Science.gov

Sample records for positron decay

  1. Resolvability of positron decay channels

    SciTech Connect

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

    1985-03-07

    Many data analysis treatments of positron experiments attempt to resolve two or more positron decay or exist channels which may be open simultaneously. Examples of the need to employ such treatments of the experimental results can be found in the resolution of the constituents of a defect ensemble, or in the analysis of the complex spectra which arise from the interaction of slow positrons at or near the surfaces of solids. Experimental one- and two-dimensional angular correlation of annihilation radiation experiments in Al single crystals have shown that two defect species (mono- and divacancies) can be resolved under suitable conditions. Recent experiments at LLNL indicate that there are a variety of complex exit channels open to positrons interacting at surfaces, and ultimely these decay channels must also be suitably resolved from one another. 6 refs., 4 figs.

  2. Cold Positrons from Decaying Dark Matter

    SciTech Connect

    Boubekeur, Lotfi; Dodelson, Scott; Vives, Oscar

    2012-11-01

    Many models of dark matter contain more than one new particle beyond those in the Standard Model. Often heavier particles decay into the lightest dark matter particle as the Universe evolves. Here we explore the possibilities that arise if one of the products in a (Heavy Particle) $\\rightarrow$ (Dark Matter) decay is a positron, and the lifetime is shorter than the age of the Universe. The positrons cool down by scattering off the cosmic microwave background and eventually annihilate when they fall into Galactic potential wells. The resulting 511 keV flux not only places constraints on this class of models but might even be consistent with that observed by the INTEGRAL satellite.

  3. Search for bound-state electron+positron pair decay

    NASA Astrophysics Data System (ADS)

    Bosch, F.; Hagmann, S.; Hillenbrand, P.-M.; Lane, G. J.; Litvinov, Yu. A.; Reed, M. W.; Sanjari, M. S.; Stöhlker, Th.; Torilov, S. Yu.; Tu, X. L.; Walke, P. M.

    2016-09-01

    The heavy ion storage rings coupled to in-flight radioactive-ion beam facilities, namely the ability to produce and store for extended periods of time radioactive nuclides in high atomic charge states, for the searchof yet unobserved decay mode - bound-state electron-positron pair decay.

  4. Positron-electron decay of 28Si at an excitation energy of 50 MeV

    NASA Astrophysics Data System (ADS)

    Buda, A.; Bacelar, J. C.; Balanda, A.; van der Ploeg, H.; Sujkowski, Z.; van der Woude, A.

    1993-03-01

    The electron-position pair decay of 28Si at 50 MeV excitation produced by the isospin T=0 (α + 24Mg) and the mixed isospin T=0,1 (3He + 25Mg) reactions has been studied using a special designed Positron-Electron pair spectrometer PEPSI.

  5. AMS-02 positron excess and indirect detection of three-body decaying dark matter

    NASA Astrophysics Data System (ADS)

    Cheng, Hsin-Chia; Huang, Wei-Chih; Huang, Xiaoyuan; Low, Ian; Sming Tsai, Yue-Lin; Yuan, Qiang

    2017-03-01

    We consider indirect detection of meta-stable dark matter particles decaying into a stable neutral particle and a pair of standard model fermions. Due to the softer energy spectra from the three-body decay, such models could potentially explain the AMS-02 positron excess without being constrained by the Fermi-LAT gamma-ray data and the cosmic ray anti-proton measurements. We scrutinize over different final state fermions, paying special attention to handling of the cosmic ray background and including various contributions from cosmic ray propagation with the help of the LIKEDM package. It is found that primary decays into an electron-positron pair and a stable neutral particle could give rise to the AMS-02 positron excess and, at the same time, stay unscathed against the gamma-ray and anti-proton constraints. Decays to a muon pair or a mixed flavor electron-muon pair may also be viable depending on the propagation models. Decays to all other standard model fermions are severely disfavored.

  6. Gamma-ray lines from novae. [relationship to radioactive decay and positron annihilation

    NASA Technical Reports Server (NTRS)

    Clayton, D. D.; Hoyle, F.

    1974-01-01

    An appropriate gamma-ray telescope could detect the gamma-rays associated with radioactive decays. The observable lines would be the annihilation radiation following the positron emission of N-13, O-14, O-15, and Na-22 and the 2.312-MeV line emitted following the O-14 decay and the 1.274-MeV line emitted following the Na-22 decay. The experimental possibility should be borne in mind for the occurrence of novae within a few kiloparsecs.

  7. Precise Measurement of the Positron Asymmetry in the Decay of Spin-polarized 37K

    NASA Astrophysics Data System (ADS)

    Fenker, Benjamin; Melconian, Dan; Behling, Spencer; Mehlman, Michael; Behr, John; Craiciu, Ioana; Gorelov, Alexandre; McNeil, James; Smale, Scott; Warner, Claire; Anholm, Melissa; Gwinner, Gerald; Ashery, Daniel; Cohen, Iuliana

    2016-09-01

    Precise low-energy measurements in nuclear β-decay provide constraints on possible physics beyond the standard model complementary to high-energy collider experiments. We report the most precise measurement of the positron asymmetry from a polarized nucleus to-date. At the TRIUMF Neutral Atom Trap, atoms of the positron emitter 37K are confined in an alternating-current magneto-optical trap and spin-polarized to 99 . 13 +/- 0 . 09 % via optical pumping. The use of atom-trapping techniques allows for an exceptionally open geometry with the decay products escaping the trapping region unperturbed by the trapping potential. We detect the emitted positrons in a pair of symmetric detectors placed along the polarization axis to measure the asymmetry in situ. The analysis was performed blind and considers β-scattering and other systematic effects. The results place limits on the mass of a hypothetical W boson coupling to right-handed neutrinos as well as contribute to an independent determination of the Vud element of the CKM matrix. U.S. DOE, the Israel Science Foundation, and NSERC . TRIUMF receives federal funding via a contribution agreement with the National Research Council of Canada.

  8. Enhanced Dark Matter Annihilation Rate for Positron and Electron Excesses from Q-Ball Decay

    SciTech Connect

    McDonald, John

    2009-10-09

    We show that Q-ball decay in Affleck-Dine baryogenesis models can account for dark matter when the annihilation cross section is sufficiently enhanced to explain the positron and electron excesses observed by PAMELA, ATIC, and PPB-BETS. For Affleck-Dine baryogenesis along a d=6 flat direction, the reheating temperature is approximately 30 GeV and the Q-ball decay temperature is in the range of 10-100 MeV. The lightest supersymmetric particles produced by Q-ball decay annihilate down to the observed dark matter density if the cross section is enhanced by a factor approx10{sup 3} relative to the thermal relic cross section.

  9. Parametric decays in relativistic magnetized electron-positron plasmas with relativistic temperatures

    SciTech Connect

    Lopez, Rodrigo A.; Munoz, Victor; Asenjo, Felipe A.; Alejandro Valdivia, J.

    2012-08-15

    The nonlinear evolution of a circularly polarized electromagnetic wave in an electron-positron plasma propagating along a constant background magnetic field is considered, by studying its parametric decays. Relativistic effects, of the particle motion in the wave field and of the plasma temperature, are included to obtain the dispersion relation of the decays. The exact dispersion relation of the pump wave has been previously calculated within the context of a relativistic fluid theory and presents two branches: an electromagnetic and an Alfven one. We investigate the parametric decays for the pump wave in these two branches, including the anomalous dispersion zone of the Alfven branch where the group velocity is negative. We solve the nonlinear dispersion relation for different pump wave amplitudes and plasma temperatures, finding various resonant and nonresonant wave couplings. We are able to identify these couplings and study their behavior as we modify the plasma parameters. Some of these couplings are suppressed for larger amplitudes or temperatures. We also find two kinds of modulational instabilities, one involving two sideband daughter waves and another involving a forward-propagating electroacoustic mode and a sideband daughter wave.

  10. Indirect and direct signatures of Higgs portal decaying vector dark matter for positron excess in cosmic rays

    SciTech Connect

    Baek, Seungwon; Ko, P.; Park, Wan-Il; Tang, Yong E-mail: pko@kias.re.kr E-mail: ytang@kias.re.kr

    2014-06-01

    We investigate the indirect signatures of the Higgs portal U(1){sub X} vector dark matter (VDM) X{sub μ} from both its pair annihilation and decay. The VDM is stable at renormalizable level by Z{sub 2} symmetry, and thermalized by Higgs-portal interactions. It can also decay by some nonrenormalizable operators with very long lifetime at cosmological time scale. If dim-6 operators for VDM decays are suppressed by 10{sup 16} GeV scale, the lifetime of VDM with mass ∼ 2 TeV is just right for explaining the positron excess in cosmic ray observed by PAMELA and AMS02 Collaborations. The VDM decaying into μ{sup +}μ{sup −} can fit the data, evading various constraints on cosmic rays. We give one UV-complete model as an example. This scenario for Higgs portal decaying VDM with mass around ∼ 2 TeV can be tested by DM direct search at XENON1T, and also at the future colliders by measuring the Higgs self-couplings.

