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Sample records for annihilation studies caracterizacion

  1. Gas Permeations Studied by Positron Annihilation

    NASA Astrophysics Data System (ADS)

    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.

  2. Microemulsion systems studied by positron annihilation techniques

    SciTech Connect

    Boussaha, A.; Djermouni, B.; Fucugauchi, L.A.; Ache, H.J.

    1980-07-02

    The formation of thermalized positronium atoms is greatly reduced if increasing amounts of water become solubilized in reversed micelles formed by sodium bis(2-ethylhexyl) sulfosuccinate in apolar solvents. Similar observations have been made if the surfactant is Triton X-100. The application of the positron annihilation technique to the study of microemulsions consisting of potassium oleate-alcohol-oil-water mixtures indicates, consistent with previous results, that microemulsion formation requires a certain water/oil ratio if the oil is a long-chain aliphatic hydrocarbon such as hexadecane. This ratio is 0.4 in the case of a 1-pentanol- and 0.2 for a 1-hexanol-containing mixture. This minimum water content is strongly reduced if the oil is an aromatic hydrocarbon. The positron annihilation data also sensitively reflect structural rearrangements in these solutions occurring upon further addition of water, such as the transition of spherical aggregates to a disk-like lamellae structure.

  3. Resolvability of defect ensembles with positron annihilation studies

    SciTech Connect

    Fluss, M.J.; Howell, R.H.; Rosenberg, I.J.; Meyer, P.

    1984-11-12

    Recent advances in the use of positron annihilation to study defect ensembles in and on the surfaces of metals, are pointing the way towards studies where particular positron-electron annihilation modes may be identified and studied in the presence of one another. Although a great deal is understood about the annihilation of positrons in ostensibly defect-free metals, much less is understood when the positron annihilates in complex defect systems such as liquid metals, amorphous solids, or at or near the vacuum-solid interface. In this paper the results of three experiments, all of which demonstrate means by which we can resolve various poistron annihilation channels from one another, are discussed.

  4. Study of Chemical Carcinogens by Positron Annihilation Lifetime Spectroscopy

    NASA Astrophysics Data System (ADS)

    Pivtsaev, A. A.; Razov, V. I.; Karasev, A. O.

    2013-11-01

    We have used positron annihilation lifetime spectroscopy to study the carcinogens C21H20BrN3, C4H7Cl2O4P, CCl4, CHCl3, AlF3, C8H12N4O, C6H4Cl2 and the non-carcinogens H2O, AlCl3, CH2Cl2, C2H6OS. We have established a correlation between the annihilation characteristics of the studied compounds and their degree of carcinogenicity.

  5. Phase behavior of microemulsion systems studied by positron annihilation techniques

    SciTech Connect

    Serrano, J.; Reynoso, R.; Lopez, R.; Olea, O.; Fucugauchi, L.A.

    1983-02-17

    The positron annihilation technique was applied to the study of phase behavior of sodium stearate (or oleate)-alcohol-oil-water microemulsion systems. The positron annihilation parameters revealed a dependence of the water/oil ratio at which microemulsion formation occurs on the hydrocarbon chain length of both alcohol cosurfactant and solvent as well as surfactant concentration. Dynamic laser light scattering has been utilized for substantiating the phase transitions determined in the different microemulsion systems by positron annihilation. The difference in the behavior between saturated and unsaturated surfactants is the most remarkable result of the investigation. Thus, replacing sodium stearate by sodium oleate in the surfactant-1-hexanol-isooctane systems obviated microemulsion formation. This behavior has been rationalized by considering packing and kink presence in microemulsion formation. 26 references.

  6. Positron annihilation studies in Li-implanted alumina

    NASA Astrophysics Data System (ADS)

    Gaikwad, Prashant V.; Sharma, S. K.; Mukherjee, S.; Sudarshan, K.; Maheshwari, P.; Pujari, P. K.; Kshirsagar, A.

    2015-06-01

    Depth dependent Doppler broadening of annihilation radiation (DBAR) measurements are carried out for a sample of Li ion implanted in alumina. The effect of Li ion implantation and the subsequent isochronal annealing at the temperatures up to 1100 °C on the Doppler broadening annihilation parameters (S-parameter) are studied. The S-parameter around the Li implantation depth (∼191 nm) increased with annealing temperature up to 700 °C and reduced beyond. The results suggest possible Li cluster formation in annealed sample.

  7. Positron annihilation studies of organic superconductivity

    SciTech Connect

    Yen, H.L.; Lou, Y.; Ali, E.H.

    1994-09-01

    The positron lifetimes of two organic superconductors, {kappa}-(ET){sub 2}Cu(NCS){sub 2} and {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br, are measured as a function of temperature across {Tc}. A drop of positron lifetime below {Tc} is observed. Positron-electron momentum densities are measured by using 2D-ACAR to search for the Fermi surface in {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br. Positron density distributions and positron-electron overlaps are calculated by using the orthogonalized linear combination atomic orbital (OLCAO) method to interprete the temperature dependence due to the local charge transfer which is inferred to relate to the superconducting transition. 2D-ACAR results in {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br are compared with theoretical band calculations based on a first-principles local density approximation. Importance of performing accurate band calculations for the interpretation of positron annihilation data is emphasized.

  8. First Study of Rapidity Gaps in e+e- Annihilation

    NASA Astrophysics Data System (ADS)

    Abe, K.; Abe, K.; Abt, I.; Akagi, T.; Allen, N. J.; Ash, W. W.; Aston, D.; Baird, K. G.; Baltay, C.; Band, H. R.; Barakat, M. B.; Baranko, G.; Bardon, O.; Barklow, T.; Bashindzhagyan, G. L.; Bazarko, A. O.; Ben-David, R.; Benvenuti, A. C.; 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.; Camanzi, B.; Carpinelli, M.; Cassell, R.; Castaldi, R.; Castro, A.; Cavalli-Sforza, M.; Chou, A.; Church, E.; Cohn, H. O.; Coller, J. A.; Cook, V.; Cotton, R.; Cowan, R. F.; Coyne, D. G.; Crawford, G.; D'Oliveira, A.; Damerell, C. J.; Daoudi, M.; de Sangro, R.; de Simone, P.; dell'Orso, R.; Dervan, P. J.; Dima, M.; Dong, D. N.; Du, P. Y.; Dubois, R.; Eisenstein, B. I.; Elia, R.; Etzion, E.; Falciai, D.; Fan, C.; Fero, M. J.; Frey, R.; Furuno, K.; Gillman, T.; Gladding, G.; Gonzalez, S.; Hallewell, G. D.; Hart, E. L.; Hasan, A.; Hasegawa, Y.; Hasuko, K.; Hedges, S.; 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.; Johnson, A. S.; Johnson, J. R.; Johnson, R. A.; Junk, T.; Kajikawa, R.; Kalelkar, M.; 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.; Lia, V.; Liu, M. X.; Liu, X.; Loreti, M.; Lu, A.; Lynch, H. L.; Ma, J.; Mancinelli, G.; Manly, S.; Mantovani, G.; Markiewicz, T. W.; Maruyama, T.; Massetti, R.; Masuda, H.; Mazzucato, E.; McKemey, A. K.; Meadows, B. T.; Messner, R.; Mockett, P. M.; Moffeit, K. C.; Mours, B.; Muller, D.; Nagamine, T.; Narita, S.; Nauenberg, U.; Neal, H.; 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.; Rowson, P. C.; Russell, J. J.; Saxton, O. H.; Schalk, T.; Schindler, R. H.; Schumm, B. A.; Sen, S.; Serbo, V. V.; Shaevitz, M. H.; Shank, J. T.; Shapiro, G.; Sherden, D. J.; Shmakov, K. D.; Simopoulos, C.; Sinev, N. B.; Smith, S. R.; Snyder, J. A.; Stamer, P.; 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.; Trandafir, A. I.; Turk, J. D.; Usher, T.; Va'Vra, J.; Vannini, C.; Vella, E.; 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.; Zdarko, R. W.; Zeitlin, C.; Zhou, J.

    1996-06-01

    We present the first study of rapidity gaps in e+e- annihilations, using Z0 decays collected by the SLAC Linear Collider Large Detector experiment. Our measured rapidity gap spectra fall 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.

  9. Positron-annihilation study of the equilibrium vacancy ensemble in aluminum

    SciTech Connect

    Fluss, M.J.; Berko, S.; Chakraborty, B.; Hoffmann, K.; Lippel, P.; Siegel, R.W.

    1982-06-01

    A preliminary report is presented of a positron-annihilation study of the equilibrium vacancy ensemble in aluminum using one- and two-dimensional angular correlation of annihilation radiation (ACAR) measurements versus temperature. The annihilation characteristics of a positron from the Bloch state, and the monovancy- and divacancy-trapped states have been calculated self-consistently within a supercell, including many-body enhancement effects, and are compared with experiment. 4 figures.

  10. INSTRUMENTS AND METHODS OF INVESTIGATION: Positron annihilation spectroscopy in materials structure studies

    NASA Astrophysics Data System (ADS)

    Grafutin, Viktor I.; Prokop'ev, Evgenii P.

    2002-01-01

    A relatively new method of materials structure analysis — positron annihilation spectroscopy (PAS) — is reviewed. Measurements of positron lifetimes, the determination of positron 3γ- and 2γ-annihilation probabilities, and an investigation of the effects of different external factors on the fundamental characteristics of annihilation constitute the basis for this promising method. The ways in which the positron annihilation process operates in ionic crystals, semiconductors, metals and some condensed matter systems are analyzed. The scope of PAS is described and its prospects for the study of the electronic and defect structures are discussed. The applications of positron annihilation spectroscopy in radiation physics and chemistry of various substances as well as in physics and chemistry of solutions are exemplified.

  11. Positron annihilation lifetime study of radiation-damaged natural zircons

    NASA Astrophysics Data System (ADS)

    Roberts, J.; Gaugliardo, P.; Farnan, I.; Zhang, M.; Vance, E. R.; Davis, J.; Karatchevtseva, I.; Knott, R. B.; Mudie, S.; Buckman, S. J.; Sullivan, J. P.

    2016-04-01

    Zircons are a well-known candidate waste form for actinides and their radiation damage behaviour has been widely studied by a range of techniques. In this study, well-characterised natural single crystal zircons have been studied using Positron Annihilation Lifetime Spectroscopy (PALS). In some, but not all, of the crystals that had incurred at least half of the alpha-event damage of ∼1019 α/g required to render them structurally amorphous, PALS spectra displayed long lifetimes corresponding to voids of ∼0.5 nm in diameter. The long lifetimes corresponded to expectations from published Small-Angle X-ray Scattering data on similar samples. However, the non-observation by PALS of such voids in some of the heavily damaged samples may reflect large size variations among the voids such that no singular size can be distinguished or. Characterisation of a range of samples was also performed using scanning electron microscopy, optical absorption spectroscopy, Raman scattering and X-ray scattering/diffraction, with the degree of alpha damage being inferred mainly from the Raman technique and X-ray diffraction. The observed void diameters and intensities of the long lifetime components were changed somewhat by annealing at 700 °C; annealing at 1200 °C removed the voids entirely. The voids themselves may derive from He gas bubbles or voids created by the inclusion of small quantities of organic and hydrous matter, notwithstanding the observation that no voidage was evidenced by PALS in two samples containing hydrous and organic matter.

  12. Positron annihilation lifetime spectroscopy source correction determination: A simulation study

    NASA Astrophysics Data System (ADS)

    Kanda, Gurmeet S.; Keeble, David J.

    2016-02-01

    Positron annihilation lifetime spectroscopy (PALS) can provide sensitive detection and identification of vacancy-related point defects in materials. These measurements are normally performed using a positron source supported, and enclosed by, a thin foil. Annihilation events from this source arrangement must be quantified and are normally subtracted from the spectrum before analysis of the material lifetime components proceeds. Here simulated PALS spectra reproducing source correction evaluation experiments have been systematically fitted and analysed using the packages PALSfit and MELT. Simulations were performed assuming a single lifetime material, and for a material with two lifetime components. Source correction terms representing a directly deposited source and various foil supported sources were added. It is shown that in principle these source terms can be extracted from suitably designed experiments, but that fitting a number of independent, nominally identical, spectra is recommended.

  13. Positron Annihilation Spectroscopy Study of Barnett Shale Core

    NASA Astrophysics Data System (ADS)

    Ameena, Fnu; Alsleben, Helge; Quarles, Carroll A.

    Measurements are reported of positron annihilation lifetime and Doppler broadening parameters on 14 samples of Barnett shale core selected from 196 samples ranging from depths of 6107 to 6402 feet. The Barnett shale core was taken from EOG well Two-O-Five 2H located in Johnson county TX. The selected samples are dark clay-rich mudstone consisting of fine-grained clay minerals. The samples are varied in shape, typically a few inches long and about 1/2 inch in width and thickness, and are representative of the predominant facies in the core. X-ray fluorescence (XRF), X-ray diffraction (XRD), petrographic analysis and geochemical analysis of total organic carbon (TOC) were already available for each of the selected samples. The lifetime data are analyzed in terms of three lifetime components with the shortest lifetime fixed at 125 ps. The second lifetime is attributed to positron annihilation in the bulk and positron trapping; and the third lifetime is due to positronium. Correlations of the lifetimes, intensities, the average lifetime and S and W parameters with TOC, XRF and XRD parameters are discussed. The observed correlations suggest that positron spectroscopy may be a useful tool in characterizing shale.

  14. Positron annihilation lifetime spectroscopy study of Kapton thin foils

    NASA Astrophysics Data System (ADS)

    Kanda, G. S.; Ravelli, L.; Löwe, B.; Egger, W.; Keeble, D. J.

    2016-01-01

    Variable energy positron annihilation lifetime spectroscopy (VE-PALS) experiments on polyimide material Kapton are reported. Thin Kapton foils are widely used in a variety of mechanical, electronic applications. PALS provides a sensitive probe of vacancy-related defects in a wide range of materials, including open volume in polymers. Varying the positron implantation energy enables direct measurement of thin foils. Thin Kapton foils are also commonly used to enclose the positron source material in conventional PALS measurements performed with unmoderated radionuclide sources. The results of depth-profiled positron lifetime measurements on 7.6 μm and 25 μm Kapton foils are reported and determine a dominant 385(1) ps lifetime component. The absence of significant nanosecond lifetime component due to positronium formation is confirmed.

  15. Jahn-Teller distortion of neutral divacancy in Si studied by positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Nagai, Y.; Inoue, K.; Tang, Z.; Yonenaga, I.; Chiba, T.; Saito, M.; Hasegawa, M.

    2003-12-01

    Jahn-Teller (JT) distortion of the diamagnetic neutral divacancy (V20) in Si is studied by positron annihilation spectroscopy. Based on the anisotropy of electron momentum distribution around the divacancies obtained by two-dimensional angular correlation of positron annihilation radiation (2D-ACAR) technique, the preferred alignment of the divacancy in a specimen by compressing uniaxial stress along the [0 1 1] axis is detected. The direction of the alignment evidences the pairing JT distortion rather than the resonant bonding distortion, which is similar to the distortion in the singly negative divacancy (V2-).

  16. Positron-annihilation 2D-ACAR studies of disordered and defected alloys

    SciTech Connect

    Bansil, A.; Prasad, R.; Smedskjaer, L.C.; Benedek, R.; Mijnarends, P.E.

    1987-09-01

    Theoretical and experimental progess in connection with 2D-ACAR positron annihilation studies of ordered, disordered, and defected alloys is discussed. We present, in particular, some of the recent developments concerning the electronic structure of disordered alloys, and the work in the area of annihilation from positrons trapped at vacancy-type defects in metals and alloys. The electronic structure and properties of a number of compounds are also discussed briefly; we comment specifically on high T/sub c/ ceramic superconductors, Heusler alloys, and transition-metal aluminides. 58 refs., 116 figs.

  17. Positron annihilation study for cadmium (electronic structure and enhancement effect)

    NASA Astrophysics Data System (ADS)

    Hamid, A.

    2003-12-01

    The three dimensional electron density in momentum space ρ(p) and in wave vector space n(k) was reconstructed for cadmium (Cd). The measurements were performed using the two dimensional angular correlation of annihilation radiation (2D-ACAR) technique. Enhanced contributions in the spectra were observed around 5.5 mrad, discussed in terms of a Kahana-like enhancement effect. From another viewpoint, Fermi radii were analyzed in the (λM K), (ALM) and (AHK) planes, and they showed a maximum deviation of about 4% from the free electron Fermi radius. Moreover, comparisons to a radio-frequency size effect (RFSE) experiment and theoretical band structure calculations (using augmented plane wave (APW), linear combination of atomic orbital (LCAO) and linear muffin tin orbital (LMTO) methods) were examined. The results showed a qualitative agreement with both APW and LCAO calculations. However, a favorable agreement with the APW method was determined via Fermi surface dimensions. The differences of bands' occupation of n(k) between the current work and the APW method were argued in view of positron wave function in Cd.

  18. The study of synthetic food dyes by positron annihilation lifetime spectroscopy.

    NASA Astrophysics Data System (ADS)

    Pivtsaev, A. A.; Razov, V. I.

    2015-06-01

    By method of positron annihilation lifetime spectroscopy (PALS), substances are food dyes were studied: E-102 (Tartrazine), E-124 (Ponso 4R), E 132 (Indigo carmine), E-133 (Brilliant Blue), E-151 (Black Shiny). They are examined for the presence of carcinogenic properties. The difference between dyes having explicit carcinogenic properties and mutagenic properties (non-explicit carcinogens) is established.

  19. Fluxes and spectra of quasimonochromatic annihilation photons for studying E1 giant resonances in nuclei

    SciTech Connect

    Dzhilavyan, L. Z.

    2014-12-15

    The fluxes and spectra of quasimonochromatic photons originating from the in-flight annihilation of positrons interacting with electrons of targets are analyzed in the energy region characteristic of the excitation of E1 giant resonances in nuclei. Targets of small thickness and low atomic number are used. The dependences of the spectra on the energy and angle (and their scatter) for positrons incident to the target, on the collimation angle for photons, and on the target thickness are studied.

  20. Theoretical studies of positron states and annihilation characteristics at the oxidized Cu(100) surface

    SciTech Connect

    Fazleev, N. G.; Weiss, A. H.

    2013-04-19

    In this work we present the results of theoretical studies of positron surface and bulk states and annihilation probabilities of surface-trapped positrons with relevant core electrons at the oxidized Cu(100) surface under conditions of high oxygen coverage. An ab-initio study of the electronic properties of the Cu(100) missing row reconstructed surface at various on surface and sub-surface oxygen coverages has been performed on the basis of the density functional theory (DFT) using the Dmol3 code and the generalized gradient approximation (GGA). Surface structures in calculations have been constructed by adding oxygen atoms to various surface hollow and sub-surface octahedral sites of the 0.5 monolayer (ML) missing row reconstructed phase of the Cu(100) surface with oxygen coverages ranging from 0.5 to 1.5 ML. The charge redistribution at the surface and variations in atomic structure and chemical composition of the topmost layers associated with oxidation and surface reconstruction have been found to affect the spatial extent and localization of the positron surface state wave function and annihilation probabilities of surface trapped positrons with relevant core electrons. Theoretical results are compared with experimental data obtained from studies of oxidation of the Cu(100) surface using positron annihilation induced Auger electron spectroscopy (PAES). It has been shown that positron annihilation probabilities with Cu 3s and 3p core electrons decrease when total (on-surface and sub-surface) oxygen coverage of the Cu(100) surface increases up to 1 ML. The calculations show that for high oxygen coverage when total oxygen coverage is 1. 5 ML the positron is not bound to the surface.

  1. Macromolecular conformation in solution. Study of carbonic anhydrase by the positron annihilation technique.

    PubMed Central

    Handel, E D; Graf, G; Glass, J C

    1980-01-01

    The structural features of carbonic anhydrase (carbonate hydro-lyase; EC 4.2.1.1) in aqueous solution were probed by the positron annihilation technique. The data obtained under varying conditions of temperature, pH, and enzyme concentration were interpreted in terms of the free volume model. The change of enzymic activity with temperature is accompanied by a change in free volume of the protein. Upon thermal denaturation an irreversible change in free volume of the molecule occurred. At low temperatures the protein-water interactions were investigated. These results are discussed in terms of current concepts of structure-function relationships in proteins. This study shows the sensitivity of the positron annihilation method toward the structure of proteins related to their overall conformation and to the nature of bound water. PMID:6789901

  2. Order-disorder transition in clathrate Ba6Ge25 studied by positron annihilation

    NASA Astrophysics Data System (ADS)

    Li, X. F.; Zhao, B.; Zhang, T.; He, H. F.; Zhang, Q.; Yang, D. W.; Chen, Z. Q.; Tang, X. F.

    2015-07-01

    Clathrate Ba6Ge25 is prepared by melt method and spark plasma sintering. Structural transition below room temperature is studied by positron annihilation and X-ray diffraction measurements. There is a pronounced transition in the temperature range of 200-250 K which might be involved with the movement of Ba atoms in Ge cages and result in disordered structure. This transition is further confirmed by the theoretical calculation of positron annihilation states. Thus our results confirm the structural models proposed by Carrillo-Cabrera et al. (2005). The measured specific heat capacity, electric resistivity and magnetic susceptibility all show anomalous transition in the same temperature range, indicating that the movement of Ba atoms in the cage has influence on the thermal, electric as well as magnetic properties of Ba6Ge25.

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

    NASA Astrophysics Data System (ADS)

    Grafutin, V.; Ilyukhina, O.; Krsjak, V.; Burcl, R.; Hähner, P.; Erak, D.; Zeman, A.

    2010-11-01

    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 64Cu 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.

  4. Study of the Interaction of Fluxes of Annihilating Particles

    NASA Astrophysics Data System (ADS)

    Nazarov, A. A.; Feropontova, N. M.

    2015-12-01

    A study of interacting particle fluxes in the form of an infinite linear queueing system with positive and negative requests is presented for different types of such systems. For the first class of systems with exponential service a stationary probability distribution of the number of positive requests in the system has been found. For the second class of systems, for the case of arbitrary service, the study is performed by the method of asymptotic analysis. Asymptotic equivalence of the systems under consideration is demonstrated.

  5. Study of gamma irradiation effect on positron annihilation mechanism in PFA

    NASA Astrophysics Data System (ADS)

    Yang, J.; Li, Z. X.; Zhao, B. Z.; Zhang, P.; Lu, E. Y.; Zhang, J.; Yuan, D. Q.; Cao, X. Z.; Yu, R. S.; Wang, B. Y.

    2014-03-01

    Gamma irradiation effect on annihilation characteristics of positronium and free positron in tetrafluoroethylene-perluoro (alkoxy vinyl ether) copolymer (PFA) were studied independently by age momentum correlation (AMOC) and the correlation between Doppler broadening S parameter and o-Ps fraction (S-Io-Ps correlation). AMOC results revealed decreases in S parameter of o-Ps, owing to accumulation of polar atoms around free volume. S-Io-Ps correlation indicated a reduced intrinsic S parameter of free positron in irradiated PFA, which was caused by enhanced positron trapping on polar atoms due to densification of local segments and variation in the elemental environment around free volumes.

  6. Study of positrons from cosmic rays interactions and cold dark matter annihilations in the galactic environment

    NASA Astrophysics Data System (ADS)

    Lineros, Roberto A.

    2008-12-01

    Positron and electron cosmic rays provide a complementary way to study the galactic environment. The actual cosmic rays experiments, for instance PAMELA and HEAT, have presented very exciting results in this field. The observed positron fraction appears larger than the actual theoretical predictions for energies larger than 10 GeV. The indirect evidences of Dark Matter in connection with Beyond the Standard Model theories would suggest the existence of an extra contribution present in the cosmic ray signal. We study and calculate the positron signal produced by the annihilation of a generic Dark Matter candidate. Especially, We analyze typical annihilation signatures and the impact of CR propagation physics on the positron signal. In addition, we study the positron signal related to spallation processes between nuclei cosmic--rays and the interstellar gas. We analyze the effects of uncertainties present in nuclear cross section, nuclei cosmic--ray and CR propagation physics. The propagation of positrons is modeled according to the Two--Zone Propagation Model which has been successfully tested in the study of nuclei cosmic--ray and present an analytical approach to study the cosmic--ray physics.

  7. Positron annihilation studies in binary solid solutions and mechanical mixtures of lanthanide dipivaloylmethanate complexes

    NASA Astrophysics Data System (ADS)

    Fulgêncio, F.; Oliveira, F. C.; Windmöller, D.; Araujo, M. H.; Marques-Netto, A.; Machado, J. C.; Magalhães, W. F.

    2015-11-01

    Measurements using positron annihilation lifetime (PALS) and Doppler broadening annihilation radiation lineshape (DBARLS) spectroscopies were performed in several lanthanide dipivaloylmethanate complexes, Ln(dpm)3 where Ln = Sm3+, Gd3+, Tb3+, Ho3+, Er3+, Yb3+ and dpm = 2,2,6,6-tetramethyl-3,5-pentanedionate, and also on their binary solid solutions and mechanical mixtures, biphasic systems, of the general formula Ln1-xEux(dpm)3. Expressive positronium formation was observed in all Ln(dpm)3 complexes, except in Eu(dpm)3 complex. The results indicate formation of solid solutions in the Sm3+, Gd3+and Tb3+ systems, where total inhibition of positronium formation was observed. A Stern-Volmer type equation, I30/I3 = 1 + kx, was used to fit the data, enabling the calculation of the inhibition constants, k. A mechanical mixture behavior, with linear variation of I3 between the I3 values of the pure complexes, was observed in systems containing Ho3+, Er3+ and Yb3+ complexes, where no effective solid solution formation occurred due to differences between the crystalline structures of these complexes and Eu(dpm)3. No positronium quenching reactions were observed in the solid solutions. DBARLS results confirmed those of PALS, evidencing that the positron annihilation spectroscopies are useful techniques to characterize the formation of solid solutions. PALS measurements at 80 K were performed in the Sm1-xEux(dpm)3 and Gd1-xEux(dpm)3 solid solutions. The results indicate that, despite a contraction in the crystalline structures, the solid solution structure remains intact at low temperatures. The temperature dependence of the inhibition constant do not seem to be understood from the positronium formation spur model and might be related to intra and intermolecular energy and charge transfer processes in the solid solutions, which is currently being studied.

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

    PubMed

    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

  9. Study of radiation damage in ODS steels by positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Bartošová, I.; Bouhaddane, A.; Dománková, M.; Slugeň, V.; Wall, D.; Selim, F. A.

    2016-01-01

    Microstructure of various oxide-dispersion-strengthened (ODS) steels with 15% chromium content was studied in term of vacancy defects presence and their accumulation after defined irradiation treatment, respectively. Studied materials originated from Kyoto University and studied via IAEA collaborative project. Samples were characterized “as received” by positron annihilation lifetime spectroscopy and their microstructure was examined by transmission electron microscopy as well. Samples were afterwards irradiated in Washington State University Nuclear Radiation Center via a strong gamma source (6TBq). Damage induced by gamma irradiation was evaluated by positron lifetime measurements in emphasis on defect accumulation in the materials. We have demonstrated strong defect production induced by gamma irradiation which results from positron measurement data.

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

    NASA Astrophysics Data System (ADS)

    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.

  11. A study of vacancy defects related to gray tracks in KTiOPO{sub 4} (KTP) using positron annihilation

    SciTech Connect

    Zhang, Yang; Li, Jing; Wang, Jiyang Jiang, Huaidong; Cao, Xingzhong; Yang, Jing

    2014-12-15

    For the first time to our knowledge, positron annihilation spectroscopy (PAS) was used to study vacancy defects in KTiOPO{sub 4} (KTP) single crystals. Positron annihilation lifetime spectroscopy combined with dielectric measurements identified the existence of oxygen vacancies and reflected the concentration of vacancy defects in three samples. The vacancy defects in KTP do not consist of monovacancies, but rather vacancy complexes. Doppler broadening indicates that the vacancy defects are distributed uniformly. A relationship is established where a crystal with a low oxygen vacancy concentration and a highly balanced stoichiometry has a higher resistance to gray track formation.

