WorldWideScience

Sample records for annihilation lifetime spectroscopy

  1. Single-shot positron annihilation lifetime spectroscopy with LYSO scintillators

    Science.gov (United States)

    Alonso, A. M.; Cooper, B. S.; Deller, A.; Cassidy, D. B.

    2016-08-01

    We have evaluated the application of a lutetium yttrium oxyorthosilicate (LYSO) based detector to single-shot positron annihilation lifetime spectroscopy. We compare this detector directly with a similarly configured PbWO4 scintillator, which is the usual choice for such measurements. We find that the signal to noise ratio obtained using LYSO is around three times higher than that obtained using PbWO4 for measurements of Ps excited to longer-lived (Rydberg) levels, or when they are ionized soon after production. This is due to the much higher light output for LYSO (75% and 1% of NaI for LYSO and PbWO4 respectively). We conclude that LYSO is an ideal scintillator for single-shot measurements of positronium production and excitation performed using a low-intensity pulsed positron beam.

  2. Novel System for Potential Nondestructive Material Inspection Using Positron Annihilation Lifetime Spectroscopy

    Science.gov (United States)

    Yamawaki, Masato; Kobayashi, Yoshinori; Hattori, Kanehisa; Watanabe, Yoshihiro

    2011-08-01

    A new positron annihilation lifetime spectrometer consisting of a start γ-ray detector, a stop γ-ray detector, a digital oscilloscope, and a positron detector, which is a plastic scintillator coupled to a photomultiplier tube, is described. A 22Na source is placed between the positron detector and a sample to be studied. γ-ray signals related to positrons annihilating in the positron detector are rejected by anti-coincidence processing. Comparison of the positron lifetime spectrum of a steel strip collected with the new system with that collected with a conventional system using two specimens sandwiching the 22Na source shows that accurate positron lifetime measurements are possible with the new system. The new system does not require cutting of the samples and is potentially applicable to truly nondestructive onsite inspection of various materials such as those used in nuclear power plants, aircraft and cars, etc., by positron annihilation lifetime spectroscopy (PALS).

  3. A Review of Studies of Polymeric Membranes by Positron Annihilation Lifetime Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    A review is presented of studies of polymeric membranes by applying positron annihilation lifetime spectroscopy (PALS). PALS has been used to study subnanometer-sized holes, to determine their size distribution and free-volume fractions, and to probe molecular-sized vacancies in glassy polymers. At present, PALS is believed to be a highly effective physical method for the examination of polymeric membranes.

  4. Study of PRIMAVERA steel samples by positron annihilation spectroscopy technique II – Lifetime measurements

    International Nuclear Information System (INIS)

    In the present article, a positron annihilation lifetime technique was used for the study of VVER-440/230 weld materials, manufactured in the frame of the international PRIMAVERA project on microstructural investigation of the irradiated WWER-440 reactor pressure vessel steel. The present results complement our previous report of positron angular correlation experiments and provide in-depth characterization of vacancy type defects behavior under irradiation and thermal treatment. The results give new insight into the previously published atom probe tomography and angular correlation of annihilation radiation studies. The measurements do not show any association of phosphorus or its segregation to the open volume defects investigated by positron annihilation spectroscopy. The embrittlement effects related to the phosphorus seem to be effectively annealed-out during 475 °C thermal treatment and the post annealing microstructure and mechanical properties of the material are consequently affected mostly by agglomerations of vacancy clusters coarsened during thermal treatment.

  5. Study of PRIMAVERA steel samples by positron annihilation spectroscopy technique II - Lifetime measurements

    Science.gov (United States)

    Krsjak, V.; Grafutin, V.; Ilyukhina, O.; Burcl, R.; Ballesteros, A.; Hähner, P.

    2012-02-01

    In the present article, a positron annihilation lifetime technique was used for the study of VVER-440/230 weld materials, manufactured in the frame of the international PRIMAVERA project on microstructural investigation of the irradiated WWER-440 reactor pressure vessel steel. The present results complement our previous report of positron angular correlation experiments and provide in-depth characterization of vacancy type defects behavior under irradiation and thermal treatment. The results give new insight into the previously published atom probe tomography and angular correlation of annihilation radiation studies. The measurements do not show any association of phosphorus or its segregation to the open volume defects investigated by positron annihilation spectroscopy. The embrittlement effects related to the phosphorus seem to be effectively annealed-out during 475 °C thermal treatment and the post annealing microstructure and mechanical properties of the material are consequently affected mostly by agglomerations of vacancy clusters coarsened during thermal treatment.

  6. Nanoscopic properties of silica filled polydimethylsiloxane by means of positron annihilation lifetime spectroscopy

    DEFF Research Database (Denmark)

    Wiinberg, P.; Eldrup, Morten Mostgaard; Maurer, F.H.J.

    2004-01-01

    Positron annihilation lifetime spectroscopy (PALS) was performed on a series of polydimethylsiloxane (PDMS)/fumed silicon dioxide (SiO2) composites at temperatures between -185 and 100degreesC to study the effect of filler content and filler particle size on the free volume properties and the...... positron annihilation characteristics. The glass transition behavior of the PDMS/SiO2 composites was determined with differential scanning calorimetry. A clear influence on the o-Ps lifetime (73) in the polymer upon addition of nano-sized fumed SiO2 was observed at all temperatures. The observed o...... behavior of ordinary molecular liquids was observed in this temperature region. The o-Ps yield was strongly reduced in the crystallization region and by addition Of SiO2. The reduction due to filler addition did, however, in the case of nano-sized SiO2 not follow a linear relationship with filler weight...

  7. Structural studies of spinel manganite ceramics with positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    The new transition-metal manganite Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics for temperature sensors with improved functional reliability are first proposed. It is established that the amount of additional NiO phase in these ceramics extracted during sintering play a decisive role. This effect is well revealed only in ceramics having a character fine-grain microstructure, while the monolithization of ceramics caused by great amount of transferred thermal energy reveals an opposite influence. The process of monolitization from the position of evolution of grain-pore structure was studied in these ceramics using positron annihilation lifetime spectroscopy.

  8. Characterization of control mesoporous glasses (CPGs) using positron annihilation lifetime spectroscopy (PALS)

    Energy Technology Data Exchange (ETDEWEB)

    Sayed Ahmed, Essmat Mahmoud Hassan

    2008-01-30

    This thesis has two main goals. Firstly and for the first time, the positron annihilation lifetime technique (PALS) is used to characterize the control porous glasses (CPGs) media. All the positron annihilation spectroscopy (PAS) investigations have been interested in the commercial Vycor glass media of pores size {<=} 4 nm. Therefore, the PALS is used to establish basic correlations between the important physical properties of the CPG (pore size, surface area, and porosity) and the orthopositronium (o-Ps) lifetime. The second goal is to use these correlations to verify the validity of some suggested models and theories to discover possible deviations from the expected behaviour and to discuss the physical point of view for these deviations. Chapter 1 presents an overview of positron, positronium and their interaction with solid materials. Chapter 2 of this thesis is concerned with characterization of porous glass materials. This chapter discusses in detail the preparation methods of porous glasses specially control porous glass and Vycor glass. The gas adsorption phenomenon in porous glass and the related definitions are discussed. The most important terms of the porous glass such as pore size, shape, volume, pore size distribution, surface area, and porosity are discussed. Chapter 3 presents in detail the well known models and the derived equations which correlate between the lifetime of the o-Ps long-lived component and the pore size, pore shape and the temperature dependence of the porous media. Chapter 4 presents an overview of the main experimental techniques used in this thesis, namely positron annihilation lifetime spectroscopy. Chapter 5 explains the sample preparation for the measurements. The chapter represents also the experimental data for the correlation between the o-Ps lifetime and pore sizes for a system of CPG media (from 1 nm to 64 nm). I also studied the temperature dependence of the o-Ps long-lived component in different pore sizes. In this

  9. Characterization of control mesoporous glasses (CPGs) using positron annihilation lifetime spectroscopy (PALS)

    International Nuclear Information System (INIS)

    This thesis has two main goals. Firstly and for the first time, the positron annihilation lifetime technique (PALS) is used to characterize the control porous glasses (CPGs) media. All the positron annihilation spectroscopy (PAS) investigations have been interested in the commercial Vycor glass media of pores size ≤ 4 nm. Therefore, the PALS is used to establish basic correlations between the important physical properties of the CPG (pore size, surface area, and porosity) and the orthopositronium (o-Ps) lifetime. The second goal is to use these correlations to verify the validity of some suggested models and theories to discover possible deviations from the expected behaviour and to discuss the physical point of view for these deviations. Chapter 1 presents an overview of positron, positronium and their interaction with solid materials. Chapter 2 of this thesis is concerned with characterization of porous glass materials. This chapter discusses in detail the preparation methods of porous glasses specially control porous glass and Vycor glass. The gas adsorption phenomenon in porous glass and the related definitions are discussed. The most important terms of the porous glass such as pore size, shape, volume, pore size distribution, surface area, and porosity are discussed. Chapter 3 presents in detail the well known models and the derived equations which correlate between the lifetime of the o-Ps long-lived component and the pore size, pore shape and the temperature dependence of the porous media. Chapter 4 presents an overview of the main experimental techniques used in this thesis, namely positron annihilation lifetime spectroscopy. Chapter 5 explains the sample preparation for the measurements. The chapter represents also the experimental data for the correlation between the o-Ps lifetime and pore sizes for a system of CPG media (from 1 nm to 64 nm). I also studied the temperature dependence of the o-Ps long-lived component in different pore sizes. In this

  10. Positron annihilation lifetime spectroscopy of carbon black- and silica-filled rubber

    International Nuclear Information System (INIS)

    Lifetime spectroscopy has been used to investigate different grades of carbon black (CB) and silica mixed into a variety of rubbers as a function of CB or silica loading. The spectra were analyzed into three lifetimes. The results show that: (1) The longest observed lifetime, τ3, attributed to ortho positronium formation depends on the rubber but not on filter loading or type of CB. The free volume size in the rubber is not affected by the addition of the filler. (2) The intensity, I3, of ortho positronium formation depends both on the loading and on the type of CB, but is less dependent on loading in the case of silica. (3) The intermediate lifetime, τ2, depends both on the loading of the filler and on the type of CB. For CB, this indicates that τ2 is not simply the additive result of bulk annihilation in the rubber and CB. Rather the CB loading creates new trapping sites at the CB-rubber interface that depend on the type of CB. (orig.)

  11. Structural studies of spinel manganite ceramics with positron annihilation lifetime spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Klym, H; Shpotyuk, O; Hadzaman, I [Institute of Materials of SRC ' Carat' , 202 Stryjska str., Lviv, 79031 (Ukraine); Ingram, A [Opole University of Technology, 75 Ozimska str., Opole, 45370 (Poland); Filipecki, J, E-mail: shpotyuk@novas.lviv.ua, E-mail: klymha@yahoo.com [Institute of Physics of Jan Dlugosz University, 13/15 Armii Krajowei, 42201, Czestochowa (Poland)

    2011-04-01

    The new transition-metal manganite Cu{sub 0.1}Ni{sub 0.8}Co{sub 0.2}Mn{sub 1.9}O{sub 4} ceramics for temperature sensors with improved functional reliability are first proposed. It is established that the amount of additional NiO phase in these ceramics extracted during sintering play a decisive role. This effect is well revealed only in ceramics having a character fine-grain microstructure, while the monolithization of ceramics caused by great amount of transferred thermal energy reveals an opposite influence. The process of monolitization from the position of evolution of grain-pore structure was studied in these ceramics using positron annihilation lifetime spectroscopy.

  12. Nanoporous Structure in Low-Dielectric Films with Positronium Annihilation Lifetime Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    HU Yi-Fan; SUN Jia-Ning; D. W. Gidley

    2005-01-01

    @@ We investigate nano-porous structures in thin low-dielectric films, i.e. the pore sizes, distributions, and interconnectivity, by using depth profiled positronium annihilation lifetime spectroscopy (PALS). It is found that PALS has good sensitivity to probe both interconnected and closed pores in the range from 0.3nm to 30nm, even in the film buried beneath a diffusion barrier. A series of low dielectric constant films of organosilicon-silsequioxane with different weight percentages of porogen have been comparatively investigated. The PALS technique can be used to distinguish the open porosity from the closed one, to determine the pore size, and to detect the percolation threshold with the increasing porosity that represents the transition from closed pores to interconnected pores.Furthermore, the pore percolation length can be derived.

  13. Positron annihilation lifetime spectroscopy (PALS) application in metal barrier layer integrity for porous low- k materials

    CERN Document Server

    Simon, Lin; Gidley, D W; Wetzel, J T; Monnig, K A; Ryan, E T; Simon, Jang; Douglas, Yu; Liang, M S; En, W G; Jones, E C; Sturm, J C; Chan, M J; Tiwari, S C; Hirose, M

    2002-01-01

    Positron Annihilation Lifetime Spectroscopy (PALS) is a useful tool to pre-screen metal barrier integrity for Si-based porous low-k dielectrics. Pore size of low-k, thickness of metal barrier Ta, positronium (Ps) leakage from PALS, trench sidewall morphology, electrical test from one level metal (1LM) pattern wafer and Cu diffusion analysis were all correlated. Macro-porous low-k (pore size >=200 AA) and large scale meso-porous low-k (>50~200 AA) encounter both Ps leakage and Cu diffusion into low-k dielectric in the 0.25 mu mL/0.3 mu mS structures when using SEMATECH in-house PVD Ta 250 AA as barrier layer. For small scale meso-porous (>20~50 AA) and micro- porous (<=20 AA) low-k, no Ps leakage and no Cu diffusion into low-k were observed even with PVD Ta 50 AA, which is proved also owing to sidewall densification to seal all sidewall pores due to plasma etch and ash. For future technology, smaller pore size of porous Si-based low-k (=<50 AA) will be preferential for dense low-k like trench sidewall to...

  14. Study of PRIMAVERA Steel Samples by Positron Annihilation Spectroscopy Technique II – Lifetime Measurements

    OpenAIRE

    KRSJAK VLADIMIR; GRAFUTIN V.; O.V. Ilyukhina; BURCL Rudolf; BALLESTEROS AVILA ANTONIO; Haehner, Peter

    2012-01-01

    In the present article, a positron annihilation lifetime technique was used for the study of VVER-440/230 weld materials, manufactured in the frame of the international PRIMAVERA project on microstructural investigation of the irradiated WWER-440 reactor pressure vessel steel. The present results complement our previous report of positron angular correlation experiments and provide in-depth characterization of vacancy type defects behavior under irradiation and thermal treatment. The results ...

  15. Using a LaBr3∶Ce scintillator for positron annihilation lifetime spectroscopy

    Institute of Scientific and Technical Information of China (English)

    LIU Jun-Hui; LI Dao-Wu; ZHANG Zhi-Ming; WANG Bao-Yi; ZHANG Tian-Bao; HAO Jia; WEI Long

    2012-01-01

    A LaBr3:Ce scintillator has a high light output (~60000 p.e/MeV) and a short decay constant (<25 ns),which makes it good for time spectrometry.Compared with a BaF2 scintillator,it can bear a much higher count rate,and can be coupled to photomultipliers without using a quartz window.In this work,a positron annihilation lifetime spectrometer (PALS) consisting of two bulks of φ25 mm×25 mm LaBr3:Ce scintillator coupled to two XP20D0 photomultipliers,respectively,was built.A time resolution of FWHM=206 ps was measured for the PALS with a 60Co source at the energy window for 22Na.With this spectrometer,a reasonable lifetime value τ=221±4 ps in a pure Si sample is obtained,which means that the utilization of LaBr3∶Ce as the detector for a PALS is feasible.

  16. Degradation of encapsulants for photovoltaic modules made of ethylene vinyl acetate studied by positron annihilation lifetime spectroscopy

    Science.gov (United States)

    Hagihara, Hideaki; Kunioka, Masao; Suda, Hiroyuki; Hara, Yukiko; Masuda, Atsushi

    2016-10-01

    The structure of ethylene vinyl acetate (EVA) encapsulants of crystalline-Si photovoltaic modules after the damp heat (DH) test was evaluated by positron annihilation lifetime spectroscopy (PALS). A reduction in free-volume hole size, which indicates the progress of deacetylation, was observed after the DH test. The difference in lifetime (Δτ) between the initial and DH-tested samples clearly increased after the DH test for 3000 h. The increase in Δτ was correlated with the acetic acid concentration in the EVA estimated by ion chromatography. The depth profile analysis by slow positron beam PALS revealed that Δτ in the near-surface region of the Si-cell side was significantly larger than that of the cover-glass side. This result indicates that deacetylation near the Si cell/EVA interface is accelerated.

  17. Probing Cu Diffusion Barrier Layers on Porous Low-Dielectric-Constant Films by Posireonium Annihilation Lifetime Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    HU Yi-Fan; SUN Jia-Ning; Gidley D.W.

    2005-01-01

    @@ Two kinds of Cu diffusion barrier layers, sealedfilms and capped fi1ms, on nanoporous low-dielectric-constant filmsare investigated by positronium annihilation lifetime spectroscopy (PALS). We have found that the minimumthickness of Ta to form an effective diffusion barrier is affected by the pore size. The films with large poresrequire thick barrier layers to form effective diffusion barriers. In addition, a possible ultra-thin diffusion barrier,i.e. a plasma-induced densification layer, has also been investigated. The PALS data confirm that a porouslow-dielectric-constant thin film can be shrunk by exposure to plasma. This shrinkage is confined to a surfacelayer of collapsed pores and forms a dense layer. The dense layer tends to behave as Ps (positronium) diffusionbarriers. Indeed, the controlled thin "skin" layer could prevent Cu diffusion into the underlying dielectrics.

  18. Positron annihilation lifetime spectroscopy study on the structural relaxation of phenylmethylsiloxane-modified epoxy hybrids at different aging temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Hsu, Chia-Wen [Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan (China); Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan (China); Ma, Chen-Chi M., E-mail: ccma@che.nthu.edu.tw [Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan (China); Tan, Chung-Sung [Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan (China); Li, Hsun-Tien [Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan (China)

    2015-07-15

    The cured network conformations and structural relaxation behaviours of the diglycidyl ether of bisphenol A (DGEBA)-methylhexahydrophthalic anhydride (MHHPA) modified with phenylmethylsiloxane-modified epoxy (PMSE) at different aging temperatures were studied using dynamic mechanical analysis (DMA) and positron annihilation lifetime spectroscopy (PALS). The DMA results revealed that the cured PMSE network can insert into the cured DGEBA network to form interpenetrating polymer networks (IPNs). The structural relaxation behaviours of DGEBA–PMSE-0.4 produced using DGEBA, PMSE, and MHHPA at a ratio of 0.6:0.4:1 by equivalent weight were studied using PALS at 150 °C and 55 °C. The aging-induced free volume relaxation parameters of DGEBA–PMSE-0.4 at 150 °C and 55 °C were investigated using the double additive exponential model and the Kohlrausch–Williams–Watts exponential model. For double additive exponential model, only one relaxation time (ζ) of 584.5 h was found at 150 °C; By contrast, there were two separate relaxation times of 37.4 h (ζ{sub 1}) and 753.6 h (ζ{sub 2}) at 55 °C. The ζ{sub 1} of the IPNs hybrid can be attributed to the network relaxation of PMSE, and the ζ{sub 2} can be attributed to the network relaxation of DGEBA at 55 °C. The results suggested the double additive exponential model can effectively predict DGEBA–PMSE hybrid relaxation behaviours. - Highlights: • The cured network conformations of DGEBA–PMSE hybrids were studied using DMA. • The structural relaxation behaviours of DGEBA–PMSE hybrids were studied using PALS. • The cured DGEBA–PMSE hybrids were interpenetrating polymer networks (IPNs). • PALS studies provided a quantitative demonstration of relaxation behaviours. • Double additive exponential model effectively predicted the relaxation times of hybrids.

  19. Design, simulation and performance of a slow positron beam with secondary electron tagging for positron annihilation lifetime spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Marinov, H. [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd, 1784 Sofia (Bulgaria); Djourelov, N., E-mail: nikdjour@inrne.bas.bg [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd, 1784 Sofia (Bulgaria); Nédélec, P. [Université de Lyon, Laboratoire IPNL, UCB Lyon 1, Bâtiment Paul Dirac, 4 rue Enrico Fermi, 69622 Villeurbanne Cedex (France); Petrov, L. [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd, 1784 Sofia (Bulgaria)

    2013-11-21

    A positron annihilation lifetime spectrometer using a magnetically guided continuous positron beam and the signal from secondary electrons (SE) emitted from the sample is presented. The positron and secondary electrons trajectories as well as the physics of SE were simulated using GEANT4 program. A special attention was paid to the consequences of positron backscattering, in particular on the shape of the lifetime spectrum. A very good agreement was obtained between simulation and measurements concerning the time resolution (∼300–400 ps FWHM) for the studied range of incident positron energies. Due to the complex shape of the resolution function, the present design of the spectrometer is not suited to study of short lifetimes, but can be used for depth profiling porosimetry of materials with Ps formation with the an excellent peak to background ratio of ∼10{sup 5}.

  20. Investigations into the free-volume changes within starch/plasticizer/nanoclay systems using Positron Annihilation Lifetime Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Huihua, E-mail: h.liu@federation.edu.au [School of Health Sciences, Federation University Australia, Ballarat, Vic (Australia); Chaudhary, Deeptangshu, E-mail: deepc@ers.com.au [ERS Environmental Risk Solutions PTY LTD, Perth, WA (Australia); Campbell, Colin, E-mail: colin.campbell@anu.edu.au [ARC Centre of Excellence for Antimatter-Matter Studies (CAMS), Research School of Physics and Engineering, Australian National University, Canberra (Australia); Roberts, Jason, E-mail: jxr107@physics.anu.edu.au [ARC Centre of Excellence for Antimatter-Matter Studies (CAMS), Research School of Physics and Engineering, Australian National University, Canberra (Australia); Buckman, Stephen, E-mail: stephen.buckman@anu.edu.au [ARC Centre of Excellence for Antimatter-Matter Studies (CAMS), Research School of Physics and Engineering, Australian National University, Canberra (Australia); Sullivan, James, E-mail: james.sullivan@anu.edu.au [ARC Centre of Excellence for Antimatter-Matter Studies (CAMS), Research School of Physics and Engineering, Australian National University, Canberra (Australia)

    2014-11-14

    The free-volume of a matrix is a fundamental parameter that relates to its molecular and bulk characteristics, such as crystalline change and glass transition behavior. In starch-based bionanocomposite, we investigated the effect of the addition of montmorillonite nanoclay (MMT) and food plasticizers (glycerol and sorbitol) on changes of molecular pore size (including pore volume and pore distribution) using the Positron Annihilation Lifetime Spectroscopy (PALS) method. The results demonstrated counter-intuitive impact of MMT on the total free-volume where the total free-volume increased within the polymeric matrix. When compared to the pure matrix free-volume, the addition of MMT also resulted in the appearance of a broader distribution of the void sizes. The plasticizers, on the other hand, apparently occupied the void spaces, and therefore decreased the free-volume of the matrix. Further, together with the small angle X-ray scattering (SAXS) analysis, we concluded that this is a result of interplay between the plasticizer-plasticizer interactions and the polymer–plasticizer interactions. For example, in the starch/glycerol/MMT system, the pore radii slightly decrease upon the increasing of glycerol amount (OG210 = O.27 nm and OG220 = 0.26 nm), but the relative weight did increase with the increasing glycerol concentration. However, increasing the sorbitol amount increased the pore size from 0.23 nm(OS210) to 0.28 nm(OS220). Furthermore, the addition MMT in the OS010 system, promote the emergence of a new dateable pore radius(0.90 nm), and the total weight significantly increased from 13.70 (OS010) to 19.5% (OS210). We suggest that the pore variation (size and distribution) due to the MMT and plasticizers are reflected in the polymer glass transition and crystallinity because ultimately, the, total free-volume is a reflection of level of interactions existing within the bulk of these nanocomposites. - Highlights: • PALS is applied to explore the

  1. Pre-martensitic phenomena of thermoelastic martensitic transformation of NiTiCu alloys studied with positron annihilation lifetime spectroscopy

    Directory of Open Access Journals (Sweden)

    J. Katsuyama, H. Araki, M. Mizuno and Y. Shirai

    2004-01-01

    Full Text Available Many anomalous phenomena have been observed in NiTi alloys above martensite start temperature, such as softening of the shear constants, increase of internal friction and diffuse scattering of TEM. However, little information has been obtained about the change in the electron system of the parent phase prior to the martensitic transformation, which should be the origin of all pre-martensitic phenomena. In this work, the temperature change of positron annihilation lifetime, which is quite sensitive to electronic-structural changes of matter, were carried out for NiTiCu alloys. The alloys show martensitic transformation from a B2 (cubic phase to a B19' (monoclinic phase via a B19 (orthorhombic phase as the temperature is lowered. We have found anomalous positron lifetime changes in Ni10Ti50Cu40 and Ni15Ti50Cu35 alloys which show a B2–B19–B19' phase transformation. Positron lifetime increases anomalously with decreasing temperature at temperatures higher than the transformation temperature into a B19' phase. On the other hand, positron lifetime does not show any anomaly in the B2 phase of Ni30Ti50Cu20 alloy which shows B2–B19 phase transformation. The positron lifetime of the parent B2 phase shows good agreement with the theoretically-calculated value. Those of the martensite phases of B19 and B19', although, are about 30 ps longer than calculated ones. This big difference between experimental and calculated positron lifetimes cannot be explained by any existing theory.

  2. A compact positron annihilation lifetime spectrometer

    Institute of Scientific and Technical Information of China (English)

    LI Dao-Wu; LIU Jun-Hui; ZHANG Zhi-Ming; WANG Bao-Yi; ZHANG Tian-Bao; WEI Long

    2011-01-01

    Using LYSO scintillator coupled on HAMAMATSU R9800(a fast photomultiplier)to form the small size γ-ray detectors,a compact lifetime spectrometer has been built for the positron annihilation experiments.The system time resolution FWHM=193 ps and the coincidence counting rate -8 cps/μCi were achieved.A lifetime value of 219±1 ps of positron annihilation in well annealed Si was tested,which is in agreement with the typical values published in the previous lectures.

  3. A compact positron annihilation lifetime spectrometer

    Institute of Scientific and Technical Information of China (English)

    李道武; 刘军辉; 章志明; 王宝义; 张天保; 魏龙

    2011-01-01

    Using LYSO scintillator coupled on HAMAMATSU R9800 (a fast photomultiplier) to form the small size γ-ray detectors, a compact lifetime spectrometer has been built for the positron annihilation experiments. The system time resolution FWHM=193 ps and the co

  4. Application of positron annihilation lifetime spectroscopy (PALS) to study the nanostructure in amphiphile self-assembly materials: phytantriol cubosomes and hexosomes.

    Science.gov (United States)

    Dong, Aurelia W; Fong, Celesta; Waddington, Lynne J; Hill, Anita J; Boyd, Ben J; Drummond, Calum J

    2015-01-21

    Self-assembled amphiphile nanostructures of colloidal dimensions such as cubosomes and hexosomes are of interest as delivery vectors in pharmaceutical and nanomedicine applications. Translation would be assisted through a better of understanding of the effects of drug loading on the internal nanostructure, and the relationship between this nanostructure and drug release profile. Positron annihilation lifetime spectroscopy (PALS) is sensitive to local microviscosity and is used as an in situ molecular probe to examine the Q2 (cubosome) → H2 (hexosome) → L2 phase transitions of the pharmaceutically relevant phytantriol-water system in the presence of a model hydrophobic drug, vitamin E acetate (VitEA). It is shown that the ortho-positronium lifetime (τ) is sensitive to molecular packing and mobility and this has been correlated with the rheological properties of individual lyotropic liquid crystalline mesophases. Characteristic PALS lifetimes for L2 (τ4∼ 4 ns) ∼ H2 (τ4∼ 4 ns) > Q(2 Pn3m) (τ4∼ 2.2 ns) are observed for the phytantriol-water system, with the addition of VitEA yielding a gradual increase in τ from τ∼ 2.2 ns for cubosomes to τ∼ 3.5 ns for hexosomes. The dynamic chain packing at higher temperatures and in the L2 and H2 phases is qualitatively less "viscous", consistent with rheological measurements. This information offers increased understanding of the relationship between internal nanostructure and species permeability.

  5. Precipitation Study in Inconel 625 Alloy by Positron Annihilation Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    M.Ahmad; W. Ahmad; M.A.Shaikh; Mahmud Ahmad; M.U. Rajput

    2003-01-01

    Precipitation in Inconel 625 alloy has been studied by positron annihilation spectroscopy and electron microscopy. The observeddependence of annihilation characteristics on aging time is attributed to the change of the positron state due to the increaseand decrease of the density and size of the γ″ precipitates. Hardness measurements and lifetime measurements are in goodagreement.

  6. Microstructure variation in fused silica irradiated by different fluence of UV laser pulses with positron annihilation lifetime and Raman scattering spectroscopy

    Science.gov (United States)

    Li, Chunhong; Zheng, Wanguo; Zhu, Qihua; Chen, Jun; Wang, B. Y.; Ju, Xin

    2016-10-01

    We present an original study on the non-destructive evaluation of the microstructure evolution of fused silica induced by pulsed UV laser irradiation at low fluence (less than 50% Fth). Positron annihilation spectroscopy discloses that the spatial size of the vacancy cluster is increased exponentially with the linearly elevated laser fluence. Particularly, the vacancy cluster size in bulk silica is significantly increased by 14.5% after irradiated by pulsed 355 nm laser at F = 14 J/cm2 (50% Fth), while the void size varies only ∼2%. UV laser-excited Raman results suggest that the bond length and average bond angle of Sisbnd Osbnd Si bridging bond are both slightly reduced. Results reveals that the rearrangement process of (Sisbnd O)n fold rings and breakage of the Sisbnd O bridging bond in bulk silica occurred during pulsed UV laser irradiation. The micro-structural changes were taken together to clarify the effect of sub-threshold laser fluence on material stability of silica glass. The obtained data provide important information for studying material stability and controlling the lifetime of fused silica optics for high power laser system.

  7. 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 (<0.5 nm) partially causes those changes. These defects were studied by positron annihilation lifetime spectroscopy at room temperature. A high concentration of Cu-O di-vacancies was found in both samples, which increased with neutron fluence. The defect concentration was significantly reduced after a heat treatment.

  8. Variation of free volume size and content of shape memory polymer -polyurethane - upon temperature studied by positron annihilation lifetime techniques and infrared spectroscopy

    International Nuclear Information System (INIS)

    Positron annihilation lifetime measurement and Fourier transform infrared spectrometry were applied to the study of temperature dependencies of free volume parameters and hydrogen bonds in segmented polyurethane, specially fabricated as a shape memory polymer. The variation of free volumes in amorphous region were correlated to that of hydrogen bonding and the shape memory mechanism of polyurethane is elucidated from a microscopic point of view. The relationship between free volume contents and the formation of hydrogen bonds significantly suggests that the shape memory occurs due to the configurational recovery of the microscopic regulation around urethane bundles of hard segment and consequent restoration of soft-segment in polyurethane. (author)

  9. Investigation of the free volume and ionic conducting mechanism of poly(ethylene oxide)-LiClO4 polymeric electrolyte by positron annihilating lifetime spectroscopy

    Institute of Scientific and Technical Information of China (English)

    Gong Jing; Gong Zhen-Li; Yan Xiao-Li; Gao Shu; Zhang Zhong-Liang; Wang Bo

    2012-01-01

    The positron annihilation lifetime and ionic conductivity are each measured as a function of organophilic rectorite (OREC) content and temperature in a range from 160 K to 300 K.According to the variation of ortho-positronium (o-Ps) lifetime with temperature,the glassy transition temperature is determined.The continuous maximum entropy lifetime (MELT) analysis clearly shows that the OREC and temperature have important effects on o-Ps lifetime and free volume distribution.The experimental results show that the temperature dependence of ionic conductivity obeys the Vogel-Tammann-Fulcher (VTF) and Williams Landel-Ferry (WLF) equations,implying a free-volume transport mechanism.A linear least-squares procedure is used to evaluate the apparent activation energy related to the ionic transport in the VTF equation and several important parameters in the WLF equation.It is worthwhile to notice that a direct linear relationship between the ionic conductivity and free volume fraction is established using the WLF equation based on the free volume theory for nanocomposite electrolyte,which indicates that the segmental chain migration and ionic migration and diffusion could be explained by the free volume theory.

  10. Positron annihilation spectroscopy in condensed matter

    International Nuclear Information System (INIS)

    The topic of positron annihilation spectroscopy (PAS) is the investigation of all aspects connected with the annihilation of slow positrons. This work deals with the application of PAS to different problems of materials science. The first chapter is an introduction to fundamental aspects of positron annihilation, as far as they are important to the different experimental techniques of PAS. Chapter 2 is concerned with the information obtainable by PAS. The three main experimental techniques of PAS (2γ-angular correlation, positron lifetime and Doppler broadening) are explained and problems in the application of these methods are discussed. Chapter 3 contains experimental results. According to the different fields of application it was subgrouped into: 1. Investigations of crystalline solids. Detection of structural defects in Cu, estimation of defect concentrations, study of the sintering of Cu powders as well as lattice defects in V3Si. 2. Chemical investigations. Structure of mixed solvents, selective solvation of mixed solvents by electrolytes as well as the micellization of sodium dodecylsulphate in aqueous solutions. 3. Investigations of glasses. Influence of heat treatment and production technology on the preorder of X-amorphous silica glass as well as preliminary measurements of pyrocerams. 4. Investigations of metallic glasses. Demonstration of the influence of production technology on parameters measurable by PAS. Chapter 4 contains a summary as well as an outlook of further applications of PAS to surface physics, medicine, biology and astrophysics. (author)

  11. Positron annihilation lifetime study of polyvinylpyrrolidone for nanoparticle-stabilizing pharmaceuticals.

    Science.gov (United States)

    Shpotyuk, O; Bujňáková, Z; Baláž, P; Ingram, A; Shpotyuk, Y

    2016-01-01

    Positron annihilation lifetime spectroscopy was applied to characterize free-volume structure of polyvinylpyrrolidone used as nonionic stabilizer in the production of many nanocomposite pharmaceuticals. The polymer samples with an average molecular weight of 40,000 g mol(-1) were pelletized in a single-punch tableting machine under an applied pressure of 0.7 GPa. Strong mixing in channels of positron and positronium trapping were revealed in the polyvinylpyrrolidone pellets. The positron lifetime spectra accumulated under normal measuring statistics were analysed in terms of unconstrained three- and four-term decomposition, the latter being also realized under fixed 0.125 ns lifetime proper to para-positronium self-annihilation in a vacuum. It was shown that average positron lifetime extracted from each decomposition was primary defined by long-lived ortho-positronium component. The positron lifetime spectra treated within unconstrained three-term fitting were in obvious preference, giving third positron lifetime dominated by ortho-positronium pick-off annihilation in a polymer matrix. This fitting procedure was most meaningful, when analysing expected positron trapping sites in polyvinylpyrrolidone-stabilized nanocomposite pharmaceuticals. PMID:26444751

  12. Positron annihilation lifetime study of polyvinylpyrrolidone for nanoparticle-stabilizing pharmaceuticals.

    Science.gov (United States)

    Shpotyuk, O; Bujňáková, Z; Baláž, P; Ingram, A; Shpotyuk, Y

    2016-01-01

    Positron annihilation lifetime spectroscopy was applied to characterize free-volume structure of polyvinylpyrrolidone used as nonionic stabilizer in the production of many nanocomposite pharmaceuticals. The polymer samples with an average molecular weight of 40,000 g mol(-1) were pelletized in a single-punch tableting machine under an applied pressure of 0.7 GPa. Strong mixing in channels of positron and positronium trapping were revealed in the polyvinylpyrrolidone pellets. The positron lifetime spectra accumulated under normal measuring statistics were analysed in terms of unconstrained three- and four-term decomposition, the latter being also realized under fixed 0.125 ns lifetime proper to para-positronium self-annihilation in a vacuum. It was shown that average positron lifetime extracted from each decomposition was primary defined by long-lived ortho-positronium component. The positron lifetime spectra treated within unconstrained three-term fitting were in obvious preference, giving third positron lifetime dominated by ortho-positronium pick-off annihilation in a polymer matrix. This fitting procedure was most meaningful, when analysing expected positron trapping sites in polyvinylpyrrolidone-stabilized nanocomposite pharmaceuticals.

  13. Positron annihilation lifetime study of Ag-ion exchanged and heat treated soda lime glass

    International Nuclear Information System (INIS)

    Slabs of soda lime silica glass (15% Na2O) were subjected to Ag+/Na+ ion exchange process and subsequent heat treatment. The change in glass structure and Ag states accompanied with these processes were studied using the positron annihilation lifetime spectroscopy. The positron annihilation lifetime measurements were performed with a fast-fast coincidence spectrometer employing a multi-parameter acquisition system. The lifetime parameters showed that the Ag+ ion reduction process takes place through two processes; the oxidation reduction reaction with Fe2+ impurities in the glass at heat treatment temperatures <500 deg. C, whereas at heat treatment ≥500 deg. C the reduction takes place through the polymerization reaction. The results also indicated that the heat treatment at 600 deg. C enhanced the formation of Ag metal nanoparticle crystals through the structural relaxation revealed by the free volume defects

  14. Positron annihilation lifetime study of low temperature irradiated metals

    Energy Technology Data Exchange (ETDEWEB)

    Kuramoto, Eiichi [Kyushu Univ., Kasuga, Fukuoka (Japan). Research Inst. for Applied Mechanics

    1997-11-01

    Positron annihilation lifetime measurements have been made for electron and neutron irradiated Fe, Fe-Cr, Fe-Cu, Fe-Si, Fe-16Cr-17Ni specimens, and isochronal annealing behaviors were obtained for these metals and alloys. It was found that vacancies start to migrate at about 200 K in Fe and form microvoids, but by the addition of small amount of alloying elements this behavior was changed depending on the alloying elements. Positron lifetime calculations were made to explain the experimental results using EAM (embedded atom method) type potential for the lattice relaxation and the atomic superposition method for the lifetime calculation. Fairly good agreements were obtained for the positron lifetime in a vacancy in Fe and other alloys. (author)

  15. Positron annihilation spectroscopy of neon ion irradiated MgB2

    International Nuclear Information System (INIS)

    Positron Annihilation Lifetime Spectroscopy (PALS) and Coincidence Doppler Broadening Spectroscopy (CDBS) were carried out on Neon ion irradiated MgB2 superconductor. CDBS of unirradiated sample shows similarity to boron spectrum. In contrast, the spectrum of the irradiated sample shows similarity to Mg spectrum. The PALS spectra show that there is decrease in the lifetime of positron in irradiated sample. The decrease in the lifetime is due to neon ion implantation. (author)

  16. On the consistency between positron annihilation lifetime and Doppler broadening results in polypropylene

    Energy Technology Data Exchange (ETDEWEB)

    Djourelov, N. [Department of Subatomic and Rad. Physics, Ghent University, Proeftuinstraat 86, 9000 Ghent (Belgium); Institute of Nuclear Research and Nuclear Energy, 72 Tzarigradsko Shoosse, 1784 Sofia (Bulgaria); Dauwe, C. [Department of Subatomic and Rad. Physics, Ghent University, Proeftuinstraat 86, 9000 Ghent (Belgium); Palacio, C.A. [Department of Subatomic and Rad. Physics, Ghent University, Proeftuinstraat 86, 9000 Ghent (Belgium); Institute of Physics, University of Antioquia, A. A. 1226, Medellin (Colombia); Laforest, N. [Department of Subatomic and Rad. Physics, Ghent University, Proeftuinstraat 86, 9000 Ghent (Belgium); University of Savoie, Batiment IUT, 73376 Le Bourget-du-lac Cedex (France); Bas, C. [University of Savoie, Batiment IUT, 73376 Le Bourget-du-lac Cedex (France)

    2007-07-01

    Polypropylene samples were measured as a function of the source exposure time at 20 K and as a function of the temperature (20-400 K) simultaneously by Positron Annihilation Lifetime (PAL) and Doppler Broadening (DB) spectroscopy. The peak shape parameter (S) measured by DB can be calculated as a sum of contributions of specific parameters corresponding to each positron state. The contributions are obtained by analysis of the PAL spectra. The confinement of positronium (Ps) in a free volume hole (FVH) determines the self annihilation shape parameter S{sub sa} of the para-Ps, the pick-off annihilation lifetime {tau}{sub po}, and supposes FVH size-dependence of the pick-off shape parameter S{sub po}. The ortho-Ps lifetime and shape parameters are used to compute S{sub sa}. In this way, the temperature and time dependences of the S parameter are modelled. The fit of this model to the experimental S parameter shows a stronger dependence of the S{sub po} on the FVH size (R) than the one as expected by taking into account only the Ps momentum. This result suggests that the penetration of Ps into the walls of the FVH must be properly considered and that the penetration depth depends on R itself. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Application of positron annihilation lifetime technique for {gamma}-irradiation stresses study in chalcogenide vitreous semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Shpotyuk, O.; Golovchak, R.; Kovalskiy, A. [Scientific Research Company ' ' Carat' ' , Stryjska str. 20279031 Lviv (Ukraine); Filipecki, J.; Hyla, M. [Physics Institute, Pedagogical University, Al. Armii Krajowej 13/1542201 Czestochowa (Poland)

    2002-08-01

    The influence of {gamma}-irradiation on the positron annihilation lifetime spectra in chalcogenide vitreous semiconductors of As-Ge-S system has been analysed. The correlations between lifetime data, structural features and chemical compositions of glasses have been discussed. The observed lifetime components are connected with bulk positron annihilation and positron annihilation on various native and {gamma}-induced open volume defects. It is concluded that after {gamma}-irradiation of investigated materials the {gamma}-induced microvoids based on S{sub 1}{sup -}, As{sub 2}{sup -}, and Ge{sub 3}{sup -} coordination defects play the major role in positron annihilation processes. (Abstract Copyright[2002], Wiley Periodicals, Inc.)

  18. Positron annihilation lifetime study of extended defects in semiconductor glasses and polymers

    Energy Technology Data Exchange (ETDEWEB)

    Boyko, Olha [Department of Pediatric Dentistry, Danylo Halytsky Lviv National Medical University, Pekarska str. 69, 79010 Lviv (Ukraine); Shpotyuk, Yaroslav [Department of Optoelectronics and Information Technologies, Ivan Franko National University of Lviv, Dragomanova str. 50, 79005 Lviv (Ukraine); Lviv Scientific Research Institute of Materials, Scientific Research Company ' ' Carat' ' , Stryjska str. 202, 79031 Lviv (Ukraine); Filipecki, Jacek [Institute of Physics, Jan Dlugosz University in Czestochowa, Armii Krajowej al. 13/15, 42200 Czestochowa (Poland)

    2013-01-15

    The processes of atomic shrinkage in network-forming solids initiated by external influences are tested using technique of positron annihilation lifetime spectroscopy at the example of chalcogenide vitreous semiconductors of arsenic sulphide type and acrylic polymers for dental application. Two state positron trapping is shown to be responsible for atomic shrinkage in chalcogenide glasses, while mixed trapping and ortho-positronium decaying is character for volumetric densification and stress propagation in acrylic dental polymers. At the basis of the obtained results it is concluded that correct analysis of externally-induced shrinkage in polymer networks under consideration can be developed by using original positron lifetime data treatment algorithms to compensate defect-free bulk annihilation channel within two-state positron trapping model and account for an interbalance between simultaneously co-existing positron trapping and orth-positronium related decaying channels within mixed three-state positron annihilation model (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Studies on microdomain structure in segmented polyether polyurethaneureas by positron annihilation lifetime and small—angle X—ray scattering

    Institute of Scientific and Technical Information of China (English)

    YinChuan-Yuan; GuQing-Chao; 等

    1997-01-01

    The microdomain structure of segmented polyether polyurethaneureas is investigated by means of positron annihilation lifetime spectroscopy,small-angle X-ray scattering and differential scanning calorimetry.The experimental results show that the decrease in the domain volume and free volume results from the increase in the hard segment (polyurethaneurea segment)contents as the number-average molecular weight Mn of the soft segments (polyethylene glycol segments)is the same,and that the increase in domain volume and free volume result from the increase in the Mn of the soft segments when the hard segment content is the same or nearly the same.These results demonstrate that positron annihilation lifetime spectroscopy is a sensitive technique to probe the microdomain structure in polymers.

  20. Studies of defects and defect agglomerates by positron annihilation spectroscopy

    DEFF Research Database (Denmark)

    Eldrup, Morten Mostgaard; Singh, B.N.

    1997-01-01

    A brief introduction to positron annihilation spectroscopy (PAS), and in particular lo its use for defect studies in metals is given. Positrons injected into a metal may become trapped in defects such as vacancies, vacancy clusters, voids, bubbles and dislocations and subsequently annihilate from...... advantages of the use of PAS are pointed out. (C) 1997 Elsevier Science B.V....

  1. Positron annihilation lifetime study of interfaces in ternary polymer blends

    Science.gov (United States)

    Meghala, D.; Ramya, P.; Pasang, T.; Raj, J. M.; Ranganathaiah, C.; Williams, J. F.

    2013-06-01

    A new method based on positron lifetime spectroscopy is developed to characterize individual interfaces in ternary polymer blends and hence determine the composition dependent miscibility level. The method owes its origin to the Kirkwood-Risemann-Zimm (KRZ) model for the evaluation of the hydrodynamic interaction parameters (αij) which was used successfully for a binary blend with a single interface. The model was revised for the present work for ternary polymer blends to account for three interfaces. The efficacy of this method is shown for two ternary blends namely poly(styrene-co-acrylonitrile)/poly (ethylene-co-vinylacetate)/poly(vinyl chloride) (SAN/EVA/PVC) and polycaprolactone /poly(styrene-co-acrylonitrile)/poly(vinyl chloride) (PCL/SAN/PVC) at different compositions. An effective hydrodynamic interaction parameter, αeff, was introduced to predict the overall miscibility of ternary blends.

  2. [Positron annihilation lifetime spectrometry (PALS) and its pharmaceutical applications].

    Science.gov (United States)

    Sebe, István; Szabó, Barnabás; Zelkó, Romána

    2012-01-01

    PALS is one of the most widely used "nuclear probe" techniques for the tracking of the structural characteristics of materials. The method is based on the matter-energy equivalence principle recognized by Einstein: the electrons and positrons as particle-antiparticle pairs disappear in mutual destruction of particles, they annihilate with high-energy gamma-radiation, thus "particle-energy transition" occurs. The properties of the resulting radiation exactly correspond to the relevant properties of the electron and positron preceding the annihilation. Since electrons occur in all types of materials, the phenomenon of positron annihilation can play in any environment; consequently the method can be used for the analysis of each type of materials (crystalline and amorphous, organic and inorganic, biotic and abiotic). The present paper provides an overview of the theoretical physical background, the practical realization and evaluation of methods, their limitations, and summarizes the pharmaceutical applications published in recent years. PMID:22570984

  3. Irradiation-induced defects in ZnO studied by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    We have used positron annihilation spectroscopy to study the point defects induced by 2 MeV electron irradiation (fluence 6 x 1017 cm-2) in single crystal n-type ZnO samples. The positron lifetime measurements have shown that the zinc vacancies in their doubly negative charge state, which act as dominant compensating centers in the as-grown material, are produced in the irradiation and their contribution to the electrical compensation is important. The lifetime measurements reveal also the presence of competing positron traps with low binding energy and lifetime close to that of the bulk lattice. The analysis of the Doppler broadening of the 511 keV annihilation line indicates that these defects can be identified as neutral oxygen vacancies. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Utility of positron annihilation lifetime technique for the assessment of spectroscopic data of some charge-transfer complexes derived from N-(1-Naphthyl)ethylenediamine dihydrochloride.

    Science.gov (United States)

    Refat, Moamen S; Adam, Abdel Majid A; Sharshar, T; Saad, Hosam A; Eldaroti, Hala H

    2014-03-25

    In this work, structural, thermal, morphological, pharmacological screening and positron annihilation lifetime measurements were performed on the interactions between a N-(1-Naphthyl)ethylenediamine dihydrochloride (NEDA·2HCl) donor and three types of acceptors to characterize these CT complexes. The three types of acceptors include π-acceptors (quinol and picric acid), σ-acceptors (iodine) and vacant orbital acceptors (tin(IV) tetrachloride and zinc chloride). The positron annihilation lifetime parameters were found to be dependent on the structure, electronic configuration, the power of acceptors and molecular weight of the CT complexes. The positron annihilation lifetime spectroscopy can be used as a probe for the formation of charge-transfer (CT) complexes. PMID:24291622

  5. Surfaces of colloidal PbSe nanocrystals probed by thin-film positron annihilation spectroscopy

    Directory of Open Access Journals (Sweden)

    L. Chai

    2013-08-01

    Full Text Available Positron annihilation lifetime spectroscopy and positron-electron momentum density (PEMD studies on multilayers of PbSe nanocrystals (NCs, supported by transmission electron microscopy, show that positrons are strongly trapped at NC surfaces, where they provide insight into the surface composition and electronic structure of PbSe NCs. Our analysis indicates abundant annihilation of positrons with Se electrons at the NC surfaces and with O electrons of the oleic ligands bound to Pb ad-atoms at the NC surfaces, which demonstrates that positrons can be used as a sensitive probe to investigate the surface physics and chemistry of nanocrystals inside multilayers. Ab initio electronic structure calculations provide detailed insight in the valence and semi-core electron contributions to the positron-electron momentum density of PbSe. Both lifetime and PEMD are found to correlate with changes in the particle morphology characteristic of partial ligand removal.

  6. Optical and microstructural characterization of porous silicon using photoluminescence, SEM and positron annihilation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Cheung, C K [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Nahid, F [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Cheng, C C [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Beling, C D [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Fung, S [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Ling, C C [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Djurisic, A B [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Pramanik, C [Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata 700032 (India); Saha, H [Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata 700032 (India); Sarkar, C K [Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata 700032 (India)

    2007-12-05

    We have studied the dependence of porous silicon morphology and porosity on fabrication conditions. N-type (100) silicon wafers with resistivity of 2-5 {omega} cm were electrochemically etched at various current densities and anodization times. Surface morphology and the thickness of the samples were examined by scanning electron microscopy (SEM). Detailed information of the porous silicon layer morphology with variation of preparation conditions was obtained by positron annihilation spectroscopy (PAS): the depth-defect profile and open pore interconnectivity on the sample surface has been studied using a slow positron beam. Coincidence Doppler broadening spectroscopy (CDBS) was used to study the chemical environment of the samples. The presence of silicon micropores with diameter varying from 1.37 to 1.51 nm was determined by positron lifetime spectroscopy (PALS). Visible luminescence from the samples was observed, which is considered to be a combination effect of quantum confinement and the effect of Si = O double bond formation near the SiO{sub 2}/Si interface according to the results from photoluminescence (PL) and positron annihilation spectroscopy measurements. The work shows that the study of the positronium formed when a positron is implanted into the porous surface provides valuable information on the pore distribution and open pore interconnectivity, which suggests that positron annihilation spectroscopy is a useful tool in the porous silicon micropores' characterization.

  7. Free volume investigation of imidazolium ionic liquids from positron lifetime spectroscopy

    OpenAIRE

    Yu, Yang; Bejan, Dana; Krause-Rehberg, Reinhard

    2014-01-01

    In this work, relationships between the free volume and various fundamental physical properties (density, surface tension and transport properties) of ionic liquids were investigated. Two imidazolium ionic liquids 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluoro phosphate ([C4MIM][FAP]) and 1-butyl-3-methylimidazolium bis[bis(pentafluoroethyl)phosphinyl]imide ([C4MIM][FPI]) were measured by positron annihilation lifetime spectroscopy (PALS). Changes of the ortho-positronium lifetim...

  8. Positron annihilation spectroscopy applied to silicon-based materials

    CERN Document Server

    Taylor, J W

    2000-01-01

    deposition on silicon substrates has been examined. The systematic correlations observed between the nitrogen content of the films and both the fitted Doppler parameters and the positron diffusion lengths are discussed in detail. Profiling measurements of silicon nitride films deposited on silicon substrates and subsequently implanted with silicon ions at a range of fluences were also performed. For higher implantation doses, damage was seen to extend beyond the film layers and into the silicon substrates. Subsequent annealing of two of the samples was seen to have a significant influence on the nature of the films. Positron annihilation spectroscopy, in conjunction with a variable-energy positron beam, has been employed to probe non-destructively the surface and near-surface regions of a selection of technologically important silicon-based samples. By measuring the Doppler broadening of the 511 keV annihilation lineshape, information on the positrons' microenvironment prior to annihilation may be obtained. T...

  9. Positron annihilation spectroscopy and specific heat study of Neon ion irradiated MgB{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Talapatra, A. [Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata 700064 (India); Bandyopadhyay, S.K. [Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata 700064 (India)], E-mail: skband@veccal.ernet.in; Nambissan, P.M.G. [Saha Institute of Nuclear Physics, 1/AF, Bidhan Nagar, Kolkata 700064 (India); Sen, Pintu [Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata 700064 (India); Ganesan, V. [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore 452017 (India)

    2008-02-25

    Specific heat studies under magnetic field and positron annihilation spectroscopy were carried out on 160 MeV Ne ion irradiated polycrystalline MgB{sub 2} samples. There is an unusual decrease in positron lifetime in the irradiated sample which may be due to neon ion implantation. This was also indicated by change in cell volume. Coincidence Doppler Broadening Spectra of Mg, B, irradiated and unirradiated MgB{sub 2} show that positrons primarily annihilate in boron sublattice in the unirradiated sample whereas there is some similarity of the spectrum of the irradiated sample with that of Mg. There is Mg deficiency in the unirradiated sample whereas predominantly boron vacancies exist in Ne ion irradiated MgB{sub 2} sample. Specific heat measurements show that there is a small increase in electronic part of the specific heat and electron-phonon coupling constant.

  10. Positron annihilation spectroscopy and specific heat study of Neon ion irradiated MgB2

    International Nuclear Information System (INIS)

    Specific heat studies under magnetic field and positron annihilation spectroscopy were carried out on 160 MeV Ne ion irradiated polycrystalline MgB2 samples. There is an unusual decrease in positron lifetime in the irradiated sample which may be due to neon ion implantation. This was also indicated by change in cell volume. Coincidence Doppler Broadening Spectra of Mg, B, irradiated and unirradiated MgB2 show that positrons primarily annihilate in boron sublattice in the unirradiated sample whereas there is some similarity of the spectrum of the irradiated sample with that of Mg. There is Mg deficiency in the unirradiated sample whereas predominantly boron vacancies exist in Ne ion irradiated MgB2 sample. Specific heat measurements show that there is a small increase in electronic part of the specific heat and electron-phonon coupling constant

  11. Defect evolution during annealing of deformed FeSi alloys studied by positron annihilation spectroscopy

    Science.gov (United States)

    Mostafa, K. M.; Cámara, F. González; Petrov, Roumen; Calvillo, P. Rodríguez; De Grave, E.; Segers, D.; Houbaert, Y.

    2011-04-01

    High silicon steel is widely used in electrical appliances. Alloying iron with silicon improves its magnetic performance. A silicon content up to 6.5 wt. % gives excellent magnetic properties such as high saturation magnetization, near zero magnetostriction and low iron loss in high frequencies. Their workability is greatly reduced by the appearance of ordered structures, namely B2 and D03, as soon as the Si content becomes higher than 3.5 wt. %. This limits the mass production by conventional rolling to this maximum percentage of Si. In this work a series of FeSi (7.5 wt. % Si) samples with different degrees of deformation are investigated with positron annihilation spectroscopy and optical microscopy (OM). The influence of annealing on the concentration of defects of different deformed FeSi alloys has been investigated by positron annihilation lifetime spectroscopy and Doppler broadening of the annihilation radiation. OM is used to investigate the microstructure of deformed samples before and after annealing. The values of the S parameter present a decrease for all studied FeSi alloys with the increase of the annealing temperature, being attributed to a decrease of the concentration of defects. A sudden increase of the S-parameter value at 600 °C was observed for all samples, which could be related to the change of the ordering of the FeSi alloys at that temperature. At 700 °C, the values of the S parameter decreased drastically and starting from 900 °C, they became constant. The microstructures of the alloys, investigated by OM, show that recrystallization is completed at 900 °C and the samples are mainly free of defects, which is in agreement with the positron annihilation lifetime data.

  12. Positron annihilation lifetime in Fe-Rh alloys deformed by high-speed compression

    Energy Technology Data Exchange (ETDEWEB)

    Fukuzumi, M. [Graduate School of Engineering, Osaka Prefecture Univ., Sakai (Japan); Hori, F.; Oshima, R. [Research Inst. for Advanced Science and Technology, Osaka Prefecture Univ., Sakai (Japan); Komatsu, M.; Kiritani, M. [Research Center for Ultra-High-Speed Plastic Deformation, Hiroshima Inst. of Tech., Saekiku (Japan)

    2001-07-01

    In order to examine the role of structural vacancies in the stress-induced phase transitions of B2-type FeRh alloys, Fe-40, 45 and 50 at%Rh specimens were deformed at room temperature with a high-speed compression machine and were studied by X-ray diffractometry (XRD) and positron annihilation measurements. It was found from the positron lifetime results that vacancies or vacancy clusters were introduced into the alloy by deformation. The longer lifetime ({tau}{sub 2}) components were changed with the deformation momenta and Rh concentrations. In the case of Fe-50 at%Rh, they were 188 ps and 254 ps after deformation with small or large momenta, respectively. Taking the X-ray results into consideration, it is concluded that an atom movement mechanism forming large vacancy clusters is associated with the B2-A1 transition. The short lifetime ({tau}{sub 1}) of the alloy is accounted for by bulk annihilation in the transformed phases and a high density of dislocations. (orig.)

  13. Positron annihilation spectroscopy study on annealing effect of CuO nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Jianjian; Wang, Jiaheng; Yang, Wei; Zhu, Zhejie; Wu, Yichu, E-mail: ycwu@whu.edu.cn [School of Physics and Technology, Hubei Key Laboratory of Nuclear Solid State Physics, Wuhan University (WHU), Wuhan (China)

    2016-03-15

    The microstructure and defects of CuO nanoparticles under isochronal annealing were investigated by positron annihilation spectroscopy (PAS), X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD and SEM results indicated that the average grain sizes of CuO nanoparticles grew slowly below 800 °C, and then increased rapidly with the annealing temperature from 800 to 1000 °C. Positron lifetime analysis exhibited that positrons were mainly annihilated in mono-vacancies (V{sub Cu}, V{sub O}) and vacancy clusters when annealing from 200 to 800 °C. Furthermore, W-S plot of Doppler broadening spectra at different annealing temperatures found that the (W, S) points distributed on two different defect species, which suggested that V{sup −}{sub Cu} - V{sup +}{sub O} complexes were produced when the grains grew to bigger size after annealing above 800 °C, and positrons might annihilate at these complexes. (author)

  14. Free-volume mean sizes of polymers probed by positron annihilation spectroscopy: a correlation of results obtained by PAL and by ACAR methods

    International Nuclear Information System (INIS)

    Positron annihilation spectroscopy (PAS) has been developed to analyze the microstructure of polymers. Both positron annihilation lifetime (PAL) and angular correlation of positron annihilation radiation (ACAR) measurements give direct information about the mean hole sizes of free-volume holes in amorhpous materials. Parallel experiments of PAL and ACAR have been performed in an epoxy polymer as a function of temperature. The free-volume mean hole radii ranging from 2.3 to 3.2 A are obtained. The results obtained by PAL and ACAR agree with each other very well. A correlation of mean free-volume hole sizes obtained by these two methods is established. (orig.)

  15. Estimation of free volumes of elastomer (polymerized siloxane rubber) by positron annihilation lifetime techniques

    International Nuclear Information System (INIS)

    In order to correlate size and content of free volumes present in amorphous region of these polymers and the mechanical and dynamical properties of elastomers, positron annihilation peak profile analysis and lifetime measurements were carried out from 30 K up to melting temperature for several poly(methyl-vinyl-siloxane) containing silica glass powders. S parameter and mean lifetime were adopted as a perspective measure for the rough estimation of the multiplied size and content of free volumes and proved that these parameters worked as a simple measure of the over-all free volumes. The free volume diameters of poly(methyl-vinyl-siloxane) (KE-931-B and KE-931) and poly(methyl-vinyl-siloxane) (KE-951 and KE-971) increased with the elevation of temperature from about 0.63 nm (30 K) to about 0.82 nm (Tm: 225 K) and from about 0.52 nm (30 K) to about 0.80 nm (Tm: 225 K), respectively. The free volume content (I3) of poly(methyl-vinyl-siloxane) (KE-951 and KE-971) is constant from 30 K (20.5% and 26.5%) to 150 K (Tg) and increased to about 29% and 37% at melting point (225 K), respectively, whereas those of poly(methyl-vinyl-siloxane) (KE-931-B and KE-931) increased from 28% and 20.5% (30 K) to 54% and 43% (225 K) monotonously. The presence of pseudo cross-linkage among silanol groups at the interface of elastomers and silica powders was suggested because both size and content of free volume were reduced by the increase of silica powder concentration in the elastomers. The Laplace inversion was applied to positron annihilation decay curve and obtained size distribution of free volume. (author)

  16. 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.

  17. Positron-annihilation spectroscopy of defects in metals: an assessment

    International Nuclear Information System (INIS)

    Positron annihilation spectroscopy (PAS) has made significant contributions to our knowledge regarding lattice defects in metals in two areas: (i) the determination of atomic defect properties, particularly those of monovacancies, and (ii) the monitoring and characterization of vacancy-like microstructure development during post-irradiation of post-quench annealing. The application of PAS to the study of defects in metals is selectively reviewed and critically assessed within the context of other available techniques for such investigations. Possibilities for using the positron as a localized probe of the structure of atomic defects are discussed. Finally, the present status and future potential of PAS as a tool for the study of defects in metals are considered relative to other available techniques. 92 references, 20 figures

  18. Influence of high pressure torsion on precipitation in Al-Cu-Mg alloys studied by positron annihilation spectroscopy.