  11. Deformed shell model results for neutrinoless positron double beta decay of nuclei in the A = 60-90 region

    NASA Astrophysics Data System (ADS)

    Sahu, R.; Srivastava, P. C.; Kota, V. K. B.

    2013-09-01

    Nuclear transition matrix elements (NTME) for neutrinoless positron double beta decay (0νβ+β+ and 0νβ+EC) of 64Zn, 74Se, 78Kr and 84Sr nuclei, which are in the A = 60-90 region, are calculated within the framework of the deformed shell model (DSM) based on Hartree-Fock states. For 64Zn, GXPF1A interaction in 1f7/2, 2p3/2, 1f5/2 and 2p1/2 space with 40Ca as the core is employed. Similarly for 74Se, 78Kr and 84Sr nuclei, 56Ni is taken as the inert core employing a modified Kuo interaction in 2p3/2, 1f5/2, 2p1/2 and 1g9/2 space. After ensuring that the DSM gives a good description of the spectroscopic properties of low-lying levels in the four nuclei considered, the NTME are calculated. The half-lives deduced with these NTME, assuming the neutrino mass is 1 eV, are smallest for 78Kr with the half-life for β+EC decay being ˜1027 yr. For all others, the half-lives are in the range of ˜1028-1029 yr.

  12. Search for Heavy Particles Decaying into Electron-Positron Pairs in ppbar Collisions

    NASA Astrophysics Data System (ADS)

    Abazov, V. M.; Abbott, B.; Abdesselam, A.; Abolins, M.; Abramov, V.; Acharya, B. S.; Adams, D. L.; Adams, M.; Ahmed, S. N.; Alexeev, G. D.; Alves, G. A.; Amos, N.; Anderson, E. W.; Baarmand, M. M.; Babintsev, V. V.; Babukhadia, L.; Bacon, T. C.; Baden, A.; Baldin, B.; Balm, P. W.; Banerjee, S.; Barberis, E.; Baringer, P.; Barreto, J.; Bartlett, J. F.; Bassler, U.; Bauer, D.; Bean, A.; Begel, M.; Belyaev, A.; Beri, S. B.; Bernardi, G.; Bertram, I.; Besson, A.; Beuselinck, R.; Bezzubov, V. A.; Bhat, P. C.; Bhatnagar, V.; Bhattacharjee, M.; Blazey, G.; Blessing, S.; Boehnlein, A.; Bojko, N. I.; Borcherding, F.; Bos, K.; Brandt, A.; Breedon, R.; Briskin, G.; Brock, R.; Brooijmans, G.; Bross, A.; Buchholz, D.; Buehler, M.; Buescher, V.; Burtovoi, V. S.; Butler, J. M.; Canelli, F.; Carvalho, W.; Casey, D.; Casilum, Z.; Castilla-Valdez, H.; Chakraborty, D.; Chan, K. M.; Chekulaev, S. V.; Cho, D. K.; Choi, S.; Chopra, S.; Christenson, J. H.; Chung, M.; Claes, D.; Clark, A. R.; Cochran, J.; Coney, L.; Connolly, B.; Cooper, W. E.; Coppage, D.; Cummings, M. A.; Cutts, D.; Davis, G. A.; Davis, K.; de, K.; de Jong, S. J.; del Signore, K.; Demarteau, M.; Demina, R.; Demine, P.; Denisov, D.; Denisov, S. P.; Desai, S.; Diehl, H. T.; Diesburg, M.; di Loreto, G.; Doulas, S.; Draper, P.; Ducros, Y.; Dudko, L. V.; Duensing, S.; Duflot, L.; Dugad, S. R.; Dyshkant, A.; Edmunds, D.; Ellison, J.; Elvira, V. D.; Engelmann, R.; Eno, S.; Eppley, G.; Ermolov, P.; Eroshin, O. V.; Estrada, J.; Evans, H.; Evdokimov, V. N.; Fahland, T.; Feher, S.; Fein, D.; Ferbel, T.; Filthaut, F.; Fisk, H. E.; Fisyak, Y.; Flattum, E.; Fleuret, F.; Fortner, M.; Frame, K. C.; Fuess, S.; Gallas, E.; Galyaev, A. N.; Gao, M.; Gavrilov, V.; Genik, R. J.; Genser, K.; Gerber, C. E.; Gershtein, Y.; Gilmartin, R.; Ginther, G.; Gómez, B.; Gómez, G.; Goncharov, P. I.; González Solís, J. L.; Gordon, H.; Goss, L. T.; Gounder, K.; Goussiou, A.; Graf, N.; Graham, G.; Grannis, P. D.; Green, J. A.; Greenlee, H.; Grinstein, S.; Groer, L.; Grünendahl, S.; Gupta, A.; Gurzhiev, S. N.; Gutierrez, G.; Gutierrez, P.; Hadley, N. J.; Haggerty, H.; Hagopian, S.; Hagopian, V.; Hall, R. E.; Hanlet, P.; Hansen, S.; Hauptman, J. M.; Hays, C.; Hebert, C.; Hedin, D.; Heinson, A. P.; Heintz, U.; Heuring, T.; Hildreth, M. D.; Hirosky, R.; Hobbs, J. D.; Hoeneisen, B.; Huang, Y.; Illingworth, R.; Ito, A. S.; Jaffré, M.; Jain, S.; Jesik, R.; Johns, K.; Johnson, M.; Jonckheere, A.; Jones, M.; Jöstlein, H.; Juste, A.; Kahn, S.; Kajfasz, E.; Kalinin, A. M.; Karmanov, D.; Karmgard, D.; Kehoe, R.; Kharchilava, A.; Kim, S. K.; Klima, B.; Knuteson, B.; Ko, W.; Kohli, J. M.; Kostritskiy, A. V.; Kotcher, J.; Kotwal, A. V.; Kozelov, A. V.; Kozlovsky, E. A.; Krane, J.; Krishnaswamy, M. R.; Krivkova, P.; Krzywdzinski, S.; Kubantsev, M.; Kuleshov, S.; Kulik, Y.; Kunori, S.; Kupco, A.; Kuznetsov, V. E.; Landsberg, G.; Leflat, A.; Leggett, C.; Lehner, F.; Li, J.; Li, Q. Z.; Lima, J. G.; Lincoln, D.; Linn, S. L.; Linnemann, J.; Lipton, R.; Lucotte, A.; Lueking, L.; Lundstedt, C.; Luo, C.; Maciel, A. K.; Madaras, R. J.; Malyshev, V. L.; Manankov, V.; Mao, H. S.; Marshall, T.; Martin, M. I.; Martin, R. D.; Mauritz, K. M.; May, B.; Mayorov, A. A.; McCarthy, R.; McDonald, J.; McMahon, T.; Melanson, H. L.; Merkin, M.; Merritt, K. W.; Miao, C.; Miettinen, H.; Mihalcea, D.; Mishra, C. S.; Mokhov, N.; Mondal, N. K.; Montgomery, H. E.; Moore, R. W.; Mostafa, M.; da Motta, H.; Nagy, E.; Nang, F.; Narain, M.; Narasimham, V. S.; Neal, H. A.; Negret, J. P.; Negroni, S.; Nunnemann, T.; O'Neil, D.; Oguri, V.; Olivier, B.; Oshima, N.; Padley, P.; Pan, L. J.; Papageorgiou, K.; Para, A.; Parashar, N.; Partridge, R.; Parua, N.; Paterno, M.; Patwa, A.; Pawlik, B.; Perkins, J.; Peters, M.; Peters, O.; Pétroff, P.; Piegaia, R.; Piekarz, H.; Pope, B. G.; Popkov, E.; Prosper, H. B.; Protopopescu, S.; Qian, J.; Raja, R.; Rajagopalan, S.; Ramberg, E.; Rapidis, P. A.; Reay, N. W.; Reucroft, S.; Rha, J.; Ridel, M.; Rijssenbeek, M.; Rockwell, T.; Roco, M.; Rubinov, P.; Ruchti, R.; Rutherfoord, J.; Sabirov, B. M.; Santoro, A.; Sawyer, L.; Schamberger, R. D.; Schellman, H.; Schwartzman, A.; Sen, N.; Shabalina, E.; Shivpuri, R. K.; Shpakov, D.; Shupe, M.; Sidwell, R. A.; Simak, V.; Singh, H.; Singh, J. B.; Sirotenko, V.; Slattery, P.; Smith, E.; Smith, R. P.; Snihur, R.; Snow, G. R.; Snow, J.; Snyder, S.; Solomon, J.; Sorín, V.; Sosebee, M.; Sotnikova, N.; Soustruznik, K.; Souza, M.; Stanton, N. R.; Steinbrück, G.; Stephens, R. W.; Stichelbaut, F.; Stoker, D.; Stolin, V.; Stoyanova, D. A.; Strauss, M.; Strovink, M.; Stutte, L.; Sznajder, A.; Taylor, W.; Tentindo-Repond, S.; Tripathi, S. M.; Trippe, T. G.; Turcot, A. S.; Tuts, P. M.; van Gemmeren, P.; Vaniev, V.; van Kooten, R.; Varelas, N.; Vertogradov, L. S.; Volkov, A. A.; Vorobiev, A. P.; Wahl, H. D.; Wang, H.; Wang, Z.-M.; Warchol, J.; Watts, G.; Wayne, M.; Weerts, H.; White, A.; White, J. T.; Whiteson, D.; Wightman, J. A.; Wijngaarden, D. A.; Willis, S.; Wimpenny, S. J.; Womersley, J.; Wood, D. R.; Yamada, R.; Yamin, P.; Yasuda, T.; Yatsunenko, Y. A.; Yip, K.; Youssef, S.; Yu, J.; Yu, Z.; Zanabria, M.; Zheng, H.; Zhou, Z.; Zielinski, M.; Zieminska, D.; Zieminski, A.; Zutshi, V.; Zverev, E. G.; Zylberstejn, A.

