Gaskell, D; Gasparian, A; Han, Y; Hashimoto, O; Horn, T; Hu, B; Hungerford, Ed V; Jones, M; Kanda, H; Kaneta, M; Kato, S; Kawai, M; Khanal, H; Kohl, M; Liyanage, A; Luo, W; Maeda, K; Margaryan, A; Markowitz, P; Maruta, T; Matsumura, A; Maxwell, V; Mkrtchyan, A; Mkrtchyan, H; Nagao, S; Nakamura, S N; Narayan, A; Neville, C; Niculescu, G; Niculescu, M I; Nunez, A; Nuruzzaman,; Okayasu, Y; Petkovic, T; Pochodzalla, J; Qiu, X; Reinhold, J; Rodriguez, V M; Samanta, C; Sawatzky, B; Seva, T; Shichijo, A; Tadevosyan, V; Tang, L; Taniya, N; Tsukada, K; Veilleux, M; Vulcan, W; Wesselmann, F R; Wood, S A; Yamamoto, T; Ya, L; Ye, Z; Yokota, K; Yuan, L; Zhamkochyan, S; Zhu, L

    2016-01-01

    The missing mass spectroscopy of the $^{7}_{\\Lambda}$He hypernucleus was performed, using the $^{7}$Li$(e,e^{\\prime}K^{+})^{7}_{\\Lambda}$He reaction at JLab Hall-C. The $\\Lambda$ binding energy of the ground state (1/2$^{+}$) was determined with a smaller error than that of the previous measurement, being $B_{\\Lambda}$ = 5.55 $\\pm$ 0.10(stat.) $\\pm$ 0.11(sys.) MeV. The experiment also provided new insight into charge symmetry breaking in p-shell hypernuclear systems. Finally, a peak at $B_{\\Lambda}$ = 3.65 $\\pm$ 0.20(stat.) $\\pm$ 0.11(sys.) MeV was observed and assigned as a mixture of 3/2$^{+}$ and 5/2$^{+}$ states, confirming the "glue-like" behavior of $\\Lambda$, which makes an unstable state in $^{6}$He stable against neutron emission.

  8. Spectroscopy of Neutron-Deficient Nuclei Near the Z=82 Closed Shell via Symmetric Fusion Reactions

    Directory of Open Access Journals (Sweden)

    Kondev F.G.

    2013-12-01

    Full Text Available In-beam and decay-spectroscopy studies of neutron-deficient nuclei near the Z=82 shell closure were carried out using the Fragment Mass Analyzer (FMA and the Gammasphere array, in conjunction with symmetric fusion reactions and the Recoil Decay Tagging (RDT technique. The primary motivation was to study properties of 179Tl and 180Tl, and their daughter, and grand-daughter isotopes. For the first time, in-beam structures associated with 179Tl and 180Tl were observed, as well as γ rays associated with the 180Tl α decay. No long-lived isomer was identified in 180Tl, in contrast with the known systematics for the heavier odd-odd Tl isotopes.

  9. Low energy nuclear spin excitations in Ho metal investigated by high resolution neutron spectroscopy.

    Science.gov (United States)

    Chatterji, Tapan; Jalarvo, Niina

    2013-04-17

    We have investigated the low energy excitations in metallic Ho by high resolution neutron spectroscopy. We found at T = 3 K clear inelastic peaks in the energy loss and energy gain sides, along with the central elastic peak. The energy of this low energy excitation, which is 26.59 ± 0.02 μeV at T = 3 K, decreased continuously and became zero at TN ≈ 130 K. By fitting the data in the temperature range 100-127.5 K with a power law we obtained the power-law exponent β = 0.37 ± 0.02, which agrees with the expected value β = 0.367 for a three-dimensional Heisenberg model. Thus the energy of the low energy excitations can be associated with the order parameter.

  10. Nuclear moments of neutron-deficient iridium isotopes from laser spectroscopy

    CERN Document Server

    Verney, D; Cabaret, L A; Crawford, J; Duong, H T; Genevey, J; Huber, G; Ibrahim, F; Krieg, M; Lee, J K P; Lunney, M D; Obert, J; Oms, J; Pinard, J; Putaux, J C; Roussière, B; Sauvage, J; Sebastian, V

    2000-01-01

    Laser spectroscopy measurements have been performed on neutron- deficient iridium isotopes. The hyperfine structure and isotope shift of the optical Ir I transition 5d/sup 7/6s/sup 2/ /sup 4/F/sub 9/2/ to 5d/sup 7/6s6p /sup 6/F/sub 11/2/ at 351.5 nm have been studied for the /sup 182-189/Ir, /sup 186/Ir/sup m/ and /sup 191,193/Ir isotopes. The nuclear magnetic and quadrupole moments were obtained from the HFS measurements and the changes of the mean square charge radii from the IS measurements. A large mean square charge radius change between /sup 187/Ir and /sup 186/Ir and between /sup 186/Ir/sup m/ and /sup 186/Ir/sup g/ has been observed. (18 refs).

  11. Gamma-ray spectroscopy of neutron-rich products of heavy-ion collisions

    Energy Technology Data Exchange (ETDEWEB)

    Carpenter, M.P.; Janssens, R.V.F.; Ahmad, I. [and others

    1995-08-01

    Thick-target {gamma}{gamma} coincidence techniques are being used to explore the spectroscopy of otherwise hard-to-reach neutron-rich products of deep-inelastic heavy ion reactions. Extensive {gamma}{gamma} coincidence measurements were performed at ATLAS using pulsed beams of {sup 80}Se, {sup 136}Xe, and {sup 238}U on lead-backed {sup 122,124}Sn targets with energies 10-15% above the Coulomb barrier. Gamma-ray coincidence intensities were used to map out yield distributions with A and Z for even-even product nuclei around the target and around the projectile. The main features of the yield patterns are understandable in terms of N/Z equilibration. We had the most success in studying the decays of yrast isomers. Thus far, more than thirty new {mu}s isomers in the Z = 50 region were found and characterized. Making isotopic assignments for previously unknown {gamma}-ray cascades proves to be one of the biggest problems. Our assignments were based (a) on rare overlaps with radioactivity data, (b) on the relative yields with different beams, and (c) on observed cross-coincidences between {gamma} rays from light and heavy reaction partners. However, the primary products of deep inelastic collisions often are sufficiently excited for subsequent neutron evaporation, so {gamma}{gamma} cross-coincidence results require careful interpretation.

  12. Gamma ray spectroscopy of neutron-rich actinides after multi-nucleon transfer reactions

    Energy Technology Data Exchange (ETDEWEB)

    Vogt, Andreas; Birkenbach, Benedikt; Reiter, Peter; Hess, Herbert; Lewandowski, Lars; Steinbach, Tim [Institut fuer Kernphysik, Universitaet zu Koeln (Germany); Collaboration: LNL 11.22-Collaboration

    2014-07-01

    Excited states in neutron-rich Th and U nuclei were investigated after multi-nucleon transfer reactions employing the AGATA demonstrator and PRISMA setup at LNL (INFN, Italy). A primary {sup 136}Xe beam of 1 GeV hitting a {sup 238}U target was used to produce the nuclei of interest in the actinide region. Beam-like reaction products in the Xe-Ba-region were identified and selected by the PRISMA spectrometer. Kinematic coincidences between the binary reaction products of beam-like and target-like nuclei are detected with an additional MCP detector. Those coincidences allow clean conditions for in-beam γ-ray spectroscopy. Background contributions from excited fission fragments are successfully discriminated. γ-rays from excited states in beam- and target-like particles were measured with the position sensitive AGATA HPGe detectors. Improved energy resolution after Doppler correction is based on the novel γ-ray tracking technique which was successfully exploited to increase the quality of the γ-spectra. γ-ray spectra of the produced beam-like isotopes in the one-proton and two-proton transfer channels will be presented. Corresponding results from the hard-to-reach neutron-rich isotopes beyond {sup 232}Th will focus on their collective properties and cross section limits for their production.

  13. {gamma} ray spectroscopy of neutron rich nuclei around N=20; Spectroscopie {gamma} des noyaux riches en neutrons autour de N=20

    Energy Technology Data Exchange (ETDEWEB)

    Gelin, M

    2007-09-15

    There is an island of inversion around {sup 32}Mg (12 protons, 20 neutrons) in contradiction with a shell closure N=20. It means a coexistence of spherical and deformed shapes. This work is devoted to the study of {gamma}-ray spectroscopy for nuclei in this region, based on an experiment done at GANIL with a composite secondary beam produced by fragmentation. The originality of the method used here lies in the possibility to study simultaneously several nuclei, and for each of them to explore several reaction channels. The VAMOS spectrometer was used for the identification of the ejectiles. The {gamma}-rays were detected with EXOGAM, a germanium clover array. The detectors used before and after the target allowed for a unique identification and a selection of the reaction channel: inelastic scattering, transfer and fragmentation reaction. In this thesis the following nuclei were studied: {sup 28}Ne, {sup 30-32}Mg {sup 31-34}Al, {sup 33-35}Si, {sup 35}P. New {gamma}-rays have been observed. The {gamma}-ray angular distributions and {gamma}-{gamma} angular correlations have been measured for some transitions. Assignment of spins and parities has been proposed for some states. In particular, in {sup 34}Si, the 3{sup -} assignment is confirmed and a new candidate for the second 0{sup +} has been proposed. In {sup 32}Mg, the state at 2.321 MeV, for which conflicting assignment existed, is deduced from the present data as a 4{sup +}, and a 6{sup +} state is proposed. (author)

  14. Theory of spin dynamics of magnetic adatoms traced by time-resolved scanning tunneling spectroscopy

    CERN Document Server

    Schüler, Michael; Berakdar, Jamal

    2012-01-01

    The inelastic scanning tunneling microscopy (STM) has been shown recently (Loth et al. Science 329, 1628 (2010)) to be extendable as to access the nanosecond, spin-resolved dynamics of magnetic adatoms and molecules. Here we analyze theoretically this novel tool by considering the time-resolved spin dynamics of a single adsorbed Fe atom excited by a tunneling current pulse from a spin-polarized STM tip. The adatom spin-configuration can be controlled and probed by applying voltage pulses between the substrate and the spin-polarized STM tip. We demonstrate how, in a pump-probe manner, the relaxation dynamics of the sample spin is manifested in the spin-dependent tunneling current. Our model calculations are based on the scattering theory in a wave-packet formulation. The scheme is nonpertubative and hence, is valid for all voltages. The numerical results for the tunneling probability and the conductance are contrasted with the prediction of simple analytical models and compared with experiments.

  15. Scanning tunneling microscopy and spectroscopy of ion-bombarded Si(111) and Si(100) surfaces

    NARCIS (Netherlands)

    Zandvliet, H.J.W.; Elswijk, H.B.; Loenen, van E.J.; Tsong, I.S.T.

    1992-01-01

    Surfaces of Si(111)-(7×7) and Si(100)-(2×1) were bombarded by 3-keV Ar+ ions at doses of ≤1012 ions cm-2 to study the effect of individual ion impacts on the atomic structure of surfaces. Atom-resolved images show damaged regions of missing and displaced atoms. Current-imaging tunneling spectroscop

  16. Modification of the mesoscopic structure in neutron irradiated EPDM viewed through positron annihilation spectroscopy and dynamic mechanical analysis

    Energy Technology Data Exchange (ETDEWEB)

    Lambri, O.A., E-mail: olambri@fceia.unr.edu.a [Instituto de Fisica Rosario - CONICET, Avda. 27 de Febrero 210 bis, 2000 Rosario (Argentina); Facultad de Ciencias Exactas, Ingenieria y Agrimensura, Universidad Nacional de Rosario, Laboratorio de Materiales, Escuela de Ingenieria Electrica, Avda. Pellegrini 250, 2000 Rosario (Argentina); Plazaola, F.; Axpe, E. [Elektrizitatea eta Elektronika Saila, Zientzia eta Teknologia Fakultatea, Euskal Herriko Unibertsitatea, P.K. 644, 48080 Bilbao (Spain); Mocellini, R.R.; Zelada-Lambri, G.I. [Facultad de Ciencias Exactas, Ingenieria y Agrimensura, Universidad Nacional de Rosario, Laboratorio de Materiales, Escuela de Ingenieria Electrica, Avda. Pellegrini 250, 2000 Rosario (Argentina); Garcia, J.A. [Departamento de Fisica Aplicada II, Facultad de Ciencias y Tecnologia, Universidad del Pais Vasco, Apdo. 644, 48080 Bilbao, Pais Vasco (Spain); Matteo, C.L.; Sorichetti, P.A. [Departamento de Fisica, Facultad de Ingenieria, Universidad de Buenos Aires, Avda. Paseo Colon 850, 1063 Buenos Aires (Argentina)

    2011-02-01

    This article focuses on the study of the mesoscopic structure in neutron irradiated EPDM both from experimental and theoretical points of view. In this work we reveal completely the modification of the mesostructure of the EPDM due to neutron irradiation, resolving volume fraction, size and distribution of the crystalline zones as a function of the irradiation dose. Positron annihilation spectroscopy and dynamic mechanical analysis techniques are applied and the results are discussed by means of new theoretical results for describing the interaction process between the crystals and amorphous zones in EPDM.

  17. Spectroscopy of Neutrons Produced by (p,n) Reactions on Lithium

    Science.gov (United States)

    Wielopolski, Lucian; Powell, J.; Ludewig, H.; Raparia, D.; Alessi, J.; Han, Guoping

    1997-05-01

    Alternative to nuclear reactors, epithermal neutron source are being developed for Boron Neutron Capture Therapy (BNCT). Ideally, BNCT requires mono-energetic neutrons from about 1eV to 20keV depending on the tumor depth in brain. Accelerator based filtered neutron beams for BNCT produce continuous neutron spectra that need to be optimised. Neutron spectra resulting from bombarding Li target with protons, with various energies, were measured using proton recoil proportional counters. These spectra were analysed using the PSNS and HEPRO codes. The results from both analysis and Monte Carlo simulations are presented and the issues involved with either of the codes are discussed.

  18. Energy gap in tunneling spectroscopy: effect of the chemical potential shift

    Science.gov (United States)

    Fedotov, N. I.; Zaitsev-Zotov, S. V.

    2016-12-01

    We study the effect of a shift of the chemical potential level on the tunneling conductance spectra. In the systems with gapped energy spectra, significant chemical-potential dependent distortions of the differential tunneling conductance curves, dI/dV, arise in the gap region. An expression is derived for the correction of the dI/dV, which in a number of cases was found to be large. The sign of the correction depends on the chemical potential level position with respect to the gap. The correction of the dI/dV associated with the chemical potential shift has a nearly linear dependence on the tip-sample separation z and vanishes at z → 0.

  19. Bistability in Scanning Tunneling Spectroscopy of Ga-terminated Si(111)

    Science.gov (United States)

    Chen, Dongmin; Altfeder, Igor

    2000-03-01

    The bistable transport characteristics have been the basis of modern power and high speed switching devices. All these devices share a common and essential double barrier structure. Here we report on a surprising observation of the bistable tunneling characteristics in an apparent single barrier tunnel junction consisted of a Ga-terminated Si(111) surface and a W-tip of a scanning tunneling microscope (STM) operating at 77K. Under a negative tip bias condition, a switching from an initially high-impedance, low-current OFF state to a low-impedance, high-current ON state occurs at a bias higher than that for the subsequent reversal transition, giving rise to a large hysteresis loops. The turn-on bias varies from 3.1V to 4.0V,showing a large inverse dependence on the tip-sample distances, indicating strong field effect. On contrary, the turn-off bias is essentially pined at 2.7V, suggesting the existence of a conductance threshold. This opens the possioblity to engineer a new type of swithching device using only single layer atomic dopping in place of a more complex double barrier structure.

  20. Neutron capture gamma-ray spectroscopy and its analytical applications for gold ore sample using the reactor neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Hassan, A.M.; El-Kady, A.A.; Rofail, N.B.; Hamouda, I.

    1981-01-01

    Prompt gamma-rays which immediately follow thermal neutrons capture have been used as a technique for non-destructive elemental analysis for gold ore sample. The thermal column of the Egyptian Research Reactor - 1 (ET-RR-1) was used. This requires a design of a well collimated and thermalized neutron beam. A high resolution and high efficiency Ge (Li) detector was required. In order to estimate the content of gold in its ore, calibration curves were constructed. For testing the results obtained, an empirical formula including the thermal neutron flux, the microscopic cross-section and the absolute efficiency of the detection system were applied. The concentration of gold in its ore sample was found to be as low as 5 ppM. Several elements beside gold could be identified in the ore sample. 10 references.

  1. Structural studies of lithium zinc borohydride by neutron powder diffraction, Raman and NMR spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ravnsbaek, D.B. [Center for Materials Crystallography (CMC), Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C (Denmark); Frommen, C. [Institute for Energy Technology, P.O. Box 40, N-2027 Kjeller (Norway); Reed, D. [School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham, B15 2TT (United Kingdom); Filinchuk, Y. [Center for Materials Crystallography (CMC), Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C (Denmark); Swiss-Norwegian Beam Lines at ESRF, BP-220, 38043 Grenoble (France); Institute of Condensed Matter and Nanosciences, Universite Catholique de Louvain, 1 Place L. Pasteur, B-1348, Louvain-la-Neuve (Belgium); Sorby, M.; Hauback, B.C. [Institute for Energy Technology, P.O. Box 40, N-2027 Kjeller (Norway); Jakobsen, H.J. [Instrument Centre for Solid-State NMR Spectroscopy and Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C (Denmark); Book, D. [School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham, B15 2TT (United Kingdom); Besenbacher, F. [Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Skibsted, J. [Instrument Centre for Solid-State NMR Spectroscopy and Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C (Denmark); Jensen, T.R., E-mail: trj@chem.au.dk [Center for Materials Crystallography (CMC), Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C (Denmark)

    2011-09-15

    Research highlights: > Structural study of the first interpenetrated framework hydride, LiZn{sub 2}(BH{sub 4}){sub 5} > Determination of deuterium positions and revision of crystal structure by PND. > Raman spectroscopy confirms the presence of isolated [Zn{sub 2}(BD{sub 4}){sub 5}]-bar complex anions. > Determination of quadrupole coupling parameters and chemical shifts by {sup 11}B MAS NMR. - Abstract: The crystal structure of LiZn{sub 2}(BH{sub 4}){sub 5} is studied in detail using a combination of powder neutron diffraction (PND), Raman spectroscopy, and {sup 11}B MAS NMR spectroscopy on LiZn{sub 2}(BH{sub 4}){sub 5} and LiZn{sub 2}({sup 11}BD{sub 4}){sub 5}. The aim is to obtain detailed structural knowledge of the first interpenetrated framework hydride compound, LiZn{sub 2}(BD{sub 4}){sub 5} which consists of doubly interpenetrated 3D frameworks built from dinuclear complex ions [Zn{sub 2}(BD{sub 4}){sub 5}]{sup -} and lithium ions. The positions of the deuterium atoms are determined using Rietveld refinement of the PND data and the orientation of one of the four independent BD{sub 4}{sup -} groups is revised. The current data reveal that the structure of [Zn{sub 2}(BD{sub 4}){sub 5}]{sup -} is more regular than previously reported, as are also the coordinations around the Zn and Li atoms. Both Zn and Li atoms are found to coordinate to the BD{sub 4}{sup -} units via the tetrahedral edges. Some distortion of the angles within the BD{sub 4} units is observed, relative to the expected angles of 109.4 for the ideal tetrahedral coordination. Raman spectroscopy confirms bending and stretching modes from the expected terminal and bridging bidentate BH{sub 4}{sup -} and BD{sub 4}{sup -} units. The {sup 11}B MAS NMR spectrum of the satellite transitions resolves two distinct manifolds of spinning sidebands, which allows estimation of the {sup 11}B quadrupole coupling parameters and isotropic chemical shifts for the four distinct {sup 11}B sites of [Zn{sub 2}(BD

  2. Adsorption of ethylene on Sn and In terminated Si(001) surface studied by photoelectron spectroscopy and scanning tunneling microscopy.

    Science.gov (United States)

    Zimmermann, Petr; Sobotík, Pavel; Kocán, Pavel; Ošt'ádal, Ivan; Vorokhta, Mykhailo; Acres, Robert George; Matolín, Vladimír

    2016-09-07

    Interaction of ethylene (C2H4) with Si(001)-Sn-2 × 2 and Si(001)-In-2 × 2 at room temperature has been studied using core level (C 1s) X-ray photoelectron spectroscopy with synchrotron radiation and scanning tunneling microscopy. Sn and In form similar dimer chains on Si(001)2 × 1, but exhibit different interaction with ethylene. While ethylene adsorbs on top of Sn dimers of the Si(001)-Sn-2 × 2 surface, the Si(001)-In-2 × 2 surface turned out to be inert. Furthermore, the reactivity of the Sn terminated surface is found to be considerably decreased in comparison with Si(001)2 × 1. According to the proposed adsorption model ethylene bonds to Sn dimers via [2 + 2] cycloaddition by interacting with their π dimer bonds. In contrast, indium dimers do not contain π bonds, which renders the In terminated Si(001) surface inert for ethylene adsorption.

  3. Adsorption of ethylene on Sn and In terminated Si(001) surface studied by photoelectron spectroscopy and scanning tunneling microscopy

    Science.gov (United States)

    Zimmermann, Petr; Sobotík, Pavel; Kocán, Pavel; Ošt'ádal, Ivan; Vorokhta, Mykhailo; Acres, Robert George; Matolín, Vladimír

    2016-09-01

    Interaction of ethylene (C2H4) with Si(001)-Sn-2 × 2 and Si(001)-In-2 × 2 at room temperature has been studied using core level (C 1s) X-ray photoelectron spectroscopy with synchrotron radiation and scanning tunneling microscopy. Sn and In form similar dimer chains on Si(001)2 × 1, but exhibit different interaction with ethylene. While ethylene adsorbs on top of Sn dimers of the Si(001)-Sn-2 × 2 surface, the Si(001)-In-2 × 2 surface turned out to be inert. Furthermore, the reactivity of the Sn terminated surface is found to be considerably decreased in comparison with Si(001)2 × 1. According to the proposed adsorption model ethylene bonds to Sn dimers via [2 + 2] cycloaddition by interacting with their π dimer bonds. In contrast, indium dimers do not contain π bonds, which renders the In terminated Si(001) surface inert for ethylene adsorption.

  4. Scanning tunneling spectroscopy of Si donors in GaAs {l_brace}110{r_brace}

    Energy Technology Data Exchange (ETDEWEB)

    Teichmann, K.; Wenderoth, M.; Loth, S.; Ulbrich, R.G. [Universitaet Goettingen, IV. Physikalisches Institut (Germany)

    2007-07-01

    Silicon donors in highly n-doped GaAs(6.5 x 10{sup 18} cm{sup -3}) are investigated by Cross-Sectional Scanning Tunneling Microscopy in UHV at 8K. Donors near the surface of the {l_brace}110{r_brace} cleavage planes are studied by spatially resolved I(V)-spectroscopy. The dopant atoms are identified by their bias dependent topographic and spectroscopic properties. In addition to the known features at negative and small positive voltages, our measurements on single donors show an additional transport channel for larger positive bias voltages. The current distribution has a circular symmetric structure. The diameter is bias dependent, and can extend up to several nanometers around the donor. The minimal bias voltage of the current onset is localized above the donors. We discuss different scenarios - including tip induced band bending - that can lead to the observed ring-like shapes.

  5. Tunnelling spectroscopy of BaFe{sub 2}As{sub 2}/Au/PbIn thin film junctions

    Energy Technology Data Exchange (ETDEWEB)

    Doering, Sebastian; Schmidt, Stefan; Schmidl, Frank; Tympel, Volker; Grosse, Veit; Seidel, Paul [Institut fuer Festkoerperphysik, Friedrich-Schiller-Universitaet Jena (Germany); Haindl, Silvia; Iida, Kazumasa; Kurth, Fritz; Holzapfel, Bernhard [IFW Dresden, Institut fuer Metallische Werkstoffe, Dresden (Germany)

    2011-07-01

    Tunnelling spectroscopy is an important tool to investigate the properties of iron-based superconductors. In contrast to commonly used point contact Andreev reflection (PCAR) technique, we fabricated hybrid superconductor / normal metal / superconductor (SNS) thin film structures, with tunable barrier thickness and area. For the base electrode we use Ba(Fe{sub 0.9}Co{sub 0.1}){sub 2}As{sub 2} thin films, produced via pulsed laser deposition (PLD). A gold layer was sputtered to form the barrier, while the counter electrode material is the conventional superconductor PbIn with a T{sub c} of 7.2 K. For temperatures below 7.2 K the spectrum shows a subharmonic gap structure (SGS), described by an extended model of Octavio, Tinkham, Blonder and Klapwijk (OTBK), while at higher temperatures the SGS vanishes and an SN-like behaviour can be observed.

  6. INTER-LAYER INTERACTION IN DOUBLE-WALLED CARBON NANOTUBES EVIDENCED BY SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY

    DEFF Research Database (Denmark)

    Giusca, Cristina E; Tison, Yann; Silva, S. Ravi P.

    2008-01-01

    Scanning Tunneling Microscopy and Spectroscopy have been used in an attempt to elucidate the electronic structure of nanotube systems containing two constituent shells. Evidence for modified electronic structure due to the inter-layer interaction in double-walled carbon nanotubes is provided...... and the overall electronic structure for double-walled carbon nanotubes, is demonstrated by our experiments, showing that the effect the inner tube has on the overall electronic structure of double-walled nanotubes cannot be neglected, and is key to the opto-electronic properties of the system. We postulate...... that previous analysis of the opto-electronic properties on multiple-walled carbon nanotubes based purely on the outer layer chirality of the tube needs significant modification based on new understanding brought forth with our analysis....

  7. Size-dependent superconducting state of individual nanosized Pb islands grown on Si(111) by tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Liu Jiepeng; Wu Xuefeng; Ming Fangfei; Zhang Xieqiu; Wang Kedong; Xiao Xudong [Department of Physics, Chinese University of Hong Kong, Shatin, NT (Hong Kong); Wang Bing, E-mail: xdxiao@phy.cuhk.edu.hk [Hefei National Laboratory for Physical Sciences at Microscales, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2011-07-06

    By measuring the temperature-dependent tunneling spectroscopy of a set of flat-top Pb islands from 3.2 to 15 K, the limiting size of a nine-monolayer-thick Pb island with superconductivity above 3.2 K was determined to be {approx} 30 nm{sup 2}, in good agreement with the Anderson criterion. Further analysis indicates that the zero-temperature energy gap decreases significantly faster than the transition temperature when the Pb island size approaches this limit. This leads to a decrease of 2{Delta}(0)/k{sub B}T{sub C} from 4.5 to 3.3, thus showing that the Pb island superconductors undergo a change from strong to weak electron-phonon coupling.

  8. Improvements in fast-neutron spectroscopy methods (1961); Amelioration des methodes de spectrometrie des neutrons rapides (1961)

    Energy Technology Data Exchange (ETDEWEB)

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

    1961-02-15

    This research aimed at improving fast-neutron electronic detectors based on n-p elastic scattering. The first part concerns proportional counters; careful constructional methods have made it possible to plot mono-energetic neutron spectra in the range 700 keV - 3 MeV with a resolution of 7 per cent. The second part concerns scintillation counters: an organic scintillator and an inorganic scintillator covered with a thin layer of a scattering agent. An exact study of the types of scintillation has made it possible to develop efficient discriminator circuits. Different neutron spectra plotted in the presence of a strong gamma background are presented. The last part deals with the development of form discrimination methods for the study, in the actual beam, of the elastic scattering of 14.58 MeV electrons. With hydrogen, the distribution f ({phi}) of the recoil protons is f({phi}) = 1 + 0.034 cos {phi} + 0.042 cos{sup 2} {phi}. With tritium the scattering is strongly anisotropic; the curve representing the variation of the differential cross-section for the elastic scattering in the centre of mass system is obtained with a target containing 1 cm{sup 3} of tritium. (author) [French] Le travail a porte sur l'amelioration des detecteurs electroniques de neutrons rapides bases sur la diffusion elastique n-p. La premiere partie est relative aux compteurs proportionnels; des methodes soignees de fabrication ont permis des traces de spectres de neutrons monoenergetiques dans le domaine 700 keV - 3 MeV avec une resolution de 7 pour cent. La deuxieme partie est relative au compteur a scintillations; scintillateur organique et scintillateur mineral recouvert d'un diffuseur mince. Une etude precise des formes de scintillations a permis la mise au point de circuits discriminateurs efficaces. Differents spectres de neutrons traces en presence d'un fond gamma intense sont presentes. La derniere partie est relative a la mise en oeuvre des methodes de discrimination de

  9. Measurement of Cosmic-ray Muons and Muon-induced Neutrons in the Aberdeen Tunnel Underground Laboratory

    CERN Document Server

    Blyth, S C; Chen, X C; Chu, M C; Cui, K X; Hahn, R L; Ho, T H; Hsiung, Y B; Hu, B Z; Kwan, K K; Kwok, M W; Kwok, T; Lau, Y P; Leung, J K C; Leung, K Y; Lin, G L; Lin, Y C; Luk, K B; Luk, W H; Ngai, H Y; Ngan, S Y; Pun, C S J; Shih, K; Tam, Y H; Tsang, R H M; Wang, C H; Wong, C M; Wong, H L; Wong, K K; Yeh, M; Zhang, B J

    2015-01-01

    We measured the muon flux and the production rate of muon-induced neutrons at a depth of 611 meters water equivalent. Our apparatus comprises of three layers of crossed plastic scintillator hodoscopes for tracking the incident cosmic-ray muons, and 760 L of gadolinium-doped liquid scintillator for both neutron production and detection targets. The vertical muon intensity was measured to be $I_{\\mu}$ = (5.7 $\\pm$ 0.6) $\\times$ 10$^{-6}$ cm$^{-2}$ s$^{-1}$ sr$^{-1}$. The muon-induced neutron yield in the liquid scintillator was determined to be $Y_{n}$ = (1.19 $\\pm$ 0.08(stat.) $\\pm$ 0.21(syst.)) $\\times$ 10$^{-4}$ neutrons / ($\\mu$ g cm$^{-2}$). A fitting to recently measured neutron yields at different depths gave a muon energy dependence of $\\left\\langle E_{\\mu} \\right\\rangle^{0.76 \\pm 0.03}$ for scintillator targets.

  10. Localised vibrational mode spectroscopy studies of self-interstitial clusters in neutron irradiated silicon

    Energy Technology Data Exchange (ETDEWEB)

    Londos, C. A.; Antonaras, G. [University of Athens, Solid State Physics Section, Panepistimiopolis Zografos, Athens 157 84 (Greece); Chroneos, A. [Materials Engineering, The Open University, Milton Keynes MK7 6AA (United Kingdom); Department of Materials, Imperial College, London SW7 2AZ (United Kingdom)

    2013-07-28

    The evolution of self-interstitial clusters in silicon (Si), produced by fast neutron irradiation of silicon crystals followed by anneals up to 750 °C, is investigated using localised vibrational mode spectroscopy. A band at 582 cm{sup −1} appears after irradiation and is stable up to 550 °C was attributed to small self-interstitial clusters (I{sub n}, n ≤ 4), with the most probable candidate the I{sub 4} structure. Two bands at 713 and 758 cm{sup −1} arising in the spectra upon annealing of the 582 cm{sup −1} band and surviving up to ∼750 °C were correlated with larger interstitial clusters (I{sub n}, 5 ≤ n ≤ 8), with the most probable candidate the I{sub 8} structure or/and with chainlike defects which are precursors of the (311) extended defects. The results illustrate the presence of different interstitial clusters I{sub n}, at the various temperature intervals of the material, in the course of an isochronal anneal sequence. As the annealing temperature increases, they evolve from first-order structures with a small number of self-interstitials (I{sub n}, n ≤ 4) for the temperatures 50 < T < 550 °C, to second order structures (I{sub n}, 5 ≤ n ≤ 8) with a larger number of interstitials, for the temperatures 550 < T < 750 °C.

  11. Shape transitions in neutron-rich Ru isotopes: spectroscopy of 109,110,111,112Ru

    Energy Technology Data Exchange (ETDEWEB)

    Hua, H; Cline, D; Hayes, A B; Teng, R; Riley, D; Clark, R M; Fallon, P; Goergen, A; Macchiavelli, A O; Vetter, K

    2005-06-29

    The spectroscopy of neutron-rich {sup 109,110,111,112}Ru nuclei was studied by measuring the prompt {gamma} rays originated from fission fragments, produced by the {sup 238}U({alpha},f) fusion-fission reaction, in coincidence with the detection of both fragments. For {sup 109,111}Ru, both the negative-parity (h{sub 11/2} orbitals) and positive-parity (g{sub 7/2} and/or d{sub 5/2} orbitals) bands were extended to substantially higher spin and excitation energy than known previously. The ground-state and {gamma}-vibrational bands of {sup 110,112}Ru also were extended to higher spin, allowing observation of the second band crossing at the rotational frequency of {approx}450 keV in {sup 112}Ru, which is {approx}50 keV above the first band crossing. At a similar rotational frequency, the first band crossing for the h{sub 11/2} band in {sup 111}Ru was observed, which is absent in {sup 109}Ru. These band crossings most likely are caused by the alignment of the g{sub 9/2} proton pair. This early onset of the band crossing for the aligned {pi}g{sub 9/2} orbitals may be evidence of a triaxial shape transition from prolate to oblate occurring in {sup 111}Ru. The data together with a comparison of cranked shell model predictions are presented.

  12. Event based neutron activation spectroscopy and analysis algorithm using MLE and metaheuristics

    Directory of Open Access Journals (Sweden)

    Wallace Barton

    2014-03-01

    Full Text Available Techniques used in neutron activation analysis are often dependent on the experimental setup. In the context of developing a portable and high efficiency detection array, good energy resolution and half-life discrimination are difficult to obtain with traditional methods [1] given the logistic and financial constraints. An approach different from that of spectrum addition and standard spectroscopy analysis [2] was needed. The use of multiple detectors prompts the need for a flexible storage of acquisition data to enable sophisticated post processing of information. Analogously to what is done in heavy ion physics, gamma detection counts are stored as two-dimensional events. This enables post-selection of energies and time frames without the need to modify the experimental setup. This method of storage also permits the use of more complex analysis tools. Given the nature of the problem at hand, a light and efficient analysis code had to be devised. A thorough understanding of the physical and statistical processes [3] involved was used to create a statistical model. Maximum likelihood estimation was combined with metaheuristics to produce a sophisticated curve-fitting algorithm. Simulated and experimental data were fed into the analysis code prompting positive results in terms of half-life discrimination, peak identification and noise reduction. The code was also adapted to other fields of research such as heavy ion identification of the quasi-target (QT and quasi-particle (QP. The approach used seems to be able to translate well into other fields of research.

  13. Decay study of neutron-rich zirconium isotopes employing a Penning trap as a spectroscopy tool

    Energy Technology Data Exchange (ETDEWEB)

    Rinta-Antila, S.; Eronen, T.; Elomaa, V.V.; Hager, U.; Hakala, J.; Jokinen, A.; Karvonen, P.; Penttilae, H.; Rissanen, J.; Sonoda, T.; Saastamoinen, A.; Aeystoe, J. [University of Jyvaeskylae, Department of Physics (Finland)

    2007-01-15

    A new technique to produce isobarically pure ion beams for decay spectroscopy by using a gas-filled Penning trap was commissioned at the ion guide isotope separator on-line facility, IGISOL. {beta}-decays of neutron-rich {sup 100}Zr, {sup 102}Zr and {sup 104}Zr isotopes were studied with this technique. In addition, the Q{sub {beta}{sup -}} values of {sup 100,102,104}Zr {beta}-decays were determined from the direct mass measurements of zirconium and niobium isotopes performed with a high-precision Penning trap. The mass of {sup 104}Nb was directly measured for the first time and the obtained mass excess value for the longer-living (1{sup +}) state is -71823{+-}10 keV. For the ground states of {sup 100}Nb and {sup 102}Nb the obtained mass excess values were -79802{+-}20 keV and -76309{+-}10 keV, respectively. The observed distribution of the {beta} strength supports a prolate deformation assignment for {sup 100,102,104}Zr isotopes. (orig.)

  14. Decay Spectroscopy of Neutron-Rich Cd Around the N = 82 Shell Closure

    Science.gov (United States)

    Bernier, Nikita; Dillmann, Iris; Kruecken, Reiner; Griffin Collaboration

    2016-09-01

    The neutron-rich region around A = 132 is of special interest for nuclear astrophysics and nuclear structure. This region is connected with the second r-process abundance peak at A 130 and the waiting-point nuclei around N = 82. For nuclear structure studies, the neighbours of the doubly-magic 132Sn (Z = 50, N = 82) are an ideal test ground for shell model predictions. The beta-decay of the N = 82 isotope 130Cd into 130In was first investigated a decade ago, but the information for states of the lighter indium isotopes (128,129In) is still limited. In the present experiment, a detailed gamma-spectroscopy of the beta-decay of 128-132Cd was achieved with the newly commissioned GRIFFIN (Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei) gamma-ray spectrometer, which is capable of measuring down to rates of 0.1 pps. The low-energy cadmium isotopes were implanted into a movable tape at the central focus of the array from the ISAC-I facility at TRIUMF. The beta-tagging was performed using the auxiliary beta-particle detector SCEPTAR. The required beta-gamma(-gamma) coincidence data in high statistics needed to fill the spectroscopic gaps described in literature were obtained. The ongoing analysis of these data will be presented. Work supported by the Natural Sciences and Engineering Research Council of Canada and the National Research Council of Canada.

  15. Essential Strategies for Revealing Nanoscale Protein Dynamics by Neutron Spin Echo Spectroscopy.

    Science.gov (United States)

    Callaway, David J E; Bu, Zimei

    2016-01-01

    Determining the internal motions of a protein on nanosecond-to-microsecond timescales and on nanometer length scales is challenging by experimental biophysical techniques. Neutron spin echo spectroscopy (NSE) offers a unique opportunity to determine such nanoscale protein domain motions. However, the major hurdle in applying NSE to determine nanoscale protein motion is that the time and length scales of internal protein motions tend to be comparable to that of the global motions of a protein. The signals detected by NSE tend to be dominated by rigid-body translational and rotational diffusion. Using theoretical analyses, our laboratory showed that selective deuteration of a protein domain or a subunit can enhance the capability of NSE to reveal the internal motions in a protein complex. Here, we discuss the essential theoretical analysis and experimental methodology in detail. Protein nanomachines are far more complex than any molecular motors that have been artificially constructed, and their skillful utilization likely represents the future of medicine. With selective deuteration, NSE will allow us to see these nanomachines in motion. © 2016 Elsevier Inc. All rights reserved.

  16. Cu-Zn disorder in Cu2ZnGeSe4: A complementary neutron diffraction and Raman spectroscopy study

    Science.gov (United States)

    Gurieva, G.; Többens, D. M.; Valakh, M. Ya.; Schorr, S.

    2016-12-01

    The crystal structure of the quaternary compound semiconductor Cu2ZnGeSe4 (CZGSe) was investigated by the complementary use of neutron diffraction, and Raman spectroscopy. The powder sample, which resulting from wavelength dispersive X-ray spectroscopy (WDX) turned out to be single phase Cu-rich CZGSe, was synthesized by solid state reaction of the pure elements in an evacuated silica tube at 700 °C. Raman spectroscopy confirmed the homogeneity and phase purity of the sample, in addition, the kesterite type structure was suggested. Rietveld analysis of the neutron diffraction data confirmed that the compound crystallizes in the tetragonal kesterite type structure. The refined site occupancy factors were used to determine the average neutron scattering lengths of the cation sites, giving insights into cation distribution and finally point defect types. Thus it has been shown, that additional to the CuZn-ZnCu anti-site defects in the lattice planes at z=¼ and ¾ (Cu-Zn disorder) also the off-stoichiometry type related point defects like Cui and CuZn occur in Cu-rich CZGSe.

  17. Superconducting tunnel junction array development for high-resolution energy-dispersive x-ray spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Barfknecht, A. T.; Cramer, S. P; Frank, M.; Friedrich, S.; Hiller, L. J.; Labov, S. E.; Mears, C. A.; Niderost, B.

    1998-07-01

    Cryogenic energy-dispersive x-ray detectors are being developed because of their superior energy resolution ((less than or equal to) 10 eV FWHM for keV x rays) compared to semiconductor EDS systems. So far, their range of application is limited due to their comparably small size and low count rate. We present data on the development of superconducting tunnel junction (STJ) detector arrays to address both of these issues. A single STJ detector has a resolution around 10 eV below 1 keV and can be operated at count rates of order 10,000 counts/s. We show that the simultaneous operation of several STJ detectors does not diminish their energy resolution significantly, while increasing the detector area and the maximum count rate by a factor given by the total number of independent channels.

  18. Tunnel Junctions between Metals and Magnetic Perovskites and their use in Spin Polarized Spectroscopy

    Science.gov (United States)

    Mieville, Laurent; Worledge, Daniel; Geballe, Theodore H.; Char, Kookrin

    1998-03-01

    The recently reported "colossal" magnetoresistance (CMR) effect in (La_1-xA_x)MnO3 (where A stands for alkaline earth element) has shed new light on the magnetic properties exhibited by some members of the perovskite family with the generic formula ABO_3. We have studied the interface resistance between metals (Al, Nb and Pd) and magnetic perovskites ((La_0.66Sr_0.34)MnO_3, SrRuO3 and (La_0.5Sr_0.5)CoO_3) thin films grown by pulsed laser deposition. Low temperature measurements of tunnel junctions which aim to measure directly the amount of spin polarized carriers present in these perovskites will be also reviewed.

  19. Tunneling spectroscopy of a 2DEG in InAs: experiment and theory

    Science.gov (United States)

    Winkler, R.; Kunze, U.; Rössler, U.

    1992-02-01

    The narrow energy gap in InAs allows us to investigate the nonparabolic subband structure of an Yb-oxide-InAs (MOS) inversion layer by measuring the tunneling current I( U) between the inversion layer and the bulk valence band. The period of Landau oscillations of d 2I/d U2 is used to determine the subband dispersion E( k‖) and the energy dependent effective mass m∗( E) of the subband electrons. The experimental results are compared with self-consistent subband calculations taking into account the nonparabolicity, the magnetic field, and - what is important here — the potential difference between inversion layer and InAs-bulk. Besides an exact numerical solution, we discuss self-consistent, but nevertheless analytical, formulations of both the triangular potential approximation and the variational approach.

  20. Resonant tunneling spectroscopy of valley eigenstates on a donor-quantum dot coupled system

    Science.gov (United States)

    Kobayashi, T.; van der Heijden, J.; House, M. G.; Hile, S. J.; Asshoff, P.; Gonzalez-Zalba, M. F.; Vinet, M.; Simmons, M. Y.; Rogge, S.

    2016-04-01

    We report on electronic transport measurements through a silicon double quantum dot consisting of a donor and a quantum dot. Transport spectra show resonant tunneling peaks involving different valley states, which illustrate the valley splitting in a quantum dot on a Si/SiO2 interface. The detailed gate bias dependence of double dot transport allows a first direct observation of the valley splitting in the quantum dot, which is controllable between 160 and 240 μeV with an electric field dependence 1.2 ± 0.2 meV/(MV/m). A large valley splitting is an essential requirement for implementing a physical electron spin qubit in a silicon quantum dot.

  1. Use of a Superconducting Tunnel Junction for X-Ray Fluorescence Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hiller, L

    2001-03-06

    A superconducting tunnel junction (STJ) in combination with a superconducting absorber of radiation may function as a highly resolving x-ray spectrometer. Electronic excitations, or quasiparticles, are created when a superconductor absorbs an x ray and are detected as an excess tunnel current through the junction. The number of quasiparticles created and the magnitude of the excess current is proportional to the energy of the absorbed x ray. This is similar to existing semiconductor-based spectrometers that measure electron-hole pairs, but with 1000 times more excitations. The energy measurement therefore can be up to 30 times more precise with a superconducting detector than with a semiconductor detector. This work describes the development and testing of an STJ spectrometer design for x-ray fluorescence applications. First, the basic principles of the STJ spectrometer are explained. This is followed by detailed simulations of the variance in the number of quasiparticles produced by absorption of an x ray. This variance is inherent in the detector and establishes an upper limit on the resolving power of the spectrometer. These simulations include effects due to the materials used in the spectrometer and to the multilayer structure of the device. Next, the spectrometer is characterized as functions of operating temperature, incident x-ray energy, and count rate. Many of these tests were performed with the spectrometer attached to a synchrotron radiation port. Finally, example x-ray fluorescence spectra of materials exposed to synchrotron radiation are presented. These materials are of interest to semiconductor processing and structural biology, two fields that will benefit immediately from the improved resolving power of the STJ spectrometer.

  2. Electron-volt spectroscopy at a pulsed neutron source using a resonance detector technique

    CERN Document Server

    Andreani, C; Senesi, R; Gorini, G; Tardocchi, M; Bracco, A; Rhodes, N; Schooneveld, E M

    2002-01-01

    The effectiveness of the neutron resonance detector spectrometer for deep inelastic neutron scattering measurements has been assessed by measuring the Pb scattering on the eVS spectrometer at ISIS pulsed neutron source and natural U foils as (n,gamma) resonance converters. A conventional NaI scintillator with massive shielding has been used as gamma detector. A neutron energy window up to 90 eV, including four distinct resonance peaks, has been assessed. A net decrease of the intrinsic width of the 6.6 eV resonance peak has also been demonstrated employing the double difference spectrum technique, with two uranium foils of different thickness.

  3. Neutron emission spectroscopy of DT plasmas at enhanced energy resolution with diamond detectors

    Science.gov (United States)

    Giacomelli, L.; Nocente, M.; Rebai, M.; Rigamonti, D.; Milocco, A.; Tardocchi, M.; Chen, Z. J.; Du, T. F.; Fan, T. S.; Hu, Z. M.; Peng, X. Y.; Hjalmarsson, A.; Gorini, G.

    2016-11-01

    This work presents measurements done at the Peking University Van de Graaff neutron source of the response of single crystal synthetic diamond (SD) detectors to quasi-monoenergetic neutrons of 14-20 MeV. The results show an energy resolution of 1% for incoming 20 MeV neutrons, which, together with 1% detection efficiency, opens up to new prospects for fast ion physics studies in high performance nuclear fusion devices such as SD neutron spectrometry of deuterium-tritium plasmas heated by neutral beam injection.

  4. Charge structure and cation distribution on Fe-Ga chalcogenide spinel by neutron diffraction and Moessbauer spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sam Jin; Son, Bae Soon; Shim, In Bo; Kim, Chul Sung [Kookmin University, Seoul (Korea, Republic of); Hong, Kun Pyo [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    2005-07-01

    FeGa{sub x}Cr{sub 2-x}S{sub 4} (x=0.1 and 0.3) have been studied with x-ray, neutron difraction, and Moessbauer spectroscopy. Rietveld refinement of x-ray, neutron diffraction, and Moessbauer spectroscopy lead to the conclusion that the samples are in inverse spinel type, where the majority of Ga ions are present at tetrahedral site (A). The neutron diffractions on FeGa{sub x}Cr{sub 2-x}S{sub 4} (x=0.1) above 10 K show long range interaction behaviors and reveal an antiferromagnetic ordering, with the magnetic moment of Fe{sup 2+}(- 3.45 {mu}{sub B}) aligned antiparallel to Cr{sup 3+} (+2.89 {mu}{sub B}) at 10 K. Fe ions migrate from the tetrahedral (A) site to the octahedral (B) site with increase of Ga substitutions. The electric quadrupole splittings of the A and B sites in Moessbauer spectra give a direct evidence that Ga ion stimulate asymmetric charge distribution of Fe ions in the A site.