    Energy Technology Data Exchange (ETDEWEB)

    Lechner, Wolfgang; Puff, Werner; Wuerschum, Roland [Institut fuer Materialphysik, Technische Universitaet Graz, Petersgasse 16, 8010 Graz (Austria); Zehetbauer, Michael; Schafler, Erhard [Fakultaet fuer Physik, Forschungsgruppe Physik Nanostrukturierter Materialien, Universitaet Wien, Boltzmanngasse 5, Universitaet Wien, 1090 Wien (Austria)

    2008-07-01

    High pressure torsion (HPT) may open up an efficient way to refine precipations of supersaturated solutions. In the present work, the influence of HPT on the precipitation in Al-Cu-Mg alloys and on the evolution of the precipitates with subsequent annealing is studied by positron annihilation spectroscopy. HPT is observed to give rise to a fragmentation of metastable nanoscaled precipitates which have formed upon pre-annealing at 200 C (3 hours). Positron lifetime spectroscopy in combination with coincident Doppler broadening of the positron-electron annihilation enables a specific and chemical sensitive distinction between interfacial vacancy-type defects associated with precipitates and the vacancy-type lattice defects formed upon high pressure torsion. Different aging behaviour is observed for undeformed and HPT-deformed samples.

  19. Gamma-induced positron annihilation spectroscopy and application to radiation-damaged alloys

    Science.gov (United States)

    Wells, D. P.; Hunt, A. W.; Tchelidze, L.; Kumar, J.; Smith, K.; Thompson, S.; Selim, F.; Williams, J.; Harmon, J. F.; Maloy, S.; Roy, A.

    2006-06-01

    Radiation damage and other defect studies of materials are limited to thin samples because of inherent limitations of well-established techniques such as diffraction methods and traditional positron annihilation spectroscopy (PAS) [P. Hautojarvi, et al., Positrons in Solids, Springer, Berlin, 1979, K.G. Lynn, et al., Appl. Phys. Lett. 47 (1985) 239]. This limitation has greatly hampered industrial and in-situ applications. ISU has developed new methods that use pair-production to produce positrons throughout the volume of thick samples [F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 192 (2002) 197, F.A. Selim, D.P. Wells, et al., Nucl. Instru. Meth. A 495 (2002) 154, F.A. Selim, et al., J. Rad. Phys. Chem. 68 (2004) 427, F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 241 (2005) 253, A.W. Hunt, D.P. Wells, et al., Nucl. Instr. and Meth. B. 241 (2005) 262]. Unlike prior work at other laboratories that use bremsstrahlung beams to create positron beams (via pair-production) that are then directed at a sample of interest, we produce electron-positron pairs directly in samples of interest, and eliminate the intermediate step of a positron beam and its attendant penetrability limitations. Our methods include accelerator-based bremsstrahlung-induced pair-production in the sample for positron annihilation energy spectroscopy measurements (PAES), coincident proton-capture gamma-rays (where one of the gammas is used for pair-production in the sample) for positron annihilation lifetime spectroscopy (PALS), or photo-nuclear activation of samples for either type of measurement. The positrons subsequently annihilate with sample electrons, emitting coincident 511 keV gamma-rays [F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 192 (2002) 197, F.A. Selim, D.P. Wells, et al., Nucl. Instru. Meth. A 495 (2002) 154, F.A. Selim, et al., J. Rad. Phys. Chem. 68 (2004) 427, F.A. Selim, D.P. Wells, et al., Nucl. Instr. and Meth. B 241 (2005) 253, A.W. Hunt, D

  20. 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......(24) n/m(2) (E > 0.1 MeV), corresponding to displacement damage levels in the range from 7.2 x 10(-5) to 2.8 x 10(-1) displacements per atom (dpa). A high density of submicroscopic cavities was observed in the neutron-irradiated Mo and their size distributions were estimated. Cavities were detected even...

  1. Study on positron annihilation lifetime spectrum of polysilicone rubber after proton radiation

    International Nuclear Information System (INIS)

    The positron annihilation lifetime spectrum (PALS) method was employed to study the effect of proton radiation on microstructure of the space grade KH-L-Y polysilicone rubber. The results show that both τ3 of I3 of the longest lifetime component and the free volume Vf decrease with the increasing of the radiation fluence at the beginning and become level off after 1015 cm-2 radiation fluence. The proton radiation causes decrease in both the free volume of polysilicone rubber, and the distance between the molecules when the radiation fluence is less than 1015 cm-2. However, the proton radiation makes the free volume of silicon rubber increase when the radiation fluence is greater than 1015 cm-2. Both the experimental results of the cross-linking density and DMA indicate that the cross-linking effect due to the proton radiation is predominant in the range of small proton radiation fluence, while the radiation degradation become superior when the proton radiation fluence is larger

  2. Lifetime positron annihilation spectroscopy and photo-inactivated bacteria

    CERN Document Server

    El'nikova, L V

    2009-01-01

    Combined positron and infrared irradiations in the applications of photodynamical therapy (PDT) are studied analytically. Objectives and goals of PDT are killing or irreversible oxidative damage of pathogenic cells, or rather their cell walls, cell membranes, peptides, and nucleic acids by photo-activated oxygen of photosentizer injected into the target cell during light irradiation. On the trial system "Escherichia coli--T$_4$MPyP" the main positron interactions with media are evaluated to validate the perspectives of that use.

  3. Gas Permeations Studied by Positron Annihilation

    Science.gov (United States)

    Yuan, Jen-Pwu; Cao, Huimin; Jean, X.; Yang, Y. C.

    1997-03-01

    The hole volumes and fractions of PC and PET polymers are measured by positron annihilation lifetime spectroscopy. Direct correlations between the measured hole properties and gas permeabilities are observed. Applications of positron annihilation spectroscopy to study gas transport and separation of polymeric materials will be discussed.

  4. Defect structures of F82H irradiated at SINQ using positron annihilation spectroscopy

    Science.gov (United States)

    Sato, K.; Ikemura, K.; Krsjak, V.; Vieh, C.; Brun, R.; Xu, Q.; Yoshiie, T.; Dai, Y.

    2016-01-01

    The growth process of He-filled vacancy clusters during annealing was investigated with positron annihilation lifetime spectroscopy and coincidence Doppler broadening (CDB) measurements. The reduced activation ferritic/martensitic steel F82H was irradiated with high-energy protons and spallation neutrons. The He-filled vacancy clusters absorbed more He atoms when annealed below 673 K, and the long and mean positron lifetimes decreased. When annealed above 873 K, the vacancies (V)-Hem or Vn-Hem complexes dissociated (n and m are the number of vacancies and He atoms, respectively). The He-filled vacancy clusters then absorb these dissociated vacancies and He atoms. Therefore, the size of the He-filled vacancy clusters increased, and the He-to-vacancy ratio decreased. These annealing-induced phenomena increased the long positron lifetime in addition to the higher positron trapping rates of the He-filled vacancy clusters. By comparing electron-irradiated samples that did not contain He atoms to the proton- and neutron-irradiated samples containing He atoms, the effects of He atoms on the CDB ratio curves were studied. The results agreed with the previous study of He-ion-implanted Fe-Cr alloys.

  5. Study of microstructure of modified polyethylene films with acrylic and methacrylic acids, by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Low density polyethylene (LDPE) was preirradiated with γ -rays and after some contact time with the monomers AA and MAA, suitable graft copolymers were obtained at different grafting grades. After their physical-chemistry characterization, the copolymers were studied using the Positron Annihilation Lifetime Spectroscopy (PALS). Owing to its sensitive and non-destructive nature PALS has proven to be very useful in studying free-volume properties -at the molecular level- during phase transitions in molecular solids, such as the graft copolymers of LDPE/AA and LDPE/MAA. Using PALS it was possible to detect the changes in the melting point of the LDPE as a function of the grafting degree, obtaining thus, valuable information about the microstructure of this kind of copolymers. The increase in the values of the o-Ps lifetime, was interpreted as suggesting that the melting transition is followed by a free-volume cavity expansion as the temperature increased. The o-Ps intensity of formation behavior is in accord with the distortions occurring in the electronic density surrounding the o-Ps as well as the changes in the number of cavities available to the formation of o-Ps. (Author)

  6. Positron annihilation spectroscopy as a tool to develop self healing in aluminium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Hautakangas, S.; Schut, H. [Faculty of Applied Physics, section NPM2, Delft University of Technology, Mekelweg 15, 2629 JB, Delft (Netherlands); Zwaag, S. van der; Rivera Diaz del Castillo, P.E.J. [Faculty of Aerospace Engineering, Section Fundamentals of Advanced Materials, Delft University of Technology, Kluyverweg 1, 2629 HS Delft (Netherlands); Dijk, N.H. van [Faculty of Applied Physics, Section FAME, Delft University of Technology, Mekelweg 15, 2629 JB, Delft (Netherlands)

    2007-07-01

    Positron lifetime and Doppler broadening spectroscopy have been applied to probe the free volume generation (vacancies, dislocations and nano-cracks) during plastic deformation of a commercial aluminium AA2024 (T3) alloy. Aim of the total program is to study how solute atoms can be driven to the areas where initial cracking may occur in order to prevent the failure of the specimen. The phenomenon of closing the nano-crack is called Self Healing, and can provide extra strength and ductility to the alloy under some loading conditions. Plastic deformation of over-aged aluminum alloy at room temperature increases the average positron lifetime from initial value of 190 ps to 203 ps. The low momentum parameter S increases in agreement with the increase of open volume defects. The elastic deformation of the sample does not have a recordable effect on the positron annihilation data. It is also shown that the induced damage does not recover after loading the sample, i.e. the AA2024 in the T3 state is non self healing material, as expected, providing important first state result in the research of self healing Al alloys. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Aspects of meson spectroscopy with N N annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Dover, C.B.

    1990-04-01

    We focus on the potentialities of nucleon-antinucleon ({bar N}N) annihilation as a means of producing new mesonic states. The case for the existence of quasinuclear {bar N}N bound states is discussed in detail. Strong evidence for a 2{sup ++}(0{sup +}) state of this type has been obtained at LEAR in annihilation from the p-wave (L = 1) {bar N}N system, in support of earlier sightings of this object in L = 0 annihilation at Brookhaven. In the next generation of LEAR experiments, the emphasis shifts to the search for mesons containing dynamical excitations of the gluonic field, namely glueballs and hybrids (Q{bar Q}g). We discuss some features of the masses, decay branching ratios and production mechanisms for these states, and suggest particular {bar N}N annihilation channels which are optimal for their discovery. 59 refs., 15 figs.

  8. Miscibility and crystallization behavior of poly (3-hydroxybutyrate) and poly (ethylene glycol) blends studied by positron annihilation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Hady, E E; Abdel-Hamed, M O; Hammam, A M, E-mail: esamhady@yahoo.com [Physics Department, Faculty of Science, Minia University, Minia (Egypt)

    2011-01-01

    Positron annihilation Lifetime (PAL) spectroscopy has been used to study the effect of PEG concentrations on the free volume properties of PHB. The data revealed that the ortho-positronium (o-Ps) lifetime {tau}{sub Ps} increases with 20% increase in concentration, decrease as the concentration increases to 40%, then rapid increase at 50% concentration of PEG. The o-Ps intensity, I{sub 3}, shows a linear dependence as the concentration increases with a discontinuity at 20% concentration of PEG. Furthermore, the results presented and discussed in this work show that the PHB and PEG are miscible up to 40% of PEG but greater than 40%, the blend is immiscible. In addition, the mechanical properties of PHB are well improved by the addition of PEG with a low concentration up to 20%, while at higher concentration the blend becomes waxy.

  9. A study of dye molecule diffusion in human hair using positron lifetime spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Chandrashekara, M.N.; Ranganathaiah, C. [Department of Studies in Physics, University of Mysore, Manasagangotri, Mysore (India)

    2009-11-15

    The diffusion behavior of a commercial permanent liquid hair dye in human hair has been investigated using Positron Annihilation Lifetime Spectroscopy (PALS) and gravimetric sorption method. The o-Ps lifetime parameters {tau}{sub 3} and I{sub 3} decrease rapidly during the first 60 minutes of sorption time. This is understood in terms of dye molecules filling the free volume cavities in hair. The sorption results suggest that the dye molecule diffusion is essentially a Fickian process. In the latter part of the sorption, where positron parameters remain almost constant, mass increase might be due to surface adhesion. These two stages of sorption are well separated by the positron technique. The study shows that the free volume theory and positron technique, widely used in polymer research, may expediently be used to understand hair properties, more importantly diffusion of dye molecules. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Annealing behaviour of reactor pressure-vessel steels studied by positron-annihilation spectroscopy, Mössbauer spectroscopy and transmission electron microscopy

    Science.gov (United States)

    Slugeǹ, V.; Segers, D.; de Bakker, P. M. A.; De Grave, E.; Magula, V.; Van Hoecke, T.; Van Waeyenberge, B.

    The annealing behaviour of commonly used reactor pressure-vessel steels was studied using positron-annihilation spectroscopy (PAS) (lifetime and Doppler broadening techniques), transmission Mössbauer spectroscopy (MS), integral low-energy electron MS (ILEEMS) and transmission electron microscopy (TEM). The results of these methods applied to different types of steels are discussed. Some significant differences in the experimental results are observed between the Russian (3 types) and Western Europe (5 types) steels and between individual specimens within these two groups. All specimens were annealed in vacuum and studied after this thermal treatment. It was confirmed that the heat affected zone (HAZ) is the most sensitive region for thermal and neutron irradiation-induced embrittlement in the reactor. Positron-annihilation lifetime measurements on HAZ specimens annealed at successively higher temperatures show the drastic increase in the vacancy-type defect formation between 525°C and 600°C. Therefore these specimens were selected for further detailed studies by TEM.

  11. Positron annihilation lifetime characterization of oxygen ion irradiated rutile TiO2

    Science.gov (United States)

    Luitel, Homnath; Sarkar, A.; Chakrabarti, Mahuya; Chattopadhyay, S.; Asokan, K.; Sanyal, D.

    2016-07-01

    Ferromagnetic ordering at room temperature has been induced in rutile phase of TiO2 polycrystalline sample by O ion irradiation. 96 MeV O ion induced defects in rutile TiO2 sample has been characterized by positron annihilation spectroscopic techniques. Positron annihilation results indicate the formation of cation vacancy (VTi, Ti vacancy) in these irradiated TiO2 samples. Ab initio density functional theoretical calculations indicate that in TiO2 magnetic moment can be induced either by creating Ti or O vacancies.

  12. A study of annealing stages in commercial pure Cu using mechanical measurements and positron annihilation lifetime technique

    International Nuclear Information System (INIS)

    Mechanical property measurements, positron annihilation lifetime (PAL) measurements and metallographic observations, have been performed to study the isochronal annealing of commercial pure Cu in the temperature range from 25 up to 850 deg. C. A positive correlation has been found between positron lifetime (τ) and both the tensile strain (ΔL/L0) and Vicker's microhardness (Hv). This correlation shows the presence of three annealing stages in commercial pure Cu which are attributed to recovery, recrystallization, and grain growth. These different stages were studied by both pure tensile and combined torsion-tension deformation for samples pre-annealed at the different annealing stages. Plastic instability behavior is observed in the case of combined torsion-tension deformation. It is observed that the onset and disappearance of this instability depend on some parameters such as mode of deformation, applied axial tensile stress and pre-annealing temperature. The activation energy is found to be 0.5 eV for the recovery stage which is attributed to the energy for dislocation annihilation by glide or cross-slip. The recrystallization stage is a multi-energy stage (1.35, 1.6, and 1.71 eV) which is attributed to lattice diffusion or boundary diffusion.

  13. Combined fiber probe for fluorescence lifetime and Raman spectroscopy

    Science.gov (United States)

    Dochow, Sebastian; Ma, Dinglong; Latka, Ines; Bocklitz, Thomas; Hartl, Brad; Bec, Julien; Fatakdawala, Hussain; Marple, Eric; Urmey, Kirk; Wachsmann-Hogiu, Sebastian; Schmitt, Michael; Marcu, Laura; Popp, Jürgen

    2016-01-01

    In this contribution we present a dual modality fiber optic probe combining fluorescence lifetime imaging (FLIm) and Raman spectroscopy for in vivo endoscopic applications. The presented multi-spectroscopy probe enables efficient excitation and collection of fluorescence lifetime signals for FLIm in the UV/visible wavelength region, as well as of Raman spectra in the near-IR for simultaneous Raman/FLIm imaging. The probe was characterized in terms of its lateral resolution and distance dependency of the Raman and FLIm signals. In addition, the feasibility of the probe for in vivo FLIm and Raman spectral characterization of tissue was demonstrated. PMID:26093843

  14. Life science research using positron annihilation spectroscopy: UV-irradiated mouse skin

    Energy Technology Data Exchange (ETDEWEB)

    Jean, Y.C. [Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110-2499 (United States)]. E-mail: jeany@umkc.edu; Chen, Hongmin [Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110-2499 (United States); Liu Guang [Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110-2499 (United States); Gadzia, Joseph E. [Dermatology, Department of Internal Medicine, University of Kansas Medical Center, Kansas City, KS 66103 (United States); Kansas Medical Clinic, Topeka, KS 66614 (United States)

    2007-02-15

    Positron annihilation spectroscopy (PAS) is applied to study mouse skin under different UV irradiations as a function of positron incident energy (0-30 keV). Significant variations in the depth profile of S parameter are observed in a period of hours and of days for UVA and UVB exposures, respectively. The high sensitivity of positron annihilation signals responding to UV irradiation shows that PAS may be developed as a new noninvasive technique for the detection of molecular damage in life science research.

  15. Determinations of phase transitions in nylon 6-12, nylon-6, polyvinyl chloride and polyethylene terephthalate by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Positron annihilation lifetime spectroscopy (PALS) was used to investigate the phase transitions, mainly the glass transition, of poly(vinyl chloride) (PVC), Nylon-6,12, Nylon-6, poly(ethylene terephthalate) during the thermal treatment of these polymers. The longest lived component lifetime and intensity, indicative of ortho-Positronium pick-off exhibit thermal dependencies that can be attributed to the anticipated free volume changes associated with structural transitions. Positron lifetime measurements were performed using an E G and G Ortec standard fast-fast coincidence system. Three spectra were collected at each temperature, each consisting of a peak height of approximately 25000 counts. The resulting spectra were consistently modeled with a three component fit using the computer program PATFIT. For nylon-6,12, nylon-6, PVC systems three transitions were obtained in both tau-3 and I-3 as a function of temperature. Changes in the slope of the curves appear for both parameters, these could be attributed to Tg1, Tg2 and Tc, respectively. In the case of PET analysis two transitions were obtained as is shown by the variations of tau-3 as a function of the heating temperature. These transitions can be attributed to Tg1 and Tg2. Similar changes can be observed for I-3 in relation with temperature. Glass transition behavior was evident in the lifetime behavior of polymers. Increases in slope of the lifetime temperature plots were interpreted free-volume cavity expansion as temperature is increased. The intensity responses in the vicinity of the upper glass transition were consistent with the association of this transition with the reduction of crystalline constraint of segmental mobility in the amorphous phase. (Author)

  16. Early Amyloidogenic Oligomerization Studied through Fluorescence Lifetime Correlation Spectroscopy

    Directory of Open Access Journals (Sweden)

    Angel Orte

    2012-07-01

    Full Text Available Amyloidogenic protein aggregation is a persistent biomedical problem. Despite active research in disease-related aggregation, the need for multidisciplinary approaches to the problem is evident. Recent advances in single-molecule fluorescence spectroscopy are valuable for examining heterogenic biomolecular systems. In this work, we have explored the initial stages of amyloidogenic aggregation by employing fluorescence lifetime correlation spectroscopy (FLCS, an advanced modification of conventional fluorescence correlation spectroscopy (FCS that utilizes time-resolved information. FLCS provides size distributions and kinetics for the oligomer growth of the SH3 domain of α-spectrin, whose N47A mutant forms amyloid fibrils at pH 3.2 and 37 °C in the presence of salt. The combination of FCS with additional fluorescence lifetime information provides an exciting approach to focus on the initial aggregation stages, allowing a better understanding of the fibrillization process, by providing multidimensional information, valuable in combination with other conventional methodologies.

  17. Free volume investigation of imidazolium ionic liquids from positron lifetime spectroscopy

    CERN Document Server

    Yu, Yang; Krause-Rehberg, Reinhard

    2014-01-01

    In this work, relationships between the free volume and various fundamental physical properties (density, surface tension and transport properties) of ionic liquids were investigated. Two imidazolium ionic liquids 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluoro phosphate ([C4MIM][FAP]) and 1-butyl-3-methylimidazolium bis[bis(pentafluoroethyl)phosphinyl]imide ([C4MIM][FPI]) were measured by positron annihilation lifetime spectroscopy (PALS). Changes of the ortho-positronium lifetime (o-Ps) with different states (amorphous and crystalline) were depicted as completely as possible. The mean local free (hole) volume was calculated from the o-Ps lifetime in amorphous state for the samples. Comparison between and specific volume obtained from the temperature dependent mass density gave the specific hole densities Nf and the occupied volumes Vocc. Thermal expansion of hole volume was compared with molecular volume VM of [C4MIM][FAP] and [C4MIM][FPI] as well as five other ionic liquids from our previous ...

  18. Study of PRIMAVERA steel samples by a positron annihilation spectroscopy technique

    Energy Technology Data Exchange (ETDEWEB)

    Grafutin, V.; Ilyukhina, O. [Institute of Theoretical and Experimental Physics, B. Cheremushkinskaya 25, 117218 Moscow (Russian Federation); Krsjak, V., E-mail: vladimir.krsjak@ec.europa.e [European Commission, Joint Research Centre, Institute for Energy, P.O. Box 2, 1755 ZG Petten (Netherlands); Burcl, R.; Haehner, P. [European Commission, Joint Research Centre, Institute for Energy, P.O. Box 2, 1755 ZG Petten (Netherlands); Erak, D. [RRC Kurchatov Institute, Kurchatov Square 1, 123182 Moscow (Russian Federation); Zeman, A. [European Commission, Joint Research Centre, Institute for Energy, P.O. Box 2, 1755 ZG Petten (Netherlands)

    2010-11-15

    In the present article, a positron annihilation spectroscopy investigation of VVER-440/230 weld materials is discussed. Important characteristics of metals such as Fermi energy, concentration of electrons in the conduction band, size and concentration of defects were experimentally determined for three model materials with higher level of copper (0.16 wt.%) and phosphorus (0.027-0.038 wt.%). The impact of neutron irradiation and subsequent annealing on crystal lattice parameters was investigated. The experiments with the angular correlation of positron annihilation radiation (ACAR) complement the published positron annihilation spectroscopy (PAS) studies of the radiation treated VVER materials as well as previous experiments on PRIMAVERA materials. The availability of the experimental reactor to prepare strong {sup 64}Cu positron sources provided for unique experimental conditions, such as good resolution of spectra (0.4 mrad) and reasonable short time of measurement (36 h). The present paper aims to contribute to further understanding of RPV (reactor pressure vessel) steels behaviour under irradiation conditions as well as annealing recovery procedures, which have already been applied at several VVER NPP units in Europe.

  19. X-ray photoelectron spectroscopy and positron annihilation spectroscopy analysis of surfactant affected FePt spintronic films

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Chun, E-mail: fengchun@ustb.edu.cn [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Li, Xujing; Liu, Fen; Wang, Qiang [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Yang, Meiyin [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); The Center for Micromagnetics and Information Technologies (MINT) and Department of Electrical and Computer Engineering, University of Minnesota, 200 Union St SE, Minneapolis, MN 55455 (United States); Zhao, Chongjun [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Gong, Kui [Centre for the Physics of Materials and Department of Physics, McGill University, Montreal, Quebec, H3A2T8 Canada (Canada); Zhang, Peng; Wang, Bao-Yi; Cao, Xing-Zhong [Key Laboratory of Nuclear Analysis Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Yu, Guanghua [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China)

    2014-07-01

    This paper reports the effects of surfactant Bi atomic diffusion on the microstructure evolution and resulted property manipulation in FePt spintronic films by the quantitative studies of X-ray photoelectron spectroscopy and positron annihilation spectroscopy. The defect density in the FePt layer, which was tunable by varying the thermal treatment temperatures, was found to be remarkably enhanced correlated with the Bi atomic diffusion behavior. The observed defect density evolution substantially favors Fe(Pt) atomic migrations and lowers the energy barrier for atomic ordering transition, resulting in a great improvement of hard magnet property of the films.

  20. Evaluation of actinic cheilitis using fluorescence lifetime spectroscopy

    Science.gov (United States)

    Saito Nogueira, Marcelo; Cosci, Alessandro; Pratavieira, Sebastião.; Takahama, Ademar; Souza Azevedo, Rebeca; Kurachi, Cristina

    2016-03-01

    Actinic cheilitis is a potentially malignant disorder that mostly affects the vermilion border of the lower lip and can lead to squamous cell carcinoma. Because of its heterogeneous clinical aspect, it is difficult to indicate representative biopsy area. Late diagnosis is a limiting factor of therapeutic possibilities available to treat oral cancer. The diagnosis of actinic cheilitis is mainly based on clinical and histopathological analysis and it is a time consuming procedure to get the results. Information about the organization and chemical composition of the tissues can be obtained using fluorescence lifetime spectroscopy techniques without the need for biopsy. The main targeted fluorophores are NADH (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide), which have free and bound states, each one with different average lifetimes. The average lifetimes for free and bound NADH and FAD change according to tissue metabolic alterations and allow a quick and non-invasive clinical investigation of injuries and to help clinicians with the early diagnosis of actinic cheilitis. This study aims to evaluate the fluorescence lifetime parameters at the discrimination of three degrees of epithelial dysplasia, the most important predictor of malignant development, described in up to 100% of actinic cheilitis cases.

  1. Prediction of free-volume-type correlations in glassy chalcogenides from positron annihilation lifetime measurements

    International Nuclear Information System (INIS)

    Highlights: • Decisive role of specific chemical environment in free-volume correlations in glass. • Realistic free volumes in As–S/Se glass are defined by newly modified τ2-R formula. • Overestimated void sizes in chalcogenide glass as compared with molecular polymers. - Abstract: A newly modified correlation equation between defect-related positron lifetime determined within two-state trapping model and radius of corresponding free-volume-type defects was proposed to describe compositional variations in atomic-deficient structure of covalent-bonded chalcogenides like binary As–S/Se glasses. Specific chemical environment of free-volume voids around neighboring network-forming polyhedrons was shown to play a decisive role in this correlation, leading to systematically enhanced volumes in comparison with typical molecular substrates, such as polymers

  2. Prediction of free-volume-type correlations in glassy chalcogenides from positron annihilation lifetime measurements

    Energy Technology Data Exchange (ETDEWEB)

    Shpotyuk, O., E-mail: shpotyuk@novas.lviv.ua [Institute of Materials of SRC “Carat”, 212 Stryjska Str., Lviv 79031 (Ukraine); Institute of Physics of Jan Dlugosz University, 13/15 al. Armii Krajowej, Czestcochowa 42200 (Poland); Ingram, A. [Opole University of Technology, 75 Ozimska Str., Opole 45370 (Poland); Shpotyuk, M. [Institute of Materials of SRC “Carat”, 212 Stryjska Str., Lviv 79031 (Ukraine); Lviv Polytechnic National University, 12 Bandery Str., Lviv 79013 (Ukraine); Filipecki, J. [Institute of Physics of Jan Dlugosz University, 13/15 al. Armii Krajowej, Czestcochowa 42200 (Poland)

    2014-11-01

    Highlights: • Decisive role of specific chemical environment in free-volume correlations in glass. • Realistic free volumes in As–S/Se glass are defined by newly modified τ{sub 2}-R formula. • Overestimated void sizes in chalcogenide glass as compared with molecular polymers. - Abstract: A newly modified correlation equation between defect-related positron lifetime determined within two-state trapping model and radius of corresponding free-volume-type defects was proposed to describe compositional variations in atomic-deficient structure of covalent-bonded chalcogenides like binary As–S/Se glasses. Specific chemical environment of free-volume voids around neighboring network-forming polyhedrons was shown to play a decisive role in this correlation, leading to systematically enhanced volumes in comparison with typical molecular substrates, such as polymers.

  3. Application of fast-digitizer card Acqiris DP-240 in positron lifetime spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Petriska, Martin; Slugen, Vladimir; Krsjak, Vladimir; Sojak, Stanislav [Slovak University of Technology, FEI, Bratislava (Slovakia); Zeman, Andrej; Debarberis, Luigi [European Commission, Joint Research Centre, Institute for Energy, Petten (Netherlands)

    2009-11-15

    Based on the available knowledge base in positron annihilation measurements, new software for digital positron lifetime spectrometry has been designed within the frame of joint activity between STU Bratislava and JRC Petten. The tests of the new positron digital-life time setup have been carried out. Detectors with BaF{sub 2} scintillators and fast-dynode outputs were chosen for such studies. As the digitiser unit, the card Acqiris DP240 was fully tested. Originally, start and stop timing signals were sampled to digital waveforms separately at a rate of 1 GS/s in 8 bit resolution. However, due to limited quality of collected waveforms which significantly affected post-processing of data, the joined delayed channel mode with 2 GS/s sampling rate was applied for further studies. The full setup was benchmarked by a series of calibration measurements of two high purity materials, specifically Si and Ni. The inter-comparison of conventional analogue- and digital-based processing are discussed in detail. Further, the optimisation of main parameters for waveform-processing are analysed too. Such a new approach in the digital life-time spectroscopy will help to improve the resolution of existing methodology which might enhance the capabilities of this technique for further applications, especially in materials science. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Characterization of point defects in CdTe by positron annihilation spectroscopy

    Science.gov (United States)

    Elsharkawy, M. R. M.; Kanda, G. S.; Abdel-Hady, E. E.; Keeble, D. J.

    2016-06-01

    Positron lifetime measurements on CdTe 0.15% Zn-doped by weight are presented, trapping to monovacancy defects is observed. At low temperatures, localization at shallow binding energy positron traps dominates. To aid defect identification density functional theory, calculated positron lifetimes and momentum distributions are obtained using relaxed geometry configurations of the monovacancy defects and the Te antisite. These calculations provide evidence that combined positron lifetime and coincidence Doppler spectroscopy measurements have the capability to identify neutral or negative charge states of the monovacancies, the Te antisite, A-centers, and divacancy defects in CdTe.

  5. Positron annihilation spectroscopy: a new frontier for understanding nanoparticle-loaded polymer brushes

    Science.gov (United States)

    Panzarasa, Guido; Aghion, Stefano; Soliveri, Guido; Consolati, Giovanni; Ferragut, Rafael

    2016-01-01

    Nanoparticle-loaded polymer brushes are powerful tools for the development of innovative devices. However, their characterization is challenging and arrays of different techniques are typically required to gain sufficient insight. Here we demonstrate for the first time the suitability of positron annihilation spectroscopy (PAS) to investigate, with unprecedented detail and without making the least damage to samples, the physico-chemical changes experienced by pH-responsive polymer brushes after protonation and after loading of silver nanoparticles. One of the most important findings is the depth profiling of silver nanoparticles inside the brushes. These results open up a completely new way to understand the structure and behavior of such complex systems.

  6. Positron lifetime measurements and positron-annihilation induced auger electron spectroscpy using slow positron beams; Teisoku yodenshi bimu wo mochiita yodenshi jumyo sokutei oyobi yodenshi shometsu reiki oje denshi bunko

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, R. [Electrotechnical Lab., Tsukuba (Japan)

    1996-02-20

    Slow positron beam with less than several eV can be controlled freely such as accelerating, throttling the beam size, shortening the pulse or making pulse with short time width and so forth. These low positron beams are applied to various measurements like Doppler broadening measurement of annihilation {gamma} rays or lifetime measurement of positron, and secondary particle measurements using positron microscope, positron electron ray diffraction, flight time method and so forth. In particular, these recent years, high intensity slow positron beams were possible using accelerators like electron linac and its application is increasing. In this report, pulse shortening method for high intensity slow positron beam, and incidence energy variable positron lifetime measurement method using this slow pulsed beam and flight time type positron-annihilation-induced auger electron spectroscopy are outlined. In future, these measurements can be possible to carry out with high resolution and also with high counting rate if higher intensity monochromatic excellent positron beam than present one is produced. 31 refs., 5 figs.

  7. Polymerization of epoxy resins studied by positron annihilation

    International Nuclear Information System (INIS)

    The polymerization process of epoxy resins (bisphenol-A dicyanate) was studied using positron-annihilation spectroscopy. The polymerization from monomer to polymer through a polymerization reaction was followed by positron-annihilation lifetime spectroscopy measurements. Resins kept at curing temperatures (120, 150 and 200 oC) changed form from of powder to a solid through a liquid. The size of the intermolecular spaces of the solid samples increased along with the progress of polymerization. (author)

  8. Variable Energy Positron Annihilation Spectroscopy of GaN Grown on Sapphire Substrates with MOCVD

    Institute of Scientific and Technical Information of China (English)

    HU Yi-Fan; C.D. Beling; S. Fung

    2005-01-01

    @@ Depth profiled Doppler broadening of positron annihilation spectroscopy (DBPAS), which is also called the variable energy positron annihilation spectroscopy (VEPAS), is used in characterization of GaN grown on sapphire substrates with metal-organic chemical vapour deposition (MOCVD). The GaN film and the film/substrate interface are investigated. The VEPFIT (variable energy positron fit) software was used for analysing the data,and the positron diffusion length of the sapphire is obtained. The results suggest that there is a highly defected region near the GaN/sapphire interface. This thin dislocated region is generated at the film/substrate interface to relieve the strain. Effects of implantation dose on defect formation, for the GaN/Sapphire samples, which implanted by Al+ ions, are also investigated. Studies on Al+ implanted GaN films (not including the interface and sapphire) have revealed that there are two different regions of implantation damage. For the low Al+ implantation dose samples, in the region close to the surface, defects are mainly composed of vacancy pairs with small amount of vacancy clusters, and in the interior region of the film the positron traps are vacancy clusters without micro-voids. For the highest dose sample, however, some positron trap centres are in the form of micro-voids in the second region.

  9. Spatially resolved positron annihilation spectroscopy on friction stir weld induced defects

    Directory of Open Access Journals (Sweden)

    Karin Hain, Christoph Hugenschmidt, Philip Pikart and Peter Böni

    2010-01-01

    Full Text Available A friction stir welded (FSW Al alloy sample was investigated by Doppler broadening spectroscopy (DBS of the positron annihilation line. The spatially resolved defect distribution showed that the material in the joint zone becomes completely annealed during the welding process at the shoulder of the FSW tool, whereas at the tip, annealing is prevailed by the deterioration of the material due to the tool movement. This might be responsible for the increased probability of cracking in the heat affected zone of friction stir welds. Examination of a material pairing of steel S235 and the Al alloy Silafont36 by coincident Doppler broadening spectroscopy (CDBS indicates the formation of annealed steel clusters in the Al alloy component of the sample. The clear visibility of Fe in the CDB spectra is explained by the very efficient trapping at the interface between steel cluster and bulk.

  10. Fluorescence lifetime spectroscopy for breast cancer margins assessment

    Science.gov (United States)

    Gorpas, Dimitris; Fatakdawala, Hussain; Zhang, Yanhong; Bold, Richard; Marcu, Laura

    2015-03-01

    During breast conserving surgery (BCS), which is the preferred approach to treat most early stage breast cancers, the surgeon attempts to excise the tumor volume, surrounded by thin margin of normal tissue. The intra-operative assessment of cancerous areas is a challenging procedure, with the surgeon usually relying on visual or tactile guidance. This study evaluates whether time-resolved fluorescence spectroscopy (TRFS) presents the potential to address this problem. Point TRFS measurements were obtained from 19 fresh tissue slices (7 patients) and parameters that characterize the transient signals were quantified via constrained least squares deconvolution scheme. Fibrotic tissue (FT, n=69), adipose tissue (AT, n=76), and invasive ductal carcinoma (IDC, n=27) were identified in histology and univariate statistical analysis, followed by multi-comparison test, was applied to the corresponding lifetime data. Significant differentiation between the three tissue types exists at 390 nm and 500 nm bands. The average lifetime is 3.23+/-0.74 ns for AT, 4.21+/-0.83 ns for FT and 4.71+/-0.35 ns (ptissue in real-time and assess tumor margins.

  11. Defect dynamics in P+ implanted 6H-SiC studied by positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    We study P+-implanted 6H-SiC samples by means of a variable energy slow positron beam. In as-grown samples we observe a slow fall of the annihilation S-parameter from the surface to the bulk value, indicating a long diffusion length, i.e. absence of positron-trapping defects. This result is also confirmed by positron-lifetime measurements yielding essentially a single-component lifetime of 148 ps. In the implanted samples we detect a wide flat region of slightly risen defectiveness. However, we note that, in order to reproduce reasonably well the depth of the damaged layer, one has to assume the presence of strong electric fields in the implanted region. With annealing, S-curves show a rising maximum, moving towards surface - probably, in as-implanted samples the defects are decorated by P+ ions and do not trap positrons in effective way. After the highest temperature annealing a highly defected region extends for the first 50 nm depth. We perform also atomic force microscopy to monitor the evolution of the surface defects. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Positron and positronium annihilation in silica-based thin films studied by a pulsed positron beam

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, R. E-mail: r-suzuki@aist.go.jp; Ohdaira, T.; Kobayashi, Y.; Ito, K.; Shioya, Y.; Ishimaru, T

    2003-11-01

    Positron and positronium annihilation in silica-based thin films has been investigated by means of measurement techniques with a monoenergetic pulsed positron beam. The age-momentum correlation study revealed that positron annihilation in thermally grown SiO{sub 2} is basically the same as that in bulk amorphous SiO{sub 2} while o-Ps in the PECVD grown SiCOH film predominantly annihilate with electrons of C and H at the microvoid surfaces. We also discuss time-dependent three-gamma annihilation in porous low-k films by two-dimensional positron annihilation lifetime spectroscopy.

  13. Bounds on Cross-sections and Lifetimes for Dark Matter Annihilation and Decay into Charged Leptons from Gamma-ray Observations of Dwarf Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Essig, Rouven; /SLAC; Sehgal, Neelima; Strigari, Louis E.; /KIPAC, Menlo Park

    2009-06-19

    We provide conservative bounds on the dark matter cross-section and lifetime from final state radiation produced by annihilation or decay into charged leptons, either directly or via an intermediate particle {phi}. Our analysis utilizes the experimental gamma-ray flux upper limits from four Milky Way dwarf satellites: HESS observations of Sagittarius and VERITAS observations of Draco, Ursa Minor, and Willman 1. Using 90% confidence level lower limits on the integrals over the dark matter distributions, we find that these constraints are largely unable to rule out dark matter annihilations or decays as an explanation of the PAMELA and ATIC/PPB-BETS excesses. However, if there is an additional Sommerfeld enhancement in dwarfs, which have a velocity dispersion {approx} 10 to 20 times lower than that of the local Galactic halo, then the cross-sections for dark matter annihilating through {phi}'s required to explain the excesses are very close to the cross-section upper bounds from Willman 1. Dark matter annihilation directly into {tau}'s is also marginally ruled out by Willman 1 as an explanation of the excesses, and the required cross-section is only a factor of a few below the upper bound from Draco. Finally, we make predictions for the gamma-ray flux expected from the dwarf galaxy Segue 1 for the Fermi Gamma-ray Space Telescope. We find that for a sizeable fraction of the parameter space in which dark matter annihilation into charged leptons explains the PAMELA excess, Fermi has good prospects for detecting a gamma-ray signal from Segue 1 after one year of observation.

  14. Evolution of native point defects in ZnO bulk probed by positron annihilation spectroscopy

    Institute of Scientific and Technical Information of China (English)

    Peng Cheng-Xiao; Wang Ke-Fan; Zhang Yang; Guo Feng-Li; Weng Hui-Min; Ye Bang-Jiao

    2009-01-01

    This paper studies the evolution of native point defects with temperature in ZnO single crystals by positron lifetime and coincidence Doppler broadening (CDB) spectroscopy, combined with the calculated results of positron lifetime and electron momentum distribution. The calculated and experimental results of the positron lifetime in ZnO bulk ensure the presence of zinc monovacancy, and zinc monovacancy concentration begins to decrease above 600℃ annealing treatment. CDB is an effective method to distinguish the elemental species, here we combine this technique with calculated electron momentum distribution to determine the oxygen vacancies, which do not trap positrons due to their positive charge. The CDB spectra show that oxygen vacancies do not appear until 600℃ annealing treatment, and increase with the increase of annealing temperature. This study supports the idea that green luminescence has a close relation with oxygen vacancies.

  15. Rectifying barrier at GaN/SiC hetero-junction studied with positron annihilation spectroscopy

    Institute of Scientific and Technical Information of China (English)

    Hu Yi-Fan; Beling C D

    2005-01-01

    Positron annihilation spectroscopy on GaN films grown on SiC substrate with MBE are presented. It is shown that the GaN/SiC interface is rectifying towards positrons, such that positrons can only travel from SiC to GaN and not vice versa. Potential steps seen by the positron at the GaN/SiC interface are calculated from experimental values of electron and positron work function. This "rectifying" effect has been successfully mimicked by inserting a thin region of very high electric field in the Variable Energy Positron Fit (VEPF) analysis. The built-in electric field is attributed to different positron affinities, dislocation and/or interface defects at the GaN/SiC interface.

  16. Positron annihilation and relaxation dynamics from dielectric spectroscopy and nuclear magnetic resonance: Cis-trans-1,4-poly(butadiene)

    Science.gov (United States)

    Bartoš, J.; Šauša, O.; Schwartz, G. A.; Alegría, A.; Alberdi, J. M.; Arbe, A.; Krištiak, J.; Colmenero, J.

    2011-04-01

    We report a joint analysis of positron annihilation lifetime spectroscopy (PALS), dielectric spectroscopy (BDS), and nuclear magnetic resonance (NMR) on cis-trans-1,4-poly(butadiene) (c-t-1,4-PBD). Phenomenological analysis of the orthopositronium lifetime τ3 - T dependence by linear fitting reveals four characteristic PALS temperatures: T_{b1} ^G = 0{.63}T_g^{PALS}, T_g^{PALS}, T_{b1} ^L = 1.22T_g^{PALS}, and T_{b2} ^L = 1.52T_g^{PALS}. Slight bend effects in the glassy and supercooled liquid states are related to the fast or slow secondary β process, from neutron scattering, respectively, the latter being connected with the trans-isomers. In addition, the first bend effect in the supercooled liquid coincides with a deviation of the slow effective secondary βeff relaxation related to the cis-isomers from low-T Arrhenius behavior to non-Arrhenius one and correlates with the onset of the primary α process from BDS. The second plateau effect in the liquid state occurs when τ3 becomes commensurable with the structural relaxation time τα(Tb2). It is also approximately related to its crossover from non-Arrhenius to Arrhenius regime in the combined BDS and NMR data. Finally, the combined BDS and NMR structural relaxation data, when analyzed in terms of the two-order parameter (TOP) model, suggest the influence of solidlike domains on both the annihilation behavior and the local and segmental chain mobility in the supercooled liquid. All these findings indicate the influence of the dynamic heterogeneity in both the primary and secondary relaxations due to the cis-trans isomerism in c-t-1,4-PBD and their impact into the PALS response.

  17. Optimization of three-dimensional positron annihilation spectroscopy system (3DPASS) for three-dimensional momentum measurements

    Energy Technology Data Exchange (ETDEWEB)

    Williams, Christopher S., E-mail: christopher.williams@afit.ed [Air Force Institute of Technology, AFIT/ENP, 2950 Hobson Way, Wright-Patterson Air Force Base, OH 45433 (United States); Burggraf, Larry W. [Air Force Institute of Technology, AFIT/ENP, 2950 Hobson Way, Wright-Patterson Air Force Base, OH 45433 (United States); Adamson, Paul E. [Stockpile Research, Development and Engineering Division, Office of Defense Programs, National Nuclear Security Administration, 1000 Independence Avenue SW, Washington, DC 20585 (United States); Petrosky, James C. [Air Force Institute of Technology, AFIT/ENP, 2950 Hobson Way, Wright-Patterson Air Force Base, OH 45433 (United States)

    2011-02-11

    A three-dimensional positron annihilation spectroscopy system (3DPASS) was characterized. 3DPASS permits determination of three-dimensional electron-positron (e{sup -}e{sup +}) momentum distributions by simultaneously measuring angles and energies for coincident two-gamma annihilation photons. 3DPASS collects a single dataset of correlated energies and positions for two coincident annihilation photons from a pair of solid-state double-sided strip detectors (DSSDs). Subpixel-interpolated positions are determined by transient charge analysis. 3DPASS performs simultaneous two-dimensional angular correlation of annihilation radiation (2D ACAR) and two-detector coincidence Doppler-broadening of annihilation radiation (CDBAR) measurements, which are typically collected independently. The 2D ACAR response of 3DPASS was measured for single-crystal Cu and 6H-SiC, with and without compensation for subpixel detection efficiency. Variation of efficiency across the width of DSSD charge collection electrodes was dominated by the event selection criteria required by the subpixel interpolation method. The DBAR resolution was optimized by adjusting the energy range of CDBAR events included in the Doppler-broadening (DB) lineshape. 2D ACAR and DBAR spectra from 3DPASS were compared to previously published results for single-crystal Cu and 6H-SiC. Detailed analysis of the ACAR spectra and the DB lineshapes highlighted momentum features not previously reported.

  18. Optimization of three-dimensional positron annihilation spectroscopy system (3DPASS) for three-dimensional momentum measurements

    Science.gov (United States)

    Williams, Christopher S.; Burggraf, Larry W.; Adamson, Paul E.; Petrosky, James C.

    2011-02-01

    A three-dimensional positron annihilation spectroscopy system (3DPASS) was characterized. 3DPASS permits determination of three-dimensional electron-positron ( e-- e+) momentum distributions by simultaneously measuring angles and energies for coincident two-gamma annihilation photons. 3DPASS collects a single dataset of correlated energies and positions for two coincident annihilation photons from a pair of solid-state double-sided strip detectors (DSSDs). Subpixel-interpolated positions are determined by transient charge analysis. 3DPASS performs simultaneous two-dimensional angular correlation of annihilation radiation (2D ACAR) and two-detector coincidence Doppler-broadening of annihilation radiation (CDBAR) measurements, which are typically collected independently. The 2D ACAR response of 3DPASS was measured for single-crystal Cu and 6H-SiC, with and without compensation for subpixel detection efficiency. Variation of efficiency across the width of DSSD charge collection electrodes was dominated by the event selection criteria required by the subpixel interpolation method. The DBAR resolution was optimized by adjusting the energy range of CDBAR events included in the Doppler-broadening (DB) lineshape. 2D ACAR and DBAR spectra from 3DPASS were compared to previously published results for single-crystal Cu and 6H-SiC. Detailed analysis of the ACAR spectra and the DB lineshapes highlighted momentum features not previously reported.

  19. Interstitial oxygen related defects and nanovoids in Au implanted a-SiO2 glass depth profiled by positron annihilation spectroscopy

    Science.gov (United States)

    Ravelli, L.; Macchi, C.; Mariazzi, S.; Mazzoldi, P.; Egger, W.; Hugenschmidt, C.; Somoza, A.; Brusa, R. S.

    2015-12-01

    Samples of amorphous silica were implanted with Au ions at an energy of 190 keV and fluences of 1× {{10}14} ions cm-2and 5× {{10}14} ions cm-2 at room temperature. The damage produced by ion implantation and its evolution with the thermal treatment at 800 °C for one hour in nitrogen atmosphere was depth profiled using three positron annihilation techniques: Doppler broadening spectroscopy, positron annihilation lifetime spectroscopy and coincidence Doppler broadening spectroscopy. Around the ion projected range of {{R}\\text{p}}=67 nm, a size reduction of the silica matrix intrinsic nanovoids points out a local densification of the material. Oxygen related defects were found to be present at depths four times the ion projected range, showing a high mobility of oxygen molecules from the densified and stressed region towards the bulk. The 800 °C thermal treatment leads to a recovery of the silica intrinsic nanovoids only in the deeper damaged region and the defect distribution, probed by positrons, shrinks around the ion projected range where the Au atoms aggregate. Open volume defects at the interface between Au and the amorphous matrix were evidenced in both the as implanted and in the thermal treated samples. A practically complete disappearance of the intrinsic nanovoids was observed around {{R}\\text{p}} when the implantation fluence was increased by two orders of magnitude (3× {{10}16} ions cm-2). In this case, the oxygen defects move to a depth five times larger than {{R}\\text{p}} .

  20. Development of positron annihilation spectroscopy for investigating deuterium decorated voids in neutron-irradiated tungsten

    International Nuclear Information System (INIS)

    The present work is a continuation of a recent research to develop and optimize positron annihilation spectroscopy (PAS) for characterizing neutron-irradiated tungsten. Tungsten samples were exposed to neutrons in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory and damaged to 0.025 and 0.3 dpa. Subsequently, they were exposed to deuterium plasmas in the Tritium Plasma Experiment (TPE) at Idaho National Laboratory. The implanted deuterium was desorbed through sample heating to 900 °C, and Doppler broadening (DB)-PAS was performed both before and after heating. Results show that deuterium impregnated tungsten is identified as having a smaller S-parameter. The S-parameter increases after deuterium desorption. Microstructural changes also occur during sample heating. These effects can be isolated from deuterium desorption by comparing the S-parameters from the deuterium-free back face with the deuterium-implanted front face. The application of using DB-PAS to examine deuterium retention in tungsten is examined

  1. Microstructural characterization of alumina-zirconia layered ceramics using positron annihilation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Parente, P., E-mail: pparente@fis.uc3m.es [Departamento de Fisica, Universidad Carlos III de Madrid, 28911 Leganes (Spain); Ortega, Y. [Departamento de Fisica de Materiales, Facultad de Ciencias Fisicas, Univ. Complutense de Madrid, 28040 Madrid (Spain); Savoini, B.; Monge, M.A. [Departamento de Fisica, Universidad Carlos III de Madrid, 28911 Leganes (Spain); Tucci, A.; Esposito, L. [Centro Ceramico Bologna, 40128 Bologna (Italy); Sanchez-Herencia, A.J. [Instituto de Ceramica y Vidrio, Consejo Superior de Investigaciones Cientificas, 28049 Madrid (Spain)

    2010-05-15

    Positron annihilation spectroscopy (PAS), indentation, nanoindentation experiments and scanning electron microscopy (SEM) observations were performed on Al{sub 2}O{sub 3}-ZrO{sub 2} laminates samples to assess the effect of residual stresses on their mechanical and microstructural properties. Layered samples were implemented by slip-casting, constituted by two thin Al{sub 2}O{sub 3} external layers and an intermediate thick one, consisting of a mixture of Al{sub 2}O{sub 3} and monoclinic ZrO{sub 2} in the range 0-30 vol.%. In these systems residual tensile stresses fields were generated inside the external layers during cooling from the sintering temperature, by the expansion of the adjacent ZrO{sub 2}-containing layer. SEM observations showed the microstructural effects due to the level of tension related to the zirconia content. A correlation between the PAS parameters and the microstructural changes caused by the presence of residual stresses was found. Nanoindentation measurements were used to trace the sign and magnitude of the residual stress gradient across the interface between the layers.

  2. Multiplexed fluorescence lifetime measurements by frequency-sweeping Fourier spectroscopy

    OpenAIRE

    Zhao, Ming; Peng, Leilei

    2010-01-01

    We report simultaneous measurements of fluorescence lifetimes at multiple excitation wavelengths with a Fourier transform frequency domain fluorescence lifetime spectrometer. The spectrometer uses a Michelson interferometer with its differential optical path length scanning at 22,000 Hz scan rate. The scan speed of the optical delay varies linearly during each scan and creates interference modulations that sweep from −150 to 150 MHz in 45.5 μs. The frequency-sweeping modulation allows nanosec...

  3. Determination of deep trapping lifetime in organic semiconductors using impedance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Takagi, Kenichiro; Nagase, Takashi; Kobayashi, Takashi; Naito, Hiroyoshi, E-mail: naito@pe.osakafu-u.ac.jp [Department of Physics and Electronics, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan)

    2016-02-01

    A method for determining deep trapping lifetime in semiconductors using an impedance spectroscopy is proposed. A unique feature of the method is the simultaneous determination of the drift mobility and deep trapping lifetime in thin-film electronic devices. The validity of the proposed method is examined by numerical calculation. Simultaneous determinations of the drift mobility and deep trapping lifetime using this method are demonstrated in prototypical hole transporting organic semiconductors.

  4. Determination of the activation enthalpy for migration of dislocations in plastically deformed 8006 Al-alloy by positron annihilation lifetime technique

    Science.gov (United States)

    Salah, Mohammed; Abdel-Rahman, M.; Badawi, Emad A.; Abdel-Rahman, M. A.

    2016-06-01

    The activation enthalpy for migration of dislocations of plastically deformed 8006 Al-alloy was investigated by positron annihilation lifetime technique. Plastic deformation using a hydraulic press produces mainly dislocations and may produce point defects. The type of defect was studied by isochronal annealing which determines the temperature range of recovery of each type. Only one type of defect (dislocations) was observed for the investigated sample and was found to be recovered within the range 455-700 K. Isothermal annealing by slow cooling was performed through this range and used in determination of the activation enthalpy of migration of dislocations which was found to be 0.26 ± 0.01 eV.

  5. Positron annihilation spectroscopy of vacancy-related defects in CdTe:Cl and CdZnTe:Ge at different stoichiometry deviations

    Science.gov (United States)

    Šedivý, L.; Čížek, J.; Belas, E.; Grill, R.; Melikhova, O.

    2016-02-01

    Positron annihilation spectroscopy (PAS) was used to examine the effect of defined Cd-rich and Te-rich annealing on point defects in Cl-doped CdTe and Ge-doped CdZnTe semi-insulating single crystals. The as-grown crystals contain open-volume defects connected with Cd vacancies . It was found that the Cd vacancies agglomerate into clusters coupled with Cl in CdTe:Cl, and in CdZnTe:Ge they are coupled with Ge donors. While annealing in Cd pressure reduces of the density, subsequent annealing in Te pressure restores . The CdTe:Cl contains negatively-charged shallow traps interpreted as Rydberg states of A-centres and representing the major positron trapping sites at low temperature. Positrons confined in the shallow traps exhibit lifetime, which is shorter than the CdTe bulk lifetime. Interpretation of the PAS data was successfully combined with electrical resistivity, Hall effect measurements and chemical analysis, and allowed us to determine the principal point defect densities.

  6. Lifetime spectroscopy a method of defect characterization in silicon for photovoltaic applications

    CERN Document Server

    Rein, Stefan

    2005-01-01

    Lifetime spectroscopy is one of the most sensitive diagnostic tools for the identification and analysis of impurities in semiconductors. Since it is based on the recombination process, it provides insight into precisely those defects that are relevant to semiconductor devices such as solar cells. This book introduces a transparent modeling procedure that allows a detailed theoretical evaluation of the spectroscopic potential of the different lifetime spectroscopic techniques. The various theoretical predictions are verified experimentally with the context of a comprehensive study on different metal impurities. The quality and consistency of the spectroscopic results, as explained here, confirms the excellent performance of lifetime spectroscopy.

  7. Early stages of precipitation in Mg-RE alloys studied by positron annihilation spectroscopy

    Science.gov (United States)

    Vlček, M.; Čížek, J.; Melikhova, O.; Hruška, P.; Procházka, I.; Vlach, M.; Stulíková, I.; Smola, B.

    2016-01-01

    Magnesium alloys with rare earth (RE) elements are promising structural materials exhibiting favourable mechanical properties at elevated temperatures. However, the processes occurring during early stages of precipitation in these alloys are still not completely understood. In this work positron lifetime spectroscopy combined with coincidence Doppler broadening was employed for investigation of early stages of precipitation in Mg-RE alloys. Presence of quenched-in vacancy clusters was observed after solution treatment of studied alloys. These quenched-in vacancy clusters are bound to RE solutes and thereby stabilized at room temperature. During natural aging, RE clusters are formed by vacancy-assisted long-range diffusion. In addition, hardness of studied materials increases and quenched-in vacancy clusters are annealed out during the course of natural aging. Simple model was developed to describe hardening during natural aging.

  8. Lifetime

    Institute of Scientific and Technical Information of China (English)

    姚祎

    2004-01-01

    @@ 继ESPN刊出同名杂志之后,2003年赫斯特公司(Hearst Corp.)和迪斯尼(Walt Disney Co.)的合作促成了一本新杂志的诞生:(Lifetime),其目标读者是成百万收看同名有线电视网节目的妇女们.

  9. Positron annihilation Doppler broadening spectroscopy study on Fe-ion irradiated NHS steel

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Huiping [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Wang, Zhiguang, E-mail: zhgwang@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Gao, Xing; Cui, Minghuan; Li, Bingsheng; Sun, Jianrong; Yao, Cunfeng; Wei, Kongfang; Shen, Tielong; Pang, Lilong; Zhu, Yabin [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Li, Yuanfei; Wang, Ji [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); University of Lanzhou, Lanzhou 730000 (China); Song, Peng [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zhang, Peng; Cao, Xingzhong [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

    2015-02-01

    Highlights: • NHS steel was irradiated by 3.25 MeV Fe ions to different fluences at room temperature and 723 K. • The evolution of vacancy type defects is studied through positron annihilation spectroscopy. • The concentration gradient of SIA can induce the decrease of S value with increasing fluence at high temperature. - Abstract: In order to study the evolution of irradiation-induced vacancy-type defects at different irradiation fluences and temperatures, a new type of ferritic/martensitic (F/M) steel named NHS (Novel High Silicon) was irradiated by 3.25 MeV Fe-ion at room temperature and 723 K to fluences of 4.3 × 10{sup 15} and 1.7 × 10{sup 16} ions/cm{sup 2}. After irradiation, vacancy-type defects were investigated with variable-energy positron beam Doppler broadening spectra. Energetic Fe-ions produced a large number of vacancy-type defects in the NHS steel, but one single main type of vacancy-type defect was observed in both unirradiated and irradiated samples. The concentration of vacancy-type defects decreased with increasing temperature. With the increase of irradiation fluence, the concentration of vacancy-type defects increased in the sample irradiated at RT, whereas for the sample irradiated at 723 K, it decreased. The enhanced recombination between vacancies and excess interstitial Fe atoms from deeper layers, and high diffusion rate of self-interstitial atoms further improved by diffusion via grain boundary and dislocations at high temperature, are thought to be the main reasons for the reversed trend of vacancy-type defects between the samples irradiated at RT and 723 K.

  10. Precise atomic radiative lifetime via photoassociative spectroscopy of ultracold lithium

    International Nuclear Information System (INIS)

    We have obtained spectra of the high-lying vibrational levels of the 13Σ+g state of 6Li2 via photoassociation of ultracold 6Li atoms confined in a magneto-optical trap. The 13Σ+g state of the diatomic molecule correlates to a 2S1/2 state atom plus a 2P1/2 state atom. The long-range part of the molecular interaction potential for this state depends on the 2P atomic radiative lifetime. By calculating the energy eigenvalues of a model potential for the 13Σ+g state and fitting them to the experimentally measured vibrational levels, we have extracted a value for the 2P lifetime of 26.99±0.16 ns. The precision is currently limited by the accuracy of a region of the model potential provided by ab initio calculations

  11. Microstructural changes and effect of variation of lattice strain on positron annihilation lifetime parameters of zinc ferrite nanocomposites prepared by high enegy ball-milling

    Directory of Open Access Journals (Sweden)

    Abhijit Banerjee

    2012-12-01

    Full Text Available Zn-ferrite nanoparticles were synthesized at room temperature by mechanical alloying the stoichiometric (1:1 mol% mixture of ZnO and α-Fe2O3 powder under open air. Formation of both normal and inverse spinel ferrite phases was noticed after 30 minutes and 2.5 hours ball milling respectively and the content of inverse spinel phase increased with increasing milling time. The phase transformation kinetics towards formation of ferrite phases and microstructure characterization of ball milled ZnFe2O4 phases was primarily investigated by X-ray powder diffraction pattern analysis. The relative phase abundances of different phases, crystallite size, r.m.s. strain, lattice parameter change etc. were estimated from the Rietveld powder structure refinement analysis of XRD data. Positron annihilation lifetime spectra of all ball milled samples were deconvoluted with three lifetime parameters and their variation with milling time duration was explained with microstructural changes and formation of different phases with increase of milling time duration.

  12. Applications of slow positrons to cancer research: Search for selectivity of positron annihilation to skin cancer

    Energy Technology Data Exchange (ETDEWEB)

    Jean, Y.C. [Department of Chemistry, University of Missouri-Kansas City, 205 Spenscer Chemistry Building, 5009 Rockhill Road, Kansas City, MO 64110 (United States)]. E-mail: jeany@umkc.edu; Li Ying [Department of Chemistry, University of Missouri-Kansas City, 205 Spenscer Chemistry Building, 5009 Rockhill Road, Kansas City, MO 64110 (United States); Liu Gaung [Department of Chemistry, University of Missouri-Kansas City, 205 Spenscer Chemistry Building, 5009 Rockhill Road, Kansas City, MO 64110 (United States); Chen, Hongmin [Department of Chemistry, University of Missouri-Kansas City, 205 Spenscer Chemistry Building, 5009 Rockhill Road, Kansas City, MO 64110 (United States); Zhang Junjie [Department of Chemistry, University of Missouri-Kansas City, 205 Spenscer Chemistry Building, 5009 Rockhill Road, Kansas City, MO 64110 (United States); Gadzia, Joseph E. [Dermatology, Department of Internal Medicine, University of Kansas Medical Center, Kansas City, KS 66103 (United States); Kansas Medical Clinic, Topeka, KS 66614 (United States)

    2006-02-28

    Slow positrons and positron annihilation spectroscopy (PAS) have been applied to medical research in searching for positron annihilation selectivity to cancer cells. We report the results of positron lifetime and Doppler broadening energy spectroscopies in human skin samples with and without cancer as a function of positron incident energy (up to 8 {mu}m depth) and found that the positronium annihilates at a significantly lower rate and forms at a lower probability in the samples having either basal cell carcinoma (BCC) or squamous cell carcinoma (SCC) than in the normal skin. The significant selectivity of positron annihilation to skin cancer may open a new research area of developing positron annihilation spectroscopy as a novel medical tool to detect cancer formation externally and non-invasively at the early stages.