    2001-08-01

    We present results of searches for technirho (ρT), techniomega (ωT), and Z' particles, using the decay channels ρT,ωT,Z'-->e+e-. The search is based on 124.8 pb-1 of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes ppbar-->ρT,ωT,Z'-->e+e- as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate ρT and ωT states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.

  13. High-energy positrons and gamma radiation from decaying constituents of a two-component dark atom model

    NASA Astrophysics Data System (ADS)

    Belotsky, K.; Khlopov, M.; Kouvaris, C.; Laletin, M.

    2015-09-01

    We study a two-component dark matter candidate inspired by the minimal walking technicolor (WTC) model. Dark matter consists of a dominant strongly interactive massive particle (SIMP)-like dark atom component made of bound states between primordial helium nuclei and a doubly charged technilepton and a small WIMP-like component made of another dark atom bound state between a doubly charged technibaryon and a technilepton. This scenario is consistent with direct search experimental findings because the dominant SIMP component interacts too strongly to reach the depths of current detectors with sufficient energy to recoil and the WIMP-like component is too small to cause significant amount of events. In this context, a metastable technibaryon that decays to e+e+, μ+μ+ and τ+τ+ can, in principle, explain the observed positron excess by AMS-02 and PAMELA, while being consistent with the photon flux observed by FERMI/LAT. We scan the parameters of the model and we find the best possible fit to the latest experimental data. We find that there is a small range of parameter space that this scenario can be realized under certain conditions regarding the cosmic ray propagation and the final state radiation (FSR). This range of parameters fall inside the region where the current run of large hadron collider (LHC) can probe, and therefore it will soon be possible to either verify or exclude conclusively this model of dark matter.

  14. Energy of atomic shakeoff electrons from positron decay of 37K

    NASA Astrophysics Data System (ADS)

    Behr, John; Fenker, Benjamin; Gorelov, Alexandre; Anholm, Melissa; Behling, Spencer; Mehlman, Michael; Melconian, Dan; Ashery, Danny; Gwinner, Gerald

    2015-10-01

    We have measured the low-energy atomic shakeoff electron spectrum from the β+ decay of 37K. We collect atomic electrons emitted from laser-cooled 37K using a nearly uniform electric field at low magnetic field into a position-sensitive microchannel plate. A coincidence with energetic β+s removes background. The differential position information translates to a differential electron energy spectrum. The energy spectrum from 1-100 eV is reproduced well by an analytic calculation for hydrogenic wavefunctions [Levinger PR 90 11 (1953)] using potassium quantum defects. Less than one percent of the electrons have energies higher than the 25 eV threshold for double DNA strand breaks, so relative biological effectiveness would not be altered by including these electrons. The average energy carried off by these electrons (a few eV) is smaller than expected from simple Thomas-Fermi estimates (65eV). Supported by NSERC, NRC through TRIUMF, U.S. D.O.E., State of Texas, Israel Science Foundation

  15. Electron capture and positron decay of /sup 206/Fr and /sup 208/Fr and the energy levels of /sup 206/Rn and /sup 208/Rn

    SciTech Connect

    Ritchie, B.G.; Avignone, F.T. III; Carter, H.K.; Mlekodaj, R.L.; Spejewski, E.H.

    1981-04-01

    The isotopes /sup 206/Fr and /sup 208/Fr were produced by the reactions Ir(/sup 20/Ne,xn)/sup 206,208/Fr and mass separated on-line. The electron-capture and positron decays to /sup 206/Rn and /sup 208/Rn were studied by collecting ..gamma.. ray and internal conversion electron singles spectra as a function of decay time as well as ..gamma..-..gamma.., ..gamma..-e/sup -/, and ..gamma..-x ray coincidence spectra. The energies and many of the spins were determined for 18 excited, even parity states in /sup 208/Rn and for 10 excited, even parity states in /sup 206/Rn. These nuclei appear to be excellent candidates for interpretation in terms of a weak coupling shell model. The energy levels were also compared to the predictions of the interacting boson approximation model.

  16. Particle-in-cell simulation for parametric decays of a circularly polarized Alfvén wave in relativistic thermal electron-positron plasma

    SciTech Connect

    López, Rodrigo A. Muñoz, Víctor; Viñas, Adolfo F.; Alejandro Valdivia, J.

    2014-03-15

    Parametric decays of a left-handed circularly polarized Alfvén wave propagating along a constant background magnetic field in a relativistic thermal electron-positron plasma are studied by means of a one dimensional relativistic particle-in-cell simulation. Relativistic effects are included in the Lorentz equation for the momentum of the particles and in their thermal motion, by considering a Maxwell-Jüttner velocity distribution function for the initial condition. In the linear stage of the simulation, we find many instabilities that match the predictions of relativistic fluid theory. In general, the growth rates of the instabilities increase as the pump wave amplitude is increased, and decrease with a raise in the plasma temperatures. We have confirmed that for very high temperatures the Alfvén branch is suppressed, consistent with analytical calculations.

  17. Search for the electron-positron decay of axions and axionlike particles at a nuclear power reactor at Bugey

    NASA Astrophysics Data System (ADS)

    Altmann, M.; Declais, Y.; Feilitzsch, F. V.; Hagner, C.; Kajfasz, E.; Oberauer, L.

    1995-06-01

    A search for the decay of isoscalar penetrating particles into an e + e-pair has been performed at the nuclear power reactor Bugey 5, situated close to Lyon (France). The detector set-up, consisting of an arrangement of large-area multiwire proportional chambers, and the data analysis are described. No excess of decay events over background has been observed. For standard axions, therefrom, stringent upper limits for the branching ratio < Γ a / Γ {/M γ}, averaged over the entire reactor gamma spectrum of magnetic multipolarity, have been obtained. Analysis in terms of the decay χ→ e ++ e - of a more general axionlike boson χ yields new constraints for the decay constant f χ which enhance existing laboratory limits considerably.

  18. Photon correlations in positron annihilation

    SciTech Connect

    Gauthier, Isabelle; Hawton, Margaret

    2010-06-15

    The two-photon positron annihilation density matrix is found to separate into a diagonal center-of-energy factor implying maximally entangled momenta, and a relative factor describing decay. For unknown positron injection time, the distribution of the difference in photon arrival times is a double exponential at the para-Ps decay rate, consistent with experiment [V. D. Irby, Meas. Sci. Technol. 15, 1799 (2004)].

  19. Matrix Isolation Spectroscopy Applied to Positron Moderatioin in Cryogenic Solids

    DTIC Science & Technology

    2011-07-01

    nanoseconds. Positrons that reach a free surface of the moderator before annihilating with an electron may escape into vacuum where they can be...0324. 3 • The positron (e+) is the antiparticle to the electron (e-). • Positrons are stable, but annihilate with electrons to produce γ-rays...Current Positron Applications • 2-γ decay exploited in Positron Emission Tomography (PET) scanners. • Positrons localize & annihilate preferentially at

  20. Positron microscopy

    SciTech Connect

    Hulett, L.D. Jr.; Xu, J.

    1995-02-01

    The negative work function property that some materials have for positrons make possible the development of positron reemission microscopy (PRM). Because of the low energies with which the positrons are emitted, some unique applications, such as the imaging of defects, can be made. The history of the concept of PRM, and its present state of development will be reviewed. The potential of positron microprobe techniques will be discussed also.