  12. A study of vacancy defects related to gray tracks in KTiOPO4 (KTP) using positron annihilation

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Li, Jing; Cao, Xingzhong; Yang, Jing; Wang, Jiyang; Jiang, Huaidong

    2014-12-01

    For the first time to our knowledge, positron annihilation spectroscopy (PAS) was used to study vacancy defects in KTiOPO4 (KTP) single crystals. Positron annihilation lifetime spectroscopy combined with dielectric measurements identified the existence of oxygen vacancies and reflected the concentration of vacancy defects in three samples. The vacancy defects in KTP do not consist of monovacancies, but rather vacancy complexes. Doppler broadening indicates that the vacancy defects are distributed uniformly. A relationship is established where a crystal with a low oxygen vacancy concentration and a highly balanced stoichiometry has a higher resistance to gray track formation.

  13. Study of baryon production mechanism in e+e- annihilation into hadrons

    NASA Astrophysics Data System (ADS)

    Topaz Collaboration; Aoki, M.; Itoh, R.; Watanabe, Y.; Kaneyuki, K.; Ohshima, Y.; Ochi, A.; Tanimori, T.; Abe, K.; Abe, T.; Adachi, I.; Adachi, K.; Aoki, M.; Emi, K.; Enomoto, R.; Fujii, H.; Fujii, T.; Fujii, K.; Fujimoto, J.; Fujiwara, N.; Hayashii, H.; Hirano, H.; Howell, B.; Ikeda, H.; Inoue, Y.; Itami, S.; Iwasaki, H.; Iwasaki, M.; Kajikawa, R.; Kato, S.; Kawabata, S.; Kichimi, H.; Kobayashi, M.; Koltick, D.; Levine, I.; Mamada, H.; Miyabayashi, K.; Miyamoto, A.; Nagai, K.; Nakabayashi, K.; Nakamura, M.; Nakano, E.; Nitoh, O.; Noguchi, S.; Ochiai, F.; Ohishi, N.; Ohnishi, Y.; Okuno, H.; Okusawa, T.; Shibata, E.; Sugiyama, A.; Suzuki, S.; Takahashi, K.; Takahashi, T.; Teramoto, Y.; Tauchi, T.; Tomoto, M.; Tsukamoto, T.; Tsumura, T.; Uno, S.; Yamamoto, A.; Yamauchi, M.

    1998-11-01

    The mechanism of baryon-anti-baryon pair production in e+e- annihilation into hadrons has been studied using the TOPAZ detector at the TRISTAN e+e- collider at an average center-of-mass energy of 58 GeV. The distributions of various p¯p correlations were compared with two prominent models: the cluster-fragmentation model and the string-fragmentation model. We rejected the cluster-fragmentation model at the 90% C.L. Furthermore, in the context of the string-fragmentation model, we favor the ``popcorn'' model, rejecting the ``diquark'' model, where a diquark is considered to be a fundamental entity, at the 95% C.L.

  14. Study of microvoids in high-rate a-Si:H using positron annihilation

    SciTech Connect

    Zou, X.; Webb, D.P.; Lin, S.H.; Lam, Y.W.; Chan, Y.C.; Hu, Y.F.; Beling, C.D.; Fung, S.

    1997-07-01

    In this paper, the authors have carried out the positron annihilation measurement on high-rate and low-rate a-Si:H thin films deposited by PECVD. By means of the slow positron beam Doppler-broadening technique, the depth profiles of microvoids in a-Si:H have been determined. They have also studied the vacancy-type defect in the surface region in high-rate grown a-Si:H, making comparison between high-rate and low-rate a-Si:H. By plotting S and W parameters in the (S, W) plane, they have shown that the vacancies in all of the high-rate and low-rate deposited intrinsic samples, and in differently doped low-rate samples are of the same nature.

  15. A study on symmetrization of 2D ACAR positron annihilation data

    NASA Astrophysics Data System (ADS)

    Smedskjaer, L. C.; Legnini, D. G.

    1990-07-01

    The important problem of symmetrization of two-dimensional angular correlation positron annihilation data is discussed in detail. Interest in this problem is motivated by the potential for a substantial improvement of the data quality. The artefacts present in our Anger cameras have been studied experimentally, and form the basis for a quantitative discussion of the symmetrization operation. The main conclusion is that symmetrization of the two-dimensional angular correlation spectra is allowed, if the symmetry center can be defined. It is argued that the center can be defined if the instrumental artefacts are small. Finally, it is shown that it is unlikely that the instrumental artefacts interfere constructively during the symmetrization operation.

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

    NASA Astrophysics Data System (ADS)

    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.

  17. Time-resolved positron annihilation spectroscopy study of relaxation dynamics of ion damage in fused quartz

    NASA Astrophysics Data System (ADS)

    Tsuchida, Hidetsugu; Mizuno, Shohei; Tsutsumi, Hironori; Kinomura, Atsushi; Suzuki, Ryoichi; Itoh, Akio

    2016-05-01

    Relaxation dynamics of ion damage in fused quartz is investigated by our newly developed pump–probe technique combining energetic ions (pump) with slow positrons (probe). This method enables determination of time-resolved positron lifetime. We study the time-dependent relaxation of ion damage, by analyzing the intensity variation in the ortho-positronium lifetime component associated with irradiation damage. For irradiation with 160 keV He ions in the temperature range of 300–573 K, the positron annihilation lifetime spectra are obtained as a function of time after ion irradiation. We observe that the relaxation time of ion damage is strongly influenced by specimen temperatures; the relaxation time constant is approximately 400 ms at room temperature (300 K) and becomes smaller with an increasing temperature. Analysis for the effect of temperature on damage accumulation reveals that the activation energy for thermal annealing of the observed damage is approximately 0.1 eV.

  18. Positron annihilation study of the micro-defects induced by cavitation in mild steel

    NASA Astrophysics Data System (ADS)

    Zhao, Ming; Wang, Jiadao; Chen, Darong; Hao, Xiaopeng; Wang, Baoyi

    2008-08-01

    Cavitation-induced micro-defects in mild steel after cavitation experiment in the fluid field have been studied by positron Doppler broadening measurement and positron annihilation lifetime spectra (PALS). Depth-resolved positron Doppler S-parameter (DPDS) results showed that S-parameter increased and micro-defects between the surface and the bulk has obvious variation with depth during the cavitation process. From the positron lifetime results, it was found that the size and number of micro-defects increase with the development of cavitation. These results suggest that more micro-defects are generated in mild steel bulk during the cavitation process than those in the mild steel surface layer region, although more mico-defects seen in the mild steel surface layer. Moreover, the size of micro-defects in mild steel bulk increases remarkably owing to their transfer and aggregation.

  19. Annihilation of defects in liquid crystals

    NASA Astrophysics Data System (ADS)

    Svetec, M.; Ambrožič, M.; Kralj, S.

    The annihilation of defect is studied theoretically in liquid crystals (LCs). We consider the annihilation of point disclinations in nematic and line edge dislocations in smectic A LC phase, respectively. We stress qualitative similarities in these processes. The whole annihilation regime is taken into account, consisting of the pre-collision, collision, and post-collision stage.

  20. Positron annihilation studies of Eu and Dy doped α'-Sr2SiO4

    NASA Astrophysics Data System (ADS)

    Gupta, S. K.; Sudarshan, K.; Sharma, S. K.; Pujari, P. K.; Natarajan, V.

    2015-06-01

    Sr2SiO4 is an important inorganic host for lanthanide doped white light emitting diodes (LEDs). Strontium silicate (Sr2SiO4) samples doped with 1.0 mol% of Eu3+ and Dy3+ content were prepared via sol-gel route and characterized by X-ray diffraction (XRD), Raman spectroscopy and positron annihilation spectroscopy (PAS). The concentration of the dopant ion and the temperature of annealing were optimized for maximum luminescence intensity. The positron annihilation lifetime and coincidence Doppler broadening (CDB) measurements indicated that the local environment around the positron annihilation site is different in Eu+3 doped and Dy+3 doped samples. The results could be explained based on the different local site occupancy of Eu+3 and Dy+3 in the matrix.

  1. Study of the Fermi surface of molybdenum and chromium via positron annihilation experiments

    NASA Astrophysics Data System (ADS)

    Biasini, Maurizio

    2000-02-01

    A quantitative mapping of the Fermi surface (FS) of molybdenum and chromium was sought by modelling the three-dimensional k-space occupancy with a small number of parameters which were determined by a least-squares fit to the two-dimensional angular correlation of the electron-positron annihilation radiation (2D-ACAR) data subjected to a Lock-Crisp-West (LCW) transformation. The resulting FS topology of molybdenum, unlike what was assumed in previous 2D-ACAR studies, does not support the nesting of its two main FS sheets. In the case of chromium, although the overall discrepancy with the FS expected from the theory is larger, the difference in shape between the same two FS sheets is of lesser extent. According to this analysis the ratio of the electron Fermi volume to the hole Fermi volume is found to deviate from unity, the value expected for compensated metals, for both materials. We suggest that these discrepancies might be due to positron wave function and/or electron-positron many-body distortions not predicted by the theory.

  2. Kinetic Monte Carlo study of triplet-triplet annihilation in organic phosphorescent emitters

    NASA Astrophysics Data System (ADS)

    van Eersel, H.; Bobbert, P. A.; Coehoorn, R.

    2015-03-01

    The triplet-triplet annihilation (TTA) rate in organic phosphorescent materials such as used in organic light-emitting diodes is determined predominantly either by the rate of single-step Förster-type triplet-triplet interactions, or by multi-step triplet diffusion. We show how kinetic Monte Carlo simulations may be used to analyze the role of both processes. Under steady state conditions, the effective triplet-triplet interaction rate coefficient, kTT, which is often regarded as a constant, is found to depend actually on the number of excitons lost upon a triplet-triplet interaction process and to show a significant higher-order dependence on the triplet volume density. Under the conditions encountered in transient photoluminescence (PL) studies, kTT is found to be effectively constant in the case of diffusion-dominated TTA. However, for the case of single-step TTA, a strongly different decay of the emission intensity is found, which also deviates from an analytic expression proposed in the literature. We discuss how the transient PL response may be used to make a distinction between both mechanisms. The simulations are applied to recently published work on the dye concentration dependence of the TTA rate in materials based on the archetypal green emitter tris[2-phenylpyridine]iridium (Ir(ppy)3).

  3. Studies of charmonium production in e+e- annihilation and B decays at BABAR

    NASA Astrophysics Data System (ADS)

    Garzia, Isabella

    2016-05-01

    In an e+e- B factory, charmonium states can be produced through different mechanisms, e.g. direct production in e+e- annihilation, double charmonium production, and in B-meson decays. Prompt production of J/ψ or ψ(2S) in association with a second charmonium states has been observed by both the BABAR and the Belle experiments. These processes provide an opportunity to study both perturbative and non perturbative effects in QCD and to search for new charmonium states recoiling against the reconstructed J/ψ or ψ(2S). Using the full BABAR data set collected at the ϒ(4S) resonance, we measure the absolute branching fractions of the two-body decays of B mesons (B → KXc), where Xc is a charmonium state. For events in which a B is fully reconstructed, the charmonium spectrum can be observed in an unbiased way by looking at the distribution of the K momentum in the rest frame of the recoiling B. We present also Dalitz plot analysis for the decays of B mesons to D- D0 K+ and D¯ 0 D0 K+, and we report about the observation of the Ds1 * (2700)+ resonance in these two channels, and obtain measurements of the mass and width.

  4. Positron annihilation study of aluminum, titanium, and iron alloys surface after shot peening

    NASA Astrophysics Data System (ADS)

    Zaleski, R.; Zaleski, K.; Gorgol, M.; Wiertel, M.

    2015-08-01

    Shot peening influence on alloys based on iron, aluminum, and titanium was studied using positron annihilation lifetime spectroscopy (PALS) and residual stress measurements. The PALS spectra were analyzed assuming two lifetime components. While the residual stresses change in a similar way in all the samples, the PALS results show an opposite tendency of a component relative intensities change with the time of shot peening for the Ti alloy as compared to steel or the Al alloy. A comparison between the depth profiles of positron implantation and the residual stress distribution reveals that the positron range covers a whole depth where residual stress is observed only in the Ti alloy. Based on this observation, the evolution of the defect concentration is presumed, consisting in migration of large defects away from the surface, while only smaller ones remain close to the surface. Furthermore, the positron lifetime distribution in the Al alloy was determined using the MELT program. The results showed that the initial single, wide distribution of lifetime splits into two narrower ones with increasing shot peening time.

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

    NASA Astrophysics Data System (ADS)

    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.

  6. Structure dependence of gamma-ray irradiation effects on polyethylenes studied by positron annihilation

    NASA Astrophysics Data System (ADS)

    Suzuki, Takenori; Oki, Yuichi; Numajiri, Masaharu; Miura, Taichi; Kondo, Kenjiro; Ito, Yasuo

    1995-05-01

    The irradiation effects on five kinds of polyethylenes (PEs) were studied from the viewpoints of mechanical properties, free radicals and positron annihilation. The degradation of the mechanical strength of samples irradiated by 60Co γ-rays was evaluated based on the elongation at break and the tensile strength. Fully stretched PE with a crystallinity larger than 99% was greatly affected by γ-irradiation. In low-density PEs free radicals were detectable only above 70 kGy, and sharply increased above 100 kGy. A detectable number of free radicals was obtained even at 0.1 kGy in PEs haaving high crystallinity. At around 100 kGy, the increase in the intensity ( I3) of ortho-positronium ( o-Ps), seems to be associated with an increase in the mechanical strength. Contrary to the expectation that the o-Ps seeks intermolecular space holes only in amorphous regions, the I3 obtained in PEs with nearly 100% crystallinity was almost half that low-density PEs, and τ 3 had similar values. This suggests that even in crystalline regions the o-Ps seeks intermolecular space holes comparable to those in the amorphous regions.

  7. Theoretical and positron annihilation study of point defects in intermetallic compound Ni{sub 3}Al

    SciTech Connect

    Jian Sun; Dongliang Lin

    1994-01-01

    The equilibrium equation of point defects in Ll{sub 2} types of intermetallic compounds was established in a new simple method, which is independent of the chemical potentials. The formation energies of the relevant point defects in Ni{sub 3}Al were calculated by EAM potentials and statical relaxations. The concentration of point defects at 1,000 K as a function of bulk composition and the effect of temperature on them were studied for Ni{sub 3}Al alloy. The results show that the Al-antisites are the constitutional defects in hypostoichiometric Ni{sub 3}Al, and the Ni-antisite defects in hyperstoichiometric Ni{sub 3}Al. The two types of vacancies belong to thermal defects. The positron annihilation technique was also conducted to measure the concentration of vacancies in Ni{sub 3}Al alloys with and without boron. Although vacancies interact with the boron dopant, the changes of vacancy concentration Ni{sub 3}Al alloys can not be considered as the main reason in explaining the effect of stoichiometry on the segregation of boron. The effect of stoichiometry on diffusion in Ni{sub 3}Al alloys was discussed additionally.

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

    SciTech Connect

    Kuznetsov, Pavel; Cizek, Jacub Hruska, Petr; Anwad, Wolfgang; Bordulev, Yuri; Lider, Andrei; Laptev, Roman; Mironov, Yuri

    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.

  9. Effect of electron- and neutron-irradiation on Fe-Cu model alloys studied by positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Nagai, Y.; Takadate, K.; Tang, Z.; Ohkubo, H.; Sunaga, H.; Takizawa, H.; Hasegawa, M.

    2011-01-01

    Electron- and neutron-irradiation effects on dilute Fe-Cu model alloys of nuclear reactor pressure vessel steels are studied by positron annihilation spectroscopy. We have found that, not only by high-dose neutron-irradiation but also by low-dose electron-irradiation, the aggregation of Cu atoms and vacancies takes place and the ultrafine Cu precipitates are formed after post-irradiation annealing at 400°C. In spite of large difference in the irradiation doses between the electron- and the neutron-irradiated samples, no significant difference is observed in the isochronal annealing behaviour above 400°C of positron annihilation and micro-hardness, indicating that small amount of extra vacancies enhance the aggregation of Cu atoms in Fe during the annealing-out process of the vacancies.

  10. Atomic scale study of the life cycle of a dislocation in graphene from birth to annihilation

    NASA Astrophysics Data System (ADS)

    Lehtinen, O.; Kurasch, S.; Krasheninnikov, A. V.; Kaiser, U.

    2013-06-01

    Dislocations, one of the key entities in materials science, govern the properties of any crystalline material. Thus, understanding their life cycle, from creation to annihilation via motion and interaction with other dislocations, point defects and surfaces, is of fundamental importance. Unfortunately, atomic-scale investigations of dislocation evolution in a bulk object are well beyond the spatial and temporal resolution limits of current characterization techniques. Here we overcome the experimental limits by investigating the two-dimensional graphene in an aberration-corrected transmission electron microscope, exploiting the impinging energetic electrons both to image and stimulate atomic-scale morphological changes in the material. The resulting transformations are followed in situ, atom-by-atom, showing the full life cycle of a dislocation from birth to annihilation. Our experiments, combined with atomistic simulations, reveal the evolution of dislocations in two-dimensional systems to be governed by markedly long-ranging out-of-plane buckling.

  11. Dynamics of defects in x-ray irradiated alkali chloride crystals studied by positron annihilation

    SciTech Connect

    Stern, S.H.

    1982-01-01

    Data on the time dependence of positron-electron annihilation characteristics in single crystals of the homologous series NaCl, KCl, RbCl, and CsCl after large doses of x irradiation are reported. A new instrument, the ..pi..-radian coincidence apparatus (PICA), recorded the coincidence count rate P of the two 0.5-MeV annihilation ..gamma.. rays emerging 180/sup 0/ apart from the crystal during isothermal and isochronal heating conditions. In most crystals an initial rapid increase of P to a maximum followed by a slow decline toward the coincidence count rate corresponding to the pre-irradiation state of the crystal was observed. Positron-annihilation data were completed by independent measurements of the optical absorption in KCl and NaCl crystals after various durations of isothermal heating. Absorption spectrophotometry revealed enhancement of the M band in KCl, of the R and N bands in NaCl, at the expense of the F band during the interpretation that positrons are trapped by radiation-induced color centers in which they annihilate with a higher P than in the bulk of the crystal. The dynamics associated with the incipient rise of P during the initial heating period is attributable to the agglomeration of F centers into aggregate centers. The rise times of P give access to the diffusion rates for agglomeration. At equal temperatures, a strong dependence of the rate of defect diffusion on the size of the cation was observed. The data must be corrected for the effects of decoloration of the crystals by the positrons during the measurements. Activation energies for defect diffusion annealing are extracted.

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

    PubMed

    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

  13. Positron annihilation study of neutron irradiated model alloys and of a reactor pressure vessel steel

    NASA Astrophysics Data System (ADS)

    Lambrecht, M.; Almazouzi, A.

    2009-03-01

    The hardening and embrittlement of reactor pressure vessel steels are of great concern in the actual nuclear power plant life assessment. This embrittlement is caused by irradiation-induced damage, and positron annihilation spectroscopy has been shown to be a suitable method for analysing most of these defects. In this paper, this technique (both positron annihilation lifetime spectroscopy and coincidence Doppler broadening) has been used to investigate neutron irradiated model alloys, with increasing chemical complexity and a reactor pressure vessel steel. It is found that the clustering of copper takes place at the very early stages of irradiation using coincidence Doppler broadening, when this element is present in the alloy. On the other hand, considerations based on positron annihilation spectroscopy analyses suggest that the main objects causing hardening are most probably self-interstitial clusters decorated with manganese in Cu-free alloys. In low-Cu reactor pressure vessel steels and in (Fe, Mn, Ni, Cu) alloys, the main effect is still due to Cu-rich precipitates at low doses, but the role of manganese-related features becomes pre-dominant at high doses.

  14. Annihilation of strained vortices

    NASA Astrophysics Data System (ADS)

    Kimura, Yoshifumi

    2014-11-01

    As an initial stage of vortex reconnection, approach of nearly anti-parallel vortices has often been observed experimentally and studied numerically. Inspired by the recent experiment by Kleckner and Irvine on the dynamics of knotted vortices, we have studied the motion of two anti-parellel Burgers vortices driven by an axisymmetric linear straining field. We first extend the Burgers vortex solution which is a steady exact solution of the Navier-Stokes equation to a time-dependent exact solution. Then by superposing two such solutions, we investigate the annihilation process analytically. We can demonstrate that during the annihilation process the total vorticity decays exponentially on a time-scale proportional to the inverse of the rate of strain, even as the kinematic viscosity tends to 0. The analytic results are compared with the numerical simulations of two strained vortices with the vortex-vortex nonlinear interaction by Buntine and Pullin.

  15. Positron annihilation and magnetic properties studies of copper substituted nickel ferrite nanoparticles

    NASA Astrophysics Data System (ADS)

    Kargar, Z.; Asgarian, S. M.; Mozaffari, M.

    2016-05-01

    Single phase copper substituted nickel ferrite Ni1-xCuxFe2O4 (x = 0.0, 0.1, 0.3 and 0.5) nanoparticles were synthesized by the sol-gel method. TEM images of the samples confirm formation of nano-sized particles. The Rietveld refinement of the X-ray diffraction patterns showed that lattice constant increase with increase in copper content from 8.331 for x = 0.0 to 8.355 Å in x = 0.5. Cation distribution of samples has been determined by the occupancy factor, using Rietveld refinement. The positron lifetime spectra of the samples were convoluted into three lifetime components. The shortest lifetime is due to the positrons that do not get trapped by the vacancy defects. The second lifetime is ascribed to annihilation of positrons in tetrahedral (A) and octahedral (B) sites in spinel structure. It is seen that for x = 0.1 and 0.3 samples, positron trapped within vacancies in A sites, but for x = 0.0 and 0.5, the positrons trapped and annihilated within occupied B sites. The longest lifetime component attributed to annihilation of positrons in the free volume between nanoparticles. The obtained results from coincidence Doppler broadening spectroscopy (CDBS) confirmed the results of positron annihilation lifetime spectroscopy (PALS) and also showed that the vacancy clusters concentration for x = 0.3 is more than those in other samples. Average defect density in the samples, determined from mean lifetime of annihilated positrons reflects that the vacancy concentration for x = 0.3 is maximum. The magnetic measurements showed that the saturation magnetization for x = 0.3 is maximum that can be explained by Néel's theory. The coercivity in nanoparticles increased with increase in copper content. This increase is ascribed to the change in anisotropy constant because of increase of the average defect density due to the substitution of Cu2+ cations and magnetocrystalline anisotropy of Cu2+ cations. Curie temperature of the samples reduces with increase in copper content which

  16. Positron annihilation study for enhanced nitrogen-vacancy center formation in diamond by electron irradiation at 77 K

    SciTech Connect

    Tang, Z.; Chiba, T.; Nagai, Y.; Inoue, K.; Toyama, T.; Hasegawa, M.

    2014-04-28

    A compact ensemble of high density nitrogen-vacancy (NV) centers in diamond is essential to sense various external fields with a high precision at the nanoscale. Here, defects in type IIa and type Ib diamonds induced by 28 MeV electron irradiation at 77 K were studied by combining the positron annihilation spectroscopy and first-principles calculations. It is shown that the electron irradiation at 77 K can significantly enhance the NV center formation by directly converting 24% vacancies into the NV centers, indicating that it is an efficient way to produce the high density NV centers in the type Ib diamond.

  17. Study of the structure of porous silicon via positron annihilation experiments

    NASA Astrophysics Data System (ADS)

    Biasini, M.; Ferro, G.; Monge, M. A.; Di Francia, G.; La Ferrara, V.

    2000-07-01

    We performed two-dimensional angular correlation of the electron-positron annihilation radiation (2D-ACAR) and positron lifetime measurements on a porous Si sample. From the width of the narrow 2D-ACAR component, attributed to the positronium atom, we estimated the average size of the pores to be ~2.4 nm and did not find evidence of a preferential propagation of the pores. Moreover, by comparing the 2D-ACAR spectrum with that observed for a pure Si crystal, we isolated a further isotropic component attributable to crystal defects of unknown origin.

  18. Thermalization of positronium atoms studied with time-resolved angular correlation of annihilation radiation

    NASA Astrophysics Data System (ADS)

    Takada, S.; Iwata, T.; Kawashima, K.; Saito, H.; Nagashima, Y.; Hyodo, T.

    2000-06-01

    Time dependence of the kinetic energy of positronium atoms in the free space between the grains of a pressed tablet (1 g/cm 3) of ultrafine silica powder (Cab-O-Sil EH-5) has been measured with time-resolved angular correlation of annihilation radiation (ACAR) apparatus. The apparatus has a momentum resolution of 1.29×10 -3 mc in full width at half maximum and a time resolution of 2.7 ns in full width at half maximum. It is found that the energy of positronium falls below 0.1e V in ˜10 ns after the formation.

  19. Dynamics of Defects in X-Ray Irradiated Alkali Chloride Crystals Studied by Positron Annihilation.

    NASA Astrophysics Data System (ADS)

    Stern, Stanley Hy.

    This thesis reports first data on the time dependence of positron-electron annihilation characteristics in single crystals of the homologous series NaCl, KCl, RbCl, and CsCl after large doses of x irradiation. A new instrument, the (pi)-radian coincidence apparatus (PICA), recorded the coincidence count rate P of the two 0.5-MeV annihilation (gamma) rays emerging 180(DEGREES) apart from the crystal during isothermal and isochronal heating conditions. In most crystals one observes an initial rapid increase of P to a maximum followed by a slow decline toward the coincidence count rate corresponding to the pre-irradiation state of the crystal. Positron-annihilation data were completed by independent measurements of the optical absorption in KCl and NaCl crystals after various durations of isothermal heating. Absorption spectrophotometry revealed enhancement of the M band in KCl, of the R and N bands in NaCl, at the expense of the F band during the interval of increasing P. The PICA results are consistent with the interpretation that positrons are trapped by radiation-induced color centers in which they annihilate with a higher P than in the bulk of the crystal. The dynamics associated with the incipient rise of P during the initial heating period is attributable to the agglomeration of F centers into aggregate centers. The rise times of P give access to the diffusion rates for agglomeration. At equal temperatures, we observe a strong dependence of the rate of defect diffusion on the size of the cation. For example, it is 100 times faster in CsCl than in NaCl at 120(DEGREES)C. The data must be corrected for the effects of decoloration of the crystals by the positrons during the measurements. Activation energies for defect diffusion annealing are extracted. They test the hypotheses underlying the theories of macroscopic transport properties in these crystals in that they are indicative of the dominant microscopic lattice processes and their dependence on the crystal

  20. Positron annihilation studies of the electronic structure and fermiology of the high-{Tc} superconductors

    SciTech Connect

    Smedskjaer, L.C.; Bansil, A.

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T{sub c} superconductors, with focus on the YBa{sub 2}Cu{sub 3}O{sub 7} system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  1. Positron annihilation studies of the electronic structure and fermiology of the high-[Tc] superconductors

    SciTech Connect

    Smedskjaer, L.C. ); Bansil, A. . Dept. of Physics)

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T[sub c] superconductors, with focus on the YBa[sub 2]Cu[sub 3]O[sub 7] system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  2. Positron annihilation in the interstellar medium

    NASA Technical Reports Server (NTRS)

    Guessoum, Nidhal; Ramaty, Reuven; Lingenfelter, Richard E.

    1991-01-01

    Positronium formation and annihilation are studied in a model for the interstellar medium consisting of cold cloud cores, warm partially ionized cloud envelopes, and hot intercloud gas. The gamma-ray spectra resulting from positron annihilation in these components of the interstellar medium are calculated. The spectra from the individual components are then combined, using two limiting assumptions for the propagation of the positrons, namely, that the positrons propagate freely throughout the interstellar medium, and that the positrons are excluded from the cold cloud cores. In the first case, the bulk of the positrons annihilate in the cloud cores and the annihilation line exhibits broad wings resulting from the annihilation of positronium formed by charge exchange in flight. In the second case, the positrons annihilate mainly in the warm envelopes, and the line wings are suppressed.

  3. Study of the equilibrium vacancy ensemble in aluminum using 1D- and 2D-angular correlation of annihilation radiation

    SciTech Connect

    Fluss, M.J.; Berko, S.; Chakraborty, B.; Hoffmann, K.R.; Lippel, P.; Siegel, R.W.

    1985-03-12

    One- and two-dimensional angular correlation of positron-electron annihilation radiation (1D and 2D-ACAR) data have been obtained between 293 and 903 K for single crystals of aluminum. The peak counting rates vs temperature, which were measured using the 1D-ACAR technique, provide a model independent value for the temperature dependence of the positron trapping probability. Using these results it is possible to strip out the Bloch state contribution from the observed 2D-ACAR surfaces and then compare the resulting defect ACAR surfaces to calculated 2D-ACAR surfaces for positrons annihilating from the Bloch, monovacancy, and divacancy-trapped states. The result of this comparison is that the presence of an increasing equilibrium divacancy population is consistent with the observed temperature dependence of ACAR data at high temperature in Al and that the present results when compared to earlier studies on Al indicate that the ratio of the trapping rates at divacancies and monovacancies is of order two.