  13. Development of pore interconnectivity/morphology in porous silica films investigated by cyclic voltammetry and slow positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Highlights: •Porous silica films were studied by cyclic voltammetry and positron annihilation. •Highly interconnected pores were formed in the film fabricated with more CTAB. •Aligned nanochannels were observed in the porous flim prepared with 25 wt.% CTAB. •I− and Ps diffusion in the films was governed by pore interconnectivity/morphology. •Cyclic voltammetry is feasible to explore pore interconnectivity/morphology. -- Abstract: Cyclic voltammetry and positronium (Ps) 3γ-annihilation spectroscopy were applied to investigate pore interconnectivity/morphology of porous silica films fabricated with various loading of cetyltrimethyl ammonium bromide (CTAB). With increasing the ratio of CTAB up to 15 wt.%, the total charge Q, resulted from I− diffusion across the silica films, increased remarkably, indicative of formation of highly interconnected pores in the films prepared with more porogen. However, it decreased dramatically with further loading CTAB of 25 wt.%. Interestingly, 3γ-annihilation fraction I3γ due to a triplet-state Ps (ortho-positronium, o-Ps) emission from the silica films showed a similar behavior as a function of CTAB loading. The abnormal decrement in Q and I3γ in the film fabricated with 25 wt.% CTAB was well explained by formation of long nanochannels aligning parallel to the film surface. The results indicated that the total charge Q and Ps 3γ-annihilation fraction were closely associated with I− and Ps diffusion governed by the pore interconnectivity/morphology of the silica films, which made cyclic voltammetry possible to be a feasible tool to characterize pore interconnectivity/morphology of porous thin films

  14. 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.

  15. Positron annihilation spectroscopy (PALS) the effect of crosslinking on free volume size in poly-methyl-methacrylate

    CERN Document Server

    Atevikj, A

    2000-01-01

    Positron annihilation Spectroscopy (PALS) is used for analyzing the samples of polymethyl-methacrylate (PMMA) with different contents of crosslinks. The measurements are performed at room temperature. The times of life (tau sub 1 , tau sub 2 , tau sub 3) and the intensities (I sub I , I sub 2 , 1 sub 3) of para-positronium, the free positrons and the orto-positrons are calculated for each type of polymer, but only (tau sub 3) and (I sub 3) are of interest because we can calculate the size of free volume. It is shown that the radius of free volume is proportional to the crosslinking density. Defects of sizes in the range of 0.1 to 1 nm are detected with Positron Spectroscopy, while other techniques do not give results. (Original)

  16. Atomic Oscillator Strengths by Emission Spectroscopy and Lifetime Measurements

    Science.gov (United States)

    Wiese, W. L.; Griesmann, U.; Kling, R.; Musielok, J.

    2002-11-01

    Over the last seven years, we have carried out numerous oscillator strength measurements for some light and medium heavy elements (Musielok et al. 1995, 1996, 1997, 1999, 2000; Veres & Wiese 1996; Griesmann et al. 1997; Bridges & Wiese 1998; Kling et al. 2001; Kling & Gries- mann 2000; Bridges & Wiese to be published). Most recently we have determined numerous transitions of Mu II (Kling et al. 2001; Kling & Griesmann 2000) and are now working on Cl I (Bridges & Wiese to be published). See the summary statement at the end of the text. For the emission measurements, we have applied either a high-current wall-stabilized arc (described for example, in Musielok et al. (1999)), or a high-current hollow cathode, or a Penning discharge. The latter two sources were used for branching ratio measurements from common upper 1ev- els, while the wall-stabilized arc was operated at atmospheric pressure under the condition of partial local thermodynamic equilibrium, which allows the measurement of relative transition probabilities. Absolute data were obtained by combining the emission results with lifetime data measured by other research groups, especially the University of Hannover, with which we have closely collaborated. This group uses the laser induced fluorescence (LIF) technique. Our emission spectra were recorded for the light elements with a 2 m grating spectrometer, or, for Mu II, with an FT 700 vacuum ultraviolet Fourier transform spectrometer. The radiometric calibration was carried out with a tungsten strip lamp for the visible part of the spectrum and with a deuterium lamp for the ultraviolet. All measurements were made under optically thin conditions, which was checked by doubling the path length with a focusing mirror setup. Typical uncertainties of the measured oscillator strengths are estimated to be in the range 15%-20% (one-standard deviation). However, discrepancies with advanced atomic structure theories are sometimes much larger. In Tables 1-3 and Fig. 1, we

  17. Assessing the photoaging process at sun exposed and non-exposed skin using fluorescence lifetime spectroscopy

    Science.gov (United States)

    Saito Nogueira, Marcelo; Kurachi, Cristina

    2016-03-01

    Photoaging is the skin premature aging due to exposure to ultraviolet light, which damage the collagen, elastin and can induce alterations on the skin cells DNA, and, then, it may evolve to precancerous lesions, which are widely investigated by fluorescence spectroscopy and lifetime. The fluorescence spectra and fluorescence lifetime analysis has been presented as a technique of great potential for biological tissue characterization at optical diagnostics. The main targeted fluorophores are NADH (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide), which have free and bound states, each one with different average lifetimes. The average lifetimes for free and bound NADH and FAD change according to tissue metabolic alterations and may contribute to a non-invasive clinical investigation of injuries such as skin lesions. These lesions and the possible areas where they may develop can be interrogated using fluorescence lifetime spectroscopy taking into account the variability of skin phototypes and the changes related to melanin, collagen and elastin, endogenous fluorophores which have emissions that spectrally overlap to the NADH and FAD emission. The objective of this study is to assess the variation on fluorescence lifetimes of normal skin at sun exposed and non-exposed areas and associate this variation to the photoaging process.

  18. Advances in Contactless Silicon Defect and Impurity Diagnostics Based on Lifetime Spectroscopy and Infrared Imaging

    Directory of Open Access Journals (Sweden)

    Jan Schmidt

    2007-01-01

    Full Text Available This paper gives a review of some recent developments in the field of contactless silicon wafer characterization techniques based on lifetime spectroscopy and infrared imaging. In the first part of the contribution, we outline the status of different lifetime spectroscopy approaches suitable for the identification of impurities in silicon and discuss—in more detail—the technique of temperature- and injection-dependent lifetime spectroscopy. The second part of the paper focuses on the application of infrared cameras to analyze spatial inhomogeneities in silicon wafers. By measuring the infrared signal absorbed or emitted from light-generated free excess carriers, high-resolution recombination lifetime mappings can be generated within seconds to minutes. In addition, mappings of non-recombination-active trapping centers can be deduced from injection-dependent infrared lifetime images. The trap density has been demonstrated to be an important additional parameter in the characterization and assessment of solar-grade multicrystalline silicon wafers, as areas of increased trap density tend to deteriorate during solar cell processing.

  19. Applications of positron annihilation to dermatology and skin cancer

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Guang; Chen, Hongmin; Chakka, Lakshmi [Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110 (United States); Gadzia, Joseph E. [Dermatology, Department of Internal Medicine, University of Kansas Medical Center, Kansas City, KS 66103 and Kansas Medical Clinic, Topeka, KS 66614 (United States); Jean, Y.C. [Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110 (United States); R and D Center for Membrane Technology, Chung Yuan Christian University, Chung-Li (China)

    2007-07-01

    Positronium annihilation lifetime experiments have been performed to investigate the interaction between skin cancer and positronium for human skin samples. Positronium annihilation lifetime is found to be shorter and intensity is found to be less for the samples with basal cell carcinoma and squamous cell carcinoma than the normal skin samples. These results indicate a reduction of free volume in the molecular level for the skin with cancer with respect to the skin without cancer. Positron annihilation spectroscopy may be potentially developed as a new noninvasive and external method for dermatology clinics, early detection of cancer, and nano-PET technology in the future. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Positron annihilation spectroscopy of vacancy-type defects hierarchy in submicrocrystalline nickel during annealing

    Energy Technology Data Exchange (ETDEWEB)

    Kuznetsov, Pavel V., E-mail: kpv@ispms.tsc.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055, Russia and National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Mironov, Yuri P., E-mail: myp@ispms.tsc.ru, E-mail: tolmach@ispms.tsc.ru, E-mail: rakhmatulina.tanya@gmail.com; Tolmachev, Aleksey I., E-mail: myp@ispms.tsc.ru, E-mail: tolmach@ispms.tsc.ru, E-mail: rakhmatulina.tanya@gmail.com; Rakhmatulina, Tanzilya V., E-mail: myp@ispms.tsc.ru, E-mail: tolmach@ispms.tsc.ru, E-mail: rakhmatulina.tanya@gmail.com [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Bordulev, Yuri S., E-mail: bordulev@gmail.com, E-mail: laptev.roman@gmail.com, E-mail: lider@tpu.ru; Laptev, Roman S., E-mail: bordulev@gmail.com, E-mail: laptev.roman@gmail.com, E-mail: lider@tpu.ru; Lider, Andrey M., E-mail: bordulev@gmail.com, E-mail: laptev.roman@gmail.com, E-mail: lider@tpu.ru; Mikhailov, Andrey A., E-mail: bordulev@gmail.com, E-mail: laptev.roman@gmail.com, E-mail: lider@tpu.ru [National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Korznikov, Alexander V., E-mail: korznikov@imsp.ru [Institute for Metals Superplasticity Problems RAS, Ufa, 450001 (Russian Federation)

    2014-11-14

    Positron annihilation and X-ray diffraction analysis have been used to study submicrocrystalline nickel samples prepared by equal channel angular pressing. In the as-prepared samples the positrons are trapped at dislocation-type defects and in vacancy clusters that can include up to 5 vacancies. The study has revealed that the main positron trap centers at the annealing temperature of ΔT= 20°C-180°C are low-angle boundaries enriched by impurities. At ΔT = 180°C-360°C, the trap centers are low-angle boundaries providing the grain growth due to recrystallization in-situ.

  1. Generation and recombination lifetime measurement in silicon wafers using impedance spectroscopy

    International Nuclear Information System (INIS)

    Minority carrier lifetime in silicon wafers has been measured by applying an impedance spectroscopy technique (IST). Induced p+–p and p–n junctions were formed on both sides of the silicon wafer by thermally evaporating semitransparent metal layers of palladium and aluminium respectively. As such, no thermal treatment was given to the device, and therefore there is no diffusion of impurities inside the semiconductor and the two junctions are induced in the form of accumulation and depletion regions of charge carriers respectively. Both generation and recombination lifetimes applicable under the reverse and forward bias conditions respectively have been measured. The generation lifetime was estimated to be around 73 µs, whereas the recombination lifetime has been found to be about 11 µs. It is shown that the effective recombination lifetime is determined mainly by surface recombination velocity at the silicon–palladium interface. The effective minority carrier lifetime as measured by the microwave-detected photoconductive decay method on the same sample is 12 µs which is close to the measured recombination value by the IST. This shows that impedance spectroscopy can be used to measure effective lifetime of the wafer using an induced junction structure prior to the formation of an actual device like the solar cell. Moreover, the series resistance (Rs), diode ideality factor (n) and barrier height (Vbi) obtained from C–V (using the IST) data as well as the I–V measurement of the device show agreement with the expected device parameters. Thus, the IST can be effectively employed as a tool in extracting many relevant characteristic parameters of the material and the device

  2. Extraction of carrier lifetime in Ge waveguides using pump probe spectroscopy

    Science.gov (United States)

    Srinivasan, S. A.; Pantouvaki, M.; Verheyen, P.; Lepage, G.; Absil, P.; Van Campenhout, J.; Van Thourhout, D.

    2016-05-01

    Carrier lifetimes in Ge-on-Si waveguides are deduced using time-resolved infrared transmission pump-probe spectroscopy. Dynamics of pump-induced excess carriers generated in waveguides with varying Ge thickness and width is probed using a CW laser. The lifetimes of these excess carriers strongly depend on the thickness and width of the waveguide due to defect assisted surface recombination. Interface recombination velocities of 0.975 × 104 cm/s and 1.45 × 104 cm/s were extracted for the Ge/Si and the Ge/SiO2 interfaces, respectively.

  3. Gamma-ray spectroscopy of Positron Annihilation in the Milky Way

    CERN Document Server

    Siegert, Thomas; Khachatryan, Gerasim; Krause, Martin G H; Guglielmetti, Fabrizia; Greiner, Jochen; Strong, Andrew W; Zhang, Xiaoling

    2015-01-01

    The annihilation of positrons in the Galaxy's interstellar medium produces characteristic gamma-rays with a line at 511 keV. This emission has been observed with the spectrometer SPI on INTEGRAL, confirming a puzzling morphology with bright emission from an extended bulge-like region, and faint disk emission. Most plausible sources of positrons are believed to be distributed throughout the disk of the Galaxy. We aim to constrain characteristic spectral shapes for different spatial components in the disk and bulge with the high-resolution gamma-ray spectrometer SPI, based on a new instrumental background method and detailed multi-component sky model fitting. We confirm the detection of the main extended components of characteristic annihilation gamma-ray signatures at 58$\\sigma$ significance in the line. The total Galactic line intensity amounts to $(2.7\\pm0.3)\\times10^{-3}~\\mathrm{ph~cm^{-2}~s^{-1}}$ for our assumed spatial model. We derive spectra for the bulge and disk, and a central point-like and at the p...

  4. Post irradiated microstructural characterization of Zr–1Nb alloy by X-ray diffraction technique and positron annihilation spectroscopy

    Indian Academy of Sciences (India)

    P S Chowdhury; P Mukherjee; N Gayathri; M Bhattacharya; A Chatterjee; P Barat; P M G Nambissan

    2011-06-01

    Zr–1Nb samples were irradiated with 116 MeV O5+ ions at different doses ranging from 5 × 1017 to 8 × 1018 O5+/m2. X-ray diffraction line profile analysis was performed to characterize the microstructural parameters of these samples. Average domain size, microstrain and dislocation density were estimated as a function of dose. An anomaly was observed in the values of these parameters at a dose of 2 × 1018 O5+/m2. Positron annihilation spectroscopy was used to determine the existence and nature of vacancy clusters in the samples. Isochronal annealing was carried out for a sample to study the evolution of defect clusters.

  5. Solid state diffusion of NaCl into NaY zeolite studied by positron annihilation

    International Nuclear Information System (INIS)

    A series of samples, prepared from mechanical mixtures of NaCl with NaY zeolite and resulting in the dispersion of NaCl in NaY, was studied by position annihilation spectroscopy. We measured the positron lifetime spectroscopy as a function of the weight ratio of the NaCl-NaY zeolite heated at 500 degree C for 1 h, as a function of the heating temperature held for 1 h, and as a function of the heating duration at 500 degree C for NaCl/NaY (15%). All the lifetime spectra were resolved into five components, in which the third, fourth and fifth components are related to the positron annihilation in β cage, supercage and interface void respectively. The experimental results showed that position annihilation spectroscopy is sensitive to the change of the dispersion of NaCl in NaY zeolite

  6. Fluorescence lifetime spectroscopy in multiple-scattering environments: an application to biotechnology

    Science.gov (United States)

    Cerussi, Albert E.; Gratton, Enrico; Fantini, Sergio

    1999-07-01

    Over the past few years, there has been significant research activity devoted to the application of fluorescence spectroscopy to strongly scattering media, where photons propagate diffusely. Much of this activity focused on fluorescence as a source of contrast enhancement in optical tomography. Our efforts have emphasized the quantitative recovery of fluorescence parameters for spectroscopy. Using a frequency-domain diffusion-based model, we have successfully recovered the lifetime, the absolute quantum yield, the fluorophore concentration, and the emission spectrum of the fluorophore, as well as the absorption and the reduced scattering coefficients at the emission wavelength of the medium in different measurements. In this contribution, we present a sensitive monitor of the binding between ethidium bromide and bovine cells in fresh milk. The spectroscopic contrast was the approximately tenfold increase in the ethidium bromide lifetime upon binding to DNA. The measurement clearly demonstrated that we could quantitatively measure the density of cells in the milk, which is an application vital to the tremendous economic burden of bovine subclinical mastitis detection. Furthermore, we may in principle use the spirit of this technique as a quantitative monitor of the binding of fluorescent drugs inside tissues. This is a first step towards lifetime spectroscopy in tissues.

  7. Positron annihilation investigation of BaSrFBr:Eu by X-ray irradiation

    Science.gov (United States)

    Lee, C. Y.

    2014-12-01

    The mechanical property of the BaSrFBr:Eu phosphor layer of X-ray image plates was investigated by using resolution (LP/mm) and coincidence Doppler broadening (CDB) positron annihilation as well as positron annihilation lifetime (PAL). The image plate samples of BaSrFBr:Eu phosphors in this experiment were irradiated by using hospital X-rays. The LP/mm values of the irradiated BaSrFBr:Eu image plates varied from 3.35 to 1.25 for up to 20,000 exposures. CDB positron annihilation and lifetime spectroscopy were used to analyze defect structures in the phosphor layer. Even when the LP/mm values were greatly decreased due to exposures, the S parameter and the lifetime ( τ 1, τ 2) values were almost constant with increasing number of exposures. A positive relationship existed between the SEM images and positron annihilation spectroscopy (PAS). According to the SEM images and the positron annihilation spectroscopy (PAS) results, measurements of the defects with PAS indicate that the image-plate phosphor can be safely used for hospital X-rays in the course of diagnostic radiography at an average rate of 20,000 times for one year.

  8. Radiative lifetime measurements for some levels in Mn I and Ni I by time-resolved laser spectroscopy

    International Nuclear Information System (INIS)

    Natural radiative lifetimes for 32 excited levels of Mn I and for 17 excited levels of Ni I were measured using time-resolved laser-induced fluorescence (TR-LIF) spectroscopy in laser-induced plasma. The energy regions are from 45,754.27 to 54,950.81 cm−1 for Mn I and from 28,578.018 to 50,851.199 cm−1 for Ni I. The uncertainties of all lifetime results are within 10%. To our best knowledge, 26 lifetime results of Mn I and 9 lifetime results of Ni I are reported for the first time. - Highlights: • The experimental lifetimes of some Mn I and Ni I levels were obtained by time-resolved laser induced fluorescence method. • Radiative lifetimes of 26 energy levels in Mn I were reported for the first time. • Radiative lifetimes of 9 energy levels in Ni I were reported for the first time

  9. Simulation and Characterization of Single Photon Detectors for Fluorescence Lifetime Spectroscopy and Gamma-ray Applications

    OpenAIRE

    Benetti, Michele

    2012-01-01

    Gamma-ray and Fluorescence Lifetime Spectroscopies are driving the development of non-imaging silicon photon sensors and, in this context, Silicon Photo-Multipliers (SiPM)s are leading the starring role. They are 2D array of optical diodes called Single Photon Avalanche Diodes (SPAD)s, and are normally fabricated with a dedicated silicon process. SPADs amplify the charge produced by the single absorbed photon in a way that recalls the avalanche amplification exploited in Photo-Multiplier Tube...

  10. The influence of antioxidant on positron annihilation in polypropylene

    International Nuclear Information System (INIS)

    The purpose of this report is to check the influence of the carbonyl groups (CG), created by oxygen naturally dissolved in a polymer matrix and by the source irradiation, on annihilation characteristics of free positrons using the positron annihilation lifetime spectroscopy (PALS) and coincidence Doppler-broadening spectroscopy (CDBS). Positron annihilation in a pure polypropylene (PP) and in an antioxidant-containing polypropylene (PPA) sample at room and low temperatures has been studied by CDBS. PALS has been used as an o-Ps (orth-positronium) formation monitor. The momentum density distributions of electrons obtained by CDBS at the beginning of measurements have been compared to that at the o-Ps intensity saturation level. It has been shown that the initial concentration of carbonyl groups in a PP sample is high, while for an antioxidant-containing sample, PPA, carbonyl groups are not detected by CDBS. CDBS spectra for a PP can be explained by annihilation of free positrons with the oxygen contained in the carbonyl groups. For a PPA sample, no significant contribution of annihilation with oxygen core electrons can be concluded. (Y. Kazumata)

  11. Thermal desorption gas chromatography and positron annihilation spectroscopy, contribution to alpha decay studies in actinide-doped matrices

    Energy Technology Data Exchange (ETDEWEB)

    Roudil, D.; Jegou, C.; Vella, F.; Folch, B.; Broudic, V. [Commissariat a l' energie Atomique, Rhone Valley Research Center, 30200 Bagnols-sur-Ceze (France); Pik, R. [CNRS-CRPG, 54506 Vandoeuvre-les-Nancy (France); Barthe, M. F. [CNRS-CEMHTI, 45071 Orleans (France); Cuney, M. [Universite de Nancy, CNRS, CREGU, 54506 Vandoeuvre-les-Nancy (France); Pipon, Y. [IPNL CNRS, IN2P3 UMR 5822, 69622 Villeurbanne (France)

    2009-07-01

    A thermal desorption system coupled with a gas analyzer has been adapted and nuclearized to investigate He behavior in actinide-doped samples used to simulate alpha decay aging. This technique widely used in standard laboratories allows measurements of the helium balance and reduced diffusion coefficients, and a preliminary evaluation of helium locations (related to defects and thermal annealing). In our system implemented in a hot cell, small samples are annealed at up to 1100 C degrees in controlled atmosphere. They are inserted in a 10 to 20 cm{sup 3} vessel connected to a micro gas chromatography detector. Initial system calibration allowed concentration measurements within about 10%. Comparisons with the CNRS/CRPG rare gas analysis laboratory at Nancy (France) were applied on natural uranium oxides originating from Oklo (Gabon) and Mistamisk (Canada). The latest results obtained on Mistamisk samples are in good agreement, with a maximum relative deviation of 14%. The data were used to determine the activation energy of about 1 eV.at{sup -1}. On (U,Pu)O{sub 2} and PuO{sub 2} samples the experiments highlight the impact of defects (up to 100 dpa) on He mobility. The defect population must now be characterized to improve our knowledge of He/defect interactions and mechanisms. In addition and synergy to the macroscopic release measurements by gas chromatography, positron annihilation spectroscopy, an effective nondestructive technique for vacancy defect investigation, was also developed and nuclearized in our hot cell laboratory as part of a project supported by the NOMADE and MATINEX research groups. Specific protocols for doped sample analysis were also developed and validated with UO{sub 2} and (U,Pu)O{sub 2} samples. (authors)

  12. Positron annihilation spectroscopy characterize PDMS-MIL-101 hybridmembrane%用正电子湮没谱学技术表征一种有机-无机杂化膜

    Institute of Scientific and Technical Information of China (English)

    王胜; 杨静; 田丽霞; 于胜楠; 曹兴忠; 潘福生; 姜忠义; 于润升; 王宝义

    2015-01-01

    应用正电子湮没寿命谱(Positron annihilation lifetime spectroscopy,PALS)和正电子湮没符合多普勒展宽能谱(Coincidence Doppler broadening energy spectroscopy,CDBES)等正电子湮没谱学技术能从微观尺度上对聚合物-金属有机骨架材料杂化膜的微观结构进行表征.结果表明,随着金属有机骨架(Metal-Organic Frameworks,MOFs)添加量的增大,杂化膜中较小的和较大的自由体积的尺寸都减小了;杂化膜的正电子湮没符合多普勒展宽能谱显示,MIL-101 (Material Institute Lavoisier-l0l)亚纳米粒子的加入使得正电子在聚二甲基硅氧烷(Poly(dimethyl siloxane),PDMS)氧原子上的偏向湮没效应减弱,部分正电子与来自MIL-101亚纳米粒子中金属原子的电子发生湮没,表明MOFs加入改变了聚合物基体自由体积周围的化学环境.

  13. Lifetime-resolved photoacoustic (LPA) spectroscopy for monitoring oxygen change and photodynamic therapy (PDT)

    Science.gov (United States)

    Jo, Janggun; Lee, Chang Heon; Kopelman, Raoul; Wang, Xueding

    2016-03-01

    The Methylene Blue loaded Polyacrylamide Nanoparticles (MB-PAA NPs) are used for oxygen sensing and Photodynamic therapy (PDT), a promising therapeutic modality employed for various tumors, with distinct advantages of delivery of biomedical agents and protection from other bio-molecules overcoming inherent limitations of molecular dyes. Lifetime-resolved photoacoustic spectroscopy using quenched-phosphorescence method is applied with MB-PAA NPs so as to sense oxygen, while the same light source is used for PDT. The dye is excited by absorbing 650 nm wavelength light from a pump laser to reach triplet state. The probe laser at 810 nm wavelength is used to excite the first triplet state at certain delayed time to measure the dye lifetime which indicates oxygen concentration. The 9L cells (106 cells/ml) incubated with MB-PAA NP solution are used for monitoring oxygen level change during PDT in situ test. The oxygen level and PDT efficacy are confirmed with a commercial oximeter, and fluorescence microscope imaging and flow cytometry results. This technique with the MB-PAA NPs allowed us to demonstrate a potential non-invasive theragnostic operation, by monitoring oxygen depletion during PDT in situ, without the addition of secondary probes. Here, we demonstrate this theragnostic operation, in vitro, performing PDT while monitoring oxygen depletion. We also show the correlation between O2 depletion and cell death.

  14. Natural Lifetimes of Excited-states of Neutral Nitrogen Determined By Time-resolved Laser Spectroscopy

    OpenAIRE

    Bengtsson, G. J; Larsson, Jörgen; Svanberg, Sune; Wang, D. D

    1992-01-01

    Radiative lifetimes were determined for three quartet states of neutral nitrogen, and sequences of Rydberg states were studied using depletion spectroscopy. Free nitrogen atoms were generated by photodissociation of N2O using frequency-tripled dye-laser radiation that was two-photon resonant with the 2p(2)3p 4S or 4D states. Further quartet states were reached by a subsequent single-photon absorption. We obtain tau(2p(2)3p 4D7/2) = 44(2) ns, tau(2p(2)3p 4S3/2) = 26.0(1.5) ns, and tau(2p(2)6s4...

  15. Evolution of microstructure of epoxy coating during UV degradation progress studied by slow positron annihilation spectroscopy and electrochemical impedance spectroscopy

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Decrements in S value and water uptake coefficient confirm the post-cure process. • Molecular chain scission leads to the formation of microporous structure. • The formation of an aged layer with high density is verified by EIS. - Abstract: Evolution of chemical functional groups, microstructure and water barrier properties of a polyamide-cured epoxy (diglycidyl ether of bisphenol-A epoxy resin, DGEBA) coating during ultraviolet A (UV-A) photo-oxidative aging is systematically investigated. At the early stage of aging, decrements of S parameter and water uptake coefficient indicate the formation of a more compact structure induced by the post-curing process. After 208 hours (h) of UV irradiation, a novel time constant at relatively high frequency (3.5 × 102 Hz) appears in the electrochemical impedance spectroscopy (EIS) spectra suggesting that a microporous layer generates near the surface of DGEBA film. With the increase in irradiation time, overlap of two time constants at frequencies around 18 Hz and 3.7 × 103 Hz is observed after 1.33 h of immersion, indicating that the micropores grow towards the bulk and form more characteristic layers with microporous structures. After irradiation for 399 h, a low S parameter region near the sample surface is observed, which implies that a surface layer with low free volume may have formed. With longer exposure, EIS results also reveal that the water barrier property of the coating can be improved, which confirms the formation of the denser surface layer near the surface as a result of radical recombination during UV-A treatment

  16. Positron annihilation spectroscopy of vacancy-related defects in CdTe:Cl and CdZnTe:Ge at different stoichiometry deviations

    OpenAIRE

    L. Šedivý; J. Čížek; Belas, E.; Grill, R.; Melikhova, O.

    2016-01-01

    Positron annihilation spectroscopy (PAS) was used to examine the effect of defined Cd-rich and Te-rich annealing on point defects in Cl-doped CdTe and Ge-doped CdZnTe semi-insulating single crystals. The as-grown crystals contain open-volume defects connected with Cd vacancies . It was found that the Cd vacancies agglomerate into clusters coupled with Cl in CdTe:Cl, and in CdZnTe:Ge they are coupled with Ge donors. While annealing in Cd pressure reduces of the density, subsequent annealing in...

  17. Filler content influence on the positron annihilation response in an epoxy resin composite

    Energy Technology Data Exchange (ETDEWEB)

    Salgueiro, W. [IFIMAT-UNCentro, Tandil (Argentina); Somoza, A. [Comision de Investigaciones Cientificas de la Provincia de Buenos Aires, Tandil (Argentina); Goyanes, S. [Buenos Aires Univ. (Argentina). Dept. de Fisica; Dept. de Materiales, CNEA, Buenos Aires (Argentina); Rubiolo, G. [Buenos Aires Univ. (Argentina). Dept. de Fisica; Consejo Nacional de Investigaciones Cientificas y Tecnicas (Argentina); Marzocca, A. [Buenos Aires Univ. (Argentina). Dept. de Fisica; Consolati, G. [Politecnico di Milano, Milan (Italy). Dipt. di Chimica Fisica Applicata

    2001-07-01

    Positron annihilation lifetime spectroscopy and mechanical properties tests were used to study the influence of the filler content on the epoxy resin DGEBA. Using a mechanical model recently developed by the authors of the present work, and the values of the long lifetime component it is possible to evaluate correctly the internal stresses introduced in the epoxy lattice for the filler. Additional information obtained from the analysis of the short-lived lifetime component is also presented. Specifically, in the case of the matrix charged with metallic particles, an interesting correlation between the associated intensity to this component and the filler volume fraction is shown. (orig.)

  18. Current-induced spin polarization on a Pt surface: A new approach using spin-polarized positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Transversely spin-polarized positrons were injected near Pt and Au surfaces under an applied electric current. The three-photon annihilation of spin-triplet positronium, which was emitted from the surfaces into vacuum, was observed. When the positron spin polarization was perpendicular to the current direction, the maximum asymmetry of the three-photon annihilation intensity was observed upon current reversal for the Pt surfaces, whereas it was significantly reduced for the Au surface. The experimental results suggest that electrons near the Pt surfaces were in-plane and transversely spin-polarized with respect to the direction of the electric current. The maximum electron spin polarization was estimated to be more than 0.01 (1%). - Highlights: • Annihilation probability of positronium emitted from the Pt surface into the vacuum under direct current exhibited asymmetry upon current reversal. • The maximum asymmetry appeared when positron spin polarization and the direct current were perpendicular to each other. • Electrons near the Pt surfaces were in-plane and transversely spin-polarized with respect to the direction of the electric current. • Spin-polarized positronium annihilation provides a unique tool for investigating spin polarization on metal surfaces

  19. Radiative lifetime measurements of some Tm I and Tm II levels by time-resolved laser spectroscopy

    Science.gov (United States)

    Tian, Yanshan; Wang, Xinghao; Yu, Qi; Li, Yongfan; Gao, Yang; Dai, Zhenwen

    2016-04-01

    Radiative lifetimes of 88 levels of Tm I in the energy range 22 791.176-48 547.98 cm-1 and 29 levels of Tm II in the range 27 294.79-65 612.85 cm-1 were measured by time-resolved laser-induced fluorescence spectroscopy in laser-ablation plasma. The lifetime values obtained are in the range from 15.4 to 7900 ns for Tm I and from 36.5 to 1000 ns for Tm II. To the best of our knowledge, 77 lifetimes of Tm I and 22 lifetimes of Tm II are reported for the first time. Good agreements between the present results and the previous experimental values were achieved for both Tm I and Tm II.

  20. Multiphoton microscopy, fluorescence lifetime imaging and optical spectroscopy for the diagnosis of neoplasia

    Science.gov (United States)

    Skala, Melissa Caroline

    2007-12-01

    Cancer morbidity and mortality is greatly reduced when the disease is diagnosed and treated early in its development. Tissue biopsies are the gold standard for cancer diagnosis, and an accurate diagnosis requires a biopsy from the malignant portion of an organ. Light, guided through a fiber optic probe, could be used to inspect regions of interest and provide real-time feedback to determine the optimal tissue site for biopsy. This approach could increase the diagnostic accuracy of current biopsy procedures. The studies in this thesis have characterized changes in tissue optical signals with carcinogenesis, increasing our understanding of the sensitivity of optical techniques for cancer detection. All in vivo studies were conducted on the dimethylbenz[alpha]anthracene treated hamster cheek pouch model of epithelial carcinogenesis. Multiphoton microscopy studies in the near infrared wavelength region quantified changes in tissue morphology and fluorescence with carcinogenesis in vivo. Statistically significant morphological changes with precancer included increased epithelial thickness, loss of stratification in the epithelium, and increased nuclear diameter. Fluorescence changes included a statistically significant decrease in the epithelial fluorescence intensity per voxel at 780 nm excitation, a decrease in the fluorescence lifetime of protein-bound nicotinamide adenine dinucleotide (NADH, an electron donor in oxidative phosphorylation), and an increase in the fluorescence lifetime of protein-bound flavin adenine dinucleotide (FAD, an electron acceptor in oxidative phosphorylation) with precancer. The redox ratio (fluorescence intensity of FAD/NADH, a measure of the cellular oxidation-reduction state) did not significantly change with precancer. Cell culture experiments (MCF10A cells) indicated that the decrease in protein-bound NADH with precancer could be due to increased levels of glycolysis. Point measurements of diffuse reflectance and fluorescence spectra in

  1. Microstructural analysis of impurity segregation around β-Nb precipitates in Zr–Nb alloy using positron annihilation spectroscopy and atom probe tomography

    International Nuclear Information System (INIS)

    Graphical abstract: Fe segregation are evident at the interface between β-Nb precipitates and α-Zr matrix by atom probe tomography (APT). Defects are observed at the interface by positron annihilation spectroscopy. It is also suggested that Fe was segregated to a concentration of several tens of percent at a local region at the interface, which is approximately one order of magnitude higher than APT and difficult to observe directly even using APT. - Abstract: Impurity segregation at the interface between β-Nb precipitates and α-Zr matrix in Zr-2.5 wt.%Nb alloy was investigated by complementary analysis with positron annihilation spectroscopy (PAS) and atom probe tomography (APT). Fe segregation and Fe-decorated defects were found at the interface. PAS also suggested that Fe was segregated to a concentration of several tens of percent at a local region at the interface, which is approximately one order of magnitude higher than APT and difficult to observe directly even using APT

  2. Time-dependent investigation of sub-monolayers of Ni on Pd using Positron-annihilation induced Auger Electron Spectroscopy and XPS

    Science.gov (United States)

    Zimnik, Samantha; Piochacz, Christian; Vohburger, Sebastian; Hugenschmidt, Christoph

    2016-01-01

    The surface of a polycrystalline Pd-substrate covered with (sub-) monolayers of Ni was investigated with Positron-annihilation induced Auger Electron Spectroscopy (PAES). Comparative studies using conventional AES induced by electrons and X-rays showed the outstanding surface sensitivity of PAES. Time-dependent PAES was performed on a 0.5 ML Ni cover layer on Pd and compared with conventional X-ray induced Photoelectron Spectroscopy (XPS) in order to observe changes in the elemental composition of the surface. The PAES results appear to show a migration of Ni atoms into the Pd substrate, whereas the Ni signal shows a decrease of 12% within 13 h with respect to the initial value.

  3. Characterization of zeolite Y pastilles for the ortho-positronium annihilation studies; Caracterizacion de pastillas de zeolita Y para estudios de aniquilacion de orto-positronio

    Energy Technology Data Exchange (ETDEWEB)

    Alvarado D, E.; Garcia S, I.; Cabral P, A. [ININ, Carretera Mexico-Toluca s/n, Ocoyoacac 52750, Estado de Mexico (Mexico)

    2008-07-01

    This paper presents the characterization of zeolite Y pastilles prior to their study by the Positronium Annihilation Lifetimes Spectroscopy. The characterization is the estimation of porosity, the determination of its purity and crystal size for X-ray diffraction, the determination of its morphology and particle size by scanning electron microscopy and its specific area by the Brunauer-Emmett-Teller method. Presenting the first lifetimes measurements of positronium in zeolites LTA and Y. (Author)

  4. Deconvolution of Positrons' Lifetime spectra

    International Nuclear Information System (INIS)

    In this paper, we explain the iterative method previously develop for the deconvolution of Doppler broadening spectra using the mathematical optimization theory. Also, we start the adaptation and application of this method to the deconvolution of positrons' lifetime annihilation spectra

  5. AC quantum efficiency harmonic analysis of exciton annihilation in organic light emitting diodes (Presentation Recording)

    Science.gov (United States)

    Giebink, Noel C.

    2015-10-01

    Exciton annihilation processes impact both the lifetime and efficiency roll-off of organic light emitting diodes (OLEDs), however it is notoriously difficult to identify the dominant mode of annihilation in operating devices (exciton-exciton vs. exciton-charge carrier) and subsequently to disentangle its magnitude from competing roll-off processes such as charge imbalance. Here, we introduce a simple analytical method to directly identify and extract OLED annihilation rates from standard light-current-voltage (LIV) measurement data. The foundation of this approach lies in a frequency domain EQE analysis and is most easily understood in analogy to impedance spectroscopy, where in this case both the current (J) and electroluminescence intensity (L) are measured using a lock-in amplifier at different harmonics of the sinusoidal dither superimposed on the DC device bias. In the presence of annihilation, the relationship between recombination current and light output (proportional to exciton density) becomes nonlinear, thereby mixing the different EQE harmonics in a manner that depends uniquely on the type and magnitude of annihilation. We derive simple expressions to extract different annihilation rate coefficients and apply this technique to a variety of OLEDs. For example, in devices dominated by triplet-triplet annihilation, the annihilation rate coefficient, K_TT, is obtained directly from the linear slope that results from plotting EQE_DC-EQE_1ω versus L_DC (2EQE_1ω-EQE_DC). We go on to show that, in certain cases it is sufficient to calculate EQE_1ω directly from the slope of the DC light versus current curve [i.e. via (dL_DC)/(dJ_DC )], thus enabling this analysis to be conducted solely from common LIV measurement data.

  6. Thermal treatment of the Fe78 Si9 B13 alloy and the analysis of it magnetic properties through Moessbauer spectroscopy and Positronium annihilation

    International Nuclear Information System (INIS)

    The present work is divided in five chapters. In the first one a general vision of the amorphous alloys is given from antecedents, structure, obtaining methods, properties and problems that at the moment, focusing us in a certain moment to the iron base alloys and the anomalous problem of hardness that it presents the alloy Fe78Si9B13 like previously mention us. The second chapter tries on the basic theory of the techniques of Moessbauer spectroscopy and Positron Annihilation spectroscopy, used for the characterization of our alloy as well as the complementary technique of X-ray diffraction (XRD) to observe that the amorphous phase was even studying. The third chapter describes the experimental conditions that were used to study the alloy Fe78Si9B13 in each one of their thermal treatments. In the fourth chapter the obtained results and their discussion are presented. In the fifth chapter the conclusions to which were arrived after analyzing the results are presented. (Author)

  7. Study of Pd--Ta on Si(100) using Auger electron spectroscopy, Rutherford backscattering spectrometry, and variable energy positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    van der Kolk, G.J.; Kuiper, A.E.T.; Duchateau, J.P.W.B.; Willemsen, M.; Nielsen, B.; Lynn, K.G.

    1989-05-01

    The applicability of Pd/sub x/Ta/sub 1-//sub x/ as a diffusion barrier on Si has been investigated. For this purpose Pd/sub x/Ta/sub 1-//sub x/ films of 200-nm thickness (x ranges from 0 to 1) were deposited on Si(100), and the reaction between overlayer and substrate was studied as a function of temperature. Interaction was found to occur at temperatures increasing with the Ta content. The as-deposited Pd/sub x/Ta/sub 1-//sub x/ films with 0.2less than or equal toxless than or equal to0.6 were found to be amorphous. The amorphous phase had a higher reaction temperature than the crystalline one, causing a discontinuous step in the reaction temperature. Rutherford backscattering spectrometry spectra revealed that for the Pd-rich compositions, first a stoichiometric Pd/sub 2/Si layer formed underneath a pure Ta layer. At higher temperatures TaSi/sub 2/ formed at the surface. For Ta-rich compositions Pd/sub 2/Si formed first as well; however, the reaction temperature was so high that Pd/sub 2/Si grains formed in a Si matrix. The defect density of the Ta layer, which remained after outdiffusion of Pd, was investigated using variable energy positron annihilation. The defect concentration is very high, as deduced from the trapped positron fraction. A model is presented that describes the composition dependence of the reaction temperature.

  8. Constitutional and/or thermal vacancies in some B2 intermetallic compounds studied by positron lifetime spectroscopy

    International Nuclear Information System (INIS)

    Constitutional vacancies have been observed in some B2 intermetallics such as NiAl, CoAl, NiGa and CoGa by using positron lifetime spectroscopy. A large amount of non-thermal vacancies have been found not only on transition-element-poor compositions but also on transition-element-rich compositions of these intermetallics. B2 CuZn does not have such constitutional vacancies, but has a very low vacancy formation enthalpy. Intermetallic compounds with B2 structure are quite unique in the manner of vacancy formation. (orig.)

  9. Early Stages of Precipitation Process in Al-(Mn-)Sc-Zr Alloy Characterized by Positron Annihilation

    KAUST Repository

    Vlach, Martin

    2015-01-29

    Thermal effects on the precipitation stages in as-cast Al-0.70 at. pct Mn-0.15 at. pct Sc-0.05 at. pct Zr alloy were studied. The role of lattice defects was elucidated by positron annihilation spectroscopy (lifetime and coincidence Doppler broadening) enabling investigation of solutes clustering at the atomic scale. This technique has never been used in the Al-Sc- and/or Al-Zr-based alloys so far. Studies by positron annihilation were combined with resistometry, hardness measurements, and microstructure observations. Positrons trapped at defects are preferentially annihilated by Sc electrons. Lifetime of trapped positrons indicates that Sc atoms segregate at dislocations. Maximum fraction of positrons annihilated by Sc electrons occurring at 453 K (180 °C) suggests that clustering of Sc bound with vacancies takes place. It is followed by peak of this fraction at 573 K (300 °C). A rise of the contribution of trapped positrons annihilated by Zr electrons starting at 513 K (240 °C) and attaining maximum also at 573 K (300 °C) confirms that Zr participates in precipitation of the Al3Sc particles already at these temperatures. The pronounced hardening at 573 K (300 °C) has its nature in the precipitation of the Al3Sc particles with a Zr-rich shell. The contribution of trapped positrons annihilated by Mn electrons was found to be negligible. © 2015, The Minerals, Metals & Materials Society and ASM International.

  10. Two-photon excited fluorescence lifetime imaging and spectroscopy of melanins in vitro and in vivo

    Science.gov (United States)

    Krasieva, Tatiana B.; Stringari, Chiara; Liu, Feng; Sun, Chung-Ho; Kong, Yu; Balu, Mihaela; Meyskens, Frank L.; Gratton, Enrico; Tromberg, Bruce J.

    2013-03-01

    Changes in the amounts of cellular eumelanin and pheomelanin have been associated with carcinogenesis. The goal of this work is to develop methods based on two-photon-excited-fluorescence (TPEF) for measuring relative concentrations of these compounds. We acquire TPEF emission spectra (λex=1000 nm) of melanin in vitro from melanoma cells, hair specimens, and in vivo from healthy volunteers. We find that the pheomelanin emission peaks at approximately 615 to 625 nm and eumelanin exhibits a broad maximum at 640 to 680 nm. Based on these data we define an optical melanin index (OMI) as the ratio of fluorescence intensities at 645 and 615 nm. The measured OMI for the MNT-1 melanoma cell line is 1.6±0.22 while the Mc1R gene knockdown lines MNT-46 and MNT-62 show substantially greater pheomelanin production (OMI=0.5±0.05 and 0.17±0.03, respectively). The measured values are in good agreement with chemistry-based melanin extraction methods. In order to better separate melanin fluorescence from other intrinsic fluorophores, we perform fluorescence lifetime imaging microscopy of in vitro specimens. The relative concentrations of keratin, eumelanin, and pheomelanin components are resolved using a phasor approach for analyzing lifetime data. Our results suggest that a noninvasive TPEF index based on spectra and lifetime could potentially be used for rapid melanin ratio characterization both in vitro and in vivo.

  11. Direct evidence for positron annihilation from shallow traps

    DEFF Research Database (Denmark)

    Linderoth, Søren; Hidalgo, C.

    1987-01-01

    For deformed Ag the temperature dependence of the positron lifetime parameters is followed between 12 and 300 K. Clear direct evidence for positron trapping and annihilation at shallow traps, with a positron binding energy of 9±2 meV and annihilation characteristics very similar to those in the...

  12. Spectroscopy and lifetime measurements of states in $^{76}$Kr populated in $^{76}$Rb decay

    CERN Document Server

    Giannatiempo, A; Perego, A; Sona, P; Mach, H; Fogelberg, B; García-Borge, M J; Tengblad, O; Fraile-Prieto, L M; Aas, A J; Gulda, K; CERN. Geneva

    2005-01-01

    The properties of the excited states of $^{76}$Kr, populated in the decay of $^{76}$Rb produced at ISOLDE isotopic separator, have been investigated by using K-conversion electron, $\\gamma$-ray, and $\\gamma\\gamma$ coincidence measurements. The lifetimes of several levels have been measured by means of the Advanced Time-Delayed $\\beta\\gamma\\gamma (t)$ method. The identification of 19 new levels and 55 transitions and the information deduced on spin and/or parity of the observed states from K-conversion coefficients, log ft values and decay properties have led to an improved knowledge of the level scheme. In particular, six 1$^-$ states have been definitely identified and $J^{\\pi} =2^{-}$ has been assigned to the 2227 keV level, on which a band proposed to have negative-parity and even-spin had been previously observed. The strengths of the $E$0 and $E$2 transitions de-exciting the 0$^{+}_{2}$ and 0$^{+}_{3}$ states (the latter is here identified with the state at 1598 keV) have been measured. The experimental ...

  13. Nanometer cavities studied by positron annihilation

    International Nuclear Information System (INIS)

    Positronium (Ps) is trapped in cavities in insulating solids, and the lifetime of ortho Ps is determined by the size of the cavity. The information on the properties of the cavities obtained by use of the standard slow positron beam and the 'normal' positron annihilation techniques is compared for several selected cases. (author)

  14. A positron annihilation study of hydrated DNA

    DEFF Research Database (Denmark)

    Warman, J. M.; Eldrup, Morten Mostgaard

    1986-01-01

    Positron annihilation measurements are reported for hydrated DNA as a function of water content and as a function of temperature (20 to -180.degree. C) for samples containing 10 and 50% wt of water. The ortho-positronium mean lifetime and its intensity show distinct variations with the degree...

  15. Electrochemical impedance spectroscopy investigation on the clinical lifetime of ProTaper rotary file system.

    Science.gov (United States)

    Penta, Virgil; Pirvu, Cristian; Demetrescu, Ioana

    2014-01-01

    The main objective of the current paper is to show that electrochemical impedance spectroscopy (EIS) could be a method for evaluating and predicting of ProTaper rotary file system clinical lifespan. This particular aspect of everyday use of the endodontic files is of great importance in each dental practice and has profound clinical implications. The method used for quantification resides in the electrochemical impedance spectroscopy theory and has in its main focus the characteristics of the surface titanium oxide layer. This electrochemical technique has been adapted successfully to identify the quality of the Ni-Ti files oxide layer. The modification of this protective layer induces changes in corrosion behavior of the alloy modifying the impedance value of the file. In order to assess the method, 14 ProTaper sets utilized on different patients in a dental clinic have been submitted for testing using EIS. The information obtained in regard to the surface oxide layer has offered an indication of use and proves that the said layer evolves with each clinical application. The novelty of this research is related to an electrochemical technique successfully adapted for Ni-Ti file investigation and correlation with surface and clinical aspects.

  16. Electrochemical Impedance Spectroscopy Investigation on the Clinical Lifetime of ProTaper Rotary File System

    Science.gov (United States)

    Pirvu, Cristian; Demetrescu, Ioana

    2014-01-01

    The main objective of the current paper is to show that electrochemical impedance spectroscopy (EIS) could be a method for evaluating and predicting of ProTaper rotary file system clinical lifespan. This particular aspect of everyday use of the endodontic files is of great importance in each dental practice and has profound clinical implications. The method used for quantification resides in the electrochemical impedance spectroscopy theory and has in its main focus the characteristics of the surface titanium oxide layer. This electrochemical technique has been adapted successfully to identify the quality of the Ni-Ti files oxide layer. The modification of this protective layer induces changes in corrosion behavior of the alloy modifying the impedance value of the file. In order to assess the method, 14 ProTaper sets utilized on different patients in a dental clinic have been submitted for testing using EIS. The information obtained in regard to the surface oxide layer has offered an indication of use and proves that the said layer evolves with each clinical application. The novelty of this research is related to an electrochemical technique successfully adapted for Ni-Ti file investigation and correlation with surface and clinical aspects. PMID:24605336

  17. Electrochemical Impedance Spectroscopy Investigation on the Clinical Lifetime of ProTaper Rotary File System

    Directory of Open Access Journals (Sweden)

    Virgil Penta

    2014-01-01

    Full Text Available The main objective of the current paper is to show that electrochemical impedance spectroscopy (EIS could be a method for evaluating and predicting of ProTaper rotary file system clinical lifespan. This particular aspect of everyday use of the endodontic files is of great importance in each dental practice and has profound clinical implications. The method used for quantification resides in the electrochemical impedance spectroscopy theory and has in its main focus the characteristics of the surface titanium oxide layer. This electrochemical technique has been adapted successfully to identify the quality of the Ni-Ti files oxide layer. The modification of this protective layer induces changes in corrosion behavior of the alloy modifying the impedance value of the file. In order to assess the method, 14 ProTaper sets utilized on different patients in a dental clinic have been submitted for testing using EIS. The information obtained in regard to the surface oxide layer has offered an indication of use and proves that the said layer evolves with each clinical application. The novelty of this research is related to an electrochemical technique successfully adapted for Ni-Ti file investigation and correlation with surface and clinical aspects.

  18. Spectroscopy and Fluorescence Lifetime Imaging Microscopy To Probe the Interaction of Bovine Serum Albumin with Graphene Oxide.

    Science.gov (United States)

    Kuchlyan, Jagannath; Kundu, Niloy; Banik, Debasis; Roy, Arpita; Sarkar, Nilmoni

    2015-12-29

    The interaction of graphene oxide (GO) with bovine serum albumin (BSA) in aqueous buffer solution has been investigated with various spectroscopic and imaging techniques. At single molecular resolution this interaction has been performed using fluorescence correlation spectroscopy (FCS) and fluorescence lifetime imaging microscopy (FLIM) techniques. The conformational dynamics of BSA on GO's influence have been explored by FCS and circular dichroism (CD) spectroscopy. For the FCS studies BSA was labeled covalently by a fluorophore, Alexa Fluor 488. On the addition of GO in phosphate buffer of 10 mM at pH 7.4 the diffusion time (τD) and the hydrodynamic radius (Rh) of BSA increase due to adsorption of BSA. Conformational relaxation time components of native BSA drastically vary with the addition of GO, signifying the change of conformational dynamics of BSA after addition of GO. The adsorption isotherm also indicates significant adsorption of BSA on the GO surface. Adsorption of BSA on the GO surface has shown in direct images of atomic force microscopy (AFM) and FLIM. Fluorescence quenching study of BSA with addition of GO also indicates that there is strong interaction between BSA and GO. PMID:26646418

  19. Positron annihilation in the hydrogenated granular superconductor of YBa 2Cu 3O 7-δ

    Science.gov (United States)

    Lam, C. C.; Shao, L. W.; Jin, X.; Chen, W. M.; Xiong, H. Q.; Feng, J.; Qi, S. R.; Hung, K. C.

    1996-02-01

    In this paper, we have used the sputtering neutral-particles mass spectroscopy (SNMS) and positron-annihilation technique to investigate the effect of hydrogenation on the physical properties of different oxygenated YBa 2Cu 3O 7-δ superconductors. Under the same of hydrogenation treatment, the hydrogenation effects on the superconductors are compared to the non-superconductors. It was shown that the hydrogen concentration in the superconductors is about eight times of the non-superconductor's. It was proven that the long lifetime of positrons in the annihilation process is determined by the variation of the concentrations of monovacancies and microvoids, which takes place in both of intragrain and intergrain samples. The hydrogenation effect can be classified into four stages. At the first stage, the hydrogen atoms fill both monovacancy and microvoid. At the end of the first stage, the long lifetime τ2 reaches the maximum value which is determined by the lifetime of the positron in the monovacancy-free and nearly microvoid-exhausted YBCO sample. In the second stage, the hydrogen charging will lead to creation of new monovacancies; this will make the long lifetime τ2 drop monotonically to its minimum value. In the third stage, further hydrogen charging promotes the formation of microvoids, and leads to an increasing τ2 up to a saturation value, which indicates the equilibrium concentrations of monovacancy and microvoid at that temperature.

  20. Radiation-induced defects in chalcogenide glasses characterized by combined optical spectroscopy, XPS and PALS methods

    International Nuclear Information System (INIS)

    Temperature-dependent optical absorption spectroscopy, high-resolution X-ray photoelectron spectroscopy and positron annihilation lifetimes spectroscopy are utilized to understand radiation-induced changes in Ge-Sb-S chalcogenide glasses. Theoretically predicted topological scheme of γ-induced coordination defect formation in stoichiometric Ge23.5Sb11.8S64.7 glass composition is supported by these measurements. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. Positronium lifetime in polymers

    CERN Document Server

    Camacho, Abel

    2004-01-01

    A model describing the relationship between the ortho--positronium lifetime and the volume of a void, located in a synthetic zeolite, is analyzed. Our idea, which allows us to take into account the effects of temperature, comprises the introduction of a non--hermitian term in the Hamiltonian, which accounts for the annihilation of the ortho--positronium. The predictions of the present model are also confronted against an already known experimental result.

  2. The application of positron annihilation lifetime spectroscopy in polystyrene%正电子淹没寿命谱在聚苯乙烯中的应用

    Institute of Scientific and Technical Information of China (English)

    林榕; Corine Bas

    2008-01-01

    采用自由基聚合方法合成了3个不同分子量的聚苯乙烯,进而用正电子淹没寿命谱(PALS)对这3个样品的拾获淹没寿命τ3及其淹没强度Ⅰ3进行了研究.实验结果表明,常温下聚苯乙烯的拾获淹没寿命τ3对分子量没有依赖性,但分子量及极性基团对其淹没强度Ⅰ3有着显著的影响.

  3. Positron annihilation studies of 4-n-butyl-4'-isothiocyanato-1,1'-biphenyl.

    Science.gov (United States)

    Dryzek, E; Juszyńska, E; Zaleski, R; Jasińska, B; Gorgol, M; Massalska-Arodź, M

    2013-08-01

    Positron annihilation lifetime spectroscopy (PALS) measurements were performed between 93 and 293 K in order to study the supercooled smectic-E (Sm-E) phase of 4-n-butyl-4'-isothiocyanato-1,1'-biphenyl (4TCB), the ordered molecular crystal of 4TCB, and the phase transition between the Sm-E phase and the ordered molecular crystal of 4TCB. The phase transition was well reflected in the abrupt increase of the ortho-positronium (o-Ps) lifetime and intensity. The value of the o-Ps lifetime in the Sm-E liquid crystalline phase of 4TCB, i.e., 2.21 ns at room temperature, was explained by the formation of bubbles induced by Ps atoms, which are created due to a liquidlike state of the butyl chains of 4TCB molecules in the Sm-E phase. The temperature dependence of the o-Ps intensity for the supercooled Sm-E phase can be explained by thermal generation of sites where bubbles are formed; an activation energy equal to 0.30±0.02 eV was estimated. This value was compared with the activation energies of molecular motions. The o-Ps lifetime in the ordered molecular crystal was interpreted as originating from the annihilation of o-Ps confined in molecular vacancy-type imperfections in the crystal lattice. The value of the o-Ps pickoff annihilation between 1.8 and 1.9 ns is in accordance with the size of the molecular vacancy for the 4TCB crystal lattice. Its intensity is lower than 5%. The isothermal crystallization of the 4TCB Sm-E phase was observed by PALS. The low-dimensional crystal growth was concluded from the Avrami equation fitted to the time dependence of the o-Ps intensity, which resulted in an Avrami exponent equal to 1.73. PMID:24032853

  4. Direct Vpr-Vpr Interaction in Cells monitored by two Photon Fluorescence Correlation Spectroscopy and Fluorescence Lifetime Imaging

    Directory of Open Access Journals (Sweden)

    Mély Yves

    2008-09-01

    Full Text Available Abstract Background The human immunodeficiency virus type 1 (HIV-1 encodes several regulatory proteins, notably Vpr which influences the survival of the infected cells by causing a G2/M arrest and apoptosis. Such an important role of Vpr in HIV-1 disease progression has fuelled a large number of studies, from its 3D structure to the characterization of specific cellular partners. However, no direct imaging and quantification of Vpr-Vpr interaction in living cells has yet been reported. To address this issue, eGFP- and mCherry proteins were tagged by Vpr, expressed in HeLa cells and their interaction was studied by two photon fluorescence lifetime imaging microscopy and fluorescence correlation spectroscopy. Results Results show that Vpr forms homo-oligomers at or close to the nuclear envelope. Moreover, Vpr dimers and trimers were found in the cytoplasm and in the nucleus. Point mutations in the three α helices of Vpr drastically impaired Vpr oligomerization and localization at the nuclear envelope while point mutations outside the helical regions had no effect. Theoretical structures of Vpr mutants reveal that mutations within the α-helices could perturb the leucine zipper like motifs. The ΔQ44 mutation has the most drastic effect since it likely disrupts the second helix. Finally, all Vpr point mutants caused cell apoptosis suggesting that Vpr-mediated apoptosis functions independently from Vpr oligomerization. Conclusion We report that Vpr oligomerization in HeLa cells relies on the hydrophobic core formed by the three α helices. This oligomerization is required for Vpr localization at the nuclear envelope but not for Vpr-mediated apoptosis.

  5. Characterization of a potentially axially symmetric europium(III) complex of a tetraacetate,tetraaza, macrocyclic ligand by luminescence excitation, emission and lifetime spectroscopy

    Science.gov (United States)

    Albin, Michael; de, William; Horrocks, W., Jr.; Liotta, Frank J.

    1982-01-01

    The Eu(III) complex of the octadentate macrocyclic ligand, 1,4,7,10-tetraazacyclododecane-N,N',N'',N''' -tetraacetate, DOTA, has been examined by luminescence excitation, emission, and lifetime spectroscopy using pulsed dye laser techniques. The results confirm the expected axially symmetric nature of the major component in solution and reveal that 1.2 ± 0.4 water molecules arc coordinatcd to the Eu(III) ion in the complex.

  6. Study of plasma sprayed copper alloy using positron annihilation

    International Nuclear Information System (INIS)

    A positron annihilation technique has been employed to study the microdefects of copper alloy sprayed on a steel substrate by plasma after being compressed in different thickness. The positron lifetime in the alloy is varied with different amount of compression. It is found that the positron lifetime decreases with increasing of the compression deformation. On the contrary, the positron lifetime is increased for normal alloy after deformation

  7. Application of positron annihilation techniques in non-destructive testing

    International Nuclear Information System (INIS)

    Background: The investigation of the material damage state is very important for industrial application. Most mechanical damage starts with a change in the microstructure of the material. Positron annihilation techniques are very sensitive probes for detecting defects and damage on an atomic scale in materials, which are of great concern in the engineering applications. Additionally they are apparatus of non-destruction, high-sensitivity and easy-use. Purpose: Our goal is to develop a system to exploit new non-destructive testing (NDT) methods using positron annihilation spectroscopy, a powerful tool to detect vacancy-type defects and their chemical environment. Methods: A positron NDT system was designed and constructed by modifying the 'sandwich structure' of sample-source-sample in conventional Doppler broadening and positron lifetime spectrometers. Doppler broadening and positron lifetime spectra of a single sample can be measured and analyzed by subtracting the contribution of a reference sample. Results: The feasibility and reliability of positron NDT system have been tested by analyzing nondestructively deformation and damage caused by mechanical treatment or by irradiation of metal alloys. This system can be used for detecting defects and damage in thick or large-size samples, as well as for measuring the two-dimension distribution of defects in portable, sensitive, fast way. Conclusion: Positron NDT measurement shows changes in real atomic-scale defects prior to changes in the mechanical properties, which are detectable by other methods of NDT, such as ultrasonic testing and eddy current testing. This system can be developed for use in both the laboratory and field in the future. (authors)

  8. Positron annihilation studies of some charge transfer molecular complexes

    CERN Document Server

    El-Sayed, A; Boraei, A A A

    2000-01-01

    Positron annihilation lifetimes were measured for some solid charge transfer (CT) molecular complexes of quinoline compounds (2,6-dimethylquinoline, 6-methoxyquinoline, quinoline, 6-methylquinoline, 3-bromoquinoline and 2-chloro-4-methylquinoline) as electron donor and picric acid as an electron acceptor. The infrared spectra (IR) of the solid complexes clearly indicated the formation of the hydrogen-bonding CT-complexes. The annihilation spectra were analyzed into two lifetime components using PATFIT program. The values of the average and bulk lifetimes divide the complexes into two groups according to the non-bonding ionization potential of the donor (electron donating power) and the molecular weight of the complexes. Also, it is found that the ionization potential of the donors and molecular weight of the complexes have a conspicuous effect on the average and bulk lifetime values. The bulk lifetime values of the complexes are consistent with the formation of stable hydrogen-bonding CT-complexes as inferred...

  9. The Structure of the Free Volume in Poly(styrene-co-acrylonitrile) from Positron Lifetime and Pressure Volume Temperature (PVT) Experiments

    OpenAIRE

    Dlubek, Gunter; Bondarenko, Vladimir; Al-Qaradawi, Ilham Y.; Kilburn, Duncan; Krause-Rehberg, Reinhard

    2004-01-01

    Summary: The structure of the free volume and its temperature dependence between 25 and 190 °C of copolymers of styrene with acrylonitrile, SAN (0 to 50 mol-% AN), is studied by pressure volume temperature (PVT) experiments and positron annihilation lifetime spectroscopy (PALS). In this second part of the work, PALS data are reported from which the temperature dependence of the mean size and size distribution of local free volumes (subnanometer size holes) is analysed. The mean hole volume, v...