  1. Positron program at the Idaho Accelerator Center

    SciTech Connect

    Stancari, Giulio

    2009-09-02

    Positron physics is an important part of the research activities at the Idaho Accelerator Center (IAC). With positron annihilation spectroscopy, maps of nanodefects in materials have been obtained. For this purpose, positrons are generated by radioactive decay, photoactivation, or pair production. Preliminary tests of positron sources in the MeV range based on electron linacs have also been carried out at the IAC, and an expansion of this program is planned. A similar positron beam at Jefferson Lab would greatly improve our knowledge of the inner structure of the proton. In this paper, research with positrons at the IAC is reviewed. After a description of the Center's facilities, results from positron annihilation spectroscopy are discussed, together with future plans for testing a prototype positron source for CEBAF.

  2. Spin polarized low-energy positron source

    NASA Astrophysics Data System (ADS)

    Petrov, V. N.; Samarin, S. N.; Sudarshan, K.; Pravica, L.; Guagliardo, P.; Williams, J. F.

    2015-06-01

    This paper presents an investigation of spin polarization of positrons from a source based on the decay of 22Na isotopes. Positrons are moderated by transmission through a tungsten film and electrostatically focussed and transported through a 90 deg deflector to produce a slow positron beam with polarization vector normal to the linear momentum. The polarization of the beam was determined to be about 10% by comparison with polarized electron scattering asymmetries from a thin Fe film on W(110) at 10-10 Torr. Low energy electron emission from Fe layer on W(100) surfaces under positron impact is explored. It is shown that the intensity asymmetry of the electron emission as a function of the incident positron energy can be used to estimate the polarization of the positron beam. Also several materials with long mean free paths for spin relaxation are considered as possible moderators with increased polarization of the emergent positrons.

  3. Positron Physics

    NASA Technical Reports Server (NTRS)

    Drachman, Richard J.

    2003-01-01

    I will give a review of the history of low-energy positron physics, experimental and theoretical, concentrating on the type of work pioneered by John Humberston and the positronics group at University College. This subject became a legitimate subfield of atomic physics under the enthusiastic direction of the late Sir Harrie Massey, and it attracted a diverse following throughout the world. At first purely theoretical, the subject has now expanded to include high brightness beams of low-energy positrons, positronium beams, and, lately, experiments involving anti-hydrogen atoms. The theory requires a certain type of persistence in its practitioners, as well as an eagerness to try new mathematical and numerical techniques. I will conclude with a short summary of some of the most interesting recent advances.

  4. Questions Students Ask: Beta Decay.

    ERIC Educational Resources Information Center

    Koss, Jordan; Hartt, Kenneth

    1988-01-01

    Answers a student's question about the emission of a positron from a nucleus. Discusses the problem from the aspects of the uncertainty principle, beta decay, the Fermi Theory, and modern physics. (YP)

  5. Positronic complexes with unnatural parity

    SciTech Connect

    Bromley, M. W. J.; Mitroy, J.; Varga, K.

    2007-06-15

    The structure of the unnatural parity states of PsH, LiPs, NaPs, and KPs are investigated with the configuration interaction and stochastic variational methods. The binding energies (in hartree) are found to be 8.17x10{sup -4}, 4.42x10{sup -4}, 15.14x10{sup -4}, and 21.80x10{sup -4}, respectively. These states are constructed by first coupling the two electrons into a configuration which is predominantly {sup 3}P{sup e}, and then adding a p-wave positron. All the active particles are in states in which the relative angular momentum between any pair of particles is at least L=1. The LiPs state is Borromean since there are no three-body bound subsystems (of the correct symmetry) of the (Li{sup +}, e{sup -}, e{sup -}, e{sup +}) particles that make up the system. The dominant decay mode of these states will be radiative decay into a configuration that autoionizes or undergoes positron annihilation.

  6. Positron-rubidium scattering

    NASA Technical Reports Server (NTRS)

    Mceachran, R. P.; Horbatsch, M.; Stauffer, A. D.

    1990-01-01

    A 5-state close-coupling calculation (5s-5p-4d-6s-6p) was carried out for positron-Rb scattering in the energy range 3.7 to 28.0 eV. In contrast to the results of similar close-coupling calculations for positron-Na and positron-K scattering the (effective) total integrated cross section has an energy dependence which is contrary to recent experimental measurements.

  7. Threshold for Trapping Positrons in the Wake Driven by a Ultra-relativistic Electron Bunch

    SciTech Connect

    Wang, X.; Muggli, P.; Katsouleas, T.; Ischebeck, R.; Hogan, M. J.; Joshi, C.; Mori, W. B.

    2009-01-22

    We have recently proposed a new concept for generating, injecting and accelerating positrons in a plasma using a double-pulse electron bunch. Monte Carlo simulations show that the number of the positrons produced in a foil target has an exponentially decay energy spectrum. The energy threshold for the trapping of these positrons in a ultra-relativistic electron wake is investigated numerically. For a typical 28.5 GeV electron drive bunch, the trapping threshold for the positrons is a few MeV, and therefore a majority of positrons generated in the foil target are focused and accelerated by the plasma wake.

  8. Van de Graaff based positron source production

    NASA Astrophysics Data System (ADS)

    Lund, Kasey Roy

    The anti-matter counterpart to the electron, the positron, can be used for a myriad of different scientific research projects to include materials research, energy storage, and deep space flight propulsion. Currently there is a demand for large numbers of positrons to aid in these mentioned research projects. There are different methods of producing and harvesting positrons but all require radioactive sources or large facilities. Positron beams produced by relatively small accelerators are attractive because they are easily shut down, and small accelerators are readily available. A 4MV Van de Graaff accelerator was used to induce the nuclear reaction 12C(d,n)13N in order to produce an intense beam of positrons. 13N is an isotope of nitrogen that decays with a 10 minute half life into 13C, a positron, and an electron neutrino. This radioactive gas is frozen onto a cryogenic freezer where it is then channeled to form an antimatter beam. The beam is then guided using axial magnetic fields into a superconducting magnet with a field strength up to 7 Tesla where it will be stored in a newly designed Micro-Penning-Malmberg trap. Several source geometries have been experimented on and found that a maximum antimatter beam with a positron flux of greater than 0.55x10 6 e+s-1 was achieved. This beam was produced using a solid rare gas moderator composed of krypton. Due to geometric restrictions on this set up, only 0.1-1.0% of the antimatter was being frozen to the desired locations. Simulations and preliminary experiments suggest that a new geometry, currently under testing, will produce a beam of 107 e+s-1 or more.

  9. Positron microprobe at LLNL

    SciTech Connect

    Asoka, P; Howell, R; Stoeffl, W

    1998-11-01

    The electron linac based positron source at Lawrence Livermore National Laboratory (LLNL) provides the world's highest current beam of keV positrons. We are building a positron microprobe that will produce a pulsed, focused positron beam for 3-dimensional scans of defect size and concentration with sub-micron resolution. The widely spaced and intense positron packets from the tungsten moderator at the end of the 100 MeV LLNL linac are captured and trapped in a magnetic bottle. The positrons are then released in 1 ns bunches at a 20 MHz repetition rate. With a three-stage re-moderation we will compress the cm-sized original beam to a 1 micro-meter diameter final spot on the target. The buncher will compress the arrival time of positrons on the target to less than 100 ps. A detector array with up to 60 BaF2 crystals in paired coincidence will measure the annihilation radiation with high efficiency and low background. The energy of the positrons can be varied from less than 1 keV up to 50 keV.

  10. Positrons in surface physics

    NASA Astrophysics Data System (ADS)

    Hugenschmidt, Christoph

    2016-12-01

    Within the last decade powerful methods have been developed to study surfaces using bright low-energy positron beams. These novel analysis tools exploit the unique properties of positron interaction with surfaces, which comprise the absence of exchange interaction, repulsive crystal potential and positron trapping in delocalized surface states at low energies. By applying reflection high-energy positron diffraction (RHEPD) one can benefit from the phenomenon of total reflection below a critical angle that is not present in electron surface diffraction. Therefore, RHEPD allows the determination of the atom positions of (reconstructed) surfaces with outstanding accuracy. The main advantages of positron annihilation induced Auger-electron spectroscopy (PAES) are the missing secondary electron background in the energy region of Auger-transitions and its topmost layer sensitivity for elemental analysis. In order to enable the investigation of the electron polarization at surfaces low-energy spin-polarized positrons are used to probe the outermost electrons of the surface. Furthermore, in fundamental research the preparation of well defined surfaces tailored for the production of bound leptonic systems plays an outstanding role. In this report, it is envisaged to cover both the fundamental aspects of positron surface interaction and the present status of surface studies using modern positron beam techniques.

  11. Positrons for linear colliders

    SciTech Connect

    Ecklund, S.