  5. Demonstrating the likely neutron star nature of five M31 globular cluster sources with Swift-NuSTAR spectroscopy

    CERN Document Server

    Maccarone, Thomas J; Hornschemeier, Ann; Lehmer, Bret D; Antoniou, Vallia; Ptak, Andrew; Wik, Daniel R; Zezas, Andreas; Boyd, Padi; Kennea, Jamie; Page, Kim; Eracleous, Mike; Williams, Benjamin F; Boggs, Steven E; Christensen, Finn E; Craig, William W; Hailey, Charles J; Harrison, Fiona; Stern, Dan; Zhang, William W

    2016-01-01

    We present the results of a joint Swift-NuSTAR spectroscopy campaign on M31. We focus on the five brightest globular cluster X-ray sources in our fields. Two of these had previously been argued to be black hole candidates on the basis of apparent hard-state spectra at luminosities above those for which neutron stars are in hard states. We show that these two sources are likely to be Z-sources (i.e. low magnetic field neutron stars accreting near their Eddington limits), or perhaps bright atoll sources (low magnetic field neutron stars which are just a bit fainter than this level) on the basis of simultaneous Swift and NuSTAR spectra which cover a broader range of energies. These new observations reveal spectral curvature above 6-8 keV that would be hard to detect without the broader energy coverage the NuSTAR data provide relative to Chandra and XMM-Newton. We show that the other three sources are also likely to be bright neutron star X-ray binaries, rather than black hole X-ray binaries. We discuss why it sh...

  6. Neutron spectroscopy by thermalization light yield measurement in a composite heterogeneous scintillator

    Energy Technology Data Exchange (ETDEWEB)

    Shi, T.; Nattress, J.; Mayer, Michael F.; Lin, M-W; Jovanovic, Igor

    2016-12-11

    An exothermic neutron capture reaction can be used to uniquely identify neutrons in particle detectors. With the use of a capture-gated coincidence technique, the sequence of scatter events that lead to neutron thermalization prior to the neutron capture can also be used to measure neutron energy. We report on the measurement of thermalization light yield via a time-of-flight technique in a polyvinyl toluene-based scintillator EJ-290 within a heterogeneous composite detector that also includes 6Li-doped glass scintillator. The thermalization light output exhibits a strong correlation with neutron energy because of the preference for near-complete energy deposition prior to the 6Li(n,t)4He neutron capture reaction. The nonproportionality of the light yield from nuclear recoils contributes to the observed broadening of the distribution of thermalization light output. The nonproportional dependence of the scintillation light output in the EJ-290 scintillator as a function of proton recoil energy has been characterized in the range of 0.3–14.1 MeV via the Birks parametrization through a combination of time-of-flight measurement and previously conducted measurements with Monoenergetic neutron sources.

  7. Development and set-up of a new low temperature scanning tunneling microscope Applications on microscopy and spectroscopy of lanthanid metals

    CERN Document Server

    Mühlig, A

    2000-01-01

    Scanning tunneling microscopy and spectroscopy are suitable methods to study the physical properties of thin magnetic metal films with a thickness of a few monolayers. These systems are of current interest because they give insight into solids states physics of metals. This thesis deals with following subjects: Introduction to scanning tunneling microscopy. Set-up of a low temperatur scanning tunneling microscope. Growth of thin Co and lanthanid metal films on W(110). Interplay of morphologie and magnetism on the example of Co/W(110). Making of Gd wires which are only a few nanometers thin. Diskussion of the studied exchange splitting of a d-like surface state in a local moment magnet. Measurement of the lifetime of hot holes and hot electrons near the fermi edge.

  8. Tunneling spectroscopy on grain boundary junctions in electron-doped high-temperature superconductors; Tunnelspektroskopie an Korngrenzenkontakten aus elektronendotierten Hochtemperatur-Supraleitern

    Energy Technology Data Exchange (ETDEWEB)

    Welter, B.

    2007-12-07

    Some methods are developed anf presented, by means of which from experimental tunnel spectra, especially on symmetric SIS contacts, informations about the properties of electrodes and tunnel barriers can be obtained. Especially a procedure for the numerical unfolding of symmetric SIS spectra is proposed. Furthermore a series of models is summarized, which can explain the linear background conductivity observed in many spectra on high-temperature superconductors. The results of resistance measurements on film bridges are presented. Especially different methods for the determination of H{sub c2}(T) respectively H{sub c2}(0) are presented and applied to the experimental data. Finally the results of the tunnel-spectroscopy measurements are shown.

  9. Inelastic neutron scattering (INS) observations of rotational tunneling within partially deuterated methane monolayers adsorbed on MgO(1 0 0) surfaces

    Science.gov (United States)

    Hicks, Andy S.; Larese, J. Z.

    2013-12-01

    High resolution inelastic neutron scattering (INS) measurements of the low temperature (T ∼ 2.0 K) rotational dynamics of isotopically substituted methane monolayers adsorbed on MgO(1 0 0) are presented. These spectra, obtained using BASIS at SNS, represent the most detailed measurements available for surface-adsorbed monolayer films of methane. Distinct excitations are readily observed at 15, 31, 45 and 127 μeV for the CH2D2 on MgO monolayer and at 40, 51, 95 and 138 μeV for CH3D/MgO. These features are attributed to tunneling transitions between sublevels within the ground librational state and are interpreted using the pocket state (PS) formalism first proposed by Hüller. This theoretical analysis employs the findings of earlier studies of CH4 on MgO(1 0 0) which suggest that molecules adsorb with their C2v axes normal to the surface plane. The comparison between theory and experiment provides direct insight into the impact of molecular versus surface symmetry on the observed tunneling spectra.

  10. Neutron induced background gamma activity in low-level Ge-spectroscopy systems

    Science.gov (United States)

    Jovančević, N.; Krmar, M.; Mrda, D.; Slivka, J.; Bikit, I.

    2010-01-01

    Two high purity germanium (HPGe) detectors were located in two different passive shields: one in pre-WW II iron and the second in commercial low background lead. Gamma lines emitted after neutron capture, as well as after inelastic scattering on the germanium crystal were detected and then analyzed. The thermal and fast neutron fluxes were calculated and their values were compared for the two different kinds of detector shield. Several materials having different neutron slowing-down properties were packed in Marinelli geometry, positioned on the lead shielded detector and measured for around 10 6 s. The main goal was to estimate a possible influence of the sample on the intensity of the neutron induced Ge gamma lines. On the iron-shielded detector a massive (3 in. thick) NaI Compton suppression system showed a measurable activity from neutron capture and inelastic scattering on sodium and iodine nuclei.

  11. Development of an high resolution neutron spectroscopy system using a diamond detector and a remote digital acquisition methodology

    Energy Technology Data Exchange (ETDEWEB)

    Pillon, Mario, E-mail: mario.pillon@enea.it [Associazione EURATOM-ENEA sulla Fusione, ENEA C.R. Frascati, via E. Fermi, 45, 00044 Frascati (Rome) (Italy); Andreoli, Fabrizio; Angelone, Maurizio [Associazione EURATOM-ENEA sulla Fusione, ENEA C.R. Frascati, via E. Fermi, 45, 00044 Frascati (Rome) (Italy); Milocco, Alberto [University of Milano Bicocca, Piazza della Scienza 3, 20126 Milano (Italy); Cardarelli, Roberto [Istituto Nazionale di Fisica Nucleare, Sezione Tor Vergata, via della Ricerca Scientifica, 1, 00133 Rome (Italy)

    2014-10-15

    Highlights: •We studied the response of a diamond detector connected, to a prototype preamplifier developed by our group. •The response was studied for quasi mono-energetic neutron energies between 5 and 20.5 MeV. •About 50 m of coaxial cable was interposed between the detector and the preamplifier. •This technique was developed in order to have the electronics located far from the high radiation zone. •Such approach could be interesting for hash environment like the Radial Neutron Camera of ITER. -- Abstract: The need of performing high resolution fast neutron spectroscopy in a very harsh environment like that of the Radial Neutron Camera (RNC) of ITER, requires to develop new detectors and methodologies. Diamond detectors have been proved to be excellent candidates but the electronics needs a substantial improvement. Because of the high radiation level and the temperatures expected near the detector positions in the RNC, the electronics must be placed several meters away. A novel Fast Charge Amplifier (FCA) was developed that, connected to a diamond detector using several tens of meters of low capacitance coaxial cable, is able to produce fast output signals suitable to be processed by digital electronics. These fast output signals allow to operate at high count rates avoiding pile-up problems. This novel amplifier connected to a digitizer is here tested in the neutron energy range from 5 to 20.5 MeV using the mono-energetic neutrons produced by the Van de Graaff (VdG) accelerator of the EC-JRC-IRMM and by the PTB cyclotron. From the measurements the experimental response functions of the diamond detector at different neutron energies were obtained. The shape of the response functions have been compared with that predicted with a routine which was implemented for the Monte Carlo code MCNPX with the scope to validate the calculations versus the experimental data. The goal is to develop a tool which allows to calculate the diamond detector response

  12. Tunneling spectroscopy of a phosphorus impurity atom on the Ge(111)-(2 × 1) surface

    Energy Technology Data Exchange (ETDEWEB)

    Savinov, S. V.; Oreshkin, A. I., E-mail: oreshkin@spmlab.phys.msu.su, E-mail: oreshkin@spmlab.ru [Moscow State University (Russian Federation); Oreshkin, S. I. [Moscow State University, Sternberg Astronomical Institute (Russian Federation); Haesendonck, C. van [Laboratorium voor Stoffysica en Magnetisme (Belgium)

    2015-06-15

    We numerically model the Ge(111)-(2 × 1) surface electronic properties in the vicinity of a P donor impurity atom located near the surface. We find a notable increase in the surface local density of states (LDOS) around the surface dopant near the bottom of the empty surface state band π*, which we call a split state due to its limited spatial extent and energetic position inside the band gap. We show that despite the well-established bulk donor impurity energy level position at the very bottom of the conduction band, a surface donor impurity on the Ge(111)-(2 × 1) surface might produce an energy level below the Fermi energy, depending on the impurity atom local environment. It is demonstrated that the impurity located in subsurface atomic layers is visible in a scanning tunneling microscope (STM) experiment on the Ge(111)-(2 × 1) surface. The quasi-1D character of the impurity image, observed in STM experiments, is confirmed by our computer simulations with a note that a few π-bonded dimer rows may be affected by the presence of the impurity atom. We elaborate a model that allows classifying atoms on the experimental low-temperature STM image. We show the presence of spatial oscillations of the LDOS by the density-functional theory method.

  13. Investigation of Two-Dimensional Transition Metal Dichalcogenides by Optical and Scanning Tunneling Spectroscopy

    Science.gov (United States)

    Rigosi, Albert F.

    The goal of this dissertation is not only to present works completed and projects initiated and accomplished, but to also attempt to teach some of the material to readers who have limited exposure to condensed matter. I will offer an introduction to two-dimensional transition metal dichalcogenide materials (2D TMDCs) and the mathematics required to understand the research conducted. Some effort will be given on explaining the experimental setups and preparations. Projects that required elaborate sample fabrication and the yielded results will be summarized. These results have heavy implications for the science behind bound electron-hole pairs, the effects of magnetic fields on such pairs, and extracting the useful optical properties from the material systems in which these pairs reside. Specialized fabrication techniques of samples for longer term projects that I led will also be presented, namely those of constructing heterostructures by stacking various 2D TMDCs for exploring the modulated properties of these novel arrangements. The latter portion of this dissertation will cover the nanoscopic dynamics of TMDC heterostructures. The Kramers-Kronig relations will be derived and discussed in detail. Data and results regarding the electronic structure of these materials, their heterostructures, and their custom alloys measured via scanning tunneling microscopy will be presented. Coupled with the measured optical properties, significant numerical quantities that characterize these materials are extracted. There will be several appendices that offer some supplementary information and basic summaries about all the projects that were initiated.

  14. Interdot carrier's transfer via tunneling pathway studied from photoluminescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Rihani, J. [Laboratoire de Photovoltaique et de Semiconducteurs, Centre de Recherche des Sciences et Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia)], E-mail: jawher.rihani@crten.rnrt.tn; Sallet, V. [Laboratoire de Photonique et de Nanostructures, CNRS Route de Nozay, 91 460 Marcoussis (France); Yahyaoui, N. [Unite nanoelectronique Faculte des Sciences de Tunis, Campus Universitaire, Elmanar 2092 Tunis (Tunisia); Harmand, J.C. [Laboratoire de Photonique et de Nanostructures, CNRS Route de Nozay, 91 460 Marcoussis (France); Oueslati, M. [Unite nanoelectronique Faculte des Sciences de Tunis, Campus Universitaire, Elmanar 2092 Tunis (Tunisia); Chtourou, R. [Laboratoire de Photovoltaique et de Semiconducteurs, Centre de Recherche des Sciences et Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia)

    2009-03-15

    Self-assembled InAs quantum dots (QDs) on GaAs(0 0 1) substrate were grown by molecular beam epitaxy (MBE) at a growth temperature of 490 deg. C. Two different families of dots were observed in the atomic force microscopy (AFM) image and ambiguously identified in the photoluminescence (PL) spectra. Temperature-dependent PL study was carried out in the 8-270 K temperature range. The integrated-PL intensity behavior of the two QDs populations was fit with the help of a rate equations model. It is found that the evolutions of the integrated-PL intensity of the two QDs population were governed by two regimes. The first one occurs in the 8-210 K temperature range and reveals an unusual enhancement of the integrated-PL intensity of the larger QDs (LQDs) class. This was attributed to the carrier supplies from the smaller QDs (SQDs) class via the tunneling process. The second one occurs in the 210-270 K temperature range and shows a common quench of the PL signals of the two QDs families, reflecting the same thermal escape mechanism of carriers.

  15. Study of a high critical temperature superconductor through Josephson effect and tunnel spectroscopy; Etude d'un supraconducteur a haute temperature critique par effet Josephson et spectroscopie tunnel

    Energy Technology Data Exchange (ETDEWEB)

    Grison, X

    2000-11-15

    This work, mainly experimental, is dedicated to the study of the Josephson effect and the tunnel spectroscopy of superconducting films. Thin films of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} oriented towards [0,0,1], [1,0,3], [1,1,0] or [1,0,0] axis have been made. The results concerning the [0,0,1] orientation are consistent with an order parameter having a d(x{sup 2}-y{sup 2}) symmetry but with a small component of s symmetry due to the orthorombicity of YBa{sub 2}Cu{sub 3}O{sub 7{delta}}. The results concerning the [1,1,0] orientation show the existence (near (1,1,0)-type surfaces) of an order parameter whose symmetry is d(x{sup 2}-y{sup 2}) {+-} i*s or more likely d(x{sup 2} - y{sup 2}) {+-} i*d(xy). The latter term implies the breaking of the time reversing symmetry. The i*d(xy) component is responsible for the Josephson coupling along the [1,1,0] axis, which means that the coupling is not or is little carried by the Andreev bound states contrarily to recent predictions. It is also shown that Josephson junctions can be fabricated by using ion irradiation. (A.C.)

  16. γ-ray spectroscopy of fission fragments from the cold-neutron 235U induced fission with EXILL

    Directory of Open Access Journals (Sweden)

    Konstantinopoulos T.

    2013-12-01

    Full Text Available A cold neutron induced fission experiment recently took place at the Institute Laue-Langevin (ILL in Grenoble. The neutron beam was provided by the nuclear reactor facility at ILL and the detector setup that was used for the γ-spectroscopy of the fission products consisted mainly of the detectors of the EXOGAM array [1], thereby the name of the campaign is EXILL. The main purpose of our measurement was to investigate the nuclei in the region with N = 50 close to 78Ni as well as the nuclei close to the N = 82 shell closure. In this paper, the motivation of the experiment is described as well as the experimental setup and the status of the ongoing data analysis.

  17. A novel liquid-Xenon detector concept for combined fast-neutrons and gamma imaging and spectroscopy

    Science.gov (United States)

    Breskin, A.; Israelashvili, I.; Cortesi, M.; Arazi, L.; Shchemelinin, S.; Chechik, R.; Dangendorf, V.; Bromberger, B.; Vartsky, D.

    2012-06-01

    A new detector concept is presented for combined imaging and spectroscopy of fast-neutrons and gamma rays. It comprises a liquid-Xenon (LXe) converter and scintillator coupled to a UV-sensitive gaseous imaging photomultiplier (GPM). Radiation imaging is obtained by localization of the scintillation-light from LXe with the position-sensitive GPM. The latter comprises a cascade of Thick Gas Electron Multipliers (THGEM), where the first element is coated with a CsI UV-photocathode. We present the concept and provide first model-simulation results of the processes involved and the expected performances of a detector having a LXe-filled capillaries converter. The new detector concept has potential applications in combined fast-neutron and gamma-ray screening of hidden explosives and fissile materials with pulsed sources.

  18. Transport in fuel cells: Electrochemical impedance spectroscopy and neutron imaging studies

    Science.gov (United States)

    Aaron, Douglas Scott

    This dissertation focuses on two powerful methods of performing in-situ studies of transport limitations in fuel cells. The first is electrochemical impedance spectroscopy (EIS) while the second is neutron imaging. Three fuel cell systems are studied in this work: polymer electrolyte membrane fuel cells (PEMFCs), microbial fuel cells (MFCs) and enzyme fuel cells (EFCs). The first experimental section of this dissertation focuses on application of EIS and neutron imaging to an operating PEMFC. The effects of cathode-side humidity and flow rate, as well as cell temperature and a transient response to cathode-side humidity, were studied for a PEMFC via EIS. It was found that increased air humidity in the cathode resulted in greatly reduced cathode resistance as well as a significant reduction in membrane resistance. The anode resistance was only slightly reduced in this case. Increased air flow rate was observed to have little effect on any resistance in the PEMFC, though slight reductions in both the anode and the cathode were observed. Increased cell temperature resulted in decreased cathode and anode resistances. Finally, the transient response to increased humidity exhibited unstable behavior for both the anode and the cathode resistances and the PEMFC power output. Neutron imaging allowed the calculation of water content throughout the PEMFC, showing a maximum in water content at the cathode gas diffusion layer - membrane interface. The second experimental section of this dissertation delves into the world of microbial fuel cells. Multiple long-term observations of changes in internal resistances were performed and illustrated the reduction in anode resistance as the bacterial community was established. Over this same time period, the cathode resistance was observed to have increased; these two phenomena suggest that the anode improved over time while the cathode suffered from degradation. Increased anode fluid ionic strength and flow rate both led to significant

  19. Compensated bismuth-loaded plastic scintillators for neutron detection using low-energy pseudo-spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Dumazert, Jonathan, E-mail: jonathan.dumazert@cea.fr [CEA, LIST, Laboratoire Capteurs Architectures Electroniques, 91191 Gif-sur-Yvette (France); Coulon, Romain; Bertrand, Guillaume H.V.; Normand, Stéphane [CEA, LIST, Laboratoire Capteurs Architectures Electroniques, 91191 Gif-sur-Yvette (France); Méchin, Laurence [CNRS, UCBN, Groupe de Recherche en Informatique, Image, Automatique et Instrumentation de Caen, 14050 Caen (France); Hamel, Matthieu [CEA, LIST, Laboratoire Capteurs Architectures Electroniques, 91191 Gif-sur-Yvette (France)

    2016-05-21

    Gadolinium-covered modified plastic scintillators show a high potential for the deployment of cost-effective neutron detectors. Taking advantage of the low-energy photon and electron signature of thermal neutron captures in gadolinium-155 and gadolinium-157 however requires a background correction. In order to display a trustable rate, dual compensation schemes appear as an alternative to Pulse Shape Discrimination. This paper presents the application of such a compensation scheme to a two-bismuth loaded plastic scintillator system. A detection scintillator interacts with incident photon and fast neutron radiations and is covered with a gadolinium converter to become thermal neutron-sensitive as well. In the meantime, an identical compensation scintillator, covered with terbium, solely interacts with the photon and fast neutron part of incident radiations. After the acquisition and the treatment of the counting signals from both sensors, a hypothesis test determines whether the resulting count rate after subtraction falls into statistical fluctuations or provides a robust image of neutron activity. A laboratory prototype is tested under both photon and neutron radiations, allowing us to investigate the performance of the overall compensation system. The study reveals satisfactory results in terms of robustness to a cesium-137 background and in terms of sensitivity in presence of a californium-252 source.

  20. Compensated bismuth-loaded plastic scintillators for neutron detection using low-energy pseudo-spectroscopy

    Science.gov (United States)

    Dumazert, Jonathan; Coulon, Romain; Bertrand, Guillaume H. V.; Normand, Stéphane; Méchin, Laurence; Hamel, Matthieu

    2016-05-01

    Gadolinium-covered modified plastic scintillators show a high potential for the deployment of cost-effective neutron detectors. Taking advantage of the low-energy photon and electron signature of thermal neutron captures in gadolinium-155 and gadolinium-157 however requires a background correction. In order to display a trustable rate, dual compensation schemes appear as an alternative to Pulse Shape Discrimination. This paper presents the application of such a compensation scheme to a two-bismuth loaded plastic scintillator system. A detection scintillator interacts with incident photon and fast neutron radiations and is covered with a gadolinium converter to become thermal neutron-sensitive as well. In the meantime, an identical compensation scintillator, covered with terbium, solely interacts with the photon and fast neutron part of incident radiations. After the acquisition and the treatment of the counting signals from both sensors, a hypothesis test determines whether the resulting count rate after subtraction falls into statistical fluctuations or provides a robust image of neutron activity. A laboratory prototype is tested under both photon and neutron radiations, allowing us to investigate the performance of the overall compensation system. The study reveals satisfactory results in terms of robustness to a cesium-137 background and in terms of sensitivity in presence of a californium-252 source.

  1. Development of Tunneling Spectroscopy Apparatus for Kelvin and Sub-Kelvin Measurements of Superconducting Energy Gaps by Multi-disciplinary students at a Liberal Arts University

    Science.gov (United States)

    Eckhardt, Matt

    2014-03-01

    Tunneling spectroscopy is an important technique used to measure the superconducting energy gap, a feature that is at the heart of the nature of superconductivity in various materials. In this presentation, we report the progress and results in developing high-resolution tunneling spectroscopy experimental platforms in a helium three cryostat, a 3 Kelvin cryocooler and a helium dip-tester. The experimental team working in a liberal arts university is a multi-disciplinary group consisting of one physics major, chemisty majors and a biology major. Students including non-physics majors learned and implemented current-voltage measurement techniques, vacuum system engineering, built electronic boxes and amplifier circuits from scratch, built custom multi-conductor cables for thermometry and current-voltage measurements, and performed conductance measurements. We report preliminary results. Acknowledgments: We acknowledge support from National Science Foundation Grant # DMR-1206561.

  2. Multiband superconductivity in 2 H -NbSe2 probed by Doppler-modulated scanning tunneling spectroscopy

    Science.gov (United States)

    Fridman, I.; Kloc, C.; Petrovic, C.; Wei, J. Y. T.

    Cooper pairing in multiband superconductors can involve carriers from bands having different dimensionalities, and the interband coupling can provide for novel pairing interactions. In addition to MgB2, recent experiments on 2 H -NbSe2 have studied the Fermi surface topology using angle- and temperature-dependent scanning tunneling spectroscopy. We present another novel method for probing multiband pairing: using a field-induced diamagnetic supercurrent, applied along different crystal axes, to perturb the quasiparticle density-of-states spectrum. By measuring the evolution of the quasiparticle spectrum under finite superfluid momentum, we characterize the pairing gaps and gap anisotropies. This approach is demonstrated on 2 H -NbSe2 at 300 mK with a magnetic field of up to 9 T applied in the ab -plane. The STM measurements revealed unambiguous evidence for multiband pairing, and evidence for a novel transition of the in-plane vortex lattice. We discuss the characteristics of this transition in light of data from other probes Work supported by NSERC, CFI/OIT, CIFAR, U.S. DOE and Brookhaven Science Associates (No. DE-AC02-98CH10886).

  3. Inelastic Tunneling Spectroscopy of Gold-Thiol and Gold-Thiolate Interfaces in Molecular Junctions: The Role of Hydrogen

    CERN Document Server

    Demir, Firuz

    2012-01-01

    It is widely believed that when a molecule with thiol (S-H) end groups bridges a pair of gold electrodes, the S atoms bond to the gold and the thiol H atoms detach from the molecule. However, little is known regarding the details of this process, its time scale, and whether molecules with and without thiol hydrogen atoms can coexist in molecular junctions. Here we explore theoretically how inelastic tunneling spectroscopy (IETS) can shed light on these issues. We present calculations of the geometries, low bias conductances and IETS of propanedithiol and propanedithiolate molecular junctions with gold electrodes. We show that IETS can distinguish between junctions with molecules having no, one or two thiol hydrogen atoms. We find that in most cases the single-molecule junctions in the IETS experiment of Hihath et al. [Nano Lett. 8, 1673 (2008)] had no thiol H atoms, but that a molecule with a single thiol H atom may have bridged their junction occasionally. We also consider the evolution of the IETS spectrum ...

  4. Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Schwarz, Udo; Albers, Boris J.; Liebmann, Marcus; Schwendemann, Todd C.; Baykara, Mehmet Z.; Heyde, Markus; Salmeron, Miquel; Altman, Eric I.; Schwarz, Udo D.

    2008-02-27

    The authors present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaround times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1 pm could successfully be resolved. In addition, lateral drifts rates of below 15 pm/h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope's performance.

  5. Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy

    Science.gov (United States)

    Albers, Boris J.; Liebmann, Marcus; Schwendemann, Todd C.; Baykara, Mehmet Z.; Heyde, Markus; Salmeron, Miquel; Altman, Eric I.; Schwarz, Udo D.

    2008-03-01

    We present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaround times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1pm could successfully be resolved. In addition, lateral drifts rates of below 15pm/h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope's performance.

  6. Encapsulation of paclitaxel into a bio-nanocomposite. A study combining inelastic neutron scattering to thermal analysis and infrared spectroscopy

    Directory of Open Access Journals (Sweden)

    Martins Murillo L.

    2015-01-01

    Full Text Available The anticancer drug paclitaxel was encapsulated into a bio-nanocomposite formed by magnetic nanoparticles, chitosan and apatite. The aim of this drug carrier is to provide a new perspective against breast cancer. The dynamics of the pure and encapsulated drug were investigated in order to verify possible molecular changes caused by the encapsulation, as well as to follow which interactions may occur between paclitaxel and the composite. Fourier transformed infrared spectroscopy, thermal analysis, inelastic and quasi-elastic neutron scattering experiments were performed. These very preliminary results suggest the successful encapsulation of the drug.

  7. Total Absorption Gamma-Ray Spectroscopy of 87Br, 88Br and 94Rb Beta-Delayed Neutron Emitters

    CERN Document Server

    Valencia, E; Algora, A; Agramunt, J; Rubio, B; Rice, S; Gelletly, W; Regan, P; Zakari-Issoufou, A -A; Fallot, M; Porta, A; Rissanen, J; Eronen, T; Aysto, J; Batist, L; Bowry, M; Bui, V M; Caballero-Folch, R; Cano-Ott, D; Elomaa, V -V; Estevez, E; Farrelly, G F; Garcia, A R; Gomez-Hornillos, B; Gorlychev, V; Hakala, J; Jordan, M D; Jokinen, A; Kolhinen, V S; Kondev, F G; Martinez, T; Mendoza, E; Moore, I; Penttila, H; Podolyak, Zs; Reponen, M; Sonnenschein, V; Sonzogni, A A

    2016-01-01

    We investigate the decay of 87Br, 88Br and 94Rb using total absorption gamma-ray spectroscopy. These important fission products are beta-delayed neutron emitters. Our data show considerable gamma-intensity, so far unobserved in high-resolution gamma-ray spectroscopy, from states at high excitation energy. We also find significant differences with the beta intensity that can be deduced from existing measurements of the beta spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discrepancy between calculations and integral measurements of the photon component for 235U fission at cooling times in the range 1 to 100 s. We also use summation calculations to evaluate the impact of present data on reactor antineutrino spectra. We find a significant effect at antineutrino energies in the range of 5 to 9 MeV. In addition, we observe an unexpected strong probability for gamma emission from neutron unbound s...

  8. Suzaku spectroscopy of the neutron star transient 4U 1608-52 during its outburst decay.

    Science.gov (United States)

    Armas Padilla, M.; Ueda, Y.; Hori, T.; Shidatsu, M.; Muñoz-Darias, T.

    2017-01-01

    We test the proposed 3-component spectral model for neutron star low mass X-ray binaries using broad-band X-ray data. We have analysed 4 X-ray spectra (0.8-30 keV) obtained with Suzaku during the 2010 outburst of 4U 1608-52, which have allowed us to perform a comprehensive spectral study covering all the classical spectral states. We use a thermally Comptonized continuum component to account for the hard emission, as well as two thermal components to constrain the accretion disc and neutron star surface contributions. We find that the proposed combination of multicolor disc, single-temperature black body and Comptonization components successfully reproduces the data from soft to hard states. In the soft state, our study supports the neutron star surface (or boundary layer) as the dominant source for the Comptonization seed photons yielding the observed weak hard emission, while in the hard state both solutions, either the disc or the neutron star surface, are equally favoured. The obtained spectral parameters as well as the spectral/timing correlations are comparable to those observed in accreting black holes, which support the idea that black hole and neutron star low mass X-ray binaries undergo a similar state evolution during their accretion episodes.

  9. Study of Neutron-Deficient $^{202-205}$Fr Isotopes with Collinear Resonance Ionization Spectroscopy

    CERN Document Server

    De Schepper, Stijn; Cocolios, Thomas; Budincevic, Ivan

    The scope of this master’s thesis is the study of neutron-deficient $^{202−205}$Fr isotopes. These isotopes are inside the neutron-deficient lead region, a region that has shown evidence of shape coexistence. For this thesis, this discussion is limited to the phenomenon where a low lying excited state has a different shape than the ground state. Shape coexistence is caused by intruder states. These are single-particle Shell Model states that are perturbed in energy due to the interaction with a deformed core. In the neutron-deficient lead region the main proton intruder orbit is the 3s$_{1/2}$orbit. When going towards more neutron-deficient isotopes, deformation increases. The $\\pi3s_{1/2}$orbit will rise in energy and will eventually become the ground state in odd- A bismuth (Z=83) isotopes. It is also observed in odd-A astatine (Z=85) isotopes, already in less neutron-deficient nuclei. The same phenomenon is expected to be present francium (Z=87) isotopes already at $^{199}$Fr. Although it is currently ...

  10. Inelastic tunneling spectroscopy of gold-thiol and gold-thiolate interfaces in molecular junctions: the role of hydrogen.

    Science.gov (United States)

    Demir, Firuz; Kirczenow, George

    2012-09-07

    It is widely believed that when a molecule with thiol (S-H) end groups bridges a pair of gold electrodes, the S atoms bond to the gold and the thiol H atoms detach from the molecule. However, little is known regarding the details of this process, its time scale, and whether molecules with and without thiol hydrogen atoms can coexist in molecular junctions. Here, we explore theoretically how inelastic tunneling spectroscopy (IETS) can shed light on these issues. We present calculations of the geometries, low bias conductances, and IETS of propanedithiol and propanedithiolate molecular junctions with gold electrodes. We show that IETS can distinguish between junctions with molecules having no, one, or two thiol hydrogen atoms. We find that in most cases, the single-molecule junctions in the IETS experiment of Hihath et al. [Nano Lett. 8, 1673 (2008)] had no thiol H atoms, but that a molecule with a single thiol H atom may have bridged their junction occasionally. We also consider the evolution of the IETS spectrum as a gold STM tip approaches the intact S-H group at the end of a molecule bound at its other end to a second electrode. We predict the frequency of a vibrational mode of the thiol H atom to increase by a factor ~2 as the gap between the tip and molecule narrows. Therefore, IETS should be able to track the approach of the tip towards the thiol group of the molecule and detect the detachment of the thiol H atom from the molecule when it occurs.

  11. Two-dimensional functional molecular nanoarchitectures - Complementary investigations with scanning tunneling microscopy and X-ray spectroscopy

    Science.gov (United States)

    Klappenberger, Florian

    2014-02-01

    Functional molecular nanoarchitectures (FMNs) are highly relevant for the development of future nanotechnology devices. Profound knowledge about the atomically controlled construction of such nanoscale assemblies is an indispensable requirement to render the implementation of such components into a real product successful. For exploiting their full potential the architectures’ functionalities have to be characterized in detail including the ways to tailor them. In recent years a plethora of sophisticated constructs were fabricated touching a wide range of research topics. The present review summarizes important achievements of bottom-up fabricated, molecular nanostructures created on single crystal metal surfaces under ultra-high vacuum conditions. This selection focuses on examples where self-assembly mechanisms played a central role for their construction. Such systems, though typically quite complex, can be comprehensively understood by the STM+XS approach combining scanning tunneling microscopy (STM) with X-ray spectroscopy (XS) and being aided in the atomic interpretation by the appropriate theoretic analysis, often from density functional theory. The symbiosis of the techniques is especially fruitful because of the complementary character of the information accessed by the local microscopy and the space-averaging spectroscopy tools. STM delivers sub-molecular spatial-resolution, but suffers from limited sensitivity for the chemical and conformational states of the building-blocks. XS compensates these weaknesses with element- and moiety-specific data, which in turn would be hard to interpret with respect to structure formation without the topographic details revealed by STM. The united merit of this methodology allows detailed geometric information to be obtained and addresses both the electronic and chemical state of the complex organic species constituting such architectures. Thus, possible changes induced by the various processes such as surface

  12. Approaching complete low-spin spectroscopy of 210Bi with a cold-neutron capture reaction

    Science.gov (United States)

    Cieplicka-Oryńczak, N.; Fornal, B.; Leoni, S.; Bazzacco, D.; Blanc, A.; Bocchi, G.; Bottoni, S.; de France, G.; Jentschel, M.; Köster, U.; Mutti, P.; Simpson, G.; Soldner, T.; Szpak, B.; Ur, C.; Urban, W.

    2016-05-01

    The low-spin structure of the 210Bi nucleus was investigated in the neutron capture experiment 209Bi(n ,γ )210Bi performed at ILL Grenoble at the PF1B cold-neutron facility. By using the EXILL multidetector array, consisting of 46 high-purity germanium crystals, and γ γ -coincidence technique, 64 primary γ rays were observed (40 new) and a total number of 70 discrete states (33 new) were located below the neutron binding energy in 210Bi. The analysis of the angular correlations of γ rays provided information about transitions multipolarities, which made it possible to confirm most of the previously known spin-parity assignments and helped establish new ones. The obtained experimental results were compared to shell-model calculations involving one-valence-proton, one-valence-neutron excitations outside the 208Pb core. It has been found that while up to the energy of ˜2 MeV each state observed in 210Bi has its calculated counterpart; at higher excitation energies some levels cannot be described by the valence particle couplings. These states may arise from couplings of valence particles to the 3- octupole phonon of the doubly magic 208Pb core and may serve as a testing ground for models which describe single particle-phonon excitations.

  13. Spectroscopy of neutron unbound states in 24O and 23N

    Science.gov (United States)

    Jones, Michael David

    Unbound states in 24O and 23N were populated from an 24O beam at 83.4 MeV/u via inelastic excitation and proton knockout on a liquid deuterium target. Using the MoNA-LISA-Sweeper setup, the decay of each nucleus could be fully reconstructed. The two-body decay energy of 23N exhibits two prominent peaks at E = 100 +/- 20 keV and E = 960 +/- 30 keV with respect to the neutron separation energy. However, due to the lack of gamma-ray detection, a definitive statement on the structure of 23N could not be made. Shell model calculations with the WBP and WBT interactions lead to several interpretations of the spectrum. Both a single state at 2.9 MeV in 23N, or two states at 2.9 MeV and 2.75 MeV are consistent with the shell model and data. In addition, a two-neutron unbound excited state of 24O, populated by (d,d'), was observed with a three-body excitation of E = 715 +/- 110 (stat) +/-45 (sys) keV, placing it at E = 7.65 +/- 0.2 MeV with respect to the ground state. Three-body correlations for the decay of 24O → 22O + 2n show clear evidence for a sequential decay through an intermediate state in 23O. Neither a di-neutron nor phase-space model were able to describe the observed correlations. This measurement constitutes the first observation of a two-neutron sequential decay through three-body energy and angular correlations, and provides valuable insight into few-body physics at the neutron dripline.

  14. Role of valence states of adsorbates in inelastic electron tunneling spectroscopy: A study of nitric oxide on Cu(110) and Cu(001)

    Science.gov (United States)

    Shiotari, Akitoshi; Okuyama, Hiroshi; Hatta, Shinichiro; Aruga, Tetsuya; Alducin, Maite; Frederiksen, Thomas

    2016-08-01

    We studied nitric oxide (NO) molecules on Cu(110) and Cu(001) surfaces with low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT). NO monomers on the surfaces are characterized by STM images reflecting 2 π* resonance states located at the Fermi level. NO is bonded vertically to the twofold short-bridge site on Cu(110) and to the fourfold hollow site on Cu(001). When NO molecules form dimers on the surfaces, the valence orbitals are modified due to the covalent bonding. We measured inelastic electron tunneling spectroscopy (IETS) for both NO monomers and dimers on the two surfaces, and detected characteristic structures assigned to frustrated rotation and translation modes by density functional theory simulations. Considering symmetries of valence orbitals and vibrational modes, we explain the intensity of the observed IETS signals in a qualitative manner.

  15. Investigation of surface defect states in CeO{sub 2-y} nanocrystals by Scanning−tunneling microscopy/spectroscopy and ellipsometry

    Energy Technology Data Exchange (ETDEWEB)

    Radović, Marko; Stojadinović, Bojan; Tomić, Nataša; Golubović, Aleksandar; Dohčević-Mitrović, Zorana, E-mail: zordoh@ipb.ac.rs [Institute of Physics, Pregrevica 118, University of Belgrade, 11 000 Belgrade (Serbia); Matović, Branko [Institute for Nuclear sciences “Vinča,” Materials Science Laboratory, University of Belgrade, 11 000 Belgrade (Serbia); Veljković, Ivana [Institute for Multidisciplinary Research, Kneza Viseslava 1a, University of Belgrade, 11 000 Belgrade (Serbia)

    2014-12-21

    Synthesis process strongly influences the nanocrystalline CeO{sub 2-y} defective structure. The presence of surface defects, in the form of oxygen vacancies in different charge states (F centers), can change the electronic properties of ceria nanocrystals. Nanocrystalline CeO{sub 2-y} samples were synthesized using three different methods (precipitation, self-propagating room temperature, and hydrothermal synthesis). Raman spectroscopy was used to identify the presence of oxygen vacancies which presumably were formed at the nanoparticle surface. The defect concentration depended on the crystallite size of differently prepared CeO{sub 2-y} samples. Scanning tunneling microscopy/spectroscopy and ellipsometry were employed to investigate the electronic band structure of defective CeO{sub 2-y} nanocrystals. Scanning tunneling spectroscopy measurements demonstrated that inside the band gap of CeO{sub 2-y} nanocrystals, besides the filled 4 f states, appeared additional states which were related to occupied and empty F center defect states. From the ellipsometric measurements, using the critical points model, the energy positions of different F centers states and the values of the reduced band gap energies were determined. The analysis of obtained data pointed out that depending on the synthesis method, different types of F centers (F{sup +} and F{sup 0}) can be formed in the CeO{sub 2-y} nanocrystals. The formation of different F center defect states inside the ceria gap have a strong impact on the electrical, optical, and magnetic properties of ceria nanocrystals.

  16. Nuclear data needs and sensitivities for illicit substance detection using fast-neutron transmission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Micklich, B.J.; Harper, M.K.; Sagalovsky, L.; Smith, D.L.

    1994-05-01

    Results from analysis of fast-neutron transmission spectra in the interrogation of luggage for illicit substances are quite sensitive to the neutron total cross section data employed. Monte Carlo and analytical techniques are used to explore the uses for such data and to demonstrate the sensitivity of these results to various total cross sections employed in the analysis. The status of total cross section information required for materials commonly found in containers having both illicit and benign substances, with particular attention to the matter of data uncertainties, is considered in the context of the available nuclear data. Deficiencies in the contemporary nuclear data base for this application are indicated and suggestions are offered for new measurements or evaluations.

  17. Anomalous thermal decoherence in a quantum magnet measured with neutron spin echo spectroscopy

    Science.gov (United States)

    Groitl, F.; Keller, T.; Rolfs, K.; Tennant, D. A.; Habicht, K.

    2016-04-01

    The effect of temperature dependent asymmetric line broadening is investigated in Cu (NO3)2.2.5 D2O , a model material for a one-dimensional bond alternating Heisenberg chain, using the high resolution neutron-resonance spin echo (NRSE) technique. Inelastic neutron scattering experiments on dispersive excitations including phase sensitive measurements demonstrate the potential of NRSE to resolve line shapes, which are non-Lorentzian, opening up a new and hitherto unexplored class of experiments for the NRSE method beyond standard linewidth measurements. The particular advantage of NRSE is its direct access to the correlations in the time domain without convolution with the resolution function of the background spectrometer. This application of NRSE is very promising and establishes a basis for further experiments on different systems, since the results for Cu(NO3)2. 2.5 D2O are applicable to a broad range of quantum systems.

  18. Structural features of membrane-bound glucocerebrosidase and α-synuclein probed by neutron reflectometry and fluorescence spectroscopy.

    Science.gov (United States)

    Yap, Thai Leong; Jiang, Zhiping; Heinrich, Frank; Gruschus, James M; Pfefferkorn, Candace M; Barros, Marilia; Curtis, Joseph E; Sidransky, Ellen; Lee, Jennifer C

    2015-01-01

    Mutations in glucocerebrosidase (GCase), the enzyme deficient in Gaucher disease, are a common genetic risk factor for the development of Parkinson disease and related disorders, implicating the role of this lysosomal hydrolase in the disease etiology. A specific physical interaction exists between the Parkinson disease-related protein α-synuclein (α-syn) and GCase both in solution and on the lipid membrane, resulting in efficient enzyme inhibition. Here, neutron reflectometry was employed as a first direct structural characterization of GCase and α-syn·GCase complex on a sparsely-tethered lipid bilayer, revealing the orientation of the membrane-bound GCase. GCase binds to and partially inserts into the bilayer with its active site most likely lying just above the membrane-water interface. The interaction was further characterized by intrinsic Trp fluorescence, circular dichroism, and surface plasmon resonance spectroscopy. Both Trp fluorescence and neutron reflectometry results suggest a rearrangement of loops surrounding the catalytic site, where they extend into the hydrocarbon chain region of the outer leaflet. Taking advantage of contrasting neutron scattering length densities, the use of deuterated α-syn versus protiated GCase showed a large change in the membrane-bound structure of α-syn in the complex. We propose a model of α-syn·GCase on the membrane, providing structural insights into inhibition of GCase by α-syn. The interaction displaces GCase away from the membrane, possibly impeding substrate access and perturbing the active site. GCase greatly alters membrane-bound α-syn, moving helical residues away from the bilayer, which could impact the degradation of α-syn in the lysosome where these two proteins interact.

  19. Structural Features of Membrane-bound Glucocerebrosidase and α-Synuclein Probed by Neutron Reflectometry and Fluorescence Spectroscopy*

    Science.gov (United States)

    Yap, Thai Leong; Jiang, Zhiping; Heinrich, Frank; Gruschus, James M.; Pfefferkorn, Candace M.; Barros, Marilia; Curtis, Joseph E.; Sidransky, Ellen; Lee, Jennifer C.

    2015-01-01

    Mutations in glucocerebrosidase (GCase), the enzyme deficient in Gaucher disease, are a common genetic risk factor for the development of Parkinson disease and related disorders, implicating the role of this lysosomal hydrolase in the disease etiology. A specific physical interaction exists between the Parkinson disease-related protein α-synuclein (α-syn) and GCase both in solution and on the lipid membrane, resulting in efficient enzyme inhibition. Here, neutron reflectometry was employed as a first direct structural characterization of GCase and α-syn·GCase complex on a sparsely-tethered lipid bilayer, revealing the orientation of the membrane-bound GCase. GCase binds to and partially inserts into the bilayer with its active site most likely lying just above the membrane-water interface. The interaction was further characterized by intrinsic Trp fluorescence, circular dichroism, and surface plasmon resonance spectroscopy. Both Trp fluorescence and neutron reflectometry results suggest a rearrangement of loops surrounding the catalytic site, where they extend into the hydrocarbon chain region of the outer leaflet. Taking advantage of contrasting neutron scattering length densities, the use of deuterated α-syn versus protiated GCase showed a large change in the membrane-bound structure of α-syn in the complex. We propose a model of α-syn·GCase on the membrane, providing structural insights into inhibition of GCase by α-syn. The interaction displaces GCase away from the membrane, possibly impeding substrate access and perturbing the active site. GCase greatly alters membrane-bound α-syn, moving helical residues away from the bilayer, which could impact the degradation of α-syn in the lysosome where these two proteins interact. PMID:25429104

  20. Single-neutron orbits near 78Ni: Spectroscopy of the N=49 isotope 79Zn

    Directory of Open Access Journals (Sweden)

    R. Orlandi

    2015-01-01

    Full Text Available Single-neutron states in the Z=30, N=49 isotope 79Zn have been populated using the 78Zn(d, p79Zn transfer reaction at REX-ISOLDE, CERN. The experimental setup allowed the combined detection of protons ejected in the reaction, and of γ rays emitted by 79Zn. The analysis reveals that the lowest excited states populated in the reaction lie at approximately 1 MeV of excitation, and involve neutron orbits above the N=50 shell gap. From the analysis of γ-ray data and of proton angular distributions, characteristic of the amount of angular momentum transferred, a 5/2+ configuration was assigned to a state at 983 keV. Comparison with large-scale-shell-model calculations supports a robust neutron N=50 shell-closure for 78Ni. These data constitute an important step towards the understanding of the magicity of 78Ni and of the structure of nuclei in the region.

  1. Spectroscopy of $^{46}$Ar by the (t,p) two-neutron transfer reaction

    CERN Document Server

    Nowak, K.; Hellgartner, S.; Mücher, D.; Bildstein, V.; Diriken, J.; Elseviers, J.; Gaffney, L.P.; Gernhäuser, R.; Iwanicki, J.; Johansen, J.G.; Huyse, M.; Konki, J.; Kröll, T.; Krücken, T.; Lutter, R.; Orlandi, R.; Pakarinen, J.; Raabe, R.; Reiter, P.; Roger, T.; Schrieder, G.; Seidlitz, M.; Sorlin, O.; Van Duppen, P.; Warr, N.; De Witte, H.; Zielinska, M.

    2016-01-01

    States in the $N=28$ nucleus $^{46}$Ar have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive $^{44}$ at an energy of 2.16~AMeV and a tritium loaded titanium target were used to populate $^{46}$ by the t($^{44}$,p) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of states in $^{46}$ have been reconstructed from the measured angles and energies of recoil protons. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695~keV has been identified as $J^\\pi = 0^+$. The angular differential cross section for the population of different states are compared to calculations using a reaction model employing both sequential and direct transfer of two neutrons. Results are compared to shell model calculations using state-of-the-art effective interactions.

  2. Neutron-rich polonium isotopes studied with in-source laser spectroscopy

    CERN Document Server

    Dexters, Wim; Cocolios, T E

    This work studies the unknown region of neutron rich polonium isotopes. The polonium isotopes, with Z=84, lie above the magic lead nuclei (Z=82). The motivation for this research can mainly be found in these lead nuclei. When looking at the changes in the mean square charge radii beyond the N=126 shell gap, a kink is observed. This kink is also found in the radon (Z=86) and radium (Z=88) isotopes. The observed effect cannot be reproduced with our current models. The polonium isotopes yield more information on the kink and they are also able to link the known charge radii in lead isotopes to those in radon and radium. Additionally, the nuclear moments of the odd-neutron isotope $^{211}$Po are investigated. This nucleus has two protons and one neutron more than the doubly magic nucleus $^{208}$Pb. Nuclear moments of isotopes close to this doubly magic nucleus are good tests for the theoretic models. Besides pushing the models to their limits, the nuclear moments of $^{211}$Po also yield new information on the f...

  3. Spherical neutron polarimetry applied to spin-echo and time-of-flight spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lelievre-Berna, E., E-mail: lelievre@ill.e [Institut Laue Langevin (ILL), 6 rue Jules Horowitz, 38042 Grenoble Cedex 9 (France); Bentley, P.; Bourgeat-Lami, E.; Thomas, M. [Institut Laue Langevin (ILL), 6 rue Jules Horowitz, 38042 Grenoble Cedex 9 (France); Pappas, C. [Helmholtz Centre Berlin for Materials and Energy (HCB), Glienickerstr. 100, 14109 Berlin (Germany); Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); Kischnik, R.; Moskvin, E. [Helmholtz Centre Berlin for Materials and Energy (HCB), Glienickerstr. 100, 14109 Berlin (Germany)

    2009-09-01

    The changes in direction of the neutron spin that take place on scattering by a magnetic interaction vector are highly dependent on their relative directions. In some circumstances, without zero-field polarimeter, it is impossible to distinguish between a simple depolarisation and a rotation of the polarisation vector. Motivated by the investigation of chiral magnetic fluctuations, we have implemented the third-generation zero-field polarimeter Cryopad on the neutron spin-echo spectrometer SPAN at the Helmholtz Centre Berlin (HCB). We present the method and the limitations of this novel technique that is now available on IN15 at the ILL. The huge progress accomplished with {sup 3}He neutron spin filters/flippers are going to facilitate the exploitation of polarised beams at spallation sources. Zero-field polarimeters like Cryopad are used routinely at several steady-state sources but their design would be inefficient at a pulse source. We have investigated the possibility to implement a zero-field polarimeter on a time-of-flight spectrometer. We propose a design that would lead to a better efficiency and present the finite element calculations.