  10. Radiative lifetime measurements of odd-parity highly-excited levels of Sn I by time-resolved laser spectroscopy

    Institute of Scientific and Technical Information of China (English)

    Xu Jia-Xin; Feng Yan-Yan; Sun Gui-Juan; Dai Zhen-Wen

    2009-01-01

    Natural radiative lifetimes of five higher-lying odd-parity levels 5pTs 3p1o,5p5d 1p1o,5p6d 3F2o,3D1o and 3F3o in neutral tin are measured by the time-resolved laser-induced fluorescence (TR-LIF) technique and the atomic beam method. All these lifetimes are not longer than 100 ns and they are found to be shorter than the lifetimes of evenparity levels in the same energy region. The results reported in this paper provide important transition parameters for highly-excited atomic Sn,which may be useful for theoretically calculating excited heavy atoms.

  11. A Position Annihilation Study of Defect Recovery in Electron-Irradiated alpha-Zr

    DEFF Research Database (Denmark)

    Hood, G. M.; Eldrup, Morten Mostgaard; Mogensen, O. E.

    1977-01-01

    The presence of vacancy defects in α-Zr, irradiated at 320 > T > 290 K with 1.5 MeV electrons, has been indicated by positron annihilation measurements. It was found that positron lifetimes associated with annihilation in well-annealed α-Zr, fell in the range 173 to 181 psec, with no obvious depe...

  12. Positron annihilation studies in solid 2-aminopyridine, 3-aminopyridine, 4-aminopyridine and 2-aminopyrimidine

    Science.gov (United States)

    Netto, A. Marques; Bicalho, S. M. C. M.; Filgueiras, Ca. L.; Machado, J. C.

    1985-09-01

    Positron annihilation lifetimes and Doppler-broadened annihilation lines have been measured in solid 2-aminopyridine (2-APY), 3-aminopyridine (3-APY), 4-aminopyridine (4-APY) and 2-aminopyrimidine (2-APYM). The results point to the formation of positronium in the solid pyridines and the yields are discussed in terms of the structures and the electron donation character of the compounds.

  13. Study of Defects in GaAs by 2D-ACAR Positron Annihilation

    OpenAIRE

    Manuel, A; Ambigapathy, R.; Hautojärvi, P.; Saarinen, K.; Corbel, C.

    1995-01-01

    We describe the two dimensional angular correlation of positron annihilation radiation (2D-ACAR) method and show that it can be advantageously used to study the electronic structure of defects, in addition to standard positron lifetime and Doppler broadening measurements. Using annihilation fractions determined by lifetime measurements, we separate 2D-ACAR distributions for negatively charged and neutral arsenic vacancies in n-type GaAs. In electron-irradiated semi-insulating GaAs, we present...

  14. Probing electronic lifetimes and phonon anharmonicities in high-quality chemical vapor deposited graphene by magneto-Raman spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Neumann, Christoph, E-mail: cneumann@physik.rwth-aachen.de; Stampfer, Christoph [JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen (Germany); Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich (Germany); Halpaap, Donatus; Banszerus, Luca; Schmitz, Michael; Beschoten, Bernd [JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen (Germany); Reichardt, Sven [JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen (Germany); Physics and Materials Science Research Unit, Université du Luxembourg, 1511 Luxembourg (Luxembourg); Watanabe, Kenji; Taniguchi, Takashi [National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan)

    2015-12-07

    We present a magneto-Raman study on high-quality single-layer graphene grown by chemical vapor deposition (CVD) that is fully encapsulated in hexagonal boron nitride by a dry transfer technique. By analyzing the Raman D, G, and 2D peaks, we find that the structural quality of the samples is comparable with state-of-the-art exfoliated graphene flakes. From B-field dependent Raman measurements, we extract the broadening and associated lifetime of the G peak due to anharmonic effects. Furthermore, we determine the decay width and lifetime of Landau level (LL) transitions from magneto-phonon resonances as a function of laser power. At low laser power, we find a minimal decay width of 140 cm{sup −1} highlighting the high electronic quality of the CVD-grown graphene. At higher laser power, we observe an increase of the LL decay width leading to a saturation, with the corresponding lifetime saturating at a minimal value of 18 fs.

  15. Probing electronic lifetimes and phonon anharmonicities in high-quality chemical vapor deposited graphene by magneto-Raman spectroscopy

    Science.gov (United States)

    Neumann, Christoph; Halpaap, Donatus; Reichardt, Sven; Banszerus, Luca; Schmitz, Michael; Watanabe, Kenji; Taniguchi, Takashi; Beschoten, Bernd; Stampfer, Christoph

    2015-12-01

    We present a magneto-Raman study on high-quality single-layer graphene grown by chemical vapor deposition (CVD) that is fully encapsulated in hexagonal boron nitride by a dry transfer technique. By analyzing the Raman D, G, and 2D peaks, we find that the structural quality of the samples is comparable with state-of-the-art exfoliated graphene flakes. From B-field dependent Raman measurements, we extract the broadening and associated lifetime of the G peak due to anharmonic effects. Furthermore, we determine the decay width and lifetime of Landau level (LL) transitions from magneto-phonon resonances as a function of laser power. At low laser power, we find a minimal decay width of 140 cm-1 highlighting the high electronic quality of the CVD-grown graphene. At higher laser power, we observe an increase of the LL decay width leading to a saturation, with the corresponding lifetime saturating at a minimal value of 18 fs.

  16. Positron annihilation characterization of free volume in micro- and macro-modified Cu0.4Co0.4Ni0.4Mn1.8O4 ceramics

    Science.gov (United States)

    Klym, H.; Ingram, A.; Shpotyuk, O.; Hadzaman, I.; Solntsev, V.; Hotra, O.; Popov, A. I.

    2016-07-01

    Free volume and pore size distribution size in functional micro and macro-micro-modified Cu0.4Co0.4Ni0.4Mn1.8O4 ceramics are characterized by positron annihilation lifetime spectroscopy in comparison with Hg-porosimetry and scanning electron microscopy technique. Positron annihilation results are interpreted in terms of model implication positron trapping and ortho-positronium decaying. It is shown that free volume of positron traps are the same type for macro and micro modified Cu0.4Co0.4Ni0.4Mn1.8O4 ceramics. Classic Tao-Eldrup model in spherical approximation is used to calculation of the size of nanopores smaller than 2 nm using the ortho-positronium lifetime.

  17. Positron Annihilation in a Rubber Modified Epoxy Resin

    DEFF Research Database (Denmark)

    Mogensen, O. E.; Jacobsen, F. M.; Pethrick, R. A.

    1979-01-01

    Positron annihilation data is reported on a rubber-modified epoxy resin. Studies of the temperature dependence of the o-positronium lifetime indicated the existence of three distinct regions; the associated transition temperatures by comparison with dilatometric data can be ascribed respectively...

  18. Antineutron-nucleus annihilation

    CERN Document Server

    Botta, E

    2001-01-01

    The n-nucleus annihilation process has been studied by the OBELIX experiment at the CERN Low Energy Antiproton Ring (LEAR) in the (50-400) MeV/c projectile momentum range on C, Al, Cu, Ag, Sn, and Pb nuclear targets. A systematic survey of the annihilation cross- section, sigma /sub alpha /(A, p/sub n/), has been performed, obtaining information on its dependence on the target mass number and on the incoming n momentum. For the first time the mass number dependence of the (inclusive) final state composition of the process has been analyzed. Production of the rho vector meson has also been examined. (13 refs).

  19. Observation of a charge delocalization from Se vacancies in Bi2Se3 : A positron annihilation study of native defects

    Science.gov (United States)

    Unzueta, I.; Zabala, N.; Marín-Borrás, V.; Muñoz-Sanjosé, V.; García, J. A.; Plazaola, F.

    2016-07-01

    By means of positron annihilation lifetime spectroscopy, we have investigated the native defects present in Bi2Se3 , which belongs to the family of topological insulators. We experimentally demonstrate that selenium vacancy defects (VSe1) are present in Bi2Se3 as-grown samples, and that their charge is delocalized as temperature increases. At least from 100 K up to room temperature both VSe10 and VSe1+ charge states coexist. The observed charge delocalization determines the contribution of VSe1 defects to the n -type conductivity of Bi2Se3 . These findings are supported by theoretical calculations, which show that vacancies of nonequivalent Se1 and Se2 selenium atoms are clearly differentiated by positron annihilation lifetime spectroscopy, enabling us to directly detect and quantify the most favorable type of selenium vacancy. In addition to open-volume defects, experimental data indicate the presence of defects that act as shallow traps, suggesting that more than one type of native defects coexist in Bi2Se3 . As will be discussed, the presence of a dislocation density around 1010cm-2 could be the source of the detected shallow traps. Understanding the one-dimensional defects and the origin of the charge delocalization that leads Bi2Se3 to be an n -type semiconductor will help in the development of high-quality topological insulators based on this material.

  20. Defect identification in semiconductors with positron annihilation: experiment and theory

    Science.gov (United States)

    Tuomisto, Filip

    2015-03-01

    Positron annihilation spectroscopy is a very powerful technique for the detection, identification and quantification of vacancy-type defects in semiconductors. In the past decades, it has been used to reveal the relationship between opto-electronic properties and specific defects in a wide variety of materials - examples include parasitic yellow luminescence in GaN, dominant acceptor defects in ZnO and broad-band absorption causing brown coloration in natural diamond. In typical binary compound semiconductors, the selective sensitivity of the technique is rather strongly limited to cation vacancies that possess significant open volume and suitable charge (negative of neutral). On the other hand, oxygen vacancies in oxide semiconductors are a widely debated topic. The properties attributed to oxygen vacancies include the inherent n-type conduction, poor p-type dopability, coloration (absorption), deep level luminescence and non-radiative recombination, while the only direct experimental evidence of their existence has been obtained on the crystal surface. We will present recent advances in combining state-of-the-art positron annihilation experiments and ab initio computational approaches. The latter can be used to model both the positron lifetime and the electron-positron momentum distribution - quantities that can be directly compared with experimental results. We have applied these methods to study vacancy-type defects in III-nitride semiconductors (GaN, AlN, InN) and oxides such as ZnO, SnO2, In2O3andGa2O3. We will show that cation-vacancy-related defects are important compensating centers in all these materials when they are n-type. In addition, we will show that anion (N, O) vacancies can be detected when they appear as complexes with cation vacancies.

  1. Measurement of Charm Meson Lifetimes

    International Nuclear Information System (INIS)

    We report measurements of the D0 , D+ , and D+s meson lifetimes using 3.7 fb-1 of e+e- annihilation data collected near the Υ(4S) resonance with the CLEO detector. The measured lifetimes of the D0 , D+ , and D+s mesons are 408.5±4.1+3.5-3.4 fs , 1033.6±22.1+9.9-12.7 fs , and 486.3±15.0+4.9-5.1 fs . The precision of these lifetimes are comparable to those of the best previous measurements, and the systematic errors are very different. In a single experiment we find that the ratio of the D+s and D0 lifetimes is 1.19±0.04 . copyright 1999 The American Physical Society

  2. Comparison of the Free Volume of LiCl-Added SPPO Membrane and SPPO-PES Blend Membrane by Positron Annihilation Method

    Institute of Scientific and Technical Information of China (English)

    Htwe Htwe YIN; HUANG Huan; MA Qingli; TANG Shibiao

    2007-01-01

    Positron annihilation lifetime spectroscopy (PALS) is a powerful technique for the study of free volume in polymers. The lifetime of ortho-positronium (o-Ps), a bound state of an electron and a positron, can be used to assess the pore size, while the intensity can be used to characterize the number of pores. Based on the values of the long-lived o-Ps components in the lifetime spectra, the radii and fractional free volumes of sulfonated poly (2,6-dimethyl-l,4-phenyleneoxide) (SPPO) membranes with added LiCl and SPPO-PES (Polyethersulfone) blend were compared. Free volume radii in both kinds of membranes are discussed.

  3. Positron annihilation microprobe

    Energy Technology Data Exchange (ETDEWEB)

    Canter, K.F. [Brandeis Univ., Waltham, MA (United States)

    1997-03-01

    Advances in positron annihilation microprobe development are reviewed. The present resolution achievable is 3 {mu}m. The ultimate resolution is expected to be 0.1 {mu}m which will enable the positron microprobe to be a valuable tool in the development of 0.1 {mu}m scale electronic devices in the future. (author)

  4. Whole-Pattern Fitting and Positron Annihilation Studies of Magnetic PVA/α-Fe2O3 Nanocomposites

    Science.gov (United States)

    Prashanth, K. S.; Mahesh, S. S.; Prakash, M. B. Nanda; Ningaraju, S.; Ravikumar, H. B.; Somashekar, R.; Nagabhushana, B. M.

    2016-06-01

    A low-temperature solution combustion method was used to synthesize α-Fe2O3 nanoparticles. Magnetic polyvinyl alcohol (PVA)/α-Fe2O3/NaCl nanocomposites were prepared by solvent cast method. The Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) results are in confirmation with X-ray diffraction (XRD) results indicating the formation of nanocomposites. The microcrystalline parameters, crystallite size ( ), lattice strain ( g in %), stacking faults ( α d ), and twin faults ( β) of prepared polymer nanocomposites were evaluated by whole-pattern fitting technique. The refinement was carried out using the computed microstructural parameters in which the twin faults and stacking faults did not vary much and statistical deviation was less than 5 %. Positron annihilation lifetime spectroscopy (PALS) was used for microstructural characterization. PALS results show that the ortho-positronium (o-Ps) lifetime (τ3) increases gradually as a function of nanoparticle concentration and about 219 ps increase observed from1.50 to1.71 ns at 3 wt%. This indicates the increase of free volume hole size ( V f ) from 54.47 to 72.18 Å3. The o-Ps intensities ( I 3) decrease indicating the inhibition of o-Ps formation upon incorporation of nanoparticles into PVA. The increase in I 2 values suggests the increased annihilation at the interface region. Positron lifetime parameters, viz., o-Ps lifetime, and its intensities indicate the effect of quenching and inhibition upon incorporation of metal oxide nanoparticles and inorganic salt into PVA.

  5. Contributions to cosmic reionization from dark matter annihilation and decay

    Science.gov (United States)

    Liu, Hongwan; Slatyer, Tracy R.; Zavala, Jesús

    2016-09-01

    Dark matter annihilation or decay could have a significant impact on the ionization and thermal history of the universe. In this paper, we study the potential contribution of dark matter annihilation (s -wave- or p -wave-dominated) or decay to cosmic reionization, via the production of electrons, positrons and photons. We map out the possible perturbations to the ionization and thermal histories of the universe due to dark matter processes, over a broad range of velocity-averaged annihilation cross sections/decay lifetimes and dark matter masses. We have employed recent numerical studies of the efficiency with which annihilation/decay products induce heating and ionization in the intergalactic medium, and in this work extended them down to a redshift of 1 +z =4 for two different reionization scenarios. We also improve on earlier studies by using the results of detailed structure formation models of dark matter haloes and subhaloes that are consistent with up-to-date N -body simulations, with estimates on the uncertainties that originate from the smallest scales. We find that for dark matter models that are consistent with experimental constraints, a contribution of more than 10% to the ionization fraction at reionization is disallowed for all annihilation scenarios. Such a contribution is possible only for decays into electron/positron pairs, for light dark matter with mass mχ≲100 MeV , and a decay lifetime τχ˜1 024- 1 025 s .

  6. Recombination activity of light-activated copper defects in p-type silicon studied by injection- and temperature-dependent lifetime spectroscopy

    Science.gov (United States)

    Inglese, Alessandro; Lindroos, Jeanette; Vahlman, Henri; Savin, Hele

    2016-09-01

    The presence of copper contamination is known to cause strong light-induced degradation (Cu-LID) in silicon. In this paper, we parametrize the recombination activity of light-activated copper defects in terms of Shockley—Read—Hall recombination statistics through injection- and temperature dependent lifetime spectroscopy (TDLS) performed on deliberately contaminated float zone silicon wafers. We obtain an accurate fit of the experimental data via two non-interacting energy levels, i.e., a deep recombination center featuring an energy level at Ec-Et=0.48 -0.62 eV with a moderate donor-like capture asymmetry ( k =1.7 -2.6 ) and an additional shallow energy state located at Ec-Et=0.1 -0.2 eV , which mostly affects the carrier lifetime only at high-injection conditions. Besides confirming these defect parameters, TDLS measurements also indicate a power-law temperature dependence of the capture cross sections associated with the deep energy state. Eventually, we compare these results with the available literature data, and we find that the formation of copper precipitates is the probable root cause behind Cu-LID.

  7. Positron Annihilation Studies of Mesoporous Silica MCM-41

    International Nuclear Information System (INIS)

    Positron annihilation has been used to study the mesoporous silica MCM-41. Lifetime spectra of evacuated MCM-41 indicate a significant contribution from 3γ annihilation events with τ4 = 116 ns and I4 = 24.5 %. This is supported by measurements of the full energy distribution, where MCM-41 shows enhanced counts in the low energy region (below 511 keV) relative to a pure 2γ sample. MCM-41 was also studied under air and oxygen atmospheres. The presence of atmosphere has a significant effect on both the lifetime and Doppler patterns, with both the lifetime data (τ4 and I4) and the 3γ-fraction decreasing with increasing oxygen concentration. This is indicative of paramagnetic quenching of o-Ps by oxygen.

  8. Positron annihilation study of Fe-ion irradiated reactor pressure vessel model alloys

    Science.gov (United States)

    Chen, L.; Li, Z. C.; Schut, H.; Sekimura, N.

    2016-01-01

    The degradation of reactor pressure vessel steels under irradiation, which results from the hardening and embrittlement caused by a high number density of nanometer scale damage, is of increasingly crucial concern for safe nuclear power plant operation and possible reactor lifetime prolongation. In this paper, the radiation damage in model alloys with increasing chemical complexity (Fe, Fe-Cu, Fe-Cu-Si, Fe-Cu-Ni and Fe-Cu-Ni-Mn) has been studied by Positron Annihilation Doppler Broadening spectroscopy after 1.5 MeV Fe-ion implantation at room temperature or high temperature (290 oC). It is found that the room temperature irradiation generally leads to the formation of vacancy-type defects in the Fe matrix. The high temperature irradiation exhibits an additional annealing effect for the radiation damage. Besides the Cu-rich clusters observed by the positron probe, the results show formation of vacancy-Mn complexes for implantation at low temperatures.

  9. Characterisation of Ion Implantation-induced Defects in Certain Technologically Important Materials by Positron Annihilation (Review Paper

    Directory of Open Access Journals (Sweden)

    P.M.G. Nambissan

    2009-07-01

    Full Text Available The application of positron annihilation spectroscopy for the studies of defects produced by different types of charged particles and ions in a variety of materials is discussed with specific examples. The ability to detect and quantify the information through the characteristic parameters of the annihilation radiation in a totally non-destructive method has made the fundamental process of electron-positron annihilation a powerful spectroscopic probe for investigating the structure and properties of materials. Ion implantation produces defects in the structure of solids and the latter can be recovered from the defects by annealing at high temperatures. Here the annealing is done in sequential steps so that the different stages of evolution of defects and their interaction with impurity atoms can be studied systematically. Defects produced by irradiation by particles like protons, alpha, boron and neon ions in materials ranging from simple metals to binary alloys are discussed.A detailed evaluation of the positron lifetimes in terms of the popular positron trapping models is also presented. Further as a special case, the method of extraction of values of several useful physical parameters of inert gas bubbles inside a metal matrix is explained with the help of a model analysis.Defence Science Journal, 2009, 59(4, pp.329-341, DOI:http://dx.doi.org/10.14429/dsj.59.1531

  10. Bubble chamber: antiproton annihilation

    CERN Multimedia

    1971-01-01

    These images show real particle tracks from the annihilation of an antiproton in the 80 cm Saclay liquid hydrogen bubble chamber. A negative kaon and a neutral kaon are produced in this process, as well as a positive pion. The invention of bubble chambers in 1952 revolutionized the field of particle physics, allowing real tracks left by particles to be seen and photographed by expanding liquid that had been heated to boiling point.

  11. Low-temperature positron annihilation study of B+-ion implanted PMMA

    International Nuclear Information System (INIS)

    Temperature dependent positron annihilation lifetime spectroscopy (PALS) measurements in the range of 50-300 K are carried out to study positronium formation in 40 keV B+-ion implanted polymethylmethacrylate(B:PMMA) with two ion doses of 3.13·1015 and 3.75·1016 ions/cm2. The investigated samples show the various temperature trends of ortho-positronium (o-Ps) lifetime τ3 and intensity I3 in PMMA before and after ion implantation. Two transitions in the vicinity of ∼150 and ∼250 K, ascribed to γ and β transitions, respectively, are observed in the PMMA and B:PMMA samples in consistent with reference data for pristine sample. The obtained results are compared with room temperature PALS study of PMMA with different molecular weight (Mw) which known from literature. It is found that B+-ion implantation leads to decreasing Mw in PMMA at lower ion dose. At higher ion dose the local destruction of polymeric structure follows to broadening of lifetime distribution (hole size distribution)

  12. Radiation-induced defects in chalcogenide glasses characterized by combined optical spectroscopy, XPS and PALS methods

    Energy Technology Data Exchange (ETDEWEB)

    Shpotyuk, O. [Institute of Physics of Jan Dlugosz University, 13/15 al. Armii Krajowej, Czestochowa 42201 (Poland); Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015-3195 (United States); Lviv Institute of Materials of SRC ' ' Carat' ' , 202, Stryjska str., 79031 Lviv (Ukraine); Kovalskiy, A.; Jain, H. [Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015-3195 (United States); Golovchak, R. [Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015-3195 (United States); Lviv Institute of Materials of SRC ' ' Carat' ' , 202, Stryjska str., 79031 Lviv (Ukraine); Zurawska, A. [Opole University of Technology, 75, Ozimska str., Opole 45370 (Poland)

    2007-03-15

    Temperature-dependent optical absorption spectroscopy, high-resolution X-ray photoelectron spectroscopy and positron annihilation lifetimes spectroscopy are utilized to understand radiation-induced changes in Ge-Sb-S chalcogenide glasses. Theoretically predicted topological scheme of {gamma}-induced coordination defect formation in stoichiometric Ge{sub 23.5}Sb{sub 11.8}S{sub 64.7} glass composition is supported by these measurements. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Design, construction, and validation of a multimodal intravascular diagnostic catheter combining IVUS and fluorescence lifetime spectroscopy detection channels

    Science.gov (United States)

    Bec, Julien; Xie, Hongtao; Yankelevich, Diego; Zhou, Feifei; Sun, Yang; Ghata, Narugopal; Aldredge, Ralph; Marcu, Laura

    2011-03-01

    We report the development and validation of an intravascular rotary catheter that enables bi-modal interrogation of arterial pathologies based on fast-frame time-resolved fluorescence spectroscopy (TRFS) and intravascular ultrasound (IVUS). The catheter is based on a parallel design that allows for independent rotation of the ultrasonic and optical channels within an 8 Fr outer diameter catheter sheath and integrates a low volume flushing channel for blood removal in the optical pathways. In current configuration, the two channels consist of a) a standard 8 Fr IVUS catheter with single element transducer (15 MHz) and b) a side-viewing UV-grade silica/silica fiber optic (400 μm core). The catheter is terminated by a small (0.82 mm internal diameter) polyimide tube to keep the fiber stable within the sheath. To clear the field of view from blood, a saline solution can be flushed in a sheath channel, concentric with the fiber optic, through the tube and in a radial opening aligned with the fiber's optical beam. The flushing function was optimized with a computational fluid dynamics (CFD) model pursued in a parallel study. The ability of the catheter to operate in intraluminal setting in blood flow, the effect of probe-to-tissue distance on optical signal and ability to generate co-registered TRFS and IVUS data were demonstrated in blood vessel phantoms. Current results demonstrate the feasibility of the described catheter for parallel interrogation of vessel walls based on TRFS and IVUS and to generate robust TRFS data. These results facilitate further development of a bi-modal TRFS-IVUS technique for intravascular diagnosis of atherosclerotic cardiovascular diseases including vulnerable plaques.

  14. KENO lifetimes

    International Nuclear Information System (INIS)

    When performing k-eigenvalue solutions with KENO-V.a, two different prompt neutron lifetimes are estimated - a system lifetime and a neutron generation time. The meaning of these two lifetimes has been ascertained by comparing values of various neutron lifespans/lifetimes predicted by MCNP and DANTSYS based on the neutron-balance theory. The system lifetime in KENO-Va corresponds to the unweighted removal lifetime calculated by both MCNP and DANTSYS. The unweighted removal lifetime is the average time between removal events resulting from a neutron absorption or a neutron leakage. The generation time in KENO-V.a corresponds to the fission lifespan calculated by MCNP, where the fission lifespan in MCNP represents the average time for a newly born neutron to cause another fission. As such, the generation time in KENO-Va does not represent the generation time that appears in the point kinetic model. The generation time in the point kinetic model is the adjoint-weighted removal lifetime divided by keff, which is identically equal to the adjoint-weighted neutron production rate. In small bare systems operating in the vicinity of delayed critical, the difference between the adjoint-weighted neutron generation time and the fission lifespan can be as small as a few percent. However, in reflected systems, the difference between these two quantities can be several orders of magnitude. In conclusion, the prompt neutron generation time predicted by KENO-Va corresponds to the fission lifespan of a prompt neutron in a given system. The fission lifespan is the average time from birth-to-fission and, in general, is not a good approximation for the adjoint-weighted neutron generation time that appears in the point-kinetic model

  15. Annihilation Mechanism of Dilepton Emission from Finite Fireball

    CERN Document Server

    Anchishkin, D V; Naryshkin, R; Ruuskanen, P V

    2004-01-01

    Medium-induced modifications of the pion and quark-antiquark annihilation mechanisms of dilepton production during relativistic heavy ion collisions are considered. Due to the dense hadron environment, the pions produced during a collision are effectively confined in a finite volume, in which they live for a finite time which is scaled as the lifetime of a fireball. Our results indicate that, due to the space-time finiteness of the pion system which generates the corresponding quantum randomization, the dilepton rates are finite in the invariant low-mass region M<2m_\\pi. It is found that the spatial finiteness of quark wave functions and the finiteness of the lifetime of excited states result in the same effect for the quark-antiquark annihilation to dileptons. The breaking of the detailed energy-momentum conservation due to the broken translation invariance is discussed.

  16. Biological Effectiveness of Antiproton Annihilation

    DEFF Research Database (Denmark)

    Maggiore, C.; Agazaryan, N.; Bassler, N.;

    2004-01-01

    from the annihilation of antiprotons produce an increase in ‘‘biological dose’’ in the vicinity of the narrow Bragg peak for antiprotons compared to protons. This experiment is the first direct measurement of the biological effects of antiproton annihilation. The background, description, and status...

  17. Annihilation Radiation in the Galaxy

    CERN Document Server

    Dermer, C D

    2000-01-01

    Observations of annihilation radiation in the Galaxy are briefly reviewed. We summarize astrophysical mechanisms leading to positron production, and recent estimates for production rates from nova and supernova nucleosynthesis in the Galaxy. The physical processes involved in the production of annihilation radiation in the interstellar medium are described. These include positron thermalization, charge exchange, radiative recombination, and direct annihilation. Calculations of 2\\gamma and 3\\gamma spectra and the positronium (Ps) fraction due to the annihilation of positrons in media containing H and He at different temperatures and ionization states are presented. Quenching of Ps by high temperature plasmas or dust could account for differences between 0.511 MeV and 3\\gamma Ps continuum maps. These results are presented in the context of the potential of INTEGRAL to map sites of annihilation radiation in the Galaxy. Positron production by compact objects is also considered.

  18. Annihilation radiation in the Galaxy

    Science.gov (United States)

    Dermer, C. D.; Murphy, R. J.

    2001-09-01

    Observations of annihilation radiation in the Galaxy are briefly reviewed. We summarize astrophysical mechanisms leading to positron production and recent estimates for production rates from nova and supernova nucleosynthesis in the Galaxy. The physical processes involved in the production of annihilation radiation in the interstellar medium are described. These include positron thermalization, charge exchange, radiative recombination, and direct annihilation. Calculations of 2γ and 3γ spectra and the positronium (Ps) fraction due to the annihilation of positrons in media containing H and He at different temperatures and ionization states are presented. Quenching of Ps by high temperature plasmas or dust could account for differences betwen 0.511 MeV and 3γ Ps continuum maps. These results are presented in the context of the potential of INTEGRAL to map sites of annihilation radiation in the Galaxy. Positron production by compact objects is also considered.

  19. Neutrino annihilation in hot plasma

    International Nuclear Information System (INIS)

    We consider neutrino annihilation in a heat bath, including annihilation via the photon. We show that the annihilation cross section has high and narrow peaks corresponding to a plasmon resonance. This yields an enormous enhancement factor of O(108) in the differential cross section as compared with the purely weak contribution. We also evaluate numerically the thermally averaged neutrino annihilation rate per particle in the heat bath of the early universe to be +e-)>≅2.93GF2T2. We have accounted for the final-state blocking factors as well as for the fact that the center-of-mass frame of collisions is not necessarily the rest frame of the heat bath. Despite the resonances, electromagnetic processes represent only a minor effect in the averaged annihilation rate. (orig.)

  20. Neutrino annihilation in hot plasma

    International Nuclear Information System (INIS)

    We consider neutrino annihilation in a heat bath, including annihilation via the photon. We show that the annihilation cross section has high and narrow peaks corresponding to a plasmon resonance. This yields an enormous enhancement factor of O(108) in the differential cross section as compared with the purely weak contribution. We also evaluate numerically the thermally averaged neutrino annihilation rate per particle in the heat bath of the early Universe to be +e-)> ≅ 2.93GF2T2. We have accounted for the final state blocking factors as well as for the fact that the center-of-mass frame of collisions is not necessarily the rest frame of the heat bath. Despite the resonances, electromagnetic processes represent only a minor effect in the averaged annihilation rate. (orig.)

  1. Characteristics of the positron annihilation process in the matter

    International Nuclear Information System (INIS)

    In this report the positrons annihilation spectroscopy, as a method for the matter study is described. The interaction of positrons of high as well as thermal energies are discussed and different models of mentioned interactions are presented. Special attention is paid for positrons interaction with crystal lattice and its defects. The influence of positron beams characteristics on measured values are also discussed

  2. Positron annihilation in modified zeolites LTA and 13X

    Energy Technology Data Exchange (ETDEWEB)

    Cabral-Prieto, A.; Garcia-Sosa, I.; Jimenez-Becerril, J. [Departamento de Quimica, Instituto Nacional de Investigaciones Nucleares, Apartado Postal 18-1027, Col. Escandon, Del. M. Hidalgo, Mexico D. F., c. p. 11801 (Mexico); Lopez-Castanares, R.; Olea-Cardoso, O. [Facultad de Quimica, Universidad Autonoma del Estado de Mexico, Paseo Tollocan esquina paseo Tollocan, esquina paseo Colon, Toluca, c. p. 50120, Estado de Mexico (Mexico)

    2007-07-01

    The pick-off annihilation lifetimes of o -Ps, {tau}{sub po}, in dehydrated Co{sup 2+} and Mn{sup 2+} exchanged zeolites LTA, in dehydrated Co{sup 2+} exchanged zeolite 13X, and in dehydrated Na{sup +} zeolites LTA and 13X, are estimated. Although {tau}{sub po} can be estimated from the lifetime spectra of the cation exchanged zeolites LTA and 13X, this lifetime can not be estimated from those spectra of Na{sup +} zeolite LTA unambiguously. The estimated pick-off lifetimes due to the annihilation of o-Ps in the internal walls of the zeolites are systematically lower than the average lifetime of p-Ps and o-Ps in vacuum {tau}{sub a}=0.5 ns. Since the pick-off process of o-Ps occurs particularly on the internal cavity walls of dehydrated zeolites, the replacement of {tau}{sub a} by {tau}{sub po} within the classical model of Tao-Eldrup to calculate cavity radius should provide more realistic cavity radii of these porous materials than when using {l_brace}{tau}{sub a}{r_brace}. This suggestion is supported by previous and present results. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Photoinduced carrier annihilation in silicon pn junction

    Science.gov (United States)

    Sameshima, Toshiyuki; Motoki, Takayuki; Yasuda, Keisuke; Nakamura, Tomohiko; Hasumi, Masahiko; Mizuno, Toshihisa

    2015-08-01

    We report analysis of the photo-induced minority carrier effective lifetime (τeff) in a p+n junction formed on the top surfaces of a n-type silicon substrate by ion implantation of boron and phosphorus atoms at the top and bottom surfaces followed by activation by microwave heating. Bias voltages were applied to the p+ boron-doped surface with n+ phosphorus-doped surface kept at 0 V. The values of τeff were lower than 1 × 10-5 s under the reverse-bias condition. On the other hand, τeff markedly increased to 1.4 × 10-4 s as the forward-bias voltage increased to 0.7 V and then it leveled off when continuous-wave 635 nm light was illuminated at 0.74 mW/cm2 on the p+ surface. The carrier annihilation velocity S\\text{p + } at the p+ surface region was numerically estimated from the experimental τeff. S\\text{p + } ranged from 4000 to 7200 cm/s under the reverse-bias condition when the carrier annihilation velocity S\\text{n + } at the n+ surface region was assumed to be a constant value of 100 cm/s. S\\text{p + } markedly decreased to 265 cm/s as the forward-bias voltage increased to 0.7 V.

  4. On the atomistic origin of radiation-structural relaxation in chalcogenide glasses: the results of positron annihilation study

    International Nuclear Information System (INIS)

    Instability effects caused by high-energy γ-irradiation are studied in (As2S3)1-x(Sb2S3)xglasses (x=0, 0.1, 0.2 and 0.3) using positron annihilation lifetime spectroscopy, the results being treated within two-state trapping model in both normal and high-measurement statistics. The observed decrease in positron trapping rate of the glasses tested just after γ-irradiation was explained due to renovation of destroyed covalent chemical bonds. This process was governed by monomolecular single-exponential relaxation kinetics agreed well with corresponding changes in the fundamental optical absorption edge. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. On the atomistic origin of radiation-structural relaxation in chalcogenide glasses: the results of positron annihilation study

    Energy Technology Data Exchange (ETDEWEB)

    Shpotyuk, Ya. [Ivan Franko National University of Lviv, Faculty of Electronics, Lviv (Ukraine); Institute of Materials of Scientific Research Company ' ' Carat' ' , Lviv (Ukraine); Institute of Physics, Jan Dlugosz University, Czestochowa (Poland); Ingram, A. [Institute of Physics, Mathematics and Chemistry, Opole Technical University (Poland); Filipecki, J.; Hyla, M. [Institute of Physics, Jan Dlugosz University, Czestochowa (Poland)

    2011-11-15

    Instability effects caused by high-energy {gamma}-irradiation are studied in (As{sub 2}S{sub 3}){sub 1-x}(Sb{sub 2}S{sub 3}){sub x}glasses (x=0, 0.1, 0.2 and 0.3) using positron annihilation lifetime spectroscopy, the results being treated within two-state trapping model in both normal and high-measurement statistics. The observed decrease in positron trapping rate of the glasses tested just after {gamma}-irradiation was explained due to renovation of destroyed covalent chemical bonds. This process was governed by monomolecular single-exponential relaxation kinetics agreed well with corresponding changes in the fundamental optical absorption edge. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. Water-Vapor Sorption Processes in Nanoporous MgO-Al2O3 Ceramics: the PAL Spectroscopy Study

    OpenAIRE

    Klym, Halyna; Ingram, Adam; Shpotyuk, Oleh; Hadzaman, Ivan; Solntsev, Viacheslav

    2016-01-01

    The water-vapor sorption processes in nanoporous MgO-Al2O3 ceramics are studied with positron annihilation lifetime (PAL) spectroscopy employing positron trapping and positronium (Ps)-decaying modes. It is demonstrated that the longest-lived components in the four-term reconstructed PAL spectra with characteristic lifetimes near 2 and 60–70 ns can be, respectively, attributed to ortho-positronium (o-Ps) traps in nanopores with 0.3- and 1.5–1.8-nm radii. The first o-Ps decaying process include...

  7. Monomer Migration and Annihilation Processes

    Institute of Scientific and Technical Information of China (English)

    KE Jian-Hong; LIN Zhen-Quan; ZHUANG You-Yi

    2005-01-01

    We propose a two-species monomer migration-annihilation model, in which monomer migration reactions occur between any two aggregates of the same species and monomer annihilation reactions occur between two different species. Based on the mean-field rate equations, we investigate the evolution behaviors of the processes. For the case with an annihilation rate kernel proportional to the sizes of the reactants, the aggregation size distribution of either species approaches the modified scaling form in the symmetrical initial case, while for the asymmetrical initial case the heavy species with a large initial data scales according to the conventional form and the light one does not scale. Moreover,at most one species can survive finally. For the case with aconstant annihilation rate kernel, both species may scale according to the conventional scaling law in the symmetrical case and survive together at the end.

  8. Positron annihilation study of iron oxide nanoparticles in mesoporous silica MCM-41 template

    International Nuclear Information System (INIS)

    The subject of investigation were the samples obtained by impregnation of MCM-41 template with an aqueous solution prepared from Fe(NO3)3·9H2O. As a result of such a procedure, iron oxides deposits on MCM-41 were formed. The Moessbauer studies revealed an occurrence of Fe3O4 nanocrystallites in the both ferri- and superparamagnetic states. Almost 80% small particles exist in a paramagnetic state. The positron annihilation lifetime spectroscopy (PALS) spectra were measured in air or in vacuum. The long-lived ortho-positronium (o-Ps) components and their intensities are time dependent due to air molecules interaction with iron oxide nanocrystallites and silica walls surfaces. The adsorption of air on the nanocrystallites surface causes a total screening of their surface and a raise of the o-Ps lifetime values. Observed anti-quenching effect is a result of competition of two phenomena: practically switching off a pick-off mechanism related to interaction of o-Ps with magnetite nanoparticles and considerably weaker usual quenching by paramagnetic oxygen molecules. (authors)

  9. ATHENA: an actual antihydrogen annihilation

    CERN Multimedia

    2002-01-01

    This is an image of an actual matter-antimatter annihilation due to an atom of antihydrogen in the ATHENA experiment, located on the Antiproton Decelerator (AD) at CERN since 2001. The antiproton produces four charged pions (yellow) whose positions are given by silicon microstrips (pink) before depositing energy in CsI crystals (yellow cubes). The positron also annihilates to produce back-to-back gamma rays (red).

  10. Evaluation of the reactor pressure vessel steels by positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Slugeň, V., E-mail: Vladimir.Slugen@elf.stuba.sk [Institute of Nuclear and Physical Engineering, Slovak University of Technology, Ilkovičova 3, 81219 Bratislava (Slovakia); Hein, H. [AREVA NP GmbH, Paul Gossen Strasse 100, 91 001 Erlangen (Germany); Sojak, S.; Simeg Veterníková, J.; Petriska, M.; Sabelová, V.; Pavúk, M.; Hinca, R.; Stacho, M. [Institute of Nuclear and Physical Engineering, Slovak University of Technology, Ilkovičova 3, 81219 Bratislava (Slovakia)

    2013-11-15

    This paper presents a comparison of commercially used German and Russian reactor pressure vessel steels from the positron annihilation spectroscopy (PAS) point of view, having in mind knowledge obtained also from other techniques from the last decades. The second generation of Russian RPV steels seems to be fully comparable with German steels and their quality allows prolongation of NPP operating lifetime over projected 40 years. The embrittlement of CrMoV steels is relatively low due to effect of higher temperature which implies partial in situ annealing of primary microstructural point defects and therefore delays the degradation processes caused by neutron irradiation. PAS techniques can be effectively applied for evaluation of microstructural changes caused by extreme external loads (characterized by high dpa values) by proton implantation, with aim to simulate irradiation and for the evaluation of the effectiveness of post-irradiation thermal treatments. We used our actual and previous results, collected during last 20 years from measurements of different RPV-steels in “as received”, irradiated and post-irradiation annealed state and compare them with the aim to contribute to general knowledge based on experimental PAS data. Actual results from irradiated German and Russian steels confirmed that no large voids or vacancy clusters were formed at defined irradiation conditions stated according to the real operational conditions at nuclear power plants. This indicate the fact that vacancy type defects bear hardly any responsibility for radiation-induced hardening and embrittlement of reactor pressure vessel steels and does not affect significantly the long-term operation of nuclear power plants from safety point of view.

  11. Evaluation of the reactor pressure vessel steels by positron annihilation

    International Nuclear Information System (INIS)

    This paper presents a comparison of commercially used German and Russian reactor pressure vessel steels from the positron annihilation spectroscopy (PAS) point of view, having in mind knowledge obtained also from other techniques from the last decades. The second generation of Russian RPV steels seems to be fully comparable with German steels and their quality allows prolongation of NPP operating lifetime over projected 40 years. The embrittlement of CrMoV steels is relatively low due to effect of higher temperature which implies partial in situ annealing of primary microstructural point defects and therefore delays the degradation processes caused by neutron irradiation. PAS techniques can be effectively applied for evaluation of microstructural changes caused by extreme external loads (characterized by high dpa values) by proton implantation, with aim to simulate irradiation and for the evaluation of the effectiveness of post-irradiation thermal treatments. We used our actual and previous results, collected during last 20 years from measurements of different RPV-steels in “as received”, irradiated and post-irradiation annealed state and compare them with the aim to contribute to general knowledge based on experimental PAS data. Actual results from irradiated German and Russian steels confirmed that no large voids or vacancy clusters were formed at defined irradiation conditions stated according to the real operational conditions at nuclear power plants. This indicate the fact that vacancy type defects bear hardly any responsibility for radiation-induced hardening and embrittlement of reactor pressure vessel steels and does not affect significantly the long-term operation of nuclear power plants from safety point of view

  12. Water-Vapor Sorption Processes in Nanoporous MgO-Al2O3 Ceramics: the PAL Spectroscopy Study.

    Science.gov (United States)

    Klym, Halyna; Ingram, Adam; Shpotyuk, Oleh; Hadzaman, Ivan; Solntsev, Viacheslav

    2016-12-01

    The water-vapor sorption processes in nanoporous MgO-Al2O3 ceramics are studied with positron annihilation lifetime (PAL) spectroscopy employing positron trapping and positronium (Ps)-decaying modes. It is demonstrated that the longest-lived components in the four-term reconstructed PAL spectra with characteristic lifetimes near 2 and 60-70 ns can be, respectively, attributed to ortho-positronium (o-Ps) traps in nanopores with 0.3- and 1.5-1.8-nm radii. The first o-Ps decaying process includes "pick-off" annihilation in the "bubbles" of liquid water, while the second is based on o-Ps interaction with physisorbed water molecules at the walls of the pores. In addition, the water vapor modifies structural defects located at the grain boundaries in a vicinity of pores, this process being accompanied by void fragmentation during water adsorption and agglomeration during water desorption after drying.

  13. Water-Vapor Sorption Processes in Nanoporous MgO-Al2O3 Ceramics: the PAL Spectroscopy Study.

    Science.gov (United States)

    Klym, Halyna; Ingram, Adam; Shpotyuk, Oleh; Hadzaman, Ivan; Solntsev, Viacheslav

    2016-12-01

    The water-vapor sorption processes in nanoporous MgO-Al2O3 ceramics are studied with positron annihilation lifetime (PAL) spectroscopy employing positron trapping and positronium (Ps)-decaying modes. It is demonstrated that the longest-lived components in the four-term reconstructed PAL spectra with characteristic lifetimes near 2 and 60-70 ns can be, respectively, attributed to ortho-positronium (o-Ps) traps in nanopores with 0.3- and 1.5-1.8-nm radii. The first o-Ps decaying process includes "pick-off" annihilation in the "bubbles" of liquid water, while the second is based on o-Ps interaction with physisorbed water molecules at the walls of the pores. In addition, the water vapor modifies structural defects located at the grain boundaries in a vicinity of pores, this process being accompanied by void fragmentation during water adsorption and agglomeration during water desorption after drying. PMID:26956602

  14. Positron Annihilation 3-D Momentum Spectrometry by Synchronous 2D-ACAR and DBAR

    Science.gov (United States)

    Burggraf, Larry W.; Bonavita, Angelo M.; Williams, Christopher S.; Fagan-Kelly, Stefan B.; Jimenez, Stephen M.

    2015-05-01

    A positron annihilation spectroscopy system capable of determining 3D electron-positron (e--e+) momentum densities has been constructed and tested. In this technique two opposed HPGe strip detectors measure angular coincidence of annihilation radiation (ACAR) and Doppler broadening of annihilation radiation (DBAR) in coincidence to produce 3D momentum datasets in which the parallel momentum component obtained from the DBAR measurement can be selected for annihilation events that possess a particular perpendicular momentum component observed in the 2D ACAR spectrum. A true 3D momentum distribution can also be produced. Measurement of 3-D momentum spectra in oxide materials has been demonstrated including O-atom defects in 6H SiC and silver atom substitution in lithium tetraborate crystals. Integration of the 3-D momentum spectrometer with a slow positron beam for future surface resonant annihilation spectrometry measurements will be described. Sponsorship from Air Force Office of Scientific Research

  15. Positron annihilation in PI189 and PI304 polyimides

    Energy Technology Data Exchange (ETDEWEB)

    Shantarovich, V.P. [N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul Kosygina 4 st., 119334 Moscow (Russian Federation)]. E-mail: shant@center.chph.ras.ru; Suzuki, T. [High Energy Accelerator Research Organization KEK, Tsukuba 305-0801 (Japan); He, C. [High Energy Accelerator Research Organization KEK, Tsukuba 305-0801 (Japan); Ito, Y. [Reasearch Center for Nuclear Science and Technology, The University of Tokyo, Tokai, Ibaraki 319-1106 (Japan); Yampolskii, Y.P. [A.V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 29 Leninskii Pr., 117912 Moscow (Russian Federation); Alentiev, A.Yu. [A.V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 29 Leninskii Pr., 117912 Moscow (Russian Federation)

    2005-05-01

    Temperature dependence of the lifetime {tau}3 and intensity I{sub 3} of the long-lived ortho-positronium (o-Ps) component was measured for two polyimides PI189 and PI304 both below and above glass-transition temperatures Tg of these polymers. First heating runs of the experiments revealed anomalous, irregular behavior of the lifetime {tau}3 in both PI in the vicinity (below) of the glass transition temperature. The effect was similar to that discussed recently for a number of PI. However, on the cooling stage of the first cycle and on the heating run of the second cycle, such irregularities disappeared. These results show that anomalous behavior of annihilation characteristics of o-Ps in our PI samples were due not to anomalous behavior of PI structure itself close to Tg point (not to a specific phase transition), but to removal of residual solvent in vicinity of Tg during the first heating cycle. Different approaches to estimations of the specific hole volume and of the holes number density N on the basis of positron annihilation data are discussed. Final estimation for PI189 gives the fractional free volume h=3.35% and N=0.44x1027m-3. The effects of positron trapping by polar-CO groups on annihilation characteristics of PI and on the obtained value of N are also considered.

  16. Positron Annihilation in Medical Substances of Insulin

    Science.gov (United States)

    Pietrzak, R.; Szatanik, R.

    2005-05-01

    Positrons lifetimes were measured in medical substances of insulin (human and animal), differing as far as the degree of purity and time of their activity in the organism are concerned. In all of the cases the spectrum of positron lifetime was distributed into three components, with the long-life component ranging from 1.8 to 2.08 ns and the intensity taking on values from 18 to 24%. Making use of Tao-Eldrup model, the average radius of the free volume, in which o-Ps annihilated, and the degree of filling in the volume were determined. It was found that the value of the long-life component for human insulin is higher than that of animal insulin. Moreover, the value of this component clearly depends on the manner of purification of the insulin. It was also noticed that there occurs a correlation between the value of this component and the time after which it begins to be active in the organism, as well as the total time of its activity.

  17. Positron annihilation in medical substances of insulin

    International Nuclear Information System (INIS)

    Positrons lifetimes were measured in medical substances of insulin (human and animal), differing as far as the degree of purity and time of their activity in the organism are concerned. In all of the cases the spectrum of positron lifetime was distributed into three components, with the long-life component ranging from 1.8 to 2.08 ns and the intensity taking on values from 18% to 24%. Making use of Tao-Eldrup model, the average radius of the free volume, in which o-Ps annihilated, and the degree of filling in the volume were determined. It was found that the value of the long-life component for human insulin is higher than that of animal insulin. Moreover, the value of this component clearly depends on the manner of purification of the insulin. It was also noticed that there occurs a correlation between the value of this component and the time after which it begins to be active in the organism, as well as the total time of its activity. (author)

  18. Possible presence of hydrophilic SO3H nanoclusters on the surface of dry ultrathin Nafion® films: a positron annihilation study.

    Science.gov (United States)

    Mohamed, Hamdy F M; Kuroda, S; Kobayashi, Y; Oshima, N; Suzuki, R; Ohira, A

    2013-02-01

    Solutions of Nafion® with an ion exchange capacity (IEC) of 0.91 meq g(-1), which are on the verge of the formation of SO(3)H nanoclusters, were spin coated on silicon (Si), glassy carbon (GC) and platinum/silicon (Pt/Si) substrates to form films of up to 256 nm thickness. Nanostructure of the films was studied using Doppler broadening of annihilation radiation (DBAR), positron annihilation lifetime (PAL), X-ray photoelectron spectroscopy (XPS), an atomic force microscope (AFM) and contact angle measurements. Contact angles as low as 10 degrees indicate that the surface of dry ultrathin Nafion® films on Si is highly hydrophilic. XPS data of 10 nm thick, ultrathin film on Si show that oxygen concentration is enhanced and the SO(3)H group concentration, in other words, IEC on the surface is much higher than other films. The S parameter measured by DBAR of an ultrathin Nafion® film on Si is much higher than that of the films on the other substrates. We consider that a large number of hydrophilic, reversed micelle like SO(3)H groups are on the surface of the ultrathin Nafion® film on Si but not on the surface of other films. Positrons implanted into the film are trapped by the SO(3)H clusters, annihilating with the electrons of oxygen and exhibit the high S parameter. The SO(3)H concentration on the surface of thin Nafion® films on GC and Pt/Si substrates may not be so high as the threshold for the formation of a large number of SO(3)H clusters. Positrons implanted into the films annihilate mostly with fluorine atoms, resulting in a low S parameter. The film-substrate interaction plays an essential role in nanostructuring of Nafion® thin films, which may also be the case for Nafion® on the catalysts of polymer electrolyte fuel cells. PMID:23238425

  19. Effect of Voids on Angular Correlation of Positron Annihilation Photons in Molybdenum

    DEFF Research Database (Denmark)

    Mogensen, O. E.; Petersen, K.; Cotterill, R. M. J.;

    1972-01-01

    of positrons may result in the increase in the positron lifetime, a narrowing of the 2-γ angular correlation distribution, and a reduction in the Doppler broadening of the annihilation line. Vacancies in metals1,2, deformation effects in metals3, and defects (F-centres or cation vacancies) in ionic crystals4...

  20. Study on the effect of atmospheric gases adsorbed in MnFe2O4/MCM-41 nanocomposite on ortho-positronium annihilation

    Directory of Open Access Journals (Sweden)

    Wiertel Marek

    2015-12-01

    Full Text Available In this paper, results of positron annihilation lifetime spectroscopy (PALS studies of MnFe2O4/MCM-41 nanocomposites in N2 and O2 atmosphere have been presented. In particular, the influence of manganese ferrite loading and gas filling on pick-off ortho-positronium (o-Ps annihilation processes in the investigated samples was a point of interest. Disappearance of the longest-lived o-Ps component with τ5 present in the PAL spectrum of initial MCM-41 mesoporous material in the PAL spectra of MnFe2O4-impregnated MCM-41 measured in vacuum is a result of either a strong chemical o-Ps quenching or the Ps inhibition effects. The intensity I4 of the medium-lived component initially increases, reaching a maximum value for the sample with minimum manganese ferrite content, and then decreases monotonically. Analogous dependence for the intensity I3 of the shortest-lived component shows a maximum at higher MnFe2O4 content. Filling of open pores present in the studied nanocomposites by N2 or O2 at ambient pressure causes partial reappearance of the τ4 and τ5 components, except a sample with maximum ferrite content. The lifetimes of these components measured in O2 are shortened in comparison to that observed in N2 because of paramagnetic quenching. Anti-inhibition and anti-quenching effects of atmospheric gases observed in the MnFe2O4/MCM-41 samples are a result of neutralization of some surface active centers acting as inhibitors and weakening of pick-off annihilation mechanism, respectively.

  1. Biological effectiveness of antiproton annihilation

    CERN Document Server

    Holzscheiter, Michael H.; Bassler, Niels; Beyer, Gerd; De Marco, John J.; Doser, Michael; Ichioka, Toshiyasu; Iwamoto, Keisuke S.; Knudsen, Helge V.; Landua, Rolf; Maggiore, Carl; McBride, William H.; Møller, Søren Pape; Petersen, Jorgen; Smathers, James B.; Skarsgard, Lloyd D.; Solberg, Timothy D.; Uggerhøj, Ulrik I.; Withers, H.Rodney; Vranjes, Sanja; Wong, Michelle; Wouters, Bradly G.

    2004-01-01

    We describe an experiment designed to determine whether or not the densely ionizing particles emanating from the annihilation of antiprotons produce an increase in “biological dose” in the vicinity of the narrow Bragg peak for antiprotons compared to protons. This experiment is the first direct measurement of the biological effects of antiproton annihilation. The experiment has been approved by the CERN Research Board for running at the CERN Antiproton Decelerator (AD) as AD-4/ACE (Antiproton Cell Experiment) and has begun data taking in June of 2003. The background, description and the current status of the experiment are given.

  2. Biological effectiveness of antiproton annihilation

    DEFF Research Database (Denmark)

    Holzscheiter, M.H.; Agazaryan, N.; Bassler, Niels;

    2004-01-01

    We describe an experiment designed to determine whether or not the densely ionizing particles emanating from the annihilation of antiprotons produce an increase in ‘‘biological dose’’ in the vicinity of the narrow Bragg peak for antiprotons compared to protons. This experiment is the first direct...... measurement of the biological effects of antiproton annihilation. The experiment has been approved by the CERN Research Board for running at the CERN Antiproton Decelerator (AD) as AD-4/ACE (Antiproton Cell Experiment) and has begun data taking in June of 2003. The background, description and the current...

  3. Measurement of hydrodynamic interaction parameter for miscibility test of polymer blends by positron lifetime method

    International Nuclear Information System (INIS)

    Positron Annihilation Lifetime Spectroscopy is used to determine the free volume content in the blends of SAN/PMMA and PS/PVC. Though the free volume data indicate the miscible/immiscible nature of the blends, the extent of miscibility for different weight compositions is not forthcoming. Therefore the hydrodynamic interaction parameter α which accounts for the excess friction between the constituents of the blend system is evaluated for this purpose. The SAN/PMMA system produces a maximum α of -209 at 20% of PMMA concentration while PS/PVC almost zero. It appears sound that hydrodynamic interaction parameter, α, is a suitable parameter to understand the composition dependent miscibility level in polymer blends. (author)

  4. 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.

  5. 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.

  6. Study of the ortho-positron annihilation process in zeolite Y

    International Nuclear Information System (INIS)

    For several years a great interest has existed for the study of the natural and synthetic zeolites due to its properties. The porosity, one of their main characteristics allows that these materials are used as molecular sieves, catalysts, gases drying, etc. In order to investigating the porosity and other zeolite properties one carries out the study of the process of positron annihilation lifetime spectroscopy (Pals). This is a technique that provides information about the size and the pores form since is highly sensitive to the free volume and the superficial area of those porous materials as the zeolites. The study began with the elaboration of zeolite Y tablets in a hydraulic press where different pressures (from 0 to 1.26 GPa) and masses (70, 80 and 100 mg) were proven to obtain the estimate porosity of each tablet. A graph was elaborated and the effect of the mass and pressure with regard to the zeolite porosity was analyzed. Later on, the powder and tablets of 70 mg were characterized by means of X-ray diffraction (the glass size, interplanar distance, length and the volume of the unitary cell); scanning electron microscopy (the particles size and morphology); thermo gravimetric analysis (dehydration temperature and the stability up to 700 C) and the Brunauer Emmett Teller method (specific area). After the zeolite Y tablets characterization was carried out the positron annihilation process by means of Pals where its free volume of zeolite Y was analyzed, which includes to the structural cavities and the interparticle volume. The powdered zeolite was analyzed to different experimental conditions (preparation of the sample and the Pals equipment) to obtain the optimal conditions (a window with a time of 400 ns and a enlarged energy window) of analysis. On the other hand, the tablets were analyzed under optimal conditions to obtain the four components of time and intensity (τ, Ι), result of the different ways of positrons annihilation in the zeolite. These

  7. Hyperfine structure and lifetime measurements in the 4s2nd 2D3/2 Rydberg sequence of Ga I by time-resolved laser spectroscopy

    Science.gov (United States)

    Liu, Chunqing; Tian, Yanshan; Yu, Qi; Bai, Wanshuang; Wang, Xinghao; Wang, Chong; Dai, Zhenwen

    2016-05-01

    The hyperfine structure (HFS) constants of the 4s2nd 2D3/2 (n=6-18) Rydberg sequence and the 4s26p 2P3/2 level for two isotopes of 69Ga and 71Ga atoms were measured by means of the time-resolved laser-induced fluorescence (TR-LIF) technique and the quantum beat method. The observed hyperfine quantum beat spectra were analyzed and the magnetic-dipole HFS constants A as well as the electric-quadrupole HFS constants B of these levels were obtained by Fourier transform and a program for multiple regression analysis. Also using TR-LIF method radiative lifetimes of the above sequence states were determined at room temperature. The measured lifetime values range from 69 to 2279 ns with uncertainties no more than 10%. To our knowledge, the HFS constants of this Rydberg sequence and the lifetimes of the 4s2nd 2D3/2 (n=10-18) levels are reported for the first time. Good agreement between our results and the previous is achieved.

  8. p -wave annihilating dark matter from a decaying predecessor and the Galactic Center excess

    Science.gov (United States)

    Choquette, Jeremie; Cline, James M.; Cornell, Jonathan M.

    2016-07-01

    Dark matter (DM) annihilations have been widely studied as a possible explanation of excess gamma rays from the Galactic Center seen by Fermi/LAT. However most such models are in conflict with constraints from dwarf spheroidals. Motivated by this tension, we show that p -wave annihilating dark matter can easily accommodate both sets of observations due to the lower DM velocity dispersion in dwarf galaxies. Explaining the DM relic abundance is then challenging. We outline a scenario in which the usual thermal abundance is obtained through s -wave annihilations of a metastable particle, that eventually decays into the p -wave annihilating DM of the present epoch. The couplings and lifetime of the decaying particle are constrained by big bang nucleosynthesis, the cosmic microwave background and direct detection, but significant regions of parameter space are viable. A sufficiently large p -wave cross section can be found by annihilation into light mediators, that also give rise to Sommerfeld enhancement. A prediction of the scenario is enhanced annihilations in galaxy clusters.

  9. AC Dielectric Properties and Positron Annihilation Study on Co and Ti Substitution Effect on Ca-Sr M-Hexaferrites

    Science.gov (United States)

    Mahmoud, K. R.; Eraky, M. R.

    2016-06-01

    The dependence of AC conductivity σ AC, dielectric constant έ, and dielectric loss tangent tan δ on frequency and composition have been investigated at room temperature for polycrystalline Ca0.5Sr0.5Co x Ti x Fe12 - 2 x O19 (where 0.0 ≤ x ≤ 0.8) hexaferrites. It was found that the parameters σ AC, ɛ ', and tan δ have maximum values at x = 0.4 of the Co and Ti substitution. The behavior of σ AC, ɛ ', and tan δ with frequency and composition was explained on the basis of the hopping conduction mechanism and the Koops model. Positron annihilation lifetime spectroscopy (PALS) was used to investigate the defects and changes in electron density for hexaferrite samples. The PAL parameters ( τ 1, I 1, τ 2, I 2, and mean lifetime) show that altering the doping percentage of the Co and Ti ions affects the size and concentration of defects. The results reveal that there are some large voids in the studied samples. The obtained results indicate the high sensitivity of the PALS technique to the enhanced structure changes with changing composition of the investigated samples and correlate the results with the measured electrical parameters.

  10. Cold rolling induced amorphization and nanocrystallization processes studied by positron lifetime and 2-dimensional Doppler broadening measurements

    International Nuclear Information System (INIS)

    In order to contribute to an atomistic understanding of the interfacial structure and processes during amorphization and nanocrystallization, the present work deals with studies of interfacial free volumes by means of positron-annihilation-spectroscopy. In addition to positron lifetime spectroscopy, coincident Doppler broadening of the positron-electron annihilation photons is applied as novel technique for studying the chemistry of interfaces. To study the amorphization process, pure foils of Cu and Zr with a nominal composition of Cu60Zr40 were mechanically intermixed by cold rolling. Starting from the constituent pure metals, a nanoscale multilayer structure of elemental layers and amorphous interlayers develops in an intermediate state of folding and rolling, where free volumes with a Zr-rich environment occur that are presumably located in the hetero-interfaces between the various layers or in grain boundaries of the Cu-layers. To analyze the nanocrystallization reaction that occurs in marginal glass formers, pure foils of Al and Sm with a composition of Al92Sm8 were produced by the abovementioned synthesis route. Specific modifications of free volumes and their chemical environment could be observed for various strain levels

  11. JRQ and JPA irradiated and annealed reactor pressure vessel steels studied by positron annihilation

    Science.gov (United States)

    Slugeň, Vladimír; Gokhman, Oleksandr; Pecko, Stanislav; Sojak, Stanislav; Bergner, Frank

    2016-03-01

    The paper is focused on a comprehensive study of JRQ and JPA reactor pressure vessel steels from the positron annihilation lifetime spectroscopy (PALS) point of view. Based on our more than 20 years' experience with characterization of irradiated reactor steels, we confirmed that defects after irradiation start to grow and/or merge into bigger clusters. Experimental results shown that JPA steel is more sensitive to the creation of irradiation-induced defects than JRQ steel. It is most probably due to high copper content (0.29 wt.% in JPA) and copper precipitation has a major impact on neutron-induced defect creation at the beginning of the irradiation. Based on current PALS results, no large vacancy clusters were formed during irradiation, which could cause dangerous embrittlement concerning operation safety of nuclear power plant. The combined PALS, small angle neutron scattering and atomic probe tomography studies support the model for JRQ and JPA steels describing the structure of irradiation-induced clusters as agglomerations of vacancy clusters (consisting of 2-6 vacancies each) and are separated from each other by a distribution of atoms.