    1987-11-01

    The requirements of a positron source for a linear collider are briefly reviewed, followed by methods of positron production and production of photons by electromagnetic cascade showers. Cross sections for the electromagnetic cascade shower processes of positron-electron pair production and Compton scattering are compared. A program used for Monte Carlo analysis of electromagnetic cascades is briefly discussed, and positron distributions obtained from several runs of the program are discussed. Photons from synchrotron radiation and from channeling are also mentioned briefly, as well as positron collection, transverse focusing techniques, and longitudinal capture. Computer ray tracing is then briefly discussed, followed by space-charge effects and thermal heating and stress due to showers. (LEW)

  12. Positron diffusion in Si

    SciTech Connect

    Nielsen, B.; Lynn, K.G.; Vehanen, A.; Schultz, P.J.

    1985-06-01

    Positron diffusion in Si(100) and Si(111) has been studied using a variable energy positron beam. The positron diffusion coefficient is found to be D/sub +/ = 2.7 +- 0.3 cm/sup 2//sec using a Makhov-type positron implantation profile, which is demonstrated to fit the data more reliably than the more commonly applied exponential profile. The diffusion related parameter, E/sub 0/, which results from the exponential profile, is found to be 4.2 +- 0.2 keV, significantly longer than previously reported values. A drastic reduction in E/sub 0/ is found after annealing the sample at 1300 K, showing that previously reported low values of E/sub 0/ are probably associated with the thermal history of the sample.

  13. Alternative positron-target design for electron-positron colliders

    SciTech Connect

    Donahue, R.J. ); Nelson, W.R. )

    1991-04-01

    Current electron-positron linear colliders are limited in luminosity by the number of positrons which can be generated from targets presently used. This paper examines the possibility of using an alternate wire-target geometry for the production of positrons via an electron-induced electromagnetic cascade shower. 39 refs., 38 figs., 5 tabs.

  14. Positron sources for Linear Colliders

    SciTech Connect

    Gai Wei; Liu Wanming

    2009-09-02

    Positron beams have many applications and there are many different concepts for positron sources. In this paper, only positron source techniques for linear colliders are covered. In order to achieve high luminosity, a linear collider positron source should have a high beam current, high beam energy, small emittance and, for some applications, a high degree of beam polarization. There are several different schemes presently being developed around the globe. Both the differences between these schemes and their common technical challenges are discussed.

  15. Positron annihilation processes update

    NASA Technical Reports Server (NTRS)

    Guessoum, Nidhal; Skibo, Jeffrey G.; Ramaty, Reuven

    1997-01-01

    The present knowledge concerning the positron annihilation processes is reviewed, with emphasis on the data of the cross sections of the various processes of interest in astrophysical applications. Recent results are presented including results on reaction rates and line widths, the validity of which is verified.

  16. Positron excitation of neon

    NASA Technical Reports Server (NTRS)

    Parcell, L. A.; Mceachran, R. P.; Stauffer, A. D.

    1990-01-01

    The differential and total cross section for the excitation of the 3s1P10 and 3p1P1 states of neon by positron impact were calculated using a distorted-wave approximation. The results agree well with experimental conclusions.

  17. The Japanese Positron Factory

    NASA Astrophysics Data System (ADS)

    Okada, S.; Sunaga, H.; Kaneko, H.; Takizawa, H.; Kawasuso, A.; Yotsumoto, K.; Tanaka, R.

    1999-06-01

    The Positron Factory has been planned at Japan Atomic Energy Research Institute (JAERI). The factory is expected to produce linac-based monoenergetic positron beams having world-highest intensities of more than 1010e+/sec, which will be applied for R&D of materials science, biotechnology and basic physics & chemistry. In this article, results of the design studies are demonstrated for the following essential components of the facilities: 1) Conceptual design of a high-power electron linac with 100 MeV in beam energy and 100 kW in averaged beam power, 2) Performance tests of the RF window in the high-power klystron and of the electron beam window, 3) Development of a self-driven rotating electron-to-positron converter and the performance tests, 4) Proposal of multi-channel beam generation system for monoenergetic positrons, with a series of moderator assemblies based on a newly developed Monte Carlo simulation and the demonstrative experiment, 5) Proposal of highly efficient moderator structures, 6) Conceptual design of a local shield to suppress the surrounding radiation and activation levels.

  18. High current pulsed positron microprobe

    SciTech Connect

    Howell, R.H.; Stoeffl, W.; Kumar, A.; Sterne, P.A.; Cowan, T.E.; Hartley, J.

    1997-05-01

    We are developing a low energy, microscopically focused, pulsed positron beam for defect analysis by positron lifetime spectroscopy to provide a new defect analysis capability at the 10{sup 10} e{sup +}s{sup -l} beam at the Lawrence Livermore National Laboratory electron linac. When completed, the pulsed positron microprobe will enable defect specific, 3-dimensional maps of defect concentrations with sub-micron resolution of defect location. By coupling these data with first principles calculations of defect specific positron lifetimes and positron implantation profiles we will both map the identity and concentration of defect distributions.

  19. Positrons and Antiprotons in Galactic Cosmic Rays

    NASA Astrophysics Data System (ADS)

    Cowsik, R.

    2016-10-01

    I consider the impact of recent measurements of positron and antiproton spectra in cosmic rays on our understanding of the origins and propagation of cosmic rays, as well as on the annihilation and decay characteristics of particles of Galactic dark matter, from the perspective of current models postulating energy-dependent leakage of cosmic rays from the Galaxy and of the nested leaky-box model, in which the leakage from the Galaxy is independent of energy. The nested leaky-box model provides a straightforward and consistent explanation of the observed spectral intensities, and finds no compelling need for a contribution from the annihilation or decay of Galactic dark matter. Improved observations and modeling efforts are needed to probe the properties of dark matter deeply enough to be significant to particle physics and cosmology.

  20. The positron excess as a smoking gun for dynamical dark matter?

    SciTech Connect

    Dienes, Keith R.; Kumar, Jason; Thomas, Brooks

    2014-06-24

    One of the most puzzling aspects of recent data from the AMS-02 experiment is an apparent rise in the cosmic-ray positron fraction as a function of energy. This feature is observed out to energies of approximately 350 GeV. One explanation of these results interprets the extra positrons as arising from the decays of dark-matter particles. This in turn typically requires that such particles have rather heavy TeV-scale masses and not undergo simple two-body decays to leptons. In this talk, by contrast, we show that Dynamical Dark Matter (DDM) can not only match existing AMS-02 data on the positron excess, but also accomplish this feat with significantly lighter dark-matter constituents undergoing simple two-body decays to leptons. We also demonstrate that the Dynamical Dark Matter framework makes a fairly robust prediction that the positron fraction should level off and then remain roughly constant out to approximately 1 TeV, without experiencing any sharp downturns. Thus, if we interpret the positron excess in terms of decaying dark matter, the existence of a plateau in the positron fraction at energies less than 1 TeV may be taken as a “smoking gun” of Dynamical Dark Matter.

  1. Generation of monoenergetic positrons

    SciTech Connect

    Hulett, L.D. Jr.; Dale, J.M.; Miller, P.D. Jr.; Moak, C.D.; Pendyala, S.; Triftshaeuser, W.; Howell, R.H.; Alvarez, R.A.

    1983-01-01

    Many experiments have been performed in the generation and application of monoenergetic positron beams using annealed tungsten moderators and fast sources of /sup 58/Co, /sup 22/Na, /sup 11/C, and LINAC bremstrahlung. This paper will compare the degrees of success from our various approaches. Moderators made from both single crystal and polycrystal tungsten have been tried. Efforts to grow thin films of tungsten to be used as transmission moderators and brightness enhancement devices are in progress.

  2. Positron lifetime spectrometer using a DC positron beam

    DOEpatents

    Xu, Jun; Moxom, Jeremy

    2003-10-21

    An entrance grid is positioned in the incident beam path of a DC beam positron lifetime spectrometer. The electrical potential difference between the sample and the entrance grid provides simultaneous acceleration of both the primary positrons and the secondary electrons. The result is a reduction in the time spread induced by the energy distribution of the secondary electrons. In addition, the sample, sample holder, entrance grid, and entrance face of the multichannel plate electron detector assembly are made parallel to each other, and are arranged at a tilt angle to the axis of the positron beam to effectively separate the path of the secondary electrons from the path of the incident positrons.

  3. Positron moderation and detection for positronic atoms

    NASA Astrophysics Data System (ADS)

    Fardad, Abolfazl

    An apparatus is under development for H--+* production, atoms consisting of a positron bound in a Rydberg state to an H-- ion. High energy e+ from radioactive N2211a are slowed (moderated) to eV energies in solid neon and captured in a Penning trap. The procedure to deposit the neon is optimized, resulting in a 1.5% efficiency for moderating high energy e +. Neutral H--+* atoms with ˜100 eV will be produced from these trapped e+ and exit the trap, hitting a metal surface where the e+ annihilates. Back-to-back annihilation gamma photons (Egamma ≈ 0.511 MeV) detected in coincidence, at the expected energy are the fingerprint for H--+* production. A N2211a test source mocks H--+* experiments with ˜2.7% of the e+ emitting disintegrations detected. This high efficiency, with a background rate of ˜2.8 events/hour is achieved by surrounding the detectors with lead and cosmic ray detectors.