  4. Laser-assisted decay and optical spectroscopy studies of neutron-deficient thallium isotopes

    CERN Document Server

    Van Beveren, Céline; Huyse, Mark

    The neutron-deficient thallium isotopes with one proton less than the Z = 82 shell closure, are situated in an interesting region of the nuclear chart, notorious for intruder states and shape coexistence. Shape coexistence is the remarkable phenomenon in which two or more distinct types of deformation occur at low energy in the same atomic nucleus. Shape coexistence has been studied intensively, experimentally as well as theoretically in different nuclei in the light-lead region and the isomerism in the thallium isotopes was among the first indications of this phenomenon. Different shapes, whose structure has been linked to specific proton orbitals above and below the Z = 82 shell closure, are present at low energy in the neutron-deficient odd-mass thallium nuclei. In the odd-odd nuclei, the coupling of an unpaired proton and unpaired neutron gives rise to multiplets of low-lying states from which some can be isomeric. Since thallium has one proton missing in the major proton shell, and when approaching neutr...

  5. Evaluation of trace elements in chewing tobacco and snuff using instrumental neutron activation analysis (INAA) and atomic absorption spectroscopy (AAS)

    Energy Technology Data Exchange (ETDEWEB)

    Waheed, S.; Siddique, N.; Rahman, S. [Chemistry Div., Directorate of Science, Pakistan Inst. of Nuclear Science and Tech., Islamabad (Pakistan)

    2009-07-01

    Nine samples of chewing tobacco, snuff, tobacco leaf and ash were analyzed using Instrumental Neutron Activation Analysis (INAA) and Atomic Absorption Spectroscopy (AAS). Almost all samples of chewing tobacco and snuff studied in this work contain substantial amounts of Mg, Mn, Na, K. V. Sc, Rb and Fe. Furthermore, varying amounts of Al, Ba, Ca, Ce, Co and Zn were also detected in all tobacco samples. Of the toxic elements which were determined using INAA. As, Sb and Hg were quantified in only few tobacco samples. However, other toxic elements, which were determined using AAS, such as Cu, Pb and Cd were detected in almost all samples of chewing tobacco and snuff. The concentration of majority of the detected elements is high in ash samples which imply that most elements in chewing tobacco and snuff may originate from the addition of ash. (orig.)

  6. Magneto-tunnelling spectroscopy for spatial mapping of orbital wavefunctions of the ground and excited electronic states in self-assembled quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Levin, A.; Vdovin, E.E.; Patane, A.; Eaves, L.; Main, P.C.; Dubrovskii, Yu.V.; Henini, M. [Nnottingham Univ. (United Kingdom). School of Physics and Astronomy; Khanin, Yu.N. [Rossijskaya Akademiya Nauk, Chernogolovka (Russian Federation). Inst. of Microelectronics Technology; Hill, G. [Sheffield Univ. (United Kingdom). Dept. of Electronic and Electrical Engineering

    2001-04-01

    We present an experimental study of electron wavefunctions in InAs/GaAs self-assembled quantum dots (QDs). Magneto-tunnelling spectroscopy is employed as a non-invasive probe to produce two-dimensional images of the probability density of an electron confined in a quantum dot. The images reveal clearly the elliptical symmetry of the ground state and the characteristic lobes of the higher energy states of the dots. We use the technique to compare the symmetry properties of the electron wavefunctions in QDs grown on (100)- and (311)B-oriented GaAs substrates. (orig.)

  7. Study of deep level characteristics in the neutrons irradiated Si structures by combining pulsed and steady-state spectroscopy techniques

    Science.gov (United States)

    Gaubas, E.; Kalendra, V.; Ceponis, T.; Uleckas, A.; Tekorius, A.; Vaitkus, J.; Velicka, A.

    2012-11-01

    The standard methods, such as capacitance deep level transient spectroscopy (C-DLTS) and thermally stimulated current (TSC) techniques are unsuitable for the analysis of heavily irradiated devices. In this work, therefore, several steady-state and pulsed techniques have been combined to comprehensively evaluate parameters of radiation defects and functional characteristics of the irradiated Si pin detectors. In order to understand defects created by radiation and evaluate their evolution with fluence, C-DLTS and TSC techniques have been employed to make a baseline identification of the radiation induced traps after irradiation with a rather small neutron fluence of 1012 cm-2. The steady-state photo-ionization spectroscopy (PIS) technique has been involved to correlate thermal- and photo- activation energies for definite radiation defects. A contactless technique for simultaneous measurements of the carrier lifetime and the parameters of deep levels based on microwave probed pulsed photo-conductivity (MW-PC) spectroscopy has been applied to correlate carrier capture cross-sections and densities of the identified different radiation defects. A technique for spectroscopy of deep levels in junction structures (BELIV) based on measurements of barrier capacitance charging current transient changes due to additional spectrally resolved pulsed illumination has been applied to evaluate the functional characteristics of the irradiated diodes. Pulsed spectroscopic measurements were implemented by combining the analysis of generation current and of barrier capacitance charging transients modified by a single fs pulse of illumination generated by an optical parametric oscillator of varied wavelength in the range from 0.5 to 10 μm. Several deep levels with activation energy in the range of 0.18-0.8 eV have been resolved from spectral analysis in the samples of Si grown by magnetic field applied Czochralski (MCz) technology.

  8. Detection of explosive substances by tomographic inspection using neutron and gamma-ray spectroscopy

    Science.gov (United States)

    Farahmand, M.; Boston, A. J.; Grint, A. N.; Nolan, P. J.; Joyce, M. J.; Mackin, R. O.; D'Mellow, B.; Aspinall, M.; Peyton, A. J.; van Silfhout, R.

    2007-08-01

    In recent years the detection and identification of hazardous materials has become increasingly important. This work discusses research and development of a technique which is capable of detecting and imaging hidden explosives. It is proposed to utilise neutron interrogation of the substances under investigation facilitating the detection of emitted gamma radiation and scattered neutrons. Pulsed fast neutron techniques are attractive because they can be used to determine the concentrations of the light elements (hydrogen, carbon, nitrogen, and oxygen) which can be the primary components of explosive materials. Using segmented High Purity Ge (HPGe) detectors and digital pulse processing [R.J. Cooper, G. Turk, A.J. Boston, H.C. Boston, J.R. Cresswell, A.R. Mather, P.J. Nolan, C.J. Hall, I. Lazarus, J. Simpson, A. Berry, T. Beveridge, J. Gillam, R.A. Lewis, in: Proceedings of the 7th International Conference on Position Sensitive Detectors, Nuclear Instruments and Methods A, in press; I. Lazarus, D.E. Appelbe, A. J. Boston, P.J. Coleman-Smith, J.R. Cresswell, M. Descovich, S.A.A. Gros, M. Lauer, J. Norman, C.J. Pearson, V.F.E. Pucknell, J.A. Sampson, G. Turk, J.J. Valiente-Dobón, IEEE Trans. Nucl. Sci., 51 (2004) 1353; R.J. Cooper, A.J. Boston, H.C. Boston, J.R. Cresswell, A.N. Grint, A.R. Mather, P.J. Nolan, D.P. Scraggs, G. Turk, C.J. Hall, I. Lazarus, A. Berry, T. Beveridge, J. Gillam, R.A. Lewis, in: Proceedings of the 11th International Symposium on Radiation Measurements and Application, 2006. [1-3

  9. Crystalline Electric Field Levels in the Neodymium Monopnictides Determined by Neutron Spectroscopy

    DEFF Research Database (Denmark)

    Furrer, A.; Kjems, Jørgen; Vogt, O.

    1972-01-01

    Neutron inelastic scattering experiments have been carried out to determine the energies and widths of the crystalline electric field levels in the neodymium monopnictides NdP, NdAs, and NdSb. The energy level sequence is derived from the observed crystal field transition peak intensities, which...... are in good agreement with calculations based on elementary crystal field theory. The energy level widths are qualitatively discussed. It is found that the point-charge model cannot reproduce the crystal field levels satisfactorily....

  10. The CARDS array for neutron-rich decay spectroscopy at HRIBF

    CERN Document Server

    Batchelder, J C; Bingham, C R; Carter, H K; Cole, J D; Fong, D; Garrett, P E; Grzywacz, R; Hamilton, J H; Hartley, D J; Hwang, J K; Krolas, W; Kulp, D C; Larochelle, Y; Piechaczek, A; Ramayya, A V; Rykaczewski, K; Spejewski, E H; Stracener, D W; Tantawy, M N; Winger, J A; Wood, J; Zganjar, E F

    2003-01-01

    An array for decay studies of neutron-rich nuclei has been commissioned for use at the UNISOR separator at Holifield Radioactive Ion Beam Facility. This array consists of three segmented clover Ge detectors, plastic scintillators, and a high-resolution (approx 1 keV) Si conversion electron spectrometer. These detectors are mounted on a support that surrounds a moving tape collector. This system has been named clover array for radioactive decay studies. The detectors have been outfitted with digital flash ADCs (XIA DGFs) that fit the preamp signals, with built-in pileup rejection.

  11. From BASIS to MIRACLES: Benchmarking and perspectives for high-resolution neutron spectroscopy at the ESS

    Science.gov (United States)

    Tsapatsaris, Nikolaos; Willendrup, Peter K.; Lechner, Ruep E.; Bordallo, Heloisa N.

    2015-01-01

    Results based on virtual instrument models for the first high-flux, high-resolution, spallation based, backscattering spectrometer, BASIS are presented in this paper. These were verified using the Monte Carlo instrument simulation packages McStas and VITESS. Excellent agreement of the neutron count rate at the sample position between the virtual instrument simulation and experiments was found, in both time and energy distributions. This achievement was only possible after a new component for a bent single crystal analyser in McStas, using a Gaussian approximation, was developed. These findings are pivotal to the conceptual design of the next generation backscattering spectrometer, MIRACLES at the European Spallation Source.

  12. New perspectives on neutron star and black hole spectroscopy and dynamic tides

    CERN Document Server

    Chakrabarti, Sayan; Steinhoff, Jan

    2013-01-01

    We elaborate on a powerful tidal interaction formalism where the multipole dynamics is kept generic and encoded in a linear response function. This response function is the gravitational counterpart of the atomic spectrum and can become of similar importance with the rise of gravitational wave astronomy. We find that the internal dynamics of nonrotating neutron stars admit a harmonic oscillator formulation yielding a simple interpretation of tides. A preliminary investigation of the black holes case is given. Our results fill the gap between Love numbers and dynamic tides.

  13. Spins, charge radii and magnetic moments of neutron-rich Mn isotopes measured with bunched beam Collinear Laser Spectroscopy

    CERN Document Server

    AUTHOR|(CDS)2085887; Heylen, Hanne

    In this work, the odd-even $^{51–63}$Mn isotopes have been analyzed using collinear laser spectroscopy, from which the magnetic dipole moment and the change in change in mean square charge radius can be determined. The magnetic moment is very sensitive to the composition of the total nuclear wave function, while the charge radius gives information about the relative size and degree of deformation of the nucleus. An additional advantage of collinear laser spectroscopy is the possibility of direct measurement of the nuclear spin. The main motivation behind the study of these isotopes is to investigate the change in nuclear structure when approaching neutron number N = 40. This region is of interest due to the apparent doubly magic nature of $^{68}$Ni , which is not seen in the N = 40 isotopes of $^{26}$Fe and $^{24}$Cr. Mn, situated between these elements, offers another perspective due to its uncoupled proton. Based on the observed spectra and extracted moments, spins were assigned to $^{59,61,63}$Mn. The ex...

  14. Spectroscopy of F26 to Probe Proton-Neutron Forces Close to the Drip Line

    Science.gov (United States)

    Lepailleur, A.; Sorlin, O.; Caceres, L.; Bastin, B.; Borcea, C.; Borcea, R.; Brown, B. A.; Gaudefroy, L.; Grévy, S.; Grinyer, G. F.; Hagen, G.; Hjorth-Jensen, M.; Jansen, G. R.; Llidoo, O.; Negoita, F.; de Oliveira, F.; Porquet, M.-G.; Rotaru, F.; Saint-Laurent, M.-G.; Sohler, D.; Stanoiu, M.; Thomas, J. C.

    2013-02-01

    A long-lived Jπ=41+ isomer, T1/2=2.2(1)ms, has been discovered at 643.4(1) keV in the weakly bound F926 nucleus. It was populated at Grand Accélérateur National d’Ions Lourds in the fragmentation of a S36 beam. It decays by an internal transition to the Jπ=11+ ground state [82(14)%], by β decay to Ne26, or β-delayed neutron emission to Ne25. From the β-decay studies of the Jπ=11+ and Jπ=41+ states, new excited states have been discovered in Ne25,26. Gathering the measured binding energies of the Jπ=11+-41+ multiplet in F926, we find that the proton-neutron π0d5/2ν0d3/2 effective force used in shell-model calculations should be reduced to properly account for the weak binding of F926. Microscopic coupled cluster theory calculations using interactions derived from chiral effective field theory are in very good agreement with the energy of the low-lying 11+, 21+, 41+ states in F26. Including three-body forces and coupling to the continuum effects improve the agreement between experiment and theory as compared to the use of two-body forces only.

  15. Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces; Rastertunnelmikroskopie und -spektroskopie an GaN- und InGaN-Oberflaechen

    Energy Technology Data Exchange (ETDEWEB)

    Krueger, David

    2009-12-02

    Optelectronic devices based on gallium nitride (GaN) and indium gallium nitride (InGaN) are in the focus of research since more than 20 years and still have great potential for optical applications. In the first part of this work non-polar surfaces of GaN are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). In SEM and AFM, the (1 anti 100)- and especially the (anti 2110)-plane are quite corrugated. For the first time, the (anti 2110)-plane of GaN is atomically resolved in STM. In the second part InGaN quantum dot layers are investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and STM. The STMmeasurements show the dependency of surface morphology on growth conditions in the metalorganic vapour phase epitaxy (MOVPE). Nucleation, a new MOVPE-strategy, is based on phase separations on surfaces. It is shown that locally varying density of states and bandgaps can be detected by STS, that means bandgap histograms and 2D-bandgap-mapping. (orig.)

  16. Noise spectroscopy of CoFeB/MgO/CoFeB magnetic tunnel junctions in the presence of thermal gradients

    Energy Technology Data Exchange (ETDEWEB)

    Liebing, N. [Physikalisch-Technische Bundesanstalt, Bundesallee 100, d-38116 Braunschweig (Germany); Serrano-Guisan, S., E-mail: santiago.serrano-guisan@inl.int [International Iberian Nanotechnology Laboratory, Avenida Mestre Jose Veiga, 4715-330 Braga (Portugal); Rott, K.; Reiss, G. [University of Bielefeld, Department of Physics, Univesitätesstr. 25, d-33615 Bielefeld (Germany); Schumacher, H.W., E-mail: hans.w.schumacher@ptb.de [Physikalisch-Technische Bundesanstalt, Bundesallee 100, d-38116 Braunschweig (Germany)

    2016-02-15

    We present experimental data of the precessional dynamics of the free layer of CoFeB/MgO/CoFeB based magnetic tunnel junctions (MTJ) in the presence of thermal gradients across the MTJ. The free layer precession is investigated by noise spectroscopy. Thermal gradients of the order of tens of mK/nm across the MTJ are generated by electrical heating. Without applied thermal gradients we find spin transfer torque modified magnetization precession. With increasing thermal gradients we generally observe a decrease of the precession frequency which could be related to an increasing overall free layer temperature. However an asymmetry of the line width behavior for parallel and antiparallel orientation points towards additional effects beyond thermal activation. This could be a hint for the modification of the precessional dynamics in magnetic tunnel junctions by thermal spin torques. - Highlights: • Thermal gradients induced magnetization dynamics on MTJ structures are explored. • Magnetic noise spectroscopy is carried out to study the efficiency of such effects. • A decrease of resonance frequency is observed at both MTJ states for large ∇T. • An asymmetric linewidth behavior is observed for both MTJ states under ∇T. • Additional thermal effects beyond thermal activation must be considered.

  17. Origin of magnetic contrast in spin-polarized scanning tunneling spectroscopy. Experiments on ultra-thin Mn films

    CERN Document Server

    Yamada, T K; Heijnen, G M M; Kempen, H V; Mizoguchi, T

    2003-01-01

    Normalized differential tunneling conductivities obtained with Fe-coated W tips show a spin-polarized peak around +0.8 V on ultrathin bct Mn films grown on Fe(001)-whiskers. This spin-polarized peak results in a clear magnetic contrast in spectroscopic images. Our normalization removes the influence of the tunneling probability and makes the spectroscopic curves most reliable for a derivation of the spin-resolved sample density of states (DOS) at positive voltages. From this analysis we conclude that the magnetic contrast in our spectroscopic maps is caused by a highly polarized DOS. Furthermore, a tip polarization of about 15% is found. (author)

  18. Study of some Ayurvedic Indian medicinal plants for the essential trace elemental contents by instrumental neutron activation analysis and atomic absorption spectroscopy techniques

    Energy Technology Data Exchange (ETDEWEB)

    Lokhande, R.S.; Singare, P.U.; Andhele, M.L. [Dept. of Chemistry, Univ. of Mumbai, Santacruz, Mumbai (India); Acharya, R.; Nair, A.G.C.; Reddy, A.V.R. [Radiochemistry Div., Bhabha Atomic Research Centre, Trombay, Mumbai (India)

    2009-07-01

    Elemental analysis of some medicinal plants used in the Indian Ayurvedic system was performed by employing instrumental neutron activation analysis (INAA) and atomic absorption spectroscopy (AAS) techniques. The samples were irradiated with thermal neutrons in a nuclear reactor and the induced activity was counted by gamma ray spectrometry using an efficiency calibrated high resolution high purity germanium (HPGe) detector. Most of the medicinal plants were found to be rich in one or more of the elements under study. The variation in elemental concentration in same medicinal plants samples collected in summer, winter and rainy seasons was studied and the biological effects of these elements on human beings are discussed. (orig.)

  19. Neutron spin echo spectroscopy under 17 T magnetic field at RESEDA

    Directory of Open Access Journals (Sweden)

    Kindervater J.

    2015-01-01

    Full Text Available We report proof-of-principle measurements at the neutron resonance spin echo spectrometer RESEDA (MLZ under large magnetic fields by means of Modulation of IntEnsity with Zero Effort (MIEZE. Our study demonstrates the feasibility of applying strong magnetic fields up to 17 T at the sample while maintaining unchanged sub-μeV resolution. We find that the MIEZE-spin-echo resolution curve remains essentially unchanged as a function of magnetic field up to the highest fields available, promising access to high fields without need for additional fine-tuning of the instrument. This sets the stage for the experimental investigations of subtle field dependent phenomena, such as magnetic field-driven phase transitions in hard and soft condensed matter physics.

  20. From BASIS to MIRACLES: Benchmarking and perspectives for high-resolution neutron spectroscopy at the ESS

    Directory of Open Access Journals (Sweden)

    Tsapatsaris Nikolaos

    2015-01-01

    Full Text Available Results based on virtual instrument models for the first high-flux, high-resolution, spallation based, backscattering spectrometer, BASIS are presented in this paper. These were verified using the Monte Carlo instrument simulation packages McStas and VITESS. Excellent agreement of the neutron count rate at the sample position between the virtual instrument simulation and experiments was found, in both time and energy distributions. This achievement was only possible after a new component for a bent single crystal analyser in McStas, using a Gaussian approximation, was developed. These findings are pivotal to the conceptual design of the next generation backscattering spectrometer, MIRACLES at the European Spallation Source.

  1. A theoretical analysis of the spin dynamics of magnetic adatoms traced by time-resolved scanning tunneling spectroscopy

    Science.gov (United States)

    Schüler, M.; Pavlyukh, Y.; Berakdar, J.

    2012-04-01

    Inelastic scanning tunneling microscopy (STM) has recently been shown (Loth et al 2010 Science 329 1628) to be extendable to access the nanosecond, spin-resolved dynamics of magnetic adatoms and molecules. Here we analyze this novel tool theoretically by considering the time-resolved spin dynamics of a single adsorbed Fe atom excited by a tunneling current pulse from a spin-polarized STM tip. The adatom spin configuration can be controlled and probed by applying voltage pulses between the substrate and the spin-polarized STM tip. We demonstrate how, in a pump-probe manner, the relaxation dynamics of the sample spin is manifested in the spin-dependent tunneling current. Our model calculations are based on the scattering theory in a wave-packet formulation. The scheme is non-perturbative and, hence, is valid for all voltages. The numerical results for the tunneling probability and the conductance are contrasted with the predictions of simple analytical models and compared with experiments.

  2. Timing and Spectroscopy Requirements for a Plastic Scintillating Fiber Bundle Time-of-Flight Neutron Spectrometer

    Science.gov (United States)

    2013-12-01

    flexibility, efficiency, timing, and position resolution in developing novel Compton camera detectors capable of detecting special nuclear material. 1.3...oscilloscope needs to be fast enough to resolve coincident pulse events on the picoseconds to nanosecond time scale. The final objective is to experimentally...Mirsaleh-Kohan, W. D. Nasrin, and R. N. Compton , “Electron ionization time-of-flight mass spectroscopy: Historical review and current applications

  3. Laser assisted nuclear decay spectroscopy: A new method for studying neutron-deficient francium

    CERN Document Server

    Lynch, Kara Marie

    2015-01-01

    Radioactive decay studies of rare isotopes produced at radioactive ion beam facilities have often been hindered by the presence of isobaric and isomeric contamination. The Collinear Resonance Ionization Spectroscopy (CRIS) experiment at ISOLDE, CERN uses laser radiation to stepwise excite and ionize an atomic beam in a particular isomeric state. Deflection of this selectively ionized beam of exotic nuclei, from the remaining neutral contaminants, allows ultra-sensitive detection of rare isotopes and nuclear structure measurements in background-free conditions.\

  4. Growth and structure of thin platinum films deposited on Co(0001) studied by low-energy electron diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and scanning tunneling microscopy

    Science.gov (United States)

    Cabeza, G. F.; Légaré, P.; Sadki, A.; Castellani, N. J.

    2000-06-01

    The growth of platinum deposited on Co(0001) at room temperature in the range of submonolayer coverage is described. The evolution of very thin Pt films has been studied using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and scanning tunneling microscopy (STM). The LEED patterns suggested a coherent epitaxial growth mode for Pt on Co(0001). Evidence for an island growth mode has been confirmed by STM together with step decoration. However, the second and third monolayers start growing before the completion of the first Pt layer. The electronic structure of the Pt deposits exhibited original properties with low Fermi level density of states and valence-band broadening. This is in agreement with theoretical calculations presented in this work.

  5. Shape coexistence in the N = 19 neutron-rich nucleus 31Mg explored by β-γ spectroscopy of spin-polarized 31Na

    Science.gov (United States)

    Nishibata, H.; Shimoda, T.; Odahara, A.; Morimoto, S.; Kanaya, S.; Yagi, A.; Kanaoka, H.; Pearson, M. R.; Levy, C. D. P.; Kimura, M.

    2017-04-01

    The structure of excited states in the neutron-rich nucleus 31Mg, which is in the region of the "island of inversion" associated with the neutron magic number N = 20, is studied by β-γ spectroscopy of spin-polarized 31Na. Among the 31Mg levels below the one neutron separation energy of 2.3 MeV, the spin values of all five positive-parity levels are unambiguously determined by observing the anisotropic β decay. Two rotational bands with Kπ = 1 /2+ and 1 /2- are proposed based on the spins and energies of the levels. Comparison on a level-by-level basis is performed between the experimental results and theoretical calculations by the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM). It is found that various nuclear structures coexist in the low excitation energy region in 31Mg.

  6. β-decay spectroscopy of neutron-rich 160,161,162Sm isotopes

    Science.gov (United States)

    Patel, Z.; Podolyák, Zs.; Walker, P. M.; Regan, P. H.; Söderström, P.-A.; Watanabe, H.; Ideguchi, E.; Simpson, G. S.; Nishimura, S.; Browne, F.; Doornenbal, P.; Lorusso, G.; Rice, S.; Sinclair, L.; Sumikama, T.; Wu, J.; Xu, Z. Y.; Aoi, N.; Baba, H.; Bello Garrote, F. L.; Benzoni, G.; Daido, R.; Dombrádi, Zs.; Fang, Y.; Fukuda, N.; Gey, G.; Go, S.; Gottardo, A.; Inabe, N.; Isobe, T.; Kameda, D.; Kobayashi, K.; Kobayashi, M.; Komatsubara, T.; Kojouharov, I.; Kubo, T.; Kurz, N.; Kuti, I.; Li, Z.; Liu, H. L.; Matsushita, M.; Michimasa, S.; Moon, C.-B.; Nishizuka, H.; Nishizuka, I.; Odahara, A.; Şahin, E.; Sakurai, H.; Schaffner, H.; Suzuki, H.; Takeda, H.; Tanaka, M.; Taprogge, J.; Vajta, Zs.; Xu, F. R.; Yagi, A.; Yokoyama, R.

    2016-09-01

    Neutron-rich 160,161,162Sm isotopes have been populated at the RIBF, RIKEN via β first time. β-coincident γ rays were observed in all three isotopes including γ rays from the isomeric decay of 160Sm and 162Sm. The isomers in 160Sm and 162Sm have previously been observed but have been populated via β decay for the first time. The isomeric state in 162Sm is assigned a {4^ - }v{{7 over 2}^ + }≤ft[ {633} right] otimes v{{1 over 2}^ - }≤ft[ {521} right] configuration based on the decay pattern. The level schemes of 160Sm and 162Sm are presented. The ground states in the parent nuclei 160Pm and 162Pm are both assigned a {6^ - }v{{7 over 2}^ + }≤ft[ {633} right] otimes π {{5 over 2}^ - }≤ft[ {532} right] configuration based on the population of states in the daughter nuclei. Blocked BCS calculations were performed to further investigate the spin-parities of the ground states in 160Pm, 161Pm, and 162Pm, and the isomeric state in 162Sm

  7. Isomer-delayed gamma-ray spectroscopy of neutron-rich 166Tb

    Science.gov (United States)

    Gurgi, L. A.; Regan, P. H.; Söderström, P.-A.; Watanabe, H.; Walker, P. M.; Podolyák, Zs.; Nishimura, S.; Berry, T. A.; Doornenbal, P.; Lorusso, G.; Isobe, T.; Baba, H.; Xu, Z. Y.; Sakurai, H.; Sumikama, T.; Catford, W. N.; Bruce, A. M.; Browne, F.; Lane, G. J.; Kondev, F. G.; Odahara, A.; Wu, J.; Liu, H. L.; Xu, F. R.; Korkulu, Z.; Lee, P.; Liu, J. J.; Phong, V. H.; Yagi, A.; Zhang, G. X.; Alharbi, T.; Carroll, R. J.; Chae, K. Y.; Dombradi, Zs.; Estrade, A.; Fukuda, N.; Griffin, C.; Ideguchi, E.; Inabe, N.; Kanaoka, H.; Kojouharov, I.; Kubo, T.; Kubono, S.; Kurz, N.; Kuti, I.; Lalkovski, S.; Lee, E. J.; Lee, C. S.; Lotay, G.; Moon, C. B.; Nishizuka, I.; Nita, C. R.; Patel, Z.; Roberts, O. J.; Schaffner, H.; Shand, C. M.; Suzuki, H.; Takeda, H.; Terashima, S.; Vajta, Zs.; Kanaya, S.; Valiente-Dobòn, J. J.

    2017-09-01

    This short paper presents the identification of a metastable, isomeric-state decay in the neutron-rich odd-odd, prolate-deformed nucleus 166Tb. The nucleus of interest was formed using the in-flight fission of a 345 MeV per nucleon 238U primary beam at the RIBF facility, RIKEN, Japan. Gamma-ray transitions decaying from the observed isomeric states in 166Tb were identified using the EURICA gamma-ray spectrometer, positioned at the final focus of the BigRIPS fragments separator. The current work identifies a single discrete gamma-ray transition of energy 119 keV which de-excites an isomeric state in 166Tb with a measured half-life of 3.5(4) μs. The multipolarity assignment for this transition is an electric dipole and is made on the basis internal conversion and decay lifetime arguments. Possible two quasi-particle Nilsson configurations for the initial and final states which are linked by this transition in 166Tb are made on the basis of comparison with Blocked BCS Nilsson calculations, with the predicted ground state configuration for this nucleus arising from the coupling of the v(1-/2)?[521] and ? π(3+/2) Nilsson orbitals.

  8. β-decay spectroscopy of neutron-rich 160,161,162Sm isotopes

    Directory of Open Access Journals (Sweden)

    Patel Z.

    2016-01-01

    Full Text Available Neutron-rich 160,161,162Sm isotopes have been populated at the RIBF, RIKEN via β first time. β-coincident γ rays were observed in all three isotopes including γ rays from the isomeric decay of 160Sm and 162Sm. The isomers in 160Sm and 162Sm have previously been observed but have been populated via β decay for the first time. The isomeric state in 162Sm is assigned a 4−v72+[ 633 ]⊗v12−[ 521 ]${4^ - }v{{7 \\over 2}^ + }\\left[ {633} \\right] \\otimes v{{1 \\over 2}^ - }\\left[ {521} \\right]$ configuration based on the decay pattern. The level schemes of 160Sm and 162Sm are presented. The ground states in the parent nuclei 160Pm and 162Pm are both assigned a 6−v72+[633]⊗π52−[532]${6^ - }v{{7 \\over 2}^ + }\\left[ {633} \\right] \\otimes \\pi {{5 \\over 2}^ - }\\left[ {532} \\right]$ configuration based on the population of states in the daughter nuclei. Blocked BCS calculations were performed to further investigate the spin-parities of the ground states in 160Pm, 161Pm, and 162Pm, and the isomeric state in 162Sm

  9. Polymorphic drugs examined with neutron spectroscopy: Is making more stable forms really that simple?

    DEFF Research Database (Denmark)

    Tsapatsaris, Nikolaos; Landsgesell, Sven; Koza, Michael Marek;

    2013-01-01

    Understanding  polymorphism  in  pharmaceutical  ingredients  is  a   long-­  standing  challenge.  A  well-­known  example  is  paracetamol,  C8H9NO2.   The  marketed  stable  form  I  crystallizes  with  corrugated  molecular  layers.   In  contrast,  form  II,  which  is  thermodynamically......  favorable  at  high   pressures,  has  relatively  planar  layers  that  can  slip  over  each  other   without  difficulty,    is  metastable  at  ambient  conditions.  By  means  of   inelastic  neutron  scattering  we  demonstrated  that  the  lattice  modes  of   form  II  exhibit  a  sudden  1  me...

  10. Neutron spectroscopy study of single-walled carbon nanotubes hydrogenated under high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Kolesnikov, A.I. [IPNS, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 (United States)], E-mail: akolesnikov@anl.gov; Bashkin, I.O.; Antonov, V.E. [Institute of Solid State Physics RAS, 142432 Chernogolovka, Moscow District (Russian Federation); Colognesi, D. [Consiglio Nazionale delle Ricerche, Istituto di Fisica Applicata ' Nello Carrara' , via Madonna del Piano, 50019 Sesto Fiorentino (Italy); Mayers, J. [ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX (United Kingdom); Moravsky, A.P. [MER Corporation, 7960, South Kolb Road, Tucson, AZ 85706 (United States)

    2007-10-31

    Single-walled carbon nanotubes (SWNT) were loaded with 5.2 wt% hydrogen at a hydrogen pressure of 3 GPa and T = 620 K, quenched to 80 K and studied at ambient pressure and 15 K by inelastic neutron scattering (INS) in the range of energy transfers 3-400 meV. An analysis of the measured INS spectra showed that the quenched SWNT and H sample contained hydrogen in two different forms, as H atoms covalently bound to the carbon atoms ({approx}4.7 wt%) and as H{sub 2} molecules ({approx}0.5 wt%) exhibiting nearly free rotational behavior. Annealing the sample in vacuum at 332 K removed about 65% of the H{sub 2} molecules and annealing at 623 K removed all of them. This demonstrates that H{sub 2} molecules were kept in this sample more tightly than in earlier studied SWNT and H samples that were hydrogenated at lower pressures and temperatures and lost all molecular hydrogen on heating in vacuum to room temperature.

  11. Neutron irradiation damage of nuclear graphite studied by high-resolution transmission electron microscopy and Raman spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Krishna, R. [Dalton Cumbrian Facility, Dalton Nuclear Institute, The University of Manchester, Westlakes Science & Technology Park, Moor Row, Whitehaven, Cumbria, CA24 3HA (United Kingdom); Jones, A.N., E-mail: Abbie.Jones@manchester.ac.uk [Nuclear Graphite Research Group, School of MACE, The University of Manchester, Manchester, M13 9PL (United Kingdom); McDermott, L.; Marsden, B.J. [Nuclear Graphite Research Group, School of MACE, The University of Manchester, Manchester, M13 9PL (United Kingdom)

    2015-12-15

    Nuclear graphite components are produced from polycrystalline artificial graphite manufacture from a binder and filler coke with approximately 20% porosity. During the operational lifetime, nuclear graphite moderator components are subjected to fast neutron irradiation which contributes to the change of material and physical properties such as thermal expansion co-efficient, young's modulus and dimensional change. These changes are directly driven by irradiation-induced changes to the crystal structure as reflected through the bulk microstructure. It is therefore of critical importance that these irradiation changes and there implication on component property changes are fully understood. This work examines a range of irradiated graphite samples removed from the British Experimental Pile Zero (BEPO) reactor; a low temperature, low fluence, air-cooled Materials Test Reactor which operated in the UK. Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) have been employed to characterise the effect of increased irradiation fluence on graphite microstructure and understand low temperature irradiation damage processes. HRTEM confirms the structural damage of the crystal lattice caused by irradiation attributed to a high number of defects generation with the accumulation of dislocation interactions at nano-scale range. Irradiation-induced crystal defects, lattice parameters and crystallite size compared to virgin nuclear graphite are characterised using selected area diffraction (SAD) patterns in TEM and Raman Spectroscopy. The consolidated ‘D’peak in the Raman spectra confirms the formation of in-plane point defects and reflected as disordered regions in the lattice. The reduced intensity and broadened peaks of ‘G’ and ‘D’ in the Raman and HRTEM results confirm the appearance of turbulence and disordering of the basal planes whilst maintaining their coherent layered graphite structure. - Highlights: • Irradiated graphite

  12. Neutron irradiation damage of nuclear graphite studied by high-resolution transmission electron microscopy and Raman spectroscopy

    Science.gov (United States)

    Krishna, R.; Jones, A. N.; McDermott, L.; Marsden, B. J.

    2015-12-01

    Nuclear graphite components are produced from polycrystalline artificial graphite manufacture from a binder and filler coke with approximately 20% porosity. During the operational lifetime, nuclear graphite moderator components are subjected to fast neutron irradiation which contributes to the change of material and physical properties such as thermal expansion co-efficient, young's modulus and dimensional change. These changes are directly driven by irradiation-induced changes to the crystal structure as reflected through the bulk microstructure. It is therefore of critical importance that these irradiation changes and there implication on component property changes are fully understood. This work examines a range of irradiated graphite samples removed from the British Experimental Pile Zero (BEPO) reactor; a low temperature, low fluence, air-cooled Materials Test Reactor which operated in the UK. Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) have been employed to characterise the effect of increased irradiation fluence on graphite microstructure and understand low temperature irradiation damage processes. HRTEM confirms the structural damage of the crystal lattice caused by irradiation attributed to a high number of defects generation with the accumulation of dislocation interactions at nano-scale range. Irradiation-induced crystal defects, lattice parameters and crystallite size compared to virgin nuclear graphite are characterised using selected area diffraction (SAD) patterns in TEM and Raman Spectroscopy. The consolidated 'D'peak in the Raman spectra confirms the formation of in-plane point defects and reflected as disordered regions in the lattice. The reduced intensity and broadened peaks of 'G' and 'D' in the Raman and HRTEM results confirm the appearance of turbulence and disordering of the basal planes whilst maintaining their coherent layered graphite structure.

  13. $\\gamma$ and fast-timing spectroscopy of the doubly magic $^{132}$Sn and its one- and two-neutron particle/hole neighbours

    CERN Multimedia

    We propose to use fast-timing and spectroscopy to study five nuclei including the doubly magic $^{132}$Sn and its four neighbours: two-neutron hole $^{130}$Sn, one-neutron hole $^{131}$Sn, one-neutron particle $^{133}$Sn and two-neutron particle $^{134}$Sn. There is an increasing interest in these nuclei since they serve to test nuclear models using state-of-the-art interactions and many body approaches, and they provide information relevant to deduce single particle states. In addition properties of these nuclei are very important to model the astrophysical $\\textit{r-process}$. The present ISOLDE facility provides unique capabilities to study these Sn nuclei populated in the $\\beta$-decay of In isomers, produced from a UCx target unit equipped with neutron converter and ionized with RILIS, capable of selective isomer ionization. The increased production yields for $^{132}$In are estimated to be 200 larger than in the previous work done at OSIRIS. We will use the recently commissioned Isolde Decay Station (I...

  14. Irradiation effects in 6H-SiC induced by neutron and heavy ions: Raman spectroscopy and high-resolution XRD analysis

    Science.gov (United States)

    Chen, Xiaofei; Zhou, Wei; Feng, Qijie; Zheng, Jian; Liu, Xiankun; Tang, Bin; Li, Jiangbo; Xue, Jianming; Peng, Shuming

    2016-09-01

    Irradiation effects of neutron and 3 MeV C+, Si+ in 6H-SiC were investigated by Raman spectroscopy and high-resolution XRD. The total disorder values of neutron irradiated SiC agree well with that of samples irradiated by ions at the same doses respectively. On the other hand, high-resolution XRD results shows that the lattice strain rate caused by neutron irradiation is 6.8%/dpa, while it is only 2.6%/dpa and 4.2%/dpa for Si+ and C+ irradiations respectively. Our results illustrate that the total disorder in neutron irradiated SiC can be accurately simulated by MeV Si+ or C+ irradiations at the same dose, but for the lattice strain and strain-related properties like surface hardness, the depth profile of irradiation damages induced by energetic ions must be considered. This research will contribute to a better understanding of the difference in irradiation effects between neutron and heavy ions.

  15. $\\beta$-delayed neutron spectroscopy of $^{130-132}$ Cd isotopes with the ISOLDE decay station and the VANDLE array

    CERN Multimedia

    We propose to use the new ISOLDE decay station and the neutron detector VANDLE to measure the $\\beta$-delayed neutron emission of N=82-84 $^{130-132}$Cd isotopes. The large delayed neutron emission probability observed in a previous ISOLDE measurement is indicative of the Gamow-Teller transitions due to the decay of deep core neutrons. Core Gamow-Teller decay has been experimentally proven in the $^{78}$Ni region for the N>50 nuclei using the VANDLE array. The spectroscopic measurement of delayed neutron emission along the cadmium isotopic chain will allow us to track the evolution of the single particle states and the shell gap.

  16. Tunneling in high-K isomeric decays

    CERN Document Server

    Shizuma, T; Shimizu, Y R

    2002-01-01

    We have systematically investigated highly-K-forbidden transitions observed in the Hf, W and Os region, using the gamma-tunneling model in which low-K and high-k states interact through a process of quantum tunneling. The measured hindrance factors are compared with the values calculated using the gamma-tunneling model. Isotope dependences of gamma-tunneling probabilities particularly for neutron-rich nuclei and the relation to stimulated decays of isomers are discussed. (author)

  17. High Resolution Spectroscopy And Timing Of The Isolated Neutron Star RBS 1774

    Science.gov (United States)

    Mushotzky, Richard (Technical Monitor); Drake, Jeremy

    2005-01-01

    The 2004 May 31 XMM-Newton observation was reprocessed using SASv6.0.0 and times of high background were filtered out. The net exposure time remaining was 23 ks. The source was clearly detected in MOS1, MOS2 and PN chips. We performed both timing and spectroscopic analysis on the data. We performed a spectral analysis by fitting data from the three EPIC detectors simultaneously, finding that the broadband spectrum can be represented by a single absorbed blackbody, with kT = 0.10 keV. The fitting revealed the presence of an absorption feature at 0:7 keV, but the data did have enough resolution to allow us to discriminate between an absorption line and an edge. We also tested magnetized models of Pavlov et a1 and Zavlin et al, but found that fits with these models were considerably worse than with a blackbody. For the timing analysis, we extracted the counts within a 3000 radius aperture in both PN and MOS 1 and MOS2 but with the aperture truncated by a chord where it approached the edge of the CCD window in each case: this maximized the counts while avoiding any edge effects. We analyzed PN, MOSl and MOS2 data both individually and combined using the Maximum Likelihood Periodogram technique of Zane et al. (2002) and Cropper et al. (2004). Periods from 10000 s to 30 ms were searched, ensuring that in each case the period grid was 2.5 times better sampled than the Nyquist frequency. The search revealed a significant period at 9.437s. Taken overall, we found the characteristics of RBS 1774 to be remarkably similar to those of another X-ray faint isolated neutron stars. These results were written up for the Astrophysical Journal, and the paper has recently been accepted for publication.

  18. High resolution collinear resonance ionization spectroscopy of neutron-rich $^{76,77,78}$Cu isotopes

    CERN Document Server

    De Groote, Ruben Pieter

    In this work, nuclear magnetic dipole moments, electric quadrupole moments, nuclear spins and changes in the mean-squared charge radii of radioactive copper isotopes are presented. Reaching up to $^{78}$Cu ($Z=29$, $N=49$), produced at rates of only 10 particles per second, these measurements represent the most exotic laser spectroscopic investigations near the doubly-magic and very exotic $^{78}$Ni ($Z=28$,$N=50$) to date. This thesis outlines the technical developments and investigations of laser-atom interactions that were performed during this thesis. These developments were crucial for establishing a high-resolution, high sensitivity collinear resonance ionization spectroscopy experiment at ISOLDE, CERN. This thesis furthermore provides a detailed description of the analysis tools that were implemented and applied to extract the nuclear observables from the experimental data. The results were compared to several large-scale shell model calculations, and provide deep insight into the structure of $^{78}$N...

  19. Low-temperature scanning tunneling microscopy/ultraviolet photoelectron spectroscopy investigation of two-dimensional crystallization of C60: pentacence binary system on Ag(111)

    Science.gov (United States)

    Lin Zhang, Jia; Hong Liang Zhang, Kelvin; Qiang Zhong, Jian; Chao Niu, Tian; Chen, Wei

    2012-02-01

    Atomic scale investigation of temperature-dependent two-dimensional (2 D) crystallization processes of fullerene-C60 on pentacene-covered Ag(111) surface has been carried out by in situ low-temperature scanning tunneling microscopy (LT-STM) experiments. To evaluate the effect of molecule-substrate interfacial interactions on the 2 D crystallization of C60: pentacene binary system, we also carried out the same self-assembly experiments of C60 on monolayer pentacene covered graphite substrate. It is revealed that temperature-dependent structural transition of various ordered C60 nanoassemblies is strongly influenced by the molecule-Ag(111) interfacial interactions, and further mediated by the weak C60-pentacene intermolecular interactions. In situ ultraviolet photoelectron spectroscopy (UPS) has been used to evaluate the nature of the intermolecular interactions between C60 and pentacene films.

  20. Structure, Mobility, and Composition of Transition Metal Catalyst Surfaces. High-Pressure Scanning Tunneling Microscopy and Ambient-Pressure X-ray Photoelectron Spectroscopy Studies

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Zhongwei [Univ. of California, Berkeley, CA (United States)

    2013-12-06

    Surface structure, mobility, and composition of transition metal catalysts were studied by high-pressure scanning tunneling microscopy (HP-STM) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) at high gas pressures. HP-STM makes it possible to determine the atomic or molecular rearrangement at catalyst surfaces, particularly at the low-coordinated active surface sites. AP-XPS monitors changes in elemental composition and chemical states of catalysts in response to variations in gas environments. Stepped Pt and Cu single crystals, the hexagonally reconstructed Pt(100) single crystal, and Pt-based bimetallic nanoparticles with controlled size, shape and composition, were employed as the model catalysts for experiments in this thesis.

  1. DESORPTION OF Te CAPPING LAYER FROM ZnTe (100: AUGER SPECTROSCOPY, LOW-ENERGY ELECTRON DIFFRACTION AND SCANNING TUNNELING MICROSCOPY

    Directory of Open Access Journals (Sweden)

    K. K. Sossoe

    2016-01-01

    Full Text Available The influence of the annealing temperature to desorb a protective Te capping layer of the zinc telluride (ZnTe (100 surface was investigated. The surface reconstruction of the ZnTe (100 upon the removal of a Te capping layer grown by the molecular beam epitaxy was characterized by different methods. Auger spectroscopy brought out the chemical composition of the surface before and after annealing; the Low-energy electron diffraction (LEED gave information about the crystallographic structure. The surface crystallographic configurations of tellurium Te (c (2x2 and Te (c (2x1 are confirmed by scanning tunneling microscopy (STM. Such a study reveals a phase transition from a rich-Te to a poor-Te surface as the annealing temperature increases. 

  2. Neutron scattering and nuclear magnetic resonance spectroscopy structural studies of protein-DNA complexes

    Energy Technology Data Exchange (ETDEWEB)

    Bradbury, E.M.; Catasti, P.; Chen, X.; Gupta, G.; Imai, B.; Moyzis, R.; Ratliff, R.; Velupillai, S.

    1996-03-01

    This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project sought to employ advanced biophysical measurements to study the structure of nucleosomes and the structure of origins of DNA replication. The fundamental repeating unit of human chromosomes is the nucleosome, which contains about 200 base pairs of DNA and 9 histone proteins. Genome replication is strictly associated with the reversible acetylations of histones that unfold chromatin to allow access of factors to origins of DNA replications. The authors have studied two major structural problems: (1) the effects of histone acetylation on nucleosome structure, and (2) the structure of DNA origins of replication. They have recently completed preliminary X-ray scattering experiments at Stanford on positioned nucleosomes with defined DNA sequence and length, histone composition and level of acetylation. These experiments have shown that lengths of the DNA and acetylations of the histone H4 result in nucleosome structural changes. To understand internucleosomal interactions and the roles of histone H1 the authors have made preliminary x-ray scatter studies on native dinucleosomes that have demonstrated the feasibility of these experiments. The DNA sequence of the yeast replication origin has been synthesized for structure determination by multi-dimensional NMR spectroscopy.

  3. Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hellman, Hal

    1968-01-01

    This booklet discusses spectroscopy, the study of absorption of radiation by matter, including X-ray, gamma-ray, microwave, mass spectroscopy, as well as others. Spectroscopy has produced more fundamental information to the study of the detailed structure of matter than any other tools.

  4. Spectroscopy

    CERN Document Server

    Walker, S

    1976-01-01

    The three volumes of Spectroscopy constitute the one comprehensive text available on the principles, practice and applications of spectroscopy. By giving full accounts of those spectroscopic techniques only recently introduced into student courses - such as Mössbauer spectroscopy and photoelectron spectroscopy - in addition to those techniques long recognised as being essential in chemistry teaching - sucha as e.s.r. and infrared spectroscopy - the book caters for the complete requirements of undergraduate students and at the same time provides a sound introduction to special topics for graduate students.