  12. Point defects in YBa2Cu3O7-x studied using positron annihilation

    Science.gov (United States)

    Chudy, Michal; Eisterer, M.; Weber, H. W.; Veterníková, J.; Sojak, S.; Slugeň, V.

    2012-07-01

    Fast neutron irradiation is a powerful technique for introducing additional pinning centers into high temperature superconductors. The spherical defects with sizes of a few nanometers are considered to be effective pinning centers, enhancing Jc. Their morphology is well-known and has already been investigated by several authors in great detail. However, only very little is known about the nature and density of smaller and point defects, which are invisible in transmission electron microscopy. Positron annihilation lifetime spectroscopy was applied to investigate the nature and the concentration of small point-like defects. In this work, the influence of small point defects, such as vacancies and vacancy clusters, on the superconducting properties of YBa2Cu3O7-x bulks was studied; these were introduced by irradiation in the TRIGA Mark II reactor in Vienna. Jc and Tc measurements were performed prior to and after each irradiation step. The samples were irradiated up to a fast neutron ( > 0.1 MeV) fluence of 6 × 1021 m-2. The two kinds of defects—the large collision cascades and the small point-like defects—contribute to the decrease of Tc as well as to the Jc enhancement in astonishingly similar ways.

  13. Positron Annihilation Study on Nickel and Iron Nano-Particles in Natural Rubber Composites

    Directory of Open Access Journals (Sweden)

    Emad H. Aly

    2011-01-01

    Full Text Available Problem statement: The effect of Ni and Fe nano-particles as a filler on the free volume properties Of Natural Rubber (NR was studied using Positron Annihilation Lifetime Spectroscopy (PALS. Approach: The PAL measurements revealed that the free volume properties are strongly affected by the amount and type of filler. Results: Particularly speaking, the free volume fraction dramatically decreased by increasing the filler content. Besides, the addition of nano-prticles created new positron trapping sites at filler-rubber interfaces. Furthermore, correlations were made between the free volume hole sizes (Vh and each of the mechanical and electrical properties successively. A negative correlation was observed between Vh and hardness in the Ni-rubber composites while a positive counterpart was found in the case of Fe-rubber composites. Finally, the polarity of the fillers, being higher than that of the rubber itself, leads to an increase in electrical parameters and an inhibition of o-Ps formation. Conclusion: These results indicate that the investigated composites are considered to be insulating materials as their conductivity values are in the order of an insulator range.

  14. PAL spectroscopy of rare-earth doped Ga-Ge-Te/Se glasses

    OpenAIRE

    Shpotyuk, Ya.; Ingram, A; Shpotyuk, O.

    2016-01-01

    Positron annihilation lifetime (PAL) spectroscopy was applied for the first time to study free-volume void evolution in chalcogenide glasses of Ga-Ge-Te/Se cut-section exemplified by glassy Ga10Ge15Te75 and Ga10Ge15Te72Se3 doped with 500 ppm of Tb3+ or Pr3+. The collected PAL spectra reconstructed within two-state trapping model reveal decaying tendency in positron trapping efficiency in these glasses under rare-earth doping. This effect results in unchanged or slightly increased defect-relat...

  15. Probing Sub-atomistic Free-Volume Imperfections in Dry-Milled Nanoarsenicals with PAL Spectroscopy

    OpenAIRE

    Shpotyuk, Oleh; Ingram, Adam; Bujňáková, Zdenka; Baláž, Peter; Shpotyuk, Yaroslav

    2016-01-01

    Structural transformations caused by coarse-grained powdering and fine-grained mechanochemical milling in a dry mode were probed in high-temperature modification of tetra-arsenic tetra-sulfide known as β-As4S4. In respect to X-ray diffraction analysis, the characteristic sizes of β-As4S4 crystallites in these coarse- and fine-grained powdered pellets were 90 and 40 nm, respectively. Positron annihilation lifetime spectroscopy was employed to characterize transformations occurred in free-volum...

  16. 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....

  17. Thermal treatment of the Fe{sub 78} Si{sub 9} B{sub 13} alloy and the analysis of it magnetic properties through Moessbauer spectroscopy and Positronium annihilation; Tratamiento termico de la aleacion Fe{sub 78} Si{sub 9} B{sub 13} y el analisis de sus propiedades magneticas mediante Espectroscopia de Moessbauer y Aniquilacion de positronio

    Energy Technology Data Exchange (ETDEWEB)

    Lopez M, A

    2005-07-01

    The present work is divided in five chapters. In the first one a general vision of the amorphous alloys is given from antecedents, structure, obtaining methods, properties and problems that at the moment, focusing us in a certain moment to the iron base alloys and the anomalous problem of hardness that it presents the alloy Fe{sub 78}Si{sub 9}B{sub 13} like previously mention us. The second chapter tries on the basic theory of the techniques of Moessbauer spectroscopy and Positron Annihilation spectroscopy, used for the characterization of our alloy as well as the complementary technique of X-ray diffraction (XRD) to observe that the amorphous phase was even studying. The third chapter describes the experimental conditions that were used to study the alloy Fe{sub 78}Si{sub 9}B{sub 13} in each one of their thermal treatments. In the fourth chapter the obtained results and their discussion are presented. In the fifth chapter the conclusions to which were arrived after analyzing the results are presented. (Author)

  18. 一种基于Windows界面的正电子湮没谱分析软件包%A Positron Annihilation Spectroscopy Analysis Program based on Windows Interface

    Institute of Scientific and Technical Information of China (English)

    李辉; 周凯; 王柱; 陈志权; 王少阶

    2011-01-01

    Based on the commonly used PATFIT and MELT program,a new program package —— Positron Annihilation Spectrum Analysis(PASA) with many user-friendly applications was developed.The main modifications are: three kinds of positron analysis methods(PATFIT,MELT,Doppler) were incorporated into PASA;MELT could run independently without being in MATLAB environment;Detailed Doppler analysis program were programmed into PASA.Experiences of using the PASA program were also introduced.%在保留正电子寿命谱分析程序PATFIT和连续谱分析程序MELT主要优点的基础上研究开发了一个新的正电子湮没谱分析软件PASA。主要的改进包括:将PATFIT、MELT和多普勒展宽谱3种正电子湮没分析方法集成在Windows界面程序中,MELT程序脱离MATLAB环境独立运行;编写了完整的多普勒展宽谱分析程序,谱文件的读取、输入参数的调节和拟合结果的输出更加方便快捷,重点加强了正电子湮没实验谱和拟合结果的图形显示。介绍PASA软件的使用经验。

  19. Detection of the opening of the bundle crossing in KcsA with fluorescence lifetime spectroscopy reveals the existence of two gates for ion conduction.

    Science.gov (United States)

    Blunck, Rikard; Cordero-Morales, Julio F; Cuello, Luis G; Perozo, Eduardo; Bezanilla, Francisco

    2006-11-01

    The closed KcsA channel structure revealed a crossing of the cytosolic ends of the transmembrane helices blocking the permeation pathway. It is generally agreed that during channel opening this helical bundle crossing has to widen in order to enable access to the inner cavity. Here, we address the question of whether the opening of the inner gate is sufficient for ion conduction, or if a second gate, located elsewhere, may interrupt the ion flow. We used fluorescence lifetime measurements on KcsA channels labeled with tetramethylrhodamine at residues in the C-terminal end of TM2 to report on the opening of the lower pore region. We found two populations of channels with different fluorescence lifetimes, whose relative distribution agrees with the open probability of the channel. The absolute fraction of channels found with an open bundle crossing is too high to explain the low open probability of the KcsA-WT channel. We found the same distribution as in the WT channel between open and closed bundle crossing for two KcsA mutants, A73E and E71A, which significantly increase open probability at low pH. These two results strongly suggest that a second gate in the ion permeation pathway exists. The location of the mutations A73E and E71A suggests that the second gate may be the selectivity filter, which resides in an inactivated state under steady-state conditions. Since the long closed times observed in KcsA-WT are not present in KcsA-A73E or -E71A, we propose that KcsA-WT remains predominantly in a state with an open bundle crossing but closed (inactivated) second gate, while the mutations A73E and E71A sharply decrease the tendency to enter in the inactivated state, and as a consequence, the second gate is predominantly open at steady state. The ability to monitor the opening of the bundle crossing optically enables the direct recording of the movement of the pore helices while the channel is functioning. PMID:17043150

  20. Study of Hg vacancies in (Hg,Cd)Te after THM growth and post-growth annealing by positron annihilation

    OpenAIRE

    Krause, R.; Klimakow, A.; Kießling, F. M.; Polity, A.; Gille, Peter; Schenk, M.

    1990-01-01

    Positron lifetime measurements have been performed to study vacancy defects in Hg0.78Cd0.22Te. Post-growth annealing under various Hg vapour pressure conditions have been used to create a well-defined number of Hg vacancies. The sensitivity range of the positron annihilation method was found to be 1015 < cHgvac

  1. Study of the effect of ionizing radiation on the structure of natural rubber latex by positron annihilation technique

    International Nuclear Information System (INIS)

    At the present research, were studied the changes in natural rubber latex structure, due to electron beam by a 3 MeV, 25 m A Dynamitron electron accelerator. The natural rubber latex was irradiated at 30, 40 and 50 kGy/s dose rate, over a total dose range from 150 to 250 kGy, for each dose rate used. From natural rubber latex irradiated films were prepared by casting with 0.7 mm. thickness. In the main part, the study was made by positron annihilation lifetime (PAL), this technique is unique in the determination of free-volume properties due to the fact that positronium atom (Ps) is found to be preferentially localized in the free-volume region of polymeric materials. The positron lifetime measurements were performing using a gamma-gamma coincidence system. These results were analyzed by PATFIT-88 program computer into three components, the long-lived component for orthopositronium (o-Ps) with parameters lifetime (τ3) and formation intensity (I3), were plotted and analyzed for each dose rate and total dose used. Besides with τ3 were calculated the mean free-volume size based on the spherical model for the free-volume bubble, found that the free-volume decrease slightly with the total dose due to the crosslinking of natural rubber latex. Besides was studied the effect of dose rate on tensile strength, the tensile strength is increased with the total dose although there was not a clear effect due to the dose rate. Also the films were subjected to aging in order to determined the thermal stability of natural rubber latex irradiated, the results show that the films have good stability. Besides was used the infrared spectroscopy to determine the changes due to the crosslinking by variations in the characteristically absorption bands for cis 1,4-polyisoprene. (Author)

  2. P-wave Annihilating Dark Matter from a Decaying Predecessor and the Galactic Center Excess

    CERN Document Server

    Choquette, Jeremie; Cornell, Jonathan M

    2016-01-01

    Dark matter (DM) annihilations have been widely studied as a possible explanation of excess gamma rays from the galactic center seen by Fermi/LAT. However most such models are in conflict with constraints from dwarf spheroidals. Motivated by this tension, we show that p-wave annihilating dark matter can easily accommodate both sets of observations due to the lower DM velocity dispersion in dwarf galaxies. Explaining the DM relic abundance is then challenging. We outline a scenario in which the usual thermal abundance is obtained through s-wave annihilations of a metastable particle, that eventually decays into the p-wave annihilating DM of the present epoch. The couplings and lifetime of the decaying particle are constrained by big bang nucleosynthesis, the cosmic microwave background and direct detection, but significant regions of parameter space are viable. A sufficiently large p-wave cross section can be found by annihilation into light mediators, that also give rise to Sommerfeld enhancement. A predictio...

  3. Different emissive states in the bulk and at the surface of methylammonium lead bromide perovskite revealed by two-photon micro-spectroscopy and lifetime measurements

    Science.gov (United States)

    Karki, Khadga Jung; Abdellah, Mohamed; Zhang, Wei; Pullerits, Tõnu

    2016-07-01

    Two photon photoluminescence (2PPL) from single crystals of methyl ammonium lead bromide (CH3NH3PbBr3, MAPbBr3) is studied. We observe two components in the 2PPL spectra, which we assign to the photoluminescence (PL) from the carrier recombination at the band edge and the recombination due to self-trapping of excitons. The PL Stokes shift of self-trapped excitons is about 100 meV from the band-gap energy. Our measurements show that about 15% of the total PL from regions about 40 μm deep inside the crystal is due to the emission from self-trapped exciton. This contribution increases to about 20% in the PL from the regions close to the surface. Time resolved measurements of 2PPL show that the PL due to band-edge recombination has a life time of about 8 ns while the PL lifetime of self-trapped excitons is in the order of 100 ns. Quantification of self-trapped excitons in the materials used in photovoltaics is important as such excitons hinder charge separation. As our results also show that an appreciable fraction of photo-generated carriers get trapped, the results are important in rational design of photovoltaics. On the other hand, our results also show that the self-trapped excitons broaden the emission spectrum, which may be useful in designing broadband light emitting devices.

  4. Nuclear Instruments and Methods in Physics Research. Section B; Microstructural Characterization of Semi-Interpenetrating Polymer Networks by Positron Lifetime Spectroscopy

    Science.gov (United States)

    Singh, Jag J.; Pater, Ruth H.; Eftekhari, Abe

    1998-01-01

    Thermoset and thermoplastic polyimides have complementary physical/mechanical properties. Whereas thermoset polyimides are brittle and generally easier to process, thermoplastic polyimides are tough but harder to process. It is expected that a combination of these two types of polyimides may help produce polymers more suitable for aerospace applications. Semi-Interpenetrating Polymer Networks (S-IPNs) of thermoset LaRC(Trademark)-RP46 and thermoplastic LARC(Trademark)-IA polyimides were prepared in weight percent ratios ranging from 100:0 to 0: 100. Positron lifetime measurements were made in these samples to correlate their free volume features with physical/mechanical properties. As expected, positronium atoms are not formed in these samples. The second life time component has been used to infer the positron trap dimensions. The "free volume" goes through a minimum at about 50:50 ratio, suggesting that S-IPN samples are not merely solid solutions of the two polymers. These data and related structural properties of the S-IPN samples have been discussed in this paper.

  5. Positron Annihilation in the Bipositronium Ps2

    Energy Technology Data Exchange (ETDEWEB)

    Bailey, David H.; Frolov, Alexei M.

    2005-07-01

    The electron-positron-pair annihilation in the bipositronium PS2 is considered. In particular, the two-, three-, one- and zero-photon annihilation rates are determined to high accuracy. The corresponding analytical expressions are also presented. Also, a large number of bound state properties have been determined for this system.

  6. Laser Spectroscopy of Antiprotonic Helium Atoms

    CERN Multimedia

    2002-01-01

    %PS205 %title\\\\ \\\\Following the discovery of metastable antiprotonic helium atoms ($\\overline{p}He^{+} $) at KEK in 1991, systematic studies of their properties were made at LEAR from 1991 to 1996. In the first two years the lifetime of $\\overline{p}He^{+}$ in liquid and gaseous helium at various temperatures and pressures was measured and the effect of foreign gases on the lifetime of these atoms was investigated. Effects were also discovered which gave the antiproton a 14\\% longer lifetime in $^4$He than in $^3$He, and resulted in important differences in the shape of the annihilation time spectra in the two isotopes.\\\\ \\\\Since 1993 laser spectroscopy of the metastable $\\overline{p}He^{+}$ atoms became the main focus of PS205. Transitions were stimulated between metastable and non-metastable states of the $\\overline{p}He^{+}$ atom by firing a pulsed dye laser beam into the helium target every time an identified metastable atom was present (Figure 1). If the laser frequency matched the transition energy, the...

  7. Fermionic Semi-Annihilating Dark Matter

    CERN Document Server

    Cai, Yi

    2015-01-01

    Semi-annihilation is a generic feature of dark matter theories with symmetries larger than Z2. We investigate two examples with multi-component dark sectors comprised of an SU(2)L singlet or triplet fermion besides a scalar singlet. These are respectively the minimal fermionic semi-annihilating model, and the minimal case for a gauge-charged fermion. We study the relevant dark matter phenomenology, including the interplay of semi-annihilation and the Sommerfeld effect. We demonstrate that semi-annihilation in the singlet model can explain the gamma ray excess from the galactic center. For the triplet model we scan the parameter space, and explore how signals and constraints are modified by semi-annihilation. We find that the entire region where the model comprises all the observed dark matter is accessible to current and planned direct and indirect searches.

  8. Skyrmion creation and annihilation by spin waves

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yizhou, E-mail: yliu062@ucr.edu; Yin, Gen; Lake, Roger K., E-mail: rlake@ece.ucr.edu [Department of Electrical and Computer Engineering, University of California, Riverside, California 92521 (United States); Zang, Jiadong [Department of Physics and Material Science Program, University of New Hampshire, Durham, New Hampshire 03824 (United States); Shi, Jing [Department of Physics and Astronomy, University of California, Riverside, California 92521 (United States)

    2015-10-12

    Single skyrmion creation and annihilation by spin waves in a crossbar geometry are theoretically analyzed. A critical spin-wave frequency is required both for the creation and the annihilation of a skyrmion. The minimum frequencies for creation and annihilation are similar, but the optimum frequency for creation is below the critical frequency for skyrmion annihilation. If a skyrmion already exists in the cross bar region, a spin wave below the critical frequency causes the skyrmion to circulate within the central region. A heat assisted creation process reduces the spin-wave frequency and amplitude required for creating a skyrmion. The effective field resulting from the Dzyaloshinskii-Moriya interaction and the emergent field of the skyrmion acting on the spin wave drive the creation and annihilation processes.

  9. Antimatter annihilation detection with AEgIS

    CERN Document Server

    Gligorova, Angela

    2015-01-01

    AE ̄ gIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is an antimatter exper- iment based at CERN, whose primary goal is to carry out the first direct measurement of the Earth’s gravitational acceleration on antimatter. A precise measurement of antimatter gravity would be the first precision test of the Weak Equivalence Principle for antimatter. The principle of the experiment is based on the formation of antihydrogen through a charge exchange reaction between laser excited (Rydberg) positronium and ultra-cold antiprotons. The antihydrogen atoms will be accelerated by an inhomogeneous electric field (Stark acceleration) to form a pulsed cold beam. The free fall of the antihydrogen due to Earth’s gravity will be measured using a moiré de- flectometer and a hybrid position detector. This detector is foreseen to consist of an active silicon part, where the annihilation of antihydrogen takes place, followed by an emulsion part coupled to a fiber time-of-flight detector. This overview prese...

  10. Electrochemical and positron annihilation studies of semicarbazones and thiosemicarbazones derived from ferrocene

    International Nuclear Information System (INIS)

    A series of six ferrocene derivates containing a semicarbazone or thiosemicarbazone side chain was investigated by cyclic voltammetry and positron annihilation lifetime measurements. Both the redox and the electron capture processes took place on the Fe atom. Correlations between the two methods were proposed. taking into account the substituents on the side chain of the compounds, their redox potentials and the probabilities of o-positronium (o-Ps), formation. (author)

  11. Electrochemical and positron annihilation studies of semicarbazones and thiosemicarbazones derived from ferrocene

    Energy Technology Data Exchange (ETDEWEB)

    Graudo, Jose Eugenio J.C. [Juiz de Fora Univ., MG (Brazil). Dept. de Quimica; Filgueiras, Carlos A.L. [Universidade Federal, Rio de Janeiro, RJ (Brazil). Inst. de Quimica. Dept. de Quimica Inorganica; Marques-Netto, Antonio [Minas Gerais Univ., Belo Horizonte, MG (Brazil). Dept. de Quimica; Batista, Alzir A. [Sao Carlos Univ., SP (Brazil). Dept. de Quimica

    2000-06-01

    A series of six ferrocene derivates containing a semicarbazone or thiosemicarbazone side chain was investigated by cyclic voltammetry and positron annihilation lifetime measurements. Both the redox and the electron capture processes took place on the Fe atom. Correlations between the two methods were proposed. taking into account the substituents on the side chain of the compounds, their redox potentials and the probabilities of o-positronium (o-Ps), formation. (author)

  12. Excited-state dynamics in diketopyrrolopyrrole-based copolymer for organic photovoltaics investigated by transient optical spectroscopy

    Science.gov (United States)

    Matsuzaki, Hiroyuki; Furube, Akihiro; Katoh, Ryuzi; Pratap Singh, Samarendra; Sonar, Prashant; Williams, Evan Laurence; Vijila, Chellappan; Sandhya Subramanian, Gomathy; Gorelik, Sergey; Hobley, Jonathan

    2014-01-01

    We investigate the photoexcited state dynamics in a donor-acceptor copolymer, poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene} (pDPP-TNT), by picosecond fluorescence and femtosecond transient absorption spectroscopies. Time-resolved fluorescence lifetime measurements of pDPP-TNT thin films reveal that the lifetime of the singlet excited state is 185 ± 5 ps and that singlet-singlet annihilation occurs at excitation photon densities above 6 × 1017 photons/cm3. From the results of singlet-singlet annihilation analysis, we estimate that the single-singlet annihilation rate constant is (6.0 ± 0.2) × 10-9 cm3 s-1 and the singlet diffusion length is ~7 nm. From the comparison of femtosecond transient absorption measurements and picosecond fluorescence measurements, it is found that the time profile of the photobleaching signal in the charge-transfer (CT) absorption band coincides with that of the fluorescence intensity and there is no indication of long-lived species, which clearly suggests that charged species, such as polaron pairs and triplet excitons, are not effectively photogenerated in the neat pDPP-TNT polymer.

  13. Geant4 Simulation of Annihilation and excitation of Positronium

    CERN Document Server

    Gad, Andreas

    2016-01-01

    The purpose of this report is to document the work done during the summer of 2016 (18/6- 26/8) as a part of the CERN Summer Student Programme. The work has been done at the AEgIS (Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy) collaboration under the supervision of Lillian Smestad and Michael Doser. The goal of the project was to create a Monte Carlo simulation in Geant4, of Positronium annihilation and excitation in the positron test chamber of the AEgIs experiment.

  14. Positron annihilation and thermally stimulated current of electron beam irradiated polyetheretherketone

    Energy Technology Data Exchange (ETDEWEB)

    Fujita, Shigetaka; Shinyama, Katsuyoshi; Baba, Makoto [Hachinohe Inst. of Tech., Hachinohe, Aomori (Japan); Suzuki, Takenori

    1997-03-01

    Positron lifetime measurements were applied to electron beam irradiated poly(ether-ether-ketone). The lifetime, {tau}{sub 3}, of the ortho-positronium of unirradiated and 5 MGy irradiated specimen became rapidly longer above about 150degC. {tau}{sub 3} of 50 MGy and 100 MGy irradiated specimen was shorter than that of unirradiated one. Thermally stimulated current (TSC) decreased with increasing the dose before voltage application. In the case of voltage application, a TSC peak appeared and the peak value decreased with increased the dose. The correlation between the results of positron annihilation and TSC was investigated. (author)

  15. Calculation of the D and B Meson Lifetimes

    OpenAIRE

    Chernyak, Victor

    1994-01-01

    Using the expansions of the heavy meson decay widths in the heavy quark mass and QCD sum rules for estimates of corresponding matrix elements,\\, we calculate the $D^{\\pm,o,s}$ decay widths and the $B^{\\pm,o,s}$ lifetime differences. The results for D mesons are in agreement with the data,\\, while it is predicted that $[\\Gamma (B^o)-\\Gamma (B^-)]/\\Gamma_B\\se 4\\%\\,,$ and the lifetime difference of the $B^o$ and $B_s$ mesons is even smaller. The role of the weak annihilation and Pauli interferen...

  16. Moisture dependence of positron annihilation spectra in nylon-6

    Science.gov (United States)

    Singh, J. J.; St. Clair, T. L.; Holt, W. H.; Mock, W., Jr.

    1984-01-01

    Positron annihilation time spectra have been measured in nylon-6 samples as a function of their moisture content. The measured average long life component lifetime values are: 1722 + or - 47 ps (dry), 1676 + or - 40 ps (14.6 percent saturation value), 1719 + or - 26 ps (29.3 percent saturation value), 1720 + or - 35 ps (50 percent of saturation value), 1857 + or - 35 ps (78.1 percent saturation value), and 1936 + or - 57 ps (saturated). It appears that nylon-6 has a special affinity for water at low concentration levels where H2O molecules enter between the (C = O - H-N) chemical bonds between nylon molecular chains. As the water concentration increases beyond a critical level, nylon-6 specimens start trapping H2O molecules in other bond sites or potential wells. The trapped water increases the free volume in the test specimens and reduces Ps atom formation as well as its subsequent decay rate.

  17. Muon Fluxes From Dark Matter Annihilation

    CERN Document Server

    Erkoca, Arif Emre; Sarcevic, Ina

    2009-01-01

    We calculate the muon flux from annihilation of the dark matter in the core of the Sun, in the core of the Earth and from cosmic diffuse neutrinos produced in dark matter annihilation in the halos. We consider model-independent direct neutrino production and secondary neutrino production from the decay of taus produced in the annihilation of dark matter. We illustrate how muon energy distribution from dark matter annihilation has a very different shape than muon flux from atmospheric neutrinos. We consider both the upward muon flux, when muons are created in the rock below the detector, and the contained flux when muons are created in the (ice) detector. We contrast our results to the ones previously obtained in the literature, illustrating the importance of properly treating muon propagation and energy loss. We comment on neutrino flavor dependence and their detection.

  18. Probing dark matter decay and annihilation with Fermi LAT observations of nearby galaxy clusters

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Xiaoyuan [Chinese Academy of Sciences, Beijing (China). National Astronomical Observatories; Max-Planck-Institut fuer Physik, Muenchen (Germany); Vertongen, Gilles [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Institut d' Astrophysique de Paris, 75 - Paris (France); Weniger, Christoph [Max-Planck-Institut fuer Physik, Muenchen (Germany)

    2011-09-15

    Galaxy clusters are promising targets for indirect dark matter searches. Gamma-ray signatures from the decay or annihilation of dark matter particles inside these clusters could be observable with the Fermi Large Area Telescope (LAT). Based on three years of Fermi LAT gamma-ray data, we analyze the flux coming from eight nearby clusters individually as well as in a combined likelihood analysis. Concentrating mostly on signals from dark matter decay, we take into account uncertainties of the cluster masses as determined by X-ray observations and model the cluster emission with extended sources. We do not find significant emission from any of the considered clusters and present limits on the dark matter lifetime and annihilation cross-section. We compare our lifetime limits derived from cluster observations with the limits that can be obtained from the extragalactic gamma-ray background, and find that in case of hadronic decay the cluster limits become competitive at dark matter masses below a few hundred GeV. Finally, we show that in presence of dark matter substructures down to 10{sup -6} solar masses the limits on the dark matter annihilation cross-section could improve by a factor of a few hundred, possibly going down to the thermal cross-section of 3 x 10{sup -26} cm{sup 3}s{sup -1} for dark matter masses annihilation into b anti b. As a direct application of our results, we derive limits on the lifetime of gravitino dark matter in scenarios with R-parity violation. Implications of these limits for the possible observation of long-lived superparticles at the LHC are discussed. (orig.)

  19. Microdefects and 3 d electrons in ordered B2-FeAl alloys investigated by positron annihilation techniques

    Science.gov (United States)

    Yuyang, Huang; Yanqiong, Lu; Yanyan, Zhu; Yuxia, Li; Wen, Deng

    2009-09-01

    Microdefects and 3d electrons in B2-FeAl alloys with different chemical composition, single crystal of Fe and cold-rolled Fe has been studied by positron lifetime and coincidence Doppler broadening spectroscopy. The coincidence Doppler broadening spectrum of the single crystal of Fe shows the highest 3d electron signal in the spectra of all tested samples. The 3d electron signal in the spectrum of Fe50Al50 alloy is much lower than that of the cold-rolled Fe. This indicates that some of the 3d electrons of Fe atoms and 3p electrons of Al atoms in B2-FeAl alloy are localized to form strong covalent bonds, thus decreasing the probability of positron annihilation with 3d electrons of Fe atoms. With the increase of Al content in B2-FeAl alloys, the 3d electron signal in the spectrum of the alloy decreases, while the open volume of defect increases.

  20. Positron lifetime study of native vacancy-like defects in chalcogenide glasses

    International Nuclear Information System (INIS)

    Modified model for positron annihilation in vitreous chalcogenide semiconductors is developed to explain a number of previously obtained results on positron lifetime measurements in glassy As-Ge-S of stoichiometric As2S3-GeS2 and non-stoichiometric As2S3-Ge2S3 cut-sections

  1. Positron annihilation study of graphite, glassy carbon and C60/C70 fullerene

    International Nuclear Information System (INIS)

    ACAR (Angular Correlation of Annihilation Radiation) and positron lifetime measurements have been made on, HOPG (Highly Oriented Pyrolytic Graphite), isotropic fine-grained graphite, glassy carbons and C60/C70 powder. HOPG showed marked bimodality along the c-axis and anisotropy in ACAR momentum distribution, which stem from characteristic annihilation between 'interlayer' positrons and π-electrons in graphite. ACAR curves of the isotropic graphite and glassy carbons are even narrower than that of HOPG perpendicular to the c-axis. Positron lifetime of 420 and 390 - 480 psec, much longer than that of 221 psec in HOPG, were observed for the isotropic graphite and glassy carbons respectively, which are due to positron trapping in structural voids in them. Positron lifetime and ACAR width (FWHM) can be well correlated to void sizes (1.7 to 5.0 nm) of glassy carbons which have been determined by small angle neutron (SAN) scattering measurements. ACAR curves and positron lifetime of C60/C70 powder agree well with those of glassy carbons. This shows that positron wave functions extend, as in the voids of glassy carbons, much wider than open spaces of the octahedral interstices of the face-centered cubic (FCC) structure of C60 crystal and strongly suggests positron trapping in the 'soccer ball' vacancy. Possible positron states in the carbon materials are discussed with a simple model of void volume-trapping. Preliminary results on neutron irradiation damage in HOPG are also presented. (author)

  2. The Darkest Hour Before Dawn: Contributions to Cosmic Reionisation from Dark Matter Annihilation and Decay

    CERN Document Server

    Liu, Hongwan; Zavala, Jesús

    2016-01-01

    Dark matter annihilation or decay could have a significant impact on the ionisation and thermal history of the universe. In this paper, we study the potential contribution of dark matter annihilation ($s$-wave- or $p$-wave-dominated) or decay to cosmic reionisation, via the production of electrons, positrons and photons. We map out the possible perturbations to the ionisation and thermal histories of the universe due to dark matter processes, over a broad range of velocity-averaged annihilation cross-sections/decay lifetimes and dark matter masses. We have employed recent numerical studies of the efficiency with which annihilation/decay products induce heating and ionization in the intergalactic medium, and in this work extended them down to a redshift of $1+z = 4$ for two different reionisation scenarios. We also improve on earlier studies by using the results of detailed structure formation models of dark matter haloes and subhaloes that are consistent with up-to-date $N$-body simulations, with estimates on...

  3. Study by the positron annihilation technique of Graft copolimerization of methyl methacrylate in polyethylene induced by gamma radiation

    International Nuclear Information System (INIS)

    Radiation initiated grafting is a very broad field which has attracted considerable interest over the last two decades. Graft copolymers may combine suitable properties of two polymeric components. Radiation methods are particulary appropiate for the production of a large variety of graft copolymers having interesting properties. Ionizing radiation has provided a convenient and clean method to activate a sustrate polymer and undoubtedly, it has added impetus to this field of research. In the present work, graft polymerization of methyl methacrylate (MMA) onto low density polyethylene (LDPE) was carried out. The effect of gamma ray irradiation dose on the grafting degree was investigated for two different methods: direct and preirradiation. The best method to prepare the copolymer for the LDPE film thickness studied: 0.05 and 0.2 mm., was direct method. In both polyethylene thickness, the grafting degree increased as a function of the reaction time. However, grafting for LDPE 0.2 mm. it is better, because the copolymer with that thickness conserve the main physical-chemistry properties of the LDPE along the different grafting degrees obtained, which it is important for practical purposes. Infrared spectroscopy was used to probe the changes ocurred in the LDPE structure with the graft of MMA, first spectrum showed typical bands for LDPE structure, while in the second spectrum new bands appeared which corresponded to PMMA structure grafted onto LDPE. Positron annihilation lifetime technique was applied to study the copolymer microstructure according to increase of grafting degree. O-PS lifetime and intensity tend to decrease. This behavior could be due to the diminution of free volume in the original LDPE matrix as grafting proceeds. Copolymer morphology was observed using optical microscopy (Author)

  4. Positron annihilation study of acryl amide/poly (metha acrylic acid) membrane

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Hady, E E; Abdel-Hamed, M O; Hammam, A M; Elsharkawy, M R M [Physics Department, Faculty of Science, Minia University, Minia (Egypt); Eltoony, M M, E-mail: esamhady@yahoo.com [Chemistry Department, Atomic Energy Authority, Cairo 11115 (Egypt)

    2011-01-01

    Gamma irradiation posses a serious role for casting the membranes. Acryl amide /poly (methacrylic acid) membrane was synthesized under {gamma}-radiation effect. The structure of the membrane was characterized by FTIR, thermo-gravimetric analysis and the scanning electron microscope. The properties of the membranes were also investigated in terms of proton conductivity and positron annihilation lifetime (PAL) parameters. On the basis of the values of the long-lived components in the lifetime spectra, the size of the free volume and their intensity were calculated. The positron lifetime study on these irradiated casted membranes shows that the cross-linking and degradation within the membrane matrix affect the free volume content and hence the microstructure.

  5. On the peculiarities of positron annihilation features in silicalite-1 and Y-zeolites

    CERN Document Server

    Kajcsos, Z; Liszka, L; Billard, I; Bonnenfant, A; Azenma, E; Lázár, K; Pal-Borbely, G; Caullet, P; Patarin, J; Lohonyai, L

    2000-01-01

    Conditions that facilitate high Ps formation and interactions that modify the o-Ps lifetime were investigated by positron annihilation techniques in silicalite-1 and various Y-zeolites. Long lifetimes, up to 135 ns, and o-Ps fractions as high as 40% were found. The influence of heat treatment (in the range of 90-520 K), capillary condensation of N sub 2 (0.085 MPa) and correlation with water removal was examined in Y-zeolites and in silicalite-1, respectively. The latter matrix was also studied in the presence of liquids. In various samples unexpected features were found (peculiar changes in the 2 gamma/3 gamma ratio, inversion in the trend of lifetime variations, disappearance of specific components, etc.), denoting the complexity of the processes governing the fate of e sup sup + and Ps.

  6. Computing Battery Lifetime Distributions

    NARCIS (Netherlands)

    Cloth, Lucia; Jongerden, Marijn R.; Haverkort, Boudewijn R.

    2007-01-01

    The usage of mobile devices like cell phones, navigation systems, or laptop computers, is limited by the lifetime of the included batteries. This lifetime depends naturally on the rate at which energy is consumed, however, it also depends on the usage pattern of the battery. Continuous drawing of a

  7. Effect of positron source irradiation on positronium annihilation in fine powdered alumina

    Science.gov (United States)

    Liu, Z. W.; Chen, Z. Q.

    2016-09-01

    Positron lifetime and Doppler broadening of positron annihilation radiation were measured as a function of time to study the irradiation effect by 22Na positron source in fine powdered alumina. The γ-Al2O3 samples were put in a vacuum chamber with a pressure of about 10-6 Torr and were cooled down to 10 K by a closed-cycle helium gas refrigerator. The irradiation of γ-Al2O3 samples by positron source was taken for a duration of about two days immediately after the sample was cooled down. After that, the sample was subjected to a warm up process from 10 K to 300 K with a step of 10 K. Positron lifetime and Doppler broadening spectra were measured simultaneously during these processes. Two long lifetime components corresponding to ortho-positronium annihilation were observed. A significant shortening of these long lifetime components and a large increase in S parameter is observed during irradiation. It is supposed that positron source irradiation creates a large number of paramagnetic centers on the surface of the γ-Al2O3 grains, which induce spin conversion quenching of positronium. The irradiation induced paramagnetic centers are unstable above 70 K and are nearly annealed out when the temperature rises to 190 K. After warming up of the sample to room temperature, the positron lifetime spectrum is identical to that before irradiation. It was also found that after irradiation, a medium long lifetime component of about 5 ns appears, of which the intensity increases with increasing irradiation time. This may be originated from the formation of the surface o-Ps state. This surface o-Ps state is also inhibited at elevated temperatures. Our results indicate that positronium is a very sensitive probe for the surface defects in porous materials.

  8. Determination of phase transitions in a lyotropic liquid crystal by Positron Annihilation technique

    International Nuclear Information System (INIS)

    Positron annihilation technique was used to determine the phase transitions in a lyotropic liquid crystal, as a function of temperature. Seven different concentrations of the surfactant cetyldimethylethylammonium bromide, were studied. The liquid crystal studied consisted of a binary system, formed by the surfactant and water. Positron annihilation technique has a very high sensitivity toward changes in the microestructure, in condensed matter, this is useful in order to detect the temperatures at which phase transitions occur and the number of these, in a liquid crystalline system. Thus, phase transitions are related with changes occurred in the ortho-positronium parameters: lifetime (τ3) and intensity of formation (I3). Six different kinds of phases were detected in the system studied in a temperature range of 35 to 140 Centigrade degrees, those phases were: hexagonal, hexagonal-lamellae, lamellae, lamellae-cubic, nematic and anisotropic. Using optical microscopic the textures of these phases were assigned. (Author)

  9. Structure of water + acetonitrile solutions from acoustic and positron annihilation measurements

    Energy Technology Data Exchange (ETDEWEB)

    Jerie, Kazimierz [Institute of Experimental Physics, University of WrocIaw, WrocIaw (Poland); Baranowski, Andrzej [Institute of Experimental Physics, University of WrocIaw, WrocIaw (Poland); Koziol, Stan [Waters Corp., 34 Maple St., Milford, MA 01757 (United States); Glinski, Jacek [Faculty of Chemistry, University of WrocIaw, WrocIaw (Poland)]. E-mail: glin@wchuwr.chem.uni.wroc.pl; Burakowski, Andrzej [Faculty of Chemistry, University of WrocIaw, WrocIaw (Poland)

    2005-03-14

    We report the results of acoustic and positron annihilation measurements in aqueous solutions of acetonitrile (CH{sub 3}CN). Hydrophobicity of the solute is discussed, as well as the possibility of describing the title system in terms of hydrophobic solvation. A new method of calculating the 'ideal' positronium lifetimes is proposed, based on the mean volume of cavities (holes) in liquid structure available for positronium pseudoatom. The results are almost identical with those obtained from molar volumes using the concept of Levay et al. On the other hand, the same calculations performed using the 'bubble' model of annihilation yield very different results. It seems that either acetonitrile forms with water clathrate-like hydrates of untypical architecture, or it is too weak hydrophobic agent to form clathrate-like hydrates at all. The former interpretation seems to be more probable.

  10. Structure of Aqueous Solutions of Acetonitrile Investigated by Acoustic and Positron Annihilation Measurements

    Science.gov (United States)

    Jerie, K.; Baranowski, A.; Koziol, S.; Burakowski, A.

    2005-05-01

    We report the results of acoustic and positron annihilation measurements in aqueous solutions of acetonitrile (CH3CN). Hydrophobicity of the solute is discussed, as well as the possibility of describing the title system in terms of hydrophobic solvation. The concept of Levay et al. of calculating the "ideal positronium lifetimes is applied, basing on the mean volume of cavities (holes) in liquid structure available for positronium pseudoatom. The same calculations performed using the Tao model of annihilation yield very different results. It can be concluded that either acetonitrile forms with water clathrate-like hydrates of untypical architecture, or it is too weak hydrophobic agent to form clathrate-like hydrates at all. The former interpretation seems to be more probable.

  11. Structure of water + acetonitrile solutions from acoustic and positron annihilation measurements

    Science.gov (United States)

    Jerie, Kazimierz; Baranowski, Andrzej; Koziol, Stan; Gliński, Jacek; Burakowski, Andrzej

    2005-03-01

    We report the results of acoustic and positron annihilation measurements in aqueous solutions of acetonitrile (CH 3CN). Hydrophobicity of the solute is discussed, as well as the possibility of describing the title system in terms of hydrophobic solvation. A new method of calculating the "ideal" positronium lifetimes is proposed, based on the mean volume of cavities (holes) in liquid structure available for positronium pseudoatom. The results are almost identical with those obtained from molar volumes using the concept of Levay et al. On the other hand, the same calculations performed using the "bubble" model of annihilation yield very different results. It seems that either acetonitrile forms with water clathrate-like hydrates of untypical architecture, or it is too weak hydrophobic agent to form clathrate-like hydrates at all. The former interpretation seems to be more probable.

  12. Exact solutions for steady reconnective annihilation revisited

    Science.gov (United States)

    Titov, Vyacheslav S.; Tassi, Emanuele; Hornig, Gunnar

    2004-10-01

    This work complements the previous studies on steady reconnective magnetic annihilation in three different geometries: the two-dimensional Cartesian and polar ones and the three-dimensional (3D) cylindrical one. A special class of diffusive solutions is found analytically in explicit form for all of the three geometries. In the 3D case it is extended to a much wider class of exact solutions describing reconnective magnetic annihilation at the separatrix spine line of a magnetic null point. One of the obtained solutions provides an explicit expression for the Craig-Fabling solution. It is also identified which of the steady flow regimes found are dynamically accessible.

  13. Lifetime of organic photovoltaics

    DEFF Research Database (Denmark)

    Corazza, Michael; Krebs, Frederik C; Gevorgyan, Suren A.

    2015-01-01

    tests. Comparison of the indoor and outdoor lifetimes was performed by means of the o-diagram, which constitutes the initial steps towards establishing a method for predicting the lifetime of an organic photovoltaic device under real operational conditions based on a selection of accelerated indoor......A comprehensive outdoor study of polymer solar cells and modules for duration of one year was conducted. Different sample geometries and encapsulations were employed in order to study the spread in the lifetimes. The study is a complimentary report to previous work that focused on indoor ageing...

  14. Theory of Beauty Lifetimes

    OpenAIRE

    Neubert, Matthias(PRISMA Cluster of Excellence and Mainz Institut for Theoretical Physics, Johannes Gutenberg University, 55099, Mainz, Germany)

    1997-01-01

    A critical review of the theoretical understanding of the lifetimes of beauty hadrons is given. A model-independent analysis using the heavy-quark expansion allows for a description of the lifetime ratios tau(B-)/tau(B0) and tau(Lambda_b)/tau(B0) in a small region of parameter space. It is demonstrated that the lifetime ratio tau(B-)/tau(B0) cannot be used to extract the decay constant of the B meson. Implications for the semileptonic branching ratio and charm yield in B decays are pointed out.

  15. Customer Lifetime Value Measurement

    OpenAIRE

    Sharad Borle; Siddharth S. Singh; Dipak C. Jain

    2008-01-01

    The measurement of customer lifetime value is important because it is used as a metric in evaluating decisions in the context of customer relationship management. For a firm, it is important to form some expectations as to the lifetime value of each customer at the time a customer starts doing business with the firm, and at each purchase by the customer. In this paper, we use a hierarchical Bayes approach to estimate the lifetime value of each customer at each purchase occasion by jointly mod...

  16. 3D-AP and positron annihilation study of precipitation behavior in Cu-Cr-Zr alloy

    DEFF Research Database (Denmark)

    Hatakeyama, M.; Toyama, T.; Yang, J.;

    2009-01-01

    Precipitation behavior in a Cu-0.78%Cr-0.13%Zr alloy during aging and reaging has been studied by laser-assisted local electrode three-dimensional atom probe (Laser-LEAP) and positron annihilation spectroscopy (PAS). After the prime aging at 460 degrees C, Cr clusters enriched with Zr were observ...

  17. Production bias and cluster annihilation: Why necessary?

    DEFF Research Database (Denmark)

    Singh, B.N.; Trinkaus, H.; Woo, C.H.

    1994-01-01

    the primary cluster density is high. Therefore, a sustained high swelling rate driven by production bias must involve the annihilation of primary clusters at sinks. A number of experimental observations which are unexplainable in terms of the conventional dislocation bias for monointerstitials is...

  18. WIMP annihilation effects on primordial star formation

    CERN Document Server

    Ripamonti, E; Bressan, A; Schneider, R; Ferrara, A; Marigo, P

    2009-01-01

    We study the effects of WIMP dark matter (DM) annihilations on the thermal and chemical evolution of the gaseous clouds where the first generation of stars in the Universe is formed. We follow the collapse of the gas inside a typical halo virializing at very high redshift, from well before virialization until a stage where the heating from DM annihilations exceeds the gas cooling rate. The DM energy input is estimated by inserting the energy released by DM annihilations (as predicted by an adiabatic contraction of the original DM profile) in a spherically symmetric radiative transfer scheme. In addition to the heating effects of the energy absorbed, we include its feedback upon the chemical properties of the gas, which is critical to determine the cooling rate in the halo, and hence the fragmentation scale and Jeans mass of the first stars. We find that DM annihilation does alter the free electron and especially the H2 fraction when the gas density is n>~ 10^4 cm^-3, for our fiducial parameter values. However...

  19. Positron annihilation studies of neutron irradiated and thermally treated reactor pressure vessel steels

    International Nuclear Information System (INIS)

    Positron annihilation lifetime measurements using the pulsed low energy positron system (PLEPS) were applied for the first time for the investigation of defects of irradiated and thermally treated reactor pressure vessel (RPV) steels. PLEPS results showed that the changes in the microstructure of the RPV-steel properties caused by neutron irradiation and post-irradiation thermal treatment can be detected. The samples originated from the Russian 15Kh2MFA and Sv10KhMFT steels, commercially used at WWER-440 reactors, were irradiated near the core at NPP Bohunice (Slovakia) to neutron fluences in the range from 7.8x1023 to 2.5x1024 m-2

  20. Probing Sub-atomistic Free-Volume Imperfections in Dry-Milled Nanoarsenicals with PAL Spectroscopy.

    Science.gov (United States)

    Shpotyuk, Oleh; Ingram, Adam; Bujňáková, Zdenka; Baláž, Peter; Shpotyuk, Yaroslav

    2016-12-01

    Structural transformations caused by coarse-grained powdering and fine-grained mechanochemical milling in a dry mode were probed in high-temperature modification of tetra-arsenic tetra-sulfide known as β-As4S4. In respect to X-ray diffraction analysis, the characteristic sizes of β-As4S4 crystallites in these coarse- and fine-grained powdered pellets were 90 and 40 nm, respectively. Positron annihilation lifetime spectroscopy was employed to characterize transformations occurred in free-volume structure of these nanoarsenicals. Experimentally measured positron lifetime spectra were parameterized in respect to three- or two-term fitting procedures and respectively compared with those accumulated for single crystalline realgar α-As4S4 polymorph. The effect of coarse-grained powdering was found to result in generation of large amount of positron and positronium Ps trapping sites inside arsenicals in addition to existing ones. In fine-grained powdered β-As4S4 pellets, the positron trapping sites with characteristic free volumes close to bi- and tri-atomic vacancies were evidently dominated. These defects were supposed to originate from grain boundary regions and interfacial free volumes near aggregated β-As4S4 crystallites. Thus, the cumulative production of different positron traps with lifetimes close to defect-related lifetimes in realgar α-As4S4 polymorph was detected in fine-grained milled samples. PMID:26754936

  1. Probing Sub-atomistic Free-Volume Imperfections in Dry-Milled Nanoarsenicals with PAL Spectroscopy.

    Science.gov (United States)

    Shpotyuk, Oleh; Ingram, Adam; Bujňáková, Zdenka; Baláž, Peter; Shpotyuk, Yaroslav

    2016-12-01

    Structural transformations caused by coarse-grained powdering and fine-grained mechanochemical milling in a dry mode were probed in high-temperature modification of tetra-arsenic tetra-sulfide known as β-As4S4. In respect to X-ray diffraction analysis, the characteristic sizes of β-As4S4 crystallites in these coarse- and fine-grained powdered pellets were 90 and 40 nm, respectively. Positron annihilation lifetime spectroscopy was employed to characterize transformations occurred in free-volume structure of these nanoarsenicals. Experimentally measured positron lifetime spectra were parameterized in respect to three- or two-term fitting procedures and respectively compared with those accumulated for single crystalline realgar α-As4S4 polymorph. The effect of coarse-grained powdering was found to result in generation of large amount of positron and positronium Ps trapping sites inside arsenicals in addition to existing ones. In fine-grained powdered β-As4S4 pellets, the positron trapping sites with characteristic free volumes close to bi- and tri-atomic vacancies were evidently dominated. These defects were supposed to originate from grain boundary regions and interfacial free volumes near aggregated β-As4S4 crystallites. Thus, the cumulative production of different positron traps with lifetimes close to defect-related lifetimes in realgar α-As4S4 polymorph was detected in fine-grained milled samples.

  2. Symposium on atomic spectroscopy

    International Nuclear Information System (INIS)

    Topics covered by the conference include: fast beam spectroscopy; astrophysical and other spectra; highly ionized spectroscopy; complex spectra; rydberg levels; fine structure, hyperfine structure and isotope shift; lineshapes; lifetimes, oscillator strengths and Einstein coefficients; and spectroscopy with lasers. Abstracts of the conference papers are presented

  3. Symposium on atomic spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    1979-01-01

    Topics covered by the conference include: fast beam spectroscopy; astrophysical and other spectra; highly ionized spectroscopy; complex spectra; rydberg levels; fine structure, hyperfine structure and isotope shift; lineshapes; lifetimes, oscillator strengths and Einstein coefficients; and spectroscopy with lasers. Abstracts of the conference papers are presented. (GHT)

  4. Study of the ortho-positron annihilation process in zeolite Y; Estudio del proceso de aniquilacion de ortopositronio en zeolita Y

    Energy Technology Data Exchange (ETDEWEB)

    Alvarado D, M. E.

    2010-07-01

    For several years a great interest has existed for the study of the natural and synthetic zeolites due to its properties. The porosity, one of their main characteristics allows that these materials are used as molecular sieves, catalysts, gases drying, etc. In order to investigating the porosity and other zeolite properties one carries out the study of the process of positron annihilation lifetime spectroscopy (Pals). This is a technique that provides information about the size and the pores form since is highly sensitive to the free volume and the superficial area of those porous materials as the zeolites. The study began with the elaboration of zeolite Y tablets in a hydraulic press where different pressures (from 0 to 1.26 GPa) and masses (70, 80 and 100 mg) were proven to obtain the estimate porosity of each tablet. A graph was elaborated and the effect of the mass and pressure with regard to the zeolite porosity was analyzed. Later on, the powder and tablets of 70 mg were characterized by means of X-ray diffraction (the glass size, interplanar distance, length and the volume of the unitary cell); scanning electron microscopy (the particles size and morphology); thermo gravimetric analysis (dehydration temperature and the stability up to 700 C) and the Brunauer Emmett Teller method (specific area). After the zeolite Y tablets characterization was carried out the positron annihilation process by means of Pals where its free volume of zeolite Y was analyzed, which includes to the structural cavities and the interparticle volume. The powdered zeolite was analyzed to different experimental conditions (preparation of the sample and the Pals equipment) to obtain the optimal conditions (a window with a time of 400 ns and a enlarged energy window) of analysis. On the other hand, the tablets were analyzed under optimal conditions to obtain the four components of time and intensity ({tau}, {Iota}), result of the different ways of positrons annihilation in the zeolite

  5. Corrosion Preventive Compounds Lifetime Testing

    Science.gov (United States)

    Hale, Stephanie M.; Kammerer, Catherine C.; Copp, Tracy L.

    2007-01-01

    Lifetime Testing of Corrosion Preventive Compounds (CPCs) was performed to quantify performance in the various environments to which the Space Shuttle Orbiter is exposed during a flight cycle. Three CPCs are approved for use on the Orbiter: RD Calcium Grease, Dinitrol AV-30, and Braycote 601 EF. These CPCs have been rigorously tested to prove that they mitigate corrosion in typical environments, but little information is available on how they perform in the unique combination of the coastal environment at the launch pad, the vacuum of low-earth orbit, and the extreme heat of reentry. Currently, there is no lifetime or reapplication schedule established for these compounds that is based on this combination of environmental conditions. Aluminum 2024 coupons were coated with the three CPCs and exposed to conditions that simulate the environments to which the Orbiter is exposed. Uncoated Aluminum 2024 coupons were exposed to the environmental conditions as a control. Visual inspection and Electro- Impedance Spectroscopy (EIS) were performed on the samples in order to determine the effectiveness of the CPCs. The samples were processed through five mission life cycles or until the visual inspection revealed the initiation of corrosion and EIS indicated severe degradation of the coating.

  6. Determination of the 3\\gamma fraction from positron annihilation in mesoporous materials for symmetry violation experiment with J-PET scanner

    CERN Document Server

    Jasińska, B; Wiertel, M; Zaleski, R; Alfs, D; Bednarski, T; Białas, P; Czerwiński, E; Dulski, K; Gajos, A; Głowacz, B; Kamińska, D; Kapłon, Ł; Korcyl, G; Kowalski, P; Kozik, T; Krzemień, W; Kubicz, E; Mohammed, M; Niedźwiecki, Sz; Pałka, M; Raczyński, L; Rudy, Z; Rundel, O; Sharma, N G; Silarski, M; Słomski, A; Strzelecki, A; Wieczorek, A; Wiślicki, W; Zgardzińska, B; Zieliński, M; Moskal, P

    2016-01-01

    Various mesoporous materials were investigated to choose the best material for experiments requiring high yield of long-lived positronium. We found that the fraction of 3\\gamma annihilation determined using \\gamma-ray energy spectra and positron annihilation lifetime spectra (PAL) changed from 20% to 25%. The 3gamma fraction and o-Ps formation probability in the polymer XAD-4 is found to be the largest. Elemental analysis performed using scanning electron microscop (SEM) equipped with energy-dispersive X-ray spectroscop EDS show high purity of the investigated materials.

  7. Search for Neutrinos from Annihilating Dark Matter in the Direction of the Galactic Center with the 40-String IceCube Neutrino Observatory

    CERN Document Server

    Abbasi, R; Ackermann, M; Adams, J; Aguilar, J A; Ahlers, M; Altmann, D; Andeen, K; Auffenberg, J; Bai, X; Baker, M; Barwick, S W; Baum, V; Bay, R; Beattie, K; Beatty, J J; Bechet, S; Tjus, J Becker; Becker, K -H; Bell, M; Benabderrahmane, M L; BenZvi, S; Berdermann, J; Berghaus, P; Berley, D; Bernardini, E; Bertrand, D; Besson, D Z; Bindig, D; Bissok, M; Blaufuss, E; Blumenthal, J; Boersma, D J; Bohm, C; Bose, D; Böser, S; Botner, O; Brayeur, L; Brown, A M; Bruijn, R; Brunner, J; Buitink, S; Carson, M; Casey, J; Casier, M; Chirkin, D; Christy, B; Clevermann, F; Cohen, S; Cowen, D F; Silva, A H Cruz; Danninger, M; Daughhetee, J; Davis, J C; De Clercq, C; Descamps, F; Desiati, P; Uiterweerd, G de Vries; DeYoung, T; Díaz-Vélez, J C; Dreyer, J; Dumm, J P; Dunkman, M; Eagan, R; Eisch, J; Ellsworth, R W; Engdegård, O; Euler, S; Evenson, P A; Fadiran, O; Fazely, A R; Fedynitch, A; Feintzeig, J; Feusels, T; Filimonov, K; Finley, C; Fischer-Wasels, T; Flis, S; Franckowiak, A; Franke, R; Frantzen, K; Fuchs, T; Gaisser, T K; Gallagher, J; Gerhardt, L; Gladstone, L; Glüsenkamp, T; Goldschmidt, A; Goodman, J A; Góra, D; Grant, D; Groß, A; Grullon, S; Gurtner, M; Ha, C; Ismail, A Haj; Hallgren, A; Halzen, F; Hanson, K; Heereman, D; Heimann, P; Heinen, D; Helbing, K; Hellauer, R; Hickford, S; Hill, G C; Hoffman, K D; Hoffmann, R; Homeier, A; Hoshina, K; Hülß, J -P; Huelsnitz, W; Hulth, P O; Hultqvist, K; Hussain, S; Ishihara, A; Jacobi, E; Jacobsen, J; Japaridze, G S; Jlelati, O; Kappes, A; Karg, T; Karle, A; Kiryluk, J; Kislat, F; Kläs, J; Klein, S R; Köhne, J -H; Kohnen, G; Kolanoski, H; Köpke, L; Kopper, C; Kopper, S; Koskinen, D J; Kowalski, M; Krasberg, M; Kroll, G; Kunnen, J; Kurahashi, N; Kuwabara, T; Labare, M; Laihem, K; Landsman, H; Larson, M J; Lauer, R; Lesiak-Bzdak, M; Lünemann, J; Madsen, J; Maruyama, R; Mase, K; Matis, H S; McNally, F; Meagher, K; Merck, M; Mészáros, P; Meures, T; Miarecki, S; Middell, E; Milke, N; Miller, J; Mohrmann, L; Montaruli, T; Morse, R; Movit, S M; Nahnhauer, R; Naumann, U; Nowicki, S C; Nygren, D R; Obertacke, A; Odrowski, S; Olivas, A; Olivo, M; O'Murchadha, A; Panknin, S; Paul, L; Pepper, J A; Heros, C Pérez de los; Pieloth, D; Pirk, N; Posselt, J; Price, P B; Przybylski, G T; Rädel, L; Rawlins, K; Redl, P; Resconi, E; Rhode, W; Ribordy, M; Richman, M; Riedel, B; Rodrigues, J P; Rothmaier, F; Rott, C; Ruhe, T; Ruzybayev, B; Ryckbosch, D; Saba, S M; Salameh, T; Sander, H -G; Santander, M; Sarkar, S; Schatto, K; Scheel, M; Scheriau, F; Schmidt, T; Schmitz, M; Schoenen, S; Schöneberg, S; Schönherr, L; Schönwald, A; Schukraft, A; Schulte, L; Schulz, O; Seckel, D; Seo, S H; Sestayo, Y; Seunarine, S; Smith, M W E; Soiron, M; Soldin, D; Spiczak, G M; Spiering, C; Stamatikos, M; Stanev, T; Stasik, A; Stezelberger, T; Stokstad, R G; Stößl, A; Strahler, E A; Ström, R; Sullivan, G W; Taavola, H; Taboada, I; Tamburro, A; Ter-Antonyan, S; Tilav, S; Toale, P A; Toscano, S; Usner, M; van der Drift, D; van Eijndhoven, N; Van Overloop, A; van Santen, J; Vehring, M; Voge, M; Walck, C; Waldenmaier, T; Wallraff, M; Walter, M; Wasserman, R; Weaver, Ch; Wendt, C; Westerhoff, S; Whitehorn, N; Wiebe, K; Wiebusch, C H; Williams, D R; Wissing, H; Wolf, M; Wood, T R; Woschnagg, K; Xu, C; Xu, D L; Xu, X W; Yanez, J P; Yodh, G; Yoshida, S; Zarzhitsky, P; Ziemann, J; Zilles, A; Zoll, M

    2012-01-01

    A search for muon neutrinos from dark matter annihilations in the Galactic Center region has been performed with the 40-string configuration of the IceCube Neutrino Observatory using data collected in 367 days of live-time starting in April 2008. The observed fluxes were consistent with the atmospheric background expectations. Upper limits on the self-annihilation cross-section are obtained for dark matter particle masses ranging from 100 GeV to 10 TeV. In the case of decaying dark matter, lower limits on the lifetime have been determined for masses between 200 GeV and 20 TeV.

  8. Positron annihilation study of microvoids in centrifugally atomized 304 stainless steel

    Science.gov (United States)

    Kim, J. Y.; Byrne, J. G.

    1993-03-01

    Positron trapping in microvoids was studied by positron-lifetime and positron Doppler line-shape measurements of centrifugally atomized 304 stainless-steel powder, which was hot-isostatically-press consolidated. This material contained a concentration of several times 1023/m3 of 1.5-nm-diam microvoids. Positron annihilation was strongly influenced by the microvoids in that a very long lifetime component τ3 of about 600 ps resulted. The intensity of the τ3 component decreased with decreasing number density of 1.5 nm microvoids. The Doppler peak shape was found to be much more strongly influenced by microvoids than by any other defects such as precipitates or grain boundaries. In particular microvoids produced significant narrowing of the Doppler distribution shape.

  9. Positron lifetime technique with applications in materials science

    International Nuclear Information System (INIS)

    This thesis deals with the positron lifetime technique as a method to measure extremely low concentrations of extremely small cavities in materials. The method is based upon the fact that the positron lieftime decreases as the electron density increases and upon the fact that a positron preferably annihilates in cavity-like defects in lattices. The theory of positron behaviour in materials and technical aspects of measuring positron liefetimes are described in ch.'s 2 and 3 respectively. Three methods for increasing the time resolution are discussed and some positron sources are described (ch.4). Some applications of the positron lifetime technique and experimental results are shown in chapter 5. 125 refs.; 61 figs.; 18 tabs

  10. Dark matter annihilation near a naked singularity

    CERN Document Server

    Patil, Mandar

    2011-01-01

    We investigate here the dark matter annihilation near a Kerr naked singularity. We show that when dark matter particles collide and annihilate in vicinity of the singularity, the escape fraction to infinity of particles produced is much larger, at least 10^2 - 10^3 times the corresponding black hole values. As high energy collisions are generically possible near a naked singularity, this provides an excellent environment for efficient conversion of dark matter into ordinary standard model particles. If the center of galaxy harbored such a naked singularity, it follows that the observed emergent flux of particles with energy comparable to mass of the dark matter particles is much larger compared to the blackhole case, thus providing an intriguing observational test on the nature of the galactic center

  11. Vector dark matter annihilation with internal bremsstrahlung

    CERN Document Server

    Bambhaniya, Gulab; Marfatia, Danny; Nayak, Alekha C; Tomar, Gaurav

    2016-01-01

    We consider scenarios in which the annihilation of self-conjugate spin-1 dark matter to a Standard Model fermion-antifermion final state is chirality suppressed, but where this suppression can be lifted by the emission of an additional photon via internal bremsstrahlung. We find that this scenario can only arise if the initial dark matter state is polarized, which can occur in the context of self-interacting dark matter. In particular, this is possible if the dark matter pair forms a bound state that decays to its ground state before the constituents annihilate. We show that the shape of the resulting photon spectrum is the same as for self-conjugate spin-0 and spin-1/2 dark matter, but the normalization is less heavily suppressed in the limit of heavy mediators.