  4. Positron Annihilation in Insulating Materials

    SciTech Connect

    Asoka-Kumar, P; Sterne, PA

    2002-10-18

    We describe positron results from a wide range of insulating materials. We have completed positron experiments on a range of zeolite-y samples, KDP crystals, alkali halides and laser damaged SiO{sub 2}. Present theoretical understanding of positron behavior in insulators is incomplete and our combined theoretical and experimental approach is aimed at developing a predictive understanding of positrons and positronium annihilation characteristics in insulators. Results from alkali halides and alkaline-earth halides show that positrons annihilate with only the halide ions, with no apparent contribution from the alkali or alkaline-earth cations. This contradicts the results of our existing theory for metals, which predicts roughly equal annihilation contributions from cation and anion. We also present result obtained using Munich positron microprobe on laser damaged SiO{sub 2} samples.

  5. Secondary positrons and electrons in the cosmic radiation

    NASA Technical Reports Server (NTRS)

    Badhwar, G. D.; Stephens, S. A.

    1978-01-01

    An improved calculation of the secondary production and equilibrium spectrum of positrons and electrons in the Galaxy in the energy range from 1 MeV to 100 GeV has been performed. This has been done by obtaining an analytic representation of the accelerator data which describes accurately the invariant cross-section of pions, kaons, and their antiparticles from threshold energy to about 1500 GeV. This calculation takes into account the correct angular distribution of electrons in the decay of muons and the effect of nuclei-nuclei collisions. The contributions of beta-decay positrons and knock-on electrons have been included. A comparison of the present calculations with earlier calculations and experiment is presented.

  6. Compact Beta Particle/Positron Imager for Plant Biology

    SciTech Connect

    Weisenberger, Andrew; Lee, Seung Joon; McKisson, John; Xi, Wenze; Zorn, Carl; Stolin, Alexander; Majewski, Stan; Majewski, Stanislaw; Howell, Calvin; Crowell, Alec; Smith, Mark

    2011-06-01

    The 11CO2 tracer is used to facilitate plant biology research towards optimization of plant productivity, biofuel development and carbon sequestration in biomass. Positron emission tomography (PET) imaging has been used to study carbon transport in live plants using 11CO2. Plants typically have very thin leaves resulting in little medium for the emitted positrons to undergo an annihilation event. For the emitted positron from 11C decay approximately 1mm of water equivalent material is needed for positron annihilation. Thus most of the positrons do not annihilate inside the leaf, resulting in limited sensitivity for PET imaging. To address this problem we have developed a compact beta-positive beta-minus particle (BPBM) imager for 11CO2 leaf imaging. The detector is based on a Hamamatsu H8500 position sensitive photomultiplier tube optically coupled via optical grease and a 3mm thick glass plate to a 0.5mm thick Eljin EJ-212 plastic scintillator. The detector is equipped with a flexible arm to allow its placement and orientation on the leaf of the plant of interest while maintaining the leaf's original orientation. We are planning to utilize the imaging device at the Duke University Phytotron to investigate dynamic carbon transport differences between invasive and native species.

  7. Positron Emission Tomography (PET)

    DOE R&D Accomplishments Database

    Welch, M. J.

    1990-01-01

    Positron emission tomography (PET) assesses biochemical processes in the living subject, producing images of function rather than form. Using PET, physicians are able to obtain not the anatomical information provided by other medical imaging techniques, but pictures of physiological activity. In metaphoric terms, traditional imaging methods supply a map of the body's roadways, its, anatomy; PET shows the traffic along those paths, its biochemistry. This document discusses the principles of PET, the radiopharmaceuticals in PET, PET research, clinical applications of PET, the cost of PET, training of individuals for PET, the role of the United States Department of Energy in PET, and the futures of PET.

  8. Quantum positron acoustic waves

    SciTech Connect

    Metref, Hassina; Tribeche, Mouloud

    2014-12-15

    Nonlinear quantum positron-acoustic (QPA) waves are investigated for the first time, within the theoretical framework of the quantum hydrodynamic model. In the small but finite amplitude limit, both deformed Korteweg-de Vries and generalized Korteweg-de Vries equations governing, respectively, the dynamics of QPA solitary waves and double-layers are derived. Moreover, a full finite amplitude analysis is undertaken, and a numerical integration of the obtained highly nonlinear equations is carried out. The results complement our previously published results on this problem.

  9. Positron Emission Tomography (PET)

    SciTech Connect

    Welch, M.J.

    1990-01-01

    Positron emission tomography (PET) assesses biochemical processes in the living subject, producing images of function rather than form. Using PET, physicians are able to obtain not the anatomical information provided by other medical imaging techniques, but pictures of physiological activity. In metaphoric terms, traditional imaging methods supply a map of the body's roadways, its, anatomy; PET shows the traffic along those paths, its biochemistry. This document discusses the principles of PET, the radiopharmaceuticals in PET, PET research, clinical applications of PET, the cost of PET, training of individuals for PET, the role of the United States Department of Energy in PET, and the futures of PET. 22 figs.

  10. Simultaneous confinement of low-energy electrons and positrons in a compact magnetic mirror trap

    NASA Astrophysics Data System (ADS)

    Higaki, H.; Kaga, C.; Fukushima, K.; Okamoto, H.; Nagata, Y.; Kanai, Y.; Yamazaki, Y.

    2017-02-01

    More than 107 electrons and 105 positrons with energy less than a few eV were confined simultaneously for the first time in a compact magnetic mirror trap with plugging potentials. The exponential decay time constant of the confined positrons exceeded 70 ms at the beginning of the simultaneous confinement. Particle simulations in the early stages of the mixing process were also conducted. The results obtained in the experiments and simulations suggested that an improved setup would make it possible to investigate the unexplored field of low-energy electron–positron plasmas experimentally.

  11. Cyclotrons and positron emitting radiopharmaceuticals

    SciTech Connect

    Wolf, A.P.; Fowler, J.S.

    1984-01-01

    The state of the art of Positron Emission Tomography (PET) technology as related to cyclotron use and radiopharmaceutical production is reviewed. The paper discusses available small cyclotrons, the positron emitters which can be produced and the yields possible, target design, and radiopharmaceutical development and application. 97 refs., 12 tabs. (ACR)

  12. Portable Positron Measurement System (PPMS)

    SciTech Connect

    2011-01-01

    Portable Positron Measurement System (PPMS) is an automated, non-destructive inspection system based on positron annihilation, which characterizes a material's in situatomic-level properties during the manufacturing processes of formation, solidification, and heat treatment. Simultaneous manufacturing and quality monitoring now are possible. Learn more about the lab's project on our facebook site http://www.facebook.com/idahonationallaboratory.

  13. Portable Positron Measurement System (PPMS)

    ScienceCinema

    None

    2016-07-12

    Portable Positron Measurement System (PPMS) is an automated, non-destructive inspection system based on positron annihilation, which characterizes a material's in situatomic-level properties during the manufacturing processes of formation, solidification, and heat treatment. Simultaneous manufacturing and quality monitoring now are possible. Learn more about the lab's project on our facebook site http://www.facebook.com/idahonationallaboratory.

  14. Undulator Production of Polarized Positrons

    SciTech Connect

    William M. Bugg

    2008-08-27

    E-166 at SLAC has demonstrated the feasibilty of production of polarized positrons for the International Linear Collider using a helical undulator to produce polarized photons which are converted in a thin target to polarized positrons. The success of the experim ent has resulted in the choice of this technique for the baseline design of ILC.

  15. Radioactive Decay

    EPA Pesticide Factsheets

    Radioactive decay is the emission of energy in the form of ionizing radiation. Example decay chains illustrate how radioactive atoms can go through many transformations as they become stable and no longer radioactive.

  16. Tooth Decay

    MedlinePlus

    You call it a cavity. Your dentist calls it tooth decay or dental caries. They're all names for a hole in your tooth. The cause of tooth decay is plaque, a sticky substance in your mouth made up mostly of germs. Tooth decay starts in the outer layer, called the enamel. Without ...

  17. Visible and dark matter genesis and cosmic positron and electron excesses

    SciTech Connect

    Gu Peihong; Sarkar, Utpal; Zhang Xinmin

    2009-10-01

    Dark and baryonic matter contribute comparable energy density to the present universe. The dark matter may also be responsible for the cosmic positron and electron excesses. We connect these phenomena with the Dirac seesaw for neutrino masses. In our model (i) the dark matter relic density is a dark matter asymmetry generated simultaneously with the baryon asymmetry so that we can naturally understand the coincidence between the dark and baryonic matter and (ii) the dark matter mostly decays into the leptons so that its decay can interpret the anomalous cosmic rays with positron and electron excesses.