  4. Study of intermittency in e sup + e sup minus annihilations at 29 GeV

    SciTech Connect

    Abachi, S.; Derrick, M.; Kooijman, P.; Musgrave, B.; Price, L.; Repond, J.; Sugano, K. ); Blockus, D.; Brabson, B.; Brom, J.M.; Jung, C.; Ogren, H.; Rust, D.R. ); Cork, B. ); Akerlof, C.; Chapman, J.; Errede, D.; Ken, M.T.; Meyer, D.I.; Neal, H.; Nitz, D.; Thun, R.; Tschirhart, R. (Michigan Univ., Ann Arbor, MI (US

    1990-06-15

    Charged particle multiplicity distributions from e{sup +}e{sup {minus}} annihilations at 29 GeV have been analyzed in selected rapidity and azimuthal angle intervals. The data were taken with the High Resolution Spectrometer at PEP. The factorial moments of the multiplicity distributions increase as the rapidity interval is decreased, the so-called intermittency phenomenon. These direct measurements of the moments agree with values derived from negative binomial fits to our multiplicity distributions in various central rapidity windows. The factorial moments are also given for the distribution in azimuthal angle around the beam direction and for the two-dimensional distribution in rapidity and azimuthal angle around the jet directions.

  5. Study on the Enhanced Contribution in Noble Metals from Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.; Ahmed, M. M.; Abu-Elmagd, M. S. M.; Rizk, R. A. M.

    2007-02-01

    Our motivations in the current work were to inspect various enhancement formulae along with to classify the electronic structure of noble metals Cu, Ag and Au. The measurements were performed via the two dimensional angular correlation of annihilation radiation 2D-ACAR apparatus. The electron density in momentum space ρ(p) was reconstructed and it displayed the following features. Initially, the reciprocal lattice points underscored the calculations, and they revealed Fermi surface features. Additionally, enhanced anisotropy exposed nearby Fermi momentum. They attributed to enhancement of the electronic wave function at the position of the positron. Finally, the high momentum contributions, due to interaction of positron with core-like-state, conducted the electronic structure of the metals under investigations. From another viewpoint, the features of Fermi surface of Cu, Ag and Au showed an expected analogous behavior as multiply connected sphere inside the first Brillouin zone.

  6. Confined water in controlled pore glass CPG-10-120 studied by positron annihilation lifetime spectroscopy and differential scanning calorimetry

    NASA Astrophysics Data System (ADS)

    Šauša, O.; Mat'ko, I.; Illeková, E.; Macová, E.; Berek, D.

    2015-06-01

    The solidification and melting of water confined in the controlled pore glass (CPG) with average pore size 12.6 nm has been studied by differential scanning calorimetry (DSC) and positron annihilation lifetime spectroscopy (PALS). The fully-filled sample of CPG by water as well as the samples of CPG with different content of water were used. The measurements show the presence of amorphous and crystalline phases of water in this type and size of pores, freezing point depression of a confined liquid and presence of certain transitions at lower temperatures, which could be detected only for cooling regime. The localization of confined water in the partially filled pores of CPG at room temperature was studied.

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

    NASA Astrophysics Data System (ADS)

    Abdel-Hady, E. E.; Abdel-Hamed, M. O.; Hammam, A. M.

    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 τPs 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, I3, 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.

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

    NASA Astrophysics Data System (ADS)

    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.

  9. Positron annihilation studies of vacancy related defects in ceramic and thin film Pb(Zr,Ti)O{sub 3} materials

    SciTech Connect

    Keeble, D.J.; Krishnan, A.; Umlor, M.T.; Lynn, K.G.; Warren, W.L.; Dimos, D.; Tuttle, B.A.; Ramesh, R.; Poindexter, E.H.

    1994-07-01

    Preliminary positron annihilation studies of ceramic and thin film Pb(Zr,Ti)O{sub 3} (PZT) materials have been completed. This paper examines effects of processing conditions on vacancy related defects. Positron lifetime measurements on bulk PLZT plates showed an increase in positron trapping to a defect state with increasing grain size consistent with trapping to lead vacancy related defects formed through lead oxide loss during processing. Variable energy positron beam measurements were completed on bulk PLZT plates, sol-gel PZT thin films and laser ablated PLZT thin films. Films processed in a reduced oxygen atmosphere were found to give a higher S-parameter, due to an increase in concentration of neutral or negatively charged vacancy type defects, compared with material processed in an oxidizing ambient.

  10. Study of Benzyl Salicylate/beta-Cyclodextrin Inclusion Complex Formation by Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Bellitto, V. J.; Hsu Hadley, F. H., Jr.; Trinh, T.

    1996-11-01

    Results of positron annihilation lifetime spectra of beta-cyclodextrin and beta-cyclodextrin complexed with benzyl salicylate,benzyl acetate, or ethyl salicylate in air and vacuum were used to determine the fraction of beta-cyclodextrin which remains uncomplexed in the benzyl salicylate/beta-cyclodextrin 1:2 molar ratio inclusion complex. The intensity of the longest-lived component in vacuum was shown to decrease when the beta-cyclodextrin cavity was filled with benzyl salicylate, benzyl acetate, or ethyl salicylate guest molecules. Comparison of the intensity for beta-cyclodextrin, benzyl salicylate/beta-cyclodextrin 1:2 molar ratio, and 1:1 molar ratio indicated that the benzyl and salicylate moieties each formed an inclusion complex with a molecule of beta-cyclodextrin in the benzyl salicylate/beta-cyclodextrin 1:2 complex. It was determined that the benzyl moiety of the benzyl salicylate molecule is preferred by the beta-cyclodextrin "host" and that only 34of the salicylate moieties are complexed in the benzyl salicylate/beta-cyclodextrin 1:2 sample.

  11. A study of photon production in hadronic events from e + e - annihilation

    NASA Astrophysics Data System (ADS)

    Pitzl, D. D.; Allison, J.; Ambrus, K.; Barlow, R. J.; Bartel, W.; Bethke, S.; Bowdery, C. K.; Cartwright, S. L.; Chrin, J.; Clarke, D.; Dieckmann, A.; Duerdoth, I. P.; Eckerlin, G.; Elsen, E.; Felst, R.; Finch, A. J.; Foster, F.; Greenshaw, T.; Hagemann, J.; Haidt, D.; Heintze, J.; Heinzelmann, G.; Hellenbrand, K. H.; Hill, P.; Hughes, G.; Kado, H.; Kawagoe, K.; Kleinwort, C.; Knies, G.; Kobayashi, T.; Komamiya, S.; Krehbiel, H.; v. Krogh, J.; Kuhlen, M.; Loebinger, F. K.; MacBeth, A. A.; Magnussen, N.; Marshall, R.; Meinke, R.; Middleton, R. P.; Minowa, H.; Murphy, P. G.; Naroska, B.; Nye, J. M.; Olsson, J.; Ould-Saada, F.; Ramcke, R.; Rieseberg, H.; Schmidt, D.; Smolik, L.; Schneekloth, U.; Skard, J. A. J.; Spitzer, P.; Steffen, P.; Stephens, K.; Wagner, A.; Walker, I. W.; Weber, G.; Zimmer, M.; Zorn, G. T.

    1990-03-01

    Results are presented on an investigation of photons produced in multihadronic final states from e + e - annihilation at 35 GeV and 44 GeV center of mass energies. Scalling violation between 14 and 44 GeV is observed in inclusive photon spectra. Comparing inclusive π0 spectra with charged pion spectra it is found that the average π0 multiplicity exceeds the charged pion multiplicity scaled by factor of 0.5 by (16±5)% and (21±7)% at 35 and 44 GeV respectively. The excess can be attributed to isospin violating decays of hadrons. The η multiplicity is found to be < n η<=0.64±0.09±0.06 at 35 GeV. With a significance of three standard deviations a signal from quark bremsstrahlung is observed. The measured charge asymmetry in hadronic final states, due to the interference between initial and final state radiation, of A=-0.141±0.041 is in accord with QED expectations. An interference effect in the azimuth angle distribution of charged jets around the photon direction is observed for the first time.

  12. Positron annihilation studies of defects in molecular beam epitaxy grown III-V layers

    SciTech Connect

    Umlor, M.T.; Keeble, D.J.; Asoka-Kumar, P.; Lynn, K.G.; Cooke, P.W.

    1994-08-01

    A summary of recent positron annihilation experiments on molecular beam epitaxy (MBE) grown III-V layers is Presented. Variable energy positron beam measurements on Al{sub 0.32}Ga{sub 0.68}As undoped and Si doped have been completed. Positron trapping at a open volume defect in Al{sub 0.32}Ga{sub 0.68}:Si for temperatures from 300 to 25 K in the dark was observed. The positron trap was lost after 1.3 eV illumination at 25K. These results indicate an open volume defect is associated with the local structure of the deep donor state of the DX center. Stability of MBE GaAs to thermal annealing war, investigated over the temperature range of 230 to 700{degrees}C, Proximity wafer furnace anneals in flowing argon were used, Samples grown above 450{degrees}C were shown to be stable but for sample below this temperature an anneal induced vacancy related defect was produced for anneals between 400 and 500{degrees}C. The nature of the defect was shown to be different for material grown at 350 and 230{degrees}C. Activation energies of 2.5 eV to 2.3 eV were obtained from isochronal anneal experiments for samples grown at 350 and 230{degrees}C, respectively.

  13. Microstructural evolution of RPV steels under proton and ion irradiation studied by positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Jiang, J.; Wu, Y. C.; Liu, X. B.; Wang, R. S.; Nagai, Y.; Inoue, K.; Shimizu, Y.; Toyama, T.

    2015-03-01

    The microstructural evolution of reactor pressure vessel (RPV) steels induced by proton and heavy ion irradiation at low temperature (∼373 K) has been investigated using positron annihilation spectroscopy (PAS), atom probe tomography (APT), transmission electron microscopy (TEM) and nanoindentation. The PAS results indicated that both proton and heavy ion irradiation produce a large number of matrix defects, which contain small-size defects such as vacancies, vacancy-solute complexes, dislocation loops, and large-size vacancy clusters. In proton irradiated RPV steels, the size and number density of vacancy cluster defects increased rapidly with increasing dose due to the migration and agglomeration of vacancies. In contrast, for Fe ion irradiated steels, high density, larger size vacancy clusters can be easily induced at low dose, showing saturation in PAS response with increasing dose. No clear precipitates, solute-enriched clusters or other forms of solute segregation were observed by APT. Furthermore, dislocation loops were observed by TEM after 1.0 dpa, 240 keV proton irradiation, and an increase of the average nanoindentation hardness was found. It is suggested that ion irradiation produces many point defects and vacancy cluster defects, which induce the formation of dislocation loops and the increase of nanoindentation hardness.

  14. Some Annihilating Particle Systems.

    NASA Astrophysics Data System (ADS)

    Balding, David

    Available from UMI in association with The British Library. Requires signed TDF. Systems of annihilating and coalescing particles on both infinite and periodic one-dimensional state spaces are studied. These systems have various applications in the physical sciences, in particular they are useful as simple models of diffusion-limited reactions. A unified approach to computing properties of the systems using duality methods is presented and it is shown that many results in the scientific literature, derived using diverse techniques, are readily obtained in this general framework. The transition distributions of the processes with arbitrary initial configurations are characterized in terms of two-particle annihilation processes. Further, a concise expression for the distribution of the cardinality of the processes with finite initial configurations is given and particular cases of interest from the applications perspective are described in detail. Asymptotic site occupancies, previously known for certain classes of initial configurations, are derived for all spatially stationary configurations. The asymptotic spatial structure is described for many cases by showing convergence to point processes whose properties are given.

  15. Fermionic semi-annihilating dark matter

    NASA Astrophysics Data System (ADS)

    Cai, Yi; Spray, Andrew

    2016-01-01

    Semi-annihilation is a generic feature of dark matter theories with symmetries larger than Z_2 . 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.

  16. A positron annihilation lifetime spectroscopic study of the corrosion protective properties of epoxy coatings

    SciTech Connect

    MacQueen, R.C.

    1992-01-01

    Positron Annihilation Lifetime Spectroscopy (PALS) was used to measure the free volume cavity sizes and free volume fractions of crosslinked epoxy coatings on steel before and after saturation with liquid water at 23[degrees]C. A direct linear relationship between the equilibrium volume fraction of water absorbed and the dry relative free volume fraction of bisphenol A epoxy coatings was found. The free volume cavity sizes and the number of free volume cavities per unit volume of these epoxies were found to decrease after water saturation. These decreases are ascribed to the occupation of 13-17% of the free volume cavities by 2-4 water molecules per cavity. The free volume cavity size of polyglycol diepoxides was found to increase after water saturation. This increase is ascribed to the expansion of the free volume cavities by water, which is substantiated by the macroscopic swelling observed in these coatings. An inverse, linear relationship between the equilibrium water uptake and the relative free volume fraction of these coatings were observed. This result coupled with the fact that less than one molecule of nitrobenzene was determined to fit into an epoxy free volume cavity, and that nitrobenzene is quite soluble in most of the epoxides, indicates that other factors besides the magnitude of the free volume fraction affect the amount of solvent absorbed by epoxy coatings. The small percentage of free volume occupied by water and the small number of water molecules capable of filling each void of the bisphenol A epoxies after water saturation correlate to the high impedance values and the good corrosion protection of these coatings, suggesting that water passes through these coatings by slow diffusion through the connected free volume cavities in the coating. Increases in the free volume cavity sizes of the polyglycol diepoxides after water saturation correlate to the low impedance and the poor corrosion protection of these coatings.

  17. Positron annihilation studies of fluorine-vacancy complexes in Si and SiGe

    SciTech Connect

    Edwardson, C. J.; Coleman, P. G.; El Mubarek, H. A. W.; Gandy, A. S.

    2012-04-01

    The formation of fluorine-vacancy (FV) complexes in strained Si-SiGe-Si multilayer structures and relaxed SiGe layers of varying Ge content has been investigated using variable-energy positron annihilation spectroscopy, including Doppler-broadened spectra ratio curves. It has been found that in all sample types there are two distinct regions defined only by the damage created by the implanted F ions. The first, shallower region (from the surface to a depth of {approx}200 nm) was found to contain a mixture of undecorated vacancies and FV complexes; there is no correlation between the vacancy or F concentration in this region and the Ge content. The multi-layer samples may also have O contamination that is not present in the relaxed samples. The second region (at depths {approx}200-440 nm) contains primarily FV complexes in all samples. In the multi-layer samples secondary ion mass spectrometry (SIMS) results show peaks of F accumulating in, or at the interfaces of, each SiGe multi-layer; the FV complexes, however, are distributed over depths similar to those in the relaxed samples, with some localization at the SiGe layer located within the second region. The positron response is primarily to FV complexes formed by the F implant in all samples. The F: FV ratios are approximately 3-7: 1 in the relaxed samples. Positrons appear to be relatively insensitive to the largest of the F SIMS peaks which lies beyond the second region. This is probably because the F has filled all the open volume at the SiGe layer, leaving no positron trapping sites.

  18. Nuclear annihilation by antinucleons

    DOE PAGESBeta

    Lee, Teck-Ghee; Wong, Cheuk-Yin

    2016-01-25

    We examine the momentum dependence ofmore » $$\\bar p$$$p$ and $$\\bar n$$$p$ annihilation cross sections by considering the transmission through a nuclear potential and the $$\\bar p p$$ Coulomb interaction. Compared to the $$\\bar n p$$ annihilation cross section, the $$\\bar p p$$ annihilation cross section is significantly enhanced by the Coulomb interaction for projectile momenta below $$p_{\\rm lab} <$$ 500 MeV/$c$$, and the two annihilation cross sections approach the Pomeranchuk's equality limit [JETP {\\bb 30}, 423 (1956)] at $$p_{\\rm lab}\\sim 500$ MeV/$c$. Using these elementary cross sections as the basic input data, the extended Glauber model is employed to evaluate the annihilation cross sections for $$\\bar n$$ and $$\\bar p$$ interaction with nuclei and the results compare well with experimental data.« less

  19. Brane annihilations during inflation

    SciTech Connect

    Battefeld, Diana; Battefeld, Thorsten; Firouzjahi, Hassan; Khosravi, Nima E-mail: tbattefe@princeton.edu E-mail: nima@ipm.ir

    2010-07-01

    We investigate brane inflation driven by two stacks of mobile branes in a throat. The stack closest to the bottom of the throat annihilates first with antibranes, resulting in particle production and a change of the equation of state parameter w. We calculate analytically some observable signatures of the collision; related decays are common in multi-field inflation, providing the motivation for this case study. The discontinuity in w enters the matching conditions relating perturbations in the remaining degree of freedom before and after the collision, affecting the power-spectrum of curvature perturbations. We find an oscillatory modulation of the power-spectrum for scales within the horizon at the time of the collision, and a slightly redder spectrum on super-horizon scales. We comment on implications for staggered inflation.

  20. Accounting for the lack of nano-effect in a thermoset/clay nanocomposite: A positron annihilation study

    NASA Astrophysics Data System (ADS)

    Rath, S. K.; Sudarshan, K.; Patri, M.; Pujari, P. K.

    2015-06-01

    The effect of nanoclay dispersion on the thermo-mechanical properties of an unsaturated polyester thermoset resin was studied by flexural and dynamic mechanical property measurements. Transmission electron microscopy studies revealed intercalated clay dispersion morphology in the nanocomposites. The thermomechanical measurements showed a steady decrease in the flexural strength and a relaxation temperature, with only moderate increase in the storage modulus at 1% clay loading, followed by a drop at higher clay loadings. In order to understand the absence of nano-effect in this case, free volume measurements were carried out by using positron annihilation lifetime spectroscopy. A bimodal distribution of o-Ps life times was observed. Nanoclay loading resulted in the increase of the o-Ps intensity corresponding to the longest life time as well as free volume fraction suggesting diminished chain packing efficiency in the nanocomposites. We posit that nanoclay induced decreased chain packing efficiency and the presence of higher free volume size elements might cause deterioration in mechanical properties of the nanocomposites.

  1. Positron Annihilation Study of Zr-2.5 wt.% Nb alloy Irradiated by Ar9+ heavy ions

    NASA Astrophysics Data System (ADS)

    Devi, Aruna; Menon, Ranjini; Maheshwari, Priya; Neogy, S.; Mukherjee, P.; Nabhiraj, P. Y.; Pujari, P. K.; Srivastava, D.; Dey, G. K.

    2015-06-01

    Zr-2.5 Nballoy is used as a pressure tube material in pressurized heavy water reactor (PHWR). It is one of the most critical component which decides the lifespan of the reactor. The in-reactor degrading phenomenon of prime concern is dimensional changes caused by irradiation induced creep and growth processes. The present study aims to understand the mechanism of irradiation damage by irradiating the alloy with heavy ion. Such type of irradiation study would facilitate larger damage of material in a shorter time. Zr-2.5Nb alloy samples were irradiated using 315 keV Ar9+ ion for different durations. The irradiation doses were varied in the range of 3.1X1015 to 4.17X1016 Ar9+/cm2. SRIM calculation was carried out to evaluate damage profile in the irradiated samples. Beam based Positron Annihilation Spectroscopy (PAS) technique was used for depth profiling to characterize defect distribution in the alloys. The no. of defects generated is seen to increase with the increase in the fluence.

  2. Effect of phosphorus on vacancy-type defect behaviour in electron-irradiated Ni studied by positron annihilation

    NASA Astrophysics Data System (ADS)

    Druzhkov, A. P.; Danilov, S. E.; Perminov, D. A.; Arbuzov, V. L.

    2015-02-01

    Very dilute Ni-P system (containing 50-240 appm phosphorus) irradiated by 5 MeV electrons at various temperatures (270-543 K) was studied by positron annihilation spectroscopy (PAS) and the electrical resistivity measurements. Under irradiation at 270 K (below stage III in Ni), the accumulation of the monovacancies in the Ni-P system is 1.5-2.0 times greater than that in pure Ni irradiated in the same conditions. This fact attests to the strong interaction between P atoms and self-interstitial atoms (SIAs). As a result of the non-mobile SIA-P complexes formation, the mutual recombination of point defects is suppressed and the vacancy accumulation is, respectively, enhanced. During post-irradiation annealing, the vacancy migration induces the transport process of the phosphorus atoms and leads to the formation of the vacancy clusters decorated with P atoms. The annealing behaviour of the defect structures in Ni-P systems after irradiation at enhanced temperatures was also studied. The influence of phosphorus on the formation and further evolution of the vacancy aggregates decrease with increasing of the irradiation temperature.

  3. Engineering Multi-scale Electrospun Structure for Integration into Architected 3-D Nanofibers for Cimex Annihilation: Fabrication and Mechanism Study

    NASA Astrophysics Data System (ADS)

    He, Shan; Zhang, Linxi; Liu, Ying; Rafailovich, Miriam; Garcia Center for Polymers at Engineered Interfaces Team

    In this study, engineered electrospun scaffolds with fibers oriented with designed curvature in three dimensions (3D) including the looped structure were developed based on the principle of electrostatic repulsion. Here we illustrate that 3D electrospun recycled polystyrene fibers could closely mimic the unique architectures of multi-direction and multi-layer nano-spiderweb. In contrast to virgin PS, the recycled PS (Dart Styrofoam) are known to contain zinc stearate which acts as a surfactant resulting in higher electrical charge and larger fiber curvature, hence, lower modulus. The surfactant, which is known to decrease the surface tension, may have also been effective at decreasing the confinement of the PS, where chain stretching was shown to occur, in response to the high surface tension at the air interface. Three dimensional flexible architecture with complex structures are shown to be necessary in order to block the motion of Cimex lectularius. Here we show how an engineered electrospun network of surfactant modified polymer fibers with calculated dimensions can be used to immobilize the insects. The mechanical response of the fibers has to be specifically tailored so that it is elastically deformed, without fracturing or flowing. Carefully controlling and tailoring the electrospinning parameters we can now utilize architected 3D nanofiber to create an environmental-friendly Cimex immobilization device which can lead to annihilation solution for all the other harmful insects.

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

    NASA Astrophysics Data System (ADS)

    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.

  5. Positron annihilation lifetime studies of changes in free volume on some biorelevant nitrogen heterocyclic compounds and their S-glycosylation.

    PubMed

    Mahmoud, K R; Khodair, A I; Shaban, S Y

    2015-11-01

    A series of N-heterocyclic compounds was investigated by positron annihilation lifetime spectroscopy as well as Doppler broadening of annihilation radiation (DBAR) at room temperature. The results showed that the formation probability and life time of ortho-positronium in this series are structure and electron-donation character dependent, and can give more information about the structure. The DBAR provides direct information about the change of core and valance electrons as well as the number of defect types present in these compounds. PMID:26272166

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

    PubMed

    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

  7. Positron annihilation spectroscopic study of high performance semi-interpenetrating network polyimids

    NASA Technical Reports Server (NTRS)

    Ray, Asit K.

    1995-01-01

    Semi-interpenetrating (S-IPN) network polyimids were made from different proportions of LaRC RP46 (a thermosetpolyimid) and LaRC BDTA-ODA (a thermoplastic polyimid). The ultimate goal of this networking is to improve the mechanical properties of the thermoset polyimid. Positron lifetime study was made to calculate lifetime based on second component of the life time spectra and the free volume & microvoid size. All these properties tend to decrease steadily with increasing thermoset content except at the 50 percent thermoset level where these properties show sudden drop. This result contradicts with the initial expectation that the blend properties should change gradually if it were a solid solution of thermoset (TSP) and thermoplastic (TPP) components. Thermal analyses (TMA, DSC, DMA & TGA) were run to complement the positron life time studies. The TMA and DSC studies confirm the contradiction mentioned above. Further experimentation with S-IPN polymers made at TSP/TTP content around 50/50 level are being conducted to explain this anomaly. Scanning electron microscope study of the S-IPN polyimid samples is under way in order to detect morphological differences which might help explain the phenomenon mentioned above.

  8. [A study of the magnetic field annihilation process in the magnetosphere and some geotechnical applications

    SciTech Connect

    Not Available

    1993-01-01

    This paper describes significant progress made in the study of magnetic field reconnection and plasma processes in the magnetosphere in the past three years. A total of 43 research and review papers have been completed under the DOE support. In this paper, some of the most important results obtained in the past three-years are described.

  9. Studies of iron exposed to heavy ion implantation using positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Horodek, P.; Dryzek, J.; Skuratov, V. A.

    2016-05-01

    Variable energy positron beam and positron lifetime spectroscopy were used to study pure iron exposed to irradiation with 167 MeV Xe26+ heavy ions with different doses of 1012, 1013, 5×1013, 1014 ions/cm2. The positron lifetime spectroscopy revealed the presence of large cluster of about 15-27 vacancies and dislocations. The dislocations are distributed at the depth of about 18 μm i.e. almost twice deeper than the ion implantation range from the surface exposed to the heavy ions implantation. Possible explanation is the long-range effect attributed to the ion implantation into materials.

  10. [A study of the magnetic field annihilation process in the magnetosphere and some geotechnical applications

    SciTech Connect

    Lee, L.C.; Akasofu, S.I.

    1993-01-01

    The basic plasma processes associated with magnetic reconnection in the Earth's magnetosphere are studied in our proposed project. In the past year, several problems associated with the 2-D and 3-D nonlinear reconnection processes were investigated. A new theory for nonlinear fast steady-state magnetic reconnection is proposed. The inflow region possesses highly curved magnetic field lines, which differs from that in the classical model of Petschek. A separatrix jet of plasma is ejected from the central diffusion region along the magnetic separatrix. Two types of outflow are studied, the simplest one possessing a potential outflow magnetic field and the other containing weak standing shock waves attached to the ends of the diffusion region. Across the separatrix jet, the outflow can be either slowed down by the fast-mode shocks or speeded up by the slow-mode shocks, depending on the downstream boundary conditions. In the 3-D MHD simulations, frayed magnetic flux ropes are found to be formed during the dayside magnetic reconnection process. Strong flux rope-aligned plasma flows are observed. Simulations of the driven reconnection process also indicate that the focusing of the Poynting flux has an important effect on the onset of reconnection and the location of reconnection sites.

  11. Nano-pore size and porosity study by means of Nuclear Magnetic Resonance and Positronium Annihilation Lifetime

    NASA Astrophysics Data System (ADS)

    Chesta, M. A.; Ramia, M. E.; Jeandrevin, S.; Martín, C. A.

    2009-11-01

    The present work involves a comprehensive experimental determination of porosity and pore size distribution in rocks from oil fields formations by deuterium (2H) Nuclear Magnetic Resonance (NMR) and Positronium Annihilation Lifetime Spectroscopy (PALS). Both techniques yield complementary results; PALS measures the average pore size providing bulk information from which the most abundant pore size can be obtained, and NMR allows for the determination of the relative pore size distribution accurately. Both techniques give complementary information to obtain an absolute pore size distribution.

  12. A Study of Double-Charm and Charm-Strange Baryons inElectron-Positron Annihilations

    SciTech Connect

    Edwards, Adam J.; /SLAC

    2007-10-15

    In this dissertation I describe a study of double-charm and charm-strange baryons based on data collected with the BABAR Detector at the Stanford Linear Accelerator Center. In this study I search for new baryons and make precise measurements of their properties and decay modes. I seek to verify and expand upon double-charm and charm-strange baryon observations made by other experiments. The BABAR Detector is used to measure subatomic particles that are produced at the PEP-II storage rings. I analyze approximately 300 million e+e- {yields} c{bar c} events in a search for the production of double-charm baryons. I search for the double-charm baryons {Xi}{sup +}{sub cc} (containing the quarks ccd) and {Xi}{sup ++}{sub cc} (ccu) in decays to {Lambda}{sup +}{sub c}K{sup -}{pi}{sup +} and {Lambda}{sup +}{sub c}K{sup -}{pi}{sup +}{pi}{sup +}, respectively. No statistically significant signals for their production are found, and upper limits on their production are determined. Statistically significant signals for excited charm-strange baryons are observed with my analysis of approximately 500 million e+e- {yields} c{bar c} events. The charged charm-strange baryons {Xi}{sub c}(2970){sup +}, {Xi}{sub c}(3055){sup +}, {Xi}{sub c}(3123){sup +} are found in decays to {Lambda}{sup +}{sub c}K{sup -}{pi}{sup +}, the same decay mode used in the {Xi}{sup +}{sub cc} search. The neutral charm-strange baryon {Xi}{sub c}(3077){sup 0} is observed in decays to {Lambda}{sup +}{sub c}K{sub 8}{pi}{sup -}. I also search for excited charm-strange baryon decays to {Lambda}{sup +}{sub c}K{sub 8}, {Lambda}{sup +}{sub c}K{sup -}, {Lambda}{sup +}{sub c}K{sub 8}{pi}{sup -}{pi}{sup +}, and {Lambda}{sup +}{sub c}K{sup -}{pi}{sup -}{pi}{sup +}. No significant charm-strange baryon signals a f h these decay modes. For each excited charm-strange baryon state that I observe, I measure its mass, natural width (lifetime), and production rate. The properties of these excited charm-strange baryons and their

  13. Free volumes in bulk nanocrystalline metals studied by the complementary techniques of positron annihilation and dilatometry.