  12. Shocking Signals of Dark Matter Annihilation

    CERN Document Server

    Davis, Jonathan H; Boehm, Celine; Kotera, Kumiko; Norman, Colin

    2015-01-01

    We examine whether charged particles injected by self-annihilating Dark Matter into regions undergoing Diffuse Shock Acceleration (DSA) can be accelerated to high energies. We consider three astrophysical sites where shock acceleration is supposed to occur, namely the Galactic Centre, galaxy clusters and Active Galactic Nuclei (AGN). For the Milky Way, we find that the acceleration of cosmic rays injected by dark matter could lead to a bump in the cosmic ray spectrum provided that the product of the efficiency of the acceleration mechanism and the concentration of DM particles is high enough. Among the various acceleration sources that we consider (namely supernova remnants (SNRs), Fermi bubbles and AGN jets), we find that the Fermi bubbles are a potentially more efficient accelerator than SNRs. However both could in principle accelerate electrons and protons injected by dark matter to very high energies. At the extragalactic level, the acceleration of dark matter annihilation products could be responsible fo...

  13. Baryon production in e+e- annihilation

    International Nuclear Information System (INIS)

    The phenomenology of baryon production in high energy e+e-annihilation is described. Much can be understood in terms of mass effects. Comparisons with the rates for different flavours and spins, with momentum and transverse momentum spectra and with particle correlations are used to confront models. Diquark models give good descriptions, except for the on/off Υ(1s) rates. Areas for experimental and theoretical development are indicated. (author)

  14. Cosmological and astrophysical signatures of dark matter annihilations into pseudo-Goldstone bosons

    International Nuclear Information System (INIS)

    We investigate a model where the dark matter particle is a chiral fermion field charged under a global U(1) symmetry which is assumed to be spontaneously broken, leading to a pseudo-Goldstone boson (PGB). We argue that the dark matter annihilation into PGBs determine the dark matter relic abundance. Besides, we also note that experimental searches for PGBs allow either for a very long lived PGB, with a lifetime much longer than the age of the Universe, or a relatively short lived PGB, with a lifetime shorter than one minute. Hence, two different scenarios arise, producing very different signatures. In the long lived PGB scenario, the PGB might contribute significantly to the radiation energy density of the Universe. On the other hand, in the short lived PGB scenario, and since the decay length is shorter than one parsec, the s-wave annihilation into a PGB and a CP even dark scalar in the Galactic center might lead to an intense box feature in the gamma-ray energy spectrum, provided the PGB decay branching ratio into two photons is sizable. We also analyze the constraints on these two scenarios from thermal production, the Higgs invisible decay width and direct dark matter searches

  15. Beam Diagnostics for Measurements of Antiproton Annihilation Cross Sections at Ultra-low Energy

    Directory of Open Access Journals (Sweden)

    Todoroki K.

    2014-03-01

    Full Text Available The ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons collaboration of CERN is currently attempting to measure the antiproton-nucleus in-flight annihilation cross sections on thin target foils of C, Pd, and Pt at 130 keV of kinetic energy. The low-energy antiprotons were supplied by the Antiproton Decelerator (AD and a radio-frequency quadrupole decelerator. For this measurement, a beam profile monitor based on secondary electron emission was developed. Data from this monitor was used to ensure that antiprotons were precisely tuned to the position of an 80-mm-diameter experimental target, by measuring the spatial profile of 200-ns-long beam pulses containing 105 − 106 antiprotons with an active area of 40 mm × 40 mm and a spatial resolution of 4 mm. By using this monitor, we succeeded in finely tuning antiproton beams on the target, and observed some annihilation events originating from the target.

  16. Positron lifetime study of native vacancy-like defects in chalcogenide glasses

    Energy Technology Data Exchange (ETDEWEB)

    Filipecki, J.; Shpotyuk, O.I. E-mail: shpotyuk@novas.lviv.ua; Kozdras, A.; Kovalskiy, A.P

    2003-11-01

    Modified model for positron annihilation in vitreous chalcogenide semiconductors is developed to explain a number of previously obtained results on positron lifetime measurements in glassy As-Ge-S of stoichiometric As{sub 2}S{sub 3}-GeS{sub 2} and non-stoichiometric As{sub 2}S{sub 3}-Ge{sub 2}S{sub 3} cut-sections.

  17. Application of the Positron Annihilation Technique to the study of vapors absorption process in polyethylene (LDPE) and in imide polymer (6FDA-TMPD PI)

    International Nuclear Information System (INIS)

    It is well recognized that positron annihilation lifetime (PAL) spectra in polymers have a long-lived component that can be ascribed to ortho-positronium (o-Ps). The lifetime, τ3, is considered to be a measure of the size of the micro-vacancies in which o-Ps is trapped and is annihilated through pick-off annihilation with the rate which depends on the size of the vacancy. Positron lifetime measurements were performed for two different kinds of polymers (low density polyethylene and a polyimide (6FDA-TMPD) during sorption of various vapors (hexane, cyclohexane, benzene, acrylic acid, methyl acrylate, water and oxygen). The vapor sorption affected the long-lived component (ortho-positronium component) in a systematic way regardless of the kind of the vapor molecules, i.e. for the polyethylene both the lifetime and the intensity of the long-lived component were enhanced, while for the polyimide they were decreased significantly. These different effects are interpreted in terms of different states of sorbed molecules in rubbery (the polyethylene) and in glassy (the polyimide) polymers. (Author)

  18. Low mass stellar evolution with WIMP capture and annihilation

    CERN Document Server

    Scott, Pat; Fairbairn, Malcolm

    2007-01-01

    Recent work has indicated that WIMP annihilation in stellar cores has the potential to contribute significantly to a star's total energy production. We report on progress in simulating the effects of WIMP capture and annihilation upon stellar structure and evolution near supermassive black holes, using the new DarkStars code. Preliminary results indicate that low-mass stars are the most influenced by WIMP annihilation, which could have consequences for upcoming observational programs.

  19. Positronium formation in NaY-zeolites studied by lifetime, positron beam Doppler broadening and 3-gamma detection techniques

    CERN Document Server

    Schut, H; Kolar, Z I; Veen, A V; Clet, G

    2000-01-01

    Results of positron annihilation measurements on NaY pressed powders and deposited thin films using slow positron beam and conventional fast positron techniques are presented. In lifetime experiments using an external sup sup 2 sup sup 2 Na source an averaged long lifetime of 1.8 ns with a sum intensity of 27% was observed in pressed powders in the presence of air at room temperature (RT). In literature this lifetime is ascribed to positrons annihilating in water filled alpha or beta cages Habrowska, A.M., Popiel, E.S., 1987. Positron annihilation in zeolite 13X. J. Appl. Phys. 62, 2419. By means of isotopic exchange some of the Na was replaced by sup sup 2 sup sup 2 Na. These powders showed a long lifetime component of 7-8 ns with an intensity increasing from 1 to 12% when heated under normal atmosphere from RT to 200 deg. C. No significant increase of the shorter (1.5 ns) lifetime was observed, while its intensity dropped from 13.4 to 6.6%. Both effects are ascribed to the loss of water from alpha cages onl...

  20. Positron annihilation and XRD studies on deformed Al-alloys with low concentrations of Mg

    Energy Technology Data Exchange (ETDEWEB)

    Badawi, E.; Abdel-Rahman, M.A.; Mahmoud, S.A. [Physics Dept., El-Minia Univ. (Egypt); Ramadan, A.A. [Physics Dept., Helwan Univ. (Egypt)

    2001-07-01

    The behaviour of positron in grain boundaries, is characterized by their bulk diffusibility D, their bulk (free) lifetime {tau}{sub f}, and their trapped lifetime {tau}{sub t} ({tau}{sub t} > {tau}{sub f}). Al-Mg{sub x} samples(x=0-1.4 at%) have been homogenized at 573 K for 12 hours. The obtained mean lifetime results showed a good fitting with Sigmodel giving {tau}{sub t} = 180.664 ps and {tau}{sub f} = 163.9 ps. The mean lifetime was found to vary exponentially with degree of deformation. XRD study showed that preferred orientation occurred at degree of deformation > 32%, whereas the peak intensity then increases with sample deformation. Recrystallization is also followed by XRD. Peak intensities decrease with increasing annealing time which is attributed to recrystallization, but it does not completely reverse to the origin condition. For all cases, no peaks of Mg were revealed indicating the positron annihilation as a sensitive technique for detecting low concentrations in alloys. (orig.)

  1. POSITRON ANNIHILATION AND CONDUCTIVITY MEASUREMENTS ON POLYANILINE

    Institute of Scientific and Technical Information of China (English)

    彭治林; 刘皓; 等

    1994-01-01

    The positron lifetime spectra and electrical conductivities have been measured for polyaniline as a function of protonation level ([H+] from 10-7-100.8 mol/L)。We observed that (1) the short lifetime τ1,which was related to electron density in bulk,decreased with the protonation level;(2) the intermediate lifetime τ2≈360ps,almost remaining constant,whereas its intensity I2 increased with increasing protonation level which was related to the conductivity of meaterial.These results are discussed in terms of conducting island model.

  2. Dark Matter Annihilation at the Galactic Center

    Energy Technology Data Exchange (ETDEWEB)

    Linden, Timothy Ryan [Univ. of California, Santa Cruz, CA (United States)

    2013-06-01

    Observations by the WMAP and PLANCK satellites have provided extraordinarily accurate observations on the densities of baryonic matter, dark matter, and dark energy in the universe. These observations indicate that our universe is composed of approximately ve times as much dark matter as baryonic matter. However, e orts to detect a particle responsible for the energy density of dark matter have been unsuccessful. Theoretical models have indicated that a leading candidate for the dark matter is the lightest supersymmetric particle, which may be stable due to a conserved R-parity. This dark matter particle would still be capable of interacting with baryons via weak-force interactions in the early universe, a process which was found to naturally explain the observed relic abundance of dark matter today. These residual annihilations can persist, albeit at a much lower rate, in the present universe, providing a detectable signal from dark matter annihilation events which occur throughout the universe. Simulations calculating the distribution of dark matter in our galaxy almost universally predict the galactic center of the Milky Way Galaxy (GC) to provide the brightest signal from dark matter annihilation due to its relative proximity and large simulated dark matter density. Recent advances in telescope technology have allowed for the rst multiwavelength analysis of the GC, with suitable e ective exposure, angular resolution, and energy resolution in order to detect dark matter particles with properties similar to those predicted by the WIMP miracle. In this work, I describe ongoing e orts which have successfully detected an excess in -ray emission from the region immediately surrounding the GC, which is di cult to describe in terms of standard di use emission predicted in the GC region. While the jury is still out on any dark matter interpretation of this excess, I describe several related observations which may indicate a dark matter origin. Finally, I discuss the

  3. Positron annihilation study of vacancy-type defects in Al single crystal foils with the tweed structures across the surface

    Energy Technology Data Exchange (ETDEWEB)

    Kuznetsov, Pavel, E-mail: kpv@ispms.tsc.ru [National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Cizek, Jacub, E-mail: jcizek@mbox.troja.mff.cuni.cz; Hruska, Petr [Charles University in Prague, Praha, CZ-18000 Czech Republic (Czech Republic); Anwad, Wolfgang [Institut für Strahlenphysik, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, D-01314 Germany (Germany); Bordulev, Yuri; Lider, Andrei; Laptev, Roman [National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Mironov, Yuri [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation)

    2015-10-27

    The vacancy-type defects in the aluminum single crystal foils after a series of the cyclic tensions were studied using positron annihilation. Two components were identified in the positron lifetime spectra associated with the annihilation of free positrons and positrons trapped by dislocations. With increasing number of cycles the dislocation density firstly increases and reaches a maximum value at N = 10 000 cycles but then it gradually decreases and at N = 70 000 cycles falls down to the level typical for the virgin samples. The direct evidence on the formation of a two-phase system “defective near-surface layer/base Al crystal” in aluminum foils at cyclic tension was obtained using a positron beam with the variable energy.

  4. Particle-antiparticle asymmetries from annihilations

    CERN Document Server

    Baldes, Iason; Petraki, Kalliopi; Volkas, Raymond R

    2014-01-01

    An extensively studied mechanism to create particle-antiparticle asymmetries is the out-of-equilibrium and CP violating decay of a heavy particle. Here we instead examine how asymmetries can arise purely from 2 2 annihilations rather than from the usual 1 2 decays and inverse decays. We review the general conditions on the reaction rates that arise from S-matrix unitarity and CPT invariance, and show how these are implemented in the context of a simple toy model. We formulate the Boltzmann equations for this model, and present an example solution.

  5. Apparatus for photon activation positron annihilation analysis

    Science.gov (United States)

    Akers, Douglas W.

    2007-06-12

    Non-destructive testing apparatus according to one embodiment of the invention comprises a photon source. The photon source produces photons having predetermined energies and directs the photons toward a specimen being tested. The photons from the photon source result in the creation of positrons within the specimen being tested. A detector positioned adjacent the specimen being tested detects gamma rays produced by annihilation of positrons with electrons. A data processing system operatively associated with the detector produces output data indicative of a lattice characteristic of the specimen being tested.

  6. Vector dark matter annihilation with internal bremsstrahlung

    OpenAIRE

    Bambhaniya, Gulab; Kumar, Jason; Marfatia, Danny; Nayak, Alekha C.; Tomar, Gaurav

    2016-01-01

    We consider scenarios in which the annihilation of self-conjugate spin-1 dark matter to a Standard Model fermion-antifermion final state is chirality suppressed, but where this suppression can be lifted by the emission of an additional photon via internal bremsstrahlung. We find that this scenario can only arise if the initial dark matter state is polarized, which can occur in the context of self-interacting dark matter. In particular, this is possible if the dark matter pair forms a bound st...

  7. The Sprint to Lifetime Sports

    Science.gov (United States)

    Ernst, Leonard

    1973-01-01

    Describes the trend in high school physical education programs toward lifetime sports, defined by the author as physical activities that will serve the interests of students for a lifetime. Included are a special report on program costs and a model of a performance-based lifetime sports program. (Author/DN)

  8. Lifetimes, branching ratios, and transition probabilities in Co ii

    OpenAIRE

    Salih, S.; Lawler, J. E.; Whaling, W.

    1985-01-01

    The radiative lifetime of 14 levels in the z^5F, z^5D, and z^5G terms of Co ii have been measured with use of time-resolved laser fluorescence spectroscopy with a Co+-ion beam. Our lifetime values are shorter by 15–50 % than earlier results from beam-foil time-of-flight measurements. The lifetimes were converted to 41 individual transition probabilities with use of branching ratios measured on spectra recorded with the 1-m Fourier-transform spectrometer at the Kitt Peak National Observatory. ...

  9. Impact of dark matter decays and annihilations on structure formation

    NARCIS (Netherlands)

    Mapelli, M.; Ripamonti, E.

    2007-01-01

    Abstract: We derived the evolution of the energy deposition in the intergalactic medium (IGM) by different decaying (or annihilating) dark matter (DM) candidates. Heavy annihilating DM particles (with mass larger than a few GeV) have no influence on reionization and heating, even if we assume that a

  10. CMB constraint on dark matter annihilation after Planck 2015

    Directory of Open Access Journals (Sweden)

    Masahiro Kawasaki

    2016-05-01

    Full Text Available We update the constraint on the dark matter annihilation cross section by using the recent measurements of the CMB anisotropy by the Planck satellite. We fully calculate the cascade of dark matter annihilation products and their effects on ionization, heating and excitation of the hydrogen, hence do not rely on any assumption on the energy fractions that cause these effects.

  11. Nucleon-antinucleon annihilation in chiral soliton model

    International Nuclear Information System (INIS)

    We investigate annihilation process of nucleons in the chiral soliton model by the path integral method. A soliton-antisoliton pair is shown to decay into mesons at range of about 1fm, defined by the S bar S potential. Contribution of the annihilation channel to the elastic scattering is discussed

  12. Cohomology of projective schemes: From annihilators to vanishing

    OpenAIRE

    Chardin, Marc

    2002-01-01

    We provide bounds on the Castelnuovo-Mumford regularity in terms of ``defining equations'' by using elements that annihilates some cohomology modules, inspired by works of Miyazaki, Nagel, Schenzel and Vogel. The elements in these annihilators are provided either by liaison or by tight closure theories. Our results hold in any characteristic.

  13. Nucleon-antinucleon annihilation in chiral soliton model

    International Nuclear Information System (INIS)

    We investigate annihilation process of nucleons in chiral soliton model by path integral method. Soliton-antisoliton pair is shown to decay into pions at range of order of about 1 fm, defined by SS-bar potential. Contribution of annihilation channel into elastic scattering is discussed. (author). 14 refs, 1 fig

  14. CMB constraint on dark matter annihilation after Planck 2015

    OpenAIRE

    Masahiro Kawasaki; Kazunori Nakayama; Toyokazu Sekiguchi

    2016-01-01

    We update the constraint on the dark matter annihilation cross section by using the recent measurements of the CMB anisotropy by the Planck satellite. We fully calculate the cascade of dark matter annihilation products and their effects on ionization, heating and excitation of the hydrogen, hence do not rely on any assumption on the energy fractions that cause these effects.

  15. Neutrino signals from electroweak bremsstrahlung in solar WIMP annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Bell, Nicole F.; Brennan, Amelia J.; Jacques, Thomas D., E-mail: n.bell@unimelb.edu.au, E-mail: a.brennan@pgrad.unimelb.edu.au, E-mail: thomas.jacques@asu.edu [ARC Centre of Excellence for Particle Physics at the Terascale, School of Physics, The University of Melbourne, Victoria 3010 (Australia)

    2012-10-01

    Bremsstrahlung of W and Z gauge bosons, or photons, can be an important dark matter annihilation channel. In many popular models in which the annihilation to a pair of light fermions is helicity suppressed, these bremsstrahlung processes can lift the suppression and thus become the dominant annihilation channels. The resulting dark matter annihilation products contain a large, energetic, neutrino component. We consider solar WIMP annihilation in the case where electroweak bremsstrahlung dominates, and calculate the resulting neutrino spectra. The flux consists of primary neutrinos produced in processes such as χχ→ν-bar νZ and χχ→ν-bar lW, and secondary neutrinos produced via the decays of gauge bosons and charged leptons. After dealing with the neutrino propagation and flavour evolution in the Sun, we consider the prospects for detection in neutrino experiments on Earth. We compare our signal with that for annihilation to W{sup +}W{sup −}, and show that, for a given annihilation rate, the bremsstrahlung annihilation channel produces a larger signal by a factor of a few.

  16. Searching for Dark Matter Annihilation in M87

    CERN Document Server

    Saxena, Sheetal; Rüger, Michael; Summa, Alexander; Mannheim, Karl

    2011-01-01

    Clusters of galaxies, such as the Virgo cluster, host enormous quantities of dark matter, making them prime targets for efforts in indirect dark matter detection via potential radiative signatures from annihilation of dark matter particles and subsequent radiative losses of annihilation products. However, a careful study of ubiquitous astrophysical backgrounds is mandatory to single out potential evidence for dark matter annihilation. Here, we construct a multiwavelength spectral energy distribution for the central radio galaxy in the Virgo cluster, M87, using a state-of-the-art numerical Synchrotron Self Compton approach. Fitting recent Chandra, Fermi-LAT and Cherenkov observations, we probe different dark matter annihilation scenarios including a full treatment of the inverse Compton losses from electrons and positrons produced in the annihilation. It is shown that such a template can substantially improve upon existing dark matter detection limits.

  17. Lifetimes and HQE

    CERN Document Server

    Lenz, Alexander

    2014-01-01

    Kolya Uraltsev was one of the inventors of the Heavy Quark Expansion (HQE), that describes inclusive weak decays of hadrons containing heavy quarks and in particular lifetimes. Besides giving a pedagogic introduction to the subject, we review the development and the current status of the HQE, which just recently passed several non-trivial experimental tests with an unprecedented precision. In view of many new experimental results for lifetimes of heavy hadrons, we also update several theory predictions: $\\tau (B^+) / \\tau (B_d) = 1.04^{+0.05}_{-0.01} \\pm 0.02 \\pm 0.01$, $\\tau (B_s) / \\tau (B_d) = 1.001 \\pm 0.002$, $\\tau (\\Lambda_b)/ \\tau (B_d) = 0.935 \\pm 0.054$ and $\\bar {\\tau} (\\Xi_b^0) / \\bar{\\tau} (\\Xi_b^+) = 0.95 \\pm 0.06$. The theoretical precision is currently strongly limited by the unknown size of the non-perturbative matrix elements of four-quark operators, which could be determined with lattice simulations.

  18. Positron states and annihilation in nanometric semiconducting superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Sekkal, Nadir, E-mail: nsekkal@yahoo.f [Departement de Physique-Chimie, Ecole Normale Superieure de l' Enseignement Technologique, BP 1523, El M' Naouer, 31000 Oran (Algeria); Arutyunov, N.Yu. [Institute of Electronics, UAS, 700170 Tashkent (Uzbekistan)

    2009-12-15

    The electron and positron states in the band structure of GaAs-AlAs, (GaAs){sub m}((AlAs){sub 1-x}(vacancy/pore){sub x}){sub n} and (GaAs){sub m}((AlAs){sub 1-x}Ge{sub x}){sub n} superlattices have been analyzed on the basis of empirical pseudopotential method of calculations. When possible, the validity of results has been checked by comparing them with the data obtained for relevant constituents of the superlattices with the help of the angular correlation of annihilation radiation (ACAR) spectroscopy. The most important finding is that positron is capable of being selectively confined in the superlattices even when they are defect-free. In the presence of defects of a vacancy-type, the regime of confinement may be changed to the one of trapping of positron. Being 'fingerprints' of certain types of defects, the ACAR spectra may be used for non-destructive characterization of superlattices. The question of sensitivity of the positron particle microprobe for studying electron structure of superlattices is discussed.

  19. Studies of the subsurface zone created in aluminium and its alloys by means of positron annihilation and complementary methods

    International Nuclear Information System (INIS)

    There are presented the results of the studies of the subsurface zone created in aluminium and its alloys during sliding or other surface modification treatments. The application of the positron annihilation techniques due to their high sensitivity to crystal lattice defects enabled to determine defects profiles in the subsurface zone. The positron annihilation studies were correlated with other conventional measurements applied in tribology, i.e. microhardness measurements, scanning electron microscopy, X-ray diffraction and in a special case stress distribution calculated theoretically. It was shown that the positron annihilation spectroscopy is a useful tool for profiling of the subsurface zone created during sliding even for light metals their alloys and composites. The total range of the subsurface zone detected by the positron annihilation extends from 50 μm to 450 μm depending on the material studied and surface modification treatment. Additionally, the type of the main defects can be determined. The studies of the pure aluminium samples after dry sliding enabled to find the defect concentration of vacancy type in the depth less then 1 μm and to correlate its value with the size of crystallites. It supports the conclusion on recovery processes taking place in this layer. There was made the attempt to apply the Doppler broadening coincidence spectroscopy to the studies of aluminium alloy and composite. In view of the interdisciplinary character the present thesis enclose also the review of the basic issues of tribology, measurement methods applied to the subsurface zone studies and positron annihilation experimental techniques. (author)

  20. Finite quasiparticle lifetime in disordered superconductors

    Science.gov (United States)

    Žemlička, M.; Neilinger, P.; Trgala, M.; Rehák, M.; Manca, D.; Grajcar, M.; Szabó, P.; Samuely, P.; Gaži, Š.; Hübner, U.; Vinokur, V. M.; Il'ichev, E.

    2015-12-01

    We investigate the complex conductivity of a highly disordered MoC superconducting film with kFl ≈1 , where kF is the Fermi wave number and l is the mean free path, derived from experimental transmission characteristics of coplanar waveguide resonators in a wide temperature range below the superconducting transition temperature Tc. We find that the original Mattis-Bardeen model with a finite quasiparticle lifetime, τ , offers a perfect description of the experimentally observed complex conductivity. We show that τ is appreciably reduced by scattering effects. Characteristics of the scattering centers are independently found by scanning tunneling spectroscopy and agree with those determined from the complex conductivity.

  1. D-brane scattering and annihilation

    CERN Document Server

    D'Amico, Guido; Kleban, Matthew; Schillo, Marjorie

    2014-01-01

    We study the dynamics of parallel brane-brane and brane-antibrane scattering in string theory in flat spacetime, focusing on the pair production of open strings that stretch between the branes. We are particularly interested in the case of scattering at small impact parameter $b < l_s$, where there is a tachyon in the spectrum when a brane and an antibrane approach within a string length. Our conclusion is that despite the tachyon, branes and antibranes can pass through each other with only a very small probability of annihilating, so long as $g_s$ is small and the relative velocity $v$ is neither too small nor too close to 1. Our analysis is relevant also to the case of charged open string production in world-volume electric fields, and we make use of this T-dual scenario in our analysis. We briefly discuss the application of our results to a stringy model of inflation involving moving branes.

  2. Holographic Vortex Pair Annihilation in Superfluid Turbulence

    CERN Document Server

    Du, Yiqiang; Tian, Yu; Zhang, Hongbao

    2014-01-01

    We make a first principles investigation of the dynamical evolution of vortex number in a two-dimensional (2D) turbulent superfluid by holography through numerically solving its highly non-trivial gravity dual. With the randomly placed vortices and antivortices prepared as initial states, we find that the temporal evolution of the vortex number can be well fit statistically by two-body decay due to the vortex pair annihilation featured relaxation process remarkably from a very early time on. In particular, subtracted by the universal offset, the power law fit indicates that our holographic turbulent superfluid exhibits an apparently different decay pattern from the superfluid recently experimented in highly oblate Bose-Einstein condensates.

  3. Simulation of the annihilation emission of galactic positrons

    International Nuclear Information System (INIS)

    Positrons annihilate in the central region of our Galaxy. This has been known since the detection of a strong emission line centered on an energy of 511 keV in the direction of the Galactic center. This gamma-ray line is emitted during the annihilation of positrons with electrons from the interstellar medium. The spectrometer SPI, onboard the INTEGRAL observatory, performed spatial and spectral analyses of the positron annihilation emission. This thesis presents a study of the Galactic positron annihilation emission based on models of the different interactions undergone by positrons in the interstellar medium. The models are relied on our present knowledge of the properties of the interstellar medium in the Galactic bulge, where most of the positrons annihilate, and of the physics of positrons (production, propagation and annihilation processes). In order to obtain constraints on the positrons sources and physical characteristics of the annihilation medium, we compared the results of the models to measurements provided by the SPI spectrometer. (author)

  4. 钼(Mo)原子奇宇称能级自然辐射寿命的测量%Natural Radiative Lifetime Measurements of Atoms and Ions in Astronomic Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    蒋红玫; 戴振文

    2012-01-01

    介绍了测量原子(离子)激发态自然辐射寿命的原理方法,并运用激光诱导荧光时间分辨光谱技术和激光烧蚀产生等离子体技术对钼(Mo)原子的5个奇宇称高激发态能级自然辐射寿命进行了测量.%The authors introduced the principles of lifertime measurement, and measured the natual radiative lifetime of Mo atom at 5 odd-parity highly-exited levels by means of the time-resolved laser-induced fluorescence and laser ablation techniques.

  5. Irradiation-induced voids in alumina single crystal studied by positron annihilation

    International Nuclear Information System (INIS)

    Angular correlation of annihilation radiation (ACAR) has been measured on α-alumina single crystals irradiated with fast neutrons to a dose of 3x1024 n/m2 at about 470 K. After post-irradiation annealing above 900 K, remarkable narrowing in ACAR curves has been observed. These ACAR curves can be decomposed into three Gaussian components: a narrow (N), an intermediate (M) and a broad (B) component, with FWHM of 2-5, about 6 and 11 mrad, respectively. The N and M components are attributed to positrons trapped in the voids. A magnetic quenching effect is observed for the N component but not for the M component. This shows that the N component is due to two photon self-annihilation of positronium (Ps) formed in voids. The FWHM of the N component indicates, through the momentum of zero-point motion of Ps, that the average void diameter is 0.6 nm after annealing at 1000 K and 1.7 nm after annealing at 1525 K. Striking similarity of the M component to a void-surface trapping component in metallic Al, together with nearly the same lifetime as that of voids in Al, suggests the existence of metallic surface-conduction-electron states in the voids in α-alumina. ((orig.))

  6. Antihyperon-hyperon production in antiproton-proton annihilations with PANDA at FAIR

    Energy Technology Data Exchange (ETDEWEB)

    Papenbrock, Michael [Department of Nuclear Physics and Astronomy, Uppsala University, Uppsala (Sweden); Collaboration: PANDA-Collaboration

    2015-07-01

    The production of antihyperon-hyperon pairs in antiproton-proton annihilations involves the annihilation of at least one light (u,d) quark-antiquark pair and the creation of a heavier (s,c,b) pair. Production of strange hyperons occur in an energy region in which QCD is difficult to predict. By studying hyperon production we learn about the strong interaction in this energy region, i.e. the confinement domain. It is an open question what the relevant degrees of freedom are: quarks and gluons, or hadrons. Spin observables is an excellent tool in order to better understand the physical processes. These are accessible via the weak, parity violating decay of the hyperon which results in an angular asymmetry of the decay products. The future PANDA experiment at FAIR is going to be ideally suited to study spin physics on hyperons with both high precision and high statistics. Since hyperons decay weakly and thus have long life-times, their decay vertices are displaced with respect to the production point. This sets high demands on precise track reconstruction. A pattern recognition algorithm is currently under development, with the ability to reconstruct tracks originating in displaced vertices. Simulation studies done by the Uppsala group as well as the status of the development will be presented and discussed.

  7. Mining the bulk positron lifetime

    Energy Technology Data Exchange (ETDEWEB)

    Aourag, H.; Guittom, A. [Centre de Recherche Nucleaire d' Alger (CRNA), Alger Gare - Algiers (Algeria)

    2009-02-15

    We introduce a new approach to investigate the bulk positron lifetimes of new systems based on data-mining techniques. Through data mining of bulk positron lifetimes, we demonstrate the ability to predict the positron lifetimes of new semiconductors on the basis of available semiconductor data already studied. Informatics techniques have been applied to bulk positron lifetimes for different tetrahedrally bounded semiconductors in order to discover computational design rules. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Mining the bulk positron lifetime

    International Nuclear Information System (INIS)

    We introduce a new approach to investigate the bulk positron lifetimes of new systems based on data-mining techniques. Through data mining of bulk positron lifetimes, we demonstrate the ability to predict the positron lifetimes of new semiconductors on the basis of available semiconductor data already studied. Informatics techniques have been applied to bulk positron lifetimes for different tetrahedrally bounded semiconductors in order to discover computational design rules. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Energy Savings Lifetimes and Persistence

    Energy Technology Data Exchange (ETDEWEB)

    Hoffman, Ian M. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Schiller, Steven R. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Todd, Annika [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Billingsley, Megan A. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Goldman, Charles A. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Schwartz, Lisa C. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2016-02-01

    This technical brief explains the concepts of energy savings lifetimes and savings persistence and discusses how program administrators use these factors to calculate savings for efficiency measures, programs and portfolios. Savings lifetime is the length of time that one or more energy efficiency measures or activities save energy, and savings persistence is the change in savings throughout the functional life of a given efficiency measure or activity. Savings lifetimes are essential for assessing the lifecycle benefits and cost effectiveness of efficiency activities and for forecasting loads in resource planning. The brief also provides estimates of savings lifetimes derived from a national collection of costs and savings for electric efficiency programs and portfolios.

  10. Copulas Between Wealth and Lifetime

    Institute of Scientific and Technical Information of China (English)

    YE Dongyan

    2009-01-01

    The life insurance industry is very interested in how a person's lifetime is related to his wealth with financial advisors interested in how even a person's portfolio choice affects his lifetime. This paper presents a statistical analysis combined with intuitive relationships between lifetime and wealth. Key properties of this relationship are given and then various copulas are analyzed to see whether they have these properties. Other advantages and disadvantages of these copulas for describing the dependence are stated. The results show that some copulas are not appropriate for relating lifetime and wealth, including the Gaussian family.

  11. Measurement of the lifetimes of the neutral and charged D mesons

    International Nuclear Information System (INIS)

    Results are presented on the use of a high-resolution drift chamber in the Mark II Detector at PEP to measure the lifetimes of D0 and D+- mesons produced in e+e- annihilations at 29 GeV. Based on a sample of 74 events for the D0 mesons and 23 events for the D+- mesons, the lifetimes are found to be tau/sub D0 = 4.7/sub -0.8//sup +0.9/ +- 0.5 x 10-13 s; tau/sub D+-/ = 8.9/sub -2.7//sup +3.8/ +- 1.3 x 10-13 s. The ratio of these lifetimes, tau/sub D0//tau/sub D+-/ = 1.9/sub -0.7//sup +0.9/ +- 0.3, indicates that the decays of these mesons cannot be explained by the simple spectator model of charmed particle decay

  12. Positron annihilation study of HVPE grown thick GaN layers

    Energy Technology Data Exchange (ETDEWEB)

    Misheva, M. [Department of Physics, Sofia University, Blvd. J. Boucher 5, 1164 Sofia (Bulgaria); Larsson, H.; Monemar, B. [Department of Physics and Measurement Technology, Linkoeping University, 58183 Linkoeping (Sweden); Gogova, D. [Department of Physics and Measurement Technology, Linkoeping University, 58183 Linkoeping (Sweden); Central Laboratory of Solar Energy and New Energy Sources at the Bulg. Acad. Sci., Blvd. Tzarigradsko shose 72, 1784 Sofia (Bulgaria)

    2005-04-01

    Single-crystalline GaN layers with a thickness up to 330 {mu}m were grown by hydride vapor phase epitaxy on basal plane sapphire at gallium stable conditions in a bottom-fed vertical reactor at atmospheric pressure. Positron annihilation spectroscopy experiments were implemented in order to identify native point defects in the as-grown non-intentionally doped n-type GaN. Comparatively low concentrations of Ga vacancy related defects in the order of 10{sup 16} to 10{sup 17} cm{sup -3} were extracted from the positron annihilation spectroscopy data. The Ga vacancy defect concentration was related to the intensity of the yellow photoluminescence band centered at 2.2 eV. The influence of the growth rate on the Ga vacancy related defect concentration was investigated. A trend of decreasing of the defect concentration with increasing of layer thickness is observed, which correlates with improving crystalline quality with the thickness. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Lifetime Improvement by Battery Scheduling

    NARCIS (Netherlands)

    Jongerden, Marijn R.; Haverkort, Boudewijn R.; Schmitt, Jens B.

    2012-01-01

    The use of mobile devices is often limited by the lifetime of their batteries. For devices that have multiple batteries or that have the option to connect an extra battery, battery scheduling, thereby exploiting the recovery properties of the batteries, can help to extend the system lifetime. Due to

  14. Lifetime improvement by battery scheduling

    NARCIS (Netherlands)

    Jongerden, Marijn R.; Haverkort, Boudewijn R.

    2011-01-01

    The use of mobile devices is often limited by the lifetime of its battery. For devices that have multiple batteries or that have the option to connect an extra battery, battery scheduling, thereby exploiting the recovery properties of the batteries, can help to extend the system lifetime. Due to t

  15. Study of local structure in hyper-eutectic Zr-Cu-Al bulk glassy alloys by positron annihilation techniques

    Science.gov (United States)

    Ishiyama, T.; Ishii, K.; Yokoyama, Y.; Konno, T. J.; Iwase, A.; Hori, F.

    2016-01-01

    The Zr-Cu-Al bulk glassy (BG) alloy, which has amorphous structure, possesses various properties such as high strength and toughness with compositional dependence. In the present study, density, positron annihilation lifetime and coincidence Doppler Broadening measurement have been performed for various compositional hyper-eutectic Zr-Cu-Al BG alloys. The density of hyper-eutectic Zr-Cu-Al BG alloys increases with decreasing of Zr fraction. In contrast, positron lifetime for all compositional alloys is almost constant about 165 psec. In addition, the CDB ratio profile is almost the same for hyper-eutectic alloys. This unchanging trend of CDB ratio profile is quite different from that of hypo-eutectic BG alloys. These results reveal that different internal structure exists in hyper and hypo-eutectic BG alloys.

  16. Positron-molecule interactions: resonant attachment, annihilation, and bound states

    CERN Document Server

    Gribakin, G F; Surko, C M; 10.1103/RevModPhys.82.2557

    2010-01-01

    This article presents an overview of current understanding of the interaction of low-energy positrons with molecules with emphasis on resonances, positron attachment and annihilation. Annihilation rates measured as a function of positron energy reveal the presence of vibrational Feshbach resonances (VFR) for many polyatomic molecules. These resonances lead to strong enhancement of the annihilation rates. They also provide evidence that positrons bind to many molecular species. A quantitative theory of VFR-mediated attachment to small molecules is presented. It is tested successfully for selected molecules (e.g., methyl halides and methanol) where all modes couple to the positron continuum. Combination and overtone resonances are observed and their role is elucidated. In larger molecules, annihilation rates from VFR far exceed those explicable on the basis of single-mode resonances. These enhancements increase rapidly with the number of vibrational degrees of freedom. While the details are as yet unclear, intr...

  17. Coincidence Doppler Broadening of Positron Annihilation Radiation in Fe

    Science.gov (United States)

    do Nascimento, E.; Vanin, V. R.; Maidana, N. L.; Helene, O.

    2013-06-01

    We measured the Doppler broadening annihilation radiation spectrum in Fe, using 22NaCl as a positron source, and two Ge detectors in coincidence arrangement. The two-dimensional coincidence energy spectrum was fitted using a model function that included positron annihilation with the conduction band and 3d electrons, 3s and 3p electrons, and in-flight positron annihilation. Detectors response functions included backscattering and a combination of Compton and pulse pileup, ballistic deficit and shaping effects. The core electrons annihilation intensity was measured as 16.4(3) %, with almost all the remainder assigned to the less bound electrons. The obtained results are in agreement with published theoretical values.

  18. Positron scattering and annihilation on noble gas atoms

    CERN Document Server

    Green, D G; Gribakin, G F

    2014-01-01

    Positron scattering and annihilation on noble gas atoms below the positronium formation threshold is studied ab initio using many-body theory methods. The many-body theory provides a near-complete understanding of the positron-noble-gas-atom system at these energies and yields accurate numerical results. It accounts for positron-atom and electron-positron correlations, e.g., polarization of the atom by the incident positron and the non-perturbative process of virtual positronium formation. These correlations have a large effect on the scattering dynamics and result in a strong enhancement of the annihilation rates compared to the independent-particle mean-field description. Computed elastic scattering cross sections are found to be in good agreement with recent experimental results and Kohn variational and convergent close-coupling calculations. The calculated values of the annihilation rate parameter $Z_{\\rm eff}$ (effective number of electrons participating in annihilation) rise steeply along the sequence o...

  19. Black Hole Window into p-Wave Dark Matter Annihilation.

    Science.gov (United States)

    Shelton, Jessie; Shapiro, Stuart L; Fields, Brian D

    2015-12-01

    We present a new method to measure or constrain p-wave-suppressed cross sections for dark matter (DM) annihilations inside the steep density spikes induced by supermassive black holes. We demonstrate that the high DM densities, together with the increased velocity dispersion, within such spikes combine to make thermal p-wave annihilation cross sections potentially visible in γ-ray observations of the Galactic center (GC). The resulting DM signal is a bright central point source with emission originating from DM annihilations in the absence of a detectable spatially extended signal from the halo. We define two simple reference theories of DM with a thermal p-wave annihilation cross section and establish new limits on the combined particle and astrophysical parameter space of these models, demonstrating that Fermi Large Area Telescope is currently sensitive to thermal p-wave DM over a wide range of possible scenarios for the DM distribution in the GC. PMID:26684108

  20. Matching Condition in γ-γ Annihilation Absorption

    Institute of Scientific and Technical Information of China (English)

    LIU Dang-Bo; CHEN Lei; LING Jia-Jie; YOU Jun-Han

    2005-01-01

    @@ Two-photon annihilation (γ-γ reaction) is an important absorption mechanism in γ-ray physics and γ-ray astronomy. Using the markedly simplified direction-averaged cross section of annihilation σ(ω, ω') for a normal isotropic ambient radiation field around the γ-ray source, we obtain a matching condition for the energies of two interacting photons, which ensures the attainment of the maximum annihilation probability. This is a new result that is helpful to obtain a better understanding for the absorption behaviour in the γ-γ annihilation process,and this predicts some possible line-like absorption structures in the emergent γ-ray continuous spectra. Some inferences of the matching condition are also presented.

  1. Semi-Annihilating Wino-Like Dark Matter

    CERN Document Server

    Spray, Andrew P

    2015-01-01

    Semi-annihilation is a generic feature of dark matter theories with symmetries larger than Z_2. We explore a model based on a Z_4-symmetric dark sector comprised of a scalar singlet and a "wino"-like fermion SU(2)_L triplet. This is the minimal example of semi-annihilation with a gauge-charged fermion. We study the interplay of the Sommerfeld effect in both annihilation and semi-annihilation channels. The modifications to the relic density allow otherwise-forbidden regions of parameter space and can substantially weaken indirect detection constraints. We perform a parameter scan and find that the entire region where the model comprises all the observed dark matter is accessible to current and planned direct and indirect searches.

  2. Neutrinos from WIMP annihilations in the Sun including neutrino oscillations

    Energy Technology Data Exchange (ETDEWEB)

    Blennow, Mattias, E-mail: emb@kth.se [Department of Theoretical Physics, School of Engineering Sciences, Royal Institute of Technology (KTH) - AlbaNova University Center, SE-106 91 Stockholm (Sweden); Edsjoe, Joakim, E-mail: edsjo@physto.se [Department of Physics, Stockholm University - AlbaNova University Center, SE-106 91 Stockholm (Sweden); Ohlsson, Tommy, E-mail: tommy@theophys.kth.se [Department of Theoretical Physics, School of Engineering Sciences, Royal Institute of Technology (KTH) - AlbaNova University Center, SE-106 91 Stockholm (Sweden)

    2011-12-15

    The prospects to detect neutrinos from the Sun arising from dark matter annihilations in the core of the Sun are reviewed. Emphasis is placed on new work investigating the effects of neutrino oscillations on the expected neutrino fluxes.

  3. Baryon production in $e^{+}e^{-}$-annihilation at PETRA

    CERN Document Server

    Bartel, Wulfrin; Dittmann, P; Eichler, R; Felst, R; Haidt, Dieter; Krehbiel, H; Meier, K; Naroska, Beate; O'Neill, L H; Steffen, P; Wenninger, Horst; Zhang, Y; Elsen, E E; Helm, M; Petersen, A; Warming, P; Weber, G; Bethke, Siegfried; Drumm, H; Heintze, J; Heinzelmann, G; Hellenbrand, K H; Heuer, R D; Von Krogh, J; Lennert, P; Kawabata, S; Matsumura, H; Nozaki, T; Olsson, J; Rieseberg, H; Wagner, A; Bell, A; Foster, F; Hughes, G; Wriedt, H; Allison, J; Ball, A H; Bamford, G; Barlow, R; Bowdery, C K; Duerdoth, I P; Hassard, J F; King, B T; Loebinger, F K; MacBeth, A A; McCann, H; Mills, H E; Murphy, P G; Prosper, H B; Stephens, K; Clarke, D; Goddard, M C; Marshall, R; Pearce, G F; Kobayashi, T; Komamiya, S; Koshiba, M; Minowa, M; Nozaki, M; Orito, S; Sato, A; Suda, T; Takeda, H; Totsuka, Y; Watanabe, Y; Yamada, S; Yanagisawa, C

    1981-01-01

    Data on p and Lambda production by e/sup +/e/sup -/-annihilation at CM energies between 30 and 36 GeV are presented. Indication for an angular anticorrelation in events with baryon-antibaryon pairs is seen.

  4. Black Hole Window into p-Wave Dark Matter Annihilation.

    Science.gov (United States)

    Shelton, Jessie; Shapiro, Stuart L; Fields, Brian D

    2015-12-01

    We present a new method to measure or constrain p-wave-suppressed cross sections for dark matter (DM) annihilations inside the steep density spikes induced by supermassive black holes. We demonstrate that the high DM densities, together with the increased velocity dispersion, within such spikes combine to make thermal p-wave annihilation cross sections potentially visible in γ-ray observations of the Galactic center (GC). The resulting DM signal is a bright central point source with emission originating from DM annihilations in the absence of a detectable spatially extended signal from the halo. We define two simple reference theories of DM with a thermal p-wave annihilation cross section and establish new limits on the combined particle and astrophysical parameter space of these models, demonstrating that Fermi Large Area Telescope is currently sensitive to thermal p-wave DM over a wide range of possible scenarios for the DM distribution in the GC.

  5. Baryon production in e+e--annihilation at PETRA

    International Nuclear Information System (INIS)

    Data on anti p and anti Λ production by e+e--annihilation at CM energies between 30 and 36 GeV are presented. Indication for an angular anticorrelation in events with baryon antibaryon pairs is seen. (orig.)

  6. ZnO Luminescence and scintillation studied via photoexcitation, X-ray excitation, and gamma-induced positron spectroscopy

    Science.gov (United States)

    Ji, J.; Colosimo, A. M.; Anwand, W.; Boatner, L. A.; Wagner, A.; Stepanov, P. S.; Trinh, T. T.; Liedke, M. O.; Krause-Rehberg, R.; Cowan, T. E.; Selim, F. A.

    2016-08-01

    The luminescence and scintillation properties of ZnO single crystals were studied by photoluminescence and X-ray-induced luminescence (XRIL) techniques. XRIL allowed a direct comparison to be made between the near-band emission (NBE) and trap emissions providing insight into the carrier recombination efficiency in the ZnO crystals. It also provided bulk luminescence measurements that were not affected by surface states. The origin of a green emission, the dominant trap emission in ZnO, was then investigated by gamma-induced positron spectroscopy (GIPS) - a unique defect spectroscopy method that enables positron lifetime measurements to be made for a sample without contributions from positron annihilation in the source materials. The measurements showed a single positron decay curve with a 175 ps lifetime component that was attributed to Zn vacancies passivated by hydrogen. Both oxygen vacancies and hydrogen-decorated Zn vacancies were suggested to contribute to the green emission. By combining scintillation measurements with XRIL, the fast scintillation in ZnO crystals was found to be strongly correlated with the ratio between the defect luminescence and NBE. This study reports the first application of GIPS to semiconductors, and it reveals the great benefits of the XRIL technique for the study of emission and scintillation properties of materials.

  7. Effects of Bound States on Dark Matter Annihilation

    OpenAIRE

    An, Haipeng; Wise, Mark B.; Zhang, Yue

    2016-01-01

    We study the impact of bound state formation on dark matter annihilation rates in models where dark matter interacts via a light mediator, the dark photon. We derive the general cross section for radiative capture into all possible bound states, and point out its non-trivial dependence on the dark matter velocity and the dark photon mass. For indirect detection, our result shows that dark matter annihilation inside bound states can play an important role in enhancing signal rates over the rat...

  8. Breit-Wigner Enhancement of Dark Matter Annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Ibe, Masahiro; /SLAC; Murayama, Hitoshi; /Tokyo U., IPMU /UC, Berkeley /LBL, Berkeley; Yanagida, T.T.; /Tokyo U. /Tokyo U., IPMU

    2009-06-19

    We point out that annihilation of dark matter in the galactic halo can be enhanced relative to that in the early universe due to a Breit-Wigner tail, if the dark matter annihilates through a pole just below the threshold. This provides a new explanation to the 'boost factor' which is suggested by the recent data of the PAMELA, ATIC and PPB-BETS cosmic-ray experiments.

  9. Dark Matter Velocity Spectroscopy

    CERN Document Server

    Speckhard, Eric G; Beacom, John F; Laha, Ranjan

    2016-01-01

    Dark matter decays or annihilations that produce line-like spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming and proposed experiments will make significant improvements. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.

  10. Dark Matter Velocity Spectroscopy.

    Science.gov (United States)

    Speckhard, Eric G; Ng, Kenny C Y; Beacom, John F; Laha, Ranjan

    2016-01-22

    Dark matter decays or annihilations that produce linelike spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming experiments will have the precision needed. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.

  11. Annihilation of antiproton on deuteron at rest

    International Nuclear Information System (INIS)

    The system of Faddeev equations for amplitudes of anti pD iteraction at rest accounting for higher partial anti NN waves is derived. From its solution the total and elastic anti pD cross sections are calculated. Predictions for the missing-mass spectrum in the anti pD annihilation are made. The P-wave anti NN states give small contribution to the anti pD cross section at rest, the theoretical value of the latter being less than the experimental cross section extrapolated to the threshold. Let us emphasize that the total anti pD cross section depending weakly on the radii of anti NN interactions is sensitive to the values of the anti NN scattering lengths. Experimental data for anti pD cross sections at rest can be obtained only by extrapolation procedure. Henceforth it is very important to investigate the anti pD interactions at low but non-zero momenta where the direct comparison to the experiment is possible

  12. On the Annihilation Rate of WIMPs

    CERN Document Server

    Baumgart, Matthew; Vaidya, Varun

    2014-01-01

    We develop a formalism that allows one to systematically calculate the WIMP annihilation rate into gamma rays whose energy far exceeds the weak scale. A factorization theorem is presented which separates the radiative corrections stemming from initial state potential interactions from loops involving the final state. This separation allows us to go beyond the fixed the order calculation, which is polluted by large infrared logarithms. For the case of Majorana WIMPs transforming in the adjoint representation of SU(2), we present the result for the resummed rate at leading double log accuracy in terms of two initial state partial wave matrix elements and one hard matching coefficient. For a given model, one may calculate the cross section by calculating the tree level matching coefficient and determining the value of a local four fermion operator. We find that the effects of resummation can be as large as 100% for a 20 TeV WIMP. The generalization of the formalism to other types of WIMPs is discussed.

  13. Nonabelian dark matter with resonant annihilation

    International Nuclear Information System (INIS)

    We construct a model based on an extra gauge symmetry, SU(2)X×U(1)B−L, which can provide gauge bosons to serve as weakly-interacting massive particle dark matter. The stability of the dark matter is naturally guaranteed by a discrete Z2 symmetry that is a subgroup of SU(2)X. The dark matter interacts with standard model fermions by exchanging gauge bosons which are linear combinations of SU(2)X×U(1)B−L gauge bosons. With the appropriate choice of representation for the new scalar multiplet whose vacuum expectation value spontaneously breaks the SU(2)X symmetry, the relation between the new gauge boson masses can naturally lead to resonant pair annihilation of the dark matter. After exploring the parameter space of the new gauge couplings subject to constraints from collider data and the observed relic density, we use the results to evaluate the cross section of the dark matter scattering off nucleons and compare it with data from the latest direct detection experiments. We find allowed parameter regions that can be probed by future direct searches for dark matter and LHC searches for new particles

  14. Charmed Mesons Produced in e+e- Annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Goldhaber, G.; Wiss, J. E.

    1980-12-01

    We shall begin our review by summarizing the first experimental indications for the existence of charm as obtained from experiments in e{sup +}e{sup -} annihilation. This will include a brief discussion of the role of charm in the understanding of the {psi} mesons, as well as the unraveling of the intricate structure present in the e{sup +} e{sup -} total hadronic cross section. Next we shall discuss the discovery of the D{sup 0}, and D{sup +}, and detail those properties crucial to their identification as charmed particles. Following will be a review of the properties of the D{sup 0} and D{sup +} learned through studies at the {psi}(3770) resonance, Compelling evidence will be summarized indicating that this state decays nearly exclusively into D{bar D}, thus making it particularly useful in establishing inclusive and exclusive D branching fractions. Our discussion of branching fractions will include two particularly important D decay modes, D{sup 0}{yields}{pi}{sup +}{pi}{sup -} and D{sup 0}{yields}K{sup +}{sup -}. These processes are suppressed relative to D{sup 0}{yields}K{sup -}{pi}{sup +} in the standard charm model, and thus serve as a critical test of that theory. This will be followed by a discussion of the D semileptonic decay modes which provide useful information on the D{sup 0} and D{sup +} lifetimes. Turning our attention to the data collected beyond the {psi}(3770) we will discuss the properties and production mechanisms of the excited charm mesons, the D*{sup 0} and the D*{sup +}. D production just above the {psi}(3770) appears to be dominated by the three quasi-two-body processes e{sup +} e{sup -} {yields} D{bar D}, D*{bar D} + {bar D}*D, and D*{bar D}*, in accordance with early theoretical predictions. The relative amounts of each process, on the other hand, is somewhat surprising, and has led to considerable theoretical speculation. Finally, we will summarize evidence for the existence of the F meson which is as yet not on as solid a footing as

  15. Lifetime costs of cerebral palsy

    DEFF Research Database (Denmark)

    Kruse, Marie; Michelsen, Susan Ishøy; Flachs, Esben Meulengracht;

    2009-01-01

    This study quantified the lifetime costs of cerebral palsy (CP) in a register-based setting. It was the first study outside the US to assess the lifetime costs of CP. The lifetime costs attributable to CP were divided into three categories: health care costs, productivity costs, and social costs....... The population analyzed was retrieved from the Danish Cerebral Palsy Register, which covers the eastern part of the country and has registered about half of the Danish population of individuals with CP since 1950. For this study we analyzed 2367 individuals with CP, who were born in 1930 to 2000 and were alive...

  16. Radiative lifetimes of odd-parity levels in Nb I

    Science.gov (United States)

    Mukund, Sheo; Bhattacharyya, Soumen; Yarlagadda, Suresh; Nakhate, S. G.

    2015-11-01

    Radiative lifetimes are reported for 37 odd-parity energy levels of neutral niobium (Nb I), out of which 33 have been measured for the first time. The levels belong to electronic configurations 4d35s5p and 4d45p between 18,790 and 35,730 cm-1. The time-resolved laser-induced fluorescence spectroscopy technique was employed. The Nb atoms were generated in a free-jet by laser vaporization of niobium metal. Lifetime values reported in this work fall in the range 12-340 ns and are accurate to ±10%.

  17. The Isotropic Radio Background and Annihilating Dark Matter

    Energy Technology Data Exchange (ETDEWEB)

    Hooper, Dan [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Belikov, Alexander V. [Institut d' Astrophysique (France); Jeltema, Tesla E. [Univ. of California, Santa Cruz, CA (United States); Linden, Tim [Univ. of California, Santa Cruz, CA (United States); Profumo, Stefano [Univ. of California, Santa Cruz, CA (United States); Slatyer, Tracy R. [Princeton Univ., Princeton, NJ (United States)

    2012-11-01

    Observations by ARCADE-2 and other telescopes sensitive to low frequency radiation have revealed the presence of an isotropic radio background with a hard spectral index. The intensity of this observed background is found to exceed the flux predicted from astrophysical sources by a factor of approximately 5-6. In this article, we consider the possibility that annihilating dark matter particles provide the primary contribution to the observed isotropic radio background through the emission of synchrotron radiation from electron and positron annihilation products. For reasonable estimates of the magnetic fields present in clusters and galaxies, we find that dark matter could potentially account for the observed radio excess, but only if it annihilates mostly to electrons and/or muons, and only if it possesses a mass in the range of approximately 5-50 GeV. For such models, the annihilation cross section required to normalize the synchrotron signal to the observed excess is sigma v ~ (0.4-30) x 10^-26 cm^3/s, similar to the value predicted for a simple thermal relic (sigma v ~ 3 x 10^-26 cm^3/s). We find that in any scenario in which dark matter annihilations are responsible for the observed excess radio emission, a significant fraction of the isotropic gamma ray background observed by Fermi must result from dark matter as well.

  18. CMB Constraints On The Thermal WIMP Annihilation Cross Section

    CERN Document Server

    Steigman, Gary

    2015-01-01

    A thermal relic, often referred to as a weakly interacting massive particle (WIMP),is a particle produced during the early evolution of the Universe whose relic abundance (e.g., at present) depends only on its mass and its thermally averaged annihilation cross section (annihilation rate factor) sigma*v_ann. Late time WIMP annihilation has the potential to affect the cosmic microwave background (CMB) power spectrum. Current observational constraints on the absence of such effects provide bounds on the mass and the annihilation cross section of relic particles that may, but need not be dark matter candidates. For a WIMP that is a dark matter candidate, the CMB constraint sets an upper bound to the annihilation cross section, leading to a lower bound to their mass that depends on whether or not the WIMP is its own antiparticle. For a self-conjugate WIMP, m_min = 50f GeV, where f is an electromagnetic energy efficiency factor. For a non self-conjugate WIMP, the minimum mass is a factor of two larger. For a WIMP t...

  19. The Effects of Dark Matter Annihilation on Cosmic Reionization

    Energy Technology Data Exchange (ETDEWEB)

    Kaurov, Alexander A. [Chicago U., Astron. Astrophys. Ctr.; Hooper, Dan [Chicago U., EFI; Gnedin, Nickolay Y. [Chicago U., KICP

    2015-12-01

    We revisit the possibility of constraining the properties of dark matter (DM) by studying the epoch of cosmic reionization. Previous studies have shown that DM annihilation was unlikely to have provided a large fraction of the photons that ionized the universe, but instead played a subdominant role relative to stars and quasars. The DM, however, begins to efficiently annihilate with the formation of primordial microhalos at $z\\sim100-200$, much earlier than the formation of the first stars. Therefore, if DM annihilation ionized the universe at even the percent level over the interval $z \\sim 20-100$, it can leave a significant imprint on the global optical depth, $\\tau$. Moreover, we show that cosmic microwave background (CMB) polarization data and future 21 cm measurements will enable us to more directly probe the DM contribution to the optical depth. In order to compute the annihilation rate throughout the epoch of reionization, we adopt the latest results from structure formation studies and explore the impact of various free parameters on our results. We show that future measurements could make it possible to place constraints on the dark matter's annihilation cross section that are at a level comparable to those obtained from the observations of dwarf galaxies, cosmic ray measurements, and studies of recombination.

  20. Double antikaonic nuclear clusters in antiproton-{sup 3}He annihilation at J-PARC

    Energy Technology Data Exchange (ETDEWEB)

    Sakuma, Fuminori, E-mail: sakuma@ribf.riken.jp [RIKEN, RIKEN Nishina Center (Japan); Curceanu, Catalina [Laboratori Nazionali di Frascati dell' INFN (Italy); Iwasaki, Masahiko [RIKEN, RIKEN Nishina Center (Japan); Kienle, Paul [Technische Universiat Munchen (Germany); Ohnishi, Hiroaki [RIKEN, RIKEN Nishina Center (Japan); Tokuda, Makoto [The University of Tokyo, Department of Physics (Japan); Tsukada, Kyo [Tohoku University, Department of Physics (Japan); Widmann, Eberhard [Stefan-Meyer-Institut fuer Subatomare Physik (Austria); Yamazaki, Toshimitsu [RIKEN, RIKEN Nishina Center (Japan); Zmeskal, Johannes [Stefan-Meyer-Institut fuer Subatomare Physik (Austria)

    2012-12-15

    We search for double anti-kaon nuclear bound states in the p-bar annihilation reaction in {sup 3}He nuclei at rest. In view of the strongly attractive K-bar N interaction, the existence of nuclear clusters with more than one K{sup }- has been predicted theoretically. The double anti-kaon production in elementary antiproton annihilation at rest is forbidden because of the negative Q-value; however, a double anti-kaon nuclear bound state, such as K{sup }- K{sup }- pp, with deep binding energy would enable double anti-kaon production in the nuclei. In order to investigate the K{sup }- K{sup }- pp production in the p-bar + {sup 3}He {yields} K{sup +} + K{sup 0} + X (X = K{sup -} K{sup -} pp) channel, the produced K{sup }- K{sup }- pp cluster is identified both using missing mass spectroscopy via the K{sup + }K{sup 0} channel with a {Lambda}-tag, and invariant mass analysis of the expected decay particles from the K{sup }- K{sup }- pp cluster such as {Lambda}{Lambda}. We propose to perform the experiment at the existing K1.8BR beam line at J-PARC with the E15 spectrometer.

  1. Finite quasiparticle lifetime in disordered superconductors.

    Energy Technology Data Exchange (ETDEWEB)

    Zemlicka, M.; Neilinger, P.; Trgala, M; Rehak, M; Manca, D.; Grajcar, M.; Szabo, P.; Samuely, P.; Gazi, S.; Hubner, U.; Vinokur, V. M.; Il' ichev, E.

    2015-12-08

    We investigate the complex conductivity of a highly disordered MoC superconducting film with k(F)l approximate to 1, where k(F) is the Fermi wave number and l is the mean free path, derived from experimental transmission characteristics of coplanar waveguide resonators in a wide temperature range below the superconducting transition temperature T-c. We find that the original Mattis-Bardeen model with a finite quasiparticle lifetime, tau, offers a perfect description of the experimentally observed complex conductivity. We show that iota is appreciably reduced by scattering effects. Characteristics of the scattering centers are independently found by scanning tunneling spectroscopy and agree with those determined from the complex conductivity.

  2. Dark matter annihilation with s-channel internal Higgsstrahlung

    Science.gov (United States)

    Kumar, Jason; Liao, Jiajun; Marfatia, Danny

    2016-08-01

    We study the scenario of fermionic dark matter that annihilates to standard model fermions through an s-channel axial vector mediator. We point out that the well-known chirality suppression of the annihilation cross section can be alleviated by s-channel internal Higgsstrahlung. The shapes of the cosmic ray spectra are identical to that of t-channel internal Higgsstrahlung in the limit of a heavy mediating particle. Unlike the general case of t-channel bremsstrahlung, s-channel Higgsstrahlung can be the dominant annihilation process even for Dirac dark matter. Since the s-channel mediator can be a standard model singlet, collider searches for the mediator are easily circumvented.