  18. First positron annihilation lifetime measurement of Pu

    SciTech Connect

    Colmenares, C.; Howell, R.H.; Ancheta, D.; Cowan, T.; Hanafee, J.; Sterne, P.

    1996-11-21

    We have made the first measurement of defects in an aged sample of {delta} phase, Ga stabilized Pu, using positron annihilation lifetime spectroscopy. This measurement validates the procedure necessary to perform measurements on this highly toxic material and obtain data representative of sample conditions. Comparison of the positron annihilation lifetime analysis of the data with calculated values suggests that He filled vacancies or vacancy clusters dominate the defect population. Such defects are the necessary precursor to void growth and swelling. The evolution of defects resulting from the radioactive decay of Pu during its life in the stockpile is one of the unknown quantities affecting our confidence in predictions of the limit on stockpile components. Radiation damage leads to changes in the size and strength of metals studied for reactor and accelerator use and similar effects may be expected in Pu. The evolution of radiation produced vacancies into larger void structures and accompanying macroscopic swelling may occur in Pu at some age. A detailed understanding of the defects in self irradiated Pu is required to predict the time scale of void swelling and related radiation effects. 1 fig.

  19. Positron Emission Tomography: A Basic Analysis

    NASA Astrophysics Data System (ADS)

    Kerbacher, M. E.; Deaton, J. W.; Phinney, L. C.; Mitchell, L. J.; Duggan, J. L.

    2007-10-01

    Positron Emission Tomography is useful in detecting biological abnormalities. The technique involves attaching radiotracers to a material used inside the body, in many cases glucose. Glucose is absorbed most readily in areas of unusual cell growth or uptake of nutrients so through natural processes the treated glucose highlights regions of tumors and other degenerative disorders such as Alzheimer's disease. The higher the concentration of isotopes, the more dynamic the area. Isotopes commonly used as tracers are 11C, 18F, 13N, and 15O due to their easy production and short half-lives. Once the tracers have saturated an area of tissue they are detected using coincidence detectors collinear with individual isotopes. As the isotope decays it emits a positron which, upon annihilating an electron, produces two oppositely directioned gamma rays. The PET machine consists of several pairs of detectors, each 180 degrees from their partner detector. When the oppositely positioned detectors are collinear with the area of the isotope, a computer registers the location of the isotope and can compile an image of the activity of the highlighted area based on the position and strength of the isotopes.

  20. The source and distribution of Galactic positrons

    NASA Technical Reports Server (NTRS)

    Purcell, W. R.; Dixon, D. D.; Cheng, L.-X.; Leventhal, M.; Kinzer, R. L.; Kurfess, J. D.; Skibo, J. G.; Smith, D. M.; Tueller, J.

    1997-01-01

    The oriented scintillation spectrometer experiment (OSSE) observations of the Galactic plane and the Galactic center region were combined with observations acquired with other instruments in order to produce a map of the Galactic 511 keV annihilation radiation. Two mapping techniques were applied to the data: the maximum entropy method, and the basis pursuit inversion method. The resulting maps are qualitatively similar and show evidence for a central bulge and a weak galactic disk component. The weak disk is consistent with that expected from positrons produced by the decay of radioactive Al-26 in the interstellar medium. Both maps suggest an enhanced region of emission near l = -4 deg, b = 7 deg, with a flux of approximately 50 percent of that of the bulge. The existence of this emission appears significant, although the location is not well determined. The source of this enhanced emission is presently unknown.

  1. Positron emission mammography imaging

    SciTech Connect

    Moses, William W.

    2003-10-02

    This paper examines current trends in Positron Emission Mammography (PEM) instrumentation and the performance tradeoffs inherent in them. The most common geometry is a pair of parallel planes of detector modules. They subtend a larger solid angle around the breast than conventional PET cameras, and so have both higher efficiency and lower cost. Extensions to this geometry include encircling the breast, measuring the depth of interaction (DOI), and dual-modality imaging (PEM and x-ray mammography, as well as PEM and x-ray guided biopsy). The ultimate utility of PEM may not be decided by instrument performance, but by biological and medical factors, such as the patient to patient variation in radiotracer uptake or the as yet undetermined role of PEM in breast cancer diagnosis and treatment.

  2. Intense source of slow positrons

    NASA Astrophysics Data System (ADS)

    Perez, P.; Rosowsky, A.

    2004-10-01

    We describe a novel design for an intense source of slow positrons based on pair production with a beam of electrons from a 10 MeV accelerator hitting a thin target at a low incidence angle. The positrons are collected with a set of coils adapted to the large production angle. The collection system is designed to inject the positrons into a Greaves-Surko trap (Phys. Rev. A 46 (1992) 5696). Such a source could be the basis for a series of experiments in fundamental and applied research and would also be a prototype source for industrial applications, which concern the field of defect characterization in the nanometer scale.

  3. Cosmic Ray Positrons from Pulsars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2010-01-01

    Pulsars are potential Galactic sources of positrons through pair cascades in their magnetospheres. There are, however, many uncertainties in establishing their contribution to the local primary positron flux. Among these are the local density of pulsars, the cascade pair multiplicities that determine the injection rate of positrons from the pulsar, the acceleration of the injected particles by the pulsar wind termination shock, their rate of escape from the pulsar wind nebula, and their propagation through the interstellar medium. I will discuss these issues in the context of what we are learning from the new Fermi pulsar detections and discoveries.

  4. Confronting recent AMS-02 positron fraction and Fermi-LAT extragalactic γ-ray background measurements with gravitino dark matter

    NASA Astrophysics Data System (ADS)

    Carquín, Edson; Díaz, Marco A.; Gómez-Vargas, Germán A.; Panes, Boris; Viaux, Nicolás

    2016-03-01

    Recent positron flux fraction measurements in cosmic-rays (CR) made by the AMS-02 detector confirm and extend the evidence on the existence of a new (yet unknown) source of high energy electrons and positrons. We test the gravitino dark matter of bilinear R-parity violating supersymmetric models as this electrons/positrons source. Being a long lived weak-interacting and spin 3/2 particle, it offers several particularities which makes it an attractive dark matter candidate. We compute the electron, positron and γ-ray fluxes produced by each gravitino decay channel as it would be detected at the Earth's position. Combining the flux from the different decay modes we are able to reproduce AMS-02 measurements of the positron fraction, as well as the electron and positron fluxes, with a gravitino dark matter mass in the range 1-3 TeV and lifetime of ˜1.0-0.7×1026 s. The high statistics measurement of electron and positron fluxes, and the flattening in the behaviour of the positron fraction recently found by AMS-02 allow us to determine that the preferred gravitino decaying mode by the fit is W±τ∓, unlike previous analyses. Then we study the viability of these scenarios through their implication in γ-ray observations. For this we use the Extragalactic γ-ray Background recently reported by the Fermi-LAT Collaboration and a state-of-the-art model of its known contributors. Based on the γ-ray analysis we exclude the gravitino parameter space which provides an acceptable explanation of the AMS-02 data. Therefore, we conclude that the gravitino of bilinear R-parity violating models is ruled out as the unique primary source of electrons and positrons needed to explain the rise in the positron fraction.

  5. Positron annihilation spectroscopy with magnetically analyzed beams

    NASA Technical Reports Server (NTRS)

    Singh, J. J.; Holt, W. H.; Mock, W., Jr.

    1982-01-01

    Lifetime measurements with magnetically analyzed positron beams were made in condensed media with uniform and non-uniform properties. As expected, the lifetime values with magnetically analyzed positron beams in uniform targets are similar to those obtained with conventional positron sources. The lifetime values with magnetically analyzed beams in targets which have non-uniform properties vary with positron energy and are different from the conventional positron source derived lifetime values in these targets.

  6. Positron trapping at grain boundaries

    SciTech Connect

    Dupasquier, A. ); Romero, R.; Somoza, A. )

    1993-10-01

    The standard positron trapping model has often been applied, as a simple approximation, to the interpretation of positron lifetime spectra in situations of diffusion-controlled trapping. This paper shows that this approximation is not sufficiently accurate, and presents a model based on the correct solution of the diffusion equation, in the version appropriate for studying positron trapping at grain boundaries. The model is used for the analysis of new experimental data on positron lifetime spectra in a fine-grained Al-Ca-Zn alloy. Previous results on similar systems are also discussed and reinterpreted. The analysis yields effective diffusion coefficients not far from the values known for the base metals of the alloys.

  7. High Power Polarized Positron Source

    NASA Astrophysics Data System (ADS)

    Mikhailichenko, Alexander

    2009-09-01

    We discuss the basics of polarized positron production by low energy polarized electrons. Efficiency of conversion ˜0.1-1% might be interesting for the Continuous Electron Beam Accelerator Facility (CEBAF) and the International Linear Collider (ILC).

  8. Modelling Positron Interactions with Matter

    NASA Astrophysics Data System (ADS)

    Garcia, G.; Petrovic, Z.; White, R.; Buckman, S.