    PubMed

    Würschum, Roland; Oberdorfer, Bernd; Steyskal, Eva-Maria; Sprengel, Wolfgang; Puff, Werner; Pikart, Philip; Hugenschmidt, Christoph; Pippan, Reinhard

    2012-07-15

    Free-volume type defects, such as vacancies, vacancy-agglomerates, dislocations, and grain boundaries represent a key parameter in the properties of ultrafine-grained and nanocrystalline materials. Such free-volume type defects are introduced in high excess concentration during the processes of structural refinement by severe plastic deformation. The direct method of time-differential dilatometry is applied in the present work to determine the total amount and the kinetics of free volume by measuring the irreversible length change upon annealing of bulk nanocrystalline metals (Fe, Cu, Ni) prepared by high-pressure torsion (HPT). In the case of HPT-deformed Ni and Cu, distinct substages of the length change upon linear heating occur due to the loss of grain boundaries in the wake of crystallite growth. The data on dilatometric length change can be directly related to the fast annealing of free-volume type defects studied by in situ Doppler broadening measurements performed at the high-intensity positron beam of the FRM II (Garching, Munich, Germany). PMID:23471443

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

    NASA Astrophysics Data System (ADS)

    Zhu, Huiping; Wang, Zhiguang; Gao, Xing; Cui, Minghuan; Li, Bingsheng; Sun, Jianrong; Yao, Cunfeng; Wei, Kongfang; Shen, Tielong; Pang, Lilong; Zhu, Yabin; Li, Yuanfei; Wang, Ji; Song, Peng; Zhang, Peng; Cao, Xingzhong

    2015-02-01

    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 × 1015 and 1.7 × 1016 ions/cm2. 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.

  15. Free volumes in bulk nanocrystalline metals studied by the complementary techniques of positron annihilation and dilatometry

    PubMed Central

    Würschum, Roland; Oberdorfer, Bernd; Steyskal, Eva-Maria; Sprengel, Wolfgang; Puff, Werner; Pikart, Philip; Hugenschmidt, Christoph; Pippan, Reinhard

    2012-01-01

    Free-volume type defects, such as vacancies, vacancy-agglomerates, dislocations, and grain boundaries represent a key parameter in the properties of ultrafine-grained and nanocrystalline materials. Such free-volume type defects are introduced in high excess concentration during the processes of structural refinement by severe plastic deformation. The direct method of time-differential dilatometry is applied in the present work to determine the total amount and the kinetics of free volume by measuring the irreversible length change upon annealing of bulk nanocrystalline metals (Fe, Cu, Ni) prepared by high-pressure torsion (HPT). In the case of HPT-deformed Ni and Cu, distinct substages of the length change upon linear heating occur due to the loss of grain boundaries in the wake of crystallite growth. The data on dilatometric length change can be directly related to the fast annealing of free-volume type defects studied by in situ Doppler broadening measurements performed at the high-intensity positron beam of the FRM II (Garching, Munich, Germany). PMID:23471443

  16. Positron annihilation studies of the AlOx/SiO2/Si interface in solar cell structures

    NASA Astrophysics Data System (ADS)

    Edwardson, C. J.; Coleman, P. G.; Li, T.-T. A.; Cuevas, A.; Ruffell, S.

    2012-03-01

    Film and film/substrate interface characteristics of 30 and 60 nm-thick AlOx films grown on Si substrates by thermal atomic layer deposition (ALD), and 30 nm-thick AlOx films by sputtering, have been probed using variable-energy positron annihilation spectroscopy (VEPAS) and Doppler-broadened spectra ratio curves. All samples were found to have an interface which traps positrons, with annealing increasing this trapping response, regardless of growth method. Thermal ALD creates an AlOx/SiOx/Si interface with positron trapping and annihilation occurring in the Si side of the SiOx/Si boundary. An induced positive charge in the Si next to the interface reduces diffusion into the oxides and increases annihilation in the Si. In this region there is a divacancy-type response (20 ± 2%) before annealing which is increased to 47 ± 2% after annealing. Sputtering seems to not produce samples with this same electrostatic shielding; instead, positron trapping occurs directly in the SiOx interface in the as-deposited sample, and the positron response to it increases after annealing as an SiO2 layer is formed. Annealing the film has the effect of lowering the film oxygen response in all film types. Compared to other structural characterization techniques, VEPAS shows larger sensitivity to differences in film preparation method and between as-deposited and annealed samples.

  17. Clarifying the mechanism of triplet-triplet annihilation in phosphorescent organic host-guest systems: A combined experimental and simulation study

    NASA Astrophysics Data System (ADS)

    Zhang, L.; van Eersel, H.; Bobbert, P. A.; Coehoorn, R.

    2016-05-01

    At high brightness, triplet-triplet annihilation (TTA) reduces the efficiency of organic light-emitting diodes. Triplet diffusion may considerably enhance this effect, which is otherwise limited by the rate of long-range interactions. Although its role can be clarified by studying the emissive dye concentration dependence of the TTA loss, we demonstrate here the practical applicability of a more direct method, requiring a study for only a single dye concentration. The method uses transient photoluminescence yield measurements, for a wide initial excitation density range. The analysis is applied to an iridium complex and is supported by the results of kinetic Monte Carlo simulations.

  18. A study of defects in iron-based binary alloys by the Mössbauer and positron annihilation spectroscopies

    SciTech Connect

    Idczak, R. Konieczny, R.; Chojcan, J.

    2014-03-14

    The room temperature positron annihilation lifetime spectra and {sup 57}Fe Mössbauer spectra were measured for pure Fe as well as for iron-based Fe{sub 1−x}Re{sub x}, Fe{sub 1−x}Os{sub x}, Fe{sub 1−x}Mo{sub x}, and Fe{sub 1−x}Cr{sub x} solid solutions, where x is in the range between 0.01 and 0.05. The measurements were performed in order to check if the known from the literature, theoretical calculations on the interactions between vacancies and solute atoms in iron can be supported by the experimental data. The vacancies were created during formation and further mechanical processing of the iron systems under consideration so the spectra mentioned above were collected at least twice for each studied sample synthesized in an arc furnace— after cold rolling to the thickness of about 40 μm as well as after subsequent annealing at 1270 K for 2 h. It was found that only in Fe and the Fe-Cr system the isolated vacancies thermally generated at high temperatures are not observed at the room temperature and cold rolling of the materials leads to creation of another type of vacancies which were associated with edge dislocations. In the case of other cold-rolled systems, positrons detect vacancies of two types mentioned above and Mössbauer nuclei “see” the vacancies mainly in the vicinity of non-iron atoms. This speaks in favour of the suggestion that in iron matrix the solute atoms of Os, Re, and Mo interact attractively with vacancies as it is predicted by theoretical computations and the energy of the interaction is large enough for existing the pairs vacancy-solute atom at the room temperature. On the other hand, the corresponding interaction for Cr atoms is either repulsive or attractive but smaller than that for Os, Re, and Mo atoms. The latter is in agreement with the theoretical calculations.

  19. Exciton annihilation in dye-sensitized nanocrystalline semiconductor films

    NASA Astrophysics Data System (ADS)

    Namekawa, Akihiro; Katoh, Ryuzi

    2016-08-01

    Exciton annihilation in dye-sensitized nanocrystalline semiconductor (Al2O3) films has been studied through laser-induced fluorescence spectroscopy. The relative quantum yield of the fluorescence decreases with increasing excitation light intensity, the indication being that exciton annihilation occurred. The rate constants of the annihilation were estimated for three dyes, N719, D149, and MK2, that are known to be sensitizing dyes for efficient dye-sensitized solar cells. The hopping time between dye molecules and the diffusion length of excitons within their lifetime were also estimated to facilitate discussion of the relevance of exciton annihilation to primary processes in dye-sensitized solar cells.

  20. Synthesis and characterization of magnesium oxide nanocrystallites and probing the vacancy-type defects through positron annihilation studies

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Reverse Micelle Formation of Triton X-100 in Butanol and n-Heptane Mixed Solvents Studied by the Positron Annihilation Technique

    PubMed

    Das; Ganguly

    1997-08-01

    The positron annihilation technique (PAT) has been applied to study the molecular association phenomenon of Triton X-100 (TX-100) and formation of reversed micelles in the mixed solvent of butanol and n-heptane. The results indicate the sensitivity of positronium (Ps) parameters to the phase transition region due to the self-aggregation phenomenon of TX-100 within the system. The intensity of the long-lived ortho-Ps component, I3, and its lifetime, tau3, show a remarkable change at a critical concentration of the surfactant at approximately 1.5 mM coined as the operational CMC of TX-100 in both (1:1) and (1:2) butanol-n-heptane (BuHp) systems. The narrow component/para-Ps intensity as computed from Doppler broadening of annihilation radiation indicates discernable changes at the same concentration region ( approximately 1.5 mM) of TX-100 in the system. Further, microphase changes due to the association of water molecules within the nonaqueous phase has been studied by Ps parameters, which reveals a clear demarcation of the polar and nonpolar zones. PMID:9268557

  3. Electronic structure and orientation relationship of Li nanoclusters embedded in MgO studied by depth-selective positron annihilation two-dimensional angular correlation

    NASA Astrophysics Data System (ADS)

    Falub, C. V.; Mijnarends, P. E.; Eijt, S. W.; van Huis, M. A.; van Veen, A.; Schut, H.

    2002-08-01

    Quantum-confined positrons are sensitive probes for determining the electronic structure of nanoclusters embedded in materials. In this work, a depth-selective positron annihilation 2D-ACAR (two-dimensional angular correlation of annihilation radiation) method is used to determine the electronic structure of Li nanoclusters formed by implantation of 1016-cm-2 30-keV 6Li ions in MgO (100) and (110) crystals and by subsequent annealing at 950 K. Owing to the difference between the positron affinities of lithium and MgO, the Li nanoclusters act as quantum dots for positrons. 2D-ACAR distributions for different projections reveal a semicoherent fitting of the embedded metallic Li nanoclusters to the host MgO lattice. Ab initio Korringa-Kohn-Rostoker calculations of the momentum density show that the anisotropies of the experimental distributions are consistent with an fcc crystal structure of the Li nanoclusters. The observed reduction of the width of the experimental 2D-ACAR distribution is attributed to positron trapping in vacancies associated with Li clusters. This work proposes a method for studying the electronic structure of metallic quantum dots embedded in an insulating material.

  4. Study on Momentum Density in Semiconductor Alloys GeC and SnC by Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Amrane, N.

    The independent particle model (IPM) coupled with empirical pseudopotential method (EPM) was used to compute the thermalized positron charge densities in specific family of binary tetrahedrally coordinated crystals of formula ANB8-N. Initial results show a clear asymmetrical positron charge distribution relative to the bond center. It is observed that the positron density is maximum in the open interstices and is excluded not only from the ion cores but also to a considerable degree from the valence bonds. Electron-positron momentum densities are calculated for the (001, 110) planes. The results are used to analyze the positron effects in GeC and SnC. Our computational technique provides the theoretical means of interpreting the k-space densities obtained experimentally using the two-dimensional angular correlation of annihilation radiation (2D-ACAR).

  5. Per-fluorinated sulfonic acid/PTFE copolymer studied by positron annihilation lifetime and gas permeation techniques

    NASA Astrophysics Data System (ADS)

    Mohamed, Hamdy F. M.; Abdel-Hady, E. E.; Ohira, A.

    2015-06-01

    The mechanism of gas permeation in per-fluorinated sulfonic acid/PTFE copolymer Fumapem® membranes for polymer electrolyte fuel cells has been investigated from the viewpoint of free volume. Three different samples, Fumapem® F-950, F-1050 and F-14100 membranes with ion exchange capacity (IEC) = 1.05, 0.95 and 0.71 meq/g, respectively were used after drying. Free volume was quantified using the positron annihilation lifetime (PAL) technique and gas permeabilities were measured for O2 and H2 as function of temperature. Good linear correlation between the logarithm of the permeabilities at different temperatures and reciprocal free volume indicate that gas permeation in dry Fumapem® is governed by the free volume. Nevertheless permeabilities are much smaller than the corresponding flexible chain polymer with a similar free volume size due to stiff chains of the perfluoroethylene backbone.

  6. Free volume study on the miscibility of PEEK/PEI blend using positron annihilation and dynamic mechanical thermal analysis

    NASA Astrophysics Data System (ADS)

    Ramani, R.; Alam, S.

    2015-06-01

    High performance polymer blend of poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) was examined for their free volume behaviour using positron annihilation lifetime spectroscopy and dynamic mechanical thermal analysis methods. The fractional free volume obtained from PALS shows a negative deviation from linear additivity rule implying good miscibility between PEEK and PEI. The dynamic modulus and loss tangent were obtained for the blends at three different frequencies 1, 10 and 100 Hz at temperatures close to and above their glass transition temperature. Applying Time-Temperature-Superposition (TTS) principle to the DMTA results, master curves were obtained at a reference temperature To and the WLF coefficients c01 and c02 were evaluated. Both the methods give similar results for the dependence of fractional free volume on PEI content in this blend. The results reveal that free volume plays an important role in determining the visco-elastic properties in miscible polymer blends.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  9. The charge-trapping and triplet-triplet annihilation processes in organic light-emitting diodes: A duty cycle dependence study on magneto-electroluminescence

    NASA Astrophysics Data System (ADS)

    Peng, Qiming; Chen, Ping; Li, Feng

    2013-01-01

    We studied the magneto-electroluminescence (MEL) in tri-(8-hydroxyquinoline)-aluminum (Alq3)-based organic light-emitting devices through both steady-state and transient methods. As the magnetic field increases, the MEL exhibits a rapid rise, followed by the saturation tendency at all voltages in the steady-state measurement, but in the transient measurement it first increases to a maximum and then decreases to negative values when the driving voltages are higher than 8V. Furthermore, we found that the MEL strongly depends on the duty cycle of the pulse voltage. Finally, by employing the triplet-triplet annihilation model combined with the charge trapping effects, we explained the duty cycle dependence of MELs.

  10. Positron annihilation in transparent ceramics

    NASA Astrophysics Data System (ADS)

    Husband, P.; Bartošová, I.; Slugeň, V.; Selim, F. A.

    2016-01-01

    Transparent ceramics are emerging as excellent candidates for many photonic applications including laser, scintillation and illumination. However achieving perfect transparency is essential in these applications and requires high technology processing and complete understanding for the ceramic microstructure and its effect on the optical properties. Positron annihilation spectroscopy (PAS) is the perfect tool to study porosity and defects. It has been applied to investigate many ceramic structures; and transparent ceramics field may be greatly advanced by applying PAS. In this work positron lifetime (PLT) measurements were carried out in parallel with optical studies on yttrium aluminum garnet transparent ceramics in order to gain an understanding for their structure at the atomic level and its effect on the transparency and light scattering. The study confirmed that PAS can provide useful information on their microstructure and guide the technology of manufacturing and advancing transparent ceramics.

  11. Positron annihilation study of the electronic structure of LaB{sub 6} and CeB{sub 6}

    SciTech Connect

    Biasini, M.; Fretwell, H.M.; Dugdale, S.B.; Alam, M.A.; Kubo, Y.; Harima, H.; Sato, N.

    1997-10-01

    We measured the two-dimensional angular correlation of the positron annihilation radiation (2D-ACAR) on a single crystal of LaB{sub 6} for two projections. The anisotropies of the 2D electron-positron momentum density were very similar to those observed for the isostructural heavy-fermion (HF) system CeB{sub 6} in the paramagnetic phase and consistent with those of the calculated electron-positron momentum density of LaB{sub 6}. The standard Lock-Crisp-West (LCW) analysis was in reasonable agreement with the LCW folding of the calculated 2D-ACAR spectrum and the de Haas{endash}van Alphen findings. From the projected {bold {ital k}}-space density we could evaluate the Fermi volume, corresponding to 1.10{plus_minus}0.04 electrons per formula unit, and deduce that the effect of the nonuniform positron density does not play a significant role. The apparent discrepancy with the LCW analysis of CeB{sub 6}, where filtering procedures were required to recover a k-space density similar to that obtained for LaB{sub 6}, is discussed. {copyright} {ital 1997} {ital The American Physical Society}

  12. A positron annihilation study on the microstructure of the interpenetration polymer networks of cyanate ester resin/epoxy resin

    NASA Astrophysics Data System (ADS)

    Chenze, Qi; Chunqing, Li; Minfeng, Zeng; Baoyi, Wang; Jian, Zhang

    2010-04-01

    Cyanate ester (CE) resin was blended with epoxy resin (EP) at different mass ratios (CE/EP: 100/0, 90/10, 70/30, 50/50, 30/70, 10/90, 0/100). The free volume size of CE/EP IPNs has been determined by positron annihilation lifetime spectroscopy (PALS). The size decreased as the epoxy resin content increased. The PALS results are consistent with the chemical structure changes for the copolymerizing between CE and EP. The crosslinking units of curing products (oxazoline, oxazolidinone, and polyether network) of the blends are all smaller in size than those of triazine ring structure from neat CE. Therefore, the free volume size of the blends decreases with increase of EP content. Examination of the mechanical properties, thermal stability, and morphology of the blend systems showed that addition of epoxy resin resulted in improved toughness but a little sacrifice in thermal stability when compared with pure CE. The correlations between the free volume properties and physical properties (thermal stability and mechanical properties) have been discussed.

  13. A comparative study on ferromagnetic C/O-implanted GaN films by positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Juping; Li, Qiang; Liu, Jiandang; Ye, Bangjiao

    2016-05-01

    Room temperature ferromagnetism was observed in both C- and O-implanted GaN films, which were irradiated by 80 keV C/O-ions with respective dose of 5 × 1016 and 2 × 1017 ions/cm2. Positron annihilation spectroscopy was used to explore the magnetic origin and the correlation between the magnetism and structural features. The results reveal that carbon-ions play an important role in the stable ferromagnetism in C-implanted GaN films, while oxygen has no effect on the magnetic properties, even than a weak hysteresis loop was observed in O-implanted sample. This weak ferromagnetism is demonstrated as originated from Ga-related vacancies which induced by implantation. With first-principle calculations, we confirmed that substitutional C-ion at N-site can introduce magnetic moment for 0.8 μB and stabilize ferromagnetic coupling with adjacent Ga-vacancy at room temperature. Moreover, the effect of O-ions was clearly ruled out. Our discussion gives an experimental and theoretical insight of the different origin of ferromagnetism between acceptor and donor non-metal-doped GaN materials.

  14. Comprehensive study on critical role of surface oxygen vacancies for 2DEG formation and annihilation in LaAlO3/SrTiO3 heterointerfaces

    NASA Astrophysics Data System (ADS)

    Moon, Seon Young; Moon, Cheon Woo; Chang, Hye Jung; Kim, Taemin; Kang, Chong-Yun; Choi, Heon-Jin; Kim, Jin-Sang; Baek, Seung-Hyub; Jang, Ho Won

    2016-03-01

    Here we report comprehensive study of 2DEG at a-LAO/STO interfaces in comparison with 2DEG at crystalline LaAlO3 (c-LAO)/STO interfaces. We observe that the oxygen deficient environment during the deposition of LAO overlayer is essentially required to create 2DEG at LAO/STO interface regardless of growth temperature from 25°C to 700°C, indicating that the oxygen-poor condition in the system is more important than the crystallinity of LAO layer. The critical thickness (2.6 nm) of 2DEG formation at a-LAO/STO heterostructure is thicker than (1.6 nm) that at c-LAO/STO. Upon ex-situ annealing at 300°C under 300 mTorr of oxygen pressure, 2DEG at a-LAO/STO interface is annihilated, while that in c-LAO/STO interface is still maintained. With combing these findings and scanning transmission electron microscope (STEM) analysis, we suggest that oxygen vacancies at the LAO surface is attributed to the origin of 2DEG formation at the LAO/STO and the crystallinity of the LAO overlayer plays a critical role in the annihilation of 2DEG at a-LAO/STO interface rather than in the formation of 2DEG. This work provides a framework to understand the importance of prohibiting the LAO surface from being oxidized for achieving thermally stable 2DEG at a-LAO/STO interface. [Figure not available: see fulltext.

  15. Microscopic basis of free-volume concept as studied by quasielastic neutron scattering and positron annihilation lifetime spectroscopy

    NASA Astrophysics Data System (ADS)

    Kanaya, T.; Tsukushi, T.; Kaji, K.; Bartos, J.; Kristiak, J.

    1999-08-01

    We have reexamined the free-volume concept presented by Cohen and Turnbull on the basis of two microscopic quantities: the excess mean-square displacement f and the total free volume VPA,t, of poly- butadiene evaluated from the quasielastic neutron scattering and the positron annihilation lifetime spectroscopy (PALS) data, respectively. Comparing with the viscosity η we found two relations, η=η0 exp u 20/f and η=η0 exp V*PA,0/VPA,t=η0 exp V*PA,0/vPA,f, where u20, V*PA,0 and v*PA,0 are the critical values for the mean-square displacement, the total PALS free volume, and the PALS free volume per molecule, respectively, and further v*PA,0=V*PA,0/N, N being the total number of molecules or segments. On the basis of these relations, we discuss the microscopic basis of the free-volume theory. The experimentally evaluated critical values u20 and v*PA,0 are much larger than the average values of f and vPA,f calculated from the distributions. This has been explained from the low probability of escaping motions from a molecular cage. The free volume per monomer and the free-volume fraction were calculated from the excess mean-square displacement f. The former was compared with the free-volume hole obtained by PALS, suggesting that 22 monomers are required for one PALS free-volume hole. The free-volume fraction obtained from the excess mean-square displacement was found to be 6.4% at 250 K, which is in reasonable agreement with that evaluated from the rheological data (9.0%).

  16. Matrix element analyses of dark matter scattering and annihilation

    NASA Astrophysics Data System (ADS)

    Kumar, Jason; Marfatia, Danny

    2013-07-01

    We provide a compendium of results at the level of matrix elements for a systematic study of dark matter scattering and annihilation. We identify interactions that yield spin-dependent and spin-independent scattering and specify whether the interactions are velocity and/or momentum suppressed. We identify the interactions that lead to s-wave or p-wave annihilation, and those that are chirality suppressed. We also list the interaction structures that can interfere in scattering and annihilation processes. Using these results, we point out situations in which deviations from the standard lore are obtained.

  17. Minimal semi-annihilating Bbb ZN scalar dark matter

    NASA Astrophysics Data System (ADS)

    Bélanger, Geneviève; Kannike, Kristjan; Pukhov, Alexander; Raidal, Martti

    2014-06-01

    We study the dark matter from an inert doublet and a complex scalar singlet stabilized by Bbb ZN symmetries. This field content is the minimal one that allows dimensionless semi-annihilation couplings for N > 2. We consider explicitly the Bbb Z3 and Bbb Z4 cases and take into account constraints from perturbativity, unitarity, vacuum stability, necessity for the electroweak Bbb ZN preserving vacuum to be the global minimum, electroweak precision tests, upper limits from direct detection and properties of the Higgs boson. Co-annihilation and semi-annihilation of dark sector particles as well as dark matter conversion significantly modify the cosmic abundance and direct detection phenomenology.

  18. Defects in metals. [Positron annihilation spectroscopy

    SciTech Connect

    Siegel, R.W.

    1982-06-01

    The application of positron annihilation spectroscopy (PAS) to the study of defects in metals has led to increased knowledge on lattice-defect properties during the past decade in two areas: the determination of atomic defect properties, particularly those of monovacancies, and the monitoring and characterization of vacancy-like microstructure development during post-irradiation and post-quench annealing. The study of defects in metals by PAS is reviewed within the context of the other available techniques for defect studies. The strengths and weaknesses of PAS as a method for the characterization of defect microstructures are considered. The additional possibilities for using the positron as a localized probe of the atomic and electronic structures of atomic defects are discussed, based upon theoretical calculations of the annihilation characteristics of defect-trapped positrons and experimental observations. Finally, the present status and future potential of PAS as a tool for the study of defects in metals is considered. 71 references, 9 figures.

  19. Annihilation in Gases and Galaxies

    NASA Technical Reports Server (NTRS)

    Drachman, Richard J. (Editor)

    1990-01-01

    This publication contains most of the papers, both invited and contributed, that were presented at the Workshop of Annihilation in Gases and Galaxies. This was the fifth in a biennial series associated with the International Conference on the Physics of Electronic and Atomic Collisions. Subjects covered included the scattering and annihilation of positrons and positronium atoms in various media, including those of astrophysical interest. In addition, the topics of antimatter and dark matter were covered.

  20. Positron Annihilation Lifetime Spectroscopy Study of Neutron Irradiated High Temperature Superconductors YBa2Cu3O7-δ for Application in Fusion Facilities

    NASA Astrophysics Data System (ADS)

    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.

  1. Application of positron annihilation in materials science

    SciTech Connect

    Siegel, R.W.; Fluss, M.J.; Smedskjaer, L.C.

    1984-05-01

    Owing to the ability of the positron to annihilate from a variety of defect-trapped states, positron annihilation spectroscopy (PAS) has been applied increasingly to the characterization and study of defects in materials in recent years. In metals particularly, it has been demonstrated that PAS can yield defect-specific information which, by itself or in conjunction with more traditional experimental techniques, has already made a significant impact upon the determination of atomic-defect properties and the monitoring and characterization of vacancy-like microstructure development, as occurs during post-irradiation annealing. The applications of PAS are now actively expanding to the study of more complex defect-related phenomena in irradiated or deformed metals and alloys, phase transformations and structural disorder, surfaces and near-surface defect characterization. A number of these applications in materials science are reviewed and discussed with respect to profitable future directions.

  2. Positron annihilation and nuclear magnetic resonance study of the phase behavior of water confined in mesopores at different levels of hydration.

    PubMed

    Maheshwari, Priya; Dutta, Dhanadeep; Mukherjee, Saurabh; Madhu, Perunthiruthy K; Mote, Kaustubh R; Pujari, Pradeep K

    2016-05-14

    We investigated the molecular origin of the phase behavior of water confined in MCM 41 mesopores at different levels of hydration using positron annihilation spectroscopic and nuclear magnetic resonance techniques. The level of hydration influenced the phase behavior of the nanoconfined water. Two transitions above and below the bulk freezing temperature were observed depending on the level of hydration. At the highest level of hydration, nucleation seemed to predominate over the effect of confinement, leading to the complete freezing of water, whereas disrupted H-bonding dominated at the lowest level of hydration, leading to the disappearance of the transitions. A transition at c. T = 188 K (close to the reported glass transition temperature of interface-affected water) was observed at intermediate hydration level. This study suggests that the H-bonding network within nanoconfined water, which can be tampered by the degree of hydration, is the key factor responsible for the phase behavior of supercooled water. This study on the phase behavior and associated transitions of nanoconfined water has implications for nanofluidics and drug-delivery systems, in addition to understanding the fundamentals of water in confinement. PMID:27105178

  3. Ballistic annihilation and deterministic surface growth

    NASA Astrophysics Data System (ADS)

    Belitsky, Vladimir; Ferrari, Pablo A.