  3. Solvable Aggregation-Migration-Annihilation Processes of a Multispecies System

    Institute of Scientific and Technical Information of China (English)

    KE Jian-Hong; LIN Zhen-Quan; CHEN Xiao-Shuang

    2006-01-01

    An aggregation-migration-annihilation model is proposed for a two-species-group system. In the system,aggregation reactions occur between any two aggregates of the same species and migration reactions between two different species in the same group and joint annihilation reactions between two species from different groups. The kinetics of the system is then investigated in the framework of the mean-field theory. It is found that the scaling solutions of the aggregate size distributions depend crucially on the ratios of the equivalent aggregation rates of species groups to the annihilation rates. Each species always scales according to a conventional or modified scaling form; moreover, the governing scaling exponents are nonuniversal and dependent on the reaction details for most cases.

  4. Consequences of dark matter self-annihilation for galaxy formation

    CERN Document Server

    Natarajan, Priyamvada; Bertone, Gianfranco

    2007-01-01

    Galaxy formation requires a process that continually heats gas and quenches star formation in order to reproduce the observed shape of the luminosity function of bright galaxies. To accomplish this, current models invoke heating from supernovae, and energy injection from active galactic nuclei. However, observations of radio-loud active galactic nuclei suggest that their feedback is likely to not be as efficient as required, signaling the need for additional heating processes. We propose the self-annihilation of weakly interacting massive particles that constitute dark matter as a steady source of heating. In this paper, we explore the circumstances under which this process may provide the required energy input. To do so, dark matter annihilations are incorporated into a galaxy formation model within the Millennium cosmological simulation. Energy input from self-annihilation can compensate for all the required gas cooling and reproduce the observed galaxy luminosity function only for what appear to be extreme...

  5. Generalized creation and annihilation operators via complex nonlinear Riccati equations

    Science.gov (United States)

    Schuch, Dieter; Castaños, Octavio; Rosas-Ortiz, Oscar

    2013-06-01

    Based on Gaussian wave packet solutions of the time-dependent Schrödinger equation, a generalization of the conventional creation and annihilation operators and the corresponding coherent states can be obtained. This generalization includes systems where also the width of the coherent states is time-dependent as they occur for harmonic oscillators with time-dependent frequency or systems in contact with a dissipative environment. The key point is the replacement of the frequency ω0 that occurs in the usual definition of the creation/annihilation operator by a complex time-dependent function that fulfils a nonlinear Riccati equation. This equation and its solutions depend on the system under consideration and on the (complex) initial conditions. Formal similarities also exist with supersymmetric quantum mechanics. The generalized creation and annihilation operators also allow to construct exact analytic solutions of the free motion Schrödinger equation in terms of Hermite polynomials with time-dependent variable.

  6. Molecular model for annihilation rates in positron complexes

    Energy Technology Data Exchange (ETDEWEB)

    Assafrao, Denise [Laboratorio de Atomos e Moleculas Especiais, Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, P.O. Box 702, 30123-970 Belo Horizonte, MG (Brazil); Department of Applied Mathematics and Theoretical Physics, Queen' s University of Belfast, Belfast BT7 1NN, Northern Ireland (United Kingdom); Walters, H.R. James [Department of Applied Mathematics and Theoretical Physics, Queen' s University of Belfast, Belfast BT7 1NN, Northern Ireland (United Kingdom); Mohallem, Jose R. [Laboratorio de Atomos e Moleculas Especiais, Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, P.O. Box 702, 30123-970 Belo Horizonte, MG (Brazil); Department of Applied Mathematics and Theoretical Physics, Queen' s University of Belfast, Belfast BT7 1NN, Northern Ireland (United Kingdom)], E-mail: rachid@fisica.ufmg.br

    2008-02-15

    The molecular approach for positron interaction with atoms is developed further. Potential energy curves for positron motion are obtained. Two procedures accounting for the nonadiabatic effective positron mass are introduced for calculating annihilation rate constants. The first one takes the bound-state energy eigenvalue as an input parameter. The second is a self-contained and self-consistent procedure. The methods are tested with quite different states of the small complexes HPs, e{sup +}He (electronic triplet) and e{sup +}Be (electronic singlet and triplet). For states yielding the positronium cluster, the annihilation rates are quite stable, irrespective of the accuracy in binding energies. For the e{sup +}Be states, annihilation rates are larger and more consistent with qualitative predictions than previously reported ones.

  7. A Critical Reevaluation of Radio Constraints on Annihilating Dark Matter

    Energy Technology Data Exchange (ETDEWEB)

    Cholis, Ilias [Fermilab; Hooper, Dan [Fermilab; Linden, Tim [Chicago U., KICP

    2015-04-03

    A number of groups have employed radio observations of the Galactic center to derive stringent constraints on the annihilation cross section of weakly interacting dark matter. In this paper, we show that electron energy losses in this region are likely to be dominated by inverse Compton scattering on the interstellar radiation field, rather than by synchrotron, considerably relaxing the constraints on the dark matter annihilation cross section compared to previous works. Strong convective winds, which are well motivated by recent observations, may also significantly weaken synchrotron constraints. After taking these factors into account, we find that radio constraints on annihilating dark matter are orders of magnitude less stringent than previously reported, and are generally weaker than those derived from current gamma-ray observations.

  8. Intrinsic spin lifetimes in GaAs (110) quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Mueller, Georg; Roemer, Michael; Huebner, Jens; Oestreich, Michael [Institut fuer Festkoerperphysik, Gottfried Wilhelm Leibniz Universitaet Hannover, Hannover (Germany); Schuh, Dieter; Wegscheider, Werner [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg (Germany)

    2009-07-01

    GaAs(110) quantum wells attract great attention due to the long spin lifetime for electron spins along the growth axis and are, therefore, of interest for future spin based optoelectronic devices. At low temperatures, optical injection of a finite spin polarization yields strongly enhanced spin dephasing due to the Bir Aronov Pikus mechanism that arises from the exchange interaction between electrons and holes. Thus, the intrinsic spin lifetime in GaAs(110) quantum wells has been unknown. In this work, the non-demolition technique of spin noise spectroscopy, which only relies on statistical spin fluctuations, is applied to GaAs(110) quantum wells in order to measure the intrinsic spin lifetimes. Furthermore, the Brownian motion of the electrons modifies the linewidth of the measured spin noise spectra due to time of flight broadening. This effect uniquely allows to study electronic motion at thermal equilibrium.

  9. Bremsstrahlung signatures of dark matter annihilation in the Sun

    CERN Document Server

    Fukushima, Keita; Kumar, Jason; Marfatia, Danny

    2012-01-01

    The nonrelativistic annihilation of Majorana dark matter in the Sun to a pair of light fermions is chirality-suppressed. Annihilation to 3-body final states $\\ell^+f^-V$, where $V=W,Z,\\gamma$, and $\\ell$ and $f$ are light fermions (that may be the same), becomes dominant since bremsstrahlung relaxes the chirality suppression. We evaluate the neutrino spectra at the source, including spin and helicity dependent effects, and assess the detectability of each significant bremsstrahlung channel at IceCube/DeepCore. We also show how to combine the sensitivities to the dark matter-nucleon scattering cross section in individual channels, since typically several channels contribute in models.

  10. On the Direct Detection of Dark Matter Annihilation

    DEFF Research Database (Denmark)

    Cherry, John F.; Frandsen, Mads T.; Shoemaker, Ian M.

    2015-01-01

    We investigate the direct detection phenomenology of a class of dark matter (DM) models in which DM does not directly interact with nuclei, {but rather} the products of its annihilation do. When these annihilation products are very light compared to the DM mass, the scattering in direct detection...... cross sections has already been reached in a class of models. Moreover, the compatibility of dark matter direct detection experiments can be compared directly in $E_{{\\rm min}}$ space without making assumptions about DM astrophysics, mass, or scattering form factors. Lastly, when DM has direct couplings...

  11. Significant enhancement of neutralino dark matter annihilation from electroweak bremsstrahlung.

    Science.gov (United States)

    Bringmann, Torsten; Calore, Francesca

    2014-02-21

    Indirect searches for the cosmological dark matter have become ever more competitive during the past years. Here, we report the first full calculation of leading electroweak corrections to the annihilation rate of supersymmetric neutralino dark matter. We find that these corrections can be huge, partially due to contributions that have been overlooked so far. Our results imply a significantly enhanced discovery potential of this well motivated dark matter candidate with current and upcoming cosmic ray experiments, in particular for gamma rays and models with somewhat small annihilation rates at the tree level.

  12. Heavy dark matter annihilation from effective field theory.

    Science.gov (United States)

    Ovanesyan, Grigory; Slatyer, Tracy R; Stewart, Iain W

    2015-05-29

    We formulate an effective field theory description for SU(2)_{L} triplet fermionic dark matter by combining nonrelativistic dark matter with gauge bosons in the soft-collinear effective theory. For a given dark matter mass, the annihilation cross section to line photons is obtained with 5% precision by simultaneously including Sommerfeld enhancement and the resummation of electroweak Sudakov logarithms at next-to-leading logarithmic order. Using these results, we present more accurate and precise predictions for the gamma-ray line signal from annihilation, updating both existing constraints and the reach of future experiments.

  13. Annihilation physics of exotic galactic dark matter particles

    Science.gov (United States)

    Stecker, F. W.

    1990-01-01

    Various theoretical arguments make exotic heavy neutral weakly interacting fermions, particularly those predicted by supersymmetry theory, attractive candidates for making up the large amount of unseen gravitating mass in galactic halos. Such particles can annihilate with each other, producing secondary particles of cosmic-ray energies, among which are antiprotons, positrons, neutrinos, and gamma-rays. Spectra and fluxes of these annihilation products can be calculated, partly by making use of positron electron collider data and quantum chromodynamic models of particle production derived therefrom. These spectra may provide detectable signatures of exotic particle remnants of the big bang.

  14. Remote forcing annihilates barrier layer in southeastern Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Shenoi, S.S.C.; Shankar, D.; Shetye, S.R.

    -1 GEOPHYSICAL RESEARCH LETTERS, VOL. ???, XXXX, DOI:10.1029/, Remote forcing annihilates barrier layer in southeastern Arabian Sea S. S. C. Shenoi, D. Shankar, and S. R. Shetye National Institute of Oceanography, Goa, India. Time-series measurements... thick barrier layer (BL) exists during March{April ow- ing to a surface layer of low-salinity waters advected earlier during December{January from the Bay of Bengal. The BL is almost annihilated by 7 April owing to upwelling. The relic BL that survives...

  15. Polarization of photons in matter–antimatter annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Moskaliuk, S.S. [Bogolyubov Institute for Theoretical Physics, Metrolohichna Street, 14-b, Kyiv-143, Ukraine, UA-03143 e-mail: mss@bitp.kiev.ua (Ukraine)

    2015-03-10

    In this work we demonstrate the possibility of generation of linear polarization of the electromagnetic field (EMF) due to the quantum effects in matter-antimatter annihilation process for anisotropic space of the I type according to Bianchi. We study the dynamics of this process to estimate the degree of polarisation of the EMF in the external gravitational field of the anisotropic Bianchi I model. It has been established that the quantum effects in matter-antimatter annihilation process in the external gravitational field of the anisotropic Bianchi I model provide contribution to the degree of polarisation of the EMF in quadrupole harmonics.

  16. Dark matter annihilation with s-channel internal Higgsstrahlung

    OpenAIRE

    Jason Kumar(Univ. of Hawaii); Jiajun Liao; Danny Marfatia

    2016-01-01

    We study the scenario of fermionic dark matter that annihilates to standard model fermions through an s-channel axial vector mediator. We point out that the well-known chirality suppression of the annihilation cross section can be alleviated by s-channel internal Higgsstrahlung. The shapes of the cosmic ray spectra are identical to that of t-channel internal Higgsstrahlung in the limit of a heavy mediating particle. Unlike the general case of t-channel bremsstrahlung, s-channel Higgsstrahlung...

  17. Revisiting Bremsstrahlung emission associated with Light Dark Matter annihilations

    OpenAIRE

    Boehm, C; Uwer, P.

    2006-01-01

    We compute the single bremsstrahlung emission associated with the pair annihilation of spin-0 particles into electrons and positrons, via the t-channel exchange of a heavy fermion. We compare our result with the work of Beacom et al. . Unlike what is stated in the literature, we show that the Bremsstrahlung cross section is not necessarily given by the tree-level annihilation cross section (for a generalized kinematics) times a factor related to the emission of a soft photon. Such a factoriza...

  18. Positron annihilation studies of fluorine-vacancy complexes in phosphorus- and fluorine-implanted germanium

    Science.gov (United States)

    Edwardson, C. J.; Coleman, P. G.; El Mubarek, H. A. W.

    2014-03-01

    The formation of FnV2 complexes, with n = 5 ± 1, near the end-of-range damage region in germanium implanted with 30 keV phosphorus and 40 keV fluorine ions, after annealing to 400 °C, has been observed using variable-energy positron annihilation spectroscopy in conjunction with secondary ion mass spectrometry. Phosphorus ions were implanted at 6 × 1013 and 1015, F at 1015 cm-2. Complexes—at lower concentrations—have also been observed at shallower depths in samples implanted with P at 1015 cm-2. The complexes break up and their components diffuse away at 450 and 500 °C for the higher and lower P dose samples, respectively.

  19. Singlet-triplet annihilation limits exciton yield in poly(3-hexylthiophene)

    CERN Document Server

    Steiner, Florian; Lupton, John M

    2014-01-01

    Control of chain length and morphology in combination with single-molecule spectroscopy techniques provide a comprehensive photophysical picture of excited-state losses in the prototypical conjugated polymer poly(3-hexylthiophene) (P3HT). A universal self-quenching mechanism is revealed, based on singlet-triplet exciton annihilation, which accounts for the dramatic loss in fluorescence quantum yield of a single P3HT chain between its solution (unfolded) and bulk-like (folded) state. Triplet excitons fundamentally limit the fluorescence of organic photovoltaic materials, which impacts on the conversion of singlet excitons to separated charge carriers, decreasing the efficiency of energy harvesting at high excitation densities. Interexcitonic interactions are so effective that a single P3HT chain of >100 kDa weight behaves like a two-level system, exhibiting perfect photon-antibunching.

  20. Exciton-exciton annihilation and biexciton stimulated emission in graphene nanoribbons

    Science.gov (United States)

    Soavi, Giancarlo; Dal Conte, Stefano; Manzoni, Cristian; Viola, Daniele; Narita, Akimitsu; Hu, Yunbin; Feng, Xinliang; Hohenester, Ulrich; Molinari, Elisa; Prezzi, Deborah; Müllen, Klaus; Cerullo, Giulio

    2016-03-01

    Graphene nanoribbons display extraordinary optical properties due to one-dimensional quantum-confinement, such as width-dependent bandgap and strong electron-hole interactions, responsible for the formation of excitons with extremely high binding energies. Here we use femtosecond transient absorption spectroscopy to explore the ultrafast optical properties of ultranarrow, structurally well-defined graphene nanoribbons as a function of the excitation fluence, and the impact of enhanced Coulomb interaction on their excited states dynamics. We show that in the high-excitation regime biexcitons are formed by nonlinear exciton-exciton annihilation, and that they radiatively recombine via stimulated emission. We obtain a biexciton binding energy of ~250 meV, in very good agreement with theoretical results from quantum Monte Carlo simulations. These observations pave the way for the application of graphene nanoribbons in photonics and optoelectronics.

  1. Segmented scintillation detectors with silicon photomultiplier readout for measuring antiproton annihilations

    CERN Document Server

    Sótér, A; Kobayashi, T; Barna, D; Horvath, D; Hori, M

    2014-01-01

    The Atomic Spectroscopy and Collisions Using Slow Antiprotons (ASACUSA) experiment at the Antiproton Decelerator (AD) facility of CERN constructed segmented scintillators to detect and track the charged pions which emerge from antiproton annihilations in a future superconducting radiofrequency Paul trap for antiprotons. A system of 541 cast and extruded scintillator bars were arranged in 11 detector modules which provided a spatial resolution of 17 mm. Green wavelength-shifting fibers were embedded in the scintillators, and read out by silicon photomultipliers which had a sensitive area of 1 x 1 mm^2. The photoelectron yields of various scintillator configurations were measured using a negative pion beam of momentum p ~ 1 GeV/c. Various fibers and silicon photomultipliers, fiber end terminations, and couplings between the fibers and scintillators were compared. The detectors were also tested using the antiproton beam of the AD. Nonlinear effects due to the saturation of the silicon photomultiplier were seen a...

  2. Origin and annihilation physics of positrons in the Galaxy

    International Nuclear Information System (INIS)

    A gamma radiation at 511 keV is observed since the early 1970's toward the Galactic bulge region. This emission is the signature of a large number of electron-positron annihilations, the positron being the electron's antiparticle. Unfortunately, the origin of the positrons responsible for this emission is still a mystery. Many positron-source candidates have been suggested but none of them can account for the galactic annihilation emission. The spatial distribution of this emission is indeed very atypical. Since 2002, the SPI spectrometer onboard the INTEGRAL space laboratory revealed an emission strongly concentrated toward the galactic bulge and a weaker emission from the galactic disk. This morphology is unusual because it does not correspond to any of the known galactic astrophysical-object or interstellar-matter distributions. The assumption that positrons annihilate close to their sources (i.e. the spatial distribution of the annihilation emission reflects the spatial distribution of the sources) has consequently been called into question. Recent studies suggest that positrons could propagate far away from their sources before annihilating. This physical aspect could be the key point to solve the riddle of the galactic positron origin. This thesis is devoted to the modelling of the propagation and annihilation of positrons in the Galaxy, in order to compare simulated spatial models of the annihilation emission with recent measurements provided by SPI/INTEGRAL. This method allows to put constraints on the origin of galactic positrons. We therefore developed a propagation Monte-Carlo code of positrons within the Galaxy in which we implemented all the theoretical and observational knowledge about positron physics (sources, transport modes, energy losses, annihilation modes) and the interstellar medium of our Galaxy (interstellar gas distributions, galactic magnetic fields, structures of the gaseous phases). Due to uncertainties in several physical parameters

  3. Positron spectroscopy of defects in submicrocrystalline nickel after low-temperature annealing

    Science.gov (United States)

    Kuznetsov, P. V.; Mironov, Yu. P.; Tolmachev, A. I.; Bordulev, Yu. S.; Laptev, R. S.; Lider, A. M.; Korznikov, A. V.

    2015-02-01

    Using the method of measuring the positron lifetime spectra and Doppler broadening annihilation line spectroscopy, the annealing of defects in submicrocrystalline nickel produced by equal channel angular pressing has been studied. In as-prepared samples, the positrons are trapped by dislocation defects and vacancy complexes inside crystallites. The size of vacancy complexes decreases with increasing annealing temperature in the interval Δ T = 20-300°C. However, at T = 360°C, the complexes start growing again. The dependence of S-parameter on W-parameter derived from the Doppler broadening spectroscopy has two parts with different inclinations to axes that correspond to different types of primary centers of positron trapping in submicrocrystalline nickel. It has been elucidated that, at recovery stage in the temperature interval Δ T = 20-180°C, the main centers of positron trapping are low-angle boundaries enriched by impurities, while at in situ recrystallization stage in the temperature interval Δ T = 180-360°C, the primary centers of positron trapping are low-angle boundaries.

  4. Positron lifetime study of electron-irradiated epoxy resins

    International Nuclear Information System (INIS)

    Two bisphenol-A type epoxy resins were irradiated by electron beam and studied afterwards by positron lifetime spectroscopy. An interesting result is that despite of the considerable amount of free-radicals, no inhibition of positronium formation was observed in the two epoxies. Nevertheless, several serious differences were detected between the studied polymers. The results suggest that the radiation-resistant properties of epoxies depend strongly on the amount of the curing agent. (author) 8 refs.; 2 figs

  5. Effect of Copper on the Carrier Lifetime in Black Silicon

    DEFF Research Database (Denmark)

    Porte, Henrik; Turchinovich, Dmitry; Persheyev, Saydulla;

    2011-01-01

    Black silicon is produced by laser annealing of a-Si:H films. During annealing, silicon microstructures are formed on the surface. We use time-resolved terahertz spectroscopy to study the photoconductivity dynamics in black silicon. We find that when a copper film is deposited on top of the a......-Si:H layer prior to laser annealing, the carrier lifetime of black silicon is significantly reduced....

  6. The Work of a Lifetime

    Science.gov (United States)

    Olson, Cathy Applefeld

    2012-01-01

    If there's one message that Joan Hillsman wants to get across to music directors, it's this: Teaching is a lifetime commitment. Hillsman is a longtime music educator, African-American music historian, author, consultant, music producer, clinician, radio show host, and current member of the Academic Board of the James Cleveland Gospel Music…

  7. Pseudoscalar boson production in e+e- annihilation

    International Nuclear Information System (INIS)

    A mechanism of pseudoscalar boson production by the heavy quark-antiquark pair via one-photon exchange in e+e- annihilation is studied. The total cross sections of this reaction and energy distributions of produced p0-boson are obtained

  8. The many faces of brane-flux annihilation

    CERN Document Server

    Gautason, Fridrik Freyr; Van Riet, Thomas

    2015-01-01

    Fluxes can decay via the nucleation of Brown-Teitelboim bubbles, but when the decaying fluxes induce D-brane charges this process must be accompanied with an annihilation of D-branes. This occurs via dynamics inside the bubble wall as was well described for (anti-)D3 branes branes annihilating against 3-form fluxes. In this paper we extend this to the other Dp branes with p smaller than seven. Generically there are two decay channels: one for the RR flux and one for the NSNS flux. The RR channel is accompanied by brane annihilation that can be understood from the Dp branes polarising into D(p+2) branes, whereas the NSNS channel corresponds to Dp branes polarising into NS5 branes or KK5 branes. We illustrate this with the decay of antibranes probing local toroidal throat geometries obtained from T-duality of the D6 solution in massive type IIA. We show that anti-Dp branes are metastable against annihilation in these backgrounds, at least at the probe level.

  9. New Limits on Thermally Annihilating Dark Matter from Neutrino Telescopes

    Science.gov (United States)

    Lopes, J.; Lopes, I.

    2016-08-01

    We used a consistent and robust solar model to obtain upper limits placed by neutrino telescopes, such as IceCube and Super-Kamiokande, on the dark matter-nucleon scattering cross-section, for a general model of dark matter with a velocity dependent (p-wave) thermally averaged cross-section. In this picture, the Boltzmann equation for the dark matter abundance is numerically solved, satisfying the dark matter density measured from the cosmic microwave background. We show that for lower cross-sections and higher masses, the dark matter annihilation rate drops sharply, resulting in upper bounds on the scattering cross-section that are one order of magnitude above those derived from a velocity independent (s-wave) annihilation cross-section. Our results show that upper limits on the scattering cross-section obtained from dark matter annihilating in the Sun are sensible to the uncertainty in current standard solar models, fluctuating by a maximum of 20% depending on the annihilation channel.

  10. The Isotropic Radio Background and Annihilating Dark Matter

    CERN Document Server

    Hooper, Dan; Jeltema, Tesla E; Linden, Tim; Profumo, Stefano; Slatyer, Tracy R

    2012-01-01

    Observations by ARCADE-2 and other telescopes sensitive to low frequency radiation have revealed the presence of an isotropic radio background with a hard spectral index. The intensity of this observed background is found to exceed the flux predicted from astrophysical sources by a factor of approximately 5-6. In this article, we consider the possibility that annihilating dark matter particles provide the primary contribution to the observed isotropic radio background through the emission of synchrotron radiation from electron and positron annihilation products. For reasonable estimates of the magnetic fields present in clusters and galaxies, we find that dark matter could potentially account for the observed radio excess, but only if it annihilates mostly to electrons and/or muons, and only if it possesses a mass in the range of approximately 5-50 GeV. For such models, the annihilation cross section required to normalize the synchrotron signal to the observed excess is sigma v ~ (0.4-30) x 10^-26 cm^3/s, sim...

  11. On the Direct Detection of Dark Matter Annihilation

    CERN Document Server

    Cherry, John F; Shoemaker, Ian M

    2015-01-01

    We investigate the direct detection phenomenology of a class of dark matter (DM) models in which DM does not directly interact with nuclei, {but rather} the products of its annihilation do. When these annihilation products are very light compared to the DM mass, the scattering in direct detection experiments is controlled by relativistic kinematics. This results in a distinctive recoil spectrum, a non-standard and or even {\\it absent} annual modulation, and the ability to probe DM masses as low as a $\\sim$10 MeV. We use current LUX data to show that experimental sensitivity to thermal relic annihilation cross sections has already been reached in a class of models. Moreover, the compatibility of dark matter direct detection experiments can be compared directly in $E_{min}$ space without making assumptions about DM astrophysics. Lastly, when DM has direct couplings to nuclei, the limit from annihilation to relativistic particles in the Sun can be stronger than that of conventional non-relativistic direct detect...

  12. New Limits on Thermally annihilating Dark Matter from Neutrino Telescopes

    CERN Document Server

    Lopes, José

    2016-01-01

    We used a consistent and robust solar model to obtain upper limits placed by neutrino telescopes, such as Ice- Cube and Super-Kamiokande, on the Dark Matter-nucleon scattering cross-section, for a general model of Dark Matter with a velocity dependent (p-wave) thermally averaged cross-section. In this picture, the Boltzmann equation for the Dark Matter abundance is numerically solved satisfying the Dark Matter density measured from the Cosmic Microwave Background (CMB). We show that for lower cross-sections and higher masses, the Dark Matter annihilation rate drops sharply, resulting in upper bounds on the scattering cross-section one order of magnitude above those derived from a velocity independent (s-wave) annihilation cross-section. Our results show that upper limits on the scattering cross-section obtained from Dark Matter annihilating in the Sun are sensible to the uncertainty in current standard solar models, fluctuating a maximum of 20 % depending on the annihilation channel.

  13. The SIRI stochastic model with creation and annihilation operators

    OpenAIRE

    Stollenwerk, Nico; Aguiar, Maira

    2008-01-01

    We generalize the well known formulation of the susceptibles, infected, susceptibles (SIS) spatial epidemics with creation and annihilation operators to the reinfection model including recovered which can be reinfected, the SIRI model, using ladder operators constructed from the Gell-Mann matrices known in quantum chromodynamics.

  14. A simple formula for the thermal pair annihilation line emissivity

    OpenAIRE

    Svensson, Roland; Larsson, Stefan; Poutanen, Juri

    1996-01-01

    We introduce a simple and convenient fitting formula for the thermal annihilation line from pair plasmas in cosmic sources. The fitting formula is accurate to 0.04\\% and is valid at all photon energies and temperatures of interest. The commonly used Gaussian line profile is not a good approximation for broader lines.

  15. Annihilation amplitudes and factorization in B to phi Kstar

    CERN Document Server

    Epele, L N; Szynkman, A

    2003-01-01

    We study the decay $B^\\pm\\to \\phi K^{\\ast\\pm}$, followed by the decay of the outgoing vector mesons into two pseudoscalars. The analysis of angular distributions of the decay products is shown to provide useful information about the annihilation contributions and possible tests of factorization.

  16. Nuclear excitation in positron-K-electron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Kaliman, Z.; Pisk, K.; Logan, B.A.

    1987-05-01

    We have calculated the cross section for nuclear excitation during positron-K-electron annihilation. The calculations allow for the effect of the nuclear Coulomb field and for relativistic effects. The results are compared to earlier predictions which were derived using the Born approximation, and to renormalized Born approximation predictions. Our calculated cross sections are well below the available experimental values.

  17. Detection of positron-atom bound states through resonant annihilation

    CERN Document Server

    Dzuba, V A; Gribakin, G F

    2010-01-01

    A method is proposed for detecting positron-atom bound states by observing Feshbach resonances in positron annihilation at electron volt energies. The method is applicable to a range of open-shell transition metal atoms which are likely to bind the positron: Si, Fe, Co, Ni, Ge, Tc, Ru, Rh, Sn, Sb, Ta, W, Os, Ir, and Pt.

  18. The Effects of Dark Matter Annihilation on Cosmic Reionization

    CERN Document Server

    Kaurov, Alexander A; Gnedin, Nickolay Y

    2015-01-01

    We revisit the possibility of constraining the properties of dark matter (DM) by studying the epoch of cosmic reionization. Previous studies have shown that DM annihilation was unlikely to have provided a large fraction of the photons that ionized the universe, but instead played a subdominant role relative to stars and quasars. The DM, however, begins to efficiently annihilate with the formation of primordial microhalos at $z\\sim100-200$, much earlier than the formation of the first stars. Therefore, if DM annihilation ionized the universe at even the percent level over the interval $z \\sim 20-100$, it can leave a significant imprint on the global optical depth, $\\tau$. Moreover, we show that cosmic microwave background (CMB) polarization data and future 21 cm measurements will enable us to more directly probe the DM contribution to the optical depth. In order to compute the annihilation rate throughout the epoch of reionization, we adopt the latest results from structure formation studies and explore the im...

  19. Constraints on Dark Matter annihilation from M87

    International Nuclear Information System (INIS)

    Clusters of galaxies and their central cD galaxies are prime targets for observing indirect signatures of dark matter annihilation owing to their huge mass concentration. The main challenge is to discriminate between high-energy emission of different origins, for example the emission from active galactic nuclei as a result of accretion of mass by the supermassive black hole at the centre of the host galaxy and the emission due to dark matter annihilation. In addition to prompt gamma rays, dark matter annihilation products can include energetic electrons and positrons which inverse Compton scatter with the cosmic microwave background or with starlight photon fields to produce potentially detectable signals going from the soft to the hard X-ray energy band. In order to constrain the dark matter annihilation emission component, a state-of-the-art radiation code for the M87 jet emission and a generic description of the prompt and secondary inverse-Compton gamma rays due to generic weakly interacting dark matter particles are employed and possibilities for identifying the signatures of dark matter in the multi-wavelength spectrum of M87 are investigated.

  20. Positron annihilation spectra and core-electron enhancement factors

    CERN Document Server

    Green, D G

    2014-01-01

    $\\gamma$-spectra for positron annihilation with core and valence electrons in the noble gases are calculated using many-body theory (MBT). We show that proper inclusion of core annihilation is crucial to accurately describe the measured spectra [Phys. Rev. Lett. 79, 39 (1997)]. We use the MBT to calculate `exact' enhancement factors $\\bar{\\gamma}_{n\\ell}$ for annihilation on individual $n\\ell$ subshells. They parameterize the important effects of (non-local) short-range electron-positron correlations, including the non-perturbative process of virtual positronium formation. We show that they follow a simple and physically motivated scaling with the subshell ionization energy $I_{n\\ell}$: $\\bar{\\gamma}_{n\\ell}=1+\\sqrt{A/I_{n\\ell}}+(B/I_{n\\ell})^{\\beta}$, where $A$, $B$ and $\\beta$ are positive constants. We suggest that this formula can be used with relatively simple independent-particle-approximation calculations to determine accurate core-annihilation spectra for atoms across the periodic table and in condens...

  1. QED at fifth order in e+e- annihilation

    International Nuclear Information System (INIS)

    We calculate the cross-section for the production of e+e-γγγ in e+e- annihilation. The results are in agreement with the first observation of such a process by the ASP experiment at SLAC. The calculation also provides another example of the power of 'spinor techniques' in calculating Feynman amplitudes. (author)

  2. Proton irradiation effects in Zr-1.0 Nb-1.0 Sn-0.1 Fe probed by positron annihilation

    International Nuclear Information System (INIS)

    Samples of a new zirconium-based alloy (zirlo) were proton-irradiated and the structural defects were characterised by positron annihilation. The lifetimes of positrons trapped in the defects generated at different doses of irradiation appeared to suggest significant interaction of the defects with the substitutional solute atoms. The isochronal recovery of the sample irradiated at the highest dose showed three distinct stages. The initial annealing of free vacancy clusters was followed by a solute atom-vacancy dissociation stage above 673 K. The vacancies thus released annealed out at 973 K. (orig.)

  3. Proton irradiation effects in Zr-1.0 Nb-1.0 Sn-0.1 Fe probed by positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Mukherjee, P.; Sen Pintu; Barat, P.; Bandyopadhyay, S.K. [Variable Energy Cyclotron Centre, Calcutta (India); Nambissan, P.M.G. [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Calcutta 700 064 (India)

    1999-08-01

    Samples of a new zirconium-based alloy (zirlo) were proton-irradiated and the structural defects were characterised by positron annihilation. The lifetimes of positrons trapped in the defects generated at different doses of irradiation appeared to suggest significant interaction of the defects with the substitutional solute atoms. The isochronal recovery of the sample irradiated at the highest dose showed three distinct stages. The initial annealing of free vacancy clusters was followed by a solute atom-vacancy dissociation stage above 673 K. The vacancies thus released annealed out at 973 K. (orig.) 17 refs.

  4. Cosmological constraints on dark matter annihilation and decay: Cross-correlation analysis of the extragalactic $\\gamma$-ray background and cosmic shear

    OpenAIRE

    Shirasaki, Masato; Macias, Oscar; Horiuchi, Shunsaku; Shirai, Satoshi; Yoshida, Naoki

    2016-01-01

    We derive constraints on dark matter (DM) annihilation cross section and decay lifetime from cross-correlation analyses of the data from Fermi-LAT and weak lensing surveys that cover a wide area of $\\sim660$ squared degrees in total. We improve upon our previous analyses by using an updated extragalactic $\\gamma$-ray background data reprocessed with the Fermi Pass 8 pipeline, and by using well-calibrated shape measurements of about twelve million galaxies in the Canada-France-Hawaii Lensing S...

  5. Study of $ \\bar{p} $ and $ \\bar{n} $ annihilations at LEAR with OBELIX, a large acceptance and high resolution detector based on the Open Axial Field Spectrometer

    CERN Multimedia

    2002-01-01

    % PS201 Study of $\\bar{p}$ and $\\bar{n}$ annihilations at LEAR with OBELIX, a large acceptance and high resolution detector based on the Open Axial Field Spectrometer \\\\ \\\\OBELIX is designed to study exclusive final states of antiproton and antineutron annihilations at low energies with protons and nuclei. \\\\ \\\\The physics motivations of the experiment are:\\\\ \\\\\\begin{itemize} \\item (gg, ggg), hybrids ($ q \\bar{q} g $), multiquarks ($ q q \\bar{q} \\bar{q} $) and light mesons ($ q \\bar{q} $) produced in $ N \\bar{N} $ annihilations and study of their spectroscopy and decays. Also broad structures will be searched for by comparing identical decay modes in exclusive final states of the same type occuring from initial states with different angular momentum or isospin. \\item Study of the dynamics of $ N \\bar{N} $ interactions and of the dependence of the final and intermediate resonant states of annihilation upon the quantum numbers of the initial $ N \\bar{N} $ state (angular momentum: S and P-wave in $\\bar{p}p $ at...

  6. Influence of structure of a crosslinked epoxy resin on its properties studied by positron annihilation and other methods

    International Nuclear Information System (INIS)

    Positron annihilation has been applied to study samples of two crosslinked epoxy resins: diglycidyl ether of bisphenol A (Epikote 828) and polyglycidyl-ether of phenol-formaldehyde novolac (Epikote 155) cured with 4,4'-diamino-diphenylo-methane (MDA), phenol-formaldehyde novolac resin (Novolac Z) and bisphenol A (formaldehyde resin). Results of measurements of positron lifetime spectra were compared with the ones coming from DMTA, flexural strength testing and density measurements. The most important features of samples (glass transition temperature, storage modulus, flexural strength, crosslinking density and tan δ) proved to be correlated with the product Ι3 x v-bar, proportional to the fractional free volume in samples. Values of v-bar have been estimated from the values of τ3, the longest lifetime in positron lifetime spectra. Ι3 corresponds to the intensity of the longest-lived component in them. Distributions of free volume radii reconstructed in the basis of PAL measurements are given for all samples. The influences of structure of both cured resin and the curing agent on the properties of the crosslinked products is clearly seen from the presented results. (author)

  7. Synthesis and characterization of magnesium oxide nanocrystallites and probing the vacancy-type defects through positron annihilation studies

    Science.gov (United States)

    Das, Anjan; Mandal, Atis Chandra; Roy, Soma; Prashanth, Pendem; Ahamed, Sk Izaz; Kar, Subhrasmita; Prasad, Mithun S.; Nambissan, P. M. G.

    2016-09-01

    Magnesium oxide nanocrystallites exhibit certain abnormal characteristics when compared to those of other wide band gap oxide semiconductors in the sense they are most prone to water absorption and formation of a hydroxide layer on the surface. The problem can be rectified by heating and pure nanocrystallites can be synthesized with controllable sizes. Inevitably the defect properties are distinctly divided between two stages, the one with the hydroxide layer (region I) and the other after the removal of the layer by annealing (region II). The lattice parameters, the optical band gap and even the positron annihilation characteristics are conspicuous by their distinct behavior in the two stages of the surface configurations of nanoparticles. While region I was specific with the formation of positronium-hydrogen complexes that drastically altered the defect-specific positron lifetimes, pick-off annihilation of orthopositronium atoms marked region II. The vacancy clusters within the nanocrystallites also trapped positrons. They agglomerated due to the effect of the higher temperatures and resulted in the growth of the nanocrystallites. The coincidence Doppler broadening spectroscopic measurements supported these findings and all the more indicated the trapping of positrons additionally into the neutral divacancies and negatively charged trivacancies. This is apart from the Mg2+ monovacancies which acted as the dominant trapping centers for positrons.

  8. Thermally-induced crystallization behaviour of 80GeSe2–20Ga2Se3 glass as probed by combined X-ray diffraction and PAL spectroscopy

    International Nuclear Information System (INIS)

    Highlights: • Chalcogenide Ge–Ga–Se glasses were annealed at 380 °C for 10, 25 and 50 h. • Crystallization of glasses during annealing indicates formation of crystals. • Structural changes are described by two-state positron trapping model. • Modification leading to nucleation and fragmentation of free volume of glasses. • The Ge–Ga–Se systems cannot be classified as typical pseudo-binary system. -- Abstract: Crystallization behaviour of 80GeSe2–20Ga2Se3 glass caused by thermal annealing at 380 °C for 10, 25 and 50 h are studied using X-ray diffraction and positron annihilation lifetime spectroscopy. It is shown that the structural changes caused by crystallization can be adequately described by positron trapping modes determined within two-state model. The observed changes in defect-related component in the fit of experimental positron lifetime spectra for annealed glasses testifies in a favour of structural fragmentation of larger free volume entities into smaller ones with preceding nucleation in the initial stage of thermal annealing. Because of strong deviation in defect-free bulk positron lifetime from corresponding additive values proper to boundary constituents, the studied glasses cannot be considered as typical representatives of pseudo-binary cut-section

  9. Thermally-induced crystallization behaviour of 80GeSe{sub 2}–20Ga{sub 2}Se{sub 3} glass as probed by combined X-ray diffraction and PAL spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Shpotyuk, O., E-mail: shpotyuk@novas.lviv.ua [Scientific Research Company “Carat”, 202, Stryjska str., Lviv 79031 (Ukraine); Institute of Physics of Jan Dlugosz University, 13/15, al. Armii Krajowej, Czestochowa 42201 (Poland); Calvez, L.; Petracovschi, E. [Equipe Verres et Céramiques, UMR-CNRS 6226, Institute des Sciences chimiques de Rennes, Université de Rennes 1, 35042 Rennes Cedex (France); Klym, H. [Lviv polytechnic National University, 12 Bandera str., Lviv 79013 (Ukraine); Ingram, A. [Physics Faculty of Opole University of Technology, 75, Ozimska str., Opole 45370 (Poland); Demchenko, P. [Ivan Franko National University of Lviv, 6, Kyryla and Mefodiya Str., Lviv 79005 (Ukraine)

    2014-01-05

    Highlights: • Chalcogenide Ge–Ga–Se glasses were annealed at 380 °C for 10, 25 and 50 h. • Crystallization of glasses during annealing indicates formation of crystals. • Structural changes are described by two-state positron trapping model. • Modification leading to nucleation and fragmentation of free volume of glasses. • The Ge–Ga–Se systems cannot be classified as typical pseudo-binary system. -- Abstract: Crystallization behaviour of 80GeSe{sub 2}–20Ga{sub 2}Se{sub 3} glass caused by thermal annealing at 380 °C for 10, 25 and 50 h are studied using X-ray diffraction and positron annihilation lifetime spectroscopy. It is shown that the structural changes caused by crystallization can be adequately described by positron trapping modes determined within two-state model. The observed changes in defect-related component in the fit of experimental positron lifetime spectra for annealed glasses testifies in a favour of structural fragmentation of larger free volume entities into smaller ones with preceding nucleation in the initial stage of thermal annealing. Because of strong deviation in defect-free bulk positron lifetime from corresponding additive values proper to boundary constituents, the studied glasses cannot be considered as typical representatives of pseudo-binary cut-section.

  10. Lifetime of Doubly Charmed Baryons

    Institute of Scientific and Technical Information of China (English)

    XU Xue-Fen; CHANG Chao-Hsi; LI Tong; LI Xue-Qian; WANG Yu-Ming

    2008-01-01

    In this work, we evaluate the lifetimes of the doubly charmed baryons cc+, cc++, and Ωcc+. We carefully calculate the non-spectator contributions at the quark level, where the Cabibbo-suppressed diagrams are also included. The hadronic matrix elements are evaluated in the simple non-relativistic harmonic oscillator model. Our numerical results are generally consistent with that obtained by other authors who used the diquark model. However, all the theoretical predictions on the lifetimes are one order larger than the upper limit set by the recent SELEX measurement. This discrepancy would be clarified by the future experiment. If more accurate experiment still confirms the value of the SELEX collaboration, there must be some unknown mechanism to be explored.

  11. Fluorescence lifetime standards for time and frequency domain fluorescence spectroscopy

    NARCIS (Netherlands)

    Boens, N.; Qin, Wenwu; Basaric, N.; Hofkens, J.; Ameloot, M.; Pouget, J.; Lefevre, J.P.; Valeur, B.; Gratton, E.; Ven, van de M.; Silva jr., D.; Engelborghs, Y.; Willaert, K.; Sillen, A.; Rumbles, G.; Philips, D.; Visser, A.J.W.G.; Hoek, van A.; Lakowicz, J.R.; Malak, H.; Gryczynski, I.; Szabo, A.G.; Krajcarski, D.T.; Tamai, N.; Miura, A.

    2007-01-01

    A series of fluorophores with single-exponential fluorescence decays in liquid solution at 20 C were measured independently by nine laboratories using single-photon timing and multifrequency phase and modulation fluorometry instruments with lasers as excitation source. The dyes that can serve as flu

  12. Spectrally resolved fluorescent lifetime imaging

    OpenAIRE

    Hanley, Quentin S.

    2008-01-01

    Placing an imaging spectrograph or related components capable of generating a spectrum between a microscope and the image intensifier of a conventional fluorescence lifetime imaging (FLIM) system creates a spectrally resolved FLIM (SFLIM). This arrangement provides a number of opportunities not readily available to conventional systems using bandpass filters. The examples include: simultaneous viewing of multiple fluorophores; tracking of both the donor and acceptor; and observation of a rang...

  13. Lifetime reproductive effort in humans

    OpenAIRE

    Burger, Oskar; Walker, Robert; Hamilton, Marcus J.

    2009-01-01

    Lifetime reproductive effort (LRE) measures the total amount of metabolized energy diverted to reproduction during the lifespan. LRE captures key components of the life history and is particularly useful for describing and comparing the life histories of different organisms. Given a simple energetic production constraint, LRE is predicted to be similar in value for very different life histories. However, humans have some unique ecological characteristics that may alter LRE, such as the long p...

  14. Lifetime of MCP-PMTs

    Science.gov (United States)

    Lehmann, A.; Britting, A.; Eyrich, W.; Pfaffinger, M.; Uhlig, F.; Belias, A.; Dzhygadlo, R.; Gerhardt, A.; Götzen, K.; Kalicy, G.; Krebs, M.; Lehmann, D.; Nerling, F.; Patsyuk, M.; Peters, K.; Schepers, G.; Schmitt, L.; Schwarz, C.; Schwiening, J.; Traxler, M.; Zühlsdorf, M.; Düren, M.; Etzelmüller, E.; Föhl, K.; Hayrapetyan, A.; Kröck, B.; Merle, O.; Rieke, J.; Schmidt, M.; Cowie, E.; Keri, T.; Achenbach, P.; Cardinali, M.; Hoek, M.; Lauth, W.; Schlimme, S.; Sfienti, C.; Thiel, M.

    2016-05-01

    The hadron identification in the PANDA experiment at FAIR will be done with DIRC detectors. Because of design and space reasons the sensors of the DIRCs have to be placed inside the strong magnetic field of the solenoid. As the favored photon sensors microchannel-plate photomultipliers (MCP-PMTs) were identified. However, these devices showed serious aging problems until very recently, which manifest themselves by a fast degrading quantum efficiency (QE) of the photo cathode (PC). This is mainly due to feedback ions from the residual gas. In this paper we discuss the recently accomplished huge improvements in the lifetime of MCP-PMTs. With innovative countermeasures applied to the MCP-PMTs in the attempt to reduce the aging effects the manufacturers were able to increase the lifetime of MCP-PMT prototypes by almost two orders of magnitude compared to the former commercially available devices. Our group has studied the aging of MCP-PMTs for more than four years by simultaneously illuminating different types of lifetime-enhanced MCP-PMTs at the same photon rate. Gain, dark count rate, and QE as a function of the wavelength and the PC surface were measured in regular time intervals and studied in dependence of the integrated anode charge. We observe that MCP-PMTs treated with an atomic layer deposition (ALD) technique are by far the best devices available now. A lifetime of up to 10 C/cm2 integrated anode charge was reached with these sensors. This is sufficient for both PANDA DIRCs.

  15. Personality, IQ, and Lifetime Earnings

    OpenAIRE

    Gensowski, Miriam

    2014-01-01

    Talented individuals are seen as drivers of long-term growth, but how do they realize their full potential? In this paper, I show that even in a group of high-IQ men and women, lifetime earnings are substantially influenced by their education and personality traits. I identify a previously undocumented interaction between education and traits in earnings generation, which results in important heterogeneity of the net present value of education. Personality traits directly affect men's earning...

  16. Migration Enthalpy of Thermal Vacancies by Positron Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    Emad A. Badawi

    2005-01-01

    @@ The trapping of positrons at vacancy site in some materials provide a new and sensitive method for the equilibrium determination of point defect migration enthalpy. Data are presented for commercial Al-Mg alloys and fitted to a model allowing presentation in the form of Arrhenius plots, hence the migration enthalpy H m iv can bedetermined by the positron annihilation lifetime technique. The results show that the value of Hm iv increases as the concentration of Mg increases.

  17. Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells

    KAUST Repository

    Dimitrov, Stoichko

    2016-01-13

    The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.

  18. Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells

    Directory of Open Access Journals (Sweden)

    Stoichko D. Dimitrov

    2016-01-01

    Full Text Available The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.

  19. Positron annihilation in non-simple liquids. Normal hexane

    International Nuclear Information System (INIS)

    Positron lifetime measurements were carried out in normal hexane vs. temperature in the range of 12.5 - 62.5 deg C. The evaluation of the lifetime spectra indicates the presence of four lifetime components, as published first by Jacobsen et al. An attempt is made to interpret the properties of the longest-living two components in terms of the microscopic structure of the liquid. (author) 11 refs.; 3 figs

  20. Lifetimes of charm and beauty hadrons

    International Nuclear Information System (INIS)

    Recent results on the lifetimes of charm and beauty hadrons at the LEP collider experiment and at the fixed target experiments E653 are reviewed and discussed. The world average of b lifetime is now =1.29±0.05 ps. The exclusive lifetime measurements for b+, b-, b0 are presented. The lifetime difference among the different species of charm and of beauty hadrons are discussed. (author) 25 refs., 13 figs., 12 tabs

  1. Inequivalence of single-particle and population lifetimes in a cuprate superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Shuolong [SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States); Sobota, J. A. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Leuenberger, D. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States); He, Y. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States); Hashimoto, M. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Lu, D. H. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Eisaki, H. [National Institute of Advanced Industrial Science and Technology, Ibaraki (Japan); Kirchmann, P. S. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Shen, Z. -X. [SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States)

    2015-06-15

    We study optimally doped Bi-2212 (Tc=96 K) using femtosecond time- and angle-resolved photoelectron spectroscopy. Energy-resolved population lifetimes are extracted and compared with single-particle lifetimes measured by equilibrium photoemission. The population lifetimes deviate from the single-particle lifetimes in the low excitation limit by 1–2 orders of magnitude. Fundamental considerations of electron scattering unveil that these two lifetimes are in general distinct, yet for systems with only electron-phonon scattering they should converge in the low-temperature, low-fluence limit. As a result, the qualitative disparity in our data, even in this limit, suggests that scattering channels beyond electron-phonon interactions play a significant role in the electron dynamics of cuprate superconductors.

  2. On thermal corrections to near-threshold co-annihilation

    CERN Document Server

    Kim, Seyong

    2016-01-01

    We consider non-relativistic "dark" particles interacting through gauge boson exchange. At finite temperature, gauge exchange is modified in many ways: virtual corrections lead to Debye screening; real corrections amount to frequent scatterings of the heavy particles on light plasma constituents; mixing angles change. In a certain temperature and energy range, these effects are of order unity. Taking them into account in a resummed form, we estimate the near-threshold spectrum of kinetically equilibrated co-annihilating TeV scale particles. Weakly bound states are shown to "melt" below freeze-out, whereas with attractive strong interactions, relevant e.g. for gluinos, bound states boost the co-annihilation rate by a factor 4...80 with respect to the Sommerfeld estimate, thereby perhaps helping to avoid overclosure of the universe. Modestly non-degenerate dark sector masses and a way to combine the contributions of channels with different gauge and spin structures are also discussed.

  3. Antiprotons from dark matter annihilation in the Galaxy: astrophysical uncertainties

    CERN Document Server

    Evoli, Carmelo; Grasso, Dario; Maccione, Luca; Ullio, Piero

    2011-01-01

    The latest years have seen steady progresses in WIMP dark matter (DM) searches, with hints of possible signals suggested by both direct and indirect detection experiments. Antiprotons can play a key role validating those interpretations since they are copiously produced by WIMP annihilations in the Galactic halo, and the secondary antiproton background produced by Cosmic Ray (CR) interactions is predicted with fair accuracy and matches the observed spectrum very well. Using the publicly available numerical DRAGON code, we reconsider antiprotons as a tool to constrain DM models discussing its power and limitations. We provide updated constraints on a wide class of annihilating DM models by comparing our predictions against the most up-to-date ap measurements, taking also into account the latest spectral information on the p, He and other CR nuclei fluxes. Doing that, we probe carefully the uncertainties associated to both secondary and DM originated antiprotons, by using a variety of distinctively different as...

  4. The Dark Matter Annihilation Boost from Low-Temperature Reheating

    CERN Document Server

    Erickcek, Adrienne L

    2015-01-01

    The evolution of the Universe between inflation and the onset of Big Bang Nucleosynthesis is difficult to probe and largely unconstrained. This ignorance profoundly limits our understanding of dark matter: we cannot calculate its thermal relic abundance without knowing when the Universe became radiation dominated. Fortunately, small-scale density perturbations provide a probe of the early Universe that could break this degeneracy. If dark matter is a thermal relic, density perturbations that enter the horizon during an early matter-dominated era grow linearly with the scale factor prior to reheating. The resulting abundance of substructure boosts the annihilation rate by several orders of magnitude, which can compensate for the smaller annihilation cross sections that are required to generate the observed dark matter density in these scenarios. In particular, thermal relics with masses less than a TeV that thermally and kinetically decouple prior to reheating may already be ruled out by Fermi-LAT observations...

  5. High nuclear temperatures by antimatter-matter annihilation

    International Nuclear Information System (INIS)

    It is suggested that the quark-gluon phase be created through the use of antiproton or antideuteron beams. The first advantage to this method, using higher energy antiprotons than 1.5 GeV/c, is that the higher momenta antiprotons penetrate more deeply so that mesons produced are more nearly contained within the nucleus. Another advantage is that the annihilation products are very forward-peaked and tend to form a beam of mesons so that the energy density does not disperse very rapidly. Calculations were performed using the intranuclear cascade to try to follow the process of annihilation in some detail. The intranuclear cascade type calculation method is compared to the hydrodynamic approach. 8 refs., 8 figs

  6. Dark Stars and Boosted Dark Matter Annihilation Rates

    CERN Document Server

    Ilie, Cosmin; Spolyar, Douglas

    2010-01-01

    Dark Stars (DS) may constitute the first phase of stellar evolution, powered by dark matter (DM) annihilation. We will investigate here the properties of DS assuming the DM particle has the required properties to explain the excess positron and elec- tron signals in the cosmic rays detected by the PAMELA and FERMI satellites. Any possible DM interpretation of these signals requires exotic DM candidates, with an- nihilation cross sections a few orders of magnitude higher than the canonical value required for correct thermal relic abundance for Weakly Interacting Dark Matter can- didates; additionally in most models the annihilation must be preferentially to lep- tons. Secondly, we study the dependence of DS properties on the concentration pa- rameter of the initial DM density profile of the halos where the first stars are formed. We restrict our study to the DM in the star due to simple (vs. extended) adiabatic contraction and minimal (vs. extended) capture; this simple study is sufficient to illustrate depend...

  7. Dark matter annihilation bound from the diffuse gamma ray flux

    Energy Technology Data Exchange (ETDEWEB)

    Kachelriess, M.; /Norwegian U. Sci. Tech.; Serpico, P.D.; /Fermilab

    2007-07-01

    An upper limit on the total annihilation rate of dark matter (DM) has been recently derived from the observed atmospheric neutrino background. It is a very conservative upper bound based on the sole hypothesis that the DM annihilation products are the least detectable final states in the Standard Model (SM), neutrinos. Any other decay channel into SM particles would lead to stronger constraints. We show that comparable bounds are obtained for DM masses around the TeV scale by observations of the diffuse gamma ray flux by EGRET, because electroweak bremsstrahlung leads to non-negligible electromagnetic branching ratios, even if DM particles only couple to neutrinos at tree level. A better mapping and the partial resolution of the diffuse gamma-ray background into astrophysical sources by the GLAST satellite will improve this bound in the near future.

  8. High nuclear temperatures by antimatter-matter annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Gibbs, W.R.; Strottman, D.

    1985-01-01

    It is suggested that the quark-gluon phase be created through the use of antiproton or antideuteron beams. The first advantage to this method, using higher energy antiprotons than 1.5 GeV/c, is that the higher momenta antiprotons penetrate more deeply so that mesons produced are more nearly contained within the nucleus. Another advantage is that the annihilation products are very forward-peaked and tend to form a beam of mesons so that the energy density does not disperse very rapidly. Calculations were performed using the intranuclear cascade to try to follow the process of annihilation in some detail. The intranuclear cascade type calculation method is compared to the hydrodynamic approach. 8 refs., 8 figs. (LEW)

  9. Annihilating dark matter and the galactic positron excess

    CERN Document Server

    Maor, I

    2006-01-01

    The possibility that the Galactic dark matter is composed of neutralinos that are just above half the $Z^o$ mass is examined, in the context of the Galactic positron excess. In particular, we check if the anomalous bump in the cosmic ray positron to electron ratio at $10~GeV$ can be explained with the ``decay'' of virtual $Z^o$ bosons produced when the neutralinos annihilate. We find that the low energy behaviour of our prediction fits well the existing data. Assuming the neutralinos annihilate primarily in the distant density concentration in the Galaxy and allowing combination of older, diffused positrons with young free-streaming ones, produces a fit which is not satisfactory on its own but is significantly better than the one obtained with homogeneous injection.

  10. A Comprehensive Search for Dark Matter Annihilation in Dwarf Galaxies

    CERN Document Server

    Geringer-Sameth, Alex; Walker, Matthew G

    2014-01-01

    We present a new formalism designed to discover dark matter annihilation occurring in the Milky Way's dwarf galaxies. The statistical framework extracts all available information in the data by simultaneously combining observations of all the dwarf galaxies and incorporating the impact of particle physics properties, the distribution of dark matter in the dwarfs, and the detector response. The method performs maximally powerful frequentist searches and produces confidence limits on particle physics parameters. Probability distributions of test statistics under various hypotheses are constructed exactly, without relying on large sample approximations. The derived limits have proper coverage by construction and claims of detection are not biased by imperfect background modeling. We implement this formalism using data from the Fermi Gamma-ray Space Telescope to search for an annihilation signal in the complete sample of Milky Way dwarfs whose dark matter distributions can be reliably determined. We find that the...

  11. Strong CMB Constraint On P-Wave Annihilating Dark Matter

    CERN Document Server

    An, Haipeng; Zhang, Yue

    2016-01-01

    We consider a dark sector consisting of dark matter that is a Dirac fermion and a scalar mediator. This model has been extensively studied in the past. If the scalar couples to the dark matter in a parity conserving manner then dark matter annihilation to two mediators is dominated by the P-wave channel and hence is suppressed at very low momentum. The indirect detection constraint from the anisotropy of the Cosmic Microwave Background is usually thought to be absent in the model because of this suppression. In this letter we show that dark matter annihilation to bound states occurs through the S-wave and hence there is a constraint on the parameter space of the model from the Cosmic Microwave Background.

  12. Rapid thermal co-annihilation through bound states

    CERN Document Server

    Kim, Seyong

    2016-01-01

    The co-annihilation rate of heavy particles close to thermal equilibrium, which plays a role in many classic dark matter scenarios, can be "simulated" in QCD by considering the pair annihilation rate of a heavy quark and antiquark at a temperature of a few hundred MeV. We show that the so-called Sommerfeld factors, parameterizing the rate, can be defined and measured non-perturbatively within the NRQCD framework. Lattice measurements indicate a modest suppression in the octet channel, in reasonable agreement with perturbation theory, and a large enhancement in the singlet channel, much above the perturbative prediction. We suggest that the additional enhancement originates from bound state formation and subsequent decay, omitted in previous estimates of thermal Sommerfeld factors, which were based on Boltzmann equations governing single-particle phase space distributions.

  13. Unified treatment of hadronic annihilation and protonium formation in slow collisions of antiprotons with hydrogen atoms

    Science.gov (United States)

    Sakimoto, Kazuhiro

    2013-07-01

    Antiproton (p¯) collisions with hydrogen atoms, resulting in the hadronic process of particle-antiparticle annihilation and the atomic process of protonium (p¯p) formation (or p¯ capture), are investigated theoretically. As the collision energy decreases, the collision time required for the p¯ capture becomes necessarily longer. Then, there is the possibility that the p¯-p annihilation occurs significantly before the p¯ capture process completes. In such a case, one can no longer consider the annihilation decay separately from the p¯ capture process. The present study develops a rigorous unified quantum-mechanical treatment of the annihilation and p¯ capture processes. For this purpose, an R-matrix approach for atomic collisions is extended to have complex-valued R-matrix elements allowing for the hadronic annihilation. Detailed calculations are carried out at low collision energies ranging from 10-8 to 10-1 eV, and the annihilation and the p¯ capture (total and product-state selected) cross sections are reported. Consideration is given to the difference between the direct annihilation occurring during the collision and the annihilation of p¯p occurring after the p¯ capture. The present annihilation process is also compared with the annihilation in two-body p¯+p collisions.

  14. Antiproton-neon annihilation at 57 MeV/c

    CERN Document Server

    Bianconi, A; Bussa, M P; Lodi-Rizzini, E; Venturelli, L; Zenoni, A; Pontecorvo, G B; Guaraldo, C; Balestra, F; Busso, L; Colantoni, M L; Ferrero, A; Ferrero, L; Grasso, A; Maggiora, A; Maggiora, M G; Piragino, G; Tosello, F

    2000-01-01

    The pNe annihilation cross section is measured for the first time in the momentum interval (53/63) MeV/c. About 9000 pictures collected by the Streamer Chamber Collaboration (PS179) at LEAR-CERN have been scanned. Four events are found, corresponding to sigma /sub ann /=2210+or-1105 mb. The result is compared to the set of measurements presently available in the region of low p momentum. (18 refs).

  15. Role of combination vibrations in resonant positron annihilation

    OpenAIRE

    Young, J A; Gribakin, Gleb; Lee, C. M. R.; Surko, C.M.

    2008-01-01

    Positrons can attach to molecules via vibrational Feshbach resonances, leading to very large annihilation rates. The predictions of a recent theory for this process are validated for deuterated methyl halides where all modes are dipole coupled to the incident positron. Data and analysis are presented for methanol and ethylene, demonstrating the importance of combination and overtone resonances and the ability of the theory to account for these features. The mechanism for these resonances and ...

  16. The three-jet rate in \\(e^{+}e^{-}\\) annihilation

    CERN Document Server

    Lovett-Turner, C N

    1994-01-01

    Abstract: Progress has been made on the calculation of \\(R_{3}\\), the three-jet rate in \\(e^{+}e^{-}\\) annihilation, in the \\(k_\\bot \\) (Durham) scheme. Using the coherent branching formalism \\cite{b,c,d}, an explicit expression for \\(R_{3}\\) is calculated. In this, leading and next-to-leading large logarithms (LL and NLL) are resummed to all orders in QCD perturbation theory. In addition to exponentials an error function is involved.

  17. Comments on charm production in electron positron annihilation

    International Nuclear Information System (INIS)

    The circumstances are discussed in which the production of D anti D: DD*: D* anti D* in electron positron annihilation is expected to be in the ratio 1:4:7 suggested by counting the available spin states. The physical significance of the requisite assumptions is discussed. The importance of taking into account the finite detector acceptance is stressed and tests for a possible 3D1 component in the D* are proposed. (author)

  18. Dark Matter Annihilations in the Large Magellanic Cloud

    OpenAIRE

    Gondolo, P.

    1993-01-01

    The flat rotation curve obtained for the outer star clusters of the Large Magellanic Cloud is suggestive of an LMC dark matter halo. From the composite HI and star cluster rotation curve, I estimate the parameters of an isothermal dark matter halo added to a `maximum disk.' I then examine the possibility of detecting high energy gamma-rays from non-baryonic dark matter annihilations in the central region of the Large Magellanic Cloud.

  19. Precision Measurements in Electron-Positron Annihilation: Theory and Experiment

    CERN Document Server

    Chetyrkin, Konstantin

    2016-01-01

    Theory results on precision measurements in electron-positron annihilation at low and high energies are collected. These cover pure QCD calculations as well as mixed electroweak and QCD results, involving light and heavy quarks. The impact of QCD corrections on the $W$-boson mass is discussed and, last not least, the status and the perspectives for the Higgs boson decay rate into $b\\bar b$, $c\\bar c$ and into two gluons.