  5. Thermal neutron capture cross-section measurements of {sup 243}Am and {sup 242}Pu using the new mini-INCA {alpha}- and {gamma}-spectroscopy station

    Energy Technology Data Exchange (ETDEWEB)

    Marie, F. [DSM/DAPNIA, CEA-Saclay, 91191 Gif sur Yvette (France); Letourneau, A. [DSM/DAPNIA, CEA-Saclay, 91191 Gif sur Yvette (France)]. E-mail: aletourneau@cea.fr; Fioni, G. [DSM/DAPNIA, CEA-Saclay, 91191 Gif sur Yvette (France); Deruelle, O. [DSM/DAPNIA, CEA-Saclay, 91191 Gif sur Yvette (France); Veyssiere, Ch. [DSM/DAPNIA, CEA-Saclay, 91191 Gif sur Yvette (France); Faust, H. [Institut Laue-Langevin, 38000 Grenoble (France); Mutti, P. [Institut Laue-Langevin, 38000 Grenoble (France); AlMahamid, I. [Lawrence Berkeley National Lab., ESH Division, Berkeley, CA 94720 (United States); Muhammad, B. [Lawrence Berkeley National Lab., ESH Division, Berkeley, CA 94720 (United States)

    2006-01-15

    In the framework of the Mini-INCA project, dedicated to the study of Minor Actinide transmutation process in high neutron fluxes, an {alpha}- and {gamma}-spectroscopy station has been developed and installed at the High Flux Reactor of the Laue-Langevin Institut. This set-up allows short irradiations as well as long irradiations in a high quasi-thermal neutron flux and post-irradiation spectroscopy analysis. It is well suited to measure precisely, in reference to {sup 59}Co cross-section, neutron capture cross-sections, for all the actinides, in the thermal energy region. The first measurements using this set-up were done on {sup 243}Am and {sup 242}Pu isotopes. Cross-section values, at E{sub n}=0.025eV, were found to be (81.8+/-3.6)b for {sup 243}Am and (22.5+/-1.1)b for {sup 242}Pu. These values differ from evaluated data libraries by a factor of 9% and 17%, respectively, but are compatible with the most recent measurements, validating by the way the experimental apparatus.

  6. DLTS and capacitance transients study of defects induced by neutron irradiation in MOS structures CCD process; Etude des defauts induits par irradiation neutron dans des structures MOS par spectroscopie DLTS et reponses transitoires de capacite en fonction du temps

    Energy Technology Data Exchange (ETDEWEB)

    Ahaitouf, A.; Losson, E.; Charles, J.P. [Metz Univ., Lab. Interfaces Composants et Microelectronique, LICM/CLOES/ Supelec, 57 (France)

    1999-07-01

    The aim of this paper is to study neutron irradiation effects on PMOS capacitors and NMOSFETs transistors. The characterization of induced defects was made by capacitance transients C(t) measurements, DLTS spectroscopy, and optical DLTS (ODLTS). DLTS spectra present three peaks due to deep levels created in the semiconductor and two peaks due to minority carrier generation. Two levels are reported in the literature. Two other minority carrier traps have been observed on ODLTS spectra after irradiation. This can explain the decrease of the minority carrier generation lifetime observed by capacitance transients measurements. (authors)

  7. Hot-Electron Tunneling sensors for high-resolution x-ray and gamma-ray spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Mears, C.A.; Labov, S.E.; Frank, M.; Netel, H.

    1997-02-07

    Over the past 2 years, we have been studying the use of Hot Electron Tunneling sensors for use in high-energy-resolution x-ray and gamma-ray spectrometers. These sensors promise several advantages over existing cryogenic sensors, including simultaneous high count rate and high resolution capability, and relative ease of use. Using simple shadow mask lithography, we verified the basic principles of operation of these devices and discovered new physics in their thermal behavior as a function applied voltage bias. We also began to develop ways to use this new sensor in practical x-ray and gamma-ray detectors based on superconducting absorbers. This requires the use of quasiparticle trapping to concentrate the signal in the sensing elements.

  8. From the tunneling dimer to the onset of microsolvation: Infrared spectroscopy of allyl radical water aggregates in helium nanodroplets

    Science.gov (United States)

    Leicht, Daniel; Kaufmann, Matin; Pal, Nitish; Schwaab, Gerhard; Havenith, Martina

    2017-03-01

    The infrared spectrum of allyl:water clusters embedded in helium nanodroplets was recorded. Allyl radicals were produced by flash vacuum pyrolysis and trapped in helium droplets. Deuterated water was added to the doped droplets, and the infrared spectrum of the radical water aggregates was recorded in the frequency range 2570-2820 cm-1. Several absorption bands are observed and assigned to 1:1 and 1:2 allyl:D2O clusters, based on pressure dependent measurements and accompanying quantum chemical calculations. The analysis of the 1:1 cluster spectrum revealed a tunneling splitting as well as a combination band. For the 1:2 cluster, we observe a water dimer-like motif that is bound by one π-hydrogen bond to the allyl radical.

  9. Scanning Tunneling Microscopy and Spectroscopy of Air Exposure Effects on Molecular Beam Epitaxy Grown WSe2 Monolayers and Bilayers.

    Science.gov (United States)

    Park, Jun Hong; Vishwanath, Suresh; Liu, Xinyu; Zhou, Huawei; Eichfeld, Sarah M; Fullerton-Shirey, Susan K; Robinson, Joshua A; Feenstra, Randall M; Furdyna, Jacek; Jena, Debdeep; Xing, Huili Grace; Kummel, Andrew C

    2016-04-26

    The effect of air exposure on 2H-WSe2/HOPG is determined via scanning tunneling microscopy (STM). WSe2 was grown by molecular beam epitaxy on highly oriented pyrolytic graphite (HOPG), and afterward, a Se adlayer was deposited in situ on WSe2/HOPG to prevent unintentional oxidation during transferring from the growth chamber to the STM chamber. After annealing at 773 K to remove the Se adlayer, STM images show that WSe2 layers nucleate at both step edges and terraces of the HOPG. Exposure to air for 1 week and 9 weeks caused air-induced adsorbates to be deposited on the WSe2 surface; however, the band gap of the terraces remained unaffected and nearly identical to those on decapped WSe2. The air-induced adsorbates can be removed by annealing at 523 K. In contrast to WSe2 terraces, air exposure caused the edges of the WSe2 to oxidize and form protrusions, resulting in a larger band gap in the scanning tunneling spectra compared to the terraces of air-exposed WSe2 monolayers. The preferential oxidation at the WSe2 edges compared to the terraces is likely the result of dangling edge bonds. In the absence of air exposure, the dangling edge bonds had a smaller band gap compared to the terraces and a shift of about 0.73 eV in the Fermi level toward the valence band. However, after air exposure, the band gap of the oxidized WSe2 edges became about 1.08 eV larger than that of the WSe2 terraces, resulting in the electronic passivation of the WSe2.

  10. Coupled multi-group neutron photon transport for the simulation of high-resolution gamma-ray spectroscopy applications

    Energy Technology Data Exchange (ETDEWEB)

    Burns, Kimberly A. [Georgia Inst. of Technology, Atlanta, GA (United States)

    2009-08-01

    The accurate and efficient simulation of coupled neutron-photon problems is necessary for several important radiation detection applications. Examples include the detection of nuclear threats concealed in cargo containers and prompt gamma neutron activation analysis for nondestructive determination of elemental composition of unknown samples.

  11. Study of the N=28 shell closure by one neutron transfer reaction: astrophysical application and {beta}-{gamma} spectroscopy of neutron rich nuclei around N=32/34 and N=40; Etude de la fermeture de couche N=28 autour du noyau {sub 18}{sup 46}Ar{sub 28} par reaction de transfert d'un neutron: application a l'astrophysique et Spectroscopie {beta}-{gamma} de noyaux riches en neutrons de N=32/34 et N=40

    Energy Technology Data Exchange (ETDEWEB)

    Gaudefroy, L

    2005-09-15

    The study of the N=28 shell closure has been presented as well as its astrophysical implications. Moreover the structure of neutron rich nuclei around N=32/34 and 40 was studied. The N=28 shell closure has been studied trough the one neutron transfer reaction on {sup 44,46}Ar nuclei. Excitation energies of states in {sup 45,47}Ar nuclei have been obtained, as well as their angular momenta and spectroscopic factors. These results were used to show that N=28 is still a good magic number in the argon isotopic chain. We interpreted the evolution of the spin-orbit partner gaps in terms of the tensor monopolar proton-neutron interaction. Thanks to this latter, we showed it is not necessary to summon up a reduction of the intensity of the spin-orbit force in order to explain this evolution in N=29 isotopes from calcium to argon chains. The neutron capture rates on {sup 44,46}Ar have been determined thanks to the results of the transfer reaction. Their influence on the nucleosynthesis of {sup 46,48}Ca was studied. We proposed stellar conditions to account for the abnormal isotopic ratio observed in the Allende meteorite concerning {sup 46,48}Ca isotopes. The beta decay and gamma spectroscopy of neutron rich nuclei in the scandium to cobalt region has been studied. We showed that beta decay process is dominated by the {nu}f{sub 5/2} {yields} {pi}f{sub 7/2} Gamow-Teller transition. Moreover, we demonstrated that the {nu}g{sub 9/2} hinders this process in the studied nuclei, and influences their structure, by implying the existence of isomers. Our results show that N=34 is not a magic number in the titanium chain and the superior ones. (author)

  12. Penning trap mass measurements and laser spectroscopy on neutron-rich fission products extracted from the research reactor TRIGA-Mainz

    Energy Technology Data Exchange (ETDEWEB)

    Eibach, Martin; Ketelaer, Jens; Ketter, Jochen; Knuth, Konstantin [Institut fuer Physik, Universitaet Mainz (Germany); Blaum, Klaus; Nagy, Szilard [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Eberhardt, Klaus; Noertershaeuser, Wilfried [Institut fuer Kernchemie, Universitaet Mainz (Germany); Herfurth, Frank [GSI, Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Smorra, Christian [Physikalisches Institut, Universitaet Heidelberg (Germany); Institut fuer Kernchemie, Universitaet Mainz (Germany)

    2009-07-01

    TRIGA-SPEC is a setup for Penning trap mass spectrometry and collinear laser spectroscopy on short-lived neutron-rich nuclides located at the research reactor TRIGA-Mainz. It is dedicated to the determination of nuclear ground-state properties like masses and charge-radii. The nuclides are produced by neutron-induced fission of an actinide target located in a target chamber near the reactor core. It is required to extract the nuclides fast and with high efficiency from the target chamber in order to make precision experiments on short-living species with half-lives in the order of 1s. To this end, they are flushed out with a helium gas jet containing carbon aerosols and transported through a skimmer region to an ECR ion source. The characterisation of the carbon aerosol generator and the verification of transported fission products are presented.

  13. OPTICAL SPECTROSCOPY OF THE HIGH-MASS γ-RAY BINARY 1FGL J1018.6−5856: A PROBABLE NEUTRON STAR PRIMARY

    Energy Technology Data Exchange (ETDEWEB)

    Strader, Jay; Chomiuk, Laura; Peacock, Mark [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Cheung, C. C. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); Salinas, Ricardo [Gemini Observatory, Casilla 603, La Serena (Chile)

    2015-11-10

    We present medium-resolution optical spectroscopy with the SOAR telescope of the O star secondary of the high-mass γ-ray binary 1FGL J1018.6–5856 to help determine whether the primary is a neutron star or black hole. We find that the secondary has a low radial velocity semi-amplitude of 11–12 km s{sup −1}, with consistent values obtained for H and He absorption lines. This low value strongly favors a neutron star primary: while a black hole cannot be excluded if the system is close to face on, such inclinations are disallowed by the observed rotation of the secondary. We also find the high-energy (X-ray and γ-ray) flux maxima occur when the star is behind the compact object along our line of sight, inconsistent with a simple model of anisotropic inverse Compton scattering for the γ-ray photons.

  14. Non-periodic multi-slit masking for a single counter rotating 2-disc chopper and channeling guides for high resolution and high intensity neutron TOF spectroscopy

    Science.gov (United States)

    Bartkowiak, M.; Hofmann, T.; Stüßer, N.

    2017-02-01

    Energy resolution is an important design goal for time-of-flight instruments and neutron spectroscopy. For high-resolution applications, it is required that the burst times of choppers be short, going down to the μs-range. To produce short pulses while maintaining high neutron flux, we propose beam masks with more than two slits on a counter-rotating 2-disc chopper, behind specially adapted focusing multi-channel guides. A novel non-regular arrangement of the slits ensures that the beam opens only once per chopper cycle, when the masks are congruently aligned. Additionally, beam splitting and intensity focusing by guides before and after the chopper position provide high intensities even for small samples. Phase-space analysis and Monte Carlo simulations on examples of four-slit masks with adapted guide geometries show the potential of the proposed setup.

  15. Multilayered cuprate superconductor Ba2Ca5Cu6O12(O1-x,Fx) 2 studied by temperature-dependent scanning tunneling microscopy and spectroscopy

    Science.gov (United States)

    Sugimoto, Akira; Ekino, Toshikazu; Gabovich, Alexander M.; Sekine, Ryotaro; Tanabe, Kenji; Tokiwa, Kazuyasu

    2017-05-01

    Scanning tunneling microscopy/spectroscopy (STM/STS) measurements were carried out on a multilayered cuprate superconductor Ba2Ca5Cu6O12 (O1 -x,Fx )2. STM topography revealed random spot structures with the characteristic length ≤0.5 nm. The conductance spectra d I /d V (V ) show the coexistence of smaller gaps ΔS and large gaps (pseudogaps) ΔL. The pseudogap-related features in the superconducting state were traced with the spatial resolution of ˜0.07 nm. Here, I and V are the tunnel current and bias voltage, respectively. The temperature, T , dependence of ΔS follows the reduced Bardeen-Cooper-Schrieffer (BCS) dependence. The hallmark ratio 2 ΔS(T =0 ) /kBTc equals to 4.9, which is smaller than those of other cuprate superconductors. Here, Tc is the superconducting critical temperature and kB is the Boltzmann constant. The larger gap ΔL survives in the normal state and even increases with T above Tc. The T dependencies of the spatial distributions for both relevant gaps (Δ map), as well as for each gap separately (ΔS and ΔL), were obtained. From the histogram of Δ map, the averaged gap values were found to be Δ¯S=˜24 meV and Δ¯L=˜79 meV. The smaller gap ΔS shows a spatially homogeneous distribution while the larger gap ΔL is quite inhomogeneous, indicating that rather homogeneous superconductivity coexists with the patchy distributed pseudogap. The spatial variation length ξΔ L of ΔL correlates with the scale of the topography spot structures, being approximately 0.4 nm. This value is considerably smaller than the coherence length of this class of superconductors, suggesting that ΔL is strongly affected by the disorder of the apical O/F.

  16. Inelastic tunneling in superconducting junctions

    Energy Technology Data Exchange (ETDEWEB)

    Hlobil, Patrik Christian

    2016-06-10

    In this dissertation a theoretical formalism of elastic and inelastic tunneling spectroscopy is developed for superconductors. The underlying physical processes behind the different two tunneling channels and their implications for the interpretation of experimental tunneling data are investigated in detail, which can explain the background conductance seen in the cuprate and iron-based superconductors. Further, the properties of the emitted light from a superconducting LED are investigated.

  17. Heterodimers formed through a partial anionic exchange process: scanning tunneling spectroscopy to monitor bands across the junction vis-à-vis photoinduced charge separation

    Science.gov (United States)

    Bera, Abhijit; Saha, Sudip K.; Pal, Amlan J.

    2015-10-01

    We report controlled formation of heterodimers and their charge separation properties. CdS|CdTe heterodimers were formed through an anionic exchange process of CdS nanostructures. With control over the duration of the anionic exchange process, bulk|dot, bulk|bulk, and then dot|bulk phases of the semiconductors could be observed to have formed. A mapping of density of states as derived from scanning tunneling spectroscopy (STS) brought out conduction and valence band-edges along the nanostructures and heterodimers. The CdS|CdTe heterodimers evidenced a type-II band-alignment between the semiconductors along with the formation of a depletion region at the interface. The width (of the depletion region) and the energy-offset at the interface depended on the size of the semiconductors. We report that the width that is instrumental for photoinduced charge separation in the heterodimers has a direct correlation with the performance of hybrid bulk-heterojunction solar cells based on the nanostructures in a polymer matrix.We report controlled formation of heterodimers and their charge separation properties. CdS|CdTe heterodimers were formed through an anionic exchange process of CdS nanostructures. With control over the duration of the anionic exchange process, bulk|dot, bulk|bulk, and then dot|bulk phases of the semiconductors could be observed to have formed. A mapping of density of states as derived from scanning tunneling spectroscopy (STS) brought out conduction and valence band-edges along the nanostructures and heterodimers. The CdS|CdTe heterodimers evidenced a type-II band-alignment between the semiconductors along with the formation of a depletion region at the interface. The width (of the depletion region) and the energy-offset at the interface depended on the size of the semiconductors. We report that the width that is instrumental for photoinduced charge separation in the heterodimers has a direct correlation with the performance of hybrid bulk

  18. BTA inhibition mechanism on clean Cu(110) surface by ultraviolet photoemission spectroscopy (UPS) and scanning tunneling microscope (STM)

    Energy Technology Data Exchange (ETDEWEB)

    Cho, K. [Yeungnam Univ., Kyungsan (Korea, Republic of); Park, Y.J.; Kuk, Y. [Seoul National Univ. (Korea, Republic of); Sakurai, T. [Tohoku Univ., Sendai (Japan). Inst. for Materials Research

    1998-12-31

    Adsorption and film growth of the Benzotriazole (BTA) on a copper (110) surface were investigated by the angle-resolved ultra-violet photoemission (UPS), and scanning tunneling microscope (STM). Coverage dependence of the BTA adsorbed structure on the Cu (110) surface exhibited well-ordered c(4 x 2)structure by STM image and sharp low-energy electron diffraction (LEED) pattern. Further deposition of BTA on monolayer film, polymerized BTA images were observed while a sharp LEED pattern changed to a c(4 x 2). In a good agreement with STM results, UPS spectra of BTA film by coverage dependence showed that BTA adsorbed flat up to 1 monolayer (ML), followed by stand-up polymerization above 1 monolayer. It is also suggested that 3-dimensional polymerization exhibited at least 2 BTA layers on Cu surface. The proposed orientation of the first adsorbed BTA layer on Cu (110) surface is the flat adsorption position based on the atomic scale resolution of STM and thickness dependence of UPS spectra. This adsorption structure and polymerized multilayer film of the BTA blocks the surface completely. Adsorption sites on the copper surface for attacking media are unavailable for oxidation reaction.

  19. Crystal structure and magnetism of YbFeMnO 5: A neutron diffraction and Mössbauer spectroscopy study

    Science.gov (United States)

    Martínez-Lope, M. J.; Retuerto, M.; Alonso, J. A.; García-Hernández, M.; Krezhov, K.; Spirov, I.; Ruskov, T.; Fernández-Díaz, M. T.

    2009-04-01

    We have studied the crystal structure and magnetic properties of Y bFeMnO 5 obtained by substituting Fe 3+ for Mn 3+ in the parent Y bMn 2O 5 compound, through x-ray (XRD) and neutron (NPD) powder diffraction, magnetometry and Mössbauer spectroscopy. The samples were prepared in polycrystalline form by a soft chemistry route, followed by thermal treatments under high-oxygen pressure. The Rietveld analysis of diffraction data shows that Y bFeMnO 5 is isostructural with the oxides of stoichiometry RMn 2O 5 (R=rare earth, Y or Bi); the crystal structure is orthorhombic, Pbam space group, formed by chains of edge-sharing Mn 4+O 6 octahedra linked together by dimer groups of square pyramids Fe 3+O 5 and Y b 3+O 8 scalenohedra. A low level of disorder was established between the two transition metal positions 4 f and 4 h, occupied ideally by Mn 4+ and by Fe 3+: about 6% of Mn cations is replaced by Fe and 16% of Fe by Mn. Mössbauer spectroscopy data confirm the existence of two distinct crystallographic sites for Fe 3+. One of them corresponds to almost regular octahedra (at 4 f positions), characterized by nearly equal Mn/Fe-O distances of 1.890 Å at RT (from NPD data), giving a quadrupole doublet in the Mössbauer spectra at RT, broadened by the Fe/Mn disorder over this site. The second environment for Fe 3+ contributes to a less broadened, but more intensive doublet in the Mössbauer spectra, which corresponds to a distorted square pyramid Fe 3+O 5 (at 4h sites), for which NPD data demonstrates an axial distortion with three sets of Fe-O distances at 2.010(2) Å, 1.859(5) Å and 1.925(3) Å. Magnetic studies and the thermal evolution of the NPD patterns show that below a transition temperature Tc˜178 K a long-range magnetic order is developed, resolved from NPD data as a ferrimagnetic structure with propagation vector k=0. The spin arrangements for the Mn 4+ ions ( 4f site) and Fe 3+ ions ( 4h site) are given by the basis vectors ( 0,0,Fz) and ( 0,0,Fz

  20. Mixed quantum/classical approach to OH-stretch inelastic incoherent neutron scattering spectroscopy for ambient and supercooled liquid water and ice Ih

    Energy Technology Data Exchange (ETDEWEB)

    Shi, L.; Skinner, J. L. [Theoretical Chemistry Institute and Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706 (United States)

    2015-07-07

    OH-stretch inelastic incoherent neutron scattering (IINS) has been measured to determine the vibrational density of states (VDOS) in the OH-stretch region for liquid water, supercooled water, and ice Ih, providing complementary information to IR and Raman spectroscopies about hydrogen bonding in these phases. In this work, we extend the combined electronic-structure/molecular-dynamics (ES/MD) method, originally developed by Skinner and co-workers to simulate OH-stretch IR and Raman spectra, to the calculation of IINS spectra with small k values. The agreement between theory and experiment in the limit k → 0 is reasonable, further validating the reliability of the ES/MD method in simulating OH-stretch spectroscopy in condensed phases. The connections and differences between IINS and IR spectra are analyzed to illustrate the advantages of IINS over IR in estimating the OH-stretch VDOS.

  1. High Pressure Scanning Tunneling Microscopy and High PressureX-ray Photoemission Spectroscopy Studies of Adsorbate Structure,Composition and Mobility during Catalytic Reactions on A Model SingleCrystal

    Energy Technology Data Exchange (ETDEWEB)

    Montano, Max O. [Univ. of California, Berkeley, CA (United States)

    2006-01-01

    Our research focuses on taking advantage of the ability of scanning tunneling microscopy (STM) to operate at high-temperatures and high-pressures while still providing real-time atomic resolution images. We also utilize high-pressure x-ray photoelectron spectroscopy (HPXPS) to monitor systems under identical conditions thus giving us chemical information to compare and contrast with the structural and dynamic data provided by STM.

  2. A study of the O/Ag(111) system with scanning tunneling microscopy and x-ray photoelectron spectroscopy at ambient pressures

    Science.gov (United States)

    Heine, Christian; Eren, Baran; Lechner, Barbara A. J.; Salmeron, Miquel

    2016-10-01

    The interaction of O2 with the Ag(111) surface was studied with scanning tunneling microscopy (STM) in the pressure range from 10- 9 Torr to 1 atm at room temperature and with X-ray photoelectron spectroscopy (XPS) up to 0.3 Torr O2 in the temperature range from RT to 413 K. STM images show that the Ag(111) surface topography is little affected in regions with large flat terraces, except for the appearance of mobile features due to oxygen atoms at pressures above 0.01 Torr. In regions where the step density is high, the surface became rough under 0.01 Torr of O2, due to the local oxidation of Ag. Various chemical states of oxygen due to chemisorbed, oxide and subsurface species were identified by XPS as a function of pressure and temperature. The findings from the STM images and XPS measurements indicate that formation of an oxide phase, the thermodynamically stable form at room temperature under ambient O2 pressure, is kinetically hindered in the flat terrace areas but proceeds readily in regions with high-step density.

  3. Si(111)-sq root 21 x sq root 21 -(Ag+Cs) surface studied by scanning tunneling microscopy and angle-resolved photoemission spectroscopy

    CERN Document Server

    Liu, C; Morikawa, H; Okino, H; Hasegawa, S; Okuda, T; Kinoshita, T

    2003-01-01

    Scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) were used to study the atomic and electronic structures of the Si(111)-sq root 21 x sq root 21-(Ag + Cs) surface (sq root 21-Cs in short), which was induced by depositing caesium atoms on the Si(111)-sq root 3 x sq root 3-Ag surface at room temperature (RT). Compared with previously reported STM images of noble-metal induced sq root 21 x sq root 21 phases including the Si(111)-sq root 21 x sq root 21-(Ag+Ag) and Si(111)-sq root 21 x sq root 21-(Ag+Au) surfaces (sq root 21-Ag and sq root 21-Au, respectively), the sq root 21-Cs surface displayed quite different features in STM images. The ARPES data of the sq root 21-Cs surface revealed an intrinsic dispersive surface-state band, together with a non-dispersive one near the Fermi level, which was also different from those of the sq root 21-Ag and sq root 21-Au surfaces. These results strongly suggest different atomic arrangements between Cs- and noble-metal induced sq root ...

  4. Electronic and geometric properties of Au nanoparticles on Highly Ordered Pyrolytic Graphite (HOPG) studied using X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM).

    Science.gov (United States)

    Lopez-Salido, Ignacio; Lim, Dong Chan; Dietsche, Rainer; Bertram, Nils; Kim, Young Dok

    2006-01-26

    Au nanoparticles grown on mildly sputtered Highly Ordered Pyrolytic Graphite (HOPG) surfaces were studied using Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS). The results were compared with those of Ag nanoparticles on the same substrate. By varying the defect densities of HOPG and the Au coverages, one can create Au nanoparticles in various sizes. At high Au coverages, the structures of the Au films significantly deviate from the ideal truncated octahedral form: the existence of many steps between different Au atomic layers can be observed, most likely due to a high activation barrier of the diffusion of Au atoms across the step edges. This implies that the particle growth at room temperature is strongly limited by kinetic factors. Hexagonal shapes of Au structures could be identified, indicating preferential growth of Au nanostructures along the (111) direction normal to the surface. In the case of Au, XPS studies reveal a weaker core level shift with decreasing particle size compared to the 3d level in similarly sized Ag particles. Also taking into account the Auger analysis of the Ag particles, the core level shifts of the metal nanoparticles on HOPG can be understood in terms of the metal/substrate charge transfer. Ag is (partially) positively charged, whereas Au negatively charged on HOPG. It is demonstrated that XPS can be a useful tool to study metal-support interactions, which plays an important role for heterogeneous catalysis, for example.

  5. Dopant Diffusion and Activation in Silicon Nanowires Fabricated by ex Situ Doping: A Correlative Study via Atom-Probe Tomography and Scanning Tunneling Spectroscopy.

    Science.gov (United States)

    Sun, Zhiyuan; Hazut, Ori; Huang, Bo-Chao; Chiu, Ya-Ping; Chang, Chia-Seng; Yerushalmi, Roie; Lauhon, Lincoln J; Seidman, David N

    2016-07-13

    Dopants play a critical role in modulating the electric properties of semiconducting materials, ranging from bulk to nanoscale semiconductors, nanowires, and quantum dots. The application of traditional doping methods developed for bulk materials involves additional considerations for nanoscale semiconductors because of the influence of surfaces and stochastic fluctuations, which may become significant at the nanometer-scale level. Monolayer doping is an ex situ doping method that permits the post growth doping of nanowires. Herein, using atom-probe tomography (APT) with subnanometer spatial resolution and atomic-ppm detection limit, we study the distributions of boron and phosphorus in ex situ doped silicon nanowires with accurate control. A highly phosphorus doped outer region and a uniformly boron doped interior are observed, which are not predicted by criteria based on bulk silicon. These phenomena are explained by fast interfacial diffusion of phosphorus and enhanced bulk diffusion of boron, respectively. The APT results are compared with scanning tunneling spectroscopy data, which yields information concerning the electrically active dopants. Overall, comparing the information obtained by the two methods permits us to evaluate the diffusivities of each different dopant type at the nanowire oxide, interface, and core regions. The combined data sets permit us to evaluate the electrical activation and compensation of the dopants in different regions of the nanowires and understand the details that lead to the sharp p-i-n junctions formed across the nanowire for the ex situ doping process.

  6. Termination-specific study of oxygen vacancy transition levels on SrTiO3(001) surfaces by scanning tunneling spectroscopy

    Science.gov (United States)

    Sitaputra, Wattaka; Sivadas, Nikhil; Skowronski, Marek; Xiao, Di; Feenstra, Randall

    2015-03-01

    We have studied the surface electronic structure of oxygen vacancies on SrTiO3(001) surfaces using scanning tunneling spectroscopy and DFT calculations with local spin density approximation (LSDA +U). With high dynamic range measurements, a mid-gap level associated with the surface oxygen vacancies was observed for SrO-terminated surfaces. TiO2-terminated surfaces, on the other hand, did not exhibit observable mid-gap states (this lack of signal is believed to be due to the nature of defect wavefunction involved, as well as possibly involving transport limitations in the STS measurements). Both vacuum-cleaved and MBE-grown surface have been studied. For the former, the Fermi level is pinned near mid-gap owing to disorder-induced surface states. The amount of surface disorder can be controlled in the case of epitaxially grown surfaces. Rougher MBE-grown surfaces were found to exhibit similar spectral characteristics to the cleaved surfaces, while a shift of the Fermi level toward the conduction band was observed for flatter grown surfaces. Notably, with a decreasing number of disorder-induced surface states, the Fermi level is found to be pinned within the observed band of oxygen vacancy levels. This research was supported by AFOSR Grant No. FA9550-12-1-0479, and it used resources of the National Energy Research Scientific Computing Center, supported by the Office of Science, US Department of Energy under Contract No. DEAC02-05CH11231.

  7. Time-resolved photoelectron spectroscopy of a dinuclear Pt(II) complex: Tunneling autodetachment from both singlet and triplet excited states of a molecular dianion

    Science.gov (United States)

    Winghart, Marc-Oliver; Yang, Ji-Ping; Vonderach, Matthias; Unterreiner, Andreas-Neil; Huang, Dao-Ling; Wang, Lai-Sheng; Kruppa, Sebastian; Riehn, Christoph; Kappes, Manfred M.

    2016-02-01

    Time-resolved pump-probe photoelectron spectroscopy has been used to study the relaxation dynamics of gaseous [Pt2(μ-P2O5H2)4 + 2H]2- after population of its first singlet excited state by 388 nm femtosecond laser irradiation. In contrast to the fluorescence and phosphorescence observed in condensed phase, a significant fraction of the photoexcited isolated dianions decays by electron loss to form the corresponding monoanions. Our transient photoelectron data reveal an ultrafast decay of the initially excited singlet 1A2u state and concomitant rise in population of the triplet 3A2u state, via sub-picosecond intersystem crossing (ISC). We find that both of the electronically excited states are metastably bound behind a repulsive Coulomb barrier and can decay via delayed autodetachment to yield electrons with characteristic kinetic energies. While excited state tunneling detachment (ESETD) from the singlet 1A2u state takes only a few picoseconds, ESETD from the triplet 3A2u state is much slower and proceeds on a time scale of hundreds of nanoseconds. The ISC rate in the gas phase is significantly higher than in solution, which can be rationalized in terms of changes to the energy dissipation mechanism in the absence of solvent molecules. [Pt2(μ-P2O5H2)4 + 2H]2- is the first example of a photoexcited multianion for which ESETD has been observed following ISC.

  8. In Situ Observation of Water Dissociation with Lattice Incorporation at FeO Particle Edges Using Scanning Tunneling Microscopy and X-ray Photoelectron Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Xingyi [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Lee, Junseok [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Wang, Congjun [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Matranga, Christopher [National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States); Aksoy, Funda [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Nigde University, Nigde (Turkey). Dept. of Physics; Liu, Zhi [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2011-03-15

    The dissociation of H2O and formation of adsorbed hydroxyl groups, on FeO particles grown on Au(111) were identified with in situ,: X:ray photoelectron spectroscopy (XPS) at water pressures ranging from 3 x 10-8 to 0.1 Torr. The facile dissociation of H2O takes place at FeO particle edges, and it was successfully observed in situ With atomically resolved scanning tunneling microscopy (STM). The in situ STM studies show that adsorbed hydroxyl groups were formed exclusively along the edges of the FeO particles with the 0 atom becoming directly incorporated into the oxide crystalline lattice The STM results are consistent with coordinatively unsaturated ferrous (CUF) sites along the FeO particle edge causing the observed reactivity with H2O. Our results also directly illustrate how structural defects and under.-coordinated sites participate in chemical reactions.

  9. Spectroscopy

    DEFF Research Database (Denmark)

    Berg, Rolf W.

    This introductory booklet covers the basics of molecular spectroscopy, infrared and Raman methods, instrumental considerations, symmetry analysis of molecules, group theory and selection rules, as well as assignments of fundamental vibrational modes in molecules.......This introductory booklet covers the basics of molecular spectroscopy, infrared and Raman methods, instrumental considerations, symmetry analysis of molecules, group theory and selection rules, as well as assignments of fundamental vibrational modes in molecules....

  10. In-beam γ -ray spectroscopy of the neutron-rich platinum isotope 200Pt toward the N =126 shell gap

    Science.gov (United States)

    John, P. R.; Valiente-Dobón, J. J.; Mengoni, D.; Modamio, V.; Lunardi, S.; Bazzacco, D.; Gadea, A.; Wheldon, C.; Rodríguez, T. R.; Alexander, T.; de Angelis, G.; Ashwood, N.; Barr, M.; Benzoni, G.; Birkenbach, B.; Bizzeti, P. G.; Bizzeti-Sona, A. M.; Bottoni, S.; Bowry, M.; Bracco, A.; Browne, F.; Bunce, M.; Camera, F.; Corradi, L.; Crespi, F. C. L.; Melon, B.; Farnea, E.; Fioretto, E.; Gottardo, A.; Grente, L.; Hess, H.; Kokalova, Tz.; Korten, W.; Kuşoǧlu, A.; Lenzi, S.; Leoni, S.; Ljungvall, J.; Menegazzo, R.; Michelagnoli, C.; Mijatović, T.; Montagnoli, G.; Montanari, D.; Napoli, D. R.; Podolyák, Zs.; Pollarolo, G.; Recchia, F.; Reiter, P.; Roberts, O. J.; Şahin, E.; Salsac, M.-D.; Scarlassara, F.; Sferrazza, M.; Söderström, P.-A.; Stefanini, A. M.; Szilner, S.; Ur, C. A.; Vogt, A.; Walshe, J.

    2017-06-01

    The neutron-rich nucleus 200Pt is investigated via in-beam γ -ray spectroscopy to study the shape evolution in the neutron-rich platinum isotopes towards the N =126 shell closure. The two-neutron transfer reaction 198Pt(82Se, 80Se)200Pt is used to populate excited states of 200Pt. The Advanced Gamma Ray Tracking Array (AGATA) demonstrator coupled with the PRISMA spectrometer detects γ rays coincident with the 80Se recoils, the binary partner of 200Pt. The binary partner method is applied to extract the γ -ray transitions and build the level scheme of 200Pt. The level at 1884 keV reported by Yates et al. [S. W. Yates, E. M. Baum, E. A. Henry, L. G. Mann, N. Roy, A. Aprahamian, R. A. Meyer, and R. Estep, Phys. Rev. C 37, 1889 (1988)] was confirmed to be at 1882.1 keV and assigned as the (61+) state. An additional γ ray was found and it presumably deexcites the (81+) state. The results are compared with state-of-the-art beyond mean-field calculations, performed for the even-even 190 -204Pt isotopes, revealing that 200Pt marks the transition from the γ -unstable behavior of lighter Pt nuclei towards a more spherical one when approaching the N =126 shell closure.

  11. Kinetics of methane-ethane gas replacement in clathrate-hydrates studied by time-resolved neutron diffraction and Raman spectroscopy.

    Science.gov (United States)

    Murshed, M Mangir; Schmidt, Burkhard C; Kuhs, Werner F

    2010-01-14

    The kinetics of CH(4)-C(2)H(6) replacement in gas hydrates has been studied by in situ neutron diffraction and Raman spectroscopy. Deuterated ethane structure type I (C(2)H(6) sI) hydrates were transformed in a closed volume into methane-ethane mixed structure type II (CH(4)-C(2)H(6) sII) hydrates at 5 MPa and various temperatures in the vicinity of 0 degrees C while followed by time-resolved neutron powder diffraction on D20 at ILL, Grenoble. The role of available surface area of the sI starting material on the formation kinetics of sII hydrates was studied. Ex situ Raman spectroscopic investigations were carried out to crosscheck the gas composition and the distribution of the gas species over the cages as a function of structure type and compared to the in situ neutron results. Raman micromapping on single hydrate grains showed compositional and structural gradients between the surface and core of the transformed hydrates. Moreover, the observed methane-ethane ratio is very far from the one expected for a formation from a constantly equilibrated gas phase. The results also prove that gas replacement in CH(4)-C(2)H(6) hydrates is a regrowth process involving the nucleation of new crystallites commencing at the surface of the parent C(2)H(6) sI hydrate with a progressively shrinking core of unreacted material. The time-resolved neutron diffraction results clearly indicate an increasing diffusion limitation of the exchange process. This diffusion limitation leads to a progressive slowing down of the exchange reaction and is likely to be responsible for the incomplete exchange of the gases.

  12. Characterization of high fluence neutron induced defect levels in high resistivity silicon detectors using a laser deep level transient spectroscopy (L-DLTS)

    Energy Technology Data Exchange (ETDEWEB)

    Li Chengji (Inst. of Semiconductors, Chinese Academy of Sciences, Beijing, BJ (China)); Li Zheng (Brookhaven National Lab., Upton, NY (United States))

    1994-03-15

    Neutron irradiated high resistivity (4-6 k[Omega]-cm) silicon detectors in the neutron fluence ([Phi][sub n]) range of 5x10[sup 11] n/cm[sup 2] to 1x10[sup 14] n/cm[sup 2] have been studied using a laser deep level transient spectroscopy (L-DLTS). It has been found that the A-center (oxygen-vacancy, E[sub c]=0.17 eV) concentration increases with neutron fluence, reaching a maximum at [Phi][sub n] [approx]5x10[sup 12] n/cm[sup 2] before decreasing with [Phi][sub n]. A broad peak has been found between 200 K and 300 K, which is the result of the overlap of three single levels: the V-V[sup -] (E[sub c]=0.38 eV), the E-center (P-V, E[sub c]=0.44 eV), and a level at E[sub c] = 0.56 eV that is probably V-V[sup 0]. At low neutron fluences ([Phi][sub n]<5x10[sup 12] n/cm[sup 2]), this broad peak is dominated by V-V[sup -] and the E-centers. However, as the fluence increases ([Phi][sub n][>=]5x10[sup 12] n/cm[sup 2]), the peak becomes dominated by the level of E[sub c]=0.56 eV. (orig.)

  13. Neutron spectroscopy of $^{26}$Mg states: constraining the stellar neutron source $^{22}$Ne($\\alpha, n$)$^{25}$Mg arXiv

    CERN Document Server

    Massimi, C.

    This work reports on accurate, high-resolution measurements of the $^{25}$Mg($n, \\gamma$)$^{26}$Mg and $^{25}$Mg($n, tot$) cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved $^{25}$Mg($n, \\gamma$)$^{26}$Mg parametrization. The relevant resonances for $n+^{25}$Mg were characterized from a combined R-matrix analysis of the experimental data. This resulted in an unambiguous spin/parity assignment of the corresponding excited states in $^{26}$Mg. With this information experimental upper limits of the reaction rates for $^{22}$Ne($\\alpha, n$)$^{25}$Mg and $^{22}$Ne($\\alpha, \\gamma$)$^{26}$Mg were established, potentially leading to a significantly higher ($\\alpha, n$)/($\\alpha, \\gamma$) ratio than previously evaluated. The impact of these results have been studied for stellar models in the mass range 2 to 25 $M_{\\odot}$.

  14. Short tunnels.

    NARCIS (Netherlands)

    Schreuder, D.A.

    1965-01-01

    Before dealing with the question of lighting short tunnels, it is necessary define what is meant by a tunnel and when it should be called 'short'. Confined to motorized road traffic the following is the most apt definition of a tunnel: every form of roofing-over a road section, irrespective of it le

  15. Neutron-emission measurements at a white neutron source

    Energy Technology Data Exchange (ETDEWEB)

    Haight, Robert C [Los Alamos National Laboratory

    2010-01-01

    Data on the spectrum of neutrons emittcd from neutron-induced reactions are important in basic nuclear physics and in applications. Our program studies neutron emission from inelastic scattering as well as fission neutron spectra. A ''white'' neutron source (continuous in energy) allows measurements over a wide range of neutron energies all in one experiment. We use the tast neutron source at the Los Alamos Neutron Science Center for incident neutron energies from 0.5 MeV to 200 MeV These experiments are based on double time-of-flight techniques to determine the energies of the incident and emitted neutrons. For the fission neutron measurements, parallel-plate ionization or avalanche detectors identify fission in actinide samples and give the required fast timing pulse. For inelastic scattering, gamma-ray detectors provide the timing and energy spectroscopy. A large neutron-detector array detects the emitted neutrons. Time-of-flight techniques are used to measure the energies of both the incident and emitted neutrons. Design considerations for the array include neutron-gamma discrimination, neutron energy resolution, angular coverage, segmentation, detector efficiency calibration and data acquisition. We have made preliminary measurements of the fission neutron spectra from {sup 235}U, {sup 238}U, {sup 237}Np and {sup 239}Pu. Neutron emission spectra from inelastic scattering on iron and nickel have also been investigated. The results obtained will be compared with evaluated data.

  16. Time-resolved photoelectron spectroscopy of a dinuclear Pt(II) complex: Tunneling autodetachment from both singlet and triplet excited states of a molecular dianion

    Energy Technology Data Exchange (ETDEWEB)

    Winghart, Marc-Oliver, E-mail: marc-oliver.winghart@kit.edu; Unterreiner, Andreas-Neil [Institute of Physical Chemistry, Karlsruhe Institute of Technology, P.O. Box 6980, 76049 Karlsruhe (Germany); Yang, Ji-Ping [Institute of Physical Chemistry, Karlsruhe Institute of Technology, P.O. Box 6980, 76049 Karlsruhe (Germany); School of Sciences, Hefei University of Technology, Hefei 230009 (China); Vonderach, Matthias [Centre for Proteome Research, Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB (United Kingdom); Huang, Dao-Ling; Wang, Lai-Sheng [Department of Chemistry, Brown University, Providence, Rhode Island 02912 (United States); Kruppa, Sebastian; Riehn, Christoph [Fachbereich Chemie und Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, Erwin-Schrödinger-Str. 52–54, 67663 Kaiserslautern (Germany); Kappes, Manfred M., E-mail: manfred.kappes@kit.edu [Institute of Physical Chemistry, Karlsruhe Institute of Technology, P.O. Box 6980, 76049 Karlsruhe (Germany); Institute of Nanotechnology, Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe (Germany)

    2016-02-07

    Time-resolved pump-probe photoelectron spectroscopy has been used to study the relaxation dynamics of gaseous [Pt{sub 2}(μ-P{sub 2}O{sub 5}H{sub 2}){sub 4} + 2H]{sup 2−} after population of its first singlet excited state by 388 nm femtosecond laser irradiation. In contrast to the fluorescence and phosphorescence observed in condensed phase, a significant fraction of the photoexcited isolated dianions decays by electron loss to form the corresponding monoanions. Our transient photoelectron data reveal an ultrafast decay of the initially excited singlet {sup 1}A{sub 2u} state and concomitant rise in population of the triplet {sup 3}A{sub 2u} state, via sub-picosecond intersystem crossing (ISC). We find that both of the electronically excited states are metastably bound behind a repulsive Coulomb barrier and can decay via delayed autodetachment to yield electrons with characteristic kinetic energies. While excited state tunneling detachment (ESETD) from the singlet {sup 1}A{sub 2u} state takes only a few picoseconds, ESETD from the triplet {sup 3}A{sub 2u} state is much slower and proceeds on a time scale of hundreds of nanoseconds. The ISC rate in the gas phase is significantly higher than in solution, which can be rationalized in terms of changes to the energy dissipation mechanism in the absence of solvent molecules. [Pt{sub 2}(μ-P{sub 2}O{sub 5}H{sub 2}){sub 4} + 2H]{sup 2−} is the first example of a photoexcited multianion for which ESETD has been observed following ISC.

  17. Possible Nodeless Superconducting Gaps in Bi2Sr2CaCu2O8+δ and YBa2Cu3O7-x Revealed by Cross-Sectional Scanning Tunneling Spectroscopy

    Science.gov (United States)

    Ren, Ming-Qiang; Yan, Ya-Jun; Zhang, Tong; Feng, Dong-Lai

    2016-12-01

    Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics. With cross-sectional scanning tunneling microscopy/ spectroscopy, we clearly reveal the spatial-dependence or inhomogeneity of the superconducting gap structure of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\\delta}$ (Bi2212) and YBa$_2$Cu$_3$O$_{7-x}$ (YBCO) along their $c$-axes on a scale shorter than the interlayer spacing. By tunneling into the (100) plane of a Bi2212 single crystal and a YBCO film, we observe both U-shaped tunneling spectra with extended flat zero-conductance bottoms, and V-shaped gap structures, in different regions of each sample. On the YBCO film, tunneling into a (110) surface only reveals a U-shaped gap without any zero-bias peak. Our analysis suggests that the U-shaped gap is likely a nodeless superconducting gap. The V-shaped gap has a very small amplitude, and is likely proximity-induced by regions having the larger U-shaped gap.

  18. Dual sightline measurements of MeV range deuterons with neutron and gamma-ray spectroscopy at JET

    DEFF Research Database (Denmark)

    Eriksson, J.; Nocente, M.; Binda, F.

    2015-01-01

    Observations made in a JET experiment aimed at accelerating deuterons to the MeV range by third harmonic radio-frequency (RF) heating coupled into a deuterium beam are reported. Measurements are based on a set of advanced neutron and gamma-ray spectrometers that, for the first time, observe the p......, more generally, to studies of the energy distribution of ions in the MeV range in high performance deuterium and deuterium-tritium plasmas....

  19. Grain boundary engineering of La{sub 0.7} Sr{sub 0.3} MnO{sub 3} films on silicon substrate: Scanning Tunneling Microscopy-Spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, Anupama [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India); Nori, Rajashree [Centre of Excellence in Nanoelectronics, Department of Electrical Engineering, Indian Institute of Technology (IIT Bombay), Mumbai 400076 (India); Dhobale, Sandip [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India); Ramgopal Rao, V. [Centre of Excellence in Nanoelectronics, Department of Electrical Engineering, Indian Institute of Technology (IIT Bombay), Mumbai 400076 (India); Kale, S.N., E-mail: sangeetakale2004@gmail.com [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India); Datar, Suwarna, E-mail: suwarna.datar@gmail.com [Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune 411025 (India)

    2014-09-01

    We employed a Scanning Tunnelling Microscope (STM) to study the surface topography and spatially resolved local electronic properties like local density of states (LDOS) of nanostructured films of La{sub 0.7} Sr{sub 0.3} MnO{sub 3} (LSMO). The nanostructured thin films of LSMO on silicon substrate were prepared using Pulsed Laser Deposition (PLD) technique. The deposition conditions were tuned to yield two different morphologies; one with uniform columnar closely packed islands and other with larger grain distribution in random fashion. The Scanning Tunnelling Spectroscopy (STS) revealed the extent of variation of density of states (DOS) near the Fermi level. From the spectroscopic features obtained we found the occurrence of phase separation between conducting and semiconducting domains and its possible correlation with the properties of the system. Semiconducting nature was observed at the grain boundaries, which could be extremely promising in futuristic nano-devices.