    1995-08-01

    A model of deterministic surface growth studied by Krug and Spohn, a model of the annihilating reaction A+B→inert studied by Elskens and Frisch, a one-dimensional three-color cyclic cellular automaton studied by Fisch, and a particular automaton that has the number 184 in the classification of Wolfram can be studied via a cellular automaton with stochastic initial data called ballistic annihilation. This automaton is defined by the following rules: At time t=0, one particle is put at each integer point of ℝ. To each particle, a velocity is assigned in such a way that it may be either +1 or -1 with probabilities 1/2, independent of the velocities of the other particles. As time goes on, each particle moves along ℝ at the velocity assigned to it and annihilates when it collides with another particle. In the present paper we compute the distribution of this automaton for each time t ∈ ℕ. We then use this result to obtain the hydrodynamic limit for the surface profile from the model of deterministic surface growth mentioned above. We also show the relation of this limit process to the process which we call moving local minimum of Brownian motion. The latter is the process B {/x min}, x ∈ ℝ, defined by B {/x min}≔min{ B y ; x-1≤ y≤ x+1} for every x ∈ ℝ, where B x , x ∈ ℝ, is the standard Brownian motion with B 0=0.

  4. Positron annihilation radiation from solar flares

    NASA Technical Reports Server (NTRS)

    Share, G. H.; Chupp, E. L.; Forrest, D. J.; Rieger, E.

    1983-01-01

    Positron-annihilation radiation has been observed from the June 21, 1980 and June 3, 1982 flares by the gamma-ray spectrometer on the Solar Maximum Mission satellite. The observed 0.511-MeV line fluences from the flares were 14.6 + or - 3.3 gamma/sq cm and 103 + or - 8 gamma/sq cm, respectively. Measurement of the line width establishes an upper limit to the temperature in the annihilation region of 3 x 10 to the 6th K. The time dependence of the 0.511-MeV line during the 1980 flare is consistent with the calculations of Ramaty et al. (1983) for positrons created in the decay of radioactive nuclei. The time dependence of the 0.511-MeV line for the 1982 flare is more complex and requires more detailed study.

  5. Graphene networks and their influence on free-volume properties of graphene-epoxidized natural rubber composites with a segregated structure: rheological and positron annihilation studies.

    PubMed

    He, Canzhong; She, Xiaodong; Peng, Zheng; Zhong, Jieping; Liao, Shuangquan; Gong, Wei; Liao, Jianhe; Kong, Lingxue

    2015-05-14

    Epoxidized natural rubber-graphene (ENR-GE) composites with segregated GE networks were successfully fabricated using the latex mixing combined in situ reduced technology. The rheological behavior and electrical conductivity of ENR-GE composites were investigated. At low frequencies, the storage modulus (G') became frequency-independent suggesting a solid-like rheological behavior and the formation of GE networks. According to the percolation theory, the rheological threshold of ENR-GE composites was calculated to be 0.17 vol%, which was lower than the electrical threshold of 0.23 vol%. Both percolation thresholds depended on the evolution of the GE networks in the composites. At low GE concentrations (<0.17 vol%), GE existed as individual units, while a "polymer-bridged GE network" was constructed in the composites when GE concentrations exceeded 0.17 vol%. Finally, a "three-dimensional GE network" with percolation conductive paths was formed with a GE concentration of 0.23 vol%, where a remarkable increase in the conductivity of ENR-GE composites was observed. The effect of GE on the atom scale free-volume properties of composites was further studied by positron annihilation lifetime spectroscopy and positron age momentum correlation measurements. The motion of ENR chains was retarded by the geometric confinement of "GE networks", producing a high-density interfacial region in the vicinity of GE nanoplatelets, which led to a lower ortho-positronium lifetime intensity and smaller free-volume hole size. PMID:25881784

  6. Positron annihilation 2D-ACAR study of semi-coherent Li nanoclusters in MgO( 1 0 0 ) and MgO( 1 1 0 )

    NASA Astrophysics Data System (ADS)

    Falub, C. V.; Mijnarends, P. E.; Eijt, S. W. H.; van Huis, M. A.; van Veen, A.; Schut, H.

    2002-05-01

    Depth selective positron annihilation two-dimensional angular correlation of annihilation radiation (2D-ACAR) is used to determine the electronic structure of Li nanoclusters formed by implantation of 10 16 cm -26Li ions (with an energy of 30 keV) in MgO(1 0 0) and (1 1 0) crystals, and subsequently annealed at 950 K. The 2D-ACAR spectra of Li-implanted MgO obtained with 4 keV positrons reveal the semi-coherent ordering state of the embedded metallic Li nanoclusters. The results agree with ab initio Korringa-Kohn-Rostoker calculations.

  7. Unified treatment of hadronic annihilation and protonium formation in slow collisions of antiprotons with hydrogen atoms

    NASA Astrophysics Data System (ADS)

    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.

  8. Structure formation constraints on Sommerfeld-enhanced dark matter annihilation

    SciTech Connect

    Armendariz-Picon, Cristian; Neelakanta, Jayanth T. E-mail: jtneelak@syr.edu

    2012-12-01

    We study the growth of cosmic structure in a ΛCDM universe under the assumption that dark matter self-annihilates with an averaged cross section times relative velocity that grows with the scale factor, an increase known as Sommerfeld-enhancement. Such an evolution is expected in models in which a light force carrier in the dark sector enhances the annihilation cross section of dark matter particles, and has been invoked, for instance, to explain anomalies in cosmic ray spectra reported in the past. In order to make our results as general as possible, we assume that dark matter annihilates into a relativistic species that only interacts gravitationally with the standard model. This assumption also allows us to test whether the additional relativistic species mildly favored by cosmic-microwave background data could originate from dark matter annihilation. We do not find evidence for Sommerfeld-enhanced dark matter annihilation and derive the corresponding upper limits on the annihilation cross-section.

  9. Energy-resolved positron annihilation rates for molecules

    SciTech Connect

    Barnes, L. D.; Young, J. A.; Surko, C. M.

    2006-07-15

    The development of high resolution positron beams has enabled measurements of annihilation rates for molecules as a function of incident positron energy. Vibrational Feshbach resonances in these spectra provide evidence for the existence of positron-molecule bound states. In this paper we present further studies of this phenomenon. Evidence is presented for positronically excited bound states (i.e., in addition to the ground state) in C{sub 12}H{sub 26} and C{sub 14}H{sub 30}. Measurements of the annihilation spectra of the halomethanes, CH{sub 3}F, CH{sub 3}Cl, and CH{sub 3}Br, exhibit strong resonances that vary significantly with the substituted halogen. Annihilation spectra for linear alkanes and ring molecules are compared. Annihilation spectra and infrared absorption spectra are compared for a number of molecules. Finally, annihilation rate measurements are presented for a variety of molecules at energies {>=}0.5 eV (i.e., above the vibrational resonances). These provide a measure of the annihilation rates in the absence of vibrational resonances.

  10. Photon spectra from WIMP annihilation

    SciTech Connect

    Cembranos, J. A. R.; Cruz-Dombriz, A. de la; Dobado, A.; Maroto, A. L.; Lineros, R. A.

    2011-04-15

    If the present dark matter in the Universe annihilates into standard model particles, it must contribute to the fluxes of cosmic rays that are detected on the Earth and, in particular, to the observed gamma-ray fluxes. The magnitude of such a contribution depends on the particular dark matter candidate, but certain features of the produced photon spectra may be analyzed in a rather model-independent fashion. In this work we provide the complete photon spectra coming from WIMP annihilation into standard model particle-antiparticle pairs obtained by extensive Monte Carlo simulations. We present results for each individual annihilation channel and provide analytical fitting formulas for the different spectra for a wide range of WIMP masses.

  11. Study of hadronization using energy flow from e/sup +/e/sup -/ annihilation into quarks and gluons at. sqrt. s of 29 GeV

    SciTech Connect

    Rosenberg, L.J.

    1985-11-01

    We have made a high statistics study of QCD jets produced in e/sup +/e/sup -/ annihilations at ..sqrt..s of 29 GeV and observed in the MAC detector located at the PEP storage ring at SLAC. The MAC detector uses calorimetry and provides a homogeneous response over much of its 98% . 4..pi.. sr instrumented solid angle. A data sample of well reconstructed hadronic events was selected by requiring that E/sub vis/ in the calorimeters be near ..sqrt..s, and almost all the energy be deposited in the central calorimeters. Fits of the jet transverse energy flow are made to the data using String (STR) model and several types of Independent Jet (IJM) model hypotheses, where ..alpha../sub s/, the strong coupling constant, and sigma/sub q/, the width of the secondary quark P/sub perpendicular/ distribution, are free parameters. The fits to O(..alpha../sub s//sup 2/ using MS-bar renormalization yield ..alpha../sub s/ approx.0.17 with the STR hypothesis, and ..alpha../sub s/ approx.0.12 with the various IJM hypotheses. The correlations between ..alpha../sub s/ and sigma/sub q/ are examined. Detailed comparisons were made with other experimental results. The energy flow projected onto the event plane of 3-jet events selected from the above data sample was studied. The data shows an asymmetric energy flow around the thin jet. Such an asymmetry was predicted by the STR model, and a cluster model (Webber) incorporating soft gluon interference. The various IJM models show no such asymmetry. We associate this asymmetry with coherence effects during hadronization. 106 refs., 58 figs., 18 tabs.

  12. [A study of the magnetic field annihilation process in the magnetosphere and some geotechnical applications]. Progress report

    SciTech Connect

    Not Available

    1993-05-01

    This paper describes significant progress made in the study of magnetic field reconnection and plasma processes in the magnetosphere in the past three years. A total of 43 research and review papers have been completed under the DOE support. In this paper, some of the most important results obtained in the past three-years are described.

  13. High Resolution Spectrometer in studies of e/sup +/e/sup -/ annihilation at. sqrt. s = 29 GeV

    SciTech Connect

    Derrick, M.

    1985-05-03

    The High Resolution Spectrometer is a general-purpose spectrometer which measures both charged particles and electromagnetic energy over 90% of the solid angle. The detection elements are in a 1.62-T magnetic field. The detector elements consist of a central drift chamber, an outer drift-chamber system, a barrel shower counter, and an end-cap shower-counter system. The goals of the program of research with the High Resolution Spectrometer include measurements of the electroweak coupling of the quarks and leptons, studies of the strong interactions of the quarks, and search for qualitatively new phenomena. 20 refs., 35 figs. (LEW)

  14. [A study of the magnetic field annihilation process in the magnetosphere and some geotechnical applications]. Progress report

    SciTech Connect

    Lee, L.C.; Akasofu, S.I.

    1993-05-01

    The basic plasma processes associated with magnetic reconnection in the Earth`s magnetosphere are studied in our proposed project. In the past year, several problems associated with the 2-D and 3-D nonlinear reconnection processes were investigated. A new theory for nonlinear fast steady-state magnetic reconnection is proposed. The inflow region possesses highly curved magnetic field lines, which differs from that in the classical model of Petschek. A separatrix jet of plasma is ejected from the central diffusion region along the magnetic separatrix. Two types of outflow are studied, the simplest one possessing a potential outflow magnetic field and the other containing weak standing shock waves attached to the ends of the diffusion region. Across the separatrix jet, the outflow can be either slowed down by the fast-mode shocks or speeded up by the slow-mode shocks, depending on the downstream boundary conditions. In the 3-D MHD simulations, frayed magnetic flux ropes are found to be formed during the dayside magnetic reconnection process. Strong flux rope-aligned plasma flows are observed. Simulations of the driven reconnection process also indicate that the focusing of the Poynting flux has an important effect on the onset of reconnection and the location of reconnection sites.

  15. SYNCHROTRON RADIATION, FREE ELECTRON LASER, APPLICATION OF NUCLEAR TECHNOLOGY, ETC.: Positronium annihilation in silica aerogel studied by a positron age-momentum correlation technique

    NASA Astrophysics Data System (ADS)

    Wang, Dan-Ni; Zhang, Lan-Zhi; Wang, Bao-Yi; Yu, Run-Sheng; Zhang, Zhi-Ming; Li, Dao-Wu; Wei, Long

    2009-01-01

    A high-performance positron age-momentum correlation (AMOC) spectrometer was newly developed. The counting rate is increased up to 200 cps much larger than the value 20 cps reported by other international groups. And at the same time, the time resolution still keeps at the international level of 220 ps. Furthermore, positronium (Ps) annihilation in silica aerogel was investigated by AMOC, which indicates: (1) Ps annihilation between the grains dominantly undergoes pick-off process and spin conversion from o-Ps to p-Ps; (2) Annealing below 400 °C changes the grain surface conditions, i. e. the desorption of hydrogen and the decrease of the defect centers concentration.

  16. Mn2+-induced substitutional structural changes in ZnS nanoparticles as observed from positron annihilation studies

    NASA Astrophysics Data System (ADS)

    Biswas, Subhajit; Kar, Soumitra; Chaudhuri, Subhadra; Nambissan, P. M. G.

    2008-06-01

    Zinc sulfide nanoparticles doped with different concentrations of manganese ions (Mn2+) were synthesized at various temperatures to investigate the effects of substitution and the associated defect evolution. Positron lifetime and Doppler broadening measurements were used as probes. The initial stage of defect recovery was dominated by the occupation of Zn2+ vacancies by Mn2+ ions, bringing in characteristic changes in the positron lifetimes, intensities and Doppler broadened lineshape parameters. Detailed analyses considering the presence of one and two types of defects were carried out to identify the type of defects which trap positrons at the different dopant concentrations. Electron paramagnetic resonance studies indicated increased Mn-Mn interaction and the formation of Mn clusters with further doping. The results are in striking contrast to those for nanorods, where vacancy recombination transformed their interior into regions free of defects.

  17. Mn(2+)-induced substitutional structural changes in ZnS nanoparticles as observed from positron annihilation studies.

    PubMed

    Biswas, Subhajit; Kar, Soumitra; Chaudhuri, Subhadra; Nambissan, P M G

    2008-06-11

    Zinc sulfide nanoparticles doped with different concentrations of manganese ions (Mn(2+)) were synthesized at various temperatures to investigate the effects of substitution and the associated defect evolution. Positron lifetime and Doppler broadening measurements were used as probes. The initial stage of defect recovery was dominated by the occupation of Zn(2+) vacancies by Mn(2+) ions, bringing in characteristic changes in the positron lifetimes, intensities and Doppler broadened lineshape parameters. Detailed analyses considering the presence of one and two types of defects were carried out to identify the type of defects which trap positrons at the different dopant concentrations. Electron paramagnetic resonance studies indicated increased Mn-Mn interaction and the formation of Mn clusters with further doping. The results are in striking contrast to those for nanorods, where vacancy recombination transformed their interior into regions free of defects. PMID:21694317

  18. Effect of carbon on copper precipitation in deformed Fe-based alloys studied by positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Schut, H.; Brück, E.; van der Zwaag, S.; van Dijk, N. H.

    2013-06-01

    The role of deformation-induced defects and carbon addition on the copper precipitation during aging at 550 °C is investigated in high-purity Fe-Cu-B-N-C alloy samples by Coincidence Doppler Broadening. In samples with 0% and 8% cold pre-strain, the influence of tensile pre-deformation on the precipitation kinetics of copper is studied. The deformation-induced defects are found to enhance the Cu precipitation kinetics. A sharp reduction in open volume defects is accompanied with a strong increase of Cu signature during the initial stage of aging, implying that the open defects (mainly dislocations) act as nucleation sites for Cu precipitates. A comparison of the time evolution of S-W plots between Fe-Cu, Fe-Cu-B-N, and Fe-Cu-B-N-C alloys indicates that the addition of carbon does not alter the Cu precipitation mechanism but decelerates the kinetics.

  19. Identification of open-volume defects in disordered and amorphized Si: A depth-resolved positron annihilation study

    SciTech Connect

    Amarendra, G.; Rajaraman, R.; Venugopal Rao, G.; Nair, K. G. M.; Viswanathan, B.; Suzuki, R.; Ohdaira, T.; Mikado, T.

    2001-06-01

    Depth-resolved positron beam studies have been carried out on Ar-irradiated Si using Doppler S parameter and lifetime measurements. Si samples have been irradiated with 140-keV Ar ions to a dose of 2{times}10{sup 13} and 5{times}10{sup 16} Ar/cm{sup 2}, respectively, so as to produce disordered and amorphous states in near-surface regions. The observed features of the defect sensitive line shape S parameter indicate the presence of small vacancylike defects in the disordered sample and higher-order vacancy clusters in an amorphous sample. Pulsed positron beam lifetime results indicate that the disordered Si sample exhibits lifetime distribution ascribable to mostly divacancies. In the case of an amorphous sample, the lifetime distribution is broad with larger lifetime values indicating the presence of a distribution of large vacancy clusters or nanovoids. By using theoretical lifetime values for Si reported in the literature, an empirical fit to the lifetime variation as a function of vacancy cluster size is obtained. By comparing the experimental lifetime distribution with this data, the vacancy cluster size distribution in disordered and amorphous Si is deduced. In disordered Si, divacancies are found to be the dominant defects species followed by small concentration of V{sub 3}. In amorphous Si, nanovoids in the size range of four to seven vacancy clusters are present with V{sub 5} and V{sub 6} clusters being the dominant defect species. The implication of these results is discussed in light of recent computer-simulation studies.

  20. On baryogenesis from dark matter annihilation

    SciTech Connect

    Bernal, Nicolás; Colucci, Stefano; Ubaldi, Lorenzo; Josse-Michaux, François-Xavier; Racker, J. E-mail: colucci@th.physik.uni-bonn.de E-mail: racker@ific.uv.es

    2013-10-01

    We study in detail the conditions to generate the baryon asymmetry of the universe from the annihilation of dark matter. This scenario requires a low energy mechanism for thermal baryogenesis, hence we first discuss some of these mechanisms together with the specific constraints due to the connection with the dark matter sector. Then we show that, contrary to what stated in previous studies, it is possible to generate the cosmological asymmetry without adding a light sterile dark sector, both in models with violation and with conservation of B−L. In addition, one of the models we propose yields some connection to neutrino masses.

  1. Positron annihilation study on the effect of Si-content on the recovery of deformed cast Al-Si alloys

    NASA Astrophysics Data System (ADS)

    El-Gamal, S.

    2013-09-01

    Isochronal annealing of Al-1100 and cast Al-Si alloys (Si-content 2, 4, 6 and 8 wt%) after deformation of 66% thickness reduction was investigated between room temperature (RT) and 500 °C. The annealing of defects was studied using Doppler Broadening Spectroscopy (DBS), Total Strain (εT) and Scanning Electron Microscope (SEM). It was found that; (i) three annealing stages of microstructure have been identified for Al-1100 and Al-Si alloys which are related to recovery, partial recrystallization and complete recrystallization (ii) the interaction between Si-precipitates and dislocations in Al-Si alloys leads to higher values of normalized line shape parameter (Snor) and lower values of εT than those for Al-1100 alloy also, it retarded the recovery and recrystallization with temperature (iii) the S-W plot revealed the presence of one type of defects in Al-1100 alloy but in Al-Si alloys the slope of the trajectory changes, which may indicate the occurrence of another defect type (Si-dislocation interaction) (iv) a negative correlation is observed between εT and Snor while a positive correlation between εT and normalized wing parameter (Wnor) is obvious.

  2. Particle-antiparticle asymmetries from annihilations.

    PubMed

    Baldes, Iason; Bell, Nicole F; Petraki, Kalliopi; Volkas, Raymond R

    2014-10-31

    An extensively studied mechanism to create particle-antiparticle asymmetries is the out-of-equilibrium and CP violating decay of a heavy particle. 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. PMID:25396359

  3. Annihilation of Quantum Magnetic Fluxes

    NASA Astrophysics Data System (ADS)

    Gonzalez, W. D.

    After introducing the concepts associated with the Aharonov and Bohm effect and with the existence of a quantum of magnetic flux (QMF), we briefly discuss the Ginzburg-Landau theory that explains its origin and fundamental consequences. Also relevant observations of QMFs obtained in the laboratory using superconducting systems (vortices) are mentioned. Next, we describe processes related with the interaction of QMFs with opposite directions in terms of the gauge field geometry related to the vector potential. Then, we discuss the use of a Lagrangian density for a scalar field theory involving radiation in order to describe the annihilation of QMFs, claimed to be responsible for the emission of photons with energies corresponding to that of the annihilated magnetic fields. Finally, a possible application of these concepts to the observed variable dynamics of neutron stars is briefly mentioned.

  4. Monopole annihilation in cosmic necklaces

    SciTech Connect

    Blanco-Pillado, Jose J.; Olum, Ken D. E-mail: kdo@cosmos.phy.tufts.edu

    2010-05-01

    A sequence of two symmetry breaking transitions in the early universe may produce monopoles whose flux is confined into two strings each, which thus assemble into ''necklaces'' with monopoles as beads. Such ''cosmic necklaces'' have been proposed as a source of ultra-high-energy cosmic rays. We analyze the evolution of these systems and show that essentially all monopoles annihilate or leave the string at early times, after which cosmic necklaces evolve in a similar way to a network of ordinary cosmic strings. We investigate several modifications to the basic picture, but in nearly all cases we find that too few monopoles remain on the necklaces to produce any observable cosmic rays. There may be a small window for superconducting condensates to prevent annihilations, but only if both the string and the condensate scale are very high.

  5. Optical-vortex pair creation and annihilation and helical astigmatism of a nonplanar ring resonator

    SciTech Connect

    Heckenberg, N.R.; Vaupel, M.; Malos, J.T.; Weiss, C.O.

    1996-09-01

    The creation and annihilation of pairs of optical vortices have been studied in transitions between patterns produced in a photorefractive oscillator. Smooth metamorphosis between stable patterns occurs through pair creation or annihilation but can be modeled using superposition of modes taking into account lifting of degeneracy of helical modes by helical astigmatism of the resonator. {copyright} {ital 1996 The American Physical Society.}

  6. Atomic Ionization at the Positron-Electron Annihilation in Process of β+-DECAY

    NASA Astrophysics Data System (ADS)

    Fedotkin, S. N.; Zheltonozhskii, V. A.

    2013-03-01

    The process of atomic shell ionization during the annihilation of a positron, emitted at β+- decay with K-electron of daughter's atom, is considered. The ratio of probabilities of these processes to the probability of ordinary β+-decay is found. It excitation of atomic shell at the positron annihilation at β+-decay of was studied the 4522Ti.

  7. Models of pair annihilation in 1E 1740.7-2942 and the HEAO 1 A-4 annihilation source

    NASA Technical Reports Server (NTRS)

    Maciolek-Niedzwiecki, Andrzej; Zdziarski, Andrzej

    1994-01-01

    We study possible models of two Galactic sources of transient pair annihilation radiation, 1E 1740.7-2942 and a source observed by High Energy Astronomy Observatory (HEAO) 1 A-4. We fit the observed spectral features by thermal annihilation spectra and find that the redshifts obtained by us are much larger than those obtained from fitting Caussian lines centered on 511 keV. This effect, which is due to the net blueshift (with respect to 511 keV) of the annihilation spectrum due to the thermal energies of pairs, puts strong constraints on models of sources. We consider those constraints first without considering the mechanism of positron production. From the shape of the observed spectra, we are able to rule out both spherical clouds and layers above cold matter as possible source geometries. The observed spectra are compatible with two source geometries: (1) a nearly face-on disk in the Kerr metric and (2) a jet close to a black hole. We consider, then, the origin of the pairs. Theories of both thermal and nonthermal pair equilibria predict that photon-pair production is unable to produce annihilation features that contain as much as half of the bolometric luminosity, which is observed. A possible solution to this problem is obscuration of a nonthermal source (in which pairs are produced by photon-photon collisions) and an outflow of pairs to an unobscured region. This makes annihilation in a jet the most likely model of the considered sources.

  8. Dark matter annihilation with s-channel internal Higgsstrahlung

    NASA Astrophysics Data System (ADS)

    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.

  9. Weak annihilation and new physics in charmless decays

    NASA Astrophysics Data System (ADS)

    Bobeth, Christoph; Gorbahn, Martin; Vickers, Stefan

    2015-07-01

    We use currently available data of nonleptonic charmless 2-body decays () that are mediated by QCD- and QED-penguin operators to study weak annihilation and new-physics effects in the framework of QCD factorization. In particular we introduce one weak-annihilation parameter for decays related by quark interchange and test this universality assumption. Within the standard model, the data supports this assumption with the only exceptions in the system, which exhibits the well-known " puzzle", and some tensions in . Beyond the standard model, we simultaneously determine weak-annihilation and new-physics parameters from data, employing model-independent scenarios that address the " puzzle", such as QED-penguins and current-current operators. We discuss also possibilities that allow further tests of our assumption once improved measurements from LHCb and Belle II become available.

  10. Polarization of photons in matter–antimatter annihilation

    SciTech Connect

    Moskaliuk, S.S.

    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.

  11. Positron annihilation induced Auger electron emission

    SciTech Connect

    Weiss, A.; Jibaly, M.; Lei, Chun; Mehl, D.; Mayer, R.; Lynn, K.G.

    1988-01-01

    We report on measurements of Auger electron emission from Cu and Fe due to core hole excitations produced by the removal of core electrons by matter-antimatter annihilation. Estimates are developed of the probability of positrons annihilating with a 3p electron in these materials. Several important advantages of Positron annihilation induced Auger Electron Spectroscopy (PAES) for surface analysis are suggested. 10 refs., 2 figs.

  12. Sensitivity of HAWC to high-mass dark matter annihilations

    NASA Astrophysics Data System (ADS)

    Abeysekara, A. U.; Alfaro, R.; Alvarez, C.; Álvarez, J. D.; Arceo, R.; Arteaga-Velázquez, J. C.; Ayala Solares, H. A.; Barber, A. S.; Baughman, B. M.; Bautista-Elivar, N.; Becerra Gonzalez, J.; Belmont, E.; BenZvi, S. Y.; Berley, D.; Bonilla Rosales, M.; Braun, J.; Caballero-Lopez, R. A.; Caballero-Mora, K. S.; Carramiñana, A.; Castillo, M.; Cotti, U.; Cotzomi, J.; de la Fuente, E.; De León, C.; DeYoung, T.; Diaz Hernandez, R.; Diaz-Cruz, L.; Díaz-Vélez, J. C.; Dingus, B. L.; DuVernois, M. A.; Ellsworth, R. W.; Fiorino, D. W.; Fraija, N.; Galindo, A.; Garfias, F.; González, M. M.; Goodman, J. A.; Grabski, V.; Gussert, M.; Hampel-Arias, Z.; Harding, J. P.; Hui, C. M.; Hüntemeyer, P.; Imran, A.; Iriarte, A.; Karn, P.; Kieda, D.; Kunde, G. J.; Lara, A.; Lauer, R. J.; Lee, W. H.; Lennarz, D.; León Vargas, H.; Linares, E. C.; Linnemann, J. T.; Longo, M.; Luna-Garcia, R.; Marinelli, A.; Martinez, H.; Martinez, O.; Martínez-Castro, J.; Matthews, J. A. J.; McEnery, J.; Mendoza Torres, E.; Miranda-Romagnoli, P.; Moreno, E.; Mostafá, M.; Nellen, L.; Newbold, M.; Noriega-Papaqui, R.; Oceguera-Becerra, T.; Patricelli, B.; Pelayo, R.; Pérez-Pérez, E. G.; Pretz, J.; Rivière, C.; Rosa-González, D.; Ryan, J.; Salazar, H.; Salesa, F.; Sanchez, F. E.; Sandoval, A.; Schneider, M.; Silich, S.; Sinnis, G.; Smith, A. J.; Sparks Woodle, K.; Springer, R. W.; Taboada, I.; Toale, P. A.; Tollefson, K.; Torres, I.; Ukwatta, T. N.; Villaseñor, L.; Weisgarber, T.; Westerhoff, S.; Wisher, I. G.; Wood, J.; Yodh, G. B.; Younk, P. W.; Zaborov, D.; Zepeda, A.; Zhou, H.; Abazajian, K. N.; Milagro Collaboration

    2014-12-01

    The High Altitude Water Cherenkov (HAWC) observatory is a wide field-of-view detector sensitive to gamma rays of 100 GeV to a few hundred TeV. Located in central Mexico at 19° North latitude and 4100 m above sea level, HAWC will observe gamma rays and cosmic rays with an array of water Cherenkov detectors. The full HAWC array is scheduled to be operational in Spring 2015. In this paper, we study the HAWC sensitivity to the gamma-ray signatures of high-mass (multi-TeV) dark matter annihilation. The HAWC observatory will be sensitive to diverse searches for dark matter annihilation, including annihilation from extended dark matter sources, the diffuse gamma-ray emission from dark matter annihilation, and gamma-ray emission from nonluminous dark matter subhalos. Here we consider the HAWC sensitivity to a subset of these sources, including dwarf galaxies, the M31 galaxy, the Virgo cluster, and the Galactic center. We simulate the HAWC response to gamma rays from these sources in several well-motivated dark matter annihilation channels. If no gamma-ray excess is observed, we show the limits HAWC can place on the dark matter cross section from these sources. In particular, in the case of dark matter annihilation into gauge bosons, HAWC will be able to detect a narrow range of dark matter masses to cross sections below thermal. HAWC should also be sensitive to nonthermal cross sections for masses up to nearly 1000 TeV. The constraints placed by HAWC on the dark matter cross section from known sources should be competitive with current limits in the mass range where HAWC has similar sensitivity. HAWC can additionally explore higher dark matter masses than are currently constrained.