  20. Gamma Rays from Top-Mediated Dark Matter Annihilations

    OpenAIRE

    Jackson, C.B.(Department of Physics, University of Texas at Arlington, Arlington, TX 76019, USA); Servant, Géraldine; Shaughnessy, Gabe; Tim M.P. Tait; Taoso, Marco

    2013-01-01

    Lines in the energy spectrum of gamma rays are a fascinating experimental signal, which are often considered "smoking gun" evidence of dark matter annihilation. The current generation of gamma ray observatories are currently closing in on parameter space of great interest in the context of dark matter which is a thermal relic. We consider theories in which the dark matter's primary connection to the Standard Model is via the top quark, realizing strong gamma ray lines consistent with a therma...

  1. Generating X-ray lines from annihilating dark matter

    CERN Document Server

    Dudas, Emilian; Mambrini, Yann

    2014-01-01

    We propose different scenarios where a keV dark matter annihilates to produce a monochromatic signal. The process is generated through the exchange of a light scalar of mass of order 300 keV - 50 MeV coupling to photon through loops or higher dimensional operators. For natural values of the couplings and scales, the model can generate a gamma-ray line which can fit with the recently identified 3.5 keV X-ray line.

  2. Complete light annihilation in an ultrathin layer of gold nanoparticles.

    Science.gov (United States)

    Svedendahl, Mikael; Johansson, Peter; Käll, Mikael

    2013-07-10

    We experimentally demonstrate that an incident light beam can be completely annihilated in a single layer of randomly distributed, widely spaced gold nanoparticle antennas. Under certain conditions, each antenna dissipates more than 10 times the number of photons that enter its geometric cross-sectional area. The underlying physics can be understood in terms of a critical coupling to localized plasmons in the nanoparticles or, equivalently, in terms of destructive optical Fano interference and so-called coherent absorption. PMID:23806090

  3. Experimental study of jets in electron-positron-annihilation

    International Nuclear Information System (INIS)

    Data on hadron production by e+e--annihilation at c.m. energies between 30 GeV and 36 GeV are presented and compared with two models both based on first order QCD but using different schemes for the fragmentation of quarks and gluons into hadrons. In one model the fragmentation proceeds along the parton momenta, in the other along the colour-anticolour axes. The data are reproduced better by fragmentation along the colour axes. (orig.)

  4. Compton-backscattered annihilation radiation from the Galactic Center region

    Science.gov (United States)

    Smith, D. M.; Lin, R. P.; Feffer, P.; Slassi, S.; Hurley, K.; Matteson, J.; Bowman, H. B.; Pelling, R. M.; Briggs, M.; Gruber, D.

    1993-01-01

    On 1989 May 22, the High Energy X-ray and Gamma-ray Observatory for Nuclear Emissions, a balloon-borne high-resolution germanium spectrometer with an 18-deg FOV, observed the Galactic Center (GC) from 25 to 2500 keV. The GC photon spectrum is obtained from the count spectrum by a model-independent method which accounts for the effects of passive material in the instrument and scattering in the atmosphere. Besides a positron annihilation line with a flux of (10.0 +/- 2.4) x 10 exp -4 photons/sq cm s and a full width at half-maximum (FWHM) of (2.9 + 1.0, -1.1) keV, the spectrum shows a peak centered at (163.7 +/- 3.4) keV with a flux of (1.55 +/- 0.47) x 10 exp -3 photons/sq cm s and a FWHM of (24.4 +/- 9.2) keV. The energy range 450-507 keV shows no positronium continuum associated with the annihilation line, with a 2-sigma upper limit of 0.90 on the positronium fraction. The 164 keV feature is interpreted as Compton backscatter of broadened and redshifted annihilation radiation, possibly from the source 1E 1740.7-2942.

  5. Dark matter annihilation via Higgs and gamma-ray channels

    Science.gov (United States)

    Chan, Man Ho

    2016-09-01

    Recent studies show that the GeV gamma-ray excess signal from the Milky Way center can be best explained by ˜ 40 GeV dark matter annihilating via bbar{b} channel. However, the recent observations of the nearby Milky Way dwarf spheroidal satellite galaxies by Fermi-LAT and the radio observations of the Milky Way center and the M31 galaxy tend to rule out this proposal. In this article, we discuss the possibility of the dark matter interpretation of the GeV gamma-ray excess by proposing 130 GeV dark matter annihilating via both Higgs and gamma-ray channels. Recent analyses show that dark matter annihilating via Higgs channel can satisfactorily explain the Milky Way GeV gamma-ray excess observed. We show that this model can satisfy the upper limits of the gamma-ray constraint of the Milky Way dwarf spheroidal satellite galaxies and the constraint from the radio observations of the M31 galaxy.

  6. CALET's sensitivity to Dark Matter annihilation in the galactic halo

    Science.gov (United States)

    Motz, H.; Asaoka, Y.; Torii, S.; Bhattacharyya, S.

    2015-12-01

    CALET (Calorimetric Electron Telescope), installed on the ISS in August 2015, directly measures the electron+positron cosmic rays flux up to 20 TeV. With its proton rejection capability of 1 : 105 and an aperture of 1200 cm2· sr, it will provide good statistics even well above one TeV, while also featuring an energy resolution of 2%, which allows it to detect fine structures in the spectrum. Such structures may originate from Dark Matter annihilation or decay, making indirect Dark Matter search one of CALET's main science objectives among others such as identification of signatures from nearby supernova remnants, study of the heavy nuclei spectra and gamma astronomy. The latest results from AMS-02 on positron fraction and total electron+positron flux can be fitted with a parametrization including a single pulsar as an extra power law source with exponential cut-off, which emits an equal amount of electrons and positrons. This single pulsar scenario for the positron excess is extrapolated into the TeV region and the expected CALET data for this case are simulated. Based on this prediction for CALET data, the sensitivity of CALET to Dark Matter annihilation in the galactic halo has been calculated. It is shown that CALET could significantly improve the limits compared to current data, especially for those Dark Matter candidates that feature a large fraction of annihilation directly into e+ + e-, such as the LKP (Lightest Kaluza-Klein particle).

  7. Antiproton constraints on dark matter annihilations from internal electroweak bremsstrahlung

    International Nuclear Information System (INIS)

    If the dark matter particle is a Majorana fermion, annihilations into two fermions and one gauge boson could have, for some choices of the parameters of the model, a non-negligible cross-section. Using a toy model of leptophilic dark matter, we calculate the constraints on the annihilation cross-section into two electrons and one weak gauge boson from the PAMELA measurements of the cosmic antiproton-to-proton flux ratio. Furthermore, we calculate the maximal astrophysical boost factor allowed in the Milky Way under the assumption that the leptophilic dark matter particle is the dominant component of dark matter in our Universe. These constraints constitute very conservative estimates on the boost factor for more realistic models where the dark matter particle also couples to quarks and weak gauge bosons, such as the lightest neutralino which we also analyze for some concrete benchmark points. The limits on the astrophysical boost factors presented here could be used to evaluate the prospects to detect a gamma-ray signal from dark matter annihilations at currently operating IACTs as well as in the projected CTA

  8. Modulation gamma resonance spectroscopy

    International Nuclear Information System (INIS)

    Possibility to control dynamic processes in a matter through gamma-resonance modulation by high-frequency external variable fields in excess of inverse lifetimes of the Moessbauer nuclei excited states, that is, within the megahertz frequency range lies in the heart of the modulation gamma-resonance spectroscopy. Through the use of the gamma-resonance process theoretical analysis methods and of the equation solution method for the density matrix with the secondary quantization of gamma-radiation field one attacks the problems dealing with the effect of both variable fields and relaxation on gamma-resonance. One has studied the gamma-radiation ultrasound modulation stages. One points out a peculiar role of the gamma-magnetic resonance effect in modulation gamma resonance spectroscopy formation. One forecasts development of the modulation gamma-resonance spectroscopy into the nonlinear gamma-resonance spectroscopy

  9. Estimation of luminescence lifetime in frequency domain

    Institute of Scientific and Technical Information of China (English)

    Zhang Fu-Jun; Xu Zheng; Zhao Su-Ling; Lou Zhi-Dong; Yang Sheng-Yi; Xu Xu-Rong

    2006-01-01

    Absorption is the origin of luminescence. But it must be noticed that the lifetime of luminescence might reversely influence the rate of absorption. In this paper, it is reported that the luminescence intensity of copper and manganese changes with the driving frequency at constant voltage. The variation of luminescent intensity depends only on the lifetime of luminescence but not on the type of quenching or other factors. Generally the rate of absorption is dominantly determined by the material property and the lifetime of luminescence centres, the absorption of shorter lifetime centre will be larger than that of the longer lifetime centre at the same excited condition.

  10. Cosmological constraints on dark matter annihilation and decay: Cross-correlation analysis of the extragalactic γ -ray background and cosmic shear

    Science.gov (United States)

    Shirasaki, Masato; Macias, Oscar; Horiuchi, Shunsaku; Shirai, Satoshi; Yoshida, Naoki

    2016-09-01

    We derive constraints on dark matter (DM) annihilation cross section and decay lifetime from cross-correlation analyses of the data from Fermi-LAT and weak lensing surveys that cover a wide area of ˜660 squared degrees in total. We improve upon our previous analyses by using an updated extragalactic γ -ray background data reprocessed with the Fermi Pass 8 pipeline, and by using well-calibrated shape measurements of about twelve million galaxies in the Canada-France-Hawaii Lensing Survey (CFHTLenS) and Red-Cluster-Sequence Lensing Survey (RCSLenS). We generate a large set of full-sky mock catalogs from cosmological N -body simulations and use them to estimate statistical errors accurately. The measured cross-correlation is consistent with null detection, which is then used to place strong cosmological constraints on annihilating and decaying DM. For leptophilic DM, the constraints are improved by a factor of ˜100 in the mass range of O (1 ) TeV when including contributions from secondary γ rays due to the inverse-Compton upscattering of background photons. Annihilation cross sections of ⟨σ v ⟩˜10-23 cm3/s are excluded for TeV-scale DM depending on channel. Lifetimes of ˜1 025 sec are also excluded for the decaying TeV-scale DM. Finally, we apply this analysis to wino DM and exclude the wino mass around 200 GeV. These constraints will be further tightened, and all the interesting wino DM parameter region can be tested, by using data from future wide-field cosmology surveys.

  11. Carrier lifetimes in thin-film photovoltaics

    Science.gov (United States)

    Baek, Dohyun

    2015-09-01

    The carrier lifetimes in thin-film solar cells are reviewed and discussed. Shockley-Read-Hall recombination is dominant at low carrier density, Auger recombination is dominant under a high injection condition and high carrier density, and surface recombination is dominant under any conditions. Because the surface photovoltage technique is insensitive to the surface condition, it is useful for bulk lifetime measurements. The photoconductance decay technique measures the effective recombination lifetime. The time-resolved photoluminescence technique is very useful for measuring thin-film semiconductor or solar-cell materials lifetime, because the sample is thin, other techniques are not suitable for measuring the lifetime. Many papers have provided time-resolved photoluminescence (TRPL) lifetimes for copper-indium-gallium-selenide (CIGS) and CdTe thin-film solar cell. The TRPL lifetime strongly depends on open-circuit voltage and conversion efficiency; however, the TRPL life time is insensitive to the short-circuit current.

  12. Argon metastable dynamics and lifetimes in a direct current microdischarge

    Science.gov (United States)

    Stefanović, Ilija; Kuschel, Thomas; Schröter, Sandra; Böke, Marc

    2014-09-01

    In this paper we study the properties of a pulsed dc microdischarge with the continuous flow of argon. Argon metastable lifetimes are measured by tunable diode laser absorption spectroscopy (TDLAS) and are compared with calculated values which yield information about excitation and de-excitation processes. By increasing the gas flow-rate about 5 times from 10 to 50 sccm, the Arm lifetime increases from 1 to 5 μs due to the reduction of metastable quenching with gas impurities. Optical emission spectroscopy reveals nitrogen and water molecules as the main gas impurities. The estimated N2 density [N2] = 0.1% is too low to explain the measured metastable lifetimes. Water impurity was found to be the main de-excitation source of argon metastable atoms due to high quenching coefficients. The water impurity level of [H2O] = 0.15% to 1% is sufficient to bring calculated metastable lifetimes in line with experiments. The maximum value of water content in the discharge compared to the argon atoms is estimated to approximately 6%, due to the large surface to volume ratio of the microdischarge. The current pulse releases the water molecules from the electrode surface and they are either re-adsorbed in the time between 0.4 ms for [H2O] = 1% and 2.6 ms for [H2O] = 0.15% or pumped out of the discharge with the speed equal to the gas flow-rate. Depending on its partial pressure, the water impurity re-adsorption time is of the order of magnitude or less then the argon gas residence time.

  13. Anti-proton and positron Cosmic Rays from Dark Matter annihilation around Intermediate Mass Black Holes

    OpenAIRE

    Lavalle, Julien

    2007-01-01

    Intermediate Mass Black Holes (IMBHs) are candidates to seed the Supermassive Black Holes (SMBHs), and some could still wander in the Galaxy. In the context of annihilating dark matter (DM), they are expected to drive huge annihilation rates, and could therefore significantly enhance the primary cosmic rays (CRs) expected from annihilation of the DM of the Galactic halo. In this proceeding (the original paper is Brun et al. 2007), we briefly explain the method to derive estimates of such exot...

  14. Nonuniversal self-similarity in a coagulation-annihilation model with constant kernels

    International Nuclear Information System (INIS)

    The large time dynamics of a two-species coagulation-annihilation system with constant coagulation and annihilation rates is studied analytically when annihilation is complete. A scaling behaviour is observed which varies with the parameter coupling, the annihilation of the two species and which is nonuniversal in the sense that it varies, in some cases, with the initial conditions as well. The latter actually occurs when either the coupling parameter is equal to one, or the initial number of particles is the same for the two species.

  15. Simulation of the annihilation emission of galactic positrons; Modelisation de l'emission d'annihilation des positrons Galactiques

    Energy Technology Data Exchange (ETDEWEB)

    Gillard, W

    2008-01-15

    Positrons annihilate in the central region of our Galaxy. This has been known since the detection of a strong emission line centered on an energy of 511 keV in the direction of the Galactic center. This gamma-ray line is emitted during the annihilation of positrons with electrons from the interstellar medium. The spectrometer SPI, onboard the INTEGRAL observatory, performed spatial and spectral analyses of the positron annihilation emission. This thesis presents a study of the Galactic positron annihilation emission based on models of the different interactions undergone by positrons in the interstellar medium. The models are relied on our present knowledge of the properties of the interstellar medium in the Galactic bulge, where most of the positrons annihilate, and of the physics of positrons (production, propagation and annihilation processes). In order to obtain constraints on the positrons sources and physical characteristics of the annihilation medium, we compared the results of the models to measurements provided by the SPI spectrometer. (author)

  16. Measurement of the BS lifetime

    International Nuclear Information System (INIS)

    This thesis presents a measurement of the Bs lifetime using 3 million hadronic Z decays collected by the DELPHI detector at LEP from 1991 to 1994. Decays of Bs mesons are tagged by the reconstruction of a Ds-→φπ-or Ds-→K*0K- decay (including the charge conjugated states of these decay modes). The decay time is obtained by reconstructing both the Bs momentum and the Bs flight distance. The combined result for the Ds-lepton and Ds-hadron samples is: τ(Bs)=1.54±0.31±0.15 ps where the first error is statistical and the second is systematic. (orig./HSI)

  17. Personality, IQ, and Lifetime Earnings

    DEFF Research Database (Denmark)

    Gensowski, Miriam

    2014-01-01

    Talented individuals are seen as drivers of long-term growth, but how do they realize their full potential? In this paper, I show that lifetime earnings of high-IQ men and women are substantially influenced by their personality traits, in addition to intelligence and education. Personality traits...... on detailed background information. This paper complements the literature on investments in education and personality traits by showing that they also have potentially high returns at the high end of the ability distribution....... through education, which has sizeable positive rates of return for men in this sample. Women’s returns to education past a bachelor’s degree are lowered through worse marriage prospects, which offset gains to education in terms of own earnings. The causal effect of education is identified through matching...

  18. Subjective probability models for lifetimes

    CERN Document Server

    Spizzichino, Fabio

    2001-01-01

    Bayesian methods in reliability cannot be fully utilized and understood without full comprehension of the essential differences that exist between frequentist probability and subjective probability. Switching from the frequentist to the subjective approach requires that some fundamental concepts be rethought and suitably redefined. Subjective Probability Models for Lifetimes details those differences and clarifies aspects of subjective probability that have a direct influence on modeling and drawing inference from failure and survival data. In particular, within a framework of Bayesian theory, the author considers the effects of different levels of information in the analysis of the phenomena of positive and negative aging.The author coherently reviews and compares the various definitions and results concerning stochastic ordering, statistical dependence, reliability, and decision theory. He offers a detailed but accessible mathematical treatment of different aspects of probability distributions for exchangea...

  19. Relationship between the microscopic and macroscopic world in optical oxygen sensing: a luminescence lifetime microscopy study.

    Science.gov (United States)

    López-Gejo, Juan; Haigh, David; Orellana, Guillermo

    2010-02-01

    An investigation based on confocal fluorescence lifetime imaging microscopy (FLIM) of silica-loaded silicone films doped with a molecular oxygen-sensitive ruthenium(II) polyazaheterocyclic complex is presented. The effect of the silica type (hydrophilic/hydrophobic), particle size and amount of silica filler on the luminescence decay of the immobilized indicator dye has thoroughly been studied. A higher amount of hydrophilic silica leads to both a higher solubility of molecular oxygen into the silicone film and to higher levels of the metal indicator dye. Thus, incorporation of 10% (by wt) pyrogenic silica into silicone shortens the mean luminescence lifetime from 1.4 to 0.9 micros. However, an excess of filler may lead to overloading of the dye into the film producing new phenomena such as triplet-triplet annihilation and excitation energy homotransfer, as observed from their influence on the emission lifetime of the metal complex. Those phenomena do not take place when trimethylated silica (hydrophobic filler) is used. In this case, no increase on the oxygen or dye concentration is observed after addition of the filler and no significant reduction of the luminescence lifetime is measured. Both the addition of silica and the possible precipitation of dye crystals lead to the appearance of microdomains where the molecular probe exhibits widely different excited state lifetimes. For the first time, such microdomains within the oxygen sensing layer are visualized and analyzed by means of FLIM, showing the potential of this technique and the usefulness of our conclusions to the future design and development of novel luminescent oxygen sensor films for environmental and process analysis. PMID:20099927

  20. Measurement of the lifetimes of the neutral and charged D mesons

    Energy Technology Data Exchange (ETDEWEB)

    Gladney, L.D.

    1985-03-01

    Results are presented on the use of a high-resolution drift chamber in the Mark II Detector at PEP to measure the lifetimes of D/sup 0/ and D/sup + -/ mesons produced in e/sup +/e/sup -/ annihilations at 29 GeV. Based on a sample of 74 events for the D/sup 0/ mesons and 23 events for the D/sup + -/ mesons, the lifetimes are found to be tau/sub D/sup 0/ = 4.7/sub -0.8//sup +0.9/ +- 0.5 x 10/sup -13/ s; tau/sub D/sup + -// = 8.9/sub -2.7//sup +3.8/ +- 1.3 x 10/sup -13/ s. The ratio of these lifetimes, tau/sub D/sup 0///tau/sub D/sup + -// = 1.9/sub -0.7//sup +0.9/ +- 0.3, indicates that the decays of these mesons cannot be explained by the simple spectator model of charmed particle decay.

  1. The Reasonable Explanation of Annihilation (fanā in Mysticism

    Directory of Open Access Journals (Sweden)

    Abulfazel Kiashemshaki

    2012-06-01

    Full Text Available Abstrak : Para mistikus melampaui tahap-tahap (derajat kesempurnaan mistik dan maqam spiritual dalam perjalanan mereka menuju Allah yang sulit dimengerti oleh non-mistikus. Karena itu, sebagian besar kalangan reflektif berusaha mengandalkan prinsip-prinsip intelektual dan teoritis mereka untuk memperoleh penjelasan atas pengalaman mistis dan ekstasi. Namun, keberhasilan penjelasannya sepenuhnya berada di bawah kuasa dan kekuatan dari prinsip-prinsip tersebut. (Fanā atau kesirnaan adalah salah satu tahap mistis atau keadaan yang sulit dimengerti oleh non-mistikus sehingga memunculkan berbagai teori yang berbeda untuk menjelaskannya. Pencapaian prestasi ilmiah dan filosofis merupakan penjelasan yang tepat atas fanā. Bagaimanapun upaya yang dilakukan dalam artikel ini membuktikan bahwa satu-satunya penjelasan yang sukses adalah penjelasan yang didasarkan pada prinsip-prinsip teosofi transendental dan mistisisme teoritis.Kata kunci : Fanā, Mistisisme, Penjelasan rasional, Mistisisme teoretis, Filsafat transendentalAbstract : Mystics are passing through stages (degrees of mystic perfection and esoteric abodes (spiritual stations in their spiritual journey to Allah which is difficult for unmystics to understand. Because of this, most of the reflective people are trying to rely on their intellectual and theoretical principles to obtain an understandable explanation of mystical experiences and ecstasy. However the success of such explanation completely lies in the power and strength of the above mentioned principles. (Fanā or annihilation is one of the mystical stages or states which unmystics find very difficult to reasonably understand, hence various and different theories have been provided for its explanation. Various scientific and philosophical achievements are appropriate explanations of annihilation (fanā which is valuable in its place; however effort had been made in this article to prove that the only successful explanation is an

  2. Three-dimensional electron-positron momentum distribution of O{sup 3+}-irradiated 6H SiC using two positron spectroscopy techniques simultaneously

    Energy Technology Data Exchange (ETDEWEB)

    Williams, Christopher; Burggraf, Larry; Petrosky, James [Air Force Institute of Technology, AFIT/ENP, 2950 Hobson Way, Wright-Patterson Air Force Base, OH 45433 (United States); Adamson, Paul, E-mail: christopher.williams@afit.edu [Stockpile Research, Development and Engineering Division, Office of Defense Programs, National Nuclear Security Administration, 1000 Independence Ave SW, Washington, DC 20585 (United States)

    2011-01-01

    A three-dimensional (3D) positron annihilation spectroscopy system (3DPASS) capable of determining 3D electron-positron (e{sup -}-e{sup +}) momentum densities from measurements of deviations from co-linearity and energies of photons from e{sup -}-e{sup +} annihilation events was employed to examine the effects of O-atom defects in 6H SiC. Three-dimensional momentum datasets were determined for 6H SiC irradiated with 24 MeV O{sup 3+} ions. Angular correlation of annihilation radiation (ACAR) and coincidence Doppler-broadening of annihilation radiation (CDBAR) analyses are presented. In addition, a novel technique is illustrated for analyzing 3D momentum datasets in which the parallel momentum component, p{sub ||} (obtained from the CDBAR measurement) is selected for annihilation events that possess a particular perpendicular momentum component, p{sub -} observed in the 2D ACAR spectrum.

  3. Computing lifetimes for battery-powered devices

    OpenAIRE

    Jongerden, Marijn; Haverkort, Boudewijn

    2010-01-01

    The battery lifetime of mobile devices depends on the usage pattern of the battery, next to the discharge rate and the battery capacity. Therefore, it is important to include the usage pattern in battery lifetime computations. We do this by combining a stochastic workload, modeled as a continuous-time Markov model, with a well-known battery model. For this combined model, we provide new algorithms to efficiently compute the expected lifetime and the distribution and expected value of the deli...

  4. Search for Dark Matter Annihilation in Draco with STACEE

    CERN Document Server

    Driscoll, D D; Carson, J E; Covault, C E; Fortin, P; Gingrich, D M; Hanna, D S; Jarvis, A; Kildea, J; Lindner, T; Müller, C; Mukherjee, R; Ong, R A; Ragan, K; Williams, D A; Zweerink, J

    2007-01-01

    For some time, the Draco dwarf spheroidal galaxy has garnered interest as a possible source for the indirect detection of dark matter. Its large mass-to-light ratio and relative proximity to the Earth provide favorable conditions for the production of detectable gamma rays from dark matter self-annihilation in its core. The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) is an air-shower Cherenkov telescope located in Albuquerque, NM capable of detecting gamma rays at energies above 100 GeV. We present the results of the STACEE observations of Draco during the 2005-2006 observing season totaling 10 hours of livetime after cuts.

  5. Collimation of the $e^{+}e^{-}$ annihilation event

    CERN Document Server

    Kimura, K

    1997-01-01

    The collimation $C$ of a hadronic event in the e^+e^- annihilation is defined as the average of $\\cos\\theta$, $C=$, where $\\theta$ is the angle of each hadron measured from the thrust axis, and the average is over all the hadrons produced in an event. It is an infrared-stable event-shape parameter. $1-\\bar C$, the difference between the unity and the average collimation at a given energy, is proportional to the anomalous dimension of the hadron multiplicity at the leading order in MLLA. Its next-to-leading order corrections are calculated.

  6. Positrons from dark matter annihilation in the galactic halo: uncertainties

    CERN Document Server

    Fornengo, N; Lineros, R; Donato, F; Salati, P

    2007-01-01

    Indirect detection signals from dark matter annihilation are studied in the positron channel. We discuss in detail the positron propagation inside the galactic medium: we present novel solutions of the diffusion and propagation equations and we focus on the determination of the astrophysical uncertainties which affect the positron dark matter signal. We show that, especially in the low energy tail of the positron spectra at Earth, the uncertainty is sizeable and we quantify the effect. Comparison of our predictions with current available and foreseen experimental data are derived.

  7. First study of rapidity gaps in e+e- annihilation

    CERN Document Server

    Abe, K; Ahn, C J; Akagi, T; Allen, N J; Ash, William W; Aston, D; Baird, K G; Baltay, C; Band, H R; Barakat, M B; Baranko, G J; Bardon, O; Barklow, Timothy L; Bazarko, A O; Ben-David, R; Benvenuti, Alberto C; Bienz, T; Bilei, G M; Bisello, D; Blaylock, G; Bogart, J R; Bolton, T; Bower, G R; Brau, J E; Breidenbach, M; Bugg, W M; Burke, D; Burnett, T H; Burrows, P N; Busza, W; Calcaterra, A; Caldwell, D O; Calloway, D H; Camanzi, B; Carpinelli, M; Cassell, R; Castaldi, R; Castro, A; Cavalli-Sforza, M; Church, E; Cohn, H O; Coller, J A; Cook, V; Cotton, R; Cowan, R F; Coyne, D G; de Oliveira, A; Damerell, C J S; Daoudi, M; De Sangro, R; De Simone, P; Dell'Orso, R; Dima, M; Du, P Y C; Dubois, R; Eisenstein, B I; Elia, R; Falciai, D; Fero, M J; Frey, R; Furuno, K; Gillman, T; Gladding, G E; González, S; Hallewell, G D; Hart, E L; Hasegawa, Y; Hedges, S J; Hertzbach, S S; Hildreth, M D; Huber, J; Huffer, M E; Hughes, E W; Hwang, H; Iwasaki, Y; Jackson, D J; Jacques, P; Jaros, J A; Johnson, A S; Johnson, J R; Johnson, R A; Junk, T R; Kajikawa, R; Kalelkar, M S; Kang, H J; Karliner, I; Kawahara, H; Kendall, H W; Kim, Y; King, M E; King, R; Kofler, R R; Krishna, N M; Kroeger, R S; Labs, J F; Langston, M; Lath, A; Lauber, J A; Leith, D W G S; Liu, M X; Liu, X; Loreti, M; Lu, A; Lynch, H L; Ma, J; Mancinelli, G; Manly, S L; Mantovani, G C; Markiewicz, T W; Maruyama, T; Massetti, R; Masuda, H; Mattison, T S; Mazzucato, E; McKemey, A K; Meadows, B T; Messner, R; Mockett, P M; Moffeit, K C; Mours, B; Müller, G; Müller, D; Nagamine, T; Narita, S; Nauenberg, U; Neal, H A; Nussbaum, M; Ohnishi, Y; Osborne, L S; Panvini, R S; Park, H; Pavel, T J; Peruzzi, I; Piccolo, M; Piemontese, L; Pieroni, E; Pitts, K T; Plano, R J; Prepost, R; Prescott, C Y; Punkar, G D; Quigley, J; Ratcliff, B N; Reeves, T W; Reidy, J; Rensing, P E; Rochester, L S; Rothberg, J E; Rowson, P C; Russell, J J; Saxton, O H; Schalk, T L; Schindler, R H; Schumm, B A; Seiden, A; Sen, S; Serbo, V V; Saevitz, M H; Shank, J T; Shapiro, G; Shapiro, S L; Sherden, D J; Shmakov, K D; Simopoulos, C; Sinev, N B; Smith, S R; Snyder, J A; Stamer, P E; Steiner, H; Steiner, R; Strauss, M G; Su, D; Suekane, F; Sugiyama, A; Suzuki, S; Swartz, M; Szumilo, A; Takahashi, T; Taylor, F E; Torrence, E; Turk, J; Usher, T; Vavra, J; Vannini, C; Vella, E N; Venuti, J P; Verdier, R; Verdini, P G; Wagner, S R; Waite, A P; Watts, S J; Weidemann, A W; Weiss, E R; Whitaker, J S; White, S L; Wickens, F J; Williams, D A; Williams, D C; Williams, S H; Willocq, S; Wilson, R J; Wisniewski, W J; Woods, M; Word, G B; Wyss, J; Yamamoto, R K; Yamartino, J M; Yang, X; Yellin, S J; Young, C C; Yuta, H; Zapalac, G H; Zdarko, R W; Zeitlin, C; Zhou, J

    1996-01-01

    We present the first study of rapidity gaps in e+e- annihilations using Z0 decays collected by the SLD experiment at SLAC. Our measured rapidity gap spectra all exponentially with increasing gap size over five decades, and we observe no anomalous class of events containing large gaps. This supports the interpretation of the large-gap events measured in pp and ep collisions in terms of exchange of color-singlet objects. The presence of heavy flavors or additional jets does not affect these conclusions.

  8. Two-Photon Total Annihilation of Molecular Positronium

    CERN Document Server

    Pérez-Ríos, Jesús; Greene, Chris H

    2014-01-01

    The rate for complete two-photon annihilation of molecular positronium Ps$_{2}$ is reported. This decay channel involves a four-body collision among the fermions forming Ps$_{2}$, and two photons of 1.022 MeV, each, as the final state. The quantum electrodynamics result for the rate of this process is found to be $\\Gamma_{Ps_{2} \\rightarrow \\gamma\\gamma}$ = 9.0 $\\times 10^{-12}$ s$^{-1}$. This decay channel completes the most comprehensive decay chart for Ps$_{2}$ up to date.

  9. Strong CMB Constraint On P-Wave Annihilating Dark Matter

    OpenAIRE

    An, Haipeng; Wise, Mark B.; Zhang, Yue(Walter Burke Institute for Theoretical Physics, California Institute of Technology, Pasadena, CA, 91125, U.S.A.)

    2016-01-01

    We consider a dark sector consisting of dark matter that is a Dirac fermion and a scalar mediator. This model has been extensively studied in the past. If the scalar couples to the dark matter in a parity conserving manner then dark matter annihilation to two mediators is dominated by the P-wave channel and hence is suppressed at very low momentum. The indirect detection constraint from the anisotropy of the Cosmic Microwave Background is usually thought to be absent in the model because of t...

  10. Signals in the Co-annihilation Region of Supersymmetry

    Science.gov (United States)

    Arnowitt, Richard; Aurisano, Adam; Dutta, Bhaskar; Kamon, Teruki; Simeon, Paul; Toback, David; Wagner, Peter; Kolev, Nikolay

    2006-04-01

    An unanswered problem in physics is the identity of the cold dark matter (CDM) in the universe. One of the leading candidates is a supersymmetric (SUSY) particle, the lightest neutralino. Recent cosmological measurements by the WMAP experiment have tightly constrained the SUSY parameter space in the mSUGRA model to the so called ``co-annihilation'' region in which the lightest supersymmetric tau lepton and the lightest neutralino are nearly degenerate in mass. We examine the prospects of using LHC detectors to measure this mass difference and present preliminary results.

  11. Compton Scattering, Pair Annihilation and Pair Production in a Plasma

    OpenAIRE

    Krishan, Vinod

    1999-01-01

    The square of the four momentum of a photon in vacuum is zero. However, in an unmagnetized plasma it is equal to the square of the plasma frequency. Further, the electron-photon coupling vertex is modified in a plasma to include the effect of the plasma medium. I calculate the cross sections of the three processes - the Compton scattering, electron-positron pair annihilation and production in a plasma. At high plasma densities, the cross sections are found to change significantly. Such high p...

  12. Hadron production in e+e- annihilation. QCD and hadronization

    International Nuclear Information System (INIS)

    Recent results on hadron production in e+e- annihilation are summarized. The topics included are: (1) inclusive hadron production, (2) comparison of light (u,d,s) and heavy (c,b) quark jets; (3) p - anti p correlations; (4) gluon vs. quark jets; (5) analysis of 3 jet events; (6) measurement of the strong coupling constant α/sub s/; and (7) forward-backward asymmetries of quarks and leptons. Experimental data are compared with predictions of several models to reveal underlying physics. 62 refs., 22 figs

  13. Study of anti-neutron annihilations at low energy

    International Nuclear Information System (INIS)

    The results of a total cross section measurement for the reactions anti np and anti pn are plotted. These results indicate that the annihilation amplitudes are predominantly I = 1 at low energy. The S-wave unitarity limit is shown, and the data support the conclusion drawn from anti pp data that even at the lowest momenta P-wave and higher waves are very important. The technique of using antineutrons to study very low energy antineutrons to study very low energy antinucleon interactions is demonstrated to be feasible

  14. Inclusive Production Λ c in the e + e - - Annihilation

    Science.gov (United States)

    Osati, T.; Movlanaei, M.

    2016-09-01

    In the framework of the quark-diquark model of baryons, Λ c can be considered as constituent c quark and ud diquark. In hadronizasion process baryon Λ c can be produced from ud scalar diquark and c quark fragmentation. So in this work, in the lowest order of perturbative QCD, fragmentation functions c → Λ c and ud → Λ c are calculated and finally in the electron-positron annihilation in LEP, the inclusive cross section production of Λ c is calculated about pole of z 0.

  15. Lifetime of Organic Photovoltaics: Status and Predictions

    DEFF Research Database (Denmark)

    Gevorgyan, Suren; Madsen, Morten Vesterager; Roth, Bérenger;

    2016-01-01

    The results of a meta-analysis conducted on organic photovoltaics (OPV) lifetime data reported in the literature is presented through the compilation of an extensive OPV lifetime database based on a large number of articles, followed by analysis of the large body of data. We fully reveal the prog......The results of a meta-analysis conducted on organic photovoltaics (OPV) lifetime data reported in the literature is presented through the compilation of an extensive OPV lifetime database based on a large number of articles, followed by analysis of the large body of data. We fully reveal...

  16. Fluorescence lifetime imaging of skin cancer

    Science.gov (United States)

    Patalay, Rakesh; Talbot, Clifford; Munro, Ian; Breunig, Hans Georg; König, Karsten; Alexandrov, Yuri; Warren, Sean; Neil, Mark A. A.; French, Paul M. W.; Chu, Anthony; Stamp, Gordon W.; Dunsby, Chris

    2011-03-01

    Fluorescence intensity imaging and fluorescence lifetime imaging microscopy (FLIM) using two photon microscopy (TPM) have been used to study tissue autofluorescence in ex vivo skin cancer samples. A commercially available system (DermaInspect®) was modified to collect fluorescence intensity and lifetimes in two spectral channels using time correlated single photon counting and depth-resolved steady state measurements of the fluorescence emission spectrum. Uniquely, image segmentation has been used to allow fluorescence lifetimes to be calculated for each cell. An analysis of lifetime values obtained from a range of pigmented and non-pigmented lesions will be presented.

  17. Experimentally Measured Radiative Lifetimes and Oscillator Strengths in Neutral Vanadium

    Science.gov (United States)

    Holmes, C. E.; Pickering, J. C.; Ruffoni, M. P.; Blackwell-Whitehead, R.; Nilsson, H.; Engström, L.; Hartman, H.; Lundberg, H.; Belmonte, M. T.

    2016-06-01

    We report a new study of the V i atom using a combination of time-resolved laser-induced fluorescence and Fourier transform spectroscopy that contains newly measured radiative lifetimes for 25 levels between 24,648 cm-1 and 37,518 cm-1 and oscillator strengths for 208 lines between 3040 and 20000 Å from 39 upper energy levels. Thirteen of these oscillator strengths have not been reported previously. This work was conducted independently of the recent studies of neutral vanadium lifetimes and oscillator strengths carried out by Den Hartog et al. and Lawler et al., and thus serves as a means to verify those measurements. Where our data overlap with their data, we generally find extremely good agreement in both level lifetimes and oscillator strengths. However, we also find evidence that Lawler et al. have systematically underestimated oscillator strengths for lines in the region of 9000 ± 100 Å. We suggest a correction of 0.18 ± 0.03 dex for these values to bring them into agreement with our results and those of Whaling et al. We also report new measurements of hyperfine structure splitting factors for three odd levels of V i lying between 24,700 and 28,400 cm-1.

  18. CMB bounds on dark matter annihilation: Nucleon energy losses after recombination

    NARCIS (Netherlands)

    C. Weniger; P.D. Serpico; F. Iocco; G. Bertone

    2013-01-01

    We consider the propagation and energy losses of protons and antiprotons produced by dark matter annihilation at redshifts 100annihilations into quarks, gluons and weak gauge bosons, protons and antiprotons carry about 20% of the energy injected into e± and γ’s, b

  19. Investigation of Scale Exponents of Complete and Incomplete Aggregation-Annihilation Processes

    Institute of Scientific and Technical Information of China (English)

    HUANG Bi-Hua; LIU Cui-Mei; YANG Zhan-Ru

    2004-01-01

    The complete and incomplete aggregation-annihilation processes are investigated with the method of generating function, and the scale exponents are obtained exactly. We find that the scale exponents of incomplete aggregation-annihilation process are different from the previous exponents obtained by different methods. The time dependence of the total number of clusters and the total mass of clusters are analytically obtained.

  20. Lifetime-Enhanced Transport in Silicon due to Spin and Valley Blockade

    NARCIS (Netherlands)

    Lansbergen, G.P.; Rahman, R.; Verduijn, J.; Tettamanzi, G.C.; Collaert, N.; Biesemans, S.; Klimeck, G.; Hollenberg, L.C.L.; Rogge, S.

    2011-01-01

    We report the observation of lifetime-enhanced transport (LET) based on perpendicular valleys in silicon by transport spectroscopy measurements of a two-electron system in a silicon transistor. The LET is manifested as a peculiar current step in the stability diagram due to a forbidden transition be

  1. Cosmology in Mr. Tompkins' Lifetime

    Science.gov (United States)

    Lindner, Rudi Paul

    2016-01-01

    Mr. Tompkins, the hero of George Gamow's most famous book, was born in the first decade of the twentieth century and lived until its end. A bank clerk by day, Mr. Tompkins had wide-ranging interests, and his curiosity led him to popular scientific presentations, and these in turn brought him a long and happy marriage to Maud, the daughter of a professor of physics. His lifetime offers an appropriate framework for a meditation on the history of cosmology during the century in which cosmology became a scientific enterprise. As it happens, Mr. Tompkins' first exposure to cosmology, in which he observed both the expansion and contraction of an oscillating universe in 1939, happened during the long night of relativity, the generation in which relativity specialists became few and, like the galaxies, far between. This talk will consider the heyday of early relativistic cosmology from 1917 to 1935, the causes and consequences of the "long night" from 1935 until 1963, and the renaissance of cosmology, which, occurring as it did upon the retirement of Mr. Tompkins, afforded him great pleasure in his later years.

  2. The Lifetime of Axion Stars

    CERN Document Server

    Eby, Joshua; Wijewardhana, L C R

    2015-01-01

    We investigate the decay of condensates of scalars in a field theory defined by $V({\\cal A})=m^2 f^2 [1-\\cos({\\cal A}/f)]$, where $m$ and $f$ are the mass and decay constant of the scalar field. An example of such a theory is that of the axion, in which case the condensates are called axion stars. The axion field, $\\cal A$, is self adjoint. As a result the axion number is not an absolutely conserved quantity. Therefore, axion stars are not stable and have finite lifetimes. Bound axions, localized on the volume of the star, have a coordinate uncertainty $\\Delta x \\sim R \\sim 1/(m_a \\Delta)$, where $R$ is the radius of the star and $\\Delta = \\sqrt{1-E_0^2/m_a^2}$. Here $m_a$ and $E_0$ are the mass and the ground state energy of the bound axion. Then the momentum distribution of axions has a width of $\\Delta p \\sim m_a\\Delta$. At strong binding, $\\Delta={\\cal O}(1)$, bound axions can easily transfer a sufficient amount of momentum to create and emit a free axion, leading to fast decay of the star with a transiti...

  3. General features of jets in e+e- annihilation

    International Nuclear Information System (INIS)

    Many facts have been gathered during the last years at PETRA and recently also at PEP. Jets occur in other types of reactions as pp/panti p-collisions or deep inelastic lepton-nucleon scattering as well. However e+e--annihilation has the special advantage that (a) no hadronic matter exists in the initial state that can influence quark fragmentation, and (b) the kinds of partons in the first stage of fragmentation are unique - all jets originate from quarks, no gluons or diquarks are around at the very first stage. One important result is that the c.m. energy W effective in the partonic reaction is uniquely known. Data on fragmentation in e+e--annihilations have by now been accumulated at several energies W with rather high statistics allowing not only a thorough analysis of jet properties at fixed W but also of their variation with W. Most of the data presented in the following sections are corrected for detector effects and experimental cuts. (orig.)

  4. Relative Biological Effectiveness and Peripheral Damage of Antiproton Annihilation

    CERN Multimedia

    Kavanagh, J N; Kaiser, F; Tegami, S; Schettino, G; Kovacevic, S; Hajdukovic, D; Welsch, C P; Currell, F J; Toelli, H T; Doser, M; Holzscheiter, M; Herrmann, R; Timson, D J; Alsner, J; Landua, R; Knudsen, H; Comor, J; Moller, S P; Beyer, G

    2002-01-01

    The use of ions to deliver radiation to a body for therapeutic purposes has the potential to be significant improvement over the use of low linear energy transfer (LET) radiation because of the improved energy deposition profile and the enhanced biological effects of ions relative to photons. Proton therapy centers exist and are being used to treat patients. In addition, the initial use of heavy ions such as carbon is promising to the point that new treatment facilities are planned. Just as with protons or heavy ions, antiprotons can be used to deliver radiation to the body in a controlled way; however antiprotons will exhibit additional energy deposition due to annihilation of the antiprotons within the body. The slowing down of antiprotons in matter is similar to that of protons except at the very end of the range beyond the Bragg peak. Gray and Kalogeropoulos estimated the additional energy deposited by heavy nuclear fragments within a few millimeters of the annihilation vertex to be approximately 30 MeV (...

  5. The dark matter annihilation boost from low-temperature reheating

    Science.gov (United States)

    Erickcek, Adrienne L.

    2015-11-01

    The evolution of the Universe between inflation and the onset of big bang nucleosynthesis is difficult to probe and largely unconstrained. This ignorance profoundly limits our understanding of dark matter: we cannot calculate its thermal relic abundance without knowing when the Universe became radiation dominated. Fortunately, small-scale density perturbations provide a probe of the early Universe that could break this degeneracy. If dark matter is a thermal relic, density perturbations that enter the horizon during an early matter-dominated era grow linearly with the scale factor prior to reheating. The resulting abundance of substructure boosts the annihilation rate by several orders of magnitude, which can compensate for the smaller annihilation cross sections that are required to generate the observed dark matter density in these scenarios. In particular, thermal relics with masses less than a TeV that thermally and kinetically decouple prior to reheating may already be ruled out by Fermi-LAT observations of dwarf spheroidal galaxies. Although these constraints are subject to uncertainties regarding the internal structure of the microhalos that form from the enhanced perturbations, they open up the possibility of using gamma-ray observations to learn about the reheating of the Universe.

  6. Detecting electron neutrinos from solar dark matter annihilation by JUNO

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Wan-Lei [Institute of High Energy Physics, Chinese Academy of Sciences,P.O. Box 918, Beijing 100049 (China)

    2016-01-21

    We explore the electron neutrino signals from light dark matter (DM) annihilation in the Sun for the large liquid scintillator detector JUNO. In terms of the spectrum features of three typical DM annihilation channels χχ→νν-bar,τ{sup +}τ{sup −},bb-bar, we take two sets of selection conditions to calculate the expected signals and atmospheric neutrino backgrounds based on the Monte Carlo simulation data. Then the JUNO sensitivities to the spin independent DM-nucleon and spin dependent DM-proton cross sections are presented. It is found that the JUNO projected sensitivities are much better than the current spin dependent direct detection experimental limits for the νν-bar and τ{sup +}τ{sup −} channels. In the spin independent case, the JUNO will give the better sensitivity to the DM-nucleon cross section than the LUX and CDMSlite limits for the νν-bar channel with the DM mass lighter than 6.5 GeV. If the νν-bar or τ{sup +}τ{sup −} channel is dominant, the future JUNO results are very helpful for us to understand the tension between the DAMA annual modulation signal and other direct detection exclusions.

  7. Annihilation photon acollinearity in PET: volunteer and phantom FDG studies

    Energy Technology Data Exchange (ETDEWEB)

    Shibuya, Kengo [Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage, Chiba 263-8555 (Japan); Yoshida, Eiji [Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage, Chiba 263-8555 (Japan); Nishikido, Fumihiko [Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage, Chiba 263-8555 (Japan); Suzuki, Toshikazu [Department of Dose Assessment, Research Center for Radiation Emergency Medicine, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage, Chiba 263-8555 (Japan); Tsuda, Tomoaki [Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage, Chiba 263-8555 (Japan); Inadama, Naoko [Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage, Chiba 263-8555 (Japan); Yamaya, Taiga [Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage, Chiba 263-8555 (Japan); Murayama, Hideo [Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage, Chiba 263-8555 (Japan)

    2007-09-07

    Annihilation photon acollinearity is a fundamental but little investigated problem in positron emission tomography (PET). In this paper, the cause of the angular deviation from 180.00{sup 0} is described as well as how to evaluate it under conditions of a spatially distributed radiation source and a limited acquisition time for the human body. A relationship between the shape of the photopeak spectrum and the angular distribution is formulated using conservation laws of momentum and energy over the pair annihilation. Then the formula is used to evaluate the acollinearity for a pool phantom and the human body with FDG injected. The angular distribution for the pool phantom agrees well with that for pure water which had been directly measured by Colombino et al in 1965 (Nuovo Cimento 38 707-23), and also with that for the human body determined in this study. Pure water can be considered as a good approximation of the human body regarding the angular deviation. The blurring coefficient to be multiplied by the ring diameter in calculations of the PET spatial resolution is experimentally determined for the first time as 0.00243 {+-} 0.00014; this is 10% larger than the value widely used by investigators.

  8. Kinetic Behavior of Aggregation—Fragmentation Process with Annihilation

    Institute of Scientific and Technical Information of China (English)

    KEJian-Hong; LINZhen-Quan

    2002-01-01

    The kinetic behavior of an aggregation-fragmentation-annihilation system with two distinct species is studied.We propose that the aggretation reaction occurs only between two clusters of the same species,and the irreversible annihilation reaction occurs only between two clusters of different species,meanwhile there exists the fragmentation reaction of a cluster into two smaller clusters for either species.Based on the mean-field theory,we investigate the rate equations of the process with constant reaction rates and obtain the asymptotic descriptions of the cluster-mass distribution.In the case of the same initial concentrations of two species,the scaling descriptions for the cluster-mass distributions of the two species are found to break down completely.It is also observed that the kinetic behaviors of distinct species are quite complicated for the case of different initial concentrations of the two species.The clusters of harger initial concentration species(heavy species) possess peculiar scaling properties,while the cluster-mass distribution of light species has not scaling behavior.The exponents describing the scaling behavior for heavy species strongly depend on its fragmentation rate and initial monomer concentrations of two kinds of reactants.

  9. Baselines for Lifetime of Organic Solar Cells

    DEFF Research Database (Denmark)

    Gevorgyan, Suren; Espinosa Martinez, Nieves; Ciammaruchi, Laura;

    2016-01-01

    The process of accurately gauging lifetime improvements in organic photovoltaics (OPVs) or other similar emerging technologies, such as perovskites solar cells is still a major challenge. The presented work is part of a larger effort of developing a worldwide database of lifetimes that can help...

  10. The 21 cm signal and the interplay between dark matter annihilations and astrophysical processes

    CERN Document Server

    Lopez-Honorez, Laura; Moliné, Ángeles; Palomares-Ruiz, Sergio; Vincent, Aaron C

    2016-01-01

    Future dedicated radio interferometers, including HERA and SKA, are very promising tools that aim to study the epoch of reionization and beyond via measurements of the 21 cm signal from neutral hydrogen. Dark matter (DM) annihilations into charged particles change the thermal history of the Universe and, as a consequence, affect the 21 cm signal. Accurately predicting the effect of DM strongly relies on the modeling of annihilations inside halos. In this work, we use up-to-date computations of the energy deposition rates by the products from DM annihilations, a proper treatment of the contribution from DM annihilations in halos, as well as values of the annihilation cross section allowed by the most recent cosmological measurements from the Planck satellite. Given current uncertainties on the description of the astrophysical processes driving the epochs of reionization, X-ray heating and Lyman-$\\alpha$ pumping, we find that disentangling DM signatures from purely astrophysical effects, related to early-time s...

  11. Positron life time and annihilation Doppler broadening measurements on transition metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    Levay, B. (Eoetvoes Lorand Tudomanyegyetem, Budapest (Hungary). Fizikai Kemiai es Radiologiai Tanszek); Varhelyi, Cs. (Babes-Bolyai Univ., Cluj (Romania)); Burger, K. (Eoetvoes Lorand Tudomanyegyetem, Budapest (Hungary). Szervetlen es Analitikai Kemiai Intezet)

    1982-01-01

    Positron life time and annihilation Doppler broadening measurements have been carried out on 44 solid coordination compounds. Several correlations have been found between the annihilation life time (tau/sub 1/) and line shape parameters (L) and the chemical structure of the compounds. Halide ligands were the most active towards positrons. This fact supports the assumption on the possible formation of (e/sup +/X/sup -/) positron-halide bound state. The life time was decreasing and the annihilation energy spectra were broadening with the increasing negative character of the halides. The aromatic base ligands affected the positron-halide interaction according to their basicity and space requirement and thus they indirectly affected the annihilation parameters, too. In the planar and tetrahedral complexes the electron density on the central met--al ion affected directly the annihilation parameters, while in the octahedral mixed complexes it had only an ind--irect effect through the polarization of the halide ligands.

  12. CMB data constraint on self-annihilation of dark matter particles

    CERN Document Server

    Kim, Jaiseung

    2010-01-01

    Recently, self-annihilation of dark matter particles is proposed to explain the "WMAP Haze" and excess of energetic positrons and electrons in ATIC and PAMELA results. If self-annihilation of dark matter occurs around the recombination of cosmic plasma, energy release from self-annihilation of dark matter delays the recombination, and hence affects CMB anisotropy. By using the recent CMB data, we have investigated the self-annihilation of dark matter particles. In this investigation, we do not find statistically significant evidence, and impose an upper bound on /m_{\\chi}. The upcoming data from Planck surveyor and the Fermi Gamma-ray telescope will allow us to break some of parameter degeneracy and improve constraints on self-annihilation of dark matter particles.

  13. High Statistics Study of $p\\bar$p Annihilation Physics at the EHS

    CERN Multimedia

    2002-01-01

    We propose to perform an experiment to study antiproton-proton annihilations at 50 GeV/c, using the EHS facility.\\\\ \\\\ We will study in detail annihilation processes in terms of the underlying quark structure, and to compare our results with the predictions of the three principal models: quark fusion, fragmentation and recombination.\\\\ \\\\ These models achieved satisfactory results for pion and non-strange resonance production but failed for strange particle production. In fact a study of the production of strange particles could lead to valuable dues in understanding the annihilation mechanisms. A possible explanation of their production is that fast gluons materialize as strange quark pairs in the annihilation process. \\\\ \\\\ We expect to obtain 35 K, well identified, annihilation events.

  14. Lifetime prediction and the economic lifetime of Proton Exchange Membrane fuel cells

    International Nuclear Information System (INIS)

    Highlights: • A formula to predict the PEMFC lifetime is presented. • A PEMFC residual life evaluation method is presented. • The evaluation method realizes online forecasting of the PEMFC residual life. • The PEMFC economic lifetime is studied to confirm the best design lifetime. - Abstract: Lifetime and cost are two main factors that restrict the commercialization of Proton Exchange Membrane (PEM) fuel cells. This paper mainly studies the prediction and the evaluation methods of PEM fuel cell lifetime. A formula to predict the PEM fuel cell lifetime is presented. The formula is based on the vehicular operation records and the tested results in the lab. Also the difference between the vehicular operation condition and the test is taken into consideration. The formula realizes the PEM fuel cell lifetime rapid prediction. A PEM fuel cell residual life evaluation method is also presented. The evaluation method realizes online forecasting of the residual life through updating the environmental affecting factor and voltage degradation rate caused by the operating conditions. Furthermore, the PEM fuel cell economic lifetime is studied. The economic lifetime is the working lifetime which gains the lowest average cost. The synthesis of the lifetime and the cost provides a basis to confirm the best design lifetime

  15. Positron annihilation study on CuInSe2 solar cell thin films

    International Nuclear Information System (INIS)

    Positron annihilation spectroscopy has been used to investigate CuInSe2 solar cell thin films. The films were grown on Mo-coated soda lime glass substrates by the electrochemical deposition processing technique. As-grown samples are found to contain large concentration of vacancy defects. The selenium (Se) atmosphere and sulfur (S) atmosphere annealing of as-grown samples at 800 K can dramatically reduce the number of vacancy defects and the film becomes crystalline. In addition, a defect layer of about 50 nm thickness was observed at the surface of the CuInSe2 thin film. This layer results from the electrochemical deposition method, but the defect concentration in the defect layer can be greatly reduced by annealing in selenium atmosphere. The Doppler broadening line shape parameter correlation plot provided evidence that the positron trapping defect states where in three samples. - Highlights: ► As-grown CuInSe2 thin films contain large concentration of defects. ► A defect layer of about 50 nm exists in the CuInSe2 thin film surface. ► The defect concentration in the defect layer can be greatly reduced.

  16. Positron annihilation study on CuInSe{sub 2} solar cell thin films

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Lijuan [Department of Modern Physics, University of Science and Technology of China, Hefei 230026 (China); Wang, Tao [Institute of Fluid Physics, CAEP, P.O. Box 919-106, Mianyang 621900 (China); Li, Ji [Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026 (China); Hao, Yingping; Liu, Jiandang [Department of Modern Physics, University of Science and Technology of China, Hefei 230026 (China); Zhang, Peng [Key Laboratory of Nuclear Analysis Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, No. 19 Yuquan Lu, Beijing 100049 (China); Cheng, Bin [Department of Modern Physics, University of Science and Technology of China, Hefei 230026 (China); Zhang, Zhongwei [Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026 (China); Wang, Baoyi [Key Laboratory of Nuclear Analysis Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, No. 19 Yuquan Lu, Beijing 100049 (China); Ye, Bangjiao, E-mail: bjye@ustc.edu.cn [Department of Modern Physics, University of Science and Technology of China, Hefei 230026 (China)

    2012-12-15

    Positron annihilation spectroscopy has been used to investigate CuInSe{sub 2} solar cell thin films. The films were grown on Mo-coated soda lime glass substrates by the electrochemical deposition processing technique. As-grown samples are found to contain large concentration of vacancy defects. The selenium (Se) atmosphere and sulfur (S) atmosphere annealing of as-grown samples at 800 K can dramatically reduce the number of vacancy defects and the film becomes crystalline. In addition, a defect layer of about 50 nm thickness was observed at the surface of the CuInSe{sub 2} thin film. This layer results from the electrochemical deposition method, but the defect concentration in the defect layer can be greatly reduced by annealing in selenium atmosphere. The Doppler broadening line shape parameter correlation plot provided evidence that the positron trapping defect states where in three samples. - Highlights: Black-Right-Pointing-Pointer As-grown CuInSe{sub 2} thin films contain large concentration of defects. Black-Right-Pointing-Pointer A defect layer of about 50 nm exists in the CuInSe{sub 2} thin film surface. Black-Right-Pointing-Pointer The defect concentration in the defect layer can be greatly reduced.

  17. Intermolecular exciton-exciton annihilation in phospholipid vesicles doped with [Ru(bpy)2dppz]2+

    Science.gov (United States)

    De la Cadena, Alejandro; Pascher, Torbjörn; Davydova, Dar'ya; Akimov, Denis; Herrmann, Felix; Presselt, Martin; Wächtler, Maria; Dietzek, Benjamin

    2016-01-01

    The ultrafast photophysics of [Ru(bpy)2dppz]2+ (dppz = dipyrido[3,2-a:2‧,3‧-c]-phenazine) embedded into the walls of phospholipid vesicles has been studied by femtosecond time-resolved pump-probe spectroscopy. While [Ru(bpy)2dppz]2+ has been studied intensively with respect to its intramolecular charge transfer processes, which are associated with the well known light-switch effect, this study focuses on intermolecular energy transfer processes taking place upon dense packing of the complexes into a phospholipid membrane composed of dipalmitoyl-L-α-phosphatidylglycerol, which can be thought of as a simplistic model of a cellular membrane. The data indicate additional quenching of excited [Ru(bpy)2dppz]2+ upon increasing the pump-pulse intensity. Hence, the observed photophysics, which is assigned to the presence of intermolecular exciton-exciton annihilation at high pump-intensities, might be related to the ultrafast photophysics of [Ru(bpy)2dppz]2+ when used as a chromophore to stain cells, an effect that may be taken into account during the employment of novel cellular markers based on Ru polypyridine complexes.

  18. DLTS study of annihilation of oxidation induced deep-level defects in Ni/SiO2/-Si MOS structures

    Indian Academy of Sciences (India)

    N Shashank; Sanjeev K Gupta; K V Madhu; J Akhtar; R Damle

    2011-12-01

    This paper describes the fabrication of MOS capacitor and DLTS study of annihilation of deeplevel defects upon thermal annealing. Ni/SiO2/-Si MOS structures fabricated on -type Si wafers were investigated for process-induced deep-level defects. The deep-level traps in Si substrates induced during the processing of Ni/SiO2/-Si have been investigated using deep-level transient spectroscopy (DLTS). A characteristic deep-level defect at C = 0.49 eV which was introduced during high-temperature thermal oxidation process was detected. The trap position was found to shift to different energy levels (C = 0.43, 0.46 and 0.34 eV) during thermal annealing process. The deep-level trap completely anneals at 350°C. Significant reduction in trap density with an increase in recombination life time and substrate doping concentration as a function of isochronal annealing were observed.

  19. The lifetime of axion stars

    Science.gov (United States)

    Eby, Joshua; Suranyi, Peter; Wijewardhana, L. C. R.

    2016-05-01

    We investigate the decay of condensates of scalars in a field theory defined by V (𝒜) = m2f2[1 -cos(𝒜/f)], where m and f are the mass and decay constant of the scalar field. An example of such a theory is that of the axion, in which case the condensates are called axion stars. The axion field, 𝒜, is self-adjoint. As a result, the axion number is not an absolutely conserved quantity. Therefore, axion stars are not stable and have finite lifetimes. Bound axions, localized on the volume of the star, have a coordinate uncertainty δx ˜ R ˜ 1/(maΔ), where R is the radius of the star and Δ = 1 - E0 2/ma 2. Here ma and E0 are the mass, and the ground state energy of the bound axion. Then the momentum distribution of axions has a width of δp ˜ maΔ. At strong binding, Δ = 𝒪(1), bound axions can easily transfer a sufficient amount of momentum to create and emit a free axion, leading to fast decay of the star with a transition rate Γ ˜ ma. However, when Δ ≪ 1, the momentum distribution is more restricted, and as shown in this paper, the transition rate for creating a free axion decreases as exp(-pδx) ˜exp(-Δ-1). Then sufficiently large, weakly bound axion stars, produced after the Big Bang, survive until the present time. We plot the region of their stability, limited by decay through axion loss and by gravitational instability, as a function of the mass of the axion and the mass of the star.

  20. Nuclear Power Plant Lifetime Management Study (I)

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Sung Yull; Jeong, Ill Seok; Jang, Chang Heui; Song, Taek Ho; Song, Woo Young [Korea Electric Power Research Institute, Taejon (Korea, Republic of); Jin, Tae Eun [Korea Power Engineering Company Consulting and Architecture Engineers, (Korea, Republic of); Kim, Woo Chul [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1996-12-31

    As the operation-year of nuclear power plant increases and finding sites for new nuclear power plant becomes harder, a comprehensive and systematic nuclear plant lifetime management(PLIM) program including life extension has to be established for stable and safe supply of electricity. A feasibility study was conducted to systematically evaluate technical, economic and regulatory aspect of plant lifetime managements and plant life extension for Kori-1 nuclear power plant. For technical evaluation of nuclear power plant, 13 major components were selected for lifetime evaluation by screening system. structure, and components(SSCs) of the plant. It was found that except reactor pressure vessel, which needs detailed integrity analysis, and low pressure turbine, which is scheduled to be replaced, 11 out of 13 major components have sufficient service life, for more than 40 years. Because domestic rules and regulations related to license renewal has not yet been written, review on the regulatory aspect of life extensions was conducted using US NRC rules and regulations. A cooperative effort with nuclear regulatory body is needed for early completion of license renewal rules and regulations. For economic evaluation of plant lifetime extension, a computer program was developed and used. It was found that 10 to 20 year of extension operation of Kori-1 nuclear power plant was proved. Based on the results, next phase of plant lifetime management program for detailed lifetime evaluation and presenting detailed implementation schedule for plant refurbishment for lifetime extension should be followed. (author). 74 refs., figs.