  20. Single-neutron orbits near {sup 78}Ni: Spectroscopy of the N=49 isotope {sup 79}Zn

    Energy Technology Data Exchange (ETDEWEB)

    Orlandi, R., E-mail: orlandi.riccardo@jaea.go.jp [Instituto de Estructura de la Materia, IEM-CSIC, Madrid, E-28006 (Spain); KU Leuven, Instituut voor Kern- en Stralingsfysica, B-3001 Heverlee (Belgium); School of Engineering, University of the West of Scotland, Paisley, PA1 2BE (United Kingdom); Scottish Universities Physics Alliance (SUPA) (United Kingdom); Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195 (Japan); Mücher, D. [Physik Department E12, Technische Universität München, D-85748 Garching (Germany); Raabe, R. [KU Leuven, Instituut voor Kern- en Stralingsfysica, B-3001 Heverlee (Belgium); Jungclaus, A. [Instituto de Estructura de la Materia, IEM-CSIC, Madrid, E-28006 (Spain); Pain, S.D. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Bildstein, V. [Physik Department E12, Technische Universität München, D-85748 Garching (Germany); Chapman, R. [School of Engineering, University of the West of Scotland, Paisley, PA1 2BE (United Kingdom); Scottish Universities Physics Alliance (SUPA) (United Kingdom); Angelis, G. de [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Legnaro, I-35020 (Italy); Johansen, J.G. [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus (Denmark); Van Duppen, P. [KU Leuven, Instituut voor Kern- en Stralingsfysica, B-3001 Heverlee (Belgium); Andreyev, A.N. [School of Engineering, University of the West of Scotland, Paisley, PA1 2BE (United Kingdom); Scottish Universities Physics Alliance (SUPA) (United Kingdom); Department of Physics, University of York, Heslington, YO10 5DD (United Kingdom); Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195 (Japan); and others

    2015-01-05

    Single-neutron states in the Z=30, N=49 isotope {sup 79}Zn have been populated using the {sup 78}Zn(d, p){sup 79}Zn transfer reaction at REX-ISOLDE, CERN. The experimental setup allowed the combined detection of protons ejected in the reaction, and of γ rays emitted by {sup 79}Zn. The analysis reveals that the lowest excited states populated in the reaction lie at approximately 1 MeV of excitation, and involve neutron orbits above the N=50 shell gap. From the analysis of γ-ray data and of proton angular distributions, characteristic of the amount of angular momentum transferred, a 5/2{sup +} configuration was assigned to a state at 983 keV. Comparison with large-scale-shell-model calculations supports a robust neutron N=50 shell-closure for {sup 78}Ni. These data constitute an important step towards the understanding of the magicity of {sup 78}Ni and of the structure of nuclei in the region.

  1. YMn2Hx and RMn(2-y)Fe(y)H6 (R = Y, Er) studied by Raman, infrared and inelastic neutron scattering spectroscopies.

    Science.gov (United States)

    Paul-Boncour, V; Parker, S F; Hagemann, H; Filipek, S M; Wierzbicki, R; Latroche, M

    2011-01-01

    YMn2 forms either interstitial YMn2Hx hydrides for x < or = 4.5 or a complex YMn2H6 hydride when submitted to high hydrogen pressure. These compounds have been studied by inelastic neutron scattering (INS) in order to clarify the different modes of H vibration. The INS spectra of YMn2Hx hydrides are strongly dependent on the H content. YMn2H6 and YMn2D6 show broad bands, also observed by Raman and IR spectroscopy, assigned to H-Mn-H (or D) and Mn-H bending and stretching modes. Both ErMn2D6 and ErMn1.8Fe0.2D6 show, in addition to the H vibration mode, an intense band at 215 cm(-1) which has been attributed to a magnetic excitation of Er3+ in view of its momentum transfer dependence.

  2. Study of atomic clusters in neutron irradiated reactor pressure vessel surveillance samples by extended X-ray absorption fine structure spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Cammelli, S. [LWV, NES, Paul Scherrer Institute, 5232 Villigen PSI (Switzerland); Fachbereich C - Physik, Bergische Universitaet Wuppertal, Gauss-Str. 20, 42097 Wuppertal (Germany)], E-mail: Sebastiano.cammelli@psi.ch; Degueldre, C.; Kuri, G.; Bertsch, J. [LWV, NES, Paul Scherrer Institute, 5232 Villigen PSI (Switzerland); Luetzenkirchen-Hecht, D.; Frahm, R. [Fachbereich C - Physik, Bergische Universitaet Wuppertal, Gauss-Str. 20, 42097 Wuppertal (Germany)

    2009-03-31

    Copper and nickel impurities in nuclear reactor pressure vessel (RPV) steel can form nano-clusters, which have a strong impact on the ductile-brittle transition temperature of the material. Thus, for control purposes and simulation of long irradiation times, surveillance samples are submitted to enhanced neutron irradiation. In this work, surveillance samples from a Swiss nuclear power plant were investigated by extended X-ray absorption fine structure spectroscopy (EXAFS). The density of Cu and Ni atoms determined in the first and second shells around the absorber is affected by the irradiation and temperature. The comparison of the EXAFS data at Cu and Ni K-edges shows that these elements reside in arrangements similar to bcc Fe. However, the EXAFS analysis reveals local irradiation damage in the form of vacancy fractions, which can be determined with a precision of {approx}5%. There are indications that the formation of Cu and Ni clusters differs significantly.

  3. Structure-Dependent Vibrational Dynamics of Mg(BH4)2 Polymorphs Probed with Neutron Vibrational Spectroscopy and First-Principles Calculations

    Energy Technology Data Exchange (ETDEWEB)

    Dimitrievska, Mirjana; White, James L.; Zhou, Wei; Stavila, Vitalie; Klebanoff, Leonard E.; Udovic, Terrence J.

    2016-09-28

    The structure-dependent vibrational properties of different Mg(BH4)2 polymorphs (..alpha.., ..beta.., ..gamma.., and ..delta.. phases) were investigated with a combination of neutron vibrational spectroscopy (NVS) measurements and density functional theory (DFT) calculations, with emphasis placed on the effects of the local structure and orientation of the BH4- anions. DFT simulations closely match the neutron vibrational spectra. The main bands in the low-energy region (20-80 meV) are associated with the BH4- librational modes. The features in the intermediate energy region (80-120 meV) are attributed to overtones and combination bands arising from the lower-energy modes. The features in the high-energy region (120-200 meV) correspond to the BH4- symmetric and asymmetric bending vibrations, of which four peaks located at 140, 142, 160, and 172 meV are especially intense. There are noticeable intensity distribution variations in the vibrational bands for different polymorphs. This is explained by the differences in the spatial distribution of BH4- anions within various structures. An example of the possible identification of products after the hydrogenation of MgB2, using NVS measurements, is presented. These results provide fundamental insights of benefit to researchers currently studying these promising hydrogen-storage materials.

  4. Scanning Tunneling Spectroscopy on polycrystalline Cu(In,Ga)(S,Se){sub 2} thin-film solar cells; Rastertunnelspektroskopie an polykristallinen Cu(In,Ga)(S,Se){sub 2}-Duennschichtsolarzellen

    Energy Technology Data Exchange (ETDEWEB)

    Herber, U.

    2006-12-21

    In case of the investigated multinary Cu(In;Ga)Se{sub 2} system with its polycrystalline structure, the question for the lateral homogeneity of its electronic properties arises. By means of the here presented method, a photo-assisted tunneling spectroscopy, such lateral inhomogeneities of the Surface Photo Voltage (SPV) and the Photo-Induced Tunneling Current (PITC) are to be detected. Modulations of the bias voltage and/or the illumination intensity have been applied to a greater number of materials in tunneling spectroscopy. Within these field, disturbing current contributions, coupled via the tip-sample-capacitance, is a known problem. Electronic compensation by using an appropriate compensating circuit is a possible solution. As will be shown in this work, such procedure is very adequate to compensate stray signals generated by bias modulation. After the introduction and careful analysis of our technique in the first part the second part of the thesis deals with its application to a series of different CIGS samples. What becomes apparent is the aforementioned inhomogeneities in PITC signal to be an immanent property of these polycrystalline semiconductor systems. Besides lateral variations in the photocurrent amplitude, also inhomogeneities within its complex phase can be demonstrated. As becomes clear, it is impossible to draw conclusions about the participating capacity of the depletion region because of the dominating admittance of the tunneling junction. However, it is possible to gain a statistical distribution of the PITC by investigating a large number of positions on the sample. For small numbers of weak diodes, the distribution exhibits a distinct maximum at higher photocurrents. Metastable effects are observed by tracking PITC values over a longer period of time. (orig.)

  5. High-resolution tunnel fluctuoscopy

    Energy Technology Data Exchange (ETDEWEB)

    Glatz, A.; Varlamov, A. A.; Vinokur, V. M.

    2014-08-01

    Electron tunneling spectroscopy pioneered by Esaki and Giaever offered a powerful tool for studying electronic spectra and density of states (DOS) in superconductors. This led to important discoveries that revealed, in particular, the pseudogap in the tunneling spectrum of superconductors above their critical temperatures. However, the phenomenological approach of Giaever and Megerle does not resolve the fine structure of low-bias behavior carrying significant information about electron scattering, interactions, and decoherence effects. Here we construct a complete microscopic theory of electron tunneling into a superconductor in the fluctuation regime. We reveal a non-trivial low-energy anomaly in tunneling conductivity due to Andreev-like reflections of injected electrons from superconducting fluctuations. Our findings enable real-time observation of fluctuating Cooper pairs dynamics by time-resolved scanning tunneling microscopy measurements and open new horizons for quantitative analysis of the fluctuation electronic spectra of superconductors.

  6. Hyperfine interaction in Co{sub 2}SiO{sub 4} investigated by high resolution neutron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Chatterji, Tapan, E-mail: chatterji@ill.f [JCNS, Forschungszentrum Juelich Outstation at Institut Laue-Langevin, B.P. 156, 38042 Grenoble Cedex 9 (France); Wuttke, J. [JCNS, Forschungszentrum Juelich Outstation at FRMII, Lichtenbergstrasse 1, 85747 Garching (Germany); Sazonov, A.P. [FRMII, Technische Universitaet Muenchen, Lichtenbergstrasse 1, 85747 Garching (Germany)

    2010-10-15

    We have investigated the hyperfine interaction in Co{sub 2}SiO{sub 4} by inelastic neutron scattering with a high resolution back-scattering neutron spectrometer. The energy spectrum measured from a Co{sub 2}SiO{sub 4} powder sample revealed inelastic peaks at E=1.387{+-}0.006{mu}eV at T=3.5 K on both energy gain and energy loss sides. The inelastic peaks move gradually towards lower energy with increasing temperature and finally merge with the elastic peak at the electronic magnetic ordering temperature T{sub N{approx}}50K. The inelastic peaks have been interpreted to be due to the transition between hyperfine-split nuclear level of the {sup 59}Co isotopes with spin I=7/2 . The temperature dependence of the energy of the inelastic peak in Co{sub 2}SiO{sub 4} showed that this energy can be considered to be the order parameter of the antiferromagnetic phase transition. The determined hyperfine splitting in Co{sub 2}SiO{sub 4} deviates from the linear relationship between the ordered electronic magnetic moment and the hyperfine splitting in Co, Co-P amorphous alloys and CoO presumably due to the presence of unquenched orbital moment. These results are very similar to those of CoF{sub 2} recently reported by Chatterji and Schneider.

  7. Study of neutron-rich nuclei structure around the N=28 shell closure using the in-beam gamma spectroscopy technique; Etude de la structure des noyaux riches en neutrons autour de la fermeture de couches N=28 par spectroscopie gamma en ligne

    Energy Technology Data Exchange (ETDEWEB)

    Bastin, B

    2007-10-15

    For a few years now, a loss of magicity in neutron-rich nuclei near the neutron drip-line at N=28 has been suggested and observed. Deformation in these nuclei has been observed. The deformation was explained in S isotopes as being due to a moderate reduction of the N=28 shell closure together with a proton induced collectivity originating from the near degeneracy of the proton d3/2 and s1/2 orbitals. As a consequence, the observed deformation seems to result from a subtle interplay between neutron and proton excitations. Since the proton configuration in the Si isotopes is expected to be more stable due to the Z=14 sub-shell gap, {sup 42}Si was considered as a key nucleus in order to distinguish the different effects responsible for the structural changes observed at N=28. Even if it is at the limits of our technical possibilities, an in-beam gamma-spectroscopy experiment using two-step fragmentation and one or several nucleons knockout reaction mechanisms was performed at GANIL. The measurement of the energy of the first excited state in {sup 42}Si, combined with the observation of {sup 38,40}Si and the spectroscopy of {sup 41,43}P, has given evidence for the loss of magicity at N=28 far from stability. Modifications of the effective interaction used in modern shell model calculations have been completed following this investigation, increasing its predictive character. This study confirms the role of the tensor force and the density dependence of the spin-orbit interaction in the collapse of the N=28 shell closure. (author)

  8. Dopant effects on 2-ethyl-1-hexanol: A dual-channel impedance spectroscopy and neutron scattering study

    Science.gov (United States)

    Singh, Lokendra P.; Raihane, Ahmed; Alba-Simionesco, Christiane; Richert, Ranko

    2015-01-01

    A two-channel impedance technique has been used to study the relaxation behavior of 2-ethyl-1-hexanol with polar and non-polar dopants at the few percent concentration level over a wide temperature and frequency range. The non-polar dopants shift both the Debye and the primary structural relaxation time in the same direction, to shorter times for 3-methylpentane and to longer times for squalane, consistent with the relative glass transition temperatures (Tg) of the components. By contrast, polar dopants such as water or methanol modify the α-process towards slower dynamics and increased amplitude, while the Debye process is accelerated and with a decreased amplitude. This effect of adding water to alcohol is explained by water promoting more compact structures with reduced Kirkwood correlation factors. This picture is consistent with a shift in the neutron scattering pre-peak to lower scattering vectors and with simulation work on alcohol-water systems.

  9. Dopant effects on 2-ethyl-1-hexanol: A dual-channel impedance spectroscopy and neutron scattering study

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Lokendra P.; Richert, Ranko, E-mail: ranko@asu.edu [Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604 (United States); Raihane, Ahmed; Alba-Simionesco, Christiane [Laboratoire Léon Brillouin, CNRS /CEA -UMR 12, DSM/IRAMIS/LLB CEA Saclay, 91191 Gif-sur-Yvette Cedex (France)

    2015-01-07

    A two-channel impedance technique has been used to study the relaxation behavior of 2-ethyl-1-hexanol with polar and non-polar dopants at the few percent concentration level over a wide temperature and frequency range. The non-polar dopants shift both the Debye and the primary structural relaxation time in the same direction, to shorter times for 3-methylpentane and to longer times for squalane, consistent with the relative glass transition temperatures (T{sub g}) of the components. By contrast, polar dopants such as water or methanol modify the α-process towards slower dynamics and increased amplitude, while the Debye process is accelerated and with a decreased amplitude. This effect of adding water to alcohol is explained by water promoting more compact structures with reduced Kirkwood correlation factors. This picture is consistent with a shift in the neutron scattering pre-peak to lower scattering vectors and with simulation work on alcohol-water systems.

  10. Structural investigation on gamma-irradiated polyacrylamide hydrogels using small-angle neutron scattering and ultraviolet–visible spectroscopy

    Indian Academy of Sciences (India)

    Sivananatham M; Tata B V R; Aswal V K

    2016-03-01

    Small-angle neutron scattering (SANS) and ultraviolet (UV)–visible spectroscopictechniques are used to investigate the microstructural changes in polyacrylamide (PAAm) hydrogels on gamma irradiation. SANS measurements have revealed the presence of inhomogeneities in nanometre scale and reduction of their size with increase in dose. Analysis of SANS data alsorevealed the increase in the correlation length with increase in dose. The extinction coefficient obtained from the UV–visible spectroscopic studies exhibited $\\lambda^{−\\beta}$ dependence between 500 and 700 nm and is understood to arise from the existence of scatterers (inhomogeneities) in submicron scale in PAAm hydrogels. The increase in value of exponent $\\beta$ with increase in dose indicates that the size of scatterers decrease with increase in dose.

  11. HORACE: software for the analysis of data from single crystal spectroscopy experiments at time-of-flight neutron instruments

    CERN Document Server

    Ewings, R A; Le, M D; van Duijn, J; Bustinduy, I; Perring, T G

    2016-01-01

    The HORACE suite of programs has been developed to work with large multiple-measurement data sets collected from time-of-flight neutron spectrometers equipped with arrays of position-sensitive detectors. The software allows exploratory studies of the four dimensions of reciprocal space and excitation energy to be undertaken, enabling multi-dimensional subsets to be visualized, algebraically manipulated, and models for the scattering to simulated or fitted to the data. The software is designed to be an extensible framework, thus allowing user-customized operations to be performed on the data. Examples of the use of its features are given for measurements exploring the spin waves of the simple antiferromagnet RbMnF$_{3}$ and ferromagnetic iron, and the phonons in URu$_{2}$Si$_{2}$.

  12. HORACE: Software for the analysis of data from single crystal spectroscopy experiments at time-of-flight neutron instruments

    Science.gov (United States)

    Ewings, R. A.; Buts, A.; Le, M. D.; van Duijn, J.; Bustinduy, I.; Perring, T. G.

    2016-10-01

    The HORACE suite of programs has been developed to work with large multiple-measurement data sets collected from time-of-flight neutron spectrometers equipped with arrays of position-sensitive detectors. The software allows exploratory studies of the four dimensions of reciprocal space and excitation energy to be undertaken, enabling multi-dimensional subsets to be visualized, algebraically manipulated, and models for the scattering to simulated or fitted to the data. The software is designed to be an extensible framework, thus allowing user-customized operations to be performed on the data. Examples of the use of its features are given for measurements exploring the spin waves of the simple antiferromagnet RbMnF3 and ferromagnetic iron, and the phonons in URu2Si2.

  13. Synchrotron VUV-UV and positron lifetime spectroscopy study of vacancy-type defects in reactor neutron-irradiated MgO·nAl2O3 (n = 2

    Directory of Open Access Journals (Sweden)

    Abu Zayed Mohammad Saliqur Rahman

    2016-12-01

    Full Text Available We investigated neutron-irradiation-induced point defects in spinel single crystals using a synchrotron VUV-UV source and positron lifetime spectroscopy. Photoexcitation (PE spectra near 230 nm and their corresponding photoluminescence (PL spectra at 475 nm were attributed to F-centers. With increasing irradiation temperature and fluence, PE efficiency and PL intensity decreased dramatically. Positron lifetimes (PLT of neutron-irradiated and non-irradiated samples were measured to identify the cation vacancies. A PLT measurement of 250 ps was obtained in a neutron-irradiated (20 K sample which is tentatively attributed to an aluminum monovacancy. Decreasing PLT with higher irradiation indicates the formation of oxygen-vacancy complex centers.

  14. Nano-confined water in the interlayers of hydrocalumite: Reorientational dynamics probed by neutron spectroscopy and molecular dynamics computer simulations

    Science.gov (United States)

    Kalinichev, A. G.; Faraone, A.; Udovic, T.; Kolesnikov, A. I.; de Souza, N. R.; Reinholdt, M. X.; Kirkpatrick, R.

    2008-12-01

    Layered double hydroxides (LDHs, anionic clays) represent excellent model systems for detailed molecular- level studies of the structure, dynamics, and energetics of nano-confined water in mineral interlayers and nano-pores, because LDH interlayers can have a well-defined structures and contain H2O molecules and a wide variety of anions in structurally well-defined positions and coordinations. [Ca2Al(OH)6]Cl·2H2O, also known as hydrocalumite or Friedel's salt, has a well- ordered Ca,Al distribution in the hydroxide layer and a very high degree of H2O,Cl ordering in the interlayer. It is also one of the only LDH phase for which a single crystal structure refinement is available. Thus, it is currently the best model compound for understanding the structure and dynamical behavior of interlayer and surface species in other, less-ordered, LDHs. We investigated the structural and dynamic behavior of water in the interlayers of hydrocalumite using inelastic (INS) and quasielastic (QENS) neutron scattering and molecular dynamics computer simulations. The comperehensive neutron scattering studies were performed for one fully hydrated and one dehydrated sample of hydrocalumite using several complementary instruments (HFBS, DCS and FANS at NCNR; HRMECS and QENS at IPNS) at temperatures above and below the previously discovered order-disorder interlayer phase transition. Together the experimental and molecular modeling results capture the important details of the dynamics of nano-confined water and the effects of the orientational ordering of H2O molecules above and below the phase transition. They provide otherwise unobtainable experimental information about the transformation of H2O librational and diffusional modes across the order-disorder phase transition and significantly add to our current understanding of the structure and dynamics of water in LDH phases based on the earlier NMR, IR, X-ray, and calorimetric measurements. The approach can now be extended to probe the

  15. Demonstrating the likely neutron star nature of five M31 globular cluster sources with Swift-NuSTAR spectroscopy

    DEFF Research Database (Denmark)

    Maccarone, Thomas J.; Yukita, Mihoko; Hornschemeier, Ann

    2016-01-01

    for which neutron stars are in hard states. We show that these two sources are likely to be Z-sources (i.e. low magnetic field neutron stars accreting near their Eddington limits), or perhaps bright atoll sources (low magnetic field neutron stars which are just a bit fainter than this level) on the basis...

  16. Quantification of some elements of nuclear and industrial interest from zircon mineral using neutron activation analysis and passive gamma-ray spectroscopy.

    Science.gov (United States)

    Attallah, M F; Hilal, M A; Moussa, S I

    2017-10-01

    A combined of various nuclear and analytical techniques were used for characterization of Egyptian zircon ore. Neutron activation analysis has been used for determination of the major, minor and trace elements from zircon ore. Non-destructive gamma-ray technique is also used for the radiometric analysis of zircon ore to quantify the natural radionuclides such as (238)U, (235)U, (232)Th, (226)Ra and (40)K. Zircon ore has been characterized by different analytical tools such as Fourier transformer infrared (FTIR), X-ray fluorescence (XRF), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM). In this study, a significant concentration of U, Th and rare earth elements (REEs) has been reported. The obtained results showed that the average activity concentration of (238)U, (235)U, (226)Ra, (232)Th and (40)K are 4771±338, 230±17.1, 3588±125, 982±47.7 and 217±48.5Bq/kg, respectively. The results indicated that 297, 318 and 838mg/Kg for U, Th, REEs, respectively, using NAA. These results are consistent with those obtained by gamma-ray spectroscopy and/or XRF. It can be concluded that zircon ore is a riche with a valuable nuclear materials such as U, Th, Zr, and Hf. It is also containing a REEs of economic and industrial interest. Also, the different radiation hazardous parameters were found much higher than the permissible values. Copyright © 2017 Elsevier Ltd. All rights reserved.

  17. Dynamics of tetrahydrofuran as minority component in a mixture with poly(2-(dimethylamino)ethyl methacrylate): A neutron scattering and dielectric spectroscopy investigation

    Energy Technology Data Exchange (ETDEWEB)

    Goracci, G., E-mail: sckgorag@ehu.es; Arbe, A. [Centro de Física de Materiales (CFM), CSIC–UPV/EHU–Materials Physics Center - MPC, Paseo Manuel de Lardizabal 5, 20018 San Sebastián (Spain); Alegría, A. [Centro de Física de Materiales (CFM), CSIC–UPV/EHU–Materials Physics Center - MPC, Paseo Manuel de Lardizabal 5, 20018 San Sebastián (Spain); Departamento de Física de Materiales (UPV/EHU), Apartado 1072, 20080 San Sebastián (Spain); Lohstroh, W. [Heinz Maier-Leibnitz Zentrum, Technische Universität München, Lichtenbergstraße 1, D-85748 Garching (Germany); Su, Y. [Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Outstation at MLZ, Lichtenbergstraße 1, 85747 Garching (Germany); Colmenero, J. [Centro de Física de Materiales - CFM, CSIC–UPV/EHU–Materials Physics Center - MPC, Paseo Manuel de Lardizabal 5, 20018 San Sebastián (Spain); Departamento de Física de Materiales (UPV/EHU), Apartado 1072, 20080 San Sebastián (Spain); Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 San Sebastián (Spain)

    2015-09-07

    We have investigated a mixture of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and tetrahydrofuran (THF) (70 wt. % PDMAEMA/30 wt. % THF) by combining dielectric spectroscopy and quasielastic neutron scattering (QENS) on a labelled sample, focusing on the dynamics of the THF molecules. Two independent processes have been identified. The “fast” one has been qualified as due to an internal motion of the THF ring leading to hydrogen displacements of about 3 Å with rather broadly distributed activation energies. The “slow” process is characterized by an Arrhenius-like temperature dependence of the characteristic time which persists over more than 9 orders of magnitude in time. The QENS results evidence the confined nature of this process, determining a size of about 8 Å for the volume within which THF hydrogens’ motions are restricted. In a complementary way, we have also investigated the structural features of the sample. This study suggests that THF molecules are well dispersed among side-groups nano-domains in the polymer matrix, ruling out a significant presence of clusters of solvent. Such a good dispersion, together with a rich mobility of the local environment, would prevent cooperativity effects to develop for the structural relaxation of solvent molecules, frustrating thereby the emergence of Vogel-Fulcher-like behavior, at least in the whole temperature interval investigated.

  18. Ground state properties of neutron-rich Mg isotopes the "island of inversion" studied with laser and $\\beta$-NMR spectroscopy

    CERN Document Server

    Kowalska, M

    2006-01-01

    Studies in regions of the nuclear chart in which the model predictions of properties of nuclei fail can bring a better understanding of the strong interaction in the nuclear medium. To such regions belongs the so called "island of inversion" centered around Ne, Na and Mg isotopes with 20 neutrons in which unexpected ground-state spins, large deformations and dense low-energy spectra appear. This is a strong argument that the magic N=20 is not a closed shell in this area. In this thesis investigations of isotope shifts of stable $^{24-26}$Mg, as well as spins and magnetic moments of short-lived $^{29,31}$Mg are presented. The successful studies were performed at the ISOLDE facility at CERN using collinear laser and $\\beta$-NMR spectroscopy techniques. The isotopes were investigated as single-charged ions in the 280 nm transition from the atomic ground state $^2\\!$S$_{1/2}$ to one of the two lowest excited states $^2\\!$P$_{1/2 ,\\,3/2}$ using continuous wave laser beams. The isotope-shift measurements with fluor...

  19. Selective spectroscopy of tunneling transitions between the Landau levels in vertical double-gate graphene-boron nitride-graphene heterostructures

    Science.gov (United States)

    Khanin, Yu. N.; Vdovin, E. E.; Mishchenko, A.; Tu, J. S.; Kozikov, A.; Gorbachev, R. V.; Novoselov, K. S.

    2016-09-01

    Resonance magnetic tunneling in heterostructures formed by graphene single sheets separated by a hexagonal boron nitride barrier and two gates has been investigated. The design has allowed studying transitions between individual Landau levels of different graphene sheets bounded by a narrow conductivity window with a width controlled by a bias voltage. Three-dimensional plots of the equilibrium tunneling conductivity against both gate voltages reflecting the displacement of resonances between various combinations of the individual Landau levels in the top and bottom sheets have been drawn and identified. The discovered step structure of the current patterns with plateaus and abrupt jumps between them is caused by pinning of chemical potentials to the Landau levels in two graphene sheets. The presence of negative differential conductivity regions in the current-voltage characteristics in the magnetic field with the peak-to-valley current ratio I p/ I v 2 indicates a high degree of the conservation of an in-plane momentum component at tunneling.

  20. Unraveling the spectroscopy of coupled intramolecular tunneling modes: a study of double proton transfer in the formic-acetic acid complex.

    Science.gov (United States)

    Tayler, Michael C D; Ouyang, Bin; Howard, Brian J

    2011-02-07

    The rotational spectrum of the hetero dimer comprising doubly hydrogen-bonded formic acid and acetic acid has been recorded between 4 and 18 GHz using a pulsed-nozzle Fourier transform microwave spectrometer. Each rigid-molecule rotational transition is split into four as a result of two concurrently ongoing tunneling motions, one being proton transfer between the two acid molecules, and the other the torsion/rotation of the methyl group within the acetyl part. We present a full assignment of the spectrum J = 1 to J = 6 for the ground vibronic states. The transitions are fitted to within a few kilohertz of the observed frequencies using a molecule-fixed effective rotational Hamiltonian for the separate A and E vibrational species of the G(12) permutation-inversion symmetry group. Interpretation of the motion problem uses an internal-vibration and overall-rotation angular momentum coupling scheme and full sets of rotational and centrifugal distortion constants are determined. The tunneling frequencies of the proton-transfer motion are measured for the ground A and E methyl rotation states as 250.4442(12) and -136.1673(30) MHz, respectively. The slight deviation of the latter tunneling frequency from being one half of the former, as simple theory otherwise predicts, is due to different degrees of mixing in wavefunctions between the ground and excited states.

  1. Electron tunneling and point contact Andreev reflection studies of superconductors

    Science.gov (United States)

    Dai, Wenqing

    The energy gap is the most fundamental property of a superconductor. Electron tunneling spectroscopy and point contact spectroscopy (PCS) are powerful techniques for studying the density of states and energy gap features of superconductors. Two different superconducting systems, multiband superconductor MgB2 and proximity induced topological superconductor NbSe2/Bi 2Se3 heterostructures were studied using either quasiparticle tunneling in planar tunnel junctions or PCS in this work. (Abstract shortened by ProQuest.).

  2. Electronic characterization of LaAlO{sub 3}-SrTiO{sub 3} interfaces by scanning tunneling spectroscopy; Elektronische Charakterisierung von LaAlO{sub 3}-SrTiO{sub 3}-Grenzflaechen mittels Rastertunnelspektroskopie

    Energy Technology Data Exchange (ETDEWEB)

    Breitschaft, Martin

    2010-10-22

    When LaAlO{sub 3} is epitaxially grown on TiO{sub 2}-terminated SrTiO{sub 3}, an electrically conducting interface is generated. In this respect, the physical properties of the interface differ substantially from those of both LaAlO{sub 3} and SrTiO{sub 3}, which are electrically insulating in bulk form. This dissertation looks into the question of the microscopic structure of the conducting two-dimensional interface electron system. Comparing the electronic density of states of LaAlO{sub 3}-SrTiO{sub 3} interfaces measured by scanning tunneling spectroscopy with results of density functional theory, the interface electron system is found to be substantially coined by the hosting transition metal lattices. The comparison yields a detailed picture of the microscopic structure of the interface electron system. (orig.)

  3. FLUKA simulations of neutron transport in the Dresden Felsenkeller

    Energy Technology Data Exchange (ETDEWEB)

    Grieger, Marcel [Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden (Germany); Technische Universitaet Dresden (Germany); Bemmerer, Daniel; Mueller, Stefan E.; Szuecs, Tamas [Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden (Germany); Zuber, Kai [Technische Universitaet Dresden (Germany)

    2015-07-01

    A new underground ion accelerator with 5 MV acceleration potential is currently being prepared for installation in the Dresden Felsenkeller. The Felsenkeller site consists of altogether nine mutually connected tunnels. It is shielded from cosmic radiation by a 45 m thick rock overburden, enabling uniquely sensitive experiments. In order to exclude any possible effect by the new accelerator in tunnel VIII on the existing low-background γ-counting facility in tunnel IV, Monte Carlo simulations of neutron transport are being performed. A realistic neutron source field is developed, and the resulting additional neutron flux at the γ-counting facility is modeled by FLUKA simulations.

  4. High Resolution GHZ and Thz (ftir) Spectroscopy and Theory of Parity Violation and Tunneling for 1,2-DITHIINE (C4H4S2) as a Candidate for Measuring the Parity Violating Energy Difference Between Enantiomers of Chiral Molecules

    Science.gov (United States)

    Albert, Sieghard; Bolotova, Irina; Chen, Ziqiu; Fábri, Csaba; Horny, Lubos; Quack, Martin; Seyfang, Georg; Zindel, Daniel

    2016-06-01

    We report high resolution spectroscopic results for 1,2-dithiine-(1,2-dithia-3,5-cyclohexadiene,C4H4S2) in the Gigahertz and Terahertz spectroscopic ranges and exploratory theoretical calculations of parity violation and tunneling processes in view of a possible experimental determination of the parity violating energy difference ΔpvE in this chiral molecule. Theory predicts that the parity violating energy difference in the ground state (ΔpvE≃11x10-11(hc) wn)is in principle measurable as it is much larger than the calculated tunneling splitting for the symmetrical potential Δ±E≃10-24(hc) wn. With a planar transition state for stereomutation at about 2500 wn tunneling splittings become appreciable above 2300 wn. This makes levels of well defined parity accessible to parity selection by available powerful infrared lasers and thus useful for one of the existing experimental approaches towards molecular parity violation. The new GHz spectra lead to greatly improved ground state rotational parameters for 1,2-dithiine. These are used as starting point for the first successful analyses of high resolution interferometric Fourier Transform Infrared (FTIR, THz) spectra for the fundamentals ν17 (1308.873 wn or 39.23903 THz), ν22 (623.094 wn or 18.67989 THz) and ν3 (1544.900 wn or 46.314937 THz) for which highly accurate spectroscopic parameters are reported. The results are discussed in relation to current efforts to measure ΔpvE.a-. M. Quack , Fundamental Symmetries and Symmetry Violations from High-resolution Spectroscopy, Handbook of High Resolution Spectroscopy, M. Quack and F. Merkt eds.,John Wiley & Sons Ltd, Chichester, New York, 2001, vol. 1, ch. 18, pp. 659-722 S. Albert, I. Bolotova, Z. Chen, C. Fábri, L. Horny, M. Quack, G. Seyfang and D. Zindel,Proceedings of the 20th Symposium on Atomic, Cluster and Surface Physics (SASP 2016), Innsbruck University Press, 2016, pp. 127-130, ISBN:978-3-903122-04-8. and to be published P. Dietiker, E. Miloglyadov, M

  5. Magnetic properties of nano-scale hematite, α-Fe2O3, studied by time-of-flight inelastic neutron spectroscopy

    DEFF Research Database (Denmark)

    Hill, Adrian H.; Jacobsen, Henrik Skåret; Stewart, J. Ross

    2014-01-01

    Samples of nanoscale hematite, α-Fe2O3, with different surface geometries and properties have been studied with inelastic time-of-flight neutron scattering. The 15 nm diameter nanoparticles previously shown to have two collective magnetic excitation modes in separate triple-axis neutron scatterin...

  6. Response function of single crystal synthetic diamond detectors to 1-4 MeV neutrons for spectroscopy of D plasmas

    Science.gov (United States)

    Rebai, M.; Giacomelli, L.; Milocco, A.; Nocente, M.; Rigamonti, D.; Tardocchi, M.; Camera, F.; Cazzaniga, C.; Chen, Z. J.; Du, T. F.; Fan, T. S.; Giaz, A.; Hu, Z. M.; Marchi, T.; Peng, X. Y.; Gorini, G.

    2016-11-01

    A Single-crystal Diamond (SD) detector prototype was installed at Joint European Torus (JET) in 2013 and the achieved results have shown its spectroscopic capability of measuring 2.5 MeV neutrons from deuterium plasmas. This paper presents measurements of the SD response function to monoenergetic neutrons, which is a key point for the development of a neutron spectrometer based on SDs and compares them with Monte Carlo simulations. The analysis procedure allows for a good reconstruction of the experimental results. The good pulse height energy resolution (equivalent FWHM of 80 keV at 2.5 MeV), gain stability, insensitivity to magnetic field, and compact size make SDs attractive as compact neutron spectrometers of high flux deuterium plasmas, such as for instance those needed for the ITER neutron camera.

  7. MAGNETIC NEUTRON SCATTERING

    Energy Technology Data Exchange (ETDEWEB)

    ZALIZNYAK,I.A.; LEE,S.H.

    2004-07-30

    Much of our understanding of the atomic-scale magnetic structure and the dynamical properties of solids and liquids was gained from neutron-scattering studies. Elastic and inelastic neutron spectroscopy provided physicists with an unprecedented, detailed access to spin structures, magnetic-excitation spectra, soft-modes and critical dynamics at magnetic-phase transitions, which is unrivaled by other experimental techniques. Because the neutron has no electric charge, it is an ideal weakly interacting and highly penetrating probe of matter's inner structure and dynamics. Unlike techniques using photon electric fields or charged particles (e.g., electrons, muons) that significantly modify the local electronic environment, neutron spectroscopy allows determination of a material's intrinsic, unperturbed physical properties. The method is not sensitive to extraneous charges, electric fields, and the imperfection of surface layers. Because the neutron is a highly penetrating and non-destructive probe, neutron spectroscopy can probe the microscopic properties of bulk materials (not just their surface layers) and study samples embedded in complex environments, such as cryostats, magnets, and pressure cells, which are essential for understanding the physical origins of magnetic phenomena. Neutron scattering is arguably the most powerful and versatile experimental tool for studying the microscopic properties of the magnetic materials. The magnitude of the cross-section of the neutron magnetic scattering is similar to the cross-section of nuclear scattering by short-range nuclear forces, and is large enough to provide measurable scattering by the ordered magnetic structures and electron spin fluctuations. In the half-a-century or so that has passed since neutron beams with sufficient intensity for scattering applications became available with the advent of the nuclear reactors, they have became indispensable tools for studying a variety of important areas of modern

  8. MAGNETIC NEUTRON SCATTERING

    Energy Technology Data Exchange (ETDEWEB)

    ZALIZNYAK,I.A.; LEE,S.H.

    2004-07-30

    Much of our understanding of the atomic-scale magnetic structure and the dynamical properties of solids and liquids was gained from neutron-scattering studies. Elastic and inelastic neutron spectroscopy provided physicists with an unprecedented, detailed access to spin structures, magnetic-excitation spectra, soft-modes and critical dynamics at magnetic-phase transitions, which is unrivaled by other experimental techniques. Because the neutron has no electric charge, it is an ideal weakly interacting and highly penetrating probe of matter's inner structure and dynamics. Unlike techniques using photon electric fields or charged particles (e.g., electrons, muons) that significantly modify the local electronic environment, neutron spectroscopy allows determination of a material's intrinsic, unperturbed physical properties. The method is not sensitive to extraneous charges, electric fields, and the imperfection of surface layers. Because the neutron is a highly penetrating and non-destructive probe, neutron spectroscopy can probe the microscopic properties of bulk materials (not just their surface layers) and study samples embedded in complex environments, such as cryostats, magnets, and pressure cells, which are essential for understanding the physical origins of magnetic phenomena. Neutron scattering is arguably the most powerful and versatile experimental tool for studying the microscopic properties of the magnetic materials. The magnitude of the cross-section of the neutron magnetic scattering is similar to the cross-section of nuclear scattering by short-range nuclear forces, and is large enough to provide measurable scattering by the ordered magnetic structures and electron spin fluctuations. In the half-a-century or so that has passed since neutron beams with sufficient intensity for scattering applications became available with the advent of the nuclear reactors, they have became indispensable tools for studying a variety of important areas of modern

  9. Scanning tunneling spectroscopy of SrFe{sub 2}(As{sub 1-x}P{sub x}){sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Jandke, Jasmin; Wild, Petra; Schackert, Michael; Wulfhekel, Wulf [Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe (Germany)

    2015-07-01

    The antiferromagnetic parent compound SrFe{sub 2}As{sub 2} shows a supression of the spin density wave and a subsequent superconducting state upon partial substitution of As by P. We investigated single crystals for four different P-concentrations x in the superconducting (x=0.35,0.46) as well as in the spin density wave phase (x=0,0.2). The superconducting samples display a v-shaped superconducting gap, which suggests nodal superconductivity in this system. Furthermore, we were able to determine the superconducting coherence length by measuring the spatial resolved superconducting density of states. From inelastic tunneling spectra it is possible to determine the Eliashberg function from the normal state. We thus investigated bosonic excitations for the four different P-concentrations. Indeed, evidence suggests peaks which can be related to bosonic modes. The phonon an non-phonon mechanism for the origin of these peaks will be discussed.

  10. Carpal Tunnel Syndrome

    Science.gov (United States)

    ... arm. Just a passing cramp? It could be carpal tunnel syndrome. The carpal tunnel is a narrow passageway of ligament and ... difficult. Often, the cause is having a smaller carpal tunnel than other people do. Other causes include ...

  11. Preliminary results of neutron spectroscopy in proton therapy treatment room in Ithemba Labs (South Africa); Resultados preliminares de espectrometria de neutrones en la sala de tratamiento de protonterapia en Ithemba Labs (Sudafrica)

    Energy Technology Data Exchange (ETDEWEB)

    Domingo, C.; Garcia-Fuste, M. J.; Amgarou, K.; Sanchez-Doblado, F.; Nieto-Camero, J.

    2011-07-01

    Proton beams originating from accelerators high energy hadrons lead to the production of neutrons when protons interact with the elements present in the beam line. Furthermore, when these protons are used for proton therapy treatments, their interaction with the patient also involves production of neutrons, mainly due to interactions with the C, O and N. This represents a source of unwanted radiation that increases the risk of developing second cancers by the patient. Assessment of risk factors is one of the goals of our project.

  12. Evidence for Time-Reversal Symmetry Breaking of the Superconducting State near Twin-Boundary Interfaces in FeSe Revealed by Scanning Tunneling Spectroscopy

    Science.gov (United States)

    Watashige, T.; Tsutsumi, Y.; Hanaguri, T.; Kohsaka, Y.; Kasahara, S.; Furusaki, A.; Sigrist, M.; Meingast, C.; Wolf, T.; Löhneysen, H. v.; Shibauchi, T.; Matsuda, Y.

    2015-07-01

    Junctions and interfaces consisting of unconventional superconductors provide an excellent experimental playground to study exotic phenomena related to the phase of the order parameter. Not only does the complex structure of unconventional order parameters have an impact on the Josephson effects, but it also may profoundly alter the quasiparticle excitation spectrum near a junction. Here, by using spectroscopic-imaging scanning tunneling microscopy, we visualize the spatial evolution of the LDOS near twin boundaries (TBs) of the nodal superconductor FeSe. The π /2 rotation of the crystallographic orientation across the TB twists the structure of the unconventional order parameter, which may, in principle, bring about a zero-energy LDOS peak at the TB. The LDOS at the TB observed in our study, in contrast, does not exhibit any signature of a zero-energy peak, and an apparent gap amplitude remains finite all the way across the TB. The low-energy quasiparticle excitations associated with the gap nodes are affected by the TB over a distance more than an order of magnitude larger than the coherence length ξa b. The modification of the low-energy states is even more prominent in the region between two neighboring TBs separated by a distance ≈7 ξa b . In this region, the spectral weight near the Fermi level (≈±0.2 meV ) due to the nodal quasiparticle spectrum is almost completely removed. These behaviors suggest that the TB induces a fully gapped state, invoking a possible twist of the order parameter structure, which breaks time-reversal symmetry.

  13. Assessment of individual organ doses in a realistic human phantom from neutron and gamma stimulated spectroscopy of the breast and liver

    Energy Technology Data Exchange (ETDEWEB)

    Belley, Matthew D. [Medical Physics Graduate Program, Duke University, Durham 27705, North Carolina (United States); Segars, William Paul; Kapadia, Anuj J., E-mail: anuj.kapadia@duke.edu [Medical Physics Graduate Program, Duke University, Durham, North Carolina and Department of Radiology, Carl E. Ravin Advanced Imaging Laboratories, Duke University Medical Center, Durham 27710, North Carolina (United States)

    2014-06-15

    Purpose: Understanding the radiation dose to a patient is essential when considering the use of an ionizing diagnostic imaging test for clinical diagnosis and screening. Using Monte Carlo simulations, the authors estimated the three-dimensional organ-dose distribution from neutron and gamma irradiation of the male liver, female liver, and female breasts for neutron- and gamma-stimulated spectroscopic imaging. Methods: Monte Carlo simulations were developed using the Geant4 GATE application and a voxelized XCAT human phantom. A male and a female whole body XCAT phantom was voxelized into 256 × 256 × 600 voxels (3.125 × 3.125 × 3.125 mm{sup 3}). A monoenergetic rectangular beam of 5.0 MeV neutrons or 7.0 MeV photons was made incident on a 2 cm thick slice of the phantom. The beam was rotated at eight different angles around the phantom ranging from 0° to 180°. Absorbed dose was calculated for each individual organ in the body and dose volume histograms were computed to analyze the absolute and relative doses in each organ. Results: The neutron irradiations of the liver showed the highest organ dose absorption in the liver, with appreciably lower doses in other proximal organs. The dose distribution within the irradiated slice exhibited substantial attenuation with increasing depth along the beam path, attenuating to ∼15% of the maximum value at the beam exit side. The gamma irradiation of the liver imparted the highest organ dose to the stomach wall. The dose distribution from the gammas showed a region of dose buildup at the beam entrance, followed by a relatively uniform dose distribution to all of the deep tissue structures, attenuating to ∼75% of the maximum value at the beam exit side. For the breast scans, both the neutron and gamma irradiation registered maximum organ doses in the breasts, with all other organs receiving less than 1% of the breast dose. Effective doses ranged from 0.22 to 0.37 mSv for the neutron scans and 41 to 66 mSv for the gamma

  14. Ordered vortex lattice and intrinsic vortex core states in Bi sub 2 Sr sub 2 CaCu sub 2 O sub x studied by scanning tunneling microscopy and spectroscopy

    CERN Document Server

    Matsuba, K; Kosugi, N; Nishimori, H; Nishida, N

    2003-01-01

    The ordered vortex lattice in Bi sub 2 Sr sub 2 CaCu sub 2 O sub x (overdoped, T sub c = 83 K) has been observed for the first time at 4.2 K in 8 T by scanning tunneling spectroscopy (STS). The vortex lattice is short-range ordered in the length scale of 100 nm. The vortices form an almost square lattice with the sides parallel to the diagonal direction of the CuO sub 2 square lattice, that is, the nodal direction of the d sub x sub sup 2 sub - sub y sub sup 2 superconductor. In all of the vortex cores of the ordered lattice, the localized states are observed at +- 9 meV symmetrically in the superconducting gap and are clearly determined to be intrinsic to the vortex in Bi sub 2 Sr sub 2 CaCu sub 2 O sub x. The intensity is found to be electron-hole asymmetric.

  15. Neutron Repulsion

    OpenAIRE

    Manuel, Oliver K.

    2011-01-01

    Earth is connected gravitationally, magnetically and electrically to its heat source - a neutron star that is obscured from view by waste products in the photosphere. Neutron repulsion is like the hot filament in an incandescent light bulb. Excited neutrons are emitted from the solar core and decay into hydrogen that glows in the photosphere like a frosted light bulb. Neutron repulsion was recognized in nuclear rest mass data in 2000 as the overlooked source of energy, the keystone of an arch...

  16. Electron tunnel sensor technology

    Science.gov (United States)

    Waltman, S. B.; Kaiser, W. J.

    1989-01-01

    The recent development of Scanning Tunneling Microscopy technology allows the application of electron tunneling to position detectors for the first time. The vacuum tunnel junction is one of the most sensitive position detection mechanisms available. It is also compact, simple, and requires little power. A prototype accelerometer based on electron tunneling, and other sensor applications of this promising new technology are described.

  17. Inelastic scanning tunneling microscopy in conventional and unconventional superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Hlobil, Patrik; Schmalian, Joerg; Wulfhekel, Wulf; Jandke, Jasmin [Karlsruhe Institute of Technologie (Germany)

    2015-07-01

    Electron tunneling spectroscopy has been used extremely successful in order to verify the microscopic phonon pairing mechanism in conventional BCS superconductors using the Eliashberg theory. Nevertheless, earlier theories and experiments focused mainly on elastic tunneling processes. We present, motivated by recent experiments, a theoretical description of inelastic tunneling in STM in which an electrons tunnels from the tip into a BCS superconductor and coherently excites a phonon during the tunneling process. This additional channel enhances the measured conductivity and we show that if the superconductor is in the normal state, within some limitations, the derivative dσ/dV will be proportional to the Eliashberg function α2F. Additionally, the influence of the inelastic contributions on the tunneling spectrum in the superconducting state will be discussed. Finally, we generalize the theory to other bosonic excitations and focus on the question if inelastic tunneling could be used to unveil the electronic pairing mechanism in the iron pnictides.

  18. Peculiarities of the modern neutron spectrometry

    Indian Academy of Sciences (India)

    Yu P Popov

    2001-08-01

    Neutron spectrometry provides many branches of science and technology with the necessary data. Usually the main part of the data is supplied by powerful neutron time-of-flight spectrometers. Nevertheless there are many other very effective but simpler and cheaper neutron spectroscopy methods on accelerators, suitable for solution of plenty of scientific and applied problems (for example, in astrophysics and radioactive waste transmutation). The methods of slowing-down spectrometry in lead and graphite, generating of neutron spectra, characteristic for nucleosynthesis in the stars, and neutron spectrometry by means of primary -transition shift are discussed in the report.