  13. Singlet-triplet annihilation in single LHCII complexes.

    PubMed

    Gruber, J Michael; Chmeliov, Jevgenij; Krüger, Tjaart P J; Valkunas, Leonas; van Grondelle, Rienk

    2015-08-14

    In light harvesting complex II (LHCII) of higher plants and green algae, carotenoids (Cars) have an important function to quench chlorophyll (Chl) triplet states and therefore avoid the production of harmful singlet oxygen. The resulting Car triplet states lead to a non-linear self-quenching mechanism called singlet-triplet (S-T) annihilation that strongly depends on the excitation density. In this work we investigated the fluorescence decay kinetics of single immobilized LHCIIs at room temperature and found a two-exponential decay with a slow (3.5 ns) and a fast (35 ps) component. The relative amplitude fraction of the fast component increases with increasing excitation intensity, and the resulting decrease in the fluorescence quantum yield suggests annihilation effects. Modulation of the excitation pattern by means of an acousto-optic modulator (AOM) furthermore allowed us to resolve the time-dependent accumulation and decay rate (∼7 μs) of the quenching species. Inspired by singlet-singlet (S-S) annihilation studies, we developed a stochastic model and then successfully applied it to describe and explain all the experimentally observed steady-state and time-dependent kinetics. That allowed us to distinctively identify the quenching mechanism as S-T annihilation. Quantitative fitting resulted in a conclusive set of parameters validating our interpretation of the experimental results. The obtained stochastic model can be generalized to describe S-T annihilation in small molecular aggregates where the equilibration time of excitations is much faster than the annihilation-free singlet excited state lifetime. PMID:26156159

  14. Positron annihilation study of the influence of doping on the 3 d electron states in the Ni3Al intermetallic compound

    NASA Astrophysics Data System (ADS)

    Druzhkov, A. P.; Perminov, D. A.; Stepanova, N. N.

    2010-10-01

    The 3 d electron states in Ni3Al single crystals doped with Fe, Co, and Nb have been investigated using angular correlation of annihilation radiation (ACAR). The ACAR spectra contain information on the momentum distribution of valence electrons and strongly bound 3 d electrons of the intermetallic compound. It has been established that the positrons in the Ni3Al crystals predominantly annihilate in the nickel sublattice from delocalized states. The doping of the compound by the third element leads to a variation in the momentum distribution of Ni 3 d electrons due to the change in the character of interatomic bonds. An analysis of the momentum distribution has demonstrated that the niobium atoms increase the covalent component of the chemical bond as compared to the binary compound due to the d Nb- d Ni hybridization. The doping with cobalt atoms also enhances the tendency toward the formation of the covalent bond. At the same time, iron atoms have a weak effect on the electronic structure of the intermetallic compound.

  15. Free volume and ionic conductivity of poly(ether urethane)-LiClO4 polymeric electrolyte studied by positron annihilation

    NASA Astrophysics Data System (ADS)

    Peng, Z. L.; Wang, B.; Li, S. Q.; Wang, S. J.

    1995-01-01

    The positron lifetime spectra and ionic conductivity have been measured for poly(ether urethane)-LiClO4 polymeric electrolyte as a function of temperature. The glass transition temperature T(sub g), free-volume V(sub f), and fractional free-volume f were derived from the positron annihilation parameters. A correlation between fractional free-volume f(T) and conductivity sigma above T(sub g), log(sigma/sigma(T(sub g))) = C(sub 1)(f(T) - f(T(sub g)))/f(T), was first experimentally confirmed using measured positron annihilation results. The comparison of the value of the obtained constant C(sub 1) with the universal values for the segmental diffusion of amorphous polymers indicated that the critical free volume required for the ion transport is much smaller than that required for polymer chain segment mobility. Carrier transport and the segmental motion are discussed in terms of the free-volume theory.

  16. Early annihilation and diffuse backgrounds in models of weakly interacting massive particles in which the cross section for pair annihilation is enhanced by 1/upsilon.

    PubMed

    Kamionkowski, Marc; Profumo, Stefano

    2008-12-31

    Recent studies have considered modifications to the standard weakly interacting massive particle scenario in which the pair annihilation cross section (times relative velocity v) is enhanced by a factor 1/upsilon to approximately 10(-3) in the Galaxy, enough to explain several puzzling Galactic radiation signals. We show that in these scenarios a burst of weakly interacting massive particle annihilation occurs in the first collapsed dark-matter halos. We show that severe constraints to the annihilation cross section derive from measurements of the diffuse extragalactic radiation and from ionization and heating of the intergalactic medium. PMID:19437633

  17. Study of b{anti b} production in e{sup +}e{sup {minus}} annihilation at {radical}s = 29 GeV with the aid of neural networks

    SciTech Connect

    Lambert, D J

    1994-11-01

    The author presents a measurement of {sigma}(b{anti b})/{sigma}(q{anti q}) in the annihilation process e{sup +}e{sup {minus}} {yields} q{anti q} {yields} hadrons at {radical}s = 29 GeV. The analysis is based on 66 pb{sup {minus}1} of data collected between 1984 and 1986 with the TPC/2{gamma} detector at PEP. To identify bottom events, he uses a neural network with inputs that are computed from the 3-momenta of all of the observed charged hadrons in each event. He also presents a study of bias in techniques for measuring inclusive {pi}{sup {+-}}, K{sup {+-}}, and p/{anti p} production in the annihilation process e{sup +}e{sup {minus}} {yields} b{anti b} {yields} hadrons at {radical}s = 29 GeV, using a neural network to identify bottom-quark jets. In this study, charged particles are identified by a simultaneous measurement of momentum and ionization energy loss (dE/dx).

  18. Applications of positron annihilation spectroscopy in materials research

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.

    1988-01-01

    Positron Annihilation Spectroscopy (PAS) has emerged as a powerful technique for research in condensed matter. It has been used extensively in the study of metals, ionic crystals, glasses and polymers. The present review concentrates on applications of positron lifetime measurements for elucidation of the physicochemical structure of polymers.

  19. Optical and positron annihilation spectroscopic studies on PMMA polymer doped by rhodamine B/chloranilic acid charge transfer complex: Special relevance to the effect of γ-ray irradiation.

    PubMed

    Hassan, H E; Refat, Moamen S; Sharshar, T

    2016-04-15

    Polymeric sheets of poly (methylmethaclyerate) (PMMA) containing charge transfer (CT) complex of rhodamine B/chloranilic acid (Rho B/CHA) were synthesized in methanol solvent at room temperature. The systematic analysis done on the Rho B and its CT complex in the form of powder or polymeric sheets confirmed their structure and thermal stability. The IR spectra interpreted the charge transfer mode of interaction between the CHA central positions and the terminal carboxylic group. The polymer sheets were irradiated with 70kGy of γ radiation using (60)Co source to study the enhanced changes in the structure and optical parameters. The microstructure changes of the PMMA sheets caused by γ-ray irradiation were analyzed using positron annihilation lifetime (PAL) and positron annihilation Doppler broadening (PADB) techniques. The positron life time components (τi) and their corresponding intensities (Ii) as well as PADB line-shape parameters (S and W) were found to be highly sensitive to the enhanced disorder occurred in the organic chains of the polymeric sheets due to γ-irradiation. PMID:26867205

  20. Optical and positron annihilation spectroscopic studies on PMMA polymer doped by rhodamine B/chloranilic acid charge transfer complex: Special relevance to the effect of γ-ray irradiation

    NASA Astrophysics Data System (ADS)

    Hassan, H. E.; Refat, Moamen S.; Sharshar, T.

    2016-04-01

    Polymeric sheets of poly (methylmethaclyerate) (PMMA) containing charge transfer (CT) complex of rhodamine B/chloranilic acid (Rho B/CHA) were synthesized in methanol solvent at room temperature. The systematic analysis done on the Rho B and its CT complex in the form of powder or polymeric sheets confirmed their structure and thermal stability. The IR spectra interpreted the charge transfer mode of interaction between the CHA central positions and the terminal carboxylic group. The polymer sheets were irradiated with 70 kGy of γ radiation using 60Co source to study the enhanced changes in the structure and optical parameters. The microstructure changes of the PMMA sheets caused by γ-ray irradiation were analyzed using positron annihilation lifetime (PAL) and positron annihilation Doppler broadening (PADB) techniques. The positron life time components (τi) and their corresponding intensities (Ii) as well as PADB line-shape parameters (S and W) were found to be highly sensitive to the enhanced disorder occurred in the organic chains of the polymeric sheets due to γ-irradiation.

  1. Positron annihilation in gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    1990-01-01

    Emission features appear at energies of 350 to 450 keV in the spectra of a number of gamma ray burst sources. These features were interpreted as electron-positron annihilation lines, redshifted by the gravitational field near the surface of a neutron star. Evidence that gamma ray bursts originate at neutron stars with magnetic field strengths of approx. 10(exp 12) Gauss came from recent observations of cyclotron scattering harmonics in the spectra of two bursts. Positrons could be produced in gamma ray burst sources either by photon-photon pair production or by one-photon pair production in a strong magnetic field. The annihilation of positrons is affected by the presence of a strong neutron star magnetic field in several ways. The relaxation of transverse momentum conservation causes an intrinsic broadening of the two-photon annihilation line and there is a decrease in the annihilation cross section below the free-space value. An additional channel for one-photon annihilation also becomes possible in high magnetic fields. The physics of pair production and annihilation near strongly magnetized neutron stars will be reviewed. Results from a self-consistent model for non-thermal synchrotron radiation and pair annihilation are beginning to identify the conditions required to produce observable annihilation features from strongly magnetized plasmas.

  2. Positron Annihilation in the Bipositronium Ps2

    SciTech Connect

    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.

  3. Role of Se vacancies on Shubnikov-de Haas oscillations in Bi2Se3: A combined magneto-resistance and positron annihilation study

    NASA Astrophysics Data System (ADS)

    Devidas, T. R.; Amaladass, E. P.; Sharma, Shilpam; Rajaraman, R.; Sornadurai, D.; Subramanian, N.; Mani, Awadhesh; Sundar, C. S.; Bharathi, A.

    2014-12-01

    Magneto-resistance measurements coupled with positron lifetime measurements, to characterize the vacancy-type defects, have been carried out on the topological insulator (TI) system Bi2Se3 of varying Se/Bi ratio. Pronounced Shubnikov-de Haas (SdH) oscillations are seen in nominal Bi2Se3.1 crystals for measurements performed in magnetic fields up to 15 T in the 4 K-10 K temperature range, with field applied perpendicularly to the (001) plane of the crystal. The quantum oscillations, characteristic of 2D electronic structure, are seen only in the crystals that have a lower concentration of Se vacancies, as inferred from positron annihilation spectroscopy.

  4. Skyrmion creation and annihilation by spin waves

    SciTech Connect

    Liu, Yizhou Yin, Gen; Lake, Roger K.; Zang, Jiadong; Shi, Jing

    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.

  5. Multiple gamma lines from semi-annihilation

    SciTech Connect

    D'Eramo, Francesco; McCullough, Matthew; Thaler, Jesse E-mail: mccull@mit.edu

    2013-04-01

    Hints in the Fermi data for a 130 GeV gamma line from the galactic center have ignited interest in potential gamma line signatures of dark matter. Explanations of this line based on dark matter annihilation face a parametric tension since they often rely on large enhancements of loop-suppressed cross sections. In this paper, we pursue an alternative possibility that dark matter gamma lines could arise from ''semi-annihilation'' among multiple dark sector states. The semi-annihilation reaction ψ{sub i}ψ{sub j} → ψ{sub k}γ with a single final state photon is typically enhanced relative to ordinary annihilation ψ{sub i}ψ-bar {sub i} → γγ into photon pairs. Semi-annihilation allows for a wide range of dark matter masses compared to the fixed mass value required by annihilation, opening the possibility to explain potential dark matter signatures at higher energies. The most striking prediction of semi-annihilation is the presence of multiple gamma lines, with as many as order N{sup 3} lines possible for N dark sector states, allowing for dark sector spectroscopy. A smoking gun signature arises in the simplest case of degenerate dark matter, where a strong semi-annihilation line at 130 GeV would be accompanied by a weaker annihilation line at 173 GeV. As a proof of principle, we construct two explicit models of dark matter semi-annihilation, one based on non-Abelian vector dark matter and the other based on retrofitting Rayleigh dark matter.

  6. Exciton bimolecular annihilation dynamics in supramolecular nanostructures of conjugated oligomers

    NASA Astrophysics Data System (ADS)

    Daniel, Clément; Herz, Laura M.; Silva, Carlos; Hoeben, Freek J.; Jonkheijm, Pascal; Schenning, Albertus P.; Meijer, E. W.

    2003-12-01

    We present femtosecond transient absorption measurements on π-conjugated supramolecular assemblies in a high-pump-fluence regime. Oligo(p-phenylenevinylene) monofunctionalized with ureido-s-triazine (MOPV) self-assembles into chiral stacks in dodecane solution below 75 °C at a concentration of 4×10-4 M. We observe exciton bimolecular annihilation in MOPV stacks at high excitation fluence, indicated by the fluence-dependent decay of 11Bu-exciton spectral signatures and by the sublinear fluence dependence of time- and wavelength-integrated photoluminescence (PL) intensity. These two characteristics are much less pronounced in MOPV solution where the phase equilibrium is shifted significantly away from supramolecular assembly, slightly below the transition temperature. A mesoscopic rate-equation model is applied to extract the bimolecular annihilation rate constant from the excitation fluence dependence of transient absorption and PL signals. The results demonstrate that the bimolecular annihilation rate is very high with a square-root dependence in time. The exciton annihilation results from a combination of fast exciton diffusion and resonance energy transfer. The supramolecular nanostructures studied here have electronic properties that are intermediate between molecular aggregates and polymeric semiconductors.

  7. Effects of bound states on dark matter annihilation

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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 nontrivial 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 rate for direct dark matter annihilation with Sommerfeld enhancement. The effects are strongest for large dark gauge coupling and when the dark photon mass is smaller than the typical momentum of dark matter in the Galaxy. As an example, we show that for thermal dark matter the Fermi gamma ray constraint is substantially increased once bound state effects are taken into account. We also find that bound state effects are not important for dark matter annihilation during the freeze-out and recombination epochs.

  8. Position-resolved Positron Annihilation Lifetime Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wagner, A.; Butterling, M.; Fiedler, F.; Fritz, F.; Kempe, M.; Cowan, T. E.

    2013-06-01

    A new method which allows for position-resolved positron lifetime spectroscopy studies in extended volume samples is presented. In addition to the existing technique of in-situ production of positrons inside large (cm3) bulk samples using high-energy photons up to 16 MeV from bremsstrahlung production, granular position-sensitive photon detectors have been employed. A beam of intense bremsstrahlung is provided by the superconducting electron linear accelerator ELBE (Electron Linear Accelerator with high Brilliance and low Emittance) which delivers electron bunches of less than 10 ps temporal width and an adjustable bunch separation of multiples of 38 ns, average beam currents of 1 mA, and energies up to 40 MeV. Since the generation of bremsstrahlung and the transport to the sample preserves the sharp timing of the electron beam, positrons generated inside the entire sample volume by pair production feature a sharp start time stamp for positron annihilation lifetime studies with high timing resolutions and high signal to background ratios due to the coincident detection of two annihilation photons. Two commercially available detectors from a high-resolution medial positron-emission tomography system are being employed with 169 individual Lu2SiO5:Ce scintillation crystals, each. In first experiments, a positron-lifetime gated image of a planar Si/SiO2 (pieces of 12.5 mm × 25 mm size) sample and a 3-D structured metal in Teflon target could be obtained proving the feasibility of a three dimensional lifetime-gated tomographic system.

  9. Positron scattering and annihilation in hydrogenlike ions

    NASA Astrophysics Data System (ADS)

    Green, D. G.; Gribakin, G. F.

    2013-09-01

    Diagrammatic many-body theory is used to calculate the scattering phase shifts, normalized annihilation rates Zeff, and annihilation γ spectra for positron collisions with the hydrogenlike ions He+, Li2+, B4+, and F8+. Short-range electron-positron correlations and longer-range positron-ion correlations are accounted for by evaluating nonlocal corrections to the annihilation vertex and the exact positron self-energy. The numerical calculation of the many-body theory diagrams is performed using B-spline basis sets. To elucidate the role of the positron-ion repulsion, the annihilation rate is also estimated analytically in the Coulomb-Born approximation. It is found that the energy dependence and magnitude of Zeff are governed by the Gamow factor that characterizes the suppression of the positron wave function near the ion. For all of the H-like ions, the correlation enhancement of the annihilation rate is found to be predominantly due to corrections to the annihilation vertex, while the corrections to the positron wave function play only a minor role. Results of the calculations for s-, p-, and d-wave incident positrons of energies up to the positronium-formation threshold are presented. Where comparison is possible, our values are in excellent agreement with the results obtained using other, e.g., variational, methods. The annihilation-vertex enhancement factors obtained in the present calculations are found to scale approximately as 1+(1.6+0.46ℓ)/Zi, where Zi is the net charge of the ion and ℓ is the positron orbital angular momentum. Our results for positron annihilation in H-like ions provide insights into the problem of positron annihilation with core electrons in atoms and condensed matter systems, which have similar binding energies.

  10. Revisiting big-bang nucleosynthesis constraints on dark-matter annihilation

    NASA Astrophysics Data System (ADS)

    Kawasaki, Masahiro; Kohri, Kazunori; Moroi, Takeo; Takaesu, Yoshitaro

    2015-12-01

    We study the effects of dark-matter annihilation during the epoch of big-bang nucleosynthesis on the primordial abundances of light elements. We improve the calculation of the light-element abundances by taking into account the effects of anti-nucleons emitted by the annihilation of dark matter and the interconversion reactions of neutron and proton at inelastic scatterings of energetic nucleons. Comparing the theoretical prediction of the primordial light-element abundances with the latest observational constraints, we derive upper bounds on the dark-matter pair-annihilation cross section. Implication to some of particle-physics models are also discussed.

  11. Ab initio study of the positronation of the CaO and SrO molecules including calculation of annihilation rates.

    PubMed

    Buenker, Robert J; Liebermann, Heinz-Peter

    2012-07-15

    Ab initio multireference single- and double-excitation configuration interaction calculations have been performed to compute potential curves for ground and excited states of the CaO and SrO molecules and their positronic complexes, e(+)CaO, and e(+)SrO. The adiabatic dissociation limit for the (2)Σ(+) lowest states of the latter systems consists of the positive metal ion ground state (M(+)) and the OPs complex (e(+)O(-)), although the lowest energy limit is thought to be e(+)M + O. Good agreement is found between the calculated and experimental spectroscopic constants for the neutral diatomics wherever available. The positron affinity of the closed-shell X (1)Σ(+) ground states of both systems is found to lie in the 0.16-0.19 eV range, less than half the corresponding values for the lighter members of the alkaline earth monoxide series, BeO and MgO. Annihilation rates (ARs) have been calculated for all four positronated systems for the first time. The variation with bond distance is generally similar to what has been found earlier for the alkali monoxide series of positronic complexes, falling off gradually from the OPs AR value at their respective dissociation limits. The e(+)SrO system shows some exceptional behavior, however, with its AR value reaching a minimum at a relatively large bond distance and then rising to more than twice the OPs value close to its equilibrium distance. PMID:22522712

  12. Accelerating an iterative process by explicit annihilation

    NASA Technical Reports Server (NTRS)

    Jespersen, D. C.; Buning, P. G.

    1983-01-01

    A slowly convergent stationary iterative process can be accelerated by explicitly annihilating (i.e., eliminating) the dominant eigenvector component of the error. The dominant eigenvalue or complex pair of eigenvalues can be estimated from the solution during the iteration. The corresponding eigenvector or complex pair of eigenvectors can then be annihilated by applying an explicit Richardson process over the basic iterative method. This can be done entirely in real arithmetic by analytically combining the complex conjugate annihilation steps. The technique is applied to an implicit algorithm for the calculation of two dimensional steady transonic flow over a circular cylinder using the equations of compressible inviscid gas dynamics. This demonstrates the use of explicit annihilation on a nonlinear problem.

  13. Accelerating an iterative process by explicit annihilation

    NASA Technical Reports Server (NTRS)

    Jespersen, D. C.; Buning, P. G.

    1985-01-01

    A slowly convergent stationary iterative process can be accelerated by explicitly annihilating (i.e., eliminating) the dominant eigenvector component of the error. The dominant eigenvalue or complex pair of eigenvalues can be estimated from the solution during the iteration. The corresponding eigenvector or complex pair of eigenvectors can then be annihilated by applying an explicit Richardson process over the basic iterative method. This can be done entirely in real arithmetic by analytically combining the complex conjugate annihilation steps. The technique is applied to an implicit algorithm for the calculation of two dimensional steady transonic flow over a circular cylinder using the equations of compressible inviscid gas dynamics. This demonstrates the use of explicit annihilation on a nonlinear problem.

  14. Quark dynamics of N anti N annihilation

    SciTech Connect

    Dover, C.B.

    1985-01-01

    It is argued that recent observations of strong L dependence and approximate selection rules in certain N anti N annihilation modes necessitate a description of the reaction mechanism in terms of quark-gluon degrees of freedom.

  15. Zero-Annihilation Periodic Control For Damping Vibrations

    NASA Technical Reports Server (NTRS)

    Bayard, David S.; Boussalis, Dhemetrios

    1995-01-01

    Report presents study on use of recently developed zero-annihilation periodic (ZAP) controller for active suppression of vibrations in flexible structures characterized by non-minimum-phase transfer functions. Non-minimum-phase situation occurs if certain kinds of vibration-sensor/vibration-actuator pairs (e.g., piezoelectric) used, and/or if vibration sensor(s) not colocated with vibration actuator(s).

  16. Fields annihilation and particles creation in DBI inflation

    SciTech Connect

    Firouzjahi, Hassan; Khoeini-Moghaddam, Salomeh E-mail: khoeini@ipm.ir

    2011-02-01

    We consider a model of DBI inflation where two stacks of mobile branes are moving ultra relativistically in a warped throat. The stack closer to the tip of the throat is annihilated with the background anti-branes while inflation proceeds by the second stack. The effects of branes annihilation and particles creation during DBI inflation on the curvature perturbations power spectrum and the scalar spectral index are studied. We show that for super-horizon scales, modes which are outside the sound horizon at the time of branes collision, the spectral index has a shift to blue spectrum compared to the standard DBI inflation. For small scales the power spectrum approaches to its background DBI inflation value with the decaying superimposed oscillatory modulations.

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

    NASA Astrophysics Data System (ADS)

    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.

  18. Effect of compressibility on the annihilation process

    NASA Astrophysics Data System (ADS)

    Hnatich, M.; Honkonen, J.; Lučivjanský, T.

    2013-07-01

    Using the renormalization group in the perturbation theory, we study the influence of a random velocity field on the kinetics of the single-species annihilation reaction at and below its critical dimension d c = 2. The advecting velocity field is modeled by a Gaussian variable self-similar in space with a finite-radius time correlation (the Antonov-Kraichnan model). We take the effect of the compressibility of the velocity field into account and analyze the model near its critical dimension using a three-parameter expansion in ∈, Δ, and η, where ∈ is the deviation from the Kolmogorov scaling, Δ is the deviation from the (critical) space dimension two, and η is the deviation from the parabolic dispersion law. Depending on the values of these exponents and the compressiblity parameter α, the studied model can exhibit various asymptotic (long-time) regimes corresponding to infrared fixed points of the renormalization group. We summarize the possible regimes and calculate the decay rates for the mean particle number in the leading order of the perturbation theory.

  19. Defect motion and annihilation in block copolymer thin films

    NASA Astrophysics Data System (ADS)

    Mueller, Marcus; Li, Weihua

    2015-03-01

    Using self-consistent field theory and computer simulation of a soft, coarse-grained particle model we study defect motion and annihilation in thin films of lamella-forming block copolymers on neutral and chemically patterned substrates. By virtue of the strain-field mediated interactions, dislocation defects with opposite orientation move towards each other. This motion depends both on the thermodynamic, strain-field mediated driving force and the single-chain dynamics that is required to alter the morphology and reduce the distance between the defect cores. This interplay results in a qualitative dependence of the time evolution on the topology of the defect morphology. Upon collision of the defects, they either spontaneously annihilate or form a metastable, tight defect pair. In the latter case, a free-energy barrier has to be overcome to finally produce a defect-free structure. Computing the minimum free-energy path within self-consistent field theory we investigate the dependence of the free-energy barriers of defect motion and annihilation on incompatibility, strength of the chemical surface pattern, and defect morphology. European Union FP7 / GA No. 619793 CoLiSA.MMP.

  20. Dark matter annihilation via Higgs and gamma-ray channels

    NASA Astrophysics Data System (ADS)

    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.

  1. CALET's sensitivity to Dark Matter annihilation in the galactic halo

    NASA Astrophysics Data System (ADS)

    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).

  2. Positron annihilation in neutron irradiated iron-based materials

    NASA Astrophysics Data System (ADS)

    Lambrecht, M.; Almazouzi, A.

    2011-01-01

    The hardening and embrittlement of reactor pressure vessel steels is of great concern in the actual nuclear power plant life assessment. This embrittlement is caused by irradiation-induced damage, like vacancies, interstitials, solutes and their clusters. But the reason for the embrittlement of the material is not yet totally known. The real nature of the irradiation damage should thus be examined as well as its evolution in time. Positron annihilation spectroscopy has been shown to be a powerful method for analyzing some of these defects. In fact, both vacancy type clusters and precipitates can be visualized by positrons. Recently, at SCK·CEN, a new setup has been constructed, calibrated and optimized to measure the coincidence Doppler broadening and lifetime of neutron irradiated materials. To be able to compare the results obtained by the positron studies, with those of other techniques (such as transmission electron microscopy, atom probe tomography and small angle neutron scattering), quantitative estimations of the size and density of the annihilation sites are needed. Using the approach proposed by Vehanen et al., an attempt is made to calculate the needed quantities in Fe and Fe-Cu binary alloys that were neutron irradiated to different doses. The results obtained are discussed highlighting the difficulties in defining the annihilation centres even in these simple model alloys, in spite of using both lifetime and Doppler broadening measurements in the same samples.

  3. Positron annihilation gamma rays from novae

    NASA Technical Reports Server (NTRS)

    Leising, Mark D.; Clayton, Donald D.

    1987-01-01

    The potential for observing annihilation gamma rays from novae is investigated. These gamma rays, a unique signature of the thermonuclear runaway models of novae, would result from the annihilation of positrons emitted by beta(+)-unstable nuclei produced near the peak of the runaway and carried by rapid convection to the surface of the nova envelope. Simple models, which are extensions of detailed published models, of the expansion of the nova atmospheres are evolved. These models serve as input into investigations of the fate of nearby Galactic fast novae could yield detectable fluxes of electron-positron annihilation gamma rays produced by the decay of N-13 and F-18. Although nuclear gamma-ray lines are produced by other nuclei, it is unlikely that the fluxes at typical nova distances would be detectable to present and near-future instruments.

  4. Positron annihilation induced Auger electron spectroscopy

    NASA Technical Reports Server (NTRS)

    Weiss, Alex; Koymen, A. R.; Mehl, David; Jensen, K. O.; Lei, Chun; Lee, K. H.

    1990-01-01

    Recently, Weiss et al. have demonstrated that it is possible to excite Auger transitions by annihilating core electrons using a low energy (less than 30eV) beam of positrons. This mechanism makes possible a new electron spectroscopy, Positron annihilation induced Auger Electron Spectroscopy (PAES). The probability of exciting an Auger transition is proportional to the overlap of the positron wavefunction with atomic core levels. Since the Auger electron energy provides a signature of the atomic species making the transition, PAES makes it possible to determine the overlap of the positron wavefunction with a particular element. PAES may therefore provide a means of detecting positron-atom complexes. Measurements of PAES intensities from clean and adsorbate covered Cu surfaces are presented which indicate that approx. 5 percent of positrons injected into CU at 25eV produce core annihilations that result in Auger transitions.