  19. Electromagnon excitation in the field-induced noncollinear ferrimagnetic phase of Ba2Mg2Fe12O22 studied by polarized inelastic neutron scattering and terahertz time-domain optical spectroscopy

    Science.gov (United States)

    Nakajima, Taro; Takahashi, Youtarou; Kibayashi, Shunsuke; Matsuda, Masaaki; Kakurai, Kazuhisa; Ishiwata, Shintaro; Taguchi, Yasujiro; Tokura, Yoshinori; Arima, Taka-hisa

    2016-01-01

    We have studied magnetic excitations in a field-induced noncollinear commensurate ferrimagnetic phase of Ba2Mg2Fe12O22 by means of polarized inelastic neutron scattering (PINS) and terahertz (THz) time-domain optical spectroscopy under magnetic field. A previous THz spectroscopy study reported that the field-induced phase exhibits electric-dipole-active excitations with energies of around 5 meV [Kida et al., Phys. Rev. B 83, 064422 (2011), 10.1103/PhysRevB.83.064422]. In the present PINS measurements, we observed inelastic scattering signals around 5 meV at the zone center in the spin-flip channel. This directly shows that the electric-dipole-active excitations are indeed of magnetic origin, that is, electromagnons. In addition, the present THz spectroscopy confirms that the excitations have oscillating electric polarization parallel to the c axis. In terms of the spin-current model (Katsura-Nagaosa-Balatsky model), the noncollinear magnetic order in the field-induced phase can induce static electric polarization perpendicular to the c axis, but not dynamic electric polarization along the c axis. We suggest that the electromagnon excitations can be explained by applying the magnetostriction model to the out-of-phase oscillations of the magnetic moments, which is deduced from the present experimental results.

  20. Isothermal equation of state and high-pressure phase transitions of synthetic meridianiite (MgSO4·11D2O) determined by neutron powder diffraction and quasielastic neutron spectroscopy

    Science.gov (United States)

    Fortes, A. Dominic; Fernandez-Alonso, Felix; Tucker, Matthew; Wood, Ian G.

    2017-01-01

    We have collected neutron powder diffraction data from MgSO4·11D2O (the deuterated analogue of meridianiite), a highly hydrated sulfate salt that is thought to be a candidate rock-forming mineral in some icy satellites of the outer solar system. Our measurements, made using the PEARL/HiPr and OSIRIS instruments at the ISIS neutron spallation source, covered the range 0.1 < P < 800 MPa and 150 < T < 280 K. The refined unit-cell volumes as a function of P and T are parameterized in the form of a Murnaghan integrated linear equation of state having a zero-pressure volume V 0 = 706.23 (8) Å3, zero-pressure bulk modulus K 0 = 19.9 (4) GPa and its first pressure derivative, K′ = 9 (1). The structure’s compressibility is highly anisotropic, as expected, with the three principal directions of the unit-strain tensor having compressibilities of 9.6 × 10−3, 3.4 × 10−2 and 3.4 × 10−3 GPa−1, the most compressible direction being perpendicular to the long axis of a discrete hexadecameric water cluster, (D2O)16. At high pressure we observed two different phase transitions. First, warming of MgSO4·11D2O at 545 MPa resulted in a change in the diffraction pattern at 275 K consistent with partial (peritectic) melting; quasielastic neutron spectra collected simultaneously evince the onset of the reorientational motion of D2O molecules with characteristic time-scales of 20–30 ps, longer than those found in bulk liquid water at the same temperature and commensurate with the lifetime of solvent-separated ion pairs in aqueous MgSO4. Second, at ∼ 0.9 GPa, 240 K, MgSO4·11D2O decomposed into high-pressure water ice phase VI and MgSO4·9D2O, a recently discovered phase that has hitherto only been formed at ambient pressure by quenching small droplets of MgSO4(aq) in liquid nitrogen. The fate of the high-pressure enneahydrate on further compression and warming is not clear from the neutron diffraction data, but its occurrence

  1. Neutron Radiography

    Science.gov (United States)

    Heller, A. K.; Brenizer, J. S.

    Neutron radiography and its related two-dimensional (2D) neutron imaging techniques have been established as invaluable nondestructive inspection methods and quantitative measurement tools. They have been used in a wide variety of applications ranging from inspection of aircraft engine turbine blades to study of two-phase fluid flow in operating proton exchange membrane fuel cells. Neutron radiography is similar to X-ray radiography in that the method produces a 2D attenuation map of neutron radiation that has penetrated the object being examined. However, the images produced differ and are often complementary due to the differences between X-ray and neutron interaction mechanisms. The uses and types of 2D neutron imaging have expanded over the past 15 years as a result of advances in imaging technology and improvements in neutron generators/sources and computers. Still, high-intensity sources such as those from reactors and spallation neutron sources, together with conventional film radiography, remain the mainstay of high-resolution, large field-of-view neutron imaging. This chapter presents a summary of the history, methods, and related variations of neutron radiography techniques.

  2. Spectroscopy of Neutron-Rich $^{168,170}$Dy: Yrast Band Evolution Close to the $N_{p}N_{n}$ Valence Maximum

    CERN Document Server

    Söderström, P A; Regan, P H; Algora, A; de Angelis, G; Ashley, S F; Aydin, S; Bazzacco, D; Casperson, R J; Catford, W N; Cederkäll, J; Chapman, R; Corradi, L; Fahlander, C; Farnea, E; Fioretto, E; Freeman, S J; Gadea, A; Gelletly, W; Gottardo, A; Grodner, E; He, C Y; Jones, G A; Keyes, K; Labiche, M; Liang, X; Liu, Z; Lunardi, S; Muarginean, N; Mason, P; Menegazzo, R; Mengoni, D; Montagnoli, G; Napoli, D; Ollier, J; Pietri, S; Podolyák, Z; Pollarolo, G; Recchia, F; Şahin, E; Scarlassara, F; Silvestri, R; Smith, J F; Spohr, K M; Steer, S J; Stefanini, A M; Szilner, S; Thompson, N J; Tveten, G M; Ur, C A; Valiente-Dobón, J J; Werner, V; Williams, S J; Xu, F R; Zhu, J Y

    2010-01-01

    The yrast sequence of the neutron-rich dysprosium isotope Dy-168 has been studied using multi-nucleon transfer reactions following the collision of a 460-MeV Se-82 beam and a Er-170 target. The reaction products were identified using the PRISMA magnetic spectrometer and the gamma rays detected using the CLARA HPGe-detector array. The 2+ and 4+ members of the previously measured ground state rotational band of Dy-168 was confirmed and the yrast band extended up to 10+. A tentative candidate for the 4+ to 2+ transition in Dy-170 was also identified. The data on this and lighter even-even dysprosium isotopes are interpreted in terms of Total Routhian Surface calculations and the evolution of collectivity approaching the proton-neutron valence product maximum is discussed.

  3. Positron Annihilation Lifetime Spectroscopy Study of Neutron Irradiated High Temperature Superconductors YBa2Cu3O7-δ for Application in Fusion Facilities

    Science.gov (United States)

    Veterníková, J.; Chudý, M.; Slugeň, V.; Eisterer, M.; Weber, H. W.; Sojak, S.; Petriska, M.; Hinca, R.; Degmová, J.; Sabelová, V.

    2012-02-01

    This study focuses on the crystallographic defects introduced by neutron irradiation and the resulting changes of the superconducting properties in the high temperature superconductor YBa2Cu3O7-δ. This material is considered to be most promising for magnet systems in future fusion reactors. Two different bulk samples, pure non-doped YBa2Cu3O7-δ (YBCO) and multi-seed YBa2Cu3O7-δ doped by platinum (MS2F) were studied prior to and after irradiation in the TRIGA MARK II reactor in Vienna. Neutron irradiation is responsible for a significant enhancement of the critical current densities as well as for a reduction in critical temperature. The accumulation of small open volume defects (treatment.

  4. Gamma/neutron competition above the neutron separation energy in delayed neutron emitters

    Directory of Open Access Journals (Sweden)

    Valencia E.

    2014-03-01

    Full Text Available To study the β-decay properties of some well known delayed neutron emitters an experiment was performed in 2009 at the IGISOL facility (University of Jyväskylä in Finland using Total Absorption γ-ray Spectroscopy (TAGS technique. The aim of these measurements is to obtain the full β-strength distribution below the neutron separation energy (Sn and the γ/neutron competition above. This information is a key parameter in nuclear technology applications as well as in nuclear astrophysics and nuclear structure. Preliminary results of the analysis show a significant γ-branching ratio above Sn.

  5. Single-Crystal Time-of-Flight Neutron Diffraction and Magic-Angle-Spinning NMR Spectroscopy Resolve the Structure and (1)H and (7)Li Dynamics of the Uranyl Peroxide Nanocluster U60.

    Science.gov (United States)

    Olds, Travis A; Dembowski, Mateusz; Wang, Xiaoping; Hoffman, Christina; Alam, Todd M; Hickam, Sarah; Pellegrini, Kristi L; He, Junhong; Burns, Peter C

    2017-08-21

    Single-crystal time-of-flight neutron diffraction has provided atomic resolution of H atoms of H2O molecules and hydroxyl groups, as well as Li cations in the uranyl peroxide nanocluster U60. Solid-state magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy was used to confirm the dynamics of these constituents, revealing the transportation of Li atoms and H2O through cluster walls. H atoms of hydroxyl units that are located on the cluster surface are involved in the transfer of H2O and Li cations from inside to outside and vice versa. This exchange occurs as a concerted motion and happens rapidly even in the solid state. As a consequence of its large size and open hexagonal pores, U60 exchanges Li cations more rapidly compared to other uranyl nanoclusters.

  6. Application of a gamma spectroscopy system to the measurement of neutron cross sections necessary to the development of nuclear energy; Mise au point d'un systeme de spectroscopie pour mesurer des sections efficaces neutroniques applicables a un possible developpement du nucleaire comme source d'energie

    Energy Technology Data Exchange (ETDEWEB)

    Deruelle, O

    2002-09-01

    This work concerns the development of nuclear energy and nuclear waste management in particular. Two parts of this study can be distinguished. In the first part (theoretical), a thorium-plutonium fuel based on MOX and dedicated for PWR was investigated in order to transmute plutonium in a potentially low waste fuel cycle. It was shown that this type of fuel is not regenerative but could be used for a transition to the industrial thorium fuel cycle without building new reactors. Thanks to moderated neutron spectra and high loaded actinide mass in the core, U-233 is quickly created ({approx}300 kg/y) for a loss of about {approx}1200 kg of fissile plutonium. In the second part (experimental), we have developed and built a new reaction chamber to measure neutron cross sections of actinides by alpha-gamma spectroscopy. This experimental device (in principle transportable) was commissioned in the high flux reactor of ILL Grenoble. Neutron flux was measured by gamma spectroscopy of irradiated Al and Co samples and was found to be of the order of 6,0. 10{sup 14} n.cm{sup -2}.s{sup -1} (4%). By the irradiation of 11{mu}g of Am-243 and Pu-242, corresponding capture cross sections were measured in the thermal neutron flux at 50 deg C. These are the results: {sup 243}Am(n,{gamma}) {sup 244fond.}Am = 4,72{+-}1,42b; {sup 243}Am(n,{gamma}) {sup 244total}Am = 74,8{+-}3,25b; {sup 242}Pu (n,{gamma}){sup 243}Pu = 22,7{+-}1,09b. Uncertainties of the measurements are mostly due to the determination of the neutron flux, efficiency of the electronics and ambiguities related to the definition of the area under {alpha}-{gamma} spectra. Although our measured cross sections deviate (by 10-30%) from the corresponding values widely used in evaluated data libraries such as ENDF, JEF and JENDL, in this work we have demonstrated the feasibility and principle of our experimental method. Furthermore, the value for the 243-americium capture cross-section is in very good agreement with the last two

  7. Cation distribution in Ba{sub 2}(Fe,W{sub 0.5}Mo{sub 0.5}){sub 2}O{sub 6} double-perovskites: A combined synchrotron and neutron diffraction, magnetization and Moessbauer spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Rammeh, N. [Laboratoire de Physique des Materiaux, Faculte des Sciences de Sfax, BP 1171, 3000 Sfax (Tunisia); Institute for Materials Science, University of Technology, D-64287 Darmstadt (Germany); Ehrenberg, H. [Institute for Materials Science, University of Technology, D-64287 Darmstadt (Germany); Ritter, C. [Institut Laue Langevin, BP 156, F-38042 Grenoble Cedex 9 (France); Fuess, H. [Institute for Materials Science, University of Technology, D-64287 Darmstadt (Germany); Cheikhrouhou, A. [Laboratoire de Physique des Materiaux, Faculte des Sciences de Sfax, BP 1171, 3000 Sfax (Tunisia)], E-mail: abdcheikhrouhou@yahoo.fr

    2009-03-20

    The crystallographic and magnetic structures of polycrystalline Ba{sub 2}(Fe,W){sub 2}O{sub 6} and Ba{sub 2}(Fe,W{sub 0.5}Mo{sub 0.5}){sub 2}O{sub 6} double-perovskites have been investigated by X-ray and neutron powder diffraction (NPD), magnetization and Moessbauer spectroscopy. The samples were synthesized by conventional solid-state reaction at temperatures about 1273 K. The compounds crystallize in the cubic structure with space group Fm3-barm. The magnetic structures were determined by neutron powder diffraction between 5 K and 310 K. Evidence for an antiferromagnetic behavior has been observed for Ba{sub 2}(Fe,W){sub 2}O{sub 6} with T{sub N} = 24.7 K and a two-phase separation for Ba{sub 2}(Fe,W{sub 0.5}Mo{sub 0.5}){sub 2}O{sub 6} into an antiferromagnetic structure of the W-type with T{sub N} = 24.7 K and the ferromagnetic Mo-type with T{sub C} = 270 K.

  8. Fusion neutronics

    CERN Document Server

    Wu, Yican

    2017-01-01

    This book provides a systematic and comprehensive introduction to fusion neutronics, covering all key topics from the fundamental theories and methodologies, as well as a wide range of fusion system designs and experiments. It is the first-ever book focusing on the subject of fusion neutronics research. Compared with other nuclear devices such as fission reactors and accelerators, fusion systems are normally characterized by their complex geometry and nuclear physics, which entail new challenges for neutronics such as complicated modeling, deep penetration, low simulation efficiency, multi-physics coupling, etc. The book focuses on the neutronics characteristics of fusion systems and introduces a series of theories and methodologies that were developed to address the challenges of fusion neutronics, and which have since been widely applied all over the world. Further, it introduces readers to neutronics design’s unique principles and procedures, experimental methodologies and technologies for fusion systems...

  9. Growth of an Ultrathin Zirconia Film on Pt3Zr Examined by High-Resolution X-ray Photoelectron Spectroscopy, Temperature-Programmed Desorption, Scanning Tunneling Microscopy, and Density Functional Theory

    Science.gov (United States)

    2014-01-01

    Ultrathin (∼3 Å) zirconium oxide films were grown on a single-crystalline Pt3Zr(0001) substrate by oxidation in 1 × 10–7 mbar of O2 at 673 K, followed by annealing at temperatures up to 1023 K. The ZrO2 films are intended to serve as model supports for reforming catalysts and fuel cell anodes. The atomic and electronic structure and composition of the ZrO2 films were determined by synchrotron-based high-resolution X-ray photoelectron spectroscopy (HR-XPS) (including depth profiling), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. Oxidation mainly leads to ultrathin trilayer (O–Zr–O) films on the alloy; only a small area fraction (10–15%) is covered by ZrO2 clusters (thickness ∼0.5–10 nm). The amount of clusters decreases with increasing annealing temperature. Temperature-programmed desorption (TPD) of CO was utilized to confirm complete coverage of the Pt3Zr substrate by ZrO2, that is, formation of a closed oxide overlayer. Experiments and DFT calculations show that the core level shifts of Zr in the trilayer ZrO2 films are between those of metallic Zr and thick (bulklike) ZrO2. Therefore, the assignment of such XPS core level shifts to substoichiometric ZrOx is not necessarily correct, because these XPS signals may equally well arise from ultrathin ZrO2 films or metal/ZrO2 interfaces. Furthermore, our results indicate that the common approach of calculating core level shifts by DFT including final-state effects should be taken with care for thicker insulating films, clusters, and bulk insulators. PMID:25688293

  10. Investigations on the electronic surface properties of the stoichiometric superconductor LiFeAs using scanning tunneling microscopy and spectroscopy; Untersuchung der elektronischen Oberflaecheneigenschaften des stoechiometrischen Supraleiters LiFeAs mittels Rastertunnelmikroskopie und -spektroskopie

    Energy Technology Data Exchange (ETDEWEB)

    Schlegel, Ronny

    2014-09-29

    This work presents scanning tunneling microscopy and spectroscopy investigations on the stoichiometric superconductor lithium iron arsenide (LiFeAs). To reveal the electronic properties, measurements on defect-free surfaces as well as near defects have been performed. The former shows a shift of atomic position with respect to the applied bias voltage. Furthermore, temperature dependent spectroscopic measurements indicate the coupling of quasiparticles in the vicinity of the superconducting coherence peaks. LiFeAs surfaces influenced by atomic defects show a spacial variation of the superconducting gap. The defects can be characterized by their symmetry and thus can be assigned to a position in the atomic lattice. Detailed spectroscopic investigations of defects reveal their influence on the quasiparticle density of states. In particular, Fe-defects show a small effect on the superconductivity while As-defects strongly disturb the superconducting gap. Measurements in magnetic field have been performed for the determination of the Ginzburg-Landau coherence length ξ{sub GL}. For this purpose, a suitable fit-function has been developed in this work. This function allows to fit the differential conductance of a magnetic vortex at E{sub F}. The fit results in a coherence length of ξ{sub GL} = 3,9 nm which corresponds to an upper critical field of 21 Tesla. Besides measurements on a single vortex, investigation on the vortex lattice have been performed. The vortex lattice constant follows thereby the predicted behavior of a trigonal vortex lattice. However, for magnetic fields larger than 6 Tesla an increasing lattice disorder sets in, presumably due to vortex-vortex-interactions.

  11. Growth of an Ultrathin Zirconia Film on Pt3Zr Examined by High-Resolution X-ray Photoelectron Spectroscopy, Temperature-Programmed Desorption, Scanning Tunneling Microscopy, and Density Functional Theory.

    Science.gov (United States)

    Li, Hao; Choi, Joong-Il Jake; Mayr-Schmölzer, Wernfried; Weilach, Christian; Rameshan, Christoph; Mittendorfer, Florian; Redinger, Josef; Schmid, Michael; Rupprechter, Günther

    2015-02-05

    Ultrathin (∼3 Å) zirconium oxide films were grown on a single-crystalline Pt3Zr(0001) substrate by oxidation in 1 × 10(-7) mbar of O2 at 673 K, followed by annealing at temperatures up to 1023 K. The ZrO2 films are intended to serve as model supports for reforming catalysts and fuel cell anodes. The atomic and electronic structure and composition of the ZrO2 films were determined by synchrotron-based high-resolution X-ray photoelectron spectroscopy (HR-XPS) (including depth profiling), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. Oxidation mainly leads to ultrathin trilayer (O-Zr-O) films on the alloy; only a small area fraction (10-15%) is covered by ZrO2 clusters (thickness ∼0.5-10 nm). The amount of clusters decreases with increasing annealing temperature. Temperature-programmed desorption (TPD) of CO was utilized to confirm complete coverage of the Pt3Zr substrate by ZrO2, that is, formation of a closed oxide overlayer. Experiments and DFT calculations show that the core level shifts of Zr in the trilayer ZrO2 films are between those of metallic Zr and thick (bulklike) ZrO2. Therefore, the assignment of such XPS core level shifts to substoichiometric ZrO x is not necessarily correct, because these XPS signals may equally well arise from ultrathin ZrO2 films or metal/ZrO2 interfaces. Furthermore, our results indicate that the common approach of calculating core level shifts by DFT including final-state effects should be taken with care for thicker insulating films, clusters, and bulk insulators.

  12. Neutron Albedo

    CERN Document Server

    Ignatovich, V K

    2005-01-01

    A new, algebraic, method is applied to calculation of neutron albedo from substance to check the claim that use of ultradispersive fuel and moderator of an active core can help to gain in size and mass of the reactor. In a model of isotropic distribution of incident and reflected neutrons it is shown that coherent scattering on separate grains in the case of thermal neutrons increases transport cross section negligibly, however it decreases albedo from a wall of finite thickness because of decrease of substance density. A visible increase of albedo takes place only for neutrons with wave length of the order of the size of a single grain.

  13. Direct control and characterization of a Schottky barrier by scanning tunneling microscopy

    Science.gov (United States)

    Bell, L. D.; Kaiser, W. J.; Hecht, M. H.; Grunthaner, F. J.

    1988-01-01

    Scanning tunneling microscopy (STM) methods are used to directly control the barrier height of a metal tunnel tip-semiconductor tunnel junction. Barrier behavior is measured by tunnel current-voltage spectroscopy and compared to theory. A unique surface preparation method is used to prepare a low surface state density Si surface. Control of band bending with this method enables STM investigation of semiconductor subsurface properties.

  14. Hypersonic Tunnel Facility (HTF)

    Data.gov (United States)

    Federal Laboratory Consortium — The Hypersonic Tunnel Facility (HTF) is a blow-down, non-vitiated (clean air) free-jet wind tunnel capable of testing large-scale, propulsion systems at Mach 5, 6,...

  15. Transonic Dynamics Tunnel (TDT)

    Data.gov (United States)

    Federal Laboratory Consortium — The Transonic Dynamics Tunnel (TDT) is a continuous flow wind-tunnel facility capable of speeds up to Mach 1.2 at stagnation pressures up to one atmosphere. The TDT...

  16. Road and Railroad Tunnels

    Data.gov (United States)

    Department of Homeland Security — Tunnels in the United States According to the HSIP Tiger Team Report, a tunnel is defined as a linear underground passageway open at both ends. This dataset is based...

  17. Quantum theory of tunneling

    CERN Document Server

    Razavy, Mohsen

    2014-01-01

    In this revised and expanded edition, in addition to a comprehensible introduction to the theoretical foundations of quantum tunneling based on different methods of formulating and solving tunneling problems, different semiclassical approximations for multidimensional systems are presented. Particular attention is given to the tunneling of composite systems, with examples taken from molecular tunneling and also from nuclear reactions. The interesting and puzzling features of tunneling times are given extensive coverage, and the possibility of measurement of these times with quantum clocks are critically examined. In addition by considering the analogy between evanescent waves in waveguides and in quantum tunneling, the times related to electromagnetic wave propagation have been used to explain certain aspects of quantum tunneling times. These topics are treated in both non-relativistic as well as relativistic regimes. Finally, a large number of examples of tunneling in atomic, molecular, condensed matter and ...

  18. Hypersonic Tunnel Facility (HTF)

    Data.gov (United States)

    Federal Laboratory Consortium — The Hypersonic Tunnel Facility (HTF) is a blow-down, non-vitiated (clean air) free-jet wind tunnel capable of testing large-scale, propulsion systems at Mach 5, 6,...

  19. The Tunnels of Samos

    Science.gov (United States)

    Apostol, Tom M. (Editor)

    1995-01-01

    This 'Project Mathematics' series video from CalTech presents the tunnel of Samos, a famous underground aquaduct tunnel located near the capital of Pithagorion (named after the famed Greek mathematician, Pythagoras, who lived there), on one of the Greek islands. This tunnel was constructed around 600 BC by King Samos and was built under a nearby mountain. Through film footage and computer animation, the mathematical principles and concepts of why and how this aquaduct tunnel was built are explained.

  20. Neutron dosimetry; Dosimetria de neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Fratin, Luciano

    1993-12-31

    A neutron irradiation facility was designed and built in order to establish a procedure for calibrating neutron monitors and dosemeters. A 185 GBq {sup 241} Am Be source of known is used as a reference source. The irradiation facility using this source in the air provides neutron dose rates between 9 nSv s{sup -1} and 0,5 {sup {mu}}Sv s{sup -1}. A calibrated 50 nSv s{sup -1} thermal neutron field is obtained by using a specially designed paraffin block in conjunction with the {sup 241} Am Be source. A Bonner multisphere spectrometer was calibrated, using a procedure based on three methods proposed by international standards. The unfold {sup 241} Am Be neutron spectrum was determined from the Bonner spheres data and resulted in a good agreement with expected values for fluence rate, dose rate and mean energy. A dosimetric system based on the electrochemical etching of CR-39 was developed for personal dosimetry. The dosemeter badge using a (n,{alpha}) converter, the etching chamber and high frequency power supply were designed and built specially for this project. The electrochemical etching (ECE) parameters used were: a 6N KOH solution, 59 deg C, 20 kV{sub pp} cm{sup -1}, 2,0 kHz, 3 hours of ECE for thermal and intermediate neutrons and 6 hours for fast neutrons. The calibration factors for thermal, intermediate and fast neutrons were determined for this personal dosemeter. The sensitivities determined for the developed dosimetric system were (1,46{+-} 0,09) 10{sup 4} tracks cm{sup -2} mSv{sup -1} for thermal neutrons, (9{+-}3) 10{sup 2} tracks cm{sup -2} mSV{sup -1} for intermediate neutrons and (26{+-}4) tracks cm{sup -2} mSv{sup -1} for fast neutrons. The lower and upper limits of detection were respectively 0,002 mSv and 0,6 mSv for thermal neutrons, 0,04 mSv and 8 mSv for intermediate neutrons and 1 mSv and 12 mSv for fast neutrons. In view of the 1990`s ICRP recommendations, it is possible to conclude that the personal dosemeter described in this work is

  1. Magnetic tunnel junctions (MTJs)

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    We review the giant tunnel magnetoresistance (TMR) in ferromagnetic-insulator-ferromagnetic junctions discovered in recent years, which is the magnetoresistance (MR) associated with the spin-dependent tunneling between two ferromagnetic metal films separated by an insulating thin tunnel barrier. The theoretical and experimental results including junction conductance, magnetoresistance and their temperature and bias dependences are described.

  2. Neutron reflectometry

    DEFF Research Database (Denmark)

    Klösgen-Buchkremer, Beate Maria

    2014-01-01

    films or films with magnetic properties. The reason is the peculiar property of neutron light since the mass of a neutron is close to the one of a proton, and since it bears a magnetic moment. The optical properties of matter, when interacting with neutrons, are described by a refractive index......Neutron (and X-ray) reflectometry constitute complementary interfacially sensitive techniques that open access to studying the structure within thin films of both soft and hard condensed matter. Film thickness starts oxide surfaces on bulk substrates, proceeding to (pauci-)molecular layers and up...... to hundreds of nanometers. Thickness resolution for flat surfaces is in the range of few Ǻngstrøm, and as a peculiar benefit, the presence and properties of buried interfaces are accessible. Focus here will be on neutron reflectometry, a technique that is unique in applications involving composite organic...

  3. Magnetic properties of nano-scale hematite, α-Fe2O3, studied by time-of-flight inelastic neutron spectroscopy.

    Science.gov (United States)

    Hill, Adrian H; Jacobsen, Henrik; Stewart, J Ross; Jiao, Feng; Jensen, Niels P; Holm, Sonja L; Mutka, Hannu; Seydel, Tilo; Harrison, Andrew; Lefmann, Kim

    2014-01-28

    Samples of nanoscale hematite, α-Fe2O3, with different surface geometries and properties have been studied with inelastic time-of-flight neutron scattering. The 15 nm diameter nanoparticles previously shown to have two collective magnetic excitation modes in separate triple-axis neutron scattering studies have been studied in further detail using the advantage of a large detector area, high resolution, and large energy transfer range of the IN5 TOF spectrometer. A mesoporous hematite sample has also been studied, showing similarities to that of the nanoparticle sample and bulk α-Fe2O3. Analysis of these modes provides temperature dependence of the magnetic anisotropy coefficient along the c-axis, κ1. This is shown to remain negative throughout the temperature range studied in both samples, providing an explanation for the previously observed suppression of the Morin transition in the mesoporous material. The values of this anisotropy coefficient are found to lie between those of bulk and nano-particulate samples, showing the hybrid nature of the mesoporous 3-dimensional structure.

  4. Proceedings of the meeting on tunneling reaction and low temperature chemistry, 97 October. Tunneling reaction and quantum medium

    Energy Technology Data Exchange (ETDEWEB)

    Miyazaki, Tetsuo; Aratono, Yasuyuki; Ichikawa, Tsuneki; Shiotani, Masaru [eds.

    1998-02-01

    Present report is the proceedings of the 3rd Meeting on Tunneling Reaction and Low Temperature Chemistry held in Oct. 13 and 14, 1997. The main subject of the meeting is `Tunneling Reaction and Quantum Medium`. In the meeting, the physical and chemical phenomena in the liquid helium such as quantum nucleation, spectroscopy of atoms and molecules, and tunneling abstraction reaction of tritium atom were discussed as the main topics as well as the tunneling reactions in the solid hydrogen and organic compounds. Through the meetings held in 1995, 1996, and 1997, the tunneling phenomena proceeding at various temperatures (room temperature to mK) in the wide fields of chemistry, biology, and physics were discussed intensively and the importance of the tunneling phenomena in the science has been getting clear. The 12 of the presented papers are indexed individually. (J.P.N.)

  5. Proceedings of the meeting on tunneling reaction and low temperature chemistry, 97 October. Tunneling reaction and quantum medium

    Energy Technology Data Exchange (ETDEWEB)

    Miyazaki, Tetsuo; Aratono, Yasuyuki; Ichikawa, Tsuneki; Shiotani, Masaru [eds.

    1998-02-01

    Present report is the proceedings of the 3rd Meeting on Tunneling Reaction and Low Temperature Chemistry held in Oct. 13 and 14, 1997. The main subject of the meeting is `Tunneling Reaction and Quantum Medium`. In the meeting, the physical and chemical phenomena in the liquid helium such as quantum nucleation, spectroscopy of atoms and molecules, and tunneling abstraction reaction of tritium atom were discussed as the main topics as well as the tunneling reactions in the solid hydrogen and organic compounds. Through the meetings held in 1995, 1996, and 1997, the tunneling phenomena proceeding at various temperatures (room temperature to mK) in the wide fields of chemistry, biology, and physics were discussed intensively and the importance of the tunneling phenomena in the science has been getting clear. The 12 of the presented papers are indexed individually. (J.P.N.)

  6. Inelastic neutron scattering study of methyl groups rotation in some methylxanthines

    Science.gov (United States)

    Prager, M.; Pawlukojc, A.; Wischnewski, A.; Wuttke, J.

    2007-12-01

    The three isomeric dimethylxanthines and trimethylxanthine are studied by neutron spectroscopy up to energy transfers of 100meV at energy resolutions ranging from 0.7μeV to some meV. The loss of elastic intensity with increasing temperature can be modeled by quasielastic methyl rotation. The number of inequivalent methyl groups is in agreement with those of the room temperature crystal structures. Activation energies are obtained. In the case of theophylline, a doublet tunneling band is observed at 15.1 and 17.5μeV. In theobromine, a single tunneling band at 0.3μeV is found. Orientational disorder in caffeine leads to a 2.7μeV broad distribution of tunneling bands around the elastic line. At the same time, broad low energy phonon spectra characterize an orientational glassy state with weak methyl rotational potentials. Librational energies of the dimethylxanthines are clearly seen in the phonon densities of states. Rotational potentials can be derived which explain consistently all observables. While their symmetry in general is threefold, theophylline shows a close to sixfold potential reflecting a mirror symmetry.

  7. Proton tunneling in solids

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, J.

    1998-10-01

    The tunneling rate of the proton and its isotopes between interstitial sites in solids is studied theoretically. The phonons and/or the electrons in the solid have two effects on the tunneling phenomenon. First, they suppress the transfer integral between two neighbouring states. Second, they give rise to a finite lifetime of the proton state. Usually the second effect is large and the tunneling probability per unit time (tunneling rate) can be defined. In some cases, however, a coherent tunneling is expected and actually observed. (author)

  8. Quantum Tunneling of Water in Beryl: A New State of the Water Molecule.

    Science.gov (United States)

    Kolesnikov, Alexander I; Reiter, George F; Choudhury, Narayani; Prisk, Timothy R; Mamontov, Eugene; Podlesnyak, Andrey; Ehlers, George; Seel, Andrew G; Wesolowski, David J; Anovitz, Lawrence M

    2016-04-22

    Using neutron scattering and ab initio simulations, we document the discovery of a new "quantum tunneling state" of the water molecule confined in 5 Å channels in the mineral beryl, characterized by extended proton and electron delocalization. We observed a number of peaks in the inelastic neutron scattering spectra that were uniquely assigned to water quantum tunneling. In addition, the water proton momentum distribution was measured with deep inelastic neutron scattering, which directly revealed coherent delocalization of the protons in the ground state.

  9. Observation of Ground-State Two-Neutron Decay

    CERN Document Server

    Thoennessen, M; Spyrou, A; Lunderberg, E; DeYoung, P A; Attanayake, H; Baumann, T; Bazin, D; Brown, B A; Christian, G; Divaratne, D; Grimes, S M; Haagsma, A; Finck, J E; Frank, N; Luther, B; Mosby, S; Nagi, T; Peaslee, G F; Peters, W A; Schiller, A; Smith, J K; Snyder, J; Strongman, M; Volya, A

    2012-01-01

    Neutron decay spectroscopy has become a successful tool to explore nuclear properties of nuclei with the largest neutron-to-proton ratios. Resonances in nuclei located beyond the neutron dripline are accessible by kinematic reconstruction of the decay products. The development of two-neutron detection capabilities of the Modular Neutron Array (MoNA) at NSCL has opened up the possibility to search for unbound nuclei which decay by the emission of two neutrons. Specifically this exotic decay mode was observed in 16Be and 26O.

  10. Magnetic and structural properties of Sc(Fe1−xSix2 Laves phases studied by Mössbauer spectroscopy and neutron diffraction

    Directory of Open Access Journals (Sweden)

    Wiertel Marek

    2015-03-01

    Full Text Available The aim of the presented paper is to study an influence of replacement of Fe atoms by Si atoms in quasibinary Sc(Fe1−xSix2 Laves phases on their structural and magnetic properties. Powder X-ray diffraction (XRD and neutron diffraction (ND measurements carried out at different temperatures from 4.3 K up to about 700 K revealed that samples were single phase with cubic C15 structure for Si concentration x from 0.05 to 0.20 and hexagonal C14 structure for higher concentration. The results of 57Fe Mössbauer measurements showed that the Sc(Fe1−xSix2 compounds with x ≤ 0.30 are ferrimagnetic at 4.3 K. At temperature 80 K in the samples with x = 0.20 and 0.30, a magnetic cluster spin-glass state has been observed, as ferrimagnetic long-range order disappears. Such picture was supported by the results of ND measurements carried out at 8 K, which confirmed the lack of long-range order for x above 0.10 and an occurrence of hyperfine field distributions in the corresponding Mössbauer spectra. At room temperature, samples with x ≥ 0.20 became paramagnetic. A substitution of Si atoms for Fe ones leads to a decreasing of mean values of hyperfine magnetic fields in samples under investigation. From the neutron diffraction pattern analysis of Sc(Fe0.90Si0.102Fe magnetic moment was determined as to be equal to 1.5 μB at 8 K. Combining this result with a value of hyperfine magnetic field on 57Fe probes, the hyperfine coupling constant A in Sc(Fe0.90Cu0.102 phases is estimated at about 11.6 T/μB at 8 K.

  11. Fission and Properties of Neutron-Rich Nuclei - Proceedings of the Second International Conference

    Science.gov (United States)

    Hamilton, J. H.; Phillips, W. R.; Carter, H. K.

    The Table of Contents for the book is as follows: * Preface * Structure of Elementary Matter: Cold Valleys and Their Importance in Fission, Fusion and for Superheavy Nuclei * Tunnelling Phenomena in Nuclear Physics * Heavy Nuclei Studies Using Transfer Reactions * Isomeric Properties of Nuclei Near 78Ni * Investigation of Light Actinide Nuclei at Yale and Beyond * U-Projectile Fission at Relativistic Energies * Cluster Description of Cold Fission Modes in 252Cf * Neutron-pair Transfer Theory for Pear-shaped Ba Fission Fragments * New RMFA Parameters of Normal and Exotic Nuclei * Study of Fission Fragments from 12C+238U Reactions: Prompt and Delayed Spectroscopy * γ-Ray Angular Correlations in 252Cf and 248Cm Fission Fragments * Fragment Angular Momentum and Descent Dynamics in 252Cf Spontaneous Fission * The Experimental Investigation of Neutron-Rich Nuclei * High-Spin Structure of Some Odd-Z Nuclei with A ≈ 100 From Heavy-Ion Induced Fission * Coexistence of Symmetric and Asymmetric Nuclear Shapes and 10Be Ternary Fission * Octupole Effects in the Lanthanides * High Spin Structure of the 113-1l6Cd Isotopes Produced by Heavy-Ion Induced Fission Reaction * Temperature-Dependent Fission Barriers and Mass Distributions for 239U * Strength Distributions for Gamow Teller Transitions in Very Weakly Bound Systems * High Spin Fragmentation Spectroscopy * Search for a Four-Neutron Transfer From 8He to 4He * Microsecond Isomers in Fission Fragments in the Vicinity of the Doubly Magic 132Sn * Recent On-Line NMR/on Nuclear Magnetic Dipole Moments Near 132Sn: Meson Exchange Current Effects at the Shell Closure and Shell Model Treatment of Variation with Proton and Neutron Number * High-spin K-Isomers Beyond the Fusion Limit * High Energy Neutron Induced Fission: Charge Yield Distributions and Search and Spectroscopy of New Isomers * Hartree-Fock Mean-Field Models Using Separable Interactions * Variation of Fission Characteristics Over the Nuclear Chart * Investigation of

  12. In-beam gamma-ray spectroscopy of neutron-rich nuclei using fragmentation of radioactive beams and half-lives measurements of excited levels in nuclei closed to {sup 68}Ni; Spectroscopie {gamma} en ligne de noyaux legers riches en neutrons produits par fragmentation de faisceau radioactif et mesures de temps de vie des niveaux excites dans des noyaux proches de {sup 68}Ni

    Energy Technology Data Exchange (ETDEWEB)

    Stanoiu, M.A

    2003-01-01

    This thesis deals with studies of nuclei far from the valley of stability produced at GANIL by projectile fragmentation at intermediate energies. It consists of two parts. The first one is dedicated to the study of very light exotic nuclei around N=14. This is the first time that online {gamma}-ray spectroscopy combined with the projectile fragmentation was used with radioactive incident beams at GANIL. The advantages and the limitations of this method were established. 40 different nuclei have been produced and studied at the same time. A strong dependence of the population of excited states on the type of projectile was observed. New information was obtained on the structure of the isotopes B{sup 14,15}, C{sup 17,18,19,20}, N{sup 18,19,20,21,22}, O{sup 22,23,24}, F{sup 24,25,26} and Ne{sup 29}. The level schemes obtained from this study have been compared with shell-model predictions. In particular, the energy of 1588(20) keV found for the first 2{sup +} excited state in C{sup 20}, as well as the non-existence of a bound state in O{sup 24}, show that the proton-neutron interaction plays an important role in the structure of these nuclei. In the second part, an experiment is presented concerning the neutron-rich isomer nuclei around Ni{sup 68} produced by the LISE spectrometer. The fast-timing method was applied for the first time for the study of nuclei produced by projectile fragmentation. Subnanosecond half-lives of several levels in Ni{sup 67,69,90} and Cu{sup 71,72} were measured simultaneously and with high precision. These results have allowed us to test the shell model predictions for several E2 transitions and their associated B(E2) transition probabilities. (author)

  13. Resonance Enhanced Tunneling

    CERN Document Server

    Matsumoto, S; Matsumoto, Sh.

    2000-01-01

    Time evolution of tunneling in thermal medium is examined using the real-time semiclassical formalism previously developed. Effect of anharmonic terms in the potential well is shown to give a new mechanism of resonance enhanced tunneling. If the friction from environment is small enough, this mechanism may give a very large enhancement for the tunneling rate. The case of the asymmetric wine bottle potential is worked out in detail.

  14. Study of Protonic Mobility in CaHPO 4·2H 2O (Brushite) and CaHPO 4(Monetite) by Infrared Spectroscopy and Neutron Scattering

    Science.gov (United States)

    Tortet, L.; Gavarri, J. R.; Nihoul, G.; Dianoux, A. J.

    1997-08-01

    We report the first quasi-elastic neutron scattering analysis of proton mobility in the solid electrolyte CaHPO4·2H2O (brushite). We have studied this hydrated phosphate, in powder state, from 190 to 520 K, using an incident wavelength of 5.12 Å. The time of flight spectra are converted inS(Q,ω) structure factor and inelastic frequency distributionP(Q,ω) in the energy range 0-200 meV (0-1600 cm)-1. A quasi-elastic contribution is clearly evidenced above room temperature; it is fitted with a jump model, involving hydrogen bonds. The quasi-elastic and inelastic scattering data are compared with FTIR results. Two kinds of motions are determined: jumps of acidic protons on hydrogen bonds and vibrations of lattice water molecules associated with the motion of their hydrogen atom on hydrogen bonds (Ea≈0.145 eV). Above 450 K the dehydration of the compound is accompanied by the appearance of a long-range diffusive motion and by the disappearance of some low-frequency inelastic bands.

  15. Tunnelling in Dante's Inferno

    Science.gov (United States)

    Furuuchi, Kazuyuki; Sperling, Marcus

    2017-05-01

    We study quantum tunnelling in Dante's Inferno model of large field inflation. Such a tunnelling process, which will terminate inflation, becomes problematic if the tunnelling rate is rapid compared to the Hubble time scale at the time of inflation. Consequently, we constrain the parameter space of Dante's Inferno model by demanding a suppressed tunnelling rate during inflation. The constraints are derived and explicit numerical bounds are provided for representative examples. Our considerations are at the level of an effective field theory; hence, the presented constraints have to hold regardless of any UV completion.

  16. Microsystem Aeromechanics Wind Tunnel

    Data.gov (United States)

    Federal Laboratory Consortium — The Microsystem Aeromechanics Wind Tunnel advances the study of fundamental flow physics relevant to micro air vehicle (MAV) flight and assesses vehicle performance...

  17. Ulnar tunnel syndrome.

    Science.gov (United States)

    Bachoura, Abdo; Jacoby, Sidney M

    2012-10-01

    Ulnar tunnel syndrome could be broadly defined as a compressive neuropathy of the ulnar nerve at the level of the wrist. The ulnar tunnel, or Guyon's canal, has a complex and variable anatomy. Various factors may precipitate the onset of ulnar tunnel syndrome. Patient presentation depends on the anatomic zone of ulnar nerve compression: zone I compression, motor and sensory signs and symptoms; zone II compression, isolated motor deficits; and zone III compression; purely sensory deficits. Conservative treatment such as activity modification may be helpful, but often, surgical exploration of the ulnar tunnel with subsequent ulnar nerve decompression is indicated.

  18. ;Study of secondary hydriding at high temperature in zirconium based nuclear fuel cladding tubes by coupling information from neutron radiography/tomography, electron probe micro analysis, micro elastic recoil detection analysis and laser induced breakdown spectroscopy microprobe

    Science.gov (United States)

    Brachet, Jean-Christophe; Hamon, Didier; Le Saux, Matthieu; Vandenberghe, Valérie; Toffolon-Masclet, Caroline; Rouesne, Elodie; Urvoy, Stéphane; Béchade, Jean-Luc; Raepsaet, Caroline; Lacour, Jean-Luc; Bayon, Guy; Ott, Frédéric

    2017-05-01

    This paper gives an overview of a multi-scale experimental study of the secondary hydriding phenomena that can occur in nuclear fuel cladding materials exposed to steam at high temperature (HT) after having burst (loss-of-coolant accident conditions). By coupling information from several facilities, including neutron radiography/tomography, electron probe micro analysis, micro elastic recoil detection analysis and micro laser induced breakdown spectroscopy, it was possible to map quantitatively, at different scales, the distribution of oxygen and hydrogen within M5™ clad segments having experienced ballooning and burst at HT followed by steam oxidation at 1100 and 1200 °C and final direct water quenching down to room temperature. The results were very reproducible and it was confirmed that internal oxidation and secondary hydriding at HT of a cladding after burst can lead to strong axial and azimuthal gradients of hydrogen and oxygen concentrations, reaching 3000-4000 wt ppm and 1.0-1.2 wt% respectively within the β phase layer for the investigated conditions. Consistent with thermodynamic and kinetics considerations, oxygen diffusion into the prior-β layer was enhanced in the regions highly enriched in hydrogen, where the α(O) phase layer is thinner and the prior-β layer thicker. Finally the induced post-quenching hardening of the prior-β layer was mainly related to the local oxygen enrichment. Hardening directly induced by hydrogen was much less significant.

  19. Neutron Repulsion

    CERN Document Server

    Manuel, Oliver K

    2011-01-01

    Earth is connected gravitationally, magnetically and electrically to its heat source - a neutron star that is obscured from view by waste products in the photosphere. Neutron repulsion is like the hot filament in an incandescent light bulb. Excited neutrons are emitted from the solar core and decay into hydrogen that glows in the photosphere like a frosted light bulb. Neutron repulsion was recognized in nuclear rest mass data in 2000 as the overlooked source of energy, the keystone of an arch that locked together these puzzling space-age observations: 1.) Excess 136Xe accompanied primordial helium in the stellar debris that formed the solar system (Fig. 1); 2.) The Sun formed on the supernova core (Fig. 2); 3.) Waste products from the core pass through an iron-rich mantle, selectively carrying lighter elements and lighter isotopes of each element into the photosphere (Figs. 3-4); and 4.) Neutron repulsion powers the Sun and sustains life (Figs. 5-7). Together these findings offer a framework for understanding...

  20. On the Sr1−xBaxFeO2F Oxyfluoride Perovskites: Structure and Magnetism from Neutron Diffraction and Mössbauer Spectroscopy

    Directory of Open Access Journals (Sweden)

    Crisanto A. García-Ramos

    2016-11-01

    Full Text Available Four oxyfluorides of the title series (x = 0.00, 0.25, 0.50, 0.75 have been stabilized by topotactic treatment of perovskite precursors Sr1−xBaxFeO3−δ prepared by soft-chemistry procedures, yielding reactive materials that can easily incorporate a substantial amount of F atoms at moderate temperatures, thus avoiding the stabilization of competitive SrF2 and BaF2 parasitic phases. XRD and Neutron Powder Diffraction (NPD measurements assess the phase purity and yield distinct features concerning the unit cell parameters’ variation, the Sr and Ba distribution, the stoichiometry of the anionic sublattice and the anisotropic displacement factors for O and F atoms. The four oxyfluorides are confirmed to be cubic in all of the compositional range, the unit cell parameters displaying Vergard’s law. All of the samples are magnetically ordered above room temperature; the magnetic structure is always G-type antiferromagnetic, as shown from NPD data. The ordered magnetic moments are substantially high, around 3.5 μB, even at room temperature (RT. Temperature-dependent Mössbauer data allow identifying Fe3+ in all of the samples, thus confirming the Sr1−xBaxFeO2F stoichiometry. The fit of the magnetic hyperfine field vs. temperature curve yields magnetic ordering TN temperatures between 740 K (x = 0.00 and 683 K (x = 0.75. These temperatures are substantially higher than those reported before for some of the samples, assessing for stronger Fe-Fe superexchange interactions for these specimens prepared by fluorination of citrate precursors in mild conditions.

  1. Anisotropic lattice thermal expansion of PbFeBO{sub 4}: A study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations

    Energy Technology Data Exchange (ETDEWEB)

    Murshed, M. Mangir, E-mail: murshed@uni-bremen.de [Chemische Kristallographie fester Stoffe, Institut für Anorganische Chemie, Universität Bremen, Leobener Straße, D-28359 Bremen (Germany); Mendive, Cecilia B.; Curti, Mariano [Departamento de Química, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Dean Funes 3350, B7600AYL, Mar del Plata (Argentina); Nénert, Gwilherm [Institut Laue-Langevin, 6 rue Jules Horowitz, 38042 Grenoble (France); Kalita, Patricia E. [Department of Physics and Astronomy and High-Pressure Science and Engineering Center, University of Nevada Las Vegas, Box 4002, Las Vegas, NV 89154-4002 (United States); Lipinska, Kris [Department of Mechanical Engineering, University of Nevada Las Vegas, 4505 Maryland Parkway, Box 454009, Las Vegas, NV 89154-4009 (United States); Cornelius, Andrew L. [Department of Physics and Astronomy and High-Pressure Science and Engineering Center, University of Nevada Las Vegas, Box 4002, Las Vegas, NV 89154-4002 (United States); Huq, Ashfia [Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6475 (United States); Gesing, Thorsten M. [Chemische Kristallographie fester Stoffe, Institut für Anorganische Chemie, Universität Bremen, Leobener Straße, D-28359 Bremen (Germany)

    2014-11-15

    Highlights: • Mullite-type PbFeBO{sub 4} shows uni-axial negative coefficient of thermal expansion. • Anisotropic thermal expansion of the metric parameters was modeled using modified Grüneisen approximation. • The model includes harmonic, quasi-harmonic and intrinsic anharmonic contributions to the internal energy. • DFT calculation, temperature- and pressure-dependent Raman spectra help understand the phonon decay and associated anharmonicity. - Abstract: The lattice thermal expansion of mullite-type PbFeBO{sub 4} is presented in this study. The thermal expansion coefficients of the metric parameters were obtained from composite data collected from temperature-dependent neutron and X-ray powder diffraction between 10 K and 700 K. The volume thermal expansion was modeled using extended Grüneisen first-order approximation to the zero-pressure equation of state. The additive frame of the model includes harmonic, quasi-harmonic and intrinsic anharmonic potentials to describe the change of the internal energy as a function of temperature. The unit-cell volume at zero-pressure and 0 K was optimized during the DFT simulations. Harmonic frequencies of the optical Raman modes at the Γ-point of the Brillouin zone at 0 K were also calculated by DFT, which help to assign and crosscheck the experimental frequencies. The low-temperature Raman spectra showed significant anomaly in the antiferromagnetic regions, leading to softening or hardening of some phonons. Selected modes were analyzed using a modified Klemens model. The shift of the frequencies and the broadening of the line-widths helped to understand the anharmonic vibrational behaviors of the PbO{sub 4}, FeO{sub 6} and BO{sub 3} polyhedra as a function of temperature.

  2. Nanostructures of Mg0.65Ti0.35Dx studied with x-ray diffraction, neutron diffraction, and magic-angle-spinning H2 NMR spectroscopy

    Science.gov (United States)

    Srinivasan, S.; Magusin, P. C. M. M.; Kalisvaart, W. P.; Notten, P. H. L.; Cuevas, F.; Latroche, M.; van Santen, R. A.

    2010-02-01

    Magnesium transition-metal alloys have a high hydrogen-storage capacity and show improved hydrogen-uptake and -release kinetics compared to magnesium alone. In the present study we have investigated the structure of bulk magnesium-titanium deuteride Mg0.65Ti0.35Dx prepared via mechanical alloying and gas-phase deuterium absorption by combined use of x-ray diffraction (XRD), neutron diffraction, and magic-angle-spinning H2 nuclear magnetic resonance (NMR). The initial ball-milled alloy has two XRD-distinct Mg and Ti fcc phases. Even after prolonged exposure to deuterium gas at 75 bar and 175°C the materials with and without palladium catalyst are only partly deuterated. Deuterium loading causes the formation of, on the one hand, bct (rutile) MgD2 nanodomains with interdispersed TiDy layers and, on the other hand, a separate fcc (fluorite) TiDz phase. The TiDy phase is XRD invisible, but shows clearly up at a H2 NMR shift of -43ppm between the shift of MgD2 (3 ppm) and the Knight shift of the TiDz phase (-143ppm) . Exchange NMR indicates complete deuterium exchange at 25°C between the MgD2 and TiDy phase within 1 s, as consistent with intimate contacts between these phases. Combined analysis of the XRD and NMR peak areas suggests that the deuterium concentrations y and z in the TiDy and TiDz domains are about 1.5 and 2.0, respectively. Comparing the intrinsic cell parameters of rutile MgH2 and fluorite TiH2 , we propose that stabilization of the mixed nanocomposite may arise from a coherent coupling between the crystal structures of the rutile MgD2 nanodomains and the thin layers of fcc TiDy .

  3. Local structures of polar wurtzites Zn1-xMgxO studied by raman and 67Zn/25Mg NMR spectroscopies and by total neutron scattering

    Energy Technology Data Exchange (ETDEWEB)

    Proffen, Thomas E [Los Alamos National Laboratory; Kim, Yiung- Il [UCSB; Cadars, Sylvian [UCSB; Shayib, Ramzy [UCSB; Feigerle, Charles S [UNIV OF TENNESSEE; Chmelka, Bradley F [UCSB; Seshadri, Ram [UCSB

    2008-01-01

    Research in the area of polar semiconductor heterostructures has been growing rapidly, driven in large part by interest in two-dimensional electron gas (2DEG) systems. 2DEGs are known to form at heterojunction interfaces that bear polarization gradients. They can display extremely high electron mobilities, especially at low temperatures, owing to spatial confinement of carrier motions. Recent reports of 2DEG behaviors in Ga{sub 1-x}Al{sub x}N/GaN and Zn{sub 1-x}Mg{sub x}O/ZnO heterostructures have great significance for the development of quantum Hall devices and novel high-electron-mobility transistors (HEMTs). 2DEG structures are usually designed by interfacing a polar semiconductor with its less or more polar alloys in an epitaxial manner. Since the quality of the 2DEG depends critically on interface perfection, as well as the polarization gradient at the heterojunction, understanding compositional and structural details of the parent and alloy semiconductors is an important component in 2DEG design and fabrication. Zn{sub 1-x}Mg{sub x}O/ZnO is one of the most promising heterostructure types for studies of 2DEGs, due to the large polarization of ZnO, the relatively small lattice mismatch, and the large conduction band offsets in the Zn{sub 1-x}Mg{sub x}O/ZnO heterointerface. Although 2DEG formation in Zn{sub 1-x}Mg{sub x}O/ZnO heterostructures have been researched for some time, a clear understanding of the alloy structure of Zn{sub 1-x}Mg{sub x}O is currently lacking. Here, we conduct a detailed and more precise study of the local structure of Zn{sub 1-x}Mg{sub x}O alloys using Raman and solid-state nuclear magnetic resonance (NMR), in conjunction with neutron diffraction techniques.

  4. a Portable Pulsed Neutron Generator

    Science.gov (United States)

    Skoulakis, A.; Androulakis, G. C.; Clark, E. L.; Hassan, S. M.; Lee, P.; Chatzakis, J.; Bakarezos, M.; Dimitriou, V.; Petridis, C.; Papadogiannis, N. A.; Tatarakis, M.

    2014-02-01

    The design and construction of a pulsed plasma focus device to be used as a portable neutron source for material analysis such as explosive detection using gamma spectroscopy is presented. The device is capable of operating at a repetitive rate of a few Hz. When deuterium gas is used, up to 105 neutrons per shot are expected to be produced with a temporal pulse width of a few tens of nanoseconds. The pulsed operation of the device and its portable size are its main advantage in comparison with the existing continuous neutron sources. Parts of the device include the electrical charging unit, the capacitor bank, the spark switch (spark gap), the trigger unit and the vacuum-fuel chamber / anode-cathode. Numerical simulations are used for the simulation of the electrical characteristics of the device including the scaling of the capacitor bank energies with total current, the pinch current, and the scaling of neutron yields with energies and currents. The MCNPX code is used to simulate the moderation of the produced neutrons in a simplified geometry and subsequently, the interaction of thermal neutrons with a test target and the corresponding prompt γ-ray generation.

  5. Virtual photons in macroscopic tunneling

    CERN Document Server

    Aichmann, Horst; Bruney, Paul

    2015-01-01

    Tunnelling processes are thought to proceed via virtual waves due to observed superluminal (faster than light) signal speeds. Some assume such speeds must violate causality. These assumptions contradict, for instance, superluminally tunnelled music and optical tunnelling couplers applied in fiber communication. Recently tunnelling barriers were conjectured to be cavities, wherein the tunnelled output signal is not causally related with the input. The tests described here resolve that tunnelling waves are virtual, propagations are superluminal, and causality is preserved.

  6. Neutron diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Heger, G. [Rheinisch-Westfaelische Technische Hochschule Aachen, Inst. fuer Kristallographie, Aachen (Germany)

    1996-12-31

    X-ray diffraction using conventional laboratory equipment and/or synchrotron installations is the most important method for structure analyses. The purpose of this paper is to discuss special cases, for which, in addition to this indispensable part, neutrons are required to solve structural problems. Even though the huge intensity of modern synchrotron sources allows in principle the study of magnetic X-ray scattering the investigation of magnetic structures is still one of the most important applications of neutron diffraction. (author) 15 figs., 1 tab., 10 refs.

  7. Neutronics of pulsed spallation neutron sources

    CERN Document Server

    Watanabe, N

    2003-01-01

    Various topics and issues on the neutronics of pulsed spallation neutron sources, mainly for neutron scattering experiments, are reviewed to give a wide circle of readers a better understanding of these sources in order to achieve a high neutronic performance. Starting from what neutrons are needed, what the spallation reaction is and how to produce slow-neutrons more efficiently, the outline of the target and moderator neutronics are explained. Various efforts with some new concepts or ideas have already been devoted to obtaining the highest possible slow-neutron intensity with desired pulse characteristics. This paper also reviews the recent progress of such efforts, mainly focused on moderator neutronics, since moderators are the final devices of a neutron source, which determine the source performance. Various governing parameters for neutron-pulse characteristics such as material issues, geometrical parameters (shape and dimensions), the target-moderator coupling scheme, the ortho-para-hydrogen ratio, po...

  8. Tunnel fire dynamics

    CERN Document Server

    Ingason, Haukur; Lönnermark, Anders

    2015-01-01

    This book covers a wide range of issues in fire safety engineering in tunnels, describes the phenomena related to tunnel fire dynamics, presents state-of-the-art research, and gives detailed solutions to these major issues. Examples for calculations are provided. The aim is to significantly improve the understanding of fire safety engineering in tunnels. Chapters on fuel and ventilation control, combustion products, gas temperatures, heat fluxes, smoke stratification, visibility, tenability, design fire curves, heat release, fire suppression and detection, CFD modeling, and scaling techniques all equip readers to create their own fire safety plans for tunnels. This book should be purchased by any engineer or public official with responsibility for tunnels. It would also be of interest to many fire protection engineers as an application of evolving technical principles of fire safety.

  9. Neutron tomography

    Science.gov (United States)

    Crump, James C., III; Richards, Wade J.; Shields, Kevin C.

    1995-07-01

    The McClellan Nuclear Radiation Center's (MNRC) staff in conjunction with a Cooperative Research and Development Agreement (CRDA) with the U.C. Santa Barbara facility has developed a system that can be used for aircraft inspection of jet engine blades. The problem was to develop an inspection system that can detect very low concentrations of hydrogen (i.e., greater than 100 ppm) in metal matricies. Specifically in Titanium alloy jet engine blades. Entrapment and precipitation of hydrogen in metals is an undesirable phenomenon which occurs in many alloys of steel and titanium. In general, metals suffer a loss of mechanical properties after long exposures to hydrogen, especially at high temperatures and pressures, thereby becoming embrittled. Neutron radiography has been used as a nondestructive testing technique for many years. Neutrons, because of their unique interactions with materials, are especially useful in the detection of hydrogen. They have an extremely high interaction cross section for low atomic number nuclei (i.e., hydrogen). Thus hydrogen in a metal matrix can be visualized using neutrons. Traditional radiography is sensitive to the total attenuation integrated over the path of radiation through the material. Increased sensitivity and quantitative cross section resolution can be obtained using three-dimensional volumetric imaging techniques such as tomography. The solution used to solve the problem was to develop a neutron tomography system. The neutron source is the McClellan Nuclear Radiation Center's 1 MW TRIGA reactor. This paper describes the hardware used in the system as well as some of the preliminary results.

  10. Ultrafast scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Botkin, D.A. [California Univ., Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States)

    1995-09-01

    I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of the time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.

  11. Compact Neutron Generators for Medical, Home Land Security, and Planetary Exploration

    CERN Document Server

    Reijonen, Jani

    2005-01-01

    The Plasma and Ion Source Technology Group at Lawrence Berkeley National Laboratory has developed various types of advanced D-D (neutron energy 2.5 MeV), D-T (14 MeV) and T-T (0 - 9 MeV) neutron generators for wide range of applications. These applications include medical (Boron Neutron Capture Therapy), homeland security (Prompt Gamma Activation Analysis, Fast Neutron Activation Analysis and Pulsed Fast Neutron Transmission Spectroscopy) and planetary exploration in form of neutron based, sub-surface hydrogen detection systems. These neutron generators utilize RF induction discharge to ionize the deuterium/tritium gas. This discharge method provides high plasma density for high output current, high atomic species from molecular gases, long life operation and versatility for various discharge chamber geometries. Three main neutron generator developments are discussed here: high neutron output co-axial neutron generator for BNCT applications, point neutron generator for security applications, compact and sub-c...

  12. Measurements of Neutron-absorbing Elements on Mercury's Surface with the MESSENGER Neutron Spectrometer

    Science.gov (United States)

    Lawrence, David J.; Feldman, William C.; Goldsten, John O.; McCoy, Timothy J.; Blewett, David T.; Boynton, William V.; Evans, Larry G.; Nittler, Larry R.; Rhodes, Edgar A.; Solomon, Sean C.

    2010-05-01

    The Neutron Spectrometer (NS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission has made measurements of cosmic-ray-generated thermal neutrons during each of MESSENGER's three Mercury flybys. These thermal neutron data have allowed us to make the first direct measurements of Mercury's surface elemental composition. Specifically, we show that Mercury's surface is enriched in neutron-absorbing elements and has a measured macroscopic neutron absorption cross section of (70-130) × 10^(-4) cm^2/g, which is similar to the neutron absorption of lunar basalts from Mare Fecunditatis. The expected neutron-absorbing elements are Fe and Ti, with possible trace amounts of Gd and Sm. Fe and Ti, in particular, are important for understanding Mercury's formation and how its surface may have changed over time through magmatic processes. With the neutron Doppler filter technique - a neutron energy separation technique based on spacecraft velocity - we demonstrate that Mercury's surface composition cannot be matched by prior models having characteristically low abundances of Fe, Ti, Gd, and Sm. While neutron spectroscopy alone cannot separate the relative contributions of individual neutron-absorbing elements, these results provide strong new constraints on the nature of Mercury's surface materials. For example, if all the measured neutron absorption were due to the presence of a Fe-Ti oxide and that oxide were ilmenite, then Mercury's surface would have an ilmenite content of 14 to 31 wt.%. This result is in agreement with the inference from color imaging and visible-near-infrared spectroscopy that Mercury's overall low reflectance is consistent with a surface composition that is enriched in Fe-Ti oxides. The incorporation of substantial Fe and Ti in oxides would imply that the oxygen fugacity of basalts on Mercury is at the upper range of oxygen fugacity inferred for basalts on the Moon.

  13. Control of defect-mediated tunneling barrier heights in ultrathin MgO films

    OpenAIRE

    Kim, D. J; Choi, W S; Schleicher, F.; Shin, R. H.; Boukari, S.; Davesne, V.; Kieber, C.; Arabski, J.; Schmerber, G.; Beaurepaire, E.; Jo, W.; Bowen, M.

    2010-01-01

    The impact of oxygen vacancies on local tunneling properties across rf-sputtered MgO thin films was investigated by optical absorption spectroscopy and conducting atomic force microscopy. Adding O$_2$ to the Ar plasma during MgO growth alters the oxygen defect populations, leading to improved local tunneling characteristics such as a lower density of current hotspots and a lower tunnel current amplitude. We discuss a defect-based potential landscape across ultrathin MgO barriers.

  14. Interface properties of magnetic tunnel junction La0.7Sr0.3MnO3/SrTiO3 superlattices studied by standing-wave excited photoemission spectroscopy

    NARCIS (Netherlands)

    Gray, A.X.; Papp, C.; Balke, B.; Yang, S.-H.; Huijben, M.; Rotenberg, E.; Bostwick, A.; Ueda, S.; Yamashita, Y.; Kobayashi, K.; Gullikson, E.M.; Kortright, J.B.; Groot, de F.M.F.; Rijnders, G.; Blank, D.H.A.; Ramesh, R.; Fadley, C.S.

    2010-01-01

    The chemical and electronic-structure profiles of magnetic tunnel junction (MTJ) La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) superlattices have been quantitatively determined via soft and hard x-ray standing-wave excited photoemission, x-ray absorption and x-ray reflectivity, in conjunction with x-ray optical

  15. Fusion neutron diagnostics on ITER tokamak

    Science.gov (United States)

    Bertalot, L.; Barnsley, R.; Direz, M. F.; Drevon, J. M.; Encheva, A.; Jakhar, S.; Kashchuk, Y.; Patel, K. M.; Arumugam, A. P.; Udintsev, V.; Walker, C.; Walsh, M.

    2012-04-01

    ITER is an experimental nuclear reactor, aiming to demonstrate the feasibility of nuclear fusion realization in order to use it as a new source of energy. ITER is a plasma device (tokamak type) which will be equipped with a set of plasma diagnostic tools to satisfy three key requirements: machine protection, plasma control and physics studies by measuring about 100 different parameters. ITER diagnostic equipment is integrated in several ports at upper, equatorial and divertor levels as well internally in many vacuum vessel locations. The Diagnostic Systems will be procured from ITER Members (Japan, Russia, India, United States, Japan, Korea and European Union) mainly with the supporting structures in the ports. The various diagnostics will be challenged by high nuclear radiation and electromagnetic fields as well by severe environmental conditions (ultra high vacuum, high thermal loads). Several neutron systems with different sensitivities are foreseen to measure ITER expected neutron emission from 1014 up to almost 1021 n/s. The measurement of total neutron emissivity is performed by means of Neutron Flux Monitors (NFM) installed in diagnostic ports and by Divertor Neutron Flux Monitors (DNFM) plus MicroFission Chambers (MFC) located inside the vacuum vessel. The neutron emission profile is measured with radial and vertical neutron cameras. Spectroscopy is accomplished with spectrometers looking particularly at 2.5 and 14 MeV neutron energy. Neutron Activation System (NAS), with irradiation ends inside the vacuum vessel, provide neutron yield data. A calibration strategy of the neutron diagnostics has been developed foreseeing in situ and cross calibration campaigns. An overview of ITER neutron diagnostic systems and of the associated challenging engineering and integration issues will be reported.

  16. Signature of the N=126 shell closure in dwell times of alpha-particle tunneling

    CERN Document Server

    Kelkar, N G

    2016-01-01

    Characteristic quantities such as the penetration and preformation probabilities, assault frequency and tunneling times in the tunneling description of alpha decay of heavy nuclei are explored to reveal their sensitivity to neutron numbers in the vicinity of the magic neutron number $N$ = 126. Using realistic nuclear potentials, the sensitivity of these quantities to the parameters of the theoretical approach is also tested. An investigation of the region from $N=116$ to $N=132$ in Po nuclei reveals that the tunneling $\\alpha$ particle spends the least amount of time with an $N=126$ magic daughter nucleus. The shell closure at $N=126$ seems to affect the behaviour of the dwell times of the tunneling alpha particles and this occurs through the influence of the $Q$-values involved.

  17. Signature of the N = 126 shell closure in dwell times of alpha-particle tunneling

    Science.gov (United States)

    Kelkar, N. G.; Nowakowski, M.

    2016-10-01

    Characteristic quantities such as the penetration and preformation probabilities, assault frequency and tunneling times in the tunneling description of alpha decay of heavy nuclei are explored to reveal their sensitivity to neutron numbers in the vicinity of the magic neutron number N = 126. Using realistic nuclear potentials, the sensitivity of these quantities to the parameters of the theoretical approach is also tested. An investigation of the region from N = 116 to N = 132 in Po nuclei reveals that the tunneling α particle spends the least amount of time with an N = 126 magic daughter nucleus. The shell closure at N = 126 seems to affect the behavior of the dwell times of the tunneling alpha particles and this occurs through the influence of the Q-values involved.

  18. Growth, shrinking, and breaking of pluronic micelles in the presence of drugs and/or beta-cyclodextrin, a study by small-angle neutron scattering and fluorescence spectroscopy.

    Science.gov (United States)

    Valero, Margarita; Dreiss, Cécile A

    2010-07-01

    The associative structures between F127 Pluronic micelles and four drugs, namely, lidocaine (LD), pentobarbital sodium salt (PB), sodium naproxen (NP), and sodium salicylate (SAL), were studied by small-angle neutron scattering (SANS). Different outcomes for the micellar aggregates are observed, which are dependent on the chemical nature of the drug and the presence of charge or otherwise: the micelles grow with LD, are hardly modified with PB, and decrease in size with both NP and SAL. The partition coefficient, determined by fluorescence spectroscopy, is directly correlated to the amount of charge, following NP approximately SAL inclusion complexes with heptakis(2,6-di-O-methyl) beta-cyclodextrin (hep2,6 beta-CD). Hep2,6 beta-CD, as shown in previous studies (Joseph, J.; Dreiss, C. A.; Cosgrove, T. Langmuir, 2008, 24, 10005-10010; Dreiss, C. A.; Nwabunwanne, E.; Liu, R.; Brooks, N. J. Soft Matter, 2009, 5, 1888-1896), is also able to form a complex with F127, resulting in micellar breakup. In the ternary mixtures, a fine balance of forces is involved, which results in drastic micellar changes, as observed from the SANS patterns. Depending on the ratio of drug, polymer, and hep2,6 beta-CD and the nature of the interactions (which is directly linked to the drug chemical structure), the presence of drug either hinders micellar breakup by beta-CD (at high enough concentration of LD or PB) or leads to micellar growth (NP). These effects are mainly attributed to a preferential drug/beta-CD interaction (except for PB), which, at least in the conditions studied here, explains the higher beta-CD concentration needed for micellar breakup to occur.

  19. Effect of band gap narrowing on GaAs tunnel diode I-V characteristics

    Science.gov (United States)

    Lebib, A.; Hannanchi, R.; Beji, L.; EL Jani, B.

    2016-12-01

    We report on experimental and theoretical study of current-voltage characteristics of C/Si-doped GaAs tunnel diode. For the investigation of the experimental data, we take into account the band-gap narrowing (BGN) effect due to heavily-doped sides of the tunnel diode. The BGN of the n- and p-sides of tunnel diode was measured by photoluminescence spectroscopy. The comparison between theoretical results and experimental data reveals that BGN effect enhances tunneling currents and hence should be considered to identify more accurately the different transport mechanisms in the junction. For C/Si-doped GaAs tunnel diode, we found that direct tunneling is the dominant transport mechanism at low voltages. At higher voltages, this mechanism is replaced by the rate-controlling tunneling via gap states in the forbidden gap.

  20. Effect of band gap narrowing on GaAs tunnel diode I-V characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Lebib, A.; Hannanchi, R. [Laboratoire d' énergie et de matériaux, LabEM-LR11ES34-Université de sousse (Tunisia); Beji, L., E-mail: lotbej_fr@yahoo.fr [Laboratoire d' énergie et de matériaux, LabEM-LR11ES34-Université de sousse (Tunisia); EL Jani, B. [Unité de Recherche sur les Hétéro-Epitaxies et Applications, Faculté des Sciences, Université de Monastir, 5019 Monastir (Tunisia)

    2016-12-01

    We report on experimental and theoretical study of current-voltage characteristics of C/Si-doped GaAs tunnel diode. For the investigation of the experimental data, we take into account the band-gap narrowing (BGN) effect due to heavily-doped sides of the tunnel diode. The BGN of the n- and p-sides of tunnel diode was measured by photoluminescence spectroscopy. The comparison between theoretical results and experimental data reveals that BGN effect enhances tunneling currents and hence should be considered to identify more accurately the different transport mechanisms in the junction. For C/Si-doped GaAs tunnel diode, we found that direct tunneling is the dominant transport mechanism at low voltages. At higher voltages, this mechanism is replaced by the rate-controlling tunneling via gap states in the forbidden gap.

  1. Neutron irradiation effects on gallium nitride-based Schottky diodes

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Chung-Han; Katz, Evan J.; Zhang, Zhichun [Department of Electrical and Computer Engineering, The Ohio State University, Columbus Ohio 43210 (United States); Qiu, Jie; Cao, Lei [Nuclear Engineering Program, Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Mishra, Umesh K. [Departments of Electrical and Computer Engineering and Materials Science and Engineering, University of California, Santa Barbara, California 93106 (United States); Brillson, Leonard J. [Department of Electrical and Computer Engineering, The Ohio State University, Columbus Ohio 43210 (United States); Department of Physics and Center for Materials Research, The Ohio State University, Columbus, Ohio 43210 (United States)

    2013-10-14

    Depth-resolved cathodoluminescence spectroscopy (DRCLS), time-resolved surface photovoltage spectroscopy, X-ray photoemission spectroscopy (XPS), and current-voltage measurements together show that fast versus thermal neutrons differ strongly in their electronic and morphological effects on metal-GaN Schottky diodes. Fast and thermal neutrons introduce GaN displacement damage and native point defects, while thermal neutrons also drive metallurgical reactions at metal/GaN interfaces. Defect densities exhibit a threshold neutron fluence below which thermal neutrons preferentially heal versus create new native point defects. Scanning XPS and DRCLS reveal strong fluence- and metal-dependent electronic and chemical changes near the free surface and metal interfaces that impact diode properties.

  2. Virtual photons in macroscopic tunneling

    OpenAIRE

    Aichmann, Horst; Nimtz, Guenter; Bruney, Paul

    2015-01-01

    Tunnelling processes are thought to proceed via virtual waves due to observed superluminal (faster than light) signal speeds. Some assume such speeds must violate causality. These assumptions contradict, for instance, superluminally tunnelled music and optical tunnelling couplers applied in fiber communication. Recently tunnelling barriers were conjectured to be cavities, wherein the tunnelled output signal is not causally related with the input. The tests described here resolve that tunnelli...

  3. Radiative neutron capture as a counting technique at pulsed spallation neutron sources: a review of current progress

    Science.gov (United States)

    Schooneveld, E. M.; Pietropaolo, A.; Andreani, C.; Perelli Cippo, E.; Rhodes, N. J.; Senesi, R.; Tardocchi, M.; Gorini, G.

    2016-09-01

    Neutron scattering techniques are attracting an increasing interest from scientists in various research fields, ranging from physics and chemistry to biology and archaeometry. The success of these neutron scattering applications is stimulated by the development of higher performance instrumentation. The development of new techniques and concepts, including radiative capture based neutron detection, is therefore a key issue to be addressed. Radiative capture based neutron detectors utilize the emission of prompt gamma rays after neutron absorption in a suitable isotope and the detection of those gammas by a photon counter. They can be used as simple counters in the thermal region and (simultaneously) as energy selector and counters for neutrons in the eV energy region. Several years of extensive development have made eV neutron spectrometers operating in the so-called resonance detector spectrometer (RDS) configuration outperform their conventional counterparts. In fact, the VESUVIO spectrometer, a flagship instrument at ISIS serving a continuous user programme for eV inelastic neutron spectroscopy measurements, is operating in the RDS configuration since 2007. In this review, we discuss the physical mechanism underlying the RDS configuration and the development of associated instrumentation. A few successful neutron scattering experiments that utilize the radiative capture counting techniques will be presented together with the potential of this technique for thermal neutron diffraction measurements. We also outline possible improvements and future perspectives for radiative capture based neutron detectors in neutron scattering application at pulsed neutron sources.

  4. Neutron reflectometry

    DEFF Research Database (Denmark)

    Klösgen-Buchkremer, Beate Maria

    2014-01-01

    to hundreds of nanometers. Thickness resolution for flat surfaces is in the range of few Ǻngstrøm, and as a peculiar benefit, the presence and properties of buried interfaces are accessible. Focus here will be on neutron reflectometry, a technique that is unique in applications involving composite organic...... of desired information. In the course, an introduction into the method and an overview on selected instruments at large scale facilities will be presented. Examples will be given that illustrate the potential of the method, mostly based on organic films. Results from the investigation of layered films...... and the detection on nanoscopic roughnesses will be shown. The potential of neutron reflectometry is not only of academic origin. It may turn out to be useful in the design and development of new functional materials even though it will never develop into a standard method to be applied in the product control...

  5. Magnetic-Field Dependence of Tunnel Couplings in Carbon Nanotube Quantum Dots

    DEFF Research Database (Denmark)

    Grove-Rasmussen, Kasper; Grap, S.; Paaske, Jens;

    2012-01-01

    By means of sequential and cotunneling spectroscopy, we study the tunnel couplings between metallic leads and individual levels in a carbon nanotube quantum dot. The levels are ordered in shells consisting of two doublets with strong- and weak-tunnel couplings, leading to gate-dependent level...

  6. Wind Tunnel Testing Facilities

    Data.gov (United States)

    Federal Laboratory Consortium — NASA Ames Research Center is pleased to offer the services of our premier wind tunnel facilities that have a broad range of proven testing capabilities to customers...

  7. INCAS TRISONIC WIND TUNNEL

    Directory of Open Access Journals (Sweden)

    Florin MUNTEANU

    2009-09-01

    Full Text Available The 1.2 m x 1.2 m Trisonic Blowdown Wind Tunnel is the largest of the experimental facilities at the National Institute for Aerospace Research - I.N.C.A.S. "Elie Carafoli", Bucharest, Romania. The tunnel has been designed by the Canadian company DSMA (now AIOLOS and since its commissioning in 1978 has performed high speed aerodynamic tests for more than 120 projects of aircraft, missiles and other objects among which the twin jet fighter IAR-93, the jet trainer IAR-99, the MIG-21 Lancer, the Polish jet fighter YRYDA and others. In the last years the wind tunnel has been used mostly for experimental research in European projects such as UFAST. The high flow quality parameters and the wide range of testing capabilities ensure the competitivity of the tunnel at an international level.

  8. Quantum tunneling with friction

    Science.gov (United States)

    Tokieda, M.; Hagino, K.

    2017-05-01

    Using the phenomenological quantum friction models introduced by P. Caldirola [Nuovo Cimento 18, 393 (1941), 10.1007/BF02960144] and E. Kanai [Prog. Theor. Phys. 3, 440 (1948), 10.1143/ptp/3.4.440], M. D. Kostin [J. Chem. Phys. 57, 3589 (1972), 10.1063/1.1678812], and K. Albrecht [Phys. Lett. B 56, 127 (1975), 10.1016/0370-2693(75)90283-X], we study quantum tunneling of a one-dimensional potential in the presence of energy dissipation. To this end, we calculate the tunneling probability using a time-dependent wave-packet method. The friction reduces the tunneling probability. We show that the three models provide similar penetrabilities to each other, among which the Caldirola-Kanai model requires the least numerical effort. We also discuss the effect of energy dissipation on quantum tunneling in terms of barrier distributions.

  9. Water Tunnel Facility

    Data.gov (United States)

    Federal Laboratory Consortium — NETL’s High-Pressure Water Tunnel Facility in Pittsburgh, PA, re-creates the conditions found 3,000 meters beneath the ocean’s surface, allowing scientists to study...

  10. Wind Tunnel Facility

    Data.gov (United States)

    Federal Laboratory Consortium — This ARDEC facility consists of subsonic, transonic, and supersonic wind tunnels to acquire aerodynamic data. Full-scale and sub-scale models of munitions are fitted...

  11. Gravity Tunnel Drag

    CERN Document Server

    Concannon, Thomas

    2016-01-01

    The time it takes to fall down a tunnel through the center of the Earth to the other side takes approximately 42 minutes, but only when given several simplifying assumptions: a uniform density Earth; a gravitational field that varies linearly with radial position; a non-rotating Earth; a tunnel evacuated of air; and zero friction along the sides of the tunnel. Though several papers have singularly relaxed the first three assumptions, in this paper we relax the final two assumptions and analyze the motion of a body experiencing these types of drag forces in the tunnel. Under such drag forces, we calculate the motion of a transport vehicle through a tunnel of the Earth under uniform density, under constant gravitational acceleration, and finally under the more realistic Preliminary Reference Earth Model (PREM) density data. We find the density profile corresponding to a constant gravitational acceleration better models the motion through the tunnel compared to the PREM density profile, and the uniform density m...

  12. Next Generation Gamma/Neutron Detectors for Planetary Science. Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Gamma ray and neutron spectroscopy are well established techniques for determining the chemical composition of planetary surfaces, and small cosmic bodies such as...

  13. Next Generation Gamma/Neutron Detectors for Planetary Science. Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Gamma-ray and neutron spectroscopy are well established techniques for determining the chemical composition of planetary surfaces, and small cosmic bodies such as...

  14. Measurement of the Surface and Underground Neutron Spectra with the UMD/NIST Fast Neutron Spectrometers

    Science.gov (United States)

    Langford, Thomas J.

    The typical fast neutron detector falls into one of two categories, Bonner sphere spectrometers and liquid scintillator proton recoil detectors. These two detector types have traditionally been used to measure fast neutrons at the surface and in low background environments. The cosmogenic neutron spectrum and flux is an important parameter for a number of experimental efforts, including procurement of low background materials and the prediction of electronic device faults. Fast neutrons can also cause problems for underground low-background experiments, through material activation or signals that mimic rare events. Current detector technology is not sufficient to properly characterize these backgrounds. To this end, the University of Maryland and the National Institute of Standards and Technology designed, developed, and deployed two Fast Neutron Spectrometers (FaNS) comprised of plastic scintillator and 3He proportional counters. The detectors are based upon capture-gated spectroscopy, a technique that demands a delayed coincidence between a neutron scatter and the resulting neutron capture after thermalization. This technique provides both particle identification and knowledge that the detected neutron fully thermalized. This improves background rejection capabilities and energy resolution. Presented are the design, development, and deployment of FaNS-1 and FaNS-2. Both detectors were characterized using standard fields at NIST, including calibrated 252Cf neutron sources and two monoenergetic neutron generators. Measurements of the surface fast neutron spectrum and flux have been made with both detectors, which are compared with previous measurements by traditional detectors. Additionally, FaNS-1 was deployed at the Kimballton Underground Research Facility (KURF) in Ripplemead, VA. A measurement of the fast neutron spectrum and flux at KURF is presented as well. FaNS-2 is currently installed in a shallow underground laboratory where it is measuring the muon

  15. Spallation Neutron Source (SNS)

    Data.gov (United States)

    Federal Laboratory Consortium — The SNS at Oak Ridge National Laboratory is a next-generation spallation neutron source for neutron scattering that is currently the most powerful neutron source in...

  16. Neutron scattering. Lectures

    Energy Technology Data Exchange (ETDEWEB)

    Brueckel, Thomas; Heger, Gernot; Richter, Dieter; Roth, Georg; Zorn, Reiner (eds.)

    2010-07-01

    The following topics are dealt with: Neutron sources, neutron properties and elastic scattering, correlation functions measured by scattering experiments, symmetry of crystals, applications of neutron scattering, polarized-neutron scattering and polarization analysis, structural analysis, magnetic and lattice excitation studied by inelastic neutron scattering, macromolecules and self-assembly, dynamics of macromolecules, correlated electrons in complex transition-metal oxides, surfaces, interfaces, and thin films investigated by neutron reflectometry, nanomagnetism. (HSI)

  17. Voltammetry and in situ scanning tunnelling spectroscopy of osmium, iron, and ruthenium complexes of 2,2′:6′,2′′-terpyridine covalently linked to Au(111)-electrodes

    DEFF Research Database (Denmark)

    Salvatore, Princia; Hansen, Allan Glargaard; Moth-Poulsen, Kasper

    2011-01-01

    prepared in situ by first linking the terpy ligand to the surface via the S-atom, followed by addition of suitable metal compounds. The metal-terpy SAMs were studied by cyclic voltammetry (CV), and in situ scanning tunnelling microscopy with full electrochemical potential control of substrate and tip (in...... of the metal coordination spheres induced voltammetric sharpening. In situ STM images of single molecular scale strong structural features were observed for the osmium and iron complexes. As expected from the voltammetric patterns, the surface coverage was by far the highest for the Ru-complex which...

  18. A versatile high resolution scanning tunneling potentiometry implementation.

    Science.gov (United States)

    Druga, T; Wenderoth, M; Homoth, J; Schneider, M A; Ulbrich, R G

    2010-08-01

    We have developed a new scanning tunneling potentiometry technique which can-with only minor changes of the electronic setup-be easily added to any standard scanning tunneling microscope (STM). This extension can be combined with common STM techniques such as constant current imaging or scanning tunneling spectroscopy. It is capable of performing measurements of the electrochemical potential with microvolt resolution. Two examples demonstrate the versatile application. First of all, we have determined local variations of the electrochemical potential due to charge transport of biased samples down to angstrom length scales. Second, with tip and sample at different temperatures we investigated the locally varying thermovoltage occurring at the tunneling junction. Aside from its use in determining the chemical identity of substances at the sample surface our method provides a controlled way to eliminate the influence of laterally varying thermovoltages on low-bias constant current topographies.

  19. Neutron-scattering study of the vibrational behavior of trehalose aqueous solutions

    CERN Document Server

    Branca, C; Migliardo, F; Romeo, G; Villari, V; Wanderlingh, U; Colognesi, D

    2002-01-01

    Neutron spectra for hydrated trehalose samples have been obtained by using the time-of-flight spectrometer TOSCA at the ISIS Pulse Neutron Facility (Rutherford Appleton Laboratory, Chilton, UK). Neutron spectra have been compared to the absorbance spectra obtained by Fourier-transform infrared spectroscopy. Finally, a comparison with findings obtained by density functional theory has been performed. 3 Refs.

  20. Atomically Thin Al2O3 Films for Tunnel Junctions

    Science.gov (United States)

    Wilt, Jamie; Gong, Youpin; Gong, Ming; Su, Feifan; Xu, Huikai; Sakidja, Ridwan; Elliot, Alan; Lu, Rongtao; Zhao, Shiping; Han, Siyuan; Wu, Judy Z.

    2017-06-01

    Metal-insulator-metal tunnel junctions are common throughout the microelectronics industry. The industry standard AlOx tunnel barrier, formed through oxygen diffusion into an Al wetting layer, is plagued by internal defects and pinholes which prevent the realization of atomically thin barriers demanded for enhanced quantum coherence. In this work, we employ in situ scanning tunneling spectroscopy along with molecular-dynamics simulations to understand and control the growth of atomically thin Al2O3 tunnel barriers using atomic-layer deposition. We find that a carefully tuned initial H2O pulse hydroxylated the Al surface and enabled the creation of an atomically thin Al2O3 tunnel barrier with a high-quality M -I interface and a significantly enhanced barrier height compared to thermal AlOx . These properties, corroborated by fabricated Josephson junctions, show that atomic-layer deposition Al2O3 is a dense, leak-free tunnel barrier with a low defect density which can be a key component for the next generation of metal-insulator-metal tunnel junctions.

  1. A clean, bright, and versatile source of neutron decay products

    CERN Document Server

    Dubbers, D; Baessler, S; Maerkisch, B; Schumann, M; Soldner, T; Zimmer, O

    2007-01-01

    We present a case study on a new type of cold neutron beam station for the investigation of angular correlations in the beta-decay of free neutrons. With this beam station, called PERC, the 'active decay volume' lies inside the neutron guide, and the charged neutron decay products are magnetically guided towards the end of the neutron guide. Hence, the guide delivers at its exit a beam of decay electrons and protons, under well-defined and precisely variable conditions, which can be well separated from the cold neutron beam. In this way a general-purpose source of neutron decay products is obtained which can be used for various different experiments in neutron decay correlation spectroscopy. A gain in phase space density of several orders of magnitude can be achieved with PERC, as compared to existing neutron decay spectrometers. Neutron beam related background is separately measurable in PERC, and magnetic mirror effects on the charged neutron decay products and edge effects in the active neutron beam volume...

  2. Neutron Therapy Facility

    Data.gov (United States)

    Federal Laboratory Consortium — The Neutron Therapy Facility provides a moderate intensity, broad energy spectrum neutron beam that can be used for short term irradiations for radiobiology (cells)...

  3. Suppression of tunneling rate fluctuations in tunnel field-effect transistors by enhancing tunneling probability

    Science.gov (United States)

    Mori, Takahiro; Migita, Shinji; Fukuda, Koichi; Asai, Hidehiro; Morita, Yukinori; Mizubayashi, Wataru; Liu, Yongxun; O’uchi, Shin-ichi; Fuketa, Hiroshi; Otsuka, Shintaro; Yasuda, Tetsuji; Masahara, Meishoku; Ota, Hiroyuki; Matsukawa, Takashi

    2017-04-01

    This paper discusses the impact of the tunneling probability on the variability of tunnel field-effect transistors (TFETs). Isoelectronic trap (IET) technology, which enhances the tunneling current in TFETs, is used to suppress the variability of the ON current and threshold voltage. The simulation results show that suppressing the tunneling rate fluctuations results in suppression of the variability. In addition, a formula describing the relationship between the tunneling rate fluctuations and the electric field strength is derived based on Kane’s band-to-band tunneling model. This formula indicates that the magnitude of the tunneling rate fluctuations is proportional to the magnitude of the fluctuations in the electric field strength and a higher tunneling probability results in a lower variability. The derived relationship is universally valid for any technologies that exploit enhancement of the tunneling probability, including IET technology, channel material engineering, heterojunctions, strain engineering, etc.

  4. Investigation of local tunneling current noise spectra on the silicon crystal surfaces by means of STM/STS

    Energy Technology Data Exchange (ETDEWEB)

    Mantsevich, V. N., E-mail: vmantsev@spmlab.phys.msu.su; Maslova, N. S. [Moscow State University, Department of Physics (Russian Federation); Cao, G. Y. [Chinese Academy of Sciences, Wuhan Institute of Physics and Mathematics (China)

    2015-08-15

    We report on a careful analysis of the local tunneling conductivity by means of ultra-high vacuum scanning tunneling microscopy/spectroscopy (STM/STS) technique in the vicinity of low-dimensional structures on the Si(111)–(7 × 7) and Si(110)–(16 × 2) surfaces. The power-law exponent α of low-frequency tunneling current noise spectra is investigated for different values of the tunneling contact parameters: relaxation rates, the localized state coupling, and the tunneling barrier width and height.

  5. Measurement of neutron flux and beam divergence at the cold neutron guide system of the new Munich research reactor FRM-II

    Science.gov (United States)

    Zeitelhack, K.; Schanzer, C.; Kastenmüller, A.; Röhrmoser, A.; Daniel, C.; Franke, J.; Gutsmiedl, E.; Kudryashov, V.; Maier, D.; Päthe, D.; Petry, W.; Schöffel, T.; Schreckenbach, K.; Urban, A.; Wildgruber, U.

    2006-05-01

    A sophisticated neutron guide system has been installed at the new Munich neutron source FRM-II to transport neutrons from the D 2 cold neutron source to several instruments, which are situated in a separate neutron guide hall. The guide system takes advantage of supermirror coatings and includes a worldwide unique "twisted" guide for a desired phase space transformation of the neutron beam. During the initial reactor commissioning in summer 2004, the integral and differential neutron flux as well as the distribution of beam divergence at the exit of two representative and the twisted neutron guide were measured using time-of-flight spectroscopy and gold-foil activation. The experimental results can be compared to extensive simulation calculations based on MCNP and McStas. The investigated guides fulfill the expectations of providing high neutron fluxes and reveal good quality with respect to the reflective coatings and the installation precision.

  6. Measurement of neutron flux and beam divergence at the cold neutron guide system of the new Munich research reactor FRM-II

    Energy Technology Data Exchange (ETDEWEB)

    Zeitelhack, K. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany)]. E-mail: karl.zeitelhack@frm2.tum.de; Schanzer, C. [Physik-Department E21, TU Muenchen, D-85747 Garching (Germany); Kastenmueller, A. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Roehrmoser, A. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Daniel, C. [Physik-Department E22, TU Muenchen, D-85747 Garching (Germany); Franke, J. [Max-Planck-Institut fuer Metallforschung, D-70569 Stuttgart (Germany); Gutsmiedl, E. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Kudryashov, V. [GKSS Forschungszentrum GmbH, D-21502 Geesthacht (Germany); Maier, D. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Paethe, D. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Petry, W. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Schoeffel, T. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Schreckenbach, K. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Urban, A. [ZWE FRM-II, TU Muenchen, D-85747 Garching (Germany); Wildgruber, U. [Max-Planck-Institut fuer Metallforschung, D-70569 Stuttgart (Germany)

    2006-05-10

    A sophisticated neutron guide system has been installed at the new Munich neutron source FRM-II to transport neutrons from the D{sub 2} cold neutron source to several instruments, which are situated in a separate neutron guide hall. The guide system takes advantage of supermirror coatings and includes a worldwide unique 'twisted' guide for a desired phase space transformation of the neutron beam. During the initial reactor commissioning in summer 2004, the integral and differential neutron flux as well as the distribution of beam divergence at the exit of two representative and the twisted neutron guide were measured using time-of-flight spectroscopy and gold-foil activation. The experimental results can be compared to extensive simulation calculations based on MCNP and McStas. The investigated guides fulfill the expectations of providing high neutron fluxes and reveal good quality with respect to the reflective coatings and the installation precision.

  7. Preparation and characterization of Boron carbide nanoparticles for use as a novel agent in T cell-guided boron neutron capture therapy

    DEFF Research Database (Denmark)

    Mortensen, M. W.; Sørensen, P. G.; Björkdahl, O.

    2006-01-01

    transmission electron microscopy, photon correlation spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, vibrational spectroscopy, gel electrophoresis and chemical assays and reveal profound changes in surface chemistry and structural characteristics. In vitro thermal neutron irradiation of B16...

  8. Two-neutron knockout from neutron-deficient $^{34}$Ar, $^{30}$S, and $^{26}$Si

    CERN Document Server

    Yoneda, K; Brown, B A; Campbell, C M; Cook, J M; Cottle, P D; Davies, A D; Dinca, D C; Gade, A; Glasmacher, T; Hansen, P G; Hoagland, T; Kemper, K W; Lecouey, J L; Müller, W F; Obertelli, A; Reynolds, R R; Terry, J R; Tostevin, J A; Zwahlen, H

    2006-01-01

    Two-neutron knockout reactions from nuclei in the proximity of the proton dripline have been studied using intermediate-energy beams of neutron-deficient $^{34}$Ar, $^{30}$S, and $^{26}$Si. The inclusive cross sections, and also the partial cross sections for the population of individual bound final states of the $^{32}$Ar, $^{28}$S and $^{24}$Si knockout residues, have been determined using the combination of particle and $\\gamma$-ray spectroscopy. Similar to the two-proton knockout mechanism on the neutron-rich side of the nuclear chart, these two-neutron removal reactions from already neutron-deficient nuclei are also shown to be consistent with a direct reaction mechanism.

  9. Evaluation of an iron-filtered epithermal neutron beam for neutron-capture therapy.

    Science.gov (United States)

    Musolino, S V; McGinley, P H; Greenwood, R C; Kliauga, P; Fairchild, R G

    1991-01-01

    An epithermal neutron filter using iron, aluminum, and sulfur was evaluated to determine if the therapeutic performance could be improved with respect to aluminum-sulfur-based filters. An empirically optimized filter was developed that delivered a 93% pure beam of 24-keV epithermal neutrons. It was expected that a thick filter using iron with a density thickness greater than 200 g/cm2 would eliminate the excess gamma contamination found in Al-S filters. This research showed that prompt gamma production from neutron interactions in iron was the dominant dose component. Dosimetric parameters of the beam were determined from the measurement of absorbed dose in air, thermal neutron flux in a head phantom, neutron and gamma spectroscopy, and microdosimetry.

  10. Reversible dimer formation and stability of the anti-tumour single-chain Fv antibody MFE-23 by neutron scattering, analytical ultracentrifugation, and NMR and FT-IR spectroscopy.