  5. Monopole annihilation and highest energy cosmic rays

    SciTech Connect

    Bhattacharjee, P. Indian Institute of Astrophysics, Sarjapur Road, Koramangala, Bangalore 560 034 ); Sigl, G. NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 )

    1995-04-15

    Cosmic rays with energies exceeding 10[sup 20] eV have been detected. The origin of these highest energy cosmic rays remains unknown. Established astrophysical acceleration mechanisms encounter severe difficulties in accelerating particles to these energies. Alternative scenarios where these particles are created by the decay of cosmic topological defects have been suggested in the literature. In this paper we study the possibility of producing the highest energy cosmic rays through a process that involves the formation of metastable magnetic monopole-antimonopole bound states and their subsequent collapse. The annihilation of the heavy monopole-antimonopole pairs constituting the monopolonia can produce energetic nucleons, [gamma] rays, and neutrinos whose expected flux we estimate and discuss in relation to experimental data so far available. The monopoles we consider are the ones that could be produced in the early Universe during a phase transition at the grand unification energy scale. We find that observable cosmic ray fluxes can be produced with monopole abundances compatible with present bounds.

  6. Position annihilation radiation from neutron stars

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Borner, G. A.; Cohen, J. M.

    1972-01-01

    Matter accreted on the surfaces of neutron stars consists of energetic particles of a few tens to a couple hundred MeV/nucleon, depending on the neutron star mass. In addition to heat, such particles produce nuclear reactions with the surface material. It is proposed that the recently observed 473 + or - 30 keV spectral feature from the galactic center is gravitationally red-shifted positron annihilation radiation produced at the surfaces of old neutron stars. The principal observational tests of the model would be the detection of nuclear gamma ray lines from the galactic center and red-shifted positron annihilation radiation from the galactic disk.

  7. Annihilation of Low Energy Antiprotons in Hydrogen

    SciTech Connect

    Ovchinnikov, S.Yu.; Macek, J.H.

    2003-08-26

    The cross sections for annihilation of antiprotons in hydrogen are very important for designing the High-Performance Antiproton Trap (HiPAT). When antiprotons are trapped they undergo atomic reactions with background gases which remove them from the trap. First, antiprotons are captured into highly excited bound states by ejecting the bound electrons, then they are radiationally deexcited and, finally, they annihilate by nuclear interaction. An understanding of these process require reliable cross sections for low-energy collisions of antiprotons with atoms. We have developed a theoretical technique for accurate calculations of these cross sections.

  8. Hydrodynamic description for ballistic annihilation systems

    SciTech Connect

    Garcia de Soria, Maria Isabel; Trizac, Emmanuel; Maynar, Pablo; Schehr, Gregory; Barrat, Alain

    2009-01-21

    The problem of the validity of a hydrodynamic description for a system in which there are no collisional invariants is addressed. Hydrodynamic equations have been derived and successfully tested against simulation data for a system where particles annihilate with a probability p, or collide elastically otherwise. The response of the system to a linear perturbation is analyzed as well.

  9. Neutrino-antineutrino annihilation around collapsing star

    NASA Technical Reports Server (NTRS)

    Berezinsky, V. S.; Prilutsky, O. F.

    1985-01-01

    Stellar collapse is accompanied by emission of E sub neutrino approximately 10 MeV neutrinos and antineutrinos with the energy output W sub neutrino approximately 10 to the 53rd power to 10 to the 54th power erg. Annihilation of these particles in the vicinity of collapsar is considered. The physical consequences are discussed.

  10. Nondestructive examination using neutron activated positron annihilation

    DOEpatents

    Akers, Douglas W.; Denison, Arthur B.

    2001-01-01

    A method is provided for performing nondestructive examination of a metal specimen using neutron activated positron annihilation wherein the positron emitter source is formed within the metal specimen. The method permits in situ nondestructive examination and has the advantage of being capable of performing bulk analysis to determine embrittlement, fatigue and dislocation within a metal specimen.

  11. Gamma ray lines from dark matter annihilation

    SciTech Connect

    Giudice, G.F.

    1989-08-01

    If direct annihilation of dark matter particles into a pair of photons occurs in the galactic halo, a narrow {gamma}-ray line can be discovered at future {gamma}-ray detectors sensitive to the GeV region. The signals predicted by different dark matter candidates are analyzed. 16 refs., 3 figs.

  12. The 21 cm signal and the interplay between dark matter annihilations and astrophysical processes

    NASA Astrophysics Data System (ADS)

    Lopez-Honorez, Laura; Mena, Olga; Moliné, Ángeles; Palomares-Ruiz, Sergio; Vincent, Aaron C.

    2016-08-01

    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-α pumping, we find that disentangling DM signatures from purely astrophysical effects, related to early-time star formation processes or late-time galaxy X-ray emissions, will be a challenging task. We conclude that only annihilations of DM particles with masses of ~100 MeV, could leave an unambiguous imprint on the 21 cm signal and, in particular, on the 21 cm power spectrum. This is in contrast to previous, more optimistic results in the literature, which have claimed that strong signatures might also be present even for much higher DM masses. Additional measurements of the 21 cm signal at different cosmic epochs will be crucial in order to break the strong parameter degeneracies between DM annihilations and astrophysical effects and undoubtedly single out a DM imprint for masses different from ~100 MeV.

  13. SUSY implications from WIMP annihilation into scalars at the Galactic Center

    NASA Astrophysics Data System (ADS)

    Gherghetta, Tony; von Harling, Benedict; Medina, Anibal D.; Schmidt, Michael A.; Trott, Timothy

    2015-05-01

    An excess in γ rays emanating from the Galactic Center has recently been observed in the Fermi-LAT data. This signal can be interpreted as resulting from weakly interacting massive particle annihilation, with the spectrum well fit by dark matter annihilating dominantly into either bottom-quark or Higgs pairs. Supersymmetric models provide a well-motivated framework to study the implications of this signal in these channels. With a neutralino dark matter candidate, the γ -ray excess cannot be easily accommodated in the minimal supersymmetric model, which in any case requires tuning below the percent level to explain the observed Higgs mass. Instead we are naturally led to consider the next-to-minimal model with a singlet superfield. This not only allows for the annihilation channel into bottom-quark pairs to be implemented but also provides new possibilities for annihilation into Higgs-pseudoscalar pairs. We show that the fit to the γ -ray excess for the Higgs-pseudoscalar channel can be just as good as for annihilation into bottom-quark pairs. Moreover, in the parameter range of interest, the next-to-minimal supersymmetric model solves the μ problem and can explain the 125 GeV Higgs mass with improved naturalness. We also consider an extension by adding a right-handed neutrino superfield with the right-handed sneutrino acting as a dark matter candidate. Interestingly, this allows for the annihilation into pseudoscalar pairs which also provide a good fit to the γ -ray excess. Furthermore, in the case of a neutralino lightest supersymmetric particle, the late decay of a sneutrino next-to-lightest supersymmetric particle can nonthermally produce the observed relic abundance. Finally, the weakly interacting massive particle annihilation into scalar pairs allows for the possibility of detecting the Higgs or pseudoscalar decay into two photons, providing a smoking-gun signal of the model.

  14. PIMC Simulation of Ps Annihilation: From Micro to Mesopores

    SciTech Connect

    Bug, A R; Sterne, P A

    2005-08-23

    Path Integral Monte Carlo (PIMC) can reproduce the results of simple analytical calculations in which a single quantum particle is used to represent positronium within an idealized, spherical pore. Our calculations improve on this approach by explicitly treating the positronium as a two-particle e{sup -}, e{sup +} system interacting via the Coulomb interaction. We study the lifetime and the internal contact density, {kappa}, which controls the self-annihilation behavior, for positronium in model spherical pores, as a function of temperature and pore size. We compare the results with both PIMC and analytical calculations for a single-particle model.

  15. The nuclear dynamo; Can a nuclear tornado annihilate nations

    SciTech Connect

    McNally, J.R. Jr.

    1991-01-01

    This paper reports on the development of the hypothesis of a nuclear dynamo for a controlled nuclear fusion reactor. This dynamo hypothesis suggests properties for a nuclear tornado that could annihilate nations if accidentally triggered by a single high yield to weight nuclear weapon detonation. The formerly classified reports on ignition of the atmosphere, the properties of a nuclear dynamo, methods to achieve a nuclear dynamo in the laboratory, and the analogy of a nuclear dynamo to a nuclear tornado are discussed. An unclassified international study of this question is urged.

  16. Bremsstrahlung and gamma ray lines in 3 scenarios of dark matter annihilation

    SciTech Connect

    Giacchino, Federica; Tytgat, Michel H.G.; Lopez-Honorez, Laura E-mail: llopezho@vub.ac.be

    2014-08-01

    Gamma ray spectral features are of interest for indirect searches of dark matter (DM). Following Barger et al. we consider 3 simple scenarios of DM that annihilates into Standard Model (SM) fermion pairs. Scenario 1 is a Majorana DM candidate coupled to a charged scalar, scenario 2 is a Majorana DM coupled to a charged gauge boson and scenario 3 is a real scalar DM coupled a charged vector-like fermion. As shown by Barger et al., these 3 scenarios share precisely the same internal Bremsstrahlung spectral signature into gamma rays. Their phenomenology is however distinct. In particular for annihilation into light SM fermions, in the chiral limit, the 2-body annihilation cross section is p-wave suppressed for the Majorana candidates while it is d-wave suppressed for the real scalar. In the present work we study the annihilation into 2 gammas, showing that these three scenarios have distinct, and so potentially distinguishable, spectral signatures into gamma rays. In the case of the real scalar candidate we provide a new calculation of the amplitude for annihilation into 2 gammas.

  17. INTEGRAL/SPI Observations of Electron-Positron Annihilation Radiation from our Galaxy

    NASA Technical Reports Server (NTRS)

    Teegarden, B. J.; Watanabe, K.; Knoedlseder, J.; Jean, P.; Lonjou, V.; Weidenspointer, G.; Skinner, G.; Vedrenne, G.; Roques, J.-P.; Schanne, S.; Schoenfelder, V.

    2005-01-01

    The spectrometer on INTEGRAL (SPI) is a coded-aperture gamma-ray telescope with moderate angular resolution (3 deg) and superior energy resolution (2 keV at 511 kev). One of it's principal science goals is the detailed study of 511 keV electron-positron annihilation from our Galaxy. The origin of this radiation remains a mystery, however current morphological studies suggest an older stellar population. There has also been recent speculation on the possibility of the existence of light (< 100 MeV) dark matter particles whose annihilation or decay could produce the observed 511 keV emission. In this paper we summarize the current results from SPI, compare them with previous results and discuss their implication on possible models for the production of the annihilation radiation.

  18. Positron-Electron Annihilation Process in (2,2)-Difluoropropane Molecule

    NASA Astrophysics Data System (ADS)

    Yang, Liu; Xiao-Guang, Ma; Ying-Hao, Zhu

    2016-04-01

    The positron-electron annihilation process in (2,2)-difluoropropane molecule and the corresponding gamma-ray spectra are studied by quantum chemistry method. The positrophilic electrons in (2,2)-difluoropropane molecule are found for the first time. The theoretical predictions show that the outermost 2s electrons of fluoride atoms play an important role in positron-electron annihilation process of (2,2)-difiuoropropane. In the present scheme, the correlation coefficient between the theoretical gamma-ray spectra and the experiments can be 99%. The present study gives an alternative annihilation model for positron-electron pair in larger molecules. Supported by the National Natural Science Foundation of China under Grant No. 11347011 and the Natural Science Foundation Project of Shandong Province under Grant No. ZR2011AM010 and 2014 Technology Innovation Fund of Ludong University under Grant Nos. 1d151007 and ld15l016

  19. Positron annihilation spectroscopic studies of Mn substitution-induced cubic to tetragonal transformation in ZnFe2-xMnxO4 (x = 0.0-2.0) spinel nanocrystallites

    NASA Astrophysics Data System (ADS)

    Cyriac, Jincemon; Mundiyaniyil Thankachan, Rahul; Raneesh, B.; Nambissan, P. M. G.; Sanyal, D.; Kalarikkal, Nandakumar

    2015-12-01

    The replacement of cations at the B-sites in the spinel ferrite ZnFe2O4 by Mn3+ ions brings in several interesting changes, the most striking among them being a transformation from the spinel cubic structure to a body-centered tetragonal one. Concomitantly, there are variations in the nanocrystallite sizes and also in the lattice parameters. These are examined through high-precision X-ray diffraction measurements and transmission electron microscopic analysis. A more interesting aspect is the success of positron annihilation spectroscopy comprising of the measurements of positron lifetime and coincidence Doppler broadening measurements in understanding the effects of cation replacement and the resultant generation of vacancy-type defects. There are definite changes in the positron lifetimes and intensities which show positron trapping in trivacancy-type defect clusters and the nanocrystallite surfaces. The presence of ortho-positronium atoms within the extended intercrystallite region is also identified, although in small concentrations. The cubic to tetragonal transformation is indicated through definite decrease in the values of the positron lifetimes. We also performed a model analysis to predict the expected effect of substitution on the positron lifetime in the bulk of the sample and the experimentally obtained positron lifetimes significantly differed, indirectly hinting at the possibility of a structural transformation. Finally, Mössbauer spectroscopic studies have indicated a ferromagnetic nature for one of the samples, i.e. the one with Mn3+ doping concentration x = 0.4, which incidentally had the lowest crystallite size ~10 nm.

  20. Two photon annihilation operators and squeezed vacuum

    NASA Technical Reports Server (NTRS)

    Roy, Anil K.; Mehta, C. L.; Saxena, G. M.

    1993-01-01

    Inverses of the harmonic oscillator creation and annihilation operators by their actions on the number states are introduced. Three of the two photon annihilation operators, viz., a(sup +/-1)a, aa(sup +/-1), and a(sup 2), have normalizable right eigenstates with nonvanishing eigenvalues. The eigenvalue equation of these operators are discussed and their normalized eigenstates are obtained. The Fock state representation in each case separates into two sets of states, one involving only the even number states while the other involving only the odd number states. It is shown that the even set of eigenstates of the operator a(sup +/-1)a is the customary squeezed vacuum S(sigma) O greater than.

  1. Shocking signals of dark matter annihilation

    NASA Astrophysics Data System (ADS)

    Davis, Jonathan H.; Silk, Joseph; BÅ`hm, Céline; Kotera, Kumiko; Norman, Colin

    2016-05-01

    We examine whether charged particles injected by self-annihilating dark matter (DM) into regions undergoing diffuse shock acceleration can be accelerated to high energies. We consider three astrophysical sites where shock acceleration is supposed to occur, namely the Galactic center and galaxy cluster mergers. 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. Within the Galaxy, we find that the Fermi bubbles are a potentially more efficient accelerator than supernovae remnants. 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 for enhanced radio emission from colliding clusters.

  2. Method for photon activation positron annihilation analysis

    DOEpatents

    Akers, Douglas W.

    2006-06-06

    A non-destructive testing method comprises providing a specimen having at least one positron emitter therein; determining a threshold energy for activating the positron emitter; and determining whether a half-life of the positron emitter is less than a selected half-life. If the half-life of the positron emitter is greater than or equal to the selected half-life, then activating the positron emitter by bombarding the specimen with photons having energies greater than the threshold energy and detecting gamma rays produced by annihilation of positrons in the specimen. If the half-life of the positron emitter is less then the selected half-life, then alternately activating the positron emitter by bombarding the specimen with photons having energies greater then the threshold energy and detecting gamma rays produced by positron annihilation within the specimen.

  3. Positron scattering and annihilation from hydrogenlike ions

    SciTech Connect

    Novikov, S.A.; Bromley, M.W.J.; Mitroy, J.

    2004-05-01

    The Kohn variational method is used with a configuration-interaction-type wave function to determine the J=0 and J=1 phase shifts and annihilation parameter Z{sub eff} for positron-hydrogenic ion scattering. The phase shifts are within 1-2% of the best previous calculations. The values of Z{sub eff} are small and do not exceed unity for any of the momenta considered. At thermal energies Z{sub eff} is minute with a value of order 10{sup -50} occurring for He{sup +} at k=0.05a{sub 0}{sup -1}. In addition to the variational calculations, analytic expressions for the phase shift and annihilation parameters within the Coulomb wave Born approximation are derived and used to help elucidate the dynamics of positron collisions with positive ions.

  4. Dark matter annihilation effects on the first stars

    NASA Astrophysics Data System (ADS)

    Iocco, F.; Bressan, A.; Ripamonti, E.; Schneider, R.; Ferrara, A.; Marigo, P.

    2008-11-01

    We study the effects of weakly interacting massive particles (WIMPs) dark matter (DM) on the collapse and evolution of the first stars in the Universe. Using a stellar evolution code, we follow the pre-main-sequence (pre-MS) phase of a grid of metal-free stars with masses in the range 5 <= M* <= 600Msolar forming in the centre of a 106Msolar halo at z = 20. DM particles of the parent halo are accreted in the protostellar interior by adiabatic contraction and scattering/capture processes, reaching central densities of O(1012 GeVcm-3) at radii of the order of 10au. Energy release from annihilation reactions can effectively counteract the gravitational collapse, in agreement with results from other groups. We find this stalling phase (known as a dark star) is transient and lasts from 2.1 × 103yr (M* = 600Msolar) to 1.8 × 104yr (M* = 9Msolar). Later in the evolution, DM scattering/capture rate becomes high enough that energy deposition from annihilations significantly alters the pre-MS evolution of the star in a way that depends on DM (i) velocity dispersion, , (ii) density, ρ, (iii) elastic scattering cross-section with baryons, σ0. For our fiducial set of parameters we find that the evolution of stars of mass M* < 40Msolar `freezes' on the HR diagram before reaching the zero-age main sequence (ZAMS). Stars with M* >= 40Msolar manage to ignite nuclear reactions; however, DM `burning' prolongs their lifetimes by a factor of 2 (5) for a 600Msolar (40Msolar) star. For ρ >~ 1012GeVcm-3, and same values of the other parameters, we find that all our models are entirely supported by DM annihilation and `freeze' on the HR diagram before igniting nuclear reactions.

  5. Neutrino Fluxes from NUHM LSP Annihilations in the Sun

    SciTech Connect

    Ellis, John; Olive, Keith A.; Savage, Christopher; Spanos, Vassilis C.; /Democritos Nucl. Res. Ctr.

    2011-08-12

    We extend our previous studies of the neutrino fluxes expected from neutralino LSP annihilations inside the Sun to include variants of the minimal supersymmetric extension of the Standard Model (MSSM) with squark, slepton and gaugino masses constrained to be universal at the GUT scale, but allowing one or two non-universal supersymmetry-breaking parameters contributing to the Higgs masses (NUHM1,2). As in the constrained MSSM (CMSSM) with universal Higgs masses, there are large regions of the NUHM parameter space where the LSP density inside the Sun is not in equilibrium, so that the annihilation rate may be far below the capture rate, and there are also large regions where the capture rate is not dominated by spin-dependent LSP-proton scattering. The spectra possible in the NUHM are qualitatively similar to those in the CMSSM. We calculate neutrino-induced muon fluxes above a threshold energy of 10 GeV, appropriate for the IceCube/DeepCore detector, for points where the NUHM yields the correct cosmological relic density for representative choices of the NUHM parameters. We find that the IceCube/DeepCore detector can probe regions of the NUHM parameter space in addition to analogues of the focus-point strip and the tip of the coannihilation strip familiar from the CMSSM. These include regions with enhanced Higgsino-gaugino mixing in the LSP composition, that occurs where neutralino mass eigenstates cross over. On the other hand, rapid-annihilation funnel regions in general yield neutrino fluxes that are unobservably small.

  6. Electroweak fragmentation functions for dark matter annihilation

    SciTech Connect

    Cavasonza, Leila Ali; Krämer, Michael; Pellen, Mathieu

    2015-02-18

    Electroweak corrections can play a crucial role in dark matter annihilation. The emission of gauge bosons, in particular, leads to a secondary flux consisting of all Standard Model particles, and may be described by electroweak fragmentation functions. To assess the quality of the fragmentation function approximation to electroweak radiation in dark matter annihilation, we have calculated the flux of secondary particles from gauge-boson emission in models with Majorana fermion and vector dark matter, respectively. For both models, we have compared cross sections and energy spectra of positrons and antiprotons after propagation through the galactic halo in the fragmentation function approximation and in the full calculation. Fragmentation functions fail to describe the particle fluxes in the case of Majorana fermion annihilation into light fermions: the helicity suppression of the lowest-order cross section in such models cannot be lifted by the leading logarithmic contributions included in the fragmentation function approach. However, for other classes of models like vector dark matter, where the lowest-order cross section is not suppressed, electroweak fragmentation functions provide a simple, model-independent and accurate description of secondary particle fluxes.

  7. Confronting Galactic center and dwarf spheroidal gamma-ray observations with cascade annihilation models

    NASA Astrophysics Data System (ADS)

    Dutta, Bhaskar; Gao, Yu; Ghosh, Tathagata; Strigari, Louis E.

    2015-10-01

    Many particle dark matter models predict that the dark matter undergoes cascade annihilations, i.e. the annihilation products are 4-body final states. In the context of model-independent cascade annihilation processes, we study the compatibility of the dark matter interpretation of the Fermi-LAT Galactic center gamma-ray emission with null detections from dwarf spheroidal galaxies. For canonical values of the Milky Way density profile and the local dark matter density, we find that the dark matter interpretation to the Galactic center emission is strongly constrained. However, uncertainties in the dark matter distribution weaken the constraints and leave open dark matter interpretations over a wide range of mass scales.

  8. Minimal semi-annihilating Z{sub N} scalar dark matter

    SciTech Connect

    Bélanger, Geneviève; Kannike, Kristjan; Raidal, Martti; Pukhov, Alexander E-mail: kristjan.kannike@cern.ch E-mail: martti.raidal@cern.ch

    2014-06-01

    We study the dark matter from an inert doublet and a complex scalar singlet stabilized by Z{sub N} symmetries. This field content is the minimal one that allows dimensionless semi-annihilation couplings for N > 2. We consider explicitly the Z{sub 3} and Z{sub 4} cases and take into account constraints from perturbativity, unitarity, vacuum stability, necessity for the electroweak Z{sub N} preserving vacuum to be the global minimum, electroweak precision tests, upper limits from direct detection and properties of the Higgs boson. Co-annihilation and semi-annihilation of dark sector particles as well as dark matter conversion significantly modify the cosmic abundance and direct detection phenomenology.

  9. The annihilation of positrons in the cold phase of the interstellar medium revisited

    NASA Technical Reports Server (NTRS)

    Wallyn, P.; Durouchoux, PH.; Chapuis, C.; Leventhal, M.

    1994-01-01

    The positron cross sections in H and H2 media are reevaluated, taking into account new experimental results. Using a Monte Carlo simulation, we find a positronium fraction before thermalization of 0.90 for H2, in good agreement with the previous experimental result given by Brown et al. (1986). For H we obtain an upper limit of 0.98. We study the behavior of the charge exchange annihilation in a cold phase (molecular cloud). We calculate a formula for the slowing-down time t, before annihilation lasting Delta t, via charge exchange, of a positron beam with a given energy for different medium densities and initial energies. An upper limit of 0.7 MeV for the initial energy of the positrons, annihilating in the molecular cloud G0.86 - 0.08 near the gamma ray source positronium and gives new time constraints on their possible observation.

  10. The annihilation of positrons in the cold phase of the interstellar medium revisited

    NASA Astrophysics Data System (ADS)

    Wallyn, P.; Durouchoux, Ph.; Chapuis, C.; Leventhal, M.

    1994-02-01

    The positron cross sections in H and H2 media are reevaluated, taking into account new experimental results. Using a Monte Carlo simulation, we find a positronium fraction before thermalization of 0.90 for H2, in good agreement with the previous experimental result given by Brown et al. (1986). For H we obtain an upper limit of 0.98. We study the behavior of the charge exchange annihilation in a cold phase (molecular cloud). We calculate a formula for the slowing-down time t, before annihilation lasting Delta t, via charge exchange, of a positron beam with a given energy for different medium densities and initial energies. An upper limit of 0.7 MeV for the initial energy of the positrons, annihilating in the molecular cloud G0.86 - 0.08 near the gamma ray source positronium and gives new time constraints on their possible observation.

  11. INTEGRAL/SPI Limits on Electron-Positron Annihilation Radiation from the Galactic Plane

    NASA Technical Reports Server (NTRS)

    Teegarden, B. J.; Watanabe, K.; Jean, P.; Knoedlseder, J.; Lonjou, V.; Roques, J. P.; Skinner, G. K.; vonBallmoos, P.; Weidenspointner, G.; Bazzano, A.

    2005-01-01

    The center of our Galaxy is a known strong source of electron-positron 511- keV annihilation radiation. Thus far, however, there have been no reliable detections of annihilation radiation outside of the central radian of our Galaxy. One of the primary objectives of the INTEGRAL (INTErnational Gamma-RAy Astrophysics Laboratory) mission, launched in Oct. 2002, is the detailed study of this radiation. The Spectrometer on INTEGRAL (SPI) is a high resolution coded-aperture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution and energy resolution. We report results from the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic Plane. No positive annihilation flux was detected outside of the central region (|l| greater than 40 degrees) of our Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511-keV flux.

  12. Minimal semi-annihilating ℤ{sub N} scalar dark matter

    SciTech Connect

    Bélanger, Geneviève; Kannike, Kristjan; Pukhov, Alexander; Raidal, Martti

    2014-06-10

    We study the dark matter from an inert doublet and a complex scalar singlet stabilized by ℤ{sub N} symmetries. This field content is the minimal one that allows dimensionless semi-annihilation couplings for N>2. We consider explicitly the ℤ{sub 3} and ℤ{sub 4} cases and take into account constraints from perturbativity, unitarity, vacuum stability, necessity for the electroweak ℤ{sub N} preserving vacuum to be the global minimum, electroweak precision tests, upper limits from direct detection and properties of the Higgs boson. Co-annihilation and semi-annihilation of dark sector particles as well as dark matter conversion significantly modify the cosmic abundance and direct detection phenomenology.

  13. Dimeric character of annihilation of fluorescence of higher electron states of metalloporphyrins

    SciTech Connect

    Ksenofontova, N.M.; Stel-makh, G.F.; Tsvirko, M.P.

    1987-01-01

    The reaction of two triplet-excited molecules can result in triplet-triplet annihilation (TTA) and the appearance of slowed annihilation fluorescence (SAF). The fluorescence of the S/sub 2/ state of a series of metalloporphyrins was studied in this article: Zn-tetraphenylporphyrin (ZnTPP), Zn-tetrabenzoporphyrin (ZnTBP), and CdTBP, in one-quantum direct excitation and two-quantum annihilation excitation. The spectral-luminescence measurements were made on a Ramalog-4 Raman scattering spectrometer and a Spex Fluorolog spectrofluorometer. The SAF was measured in oxygen-free solutions with excitation by steady-state radiation from an argon, krypton, or helium-neon laser falling in the S/sub 0/ ..-->.. S/sub 1/ absorption bands of the metalloporphyrins. The use of steady-state anti-Stokes excitation permits recording the SAF from the S/sub 2/ state.

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

    NASA Astrophysics Data System (ADS)

    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).

  15. Positron annihilation study of Sr Doping in La{sub 2-x}Sr{sub x}CuO{sub 4}

    SciTech Connect

    Sterne, P.A. |; Howell, R.H.; Fluss, M.J.; Kaiser, J.H.; Kitazawa, K.; Kojima, H.

    1993-04-22

    We present a combined experimental and threshold study of effects of Sr doping on electronic structure of La{sub 2-x}Sr{sub x}CuO{sub 4}. Electron-positron momentum distributions have been measured to high statistical precision (> 4 {times} 10{sup 8} counts) at room temperature for samples with Sr concentrations of x = 0.0, 0.1, 0.13 and 0.2. Analysis of all four spectra reveal strong features due to electron-positron wavefunction overlap, in quantitative agreement with theoretical calculations. The Sr doped samples show discontinuities consistent with presence of a Fermi surface. The form and position of these features are in general agreement with the predictions of band theory. Correspondence between theory and experiment, as well as some differences, are revealed by a detailed study of the changes in electron-position momentum density with increasing Sr doping.

  16. Temperature Dependence of Positron Annihilation in beta-Cyclodextrin and beta-Cyclodextrin Complexes

    NASA Astrophysics Data System (ADS)

    Hu, Y.; Hsu Hadley, F. H., Jr.; Trinh, T.