    Science.gov (United States)

    Lee, Yie Chia; Boehm, Mark K; Chester, Kerry A; Begent, Richard H J; Perkins, Stephen J

    2002-06-28

    MFE-23 is a single chain Fv (scFv) antibody molecule used to target colorectal cancer through its high affinity for the tumour marker carcinoembryonic antigen (CEA). ScFv molecules are formed from peptide-linked antibody V(H) and V(L) domains, and many of these form dimers. Our recent crystal structure for MFE-23 showed that this formed an unusual symmetric back-to-back association of two monomers that is consistent with a domain-swapped diabody structure. Neutron scattering and modelling fits showed that MFE-23 existed as compact V(H)-V(L)-linked monomers at therapeutically relevant concentrations below 1 mg/ml. Size-exclusion gel chromatography showed that the monomeric and dimeric forms of MFE-23 could be separated, and that the proportions of these two forms depended on the starting MFE-23 concentration. Sedimentation equilibrium experiments by analytical ultracentrifugation at nine concentrations of MFE-23 indicated a reversible monomer-dimer self-association equilibrium with an association constant of 1.9x10(3)-2.2x10(3) M(-1). Sedimentation velocity experiments using the time derivative g(s(*)) method showed that MFE-23-His has a concentration-dependent weight average sedimentation coefficient that increased from 1.8 S for the monomer to about 3-6 S for the dimer. Both values agreed with those calculated from the MFE-23 crystal structure. In relation to the thermal stability of MFE-23, denaturation experiments by (1)H NMR and FT-IR spectroscopy showed that the molecule is stable up to 47 degrees C, after which denaturation was irreversible. MFE-23 dimerisation is discussed in terms of a new model for diabody structures, in which the V(H) and V(L) domains in the monomer are able to dissociate and reassociate to form a dimer, or diabody, but in which symmetric back-to-back contacts between the two monomers are formed. This dimerisation in solution is attributed to the complementary nature of the C-terminal surface of the MFE-23 monomer. Crystal structures for

  11. Early times in tunneling

    CERN Document Server

    García-Calderón, G; Garcia-Calderon, Gaston; Villavicencio, Jorge

    2000-01-01

    Exact analytical solutions of the time-dependent Schr\\"odinger equation with the initial condition of an incident cutoff wave are used to investigate the traversal time for tunneling. The probability density starts from a vanishing value along the tunneling and transmitted regions of the potential. At the barrier width it exhibits, at early times, a distribution of traversal times that typically has a peak $\\tau_p$ and a width $\\Delta \\tau$. Numerical results for other tunneling times, as the phase-delay time, fall within $\\Delta \\tau$. The B\\"uttiker traversal time is the closest to $\\tau_p$. Our results resemble calculations based on Feynman paths if its noisy behaviour is ignored.

  12. Tunneling Through Black Rings

    Institute of Scientific and Technical Information of China (English)

    ZHAO Liu

    2007-01-01

    Hawking radiation of black ring solutions to 5-dimensional Einstein-Maxwell-dilaton theory is analyzed by use of the Parikh-Wilczek tunneling method. To get the correct tunneling amplitude and emission rate, we adopt and develop the Angheben-Nadalini-Vanzo-Zerbini covariant approach to cover the effects of rotation and electronic discharge all at once, and the effect of back reaction is also taken into account. This constitutes a unified approach to the tunneling problem. Provided the first law of thermodynamics for black rings holds, the emission rate is proportional to the exponential of the change of Bekenstein-Hawking entropy. Explicit calculation for black ring temperatures agrees exactly with the results obtained via the classical surface gravity method and the quasi-local formalism.

  13. Femtosecond scanning tunneling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, A.J.; Donati, G.P.; Rodriguez, G.; Gosnell, T.R.; Trugman, S.A.; Some, D.I.

    1998-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). By combining scanning tunneling microscopy with ultrafast optical techniques we have developed a novel tool to probe phenomena on atomic time and length scales. We have built and characterized an ultrafast scanning tunneling microscope in terms of temporal resolution, sensitivity and dynamic range. Using a novel photoconductive low-temperature-grown GaAs tip, we have achieved a temporal resolution of 1.5 picoseconds and a spatial resolution of 10 nanometers. This scanning tunneling microscope has both cryogenic and ultra-high vacuum capabilities, enabling the study of a wide range of important scientific problems.

  14. Isotopic characterization and thermal neutron flux determination of a PuBe neutron source.

    Science.gov (United States)

    Purty, Ravi Ankit; Akanchha; Prasad, Shikha

    2017-07-01

    The Indian Institute of Technology Kanpur (IIT Kanpur) possesses a PuBe neutron source facility with an initial activity of 5 Ci, dated September 1966 (nearly 50 years ago). An understanding of the present activity and the rate of its change will allow implementation of proper radiological safety procedures and future radiological safety planning. Knowing the absolute neutron flux will help us in future neutron activation studies. These details are also important to ensure proper security precautions. In our work, we attempt to identify the isotopic composition to determine the rate of change of the source and the absolute thermal neutron flux of plutonium beryllium (PuBe) sample at IIT Kanpur. We have used gamma-ray spectroscopy for determining the isotopic composition of the PuBe neutron source. After utilizing gamma-ray spectroscopy it is found that the source is composed of (239)Pu and a small amount of (241)Am is present as an impurity. The mass ratio of (241)Am to (239)Pu is found to be approximately 18.1µg/g with an uncertainty of 1.39%. Delayed gamma neutron activation analysis (DGNAA) is used to determine the thermal neutron flux of the same PuBe neutron source using copper, cobalt, nickel and cadmium samples. The average thermal neutron flux as calculated from DGNAA is approximately 1.27×10(3)n/(cm(2)-s) at 1cm above the PuBe neutron source. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. The Neutron Star Interior Composition Explorer (NICER)

    Science.gov (United States)

    Wilson-Hodge, Colleen A.; Gendreau, K.; Arzoumanian, Z.

    2014-01-01

    The Neutron Star Interior Composition Explorer (NICER) is an approved NASA Explorer Mission of Opportunity dedicated to the study of the extraordinary gravitational, electromagnetic, and nuclear-physics environments embodied by neutron stars. Scheduled to be launched in 2016 as an International Space Station payload, NICER will explore the exotic states of matter, using rotation-resolved spectroscopy of the thermal and non-thermal emissions of neutron stars in the soft (0.2-12 keV) X-ray band. Grazing-incidence "concentrator" optics coupled with silicon drift detectors, actively pointed for a full hemisphere of sky coverage, will provide photon-counting spectroscopy and timing registered to GPS time and position, with high throughput and relatively low background. The NICER project plans to implement a Guest Observer Program, which includes competitively selected user targets after the first year of flight operations. I will describe NICER and discuss ideas for potential Be/X-ray binary science.

  16. Tunneling in Axion Monodromy

    CERN Document Server

    Brown, Jon; Shiu, Gary; Soler, Pablo

    2016-01-01

    The Coleman formula for vacuum decay and bubble nucleation has been used to estimate the tunneling rate in models of axion monodromy in recent literature. However, several of Coleman's original assumptions do not hold for such models. Here we derive a new estimate with this in mind using a similar Euclidean procedure. We find that there are significant regions of parameter space for which the tunneling rate in axion monodromy is not well approximated by the Coleman formula. However, there is also a regime relevant to large field inflation in which both estimates parametrically agree. We also briefly comment on the applications of our results to the relaxion scenario.

  17. Tunneling in axion monodromy

    Science.gov (United States)

    Brown, Jon; Cottrell, William; Shiu, Gary; Soler, Pablo

    2016-10-01

    The Coleman formula for vacuum decay and bubble nucleation has been used to estimate the tunneling rate in models of axion monodromy in recent literature. However, several of Coleman's original assumptions do not hold for such models. Here we derive a new estimate with this in mind using a similar Euclidean procedure. We find that there are significant regions of parameter space for which the tunneling rate in axion monodromy is not well approximated by the Coleman formula. However, there is also a regime relevant to large field inflation in which both estimates parametrically agree. We also briefly comment on the applications of our results to the relaxion scenario.

  18. Long distance tunneling

    CERN Document Server

    Ivlev, B I

    2005-01-01

    Quantum tunneling between two potential wells in a magnetic field can be strongly increased when the potential barrier varies in the direction perpendicular to the line connecting the two wells and remains constant along this line. A periodic structure of the wave function is formed in the direction joining the wells. The resulting motion can be coherent like motion in a conventional narrow band periodic structure. A particle penetrates the barrier over a long distance which strongly contrasts to WKB-like tunneling. The whole problem is stationary. The coherent process can be influenced by dissipation.

  19. Applications of neutron scattering to heterogeneous catalysis

    Science.gov (United States)

    Parker, Stewart F.; Lennon, David

    2016-09-01

    Historically, most studies of heterogeneous catalysts that have used neutron vibrational spectroscopy have employed indirect geometry instruments with a low (methane to synthesis gas (CO + H2) over Ni/Al2O3 catalysts and an operando study of CO oxidation. We conclude with a proposal for a unique instrument that combines both indirect and direct geometry spectrometers.

  20. Breaking through the tranfer tunnel

    CERN Multimedia

    Laurent Guiraud

    2001-01-01

    This image shows the tunnel boring machine breaking through the transfer tunnel into the LHC tunnel. Proton beams will be transferred from the SPS pre-accelerator to the LHC at 450 GeV through two specially constructed transfer tunnels. From left to right: LHC Project Director, Lyn Evans; CERN Director-General (at the time), Luciano Maiani, and Director for Accelerators, Kurt Hubner.

  1. The first neutron beam hits EAR2

    CERN Multimedia

    Antonella Del Rosso

    2014-01-01

    On 25 July 2014, about a year after construction work began, the Experimental Area 2 (EAR2) of CERN’s neutron facility n_TOF recorded its first beam. Unique in many aspects, EAR2 will start its rich programme of experimental physics this autumn.   The last part of the EAR2 beamline: the neutrons come from the underground target and reach the top of the beamline, where they hit the samples. Built about 20 metres above the neutron production target, EAR2 is in fact a bunker connected to the n_TOF underground facilities via a duct 80 cm in diameter, where the beamline is installed. The feet of the bunker support pillars are located on the concrete structure of the n_TOF tunnel and part of the structure lies above the old ISR building. A beam dump located on the roof of the building completes the structure. Neutrons are used by physicists to study neutron-induced reactions with applications in a number of fields, including nuclear waste transmutation, nuclear technology, nuclear astrop...

  2. Neutron Decay with PERC: a Progress Report

    Science.gov (United States)

    Konrad, G.; Abele, H.; Beck, M.; Drescher, C.; Dubbers, D.; Erhart, J.; Fillunger, H.; Gösselsberger, C.; Heil, W.; Horvath, M.; Jericha, E.; Klauser, C.; Klenke, J.; Märkisch, B.; Maix, R. K.; Mest, H.; Nowak, S.; Rebrova, N.; Roick, C.; Sauerzopf, C.; Schmidt, U.; Soldner, T.; Wang, X.; Zimmer, O.; Perc Collaboration

    2012-02-01

    The PERC collaboration will perform high-precision measurements of angular correlations in neutron beta decay at the beam facility MEPHISTO of the Forschungs-Neutronenquelle Heinz Maier-Leibnitz in Munich, Germany. The new beam station PERC, a clean, bright, and versatile source of neutron decay products, is designed to improve the sensitivity of neutron decay studies by one order of magnitude. The charged decay products are collected by a strong longitudinal magnetic field directly from inside a neutron guide. This combination provides the highest phase space density of decay products. A magnetic mirror serves to perform precise cuts in phase space, reducing related systematic errors. The new instrument PERC is under development by an international collaboration. The physics motivation, sensitivity, and applications of PERC as well as the status of the design and preliminary results on uncertainties in proton spectroscopy are presented in this paper.

  3. Neutron scattering. Lectures

    Energy Technology Data Exchange (ETDEWEB)

    Brueckel, Thomas; Heger, Gernot; Richter, Dieter; Roth, Georg; Zorn, Reiner (eds.)

    2010-07-01

    The following topics are dealt with: Neutron sources, symmetry of crystals, diffraction, nanostructures investigated by small-angle neutron scattering, the structure of macromolecules, spin dependent and magnetic scattering, structural analysis, neutron reflectometry, magnetic nanostructures, inelastic scattering, strongly correlated electrons, dynamics of macromolecules, applications of neutron scattering. (HSI)

  4. Neutron Capture Nucleosynthesis

    CERN Document Server

    Kiss, Miklos

    2016-01-01

    Heavy elements (beyond iron) are formed in neutron capture nucleosynthesis processes. We have proposed a simple unified model to investigate the neutron capture nucleosynthesis in arbitrary neutron density environment. We have also investigated what neutron density is required to reproduce the measured abundance of nuclei assuming equilibrium processes. We found both of these that the medium neutron density has a particularly important role at neutron capture nucleosynthesis. About these results most of the nuclei can formed at medium neutron capture density environment e.g. in some kind of AGB stars. Besides these observations our model is capable to use educational purpose.

  5. Nuclear reactor neutron shielding

    Energy Technology Data Exchange (ETDEWEB)

    Speaker, Daniel P; Neeley, Gary W; Inman, James B

    2017-09-12

    A nuclear reactor includes a reactor pressure vessel and a nuclear reactor core comprising fissile material disposed in a lower portion of the reactor pressure vessel. The lower portion of the reactor pressure vessel is disposed in a reactor cavity. An annular neutron stop is located at an elevation above the uppermost elevation of the nuclear reactor core. The annular neutron stop comprises neutron absorbing material filling an annular gap between the reactor pressure vessel and the wall of the reactor cavity. The annular neutron stop may comprise an outer neutron stop ring attached to the wall of the reactor cavity, and an inner neutron stop ring attached to the reactor pressure vessel. An excore instrument guide tube penetrates through the annular neutron stop, and a neutron plug comprising neutron absorbing material is disposed in the tube at the penetration through the neutron stop.

  6. Communication: Tunnelling splitting in the phosphine molecule

    Science.gov (United States)

    Sousa-Silva, Clara; Tennyson, Jonathan; Yurchenko, Sergey N.

    2016-09-01

    Splitting due to tunnelling via the potential energy barrier has played a significant role in the study of molecular spectra since the early days of spectroscopy. The observation of the ammonia doublet led to attempts to find a phosphine analogous, but these have so far failed due to its considerably higher barrier. Full dimensional, variational nuclear motion calculations are used to predict splittings as a function of excitation energy. Simulated spectra suggest that such splittings should be observable in the near infrared via overtones of the ν2 bending mode starting with 4ν2.

  7. Tunnelling splitting in the phosphine molecule

    CERN Document Server

    Sousa-Silva, Clara; Yurchenko, Sergey N

    2016-01-01

    Splitting due to tunnelling via the potential energy barrier has played a significant role in the study of molecular spectra since the early days of spectroscopy. The observation of the ammonia doublet led to attempts to find a phosphine analogous, but these have so far failed due to its considerably higher barrier. Full dimensional, variational nuclear motion calculations are used to predict splittings as a function of excitation energy. Simulated spectra suggest that such splittings should be observable in the near infrared via overtones of the $\

  8. Tunnelling with wormhole creation

    Energy Technology Data Exchange (ETDEWEB)

    Ansoldi, S. [National Institute of Nuclear Physics (INFN) (Italy); Tanaka, T., E-mail: tanaka@yukawa.kyoto-u.ac.jp [Kyoto University, Department of Physics (Japan)

    2015-03-15

    The description of quantum tunnelling in the presence of gravity shows subtleties in some cases. We discuss wormhole production in the context of the spherically symmetric thin-shell approximation. By presenting a fully consistent treatment based on canonical quantization, we solve a controversy present in the literature.

  9. INCAS SUBSONIC WIND TUNNEL

    Directory of Open Access Journals (Sweden)

    Corneliu STOICA

    2009-09-01

    Full Text Available The INCAS Subsonic Wind Tunnel is a closed circuit, continuous, atmospheric pressure facility with a maximum speed of 110 m/s. The test section is octagonal ,of 2.5 m wide, 2.0 m high and 4 m long. The tunnel is powered by a 1200 kW, air cooled variable speed DC motor which drives a 12 blade, 3.5 m diameter fan and is equipped with a six component pyramidal type external mechanical balance with a 700 Kgf maximum lift capacity.The angle of attack range is between -45º and +45º while the yaw angle range is between -140º and +216º .The data acquisition system has been modified recently to allow the recording of all test data on a PC - type computer using LABVIEW and a PXI – type chassis containing specialized data acquisition modules.The tunnel is equipped with a variable frequency electrical supply system for powered models and a 10 bar compressed air supply for pneumatic flow control applications.In the recent years the subsonic wind tunnel has been intensively used for tests within several European projects (AVERT, CESAR and others.

  10. Weapons Neutron Research Facility (WNR)

    Data.gov (United States)

    Federal Laboratory Consortium — The Weapons Neutron Research Facility (WNR) provides neutron and proton beams for basic, applied, and defense-related research. Neutron beams with energies ranging...

  11. Classical trajectories and quantum tunneling

    CERN Document Server

    Ivlev, B I

    2003-01-01

    The problem of inter-band tunneling in a semiconductor (Zener breakdown) in a nonstationary and homogeneous electric field is solved exactly. Using the exact analytical solution, the approximation based on classical trajectories is studied. A new mechanism of enhanced tunneling through static non-one-dimensional barriers is proposed in addition to well known normal tunneling solely described by a trajectory in imaginary time. Under certain conditions on the barrier shape and the particle energy, the probability of enhanced tunneling is not exponentially small even for non-transparent barriers, in contrast to the case of normal tunneling.

  12. Magnetoelectric coupling in supercoducting Sr2 VO3 FeAs revealed by scanning tunneling microscopy

    Science.gov (United States)

    Choi, Seokhwan; Choi, Hyunwoo; Lee, Hyun-Jung; Jung, Jin-Oh; Son, Donghyun; Kim, Jun Sung; Ok, Jong Mok; Lee, Jhinhwan

    2015-03-01

    Sr2VO3FeAs is known to exhibit high Tc (~ 37K) superconductivity with no magnetic ordering in the FeAs layer but weak magnetic moment in the V sublattice. An angle resolved photo emission spectroscopy also shows the non-trivial Fermi surface due to the V 3d orbitals. We have studied on Sr2VO3FeAs single crystal using spectroscopic imaging scanning tunneling microscopy (SI-STM) with variable temperature from 4.6K to 100K, and magnetic field up to 7T. Our results show that Sr2VO3FeAs has charge density wave (CDW) modulation in the V sublattice with the same wave vector observed in the neutron scattering experiment. The modulation strength is reduced with applying magnetic field. An electronic Fermi surface with largest V 3d character shows suppressed superconductivity possibly due to strong V-site correlation. However the multi-orbital nature of FeAs allows overall unsuppressed superconductivity at high Tc.

  13. Total absorption γ -ray spectroscopy of the β -delayed neutron emitters Br87 , Br88 , and Rb94

    Energy Technology Data Exchange (ETDEWEB)

    Valencia, E.; Tain, J. L.; Algora, A.; Agramunt, J.; Estevez, E.; Jordan, M. D.; Rubio, B.; Rice, S.; Regan, P.; Gelletly, W.; Podolyák, Z.; Bowry, M.; Mason, P.; Farrelly, G. F.; Zakari-Issoufou, A.; Fallot, M.; Porta, A.; Bui, V. M.; Rissanen, J.; Eronen, T.; Moore, I.; Penttilä, H.; Äystö, J.; Elomaa, V. -V.; Hakala, J.; Jokinen, A.; Kolhinen, V. S.; Reponen, M.; Sonnenschein, V.; Cano-Ott, D.; Garcia, A. R.; Martínez, T.; Mendoza, E.; Caballero-Folch, R.; Gomez-Hornillos, B.; Gorlichev, V.; Kondev, F. G.; Sonzogni, A. A.; Batist, L.

    2017-02-01

    We investigate the decay of Br-87,Br-88 and Rb-94 using total absorption gamma-ray spectroscopy. These important fission products are beta-delayed neutron emitters. Our data show considerable beta gamma intensity, so far unobserved in high-resolution gamma-ray spectroscopy, from states at high excitation energy. We also find significant differences with the beta intensity that can be deduced from existing measurements of the beta spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discrepancy between calculations and integral measurements of the photon component for U-235 fission at cooling times in the range 1-100 s. We also use summation calculations to evaluate the impact of present data on reactor antineutrino spectra. We find a significant effect at antineutrino energies in the range of 5 to 9 MeV. In addition, we observe an unexpected strong probability for. emission from neutron unbound states populated in the daughter nucleus. The. branching is compared to Hauser-Feshbach calculations, which allow one to explain the large value for bromine isotopes as due to nuclear structure. However the branching for Rb-94, although much smaller, hints of the need to increase the radiative width gamma by one order of magnitude. This increase in gamma would lead to a similar increase in the calculated (n, gamma) cross section for this very neutron-rich nucleus with a potential impact on r process abundance calculations.

  14. Tunneling spectra of graphene on copper unraveled.

    Science.gov (United States)

    Zhang, Xin; Stradi, Daniele; Liu, Lei; Luo, Hong; Brandbyge, Mads; Gu, Gong

    2016-06-22

    Scanning tunneling spectroscopy is often employed to study two-dimensional (2D) materials on conductive growth substrates, in order to gain information on the electronic structures of the 2D material-substrate systems, which can lead to insight into 2D material-substrate interactions, growth mechanisms, etc. The interpretation of the spectra can be complicated, however. Specifically for graphene grown on copper, there have been conflicting reports of tunneling spectra. A clear understanding of the mechanisms behind the variability is desired. In this work, we have revealed that the root cause of the variability in tunneling spectra is the variation in graphene-substrate coupling under various experimental conditions, providing a salutary perspective on the important role of 2D material-substrate interactions. The conclusions are drawn from measured data and theoretical calculations for monolayer, AB-stacked bilayer, and twisted bilayer graphene coexisting on the same substrates in areas with and without intercalated oxygen, demonstrating a high degree of consistency. The Van Hove singularities of the twisted graphene unambiguously indicate the Dirac energy between them, lending strong evidence to our assignment of the spectral features. In addition, we have discovered an O-Cu superstructure that has never been observed before.

  15. Spin distribution in neutron induced preequilibrium reactions

    Energy Technology Data Exchange (ETDEWEB)

    Dashdorj, D; Kawano, T; Chadwick, M; Devlin, M; Fotiades, N; Nelson, R O; Mitchell, G E; Garrett, P E; Agvaanluvsan, U; Becker, J A; Bernstein, L A; Macri, R; Younes, W

    2005-10-04

    The preequilibrium reaction mechanism makes an important contribution to neutron-induced reactions above E{sub n} {approx} 10 MeV. The preequilibrium process has been studied exclusively via the characteristic high energy neutrons produced at bombarding energies greater than 10 MeV. They are expanding the study of the preequilibrium reaction mechanism through {gamma}-ray spectroscopy. Cross-section measurements were made of prompt {gamma}-ray production as a function of incident neutron energy (E{sub n} = 1 to 250 MeV) on a {sup 48}Ti sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center facility. The prompt-reaction {gamma} rays were detected with the large-scale Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Neutron energies were determined by the time-of-flight technique. The {gamma}-ray excitation functions were converted to partial {gamma}-ray cross sections taking into account the dead-time correction, target thickness, detector efficiency and neutron flux (monitored with an in-line fission chamber). Residual state population was predicted using the GNASH reaction code, enhanced for preequilibrium. The preequilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshback, Kerman, and Koonin (FKK). The multistep direct part of the FKK theory was calculated for a one-step process. The FKK preequilibrium spin distribution was incorporated into the GNASH calculations and the {gamma}-ray production cross sections were calculated and compared with experimental data. The difference in the partial {gamma}-ray cross sections using spin distributions with and without preequilibrium effects is significant.

  16. Tunneling and Transport in Nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Goldman, Allen M. [Univ. of Minnesota, Minneapolis, MN (United States)

    2016-08-16

    The goal of this program was to study new physical phenomena that might be relevant to the performance of conductive devices and circuits of the smallest realizable feature sizes possible using physical rather than biological techniques. Although the initial scientific work supported involved the use of scanning tunneling microscopy and spectroscopy to ascertain the statistics of the energy level distribution of randomly sized and randomly shaped quantum dots, or nano-crystals, the main focus was on the investigation of selected properties, including superconductivity, of conducting and superconducting nanowires prepared using electron-beam-lithography. We discovered a magnetic-field-restoration of superconductivity in out-of-equilibrium nanowires driven resistive by current. This phenomenon was explained by the existence of a state in which dissipation coexisted with nonvanishing superconducting order. We also produced ultra-small superconducting loops to study a predicted anomalous fluxoid quantization, but instead, found a magnetic-field-dependent, high-resistance state, rather than superconductivity. Finally, we developed a simple and controllable nanowire in an induced charged layer near the surface of a masked single-crystal insulator, SrTiO3. The layer was induced using an electric double layer transistor employing an ionic liquid (IL). The transport properties of the induced nanowire resembled those of collective electronic transport through an array of quantum dots.

  17. Tunneling and Transport in Nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Goldman, Allen M. [Univ. of Minnesota, Minneapolis, MN (United States)

    2016-08-16

    The goal of this program was to study new physical phenomena that might be relevant to the performance of conductive devices and circuits of the smallest realizable feature sizes possible using physical rather than biological techniques. Although the initial scientific work supported involved the use of scanning tunneling microscopy and spectroscopy to ascertain the statistics of the energy level distribution of randomly sized and randomly shaped quantum dots, or nano-crystals, the main focus was on the investigation of selected properties, including superconductivity, of conducting and superconducting nanowires prepared using electron-beam-lithography. We discovered a magnetic-field-restoration of superconductivity in out-of-equilibrium nanowires driven resistive by current. This phenomenon was explained by the existence of a state in which dissipation coexisted with nonvanishing superconducting order. We also produced ultra-small superconducting loops to study a predicted anomalous fluxoid quantization, but instead, found a magnetic-field-dependent, high-resistance state, rather than superconductivity. Finally, we developed a simple and controllable nanowire in an induced charged layer near the surface of a masked single-crystal insulator, SrTiO3. The layer was induced using an electric double layer transistor employing an ionic liquid (IL). The transport properties of the induced nanowire resembled those of collective electronic transport through an array of quantum dots.

  18. Superheated drop neutron spectrometer

    CERN Document Server

    Das, M; Roy, B; Roy, S C; Das, Mala

    2000-01-01

    Superheated drops are known to detect neutrons through the nucleation caused by the recoil nuclei produced by the interactions of neutrons with the atoms constituting the superheated liquid molecule. A novel method of finding the neutron energy from the temperature dependence response of SDD has been developed. From the equivalence between the dependence of threshold energy for nucleation on temperature of SDD and the dependence of dE/dx of the recoil ions with the energy of the neutron, a new method of finding the neutron energy spectrum of a polychromatic as well as monochromatic neutron source has been developed.

  19. Neutron streak camera

    Science.gov (United States)

    Wang, Ching L.

    1983-09-13

    Apparatus for improved sensitivity and time resolution of a neutron measurement. The detector is provided with an electrode assembly having a neutron sensitive cathode which emits relatively low energy secondary electrons. The neutron sensitive cathode has a large surface area which provides increased sensitivity by intercepting a greater number of neutrons. The cathode is also curved to compensate for differences in transit time of the neutrons emanating from the point source. The slower speeds of the secondary electrons emitted from a certain portion of the cathode are matched to the transit times of the neutrons impinging thereupon.

  20. Ionization signals from diamond detectors in fast-neutron fields

    Energy Technology Data Exchange (ETDEWEB)

    Weiss, C. [European Organization for Nuclear Research (CERN), Geneva (Switzerland); CIVIDEC Instrumentation, Wien (Austria); Frais-Koelbl, H. [University of Applied Sciences, Wiener Neustadt (Austria); Griesmayer, E.; Kavrigin, P. [CIVIDEC Instrumentation, Wien (Austria); Vienna University of Technology, Wien (Austria)

    2016-09-15

    In this paper we introduce a novel analysis technique for measurements with single-crystal chemical vapor deposition (sCVD) diamond detectors in fast-neutron fields. This method exploits the unique electronic property of sCVD diamond sensors that the signal shape of the detector current is directly proportional to the initial ionization profile. In fast-neutron fields the diamond sensor acts simultaneously as target and sensor. The interaction of neutrons with the stable isotopes {sup 12}C and {sup 13}C is of interest for fast-neutron diagnostics. The measured signal shapes of detector current pulses are used to identify individual types of interactions in the diamond with the goal to select neutron-induced reactions in the diamond and to suppress neutron-induced background reactions as well as γ-background. The method is verified with experimental data from a measurement in a 14.3 MeV neutron beam at JRC-IRMM, Geel/Belgium, where the {sup 13}C(n, α){sup 10}Be reaction was successfully extracted from the dominating background of recoil protons and γ-rays and the energy resolution of the {sup 12}C(n, α){sup 9}Be reaction was substantially improved. The presented analysis technique is especially relevant for diagnostics in harsh radiation environments, like fission and fusion reactors. It allows to extract the neutron spectrum from the background, and is particularly applicable to neutron flux monitoring and neutron spectroscopy. (orig.)

  1. Ionization signals from diamond detectors in fast-neutron fields

    Science.gov (United States)

    Weiss, C.; Frais-Kölbl, H.; Griesmayer, E.; Kavrigin, P.

    2016-09-01

    In this paper we introduce a novel analysis technique for measurements with single-crystal chemical vapor deposition (sCVD) diamond detectors in fast-neutron fields. This method exploits the unique electronic property of sCVD diamond sensors that the signal shape of the detector current is directly proportional to the initial ionization profile. In fast-neutron fields the diamond sensor acts simultaneously as target and sensor. The interaction of neutrons with the stable isotopes 12 C and 13 C is of interest for fast-neutron diagnostics. The measured signal shapes of detector current pulses are used to identify individual types of interactions in the diamond with the goal to select neutron-induced reactions in the diamond and to suppress neutron-induced background reactions as well as γ-background. The method is verified with experimental data from a measurement in a 14.3 MeV neutron beam at JRC-IRMM, Geel/Belgium, where the 13C(n, α)10Be reaction was successfully extracted from the dominating background of recoil protons and γ-rays and the energy resolution of the 12C(n, α)9Be reaction was substantially improved. The presented analysis technique is especially relevant for diagnostics in harsh radiation environments, like fission and fusion reactors. It allows to extract the neutron spectrum from the background, and is particularly applicable to neutron flux monitoring and neutron spectroscopy.

  2. Educational Wind Tunnel

    Directory of Open Access Journals (Sweden)

    Juozas Bielskus

    2012-12-01

    Full Text Available The paper analyzes an educational wind tunnel produced by the Department of Building Energetics (DBE of Vilnius Gediminas Technical University. The equipment could be used for performing laboratory works and simple research. The article presents the projection of inflow and outlet velocity in the working chamber of DBE wind tunnel and carries out actual noise level measurement. The received data are compared with information on the level of noise generated by the fan considering instructions provided by the manufacturer. In order to assess the reliability of the computer program, simulation applying PHOENICS software has been conducted. The aim of modeling is to simulate a pilot model and to compare the obtained results with those of an analogous test presented in scientific articles.Article in Lithuanian

  3. "Phantom" carpal tunnel syndrome.

    Science.gov (United States)

    Braverman, D L; Root, B C

    1997-10-01

    Phantom sensation is ubiquitous among persons who have had amputation; however, if it develops into phantom pain, a thorough clinical investigation must ensue. We illustrate this with the case of a 49-year-old woman, 14 years after traumatic amputation of her left 2nd through 5th fingers, and 10 years after traumatic left transfemoral amputation. She had had phantom sensation in her absent fingers for years and developed progressive pain in her phantom fingers 3 months before presentation. Nerve conduction study revealed a high-normal distal motor latency of the left median nerve and a positive Bactrian test (sensitivity 87%). She was diagnosed with "phantom" carpal tunnel syndrome and treated with a resting wrist splint, decreased weight bearing on the left upper limb, and two corticosteroid carpal tunnel injections with marked improvement. Clinicians should recognize that phantom pain may be referred from a more proximal region and may be amenable to conservative management.

  4. Carpal tunnel syndrome treatment

    Directory of Open Access Journals (Sweden)

    Emilio Filippucci

    2011-09-01

    Full Text Available Carpal tunnel syndrome, the most common peripheral neuropathy, results from compression of the median nerve at the wrist, and is a cause of pain, numbness and tingling in the upper extremities and an increasingly recognized cause of work disability. If carpal tunnel syndrome seems likely, conservative management with splinting should be initiated. Moreover, it has suggested that patients reduce activities at home and work that exacerbate symptoms. Pyridoxine and diuretics, since are largely utilised, are no more effective than placebo in relieving the symptoms. Non steroidal anti-inflammatory drugs and orally administered corticosteroids can be effective for short-term management (two to four weeks, but local corticosteroid injection may improve symptoms for a longer period. Injection is especially effective if there is no loss of sensibility or thenar-muscle atrophy and weakness, and if symptoms are intermittent rather than constant. If symptoms are refractory to conservative measures, the option of surgical therapy may be considered.

  5. [Carpal tunnel syndrome treatment].

    Science.gov (United States)

    De Angelis, Rossella; Salaffi, Fausto; Filippucci, Emilio; Grassi, Walter

    2006-01-01

    Carpal tunnel syndrome, the most common peripheral neuropathy, results from compression of the median nerve at the wrist, and is a cause of pain, numbness and tingling in the upper extremities and an increasingly recognized cause of work disability. If carpal tunnel syndrome seems likely, conservative management with splinting should be initiated. Moreover, it has suggested that patients reduce activities at home and work that exacerbate symptoms. Pyridoxine and diuretics, since are largely utilised, are no more effective than placebo in relieving the symptoms. Non steroidal anti-inflammatory drugs and orally administered corticosteroids can be effective for short-term management (two to four weeks), but local corticosteroid injection may improve symptoms for a longer period. Injection is especially effective if there is no loss of sensibility or thenar-muscle atrophy and weakness, and if symptoms are intermittent rather than constant. If symptoms are refractory to conservative measures, the option of surgical therapy may be considered.

  6. Programmable ferroelectric tunnel memristor

    Directory of Open Access Journals (Sweden)

    Andy eQuindeau

    2014-02-01

    Full Text Available We report an analogously programmable memristor based on genuine electronic resistive switching combining ferroelectric switching and electron tunneling. The tunnel current through an 8 unit cell thick epitaxial Pb(Zr[0.2]Ti[0.8]O[3] film sandwiched between La[0.7]Sr[0.3]MnO[3] and cobalt electrodes obeys the Kolmogorov-Avrami-Ishibashi model for bidimensional growth with a characteristic switching time in the order of 10^-7 seconds. The analytical description of switching kinetics allows us to develop a characteristic transfer function that has only one parameter viz. the characteristic switching time and fully predicts the resistive states of this type of memristor.

  7. The beam dump tunnels

    CERN Multimedia

    Patrice Loïez

    2002-01-01

    In these images workers are digging the tunnels that will be used to dump the counter-circulating beams. Travelling just a fraction under the speed of light, the beams at the LHC will each carry the energy of an aircraft carrier travelling at 12 knots. In order to dispose of these beams safely, a beam dump is used to extract the beam and diffuse it before it collides with a radiation shielded graphite target.

  8. Carpal tunnel release

    DEFF Research Database (Denmark)

    Larsen, Morten Bo; Sørensen, A I; Crone, K L;

    2013-01-01

    A single-blind, randomized, controlled trial was done to compare the results of carpal tunnel release using classic incision, short incision, or endoscopic technique. In total, 90 consecutive cases were included. Follow-up was 24 weeks. We found a significantly shorter sick leave in the endoscopi...... incision could be found. There were no serious complications in either group. The results indicate that the endoscopic procedure is safe and has the benefit of faster rehabilitation and return to work....

  9. An Exploration of Neutron Detection in Semiconducting Boron Carbide

    Science.gov (United States)

    Hong, Nina

    The 3He supply problem in the U.S. has necessitated the search for alternatives for neutron detection. The neutron detection efficiency is a function of density, atomic composition, neutron absorption cross section, and thickness of the neutron capture material. The isotope 10B is one of only a handful of isotopes with a high neutron absorption cross section---3840 barns for thermal neutrons. So a boron carbide semiconductor represents a viable alternative to 3He. This dissertation provides an evaluation of the performance of semiconducting boron carbide neutron detectors grown by plasma enhance chemical vapor deposition (PECVD) in order to determine the advantages and drawbacks of these devices for neutron detection. Improved handling of the PECVD system has resulted in an extremely stable plasma, enabling deposition of thick films of semiconducting boron carbide. A variety of material and semiconducting characterization tools have been used to investigate the structure and electronic properties of boron carbide thin films, including X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, infrared/Raman spectroscopy, current-voltage measurements and capacitance-voltage measurements. Elemental concentrations in the boron carbide films have been obtained from Rutherford backscattering and elastic recoil detection analysis. Solid state neutron detection devices have been fabricated in the form of heterostructured p-n diodes, p-type boron carbide/n-type Si. Operating conditions, including applied bias voltage, and time constants, have been optimized for maximum detection efficiency and correlated to the semiconducting properties investigated in separate electronic measurements. Accurate measurements of the neutron detection efficiency and the response of the detector to a wide range of neutron wavelengths have been performed at a well calibrated, tightly collimated, "white" cold neutron beam source using time-of-flight neutron detection technique

  10. Neutron anatomy

    Energy Technology Data Exchange (ETDEWEB)

    Bacon, G.E. [Univ. of Sheffield (United Kingdom)

    1994-12-31

    The familiar extremes of crystalline material are single-crystals and random powders. In between these two extremes are polycrystalline aggregates, not randomly arranged but possessing some preferred orientation and this is the form taken by constructional materials, be they steel girders or the bones of a human or animal skeleton. The details of the preferred orientation determine the ability of the material to withstand stress in any direction. In the case of bone the crucial factor is the orientation of the c-axes of the mineral content - the crystals of the hexagonal hydroxyapatite - and this can readily be determined by neutron diffraction. In particular it can be measured over the volume of a piece of bone, utilizing distances ranging from 1mm to 10mm. The major practical problem is to avoid the intense incoherent scattering from the hydrogen in the accompanying collagen; this can best be achieved by heat-treatment and it is demonstrated that this does not affect the underlying apatite. These studies of bone give leading anatomical information on the life and activities of humans and animals - including, for example, the life history of the human femur, the locomotion of sheep, the fracture of the legs of racehorses and the life-styles of Neolithic tribes. We conclude that the material is placed economically in the bone to withstand the expected stresses of life and the environment. The experimental results are presented in terms of the magnitude of the 0002 apatite reflection. It so happens that for a random powder the 0002, 1121 reflections, which are neighboring lines in the powder pattern, are approximately equal in intensity. The latter reflection, being of manifold multiplicity, is scarcely affected by preferred orientation so that the numerical value of the 0002/1121 ratio serves quite accurately as a quantitative measure of the degree of orientation of the c-axes in any chosen direction for a sample of bone.

  11. Computational program to neutron flux calculation; Programa computacional para calculo de fluxo de neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Souza, Maria Ines Silvani; Furieri, Rosanne Cefaly de Aranda Amado [Instituto de Engenharia Nuclear (IEN), Rio de Janeiro, RJ (Brazil)

    2000-07-01

    The absolute value of the neutron flux is of paramount importance in reactor physics and other application on the nuclear field. Due to several corrections which should be done, such as radioactive decay of the produced nuclides, normalization factors between different irradiations, neutron spectrum perturbation, cross section behaviour and growing of the reactor power, among other factors, make the calculation of the neutron flux very cumbersome. the software FLUXO was developed to overcome these inconveniences. It is programmed in FORTRAN language, and was written to calculate the absolute flux of thermal, epithermal and fast neutrons, through the foil activation technique. The magnitude of this activation can be measured by a 4{pi} {beta}-{gamma} coincidence measurement or by gamma spectroscopy alone. The software calculates as well, the absolute activity of radioactive sources, and reactor-irradiated samples. (author)

  12. Air pollution at an urban traffic tunnel in Lisbon, Portugal-an INAA study

    Energy Technology Data Exchange (ETDEWEB)

    Almeida-Silva, M.; Canha, N. [Instituto Tecnologico e Nuclear, URSN, E.N. 10, 2686-953 Sacavem (Portugal); Freitas, M.C., E-mail: cfreitas@itn.pt [Instituto Tecnologico e Nuclear, URSN, E.N. 10, 2686-953 Sacavem (Portugal); Dung, H.M; Dionisio, I. [Instituto Tecnologico e Nuclear, URSN, E.N. 10, 2686-953 Sacavem (Portugal)

    2011-11-15

    In this study, the results of chemical concentrations inside and outside of a Lisbon (Portugal) traffic tunnel were compared, during one week. They were obtained by Instrumental Neutron Activation Analysis (INAA). The tunnel values largely exceed the Air Ambient legislated values and the Pearson Correlations Coefficients point out to soil re-suspension/dispersed road dust (As, Ce, Eu, Hf, Fe, Mo, Sc, Zn), traffic-markers (Ba, Cr), tire wear (Cr, Zn), break wear (Fe, Zn, Ba, Cu, Sb), exhaust and motor oil (Zn) and sea-spray (Br, Na). On all days these elements inside the tunnel were more enriched than outside; significant statistical differences were found for Co (p=0.005), Br (p=0.008), Zn (p=0.01) and Sb (p=0.005), while enrichment factors of As and Sc are statistically identical. The highest values were found for As, Br, Zn and Sb, for both inside and outside the tunnel.

  13. Coupling molecular spin states by photon-assisted tunneling

    CERN Document Server

    Schreiber, L R; Meunier, T; Calado, V; Danon, J; Taylor, J M; Wegscheider, W; Vandersypen, L M K

    2010-01-01

    Artificial molecules containing just one or two electrons provide a powerful platform for studies of orbital and spin quantum dynamics in nanoscale devices. A well-known example of these dynamics is tunneling of electrons between two coupled quantum dots triggered by microwave irradiation. So far, these tunneling processes have been treated as electric dipole-allowed spin-conserving events. Here we report that microwaves can also excite tunneling transitions between states with different spin. In this work, the dominant mechanism responsible for violation of spin conservation is the spin-orbit interaction. These transitions make it possible to perform detailed microwave spectroscopy of the molecular spin states of an artificial hydrogen molecule and open up the possibility of realizing full quantum control of a two spin system via microwave excitation.

  14. Imaging with Scattered Neutrons

    OpenAIRE

    Ballhausen, H.; Abele, H.; Gaehler, R.; Trapp, M.; Van Overberghe, A.

    2006-01-01

    We describe a novel experimental technique for neutron imaging with scattered neutrons. These scattered neutrons are of interest for condensed matter physics, because they permit to reveal the local distribution of incoherent and coherent scattering within a sample. In contrast to standard attenuation based imaging, scattered neutron imaging distinguishes between the scattering cross section and the total attenuation cross section including absorption. First successful low-noise millimeter-re...

  15. Intense fusion neutron sources

    Science.gov (United States)

    Kuteev, B. V.; Goncharov, P. R.; Sergeev, V. Yu.; Khripunov, V. I.

    2010-04-01

    The review describes physical principles underlying efficient production of free neutrons, up-to-date possibilities and prospects of creating fission and fusion neutron sources with intensities of 1015-1021 neutrons/s, and schemes of production and application of neutrons in fusion-fission hybrid systems. The physical processes and parameters of high-temperature plasmas are considered at which optimal conditions for producing the largest number of fusion neutrons in systems with magnetic and inertial plasma confinement are achieved. The proposed plasma methods for neutron production are compared with other methods based on fusion reactions in nonplasma media, fission reactions, spallation, and muon catalysis. At present, intense neutron fluxes are mainly used in nanotechnology, biotechnology, material science, and military and fundamental research. In the near future (10-20 years), it will be possible to apply high-power neutron sources in fusion-fission hybrid systems for producing hydrogen, electric power, and technological heat, as well as for manufacturing synthetic nuclear fuel and closing the nuclear fuel cycle. Neutron sources with intensities approaching 1020 neutrons/s may radically change the structure of power industry and considerably influence the fundamental and applied science and innovation technologies. Along with utilizing the energy produced in fusion reactions, the achievement of such high neutron intensities may stimulate wide application of subcritical fast nuclear reactors controlled by neutron sources. Superpower neutron sources will allow one to solve many problems of neutron diagnostics, monitor nano-and biological objects, and carry out radiation testing and modification of volumetric properties of materials at the industrial level. Such sources will considerably (up to 100 times) improve the accuracy of neutron physics experiments and will provide a better understanding of the structure of matter, including that of the neutron itself.

  16. International Neutron Radiography Newsletter

    DEFF Research Database (Denmark)

    Domanus, Joseph Czeslaw

    1986-01-01

    At the First World Conference on Neutron Radiography i t was decided to continue the "Neutron Radiography Newsletter", published previously by J.P. Barton, as the "International Neutron Radiography Newsletter" (INRNL), with J.C. Doraanus as editor. The British Journal of Non-Destructive Testing...

  17. Advanced neutron absorber materials

    Science.gov (United States)

    Branagan, Daniel J.; Smolik, Galen R.

    2000-01-01

    A neutron absorbing material and method utilizing rare earth elements such as gadolinium, europium and samarium to form metallic glasses and/or noble base nano/microcrystalline materials, the neutron absorbing material having a combination of superior neutron capture cross sections coupled with enhanced resistance to corrosion, oxidation and leaching.

  18. Prototype Neutron Energy Spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Stephen Mitchell, Sanjoy Mukhopadhyay, Richard Maurer, Ronald Wolff

    2010-06-16

    The project goals are: (1) Use three to five pressurized helium tubes with varying polyethylene moderators to build a neutron energy spectrometer that is most sensitive to the incident neutron energy of interest. Neutron energies that are of particular interest are those from the fission neutrons (typically around 1-2 MeV); (2) Neutron Source Identification - Use the neutron energy 'selectivity' property as a tool to discriminate against other competing processes by which neutrons are generated (viz. Cosmic ray induced neutron production [ship effect], [a, n] reactions); (3) Determine the efficiency as a function of neutron energy (response function) of each of the detectors, and thereby obtain the composite neutron energy spectrum from the detector count rates; and (4) Far-field data characterization and effectively discerning shielded fission source. Summary of the presentation is: (1) A light weight simple form factor compact neutron energy spectrometer ready to be used in maritime missions has been built; (2) Under laboratory conditions, individual Single Neutron Source Identification is possible within 30 minutes. (3) Sources belonging to the same type of origin viz., (a, n), fission, cosmic cluster in the same place in the 2-D plot shown; and (4) Isotopes belonging to the same source origin like Cm-Be, Am-Be (a, n) or Pu-239, U-235 (fission) do have some overlap in the 2-D plot.

  19. Spectroscopic neutron detection using composite scintillators

    Science.gov (United States)

    Jovanovic, I.; Foster, A.; Kukharev, V.; Mayer, M.; Meddeb, A.; Nattress, J.; Ounaies, Z.; Trivelpiece, C.

    2016-09-01

    Shielded special nuclear material (SNM), especially highly enriched uranium, is exceptionally difficult to detect without the use of active interrogation (AI). We are investigating the potential use of low-dose active interrogation to realize simultaneous high-contrast imaging and photofission of SNM using energetic gamma-rays produced by low-energy nuclear reactions, such as 11B(d,nγ)12C and 12C(p,p‧)12C. Neutrons produced via fission are one reliable signature of the presence of SNM and are usually identified by their unique timing characteristics, such as the delayed neutron die-away. Fast neutron spectroscopy may provide additional useful discriminating characteristics for SNM detection. Spectroscopic measurements can be conducted by recoil-based or thermalization and capture-gated detectors; the latter may offer unique advantages since they facilitate low-statistics and event-by-event neutron energy measurements without spectrum unfolding. We describe the results of the development and characterization of a new type of capture-gated spectroscopic neutron detector based on a composite of scintillating polyvinyltoluene and lithium-doped scintillating glass in the form of millimeter-thick rods. The detector achieves >108 neutron-gamma discrimination resulting from its geometric properties and material selection. The design facilitates simultaneous pulse shape and pulse height discrimination, despite the fact that no materials intrinsically capable of pulse shape discrimination have been used to construct the detector. Accurate single-event measurements of neutron energy may be possible even when the energy is relatively low, such as with delayed fission neutrons. Simulation and preliminary measurements using the new composite detector are described, including those conducted using radioisotope sources and the low-dose active interrogation system based on low-energy nuclear reactions.

  20. Neutron Capture Cross Sections of Zr and La: Probing Neutron Exposure and Neutron Flux in Red Giant Stars

    CERN Multimedia

    Kitis, G; Wiescher, M; Dahlfors, M; Soares, J

    2002-01-01

    We propose to measure the neutron capture cross sections of $^{139}$La, of $^{93}$Zr (t$_{1/2}$)=1.5 10$^{6}$ yr), and of all the stable Zr isotopes at n_TOF. The aim of these measurements is to improve the accuracy of existing results by at least a factor of three in order to meet the quality required for using the s-process nucleosynthesis as a diagnostic tool for neutron exposure and neutron flux during the He burning stages of stellar evolution. Combining these results with a wealth of recent information coming from high-resolution stellar spectroscopy and from the detailed analysis of presolar dust grains will shed new light on the chemical history of the universe. The investigated cross sections are also needed for technological applications, in particular since $^{93}$Zr is one of the major long-lived fission products.