    1996-11-01

    The effects of temperature on positron annihilation in beta-cyclodextrin and beta-cyclodextrin complexed with benzyl salicylate, benzyl acetate, ethyl salicylate, geraniol, linalool and nerol were studied. Samples were prepared by slurry, air-dried and freeze-dried methods. Lifetime spectra were measured as a function of temperature for each sample. Comparison of the annihilation rate and intensity of the longer-lived component showed that positronium formation was affected by guest molecules, preparation methods and temperature variations. Results can be used to explain beta-cyclodextrin complex formation with different guest molecules.

  17. Asymmetries involving dihadron fragmentation functions: from DIS to e+ e- annihilation

    SciTech Connect

    Bacchetta, Alessandro; Radici, M.; Mukherjee, Asmita; Ceccopieri, Federico

    2009-01-01

    Using a model calculation of dihadron fragmentation functions, we fit the spin asymmetry recently extracted by HERMES for the semi-inclusive pion pair production in deep-inelastic scattering on a transversely polarized proton target. By evolving the obtained dihadron fragmentation functions, we make predictions for the correlation of the angular distributions of two pion pairs produced in electron-positron annihilations at BELLE kinematics. Our study shows that the combination of two-hadron inclusive deep-inelastic scattering and electron-positron annihilation measurements can provide a valid alternative to Collins effect for the extraction of the quark transversity distribution in the nucleon.

  18. Jet algorithms in electron-positron annihilation: perturbative higher order predictions

    NASA Astrophysics Data System (ADS)

    Weinzierl, Stefan

    2011-02-01

    This article gives results on several jet algorithms in electron-positron annihilation: Considered are the exclusive sequential recombination algorithms Durham, Geneva, Jade-E0 and Cambridge, which are typically used in electron-positron annihilation. In addition also inclusive jet algorithms are studied. Results are provided for the inclusive sequential recombination algorithms Durham, Aachen and anti- k t , as well as the infrared-safe cone algorithm SISCone. The results are obtained in perturbative QCD and are N3LO for the two-jet rates, NNLO for the three-jet rates, NLO for the four-jet rates and LO for the five-jet rates.

  19. A global model study of oxygen discharges - formation and annihilation of the singlet molecular metastables and effects of the electron energy distribution function

    NASA Astrophysics Data System (ADS)

    Roberto, Marisa; Toneli, David Arruda; Pessoa, Rodrigo Savio; Gudmundsson, Jon

    2015-09-01

    A revised reaction set for oxygen plasma modelling was implemented in a volume average global model that considers only Maxwellian electron energy distribution function. The results showed that the state could be present in the discharge in amounts higher than the state. A further study has been realized through changes in the electron energy distribution function. Differences in the results calculated using Maxwellian and non-Maxwellian distributions demonstrate the importance of using a proper electron energy distribution function in plasma modelling. This work was supported by Brazilian Agencies CNPq - (153528/2012-5), CAPES,FAPESP/PRONEX - (2011/50733-0 and 2013/03401-6), the Icelandic Research Fund Grant (130029-053), and the Swedish Government Agency for Innovation Systems (VINNOVA - 2014-04876).

  20. CONSTRAINTS ON DARK MATTER ANNIHILATION IN CLUSTERS OF GALAXIES FROM DIFFUSE RADIO EMISSION

    SciTech Connect

    Storm, Emma; Jeltema, Tesla E.; Profumo, Stefano; Rudnick, Lawrence

    2013-05-10

    Annihilation of dark matter can result in the production of stable Standard Model particles including electrons and positrons that, in the presence of magnetic fields, lose energy via synchrotron radiation, observable as radio emission. Galaxy clusters are excellent targets to search for or to constrain the rate of dark matter annihilation, as they are both massive and dark matter dominated. In this study, we place limits on dark matter annihilation in a sample of nearby clusters using upper limits on the diffuse radio emission, low levels of observed diffuse emission, or detections of radio mini-halos. We find that the strongest limits on the annihilation cross section are better than limits derived from the non-detection of clusters in the gamma-ray band by a factor of {approx}3 or more when the same annihilation channel and substructure model, but different best-case clusters, are compared. The limits on the cross section depend on the assumed amount of substructure, varying by as much as two orders of magnitude for increasingly optimistic substructure models as compared to a smooth Navarro-Frenk-White profile. In our most optimistic case, using the results of the Phoenix Project, we find that the derived limits reach below the thermal relic cross section of 3 Multiplication-Sign 10{sup -26} cm{sup 3} s{sup -1} for dark matter masses as large as 400 GeV, for the b b-bar annihilation channel. We discuss uncertainties due to the limited available data on the magnetic field structure of individual clusters. We also report the discovery of diffuse radio emission from the central 30-40 kpc regions of the groups M49 and NGC 4636.

  1. Energy-Resolved Positron Annihilation in Flight in Solid Targets

    NASA Astrophysics Data System (ADS)

    Weber, M. H.; Hunt, A. W.; Golovchenko, J. A.; Lynn, K. G.

    1999-11-01

    Energy-resolved two-quantum annihilation in flight of positrons with energies ranging from 10 to 71.6 keV was observed. An energy-dispersive two-detector coincidence system was used to observe the sum and difference energies of the γ rays from annihilating positron-electron pairs. For positrons penetrating carbon foils the c/v dependence of the annihilation cross section is confirmed. Spectra obtained from gold-coated carbon foils show evidence of in-flight annihilation with gold M-shell electrons.

  2. Concepts for the design of an antimatter annihilation rocket

    NASA Technical Reports Server (NTRS)

    Morgan, D. L., Jr.

    1982-01-01

    Matter-antimatter annihilation is considered for spacecraft propulsion. Annihilation produces considerably more energy per unit mass of propellant than any other known means of energy production. An antimatter annihilation rocket requires several systems and components that are unique to its nature. Among these are an antimatter storage system, a means to extract the antimatter from storage, a system to transport the antimatter to the rocket engine, and the engine wherein annihilation occurs and thrust is produced. Design concepts of these systems and components are presented and discussed.

  3. Positron-annihilation spectroscopy of vacancy defects in aluminum

    SciTech Connect

    Chakraborty, B.; Berko, S.; Fluss, M.J.; Hoffmann, K.; Lippel, P.; Siegel, R.W.

    1982-06-01

    Positron-annihilation characteristics in a monovacancy and a divacancy in aluminium have been calculated self-consistently using a local density functional formalism, into which the many-body enhancement effects have been incorporated. Results for the theoretical two-dimensional angular correlation of annihilation radiation spectra are compared to experimental results obtained from an aluminum single crystal at 20/sup 0/C, where positrons annihilate from a Bloch-state, and at higher temperatures, 500/sup 0/C and 630/sup 0/C, where they annihilate primarily from vacancy-trapped states.

  4. Branching-rate expansion around annihilating random walks.

    PubMed

    Benitez, Federico; Wschebor, Nicolás

    2012-07-01

    We present some exact results for branching and annihilating random walks. We compute the nonuniversal threshold value of the annihilation rate for having a phase transition in the simplest reaction-diffusion system belonging to the directed percolation universality class. Also, we show that the accepted scenario for the appearance of a phase transition in the parity conserving universality class must be improved. In order to obtain these results we perform an expansion in the branching rate around pure annihilation, a theory without branching. This expansion is possible because we manage to solve pure annihilation exactly in any dimension. PMID:23005353

  5. Dark matter annihilation at the galactic center

    NASA Astrophysics Data System (ADS)

    Linden, Tim

    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 five times as much dark matter as baryonic matter. However, efforts 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 first multiwavelength analysis of the GC, with suitable effective 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 efforts which have successfully detected an excess in gamma-ray emission from the region immediately surrounding the GC, which is difficult to describe in terms of standard diffuse 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

  6. Dark Matter Annihilation at the Galactic Center

    SciTech Connect

    Linden, Timothy Ryan

    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

  7. Experimental results on QCD (Quantum Chromodynamics) from e/sup +/e/sup -/ annihilation

    SciTech Connect

    de Boer, W.

    1987-09-01

    A review is given on QCD results from studying e/sup +/e/sup -/ annihilation with the PEP and PETRA storage rings with special emphasis on jet physics and the determination of the strong coupling constant ..cap alpha../sub s/. 92 refs., 28 figs., 3 tabs.

  8. Apparatus for photon activation positron annihilation analysis

    DOEpatents

    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.

  9. Minimal electroweak model for monopole annihilation

    SciTech Connect

    Farris, T.H. ); Kephart, T.W.; Weiler, T.J. ); Yuan, T.C. )

    1992-02-03

    We construct the minimal (most economical in fields) extension of the standard model implementing the Langacker-Pi mechanism for reducing the grand unified theory (GUT) monopole cosmic density to an allowed level. The model contains just a single charged scalar field in addition to the standard Higgs doublet, and is easily embeddable in any GUT. We identify the region of parameter space where monopoles annihilate in the higher temperature early Universe. A particularly alluring possibility is that the demise of monopoles at the electroweak scale is in fact the origin of the Universe's net baryon number.

  10. Nucleon-antinucleon annihilation in chiral soliton model

    SciTech Connect

    Musakhanov, M.M. . Inst. for Nuclear Theory Tashkentskij Gosudarstvennyj Univ., Tashkent . Dept. of Theoretical Physics); Musatov, I.V. . Research Inst. of Applied Physics)

    1991-09-07

    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.

  11. CMB constraint on dark matter annihilation after Planck 2015

    NASA Astrophysics Data System (ADS)

    Kawasaki, Masahiro; Nakayama, Kazunori; Sekiguchi, Toyokazu

    2016-05-01

    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.

  12. The Antiproton-Nucleon Annihilation Process (Antiproton Collaboration Experiment)

    DOE R&D Accomplishments Database

    Barkas, W. H.; Birge, R. W.; Chupp, W. W.; Ekspong, A. G.; Goldhaber, G.; Goldhaber, S.; Heckman, H. H.; Perkins, D. H.; Sandweiss, J.; Segre, E.; Smith, F. M.; Stork, D. H.; Rossum, L. Van; Amaldi, E.; Baroni, G.; Castagnoli, C.; Franzinetti, C.; Manfredini, A.

    1956-09-10

    In the exposure to a 700-MeV/c negative particle beam, 35 antiproton stars have been found. Of these antiprotons, 21 annihilate in flight and three give large-angle scatters ({Theta} > 15 , T{sub P-} > 50 Mev), while 14 annihilate at rest. From the interactions in flight we obtain the total cross section for antiproton interaction.

  13. Influence of O-Co-O layer thickness on the thermal conductivity of Na{sub x}Co{sub 2}O{sub 4} studied by positron annihilation

    SciTech Connect

    Li, H. Q.; Zhao, B.; Zhang, T.; Li, X. F.; He, H. F.; Chen, Z. Q.; Su, X. L.; Tang, X. F.

    2015-07-21

    Nominal stoichiometric Na{sub x}Co{sub 2}O{sub 4} (x = 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0) polycrystals were synthesized by a solid-state reaction method. They were further pressed into pellets by the spark plasma sintering. The crystal structure and morphology of Na{sub x}Co{sub 2}O{sub 4} samples were characterized by X-ray diffraction and scanning electron microscopy measurements. Good crystallinity and layered structures were observed for all the samples. Positron annihilation measurements were performed for Na{sub x}Co{sub 2}O{sub 4} as a function of Na content. Two lifetime components are resolved. τ{sub 1} is attributed mainly to positron annihilation in the O-Co-O layers and shifts to Na layers only in the H3 phase. The second lifetime τ{sub 2} is due to positron annihilation in vacancy clusters which may exist in the Na layers or grain boundary region. The size of vacancy clusters grow larger but their concentration decreases with increasing Na content in the range of 1.0 < x < 1.8. The thickness of O-Co-O layer also shows continuous increase with increasing Na content, which is reflected by the increase of τ{sub 1}. The thermal conductivity κ, on the other hand, shows systematic decrease with increasing Na content. This suggests that the increasing spacing of O-Co-O layer could effectively reduce the thermal conductivity of Na{sub x}Co{sub 2}O{sub 4}.

  14. Photoinduced carrier annihilation in silicon pn junction

    NASA Astrophysics Data System (ADS)

    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.

  15. Diffuse galactic annihilation radiation from supernova nucleosynthesis

    NASA Technical Reports Server (NTRS)

    Higdon, J. C.

    1985-01-01

    The propagation of MeV positrons in the outer ejecta of type I supernovae was investigated. It was found that the positrons created at times of approx 100 days propagated along magnetic field lines in the outer ejecta without any appreciable pitch-angle scattering or excitation of hydromagnetic waves. The lack of significant pitch-angle scattering is well consistent with models of wave excitation and scattering by resonant interactions. This occurs because time periods to scatter the particles or to excite waves are significantly longer than escape times. Thus it is expected that, when positrons are not coupled to the ejecta by Coulomb collisions, they escape from the relatively cold, dense ejecta and reside predominantly in the tenuous, hotter, shock-heated interstellar gas. In the tenuous shock-heated gas the positron lifetime against annihilation is much greater than lifetimes in the dense ejectra. Thus the production of steady-state diffuse annihilation radiation by some fraction of these escaped positrons seems probable.

  16. Positron-Annihilation Lifetime Spectroscopy using Electron Bremsstrahlung

    NASA Astrophysics Data System (ADS)

    Wagner, A.; Anwand, W.; Butterling, M.; Cowan, T. E.; Fiedler, F.; Fritz, F.; Kempe, M.; Krause-Rehberg, R.

    2015-06-01

    A new type of an intense source of positrons for materials research has been set up at the superconducting electron linear. The source employs hard X-rays from electron- bremsstrahlung production generating energetic electron-positron pairs inside the sample under investigation. CW-operation allows performing experiments with significantly reduced pile-up artefacts in the detectors compared to pulsed mode operation in conventional accelerators. The high-resolution timing of the accelerator with bunch lengths below 10 ps full width at half maximum (FWHM) allows positron annihilation lifetime spectroscopy (PALS) measurements with high time resolution. A single-component annihilation lifetime of Kaptonhas been measured as (381.3 ± 0.3) ps. Employing segmented detectors for the detection of both annihilation photons allows for the first time to perform a 4D tomographic reconstruction of the annihilation sites including the annihilation lifetime.

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

    SciTech Connect

    Siegel, R.W.

    1982-06-01

    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. Positron and Positronium Annihilation Lifetime, and Free Volume in Polymers.

    NASA Astrophysics Data System (ADS)

    Yu, Zhibin

    1995-01-01

    Positron annihilation lifetime measurements were carried out for six polycarbonates of different structures and four polystyrenes of different molecular weight over a wide temperature range covering the glass transition region. The o-Ps mean lifetime is very sensitive to the changes of free volume in those polymers which occur due to change of molecular structure, chain length, and temperature. The influence of the unavoidable e^{+} irradiation and physical aging on the mean lifetime and the intensity of o-Ps annihilation were studied by conducting time dependent measurements on both very aged and rejuvenated samples. Both irradiation and physical aging reduce the formation of positronium, but have no effect on the mean lifetime of Ps atoms. The free volume fraction h obtained from the positron lifetime measurements was compared with the prediction of the statistical mechanical theory of Simha and Somcynsky; good agreement was found in the melt state though clear deviations were observed in the glassy state. A free volume quantity, computed from the bulk volume, which is in a good numerical agreement with the Simha-Somcynsky h-function in the melt, gives improved agreement with the h value calculated from the positron lifetime measurements. To investigate certain anomalies observed in the computer analysis of the positron annihilation lifetime spectra on polymers, we developed a computer simulation of the experimental data, which then was used to test the accuracy of the fitting results in the different circumstances. The influence caused by a possible distribution of the o-Ps mean lifetimes and the width of the spectrometer time resolution function were studied. The theoretical connection between the o-Ps mean lifetime and the free volume hole size was reviewed based on a finite spherical potential well model, and the status of the localized Ps atom in polymers was evaluated by calculation of the barrier transmission probability and the escaping probability of the

  19. Dark matter annihilations into two light fermions and one gauge boson: general analysis and antiproton constraints

    SciTech Connect

    Garny, Mathias; Ibarra, Alejandro; Vogl, Stefan E-mail: alejandro.ibarra@ph.tum.de

    2012-04-01

    We study in this paper the scenario where the dark matter is constituted by Majorana particles which couple to a light Standard Model fermion and an extra scalar via a Yukawa coupling. In this scenario, the annihilation rate into the light fermions with the mediation of the scalar particle is strongly suppressed by the mass of the fermion. Nevertheless, the helicity suppression is lifted by the associated emission of a gauge boson, yielding annihilation rates which could be large enough to allow the indirect detection of the dark matter particles. We perform a general analysis of this scenario, calculating the annihilation cross section of the processes χχ→f f-bar V when the dark matter particle is a SU(2){sub L} singlet or doublet, f is a lepton or a quark, and V is a photon, a weak gauge boson or a gluon. We point out that the annihilation rate is particularly enhanced when the dark matter particle is degenerate in mass to the intermediate scalar particle, which is a scenario barely constrained by collider searches of exotic charged or colored particles. Lastly, we derive upper limits on the relevant cross sections from the non-observation of an excess in the cosmic antiproton-to-proton ratio measured by PAMELA.

  20. Gamma-ray lines and one-loop continuum from s-channel dark matter annihilations

    NASA Astrophysics Data System (ADS)

    Jackson, C. B.; Servant, Géraldine; Shaughnessy, Gabe; Tait, Tim M. P.; Taoso, Marco

    2013-07-01

    The era of indirect detection searches for dark matter has begun, with the sensitivities of gamma-ray detectors now approaching the parameter space relevant for weakly interacting massive particles. In particular, gamma ray lines would be smoking gun signatures of dark matter annihilation, although they are typically suppressed compared to the continuum. In this paper, we pay particular attention to the 1-loop continuum generated together with the gamma-ray lines and investigate under which conditions a dark matter model can naturally lead to a line signal that is relatively enhanced. We study generic classes of models in which DM is a fermion that annihilates through an s-channel mediator which is either a vector or scalar and identify the coupling and mass conditions under which large line signals occur. We focus on the ``forbidden channel mechanism" advocated a few years ago in the ``Higgs in space" scenario for which tree level annihilation is kinematically forbidden today. Detailed calculations of all 1-loop annihilation channels are provided. We single out very simple models with a large line over continuum ratio and present general predictions for a large range of WIMP masses that are relevant not only for Fermi and Hess II but also for the next generation of telescopes such as CTA and Gamma-400. Constraints from the relic abundance, direct detection and collider bounds are also discussed.

  1. Gamma-ray lines and one-loop continuum from s-channel dark matter annihilations

    SciTech Connect

    Jackson, C.B.; Servant, Géraldine; Shaughnessy, Gabe; Tait, Tim M.P.; Taoso, Marco E-mail: chris@uta.edu E-mail: ttait@uci.edu

    2013-07-01

    The era of indirect detection searches for dark matter has begun, with the sensitivities of gamma-ray detectors now approaching the parameter space relevant for weakly interacting massive particles. In particular, gamma ray lines would be smoking gun signatures of dark matter annihilation, although they are typically suppressed compared to the continuum. In this paper, we pay particular attention to the 1-loop continuum generated together with the gamma-ray lines and investigate under which conditions a dark matter model can naturally lead to a line signal that is relatively enhanced. We study generic classes of models in which DM is a fermion that annihilates through an s-channel mediator which is either a vector or scalar and identify the coupling and mass conditions under which large line signals occur. We focus on the ''forbidden channel mechanism'' advocated a few years ago in the ''Higgs in space'' scenario for which tree level annihilation is kinematically forbidden today. Detailed calculations of all 1-loop annihilation channels are provided. We single out very simple models with a large line over continuum ratio and present general predictions for a large range of WIMP masses that are relevant not only for Fermi and Hess II but also for the next generation of telescopes such as CTA and Gamma-400. Constraints from the relic abundance, direct detection and collider bounds are also discussed.

  2. Surface states and annihilation characteristics of positrons trapped at the (100) and (111) surfaces of silicon

    NASA Astrophysics Data System (ADS)

    Fazleev, N. G.; Fry, J. L.; Weiss, A. H.

    2004-10-01

    Recent studies of Si(100) and Si(111) using positron annihilation induced Auger-electron spectroscopy (PAES) reveal that experimental annihilation probabilities of surface trapped positrons with relevant Si core-level electrons differ significantly for two faces of clean Si, an elemental semiconductor. These experimental results are investigated theoretically by performing calculations of the “image-potential” positron surface states and annihilation characteristics of the surface trapped positrons with relevant Si core-level electrons for the ideally terminated, nonreconstructed and reconstructed Si(100)-(2×1) and Si(111)-(7×7) surfaces. Computed positron surface binding energies demonstrate their sensitivity to the specific atomic structure of the topmost layers of surfaces, and, when compared to positron work functions, the stability of positron surface states on all studied Si(100) and Si(111) surfaces. The positron surface state wave function was found to be localized in a potential well on the vacuum side at both nonreconstructed semiconductor surfaces. The (2×1) reconstruction of the Si(100) surface causes the positron surface state wave function to extend into the lattice in the regions where atoms are displaced away from their ideal terminated positions. A comparison of theoretical and experimental positron surface binding energies for Si(100) shows that the best agreement is achieved when the reconstructed Si(100)-(2×1) surface is described within the asymmetric dimer model. Calculations indicate that the positron surface state wave function is localized in all three dimensions in the corner hole regions of the reconstructed Si(111)-(7×7) surface. This localization provides an explanation for previous experiments that failed to show the anisotropy in the electron-positron pair momentum density distribution expected for a positron surface state delocalized in the plane of the surface. Positron annihilation characteristics are calculated for each

  3. Dynamics of annihilation. I. Linearized Boltzmann equation and hydrodynamics.

    PubMed

    García de Soria, María Isabel; Maynar, Pablo; Schehr, Grégory; Barrat, Alain; Trizac, Emmanuel

    2008-05-01

    We study the nonequilibrium statistical mechanics of a system of freely moving particles, in which binary encounters lead either to an elastic collision or to the disappearance of the pair. Such a system of ballistic annihilation therefore constantly loses particles. The dynamics of perturbations around the free decay regime is investigated using the spectral properties of the linearized Boltzmann operator, which characterize linear excitations on all time scales. The linearized Boltzmann equation is solved in the hydrodynamic limit by a projection technique, which yields the evolution equations for the relevant coarse-grained fields and expressions for the transport coefficients. We finally present the results of molecular dynamics simulations that validate the theoretical predictions. PMID:18643046

  4. Induced absorption and annihilation in hadronic hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Pomerantsev, Vladimir N.; Popov, Vladimir P.

    The induced absorption or annihilation in the collisions of the hydrogen hadronic atoms in the excited states with ordinary hydrogen have been described in a unified manner with the elastic scattering, Stark transitions, and Coulomb de-excitation in the framework of a close-coupling approach including both the open and closed channels corresponding to both the stationary and non-stationary states of hadronic atom. The general features of the induced absorption cross sections have been studied in a wide range of the complex energy-shift values. The total and differential cross sections of all processes have been calculated for π - p, K - p, and bar p p atoms with the principal quantum numbers n = 2 - 8 and kinetic energy from 0.001 eV up to 100 eV.

  5. Induced absorption and annihilation in hadronic hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Pomerantsev, Vladimir N.; Popov, Vladimir P.

    2012-05-01

    The induced absorption or annihilation in the collisions of the hydrogen hadronic atoms in the excited states with ordinary hydrogen have been described in a unified manner with the elastic scattering, Stark transitions, and Coulomb de-excitation in the framework of a close-coupling approach including both the open and closed channels corresponding to both the stationary and non-stationary states of hadronic atom. The general features of the induced absorption cross sections have been studied in a wide range of the complex energy-shift values. The total and differential cross sections of all processes have been calculated for π - p, K - p, and bar p p atoms with the principal quantum numbers n = 2 - 8 and kinetic energy from 0.001 eV up to 100 eV.

  6. Semi-inclusive wino and higgsino annihilation to LL'

    NASA Astrophysics Data System (ADS)

    Baumgart, Matthew; Vaidya, Varun

    2016-03-01

    We systematically compute the annihilation rate for winos and higgsinos into the final state relevant for indirect detection experiments, γ + X. The radiative corrections to this process receive enhancement from the large Bloch-Nordsieck-Violating Sudakov logarithm, log(2 M χ /M W ). We resum the double logs and include single logs to fixed order using a formalism that combines nonrelativistic and soft-collinear effective field theories. For the wino case, we update an earlier exclusion adapting results of the HESS experiment. At the thermal relic mass of 3 TeV, LL' corrections result in a ˜30% reduction in rate relative to LL. Nonetheless, single logs do not save the wino, and it is still excluded by an order of magnitude. Experimental cuts produce an endpoint region which, our results show, significantly effects the higgsino rate at its thermal-relic mass near 1 TeV and is deserving of further study.

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

    SciTech Connect

    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.

  8. Monte Carlo modelling of the propagation and annihilation of nucleosynthesis positrons in the Galaxy

    NASA Astrophysics Data System (ADS)

    Alexis, A.; Jean, P.; Martin, P.; Ferrière, K.

    2014-04-01

    Aims: We want to estimate whether the positrons produced by the β+-decay of 26Al, 44Ti, and 56Ni synthesised in massive stars and supernovae are sufficient to explain the 511 keV annihilation emission observed in our Galaxy. Such a possibility has often been put forward in the past. In a previous study, we showed that nucleosynthesis positrons cannot explain the full annihilation emission. Here, we extend this work using an improved propagation model. Methods: We developed a Monte Carlo Galactic propagation code for ~MeV positrons in which the Galactic interstellar medium, the Galactic magnetic field, and the propagation are finely described. This code allows us to simulate the spatial distribution of the 511 keV annihilation emission. We tested several Galactic magnetic fields models and several positron escape fractions from type-Ia supernova for 56Ni positrons to account for the large uncertainties in these two parameters. We considered the collisional/ballistic transport mode and then compared the simulated 511 keV intensity spatial distributions to the INTEGRAL/SPI data. Results: Regardless of the Galactic magnetic field configuration and the escape fraction chosen for 56Ni positrons, the 511 keV intensity distributions are very similar. The main reason is that ~MeV positrons do not propagate very far away from their birth sites in our model. The direct comparison to the data does not allow us to constrain the Galactic magnetic field configuration and the escape fraction for 56Ni positrons. In any case, nucleosynthesis positrons produced in steady state cannot explain the full annihilation emission. The comparison to the data shows that (a) the annihilation emission from the Galactic disk can be accounted for; (b) the strongly peaked annihilation emission from the inner Galactic bulge can be explained by positrons annihilating in the central molecular zone, but this seems to require more positron sources than the population of massive stars and type Ia

  9. Constraining weak annihilation using semileptonic D decays

    SciTech Connect

    Ligeti, Zoltan; Luke, Michael; Manohar, Aneesh V.

    2010-08-01

    The recently measured semileptonic D{sub s} decay rate can be used to constrain weak annihilation (WA) effects in semileptonic D and B decays. We revisit the theoretical predictions for inclusive semileptonic D{sub (s)} decays using a variety of quark mass schemes. The most reliable results are obtained if the fits to B decay distributions are used to eliminate the charm quark mass dependence, without using any specific charm mass scheme. Our fit to the available data shows that WA is smaller than commonly assumed. There is no indication that the WA octet contribution (which is better constrained than the singlet contribution) dominates. The results constrain an important source of uncertainty in the extraction of |V{sub ub}| from inclusive semileptonic B decays.

  10. Detecting Dark Matter annihilation lines with Fermi

    SciTech Connect

    Ylinen, Tomi; Edmonds, Yvonne; Bloom, Elliott D.; Conrad, Jan; /Royal Inst. Tech., Stockholm /Kalmar U. /KIPAC, Menlo Park /SLAC /Stockholm U.

    2009-05-15

    Dark matter constitutes one of the most intriguing but so far unresolved issues in physics today. In many extensions of the Standard Model the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent dark matter particle candidate and one of the most interesting scenarios include an annihilation of two WIMPs into two gamma-rays. If the WIMPs are assumed to be non-relativistic, the resulting photons will both have an energy equal to the mass of the WIMP and manifest themselves as a monochromatic spectral line in the energy spectrum. This type of signal would represent a 'smoking gun' for dark matter, since no other known astrophysical process should be able to produce it. In these proceedings we give an overview of the different approaches to a search for dark matter lines that the Fermi-LAT collaboration is pursuing and the various challenges involved.