    2011-05-01

    In this work we link fundamental measurements of positron interactions with biomolecules, with the development of computer codes for positron transport and track structure calculations. We model positron transport in a medium from a knowledge of the fundamental scattering cross section for the atoms and molecules comprising the medium, combined with a transport analysis based on statistical mechanics and Monte-Carlo techniques. The accurate knowledge of the scattering is most important at low energies, a few tens of electron volts or less. The ultimate goal of this work is to do this in soft condensed matter, with a view to ultimately developing a dosimetry model for Positron Emission Tomography (PET). The high-energy positrons first emitted by a radionuclide in PET may well be described by standard formulas for energy loss of charged particles in matter, but it is incorrect to extrapolate these formulas to low energies. Likewise, using electron cross-sections to model positron transport at these low energies has been shown to be in serious error due to the effects of positronium formation. Work was supported by the Australian Research Council, the Serbian Government, and the Ministerio de Ciencia e Innovación, Spain.

  9. Harvesting the Decay Energy of 26-Al to Drive Lightning Discharge and Chondrule Formation

    NASA Astrophysics Data System (ADS)

    Johansen, A.; Okuzumi, S.

    2017-02-01

    We demonstrate that positrons released in the decay of 26-Al cause large-scale charging of dense pebble regions. The charge separation is neutralized by lightning discharge and this can lead to the formation of chondrules.

  10. Meson spectroscopy viewed from J//PSI/ decay: Gluonic states at BEPC

    SciTech Connect

    Chanowitz, M.S.

    1987-07-01

    The theoretical and experimental status of the search for gluonic states is reviewed. Progress clearly requires much higher statistics studies of J//psi/ decay, as will be possible at the Beijing Electron Positron Collider. 83 refs.

  11. Conceptual design of a high-intensity positron source for the Advanced Neutron Source

    SciTech Connect

    Hulett, L.D.; Eberle, C.C.

    1994-12-01

    The Advanced Neutron Source (ANS) is a planned new basic and applied research facility based on a powerful steady-state research reactor that provides neutrons for measurements and experiments in the fields of materials science and engineering, biology, chemistry, materials analysis, and nuclear science. The useful neutron flux will be at least five times more than is available in the world`s best existing reactor facility. Construction of the ANS provides a unique opportunity to build a positron spectroscopy facility (PSF) with very-high-intensity beams based on the radioactive decay of a positron-generating isotope. The estimated maximum beam current is 1000 to 5000 times higher than that available at the world`s best existing positron research facility. Such an improvement in beam capability, coupled with complementary detectors, will reduce experiment durations from months to less than one hour while simultaneously improving output resolution. This facility will remove the existing barriers to the routine use of positron-based analytical techniques and will be a giant step toward realization of the full potential of the application of positron spectroscopy to materials science. The ANS PSF is based on a batch cycle process using {sup 64}Cu isotope as the positron emitter and represents the status of the design at the end of last year. Recent work not included in this report, has led to a proposal for placing the laboratory space for the positron experiments outside the ANS containment; however, the design of the positron source is not changed by that relocation. Hydraulic and pneumatic flight tubes transport the source material between the reactor and the positron source where the beam is generated and conditioned. The beam is then transported through a beam pipe to one of several available detectors. The design presented here includes all systems necessary to support the positron source, but the beam pipe and detectors have not been addressed yet.

  12. Radioactive decay.

    PubMed

    Groch, M W

    1998-01-01

    When a parent radionuclide decays to its daughter radionuclide by means of alpha, beta, or isomeric transition, the decay follows an exponential form, which is characterized by the decay constant lambda. The decay constant represents the probability per unit time that a single radioatom will decay. The decay equation can be used to provide a useful expression for radionuclide decay, the half-life, the time when 50% of the radioatoms present will have decayed. Radiotracer half-life has direct implications in nuclear imaging, radiation therapy, and radiation safety because radionuclide half-life affects the ability to evaluate tracer kinetics and create appropriate nuclear images and also affects organ, tumor, and whole-body radiation dose. The number of radioatoms present in a sample is equal to the activity, defined as the number of transitions per unit time, divided by the decay constant; the mass of radioatoms present in a sample can be calculated to determine the specific activity (activity per unit mass). The dynamic relationship between the number of parent and daughter atoms present over time may lead to radioactive equilibrium, which takes two forms--secular and transient--and has direct relevance to generator-produced radionuclides.

  13. Positron Annihilation Ratio Spectroscopy Study of Electric Fields Applied to Positronium at Material Interfaces

    DTIC Science & Technology

    2011-03-01

    positron and neutrino are 14 emitted. When Na-22 decays, 90.4% of the time it decays via β + to an excited state of Ne-22. 3.7 psec after the...of Na-22 [12:7]. 22 22 11 10Na Ne e       (8) where γ is the gamma ray and ν is the neutrino . Due to the fact that the neutrino can

  14. Recoil ion charge state distribution following the beta(sup +) decay of {sup 21}Na

    SciTech Connect

    Scielzo, Nicholas D.; Freedman, Stuart J.; Fujikawa, Brian K.; Vetter, Paul A.

    2003-01-03

    The charge state distribution following the positron decay of 21Na has been measured, with a larger than expected fraction of the daughter 21Ne in positive charge states. No dependence on either the positron or recoil nucleus energy is observed. The data is compared to a simple model based on the sudden approximation. Calculations suggest a small but important contribution from recoil ionization has important consequences for precision beta decay correlation experiments detecting recoil ions.

  15. 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.

  16. The stationary non-equilibrium plasma of cosmic-ray electrons and positrons

    NASA Astrophysics Data System (ADS)

    Tomaschitz, Roman

    2016-06-01

    The statistical properties of the two-component plasma of cosmic-ray electrons and positrons measured by the AMS-02 experiment on the International Space Station and the HESS array of imaging atmospheric Cherenkov telescopes are analyzed. Stationary non-equilibrium distributions defining the relativistic electron-positron plasma are derived semi-empirically by performing spectral fits to the flux data and reconstructing the spectral number densities of the electronic and positronic components in phase space. These distributions are relativistic power-law densities with exponential cutoff, admitting an extensive entropy variable and converging to the Maxwell-Boltzmann or Fermi-Dirac distributions in the non-relativistic limit. Cosmic-ray electrons and positrons constitute a classical (low-density high-temperature) plasma due to the low fugacity in the quantized partition function. The positron fraction is assembled from the flux densities inferred from least-squares fits to the electron and positron spectra and is subjected to test by comparing with the AMS-02 flux ratio measured in the GeV interval. The calculated positron fraction extends to TeV energies, predicting a broad spectral peak at about 1 TeV followed by exponential decay.

  17. Positron spectroscopy for materials characterization

    SciTech Connect

    Schultz, P.J.; Snead, C.L. Jr.

    1988-01-01

    One of the more active areas of research on materials involves the observation and characterization of defects. The discovery of positron localization in vacancy-type defects in solids in the 1960's initiated a vast number of experimental and theoretical investigations which continue to this day. Traditional positron annihilation spectroscopic techniques, including lifetime studies, angular correlation, and Doppler broadening of annihilation radiation, are still being applied to new problems in the bulk properties of simple metals and their alloys. In addition new techniques based on tunable sources of monoenergetic positron beams have, in the last 5 years, expanded the horizons to studies of surfaces, thin films, and interfaces. In the present paper we briefly review these experimental techniques, illustrating with some of the important accomplishments of the field. 40 refs., 19 figs.

  18. Positron emitter labeled enzyme inhibitors

    DOEpatents

    Fowler, Joanna S.; MacGregor, Robert R.; Wolf, Alfred P.; Langstrom, Bengt

    1990-01-01

    This invention involves a new strategy for imaging and mapping enzyme activity in the living human and animal body using positron emitter-labeled suicide enzyme inactivators or inhibitors which become covalently bound to the enzyme as a result of enzymatic catalysis. Two such suicide inactivators for monoamine oxidase have been labeled with carbon-11 and used to map the enzyme subtypes in the living human and animal body using PET. By using positron emission tomography to image the distribution of radioactivity produced by the body penetrating radiation emitted by carbon-11, a map of functionally active monoamine oxidase activity is obtained. Clorgyline and L-deprenyl are suicide enzyme inhibitors and irreversibly inhibit monoamine oxidase. When these inhibitors are labeled with carbon-11 they provide selective probes for monoamine oxidase localization and reactivity in vivo using positron emission tomography.

  19. Positron emitter labeled enzyme inhibitors

    SciTech Connect

    Fowler, J.S.; MacGregor, R.R.; Wolf, A.P.; Langstrom, B.

    1990-04-03

    This invention involves a new strategy for imaging and mapping enzyme activity in the living human and animal body using positron emitter-labeled suicide enzyme inactivators or inhibitors which become covalently bound to the enzyme as a result of enzymatic catalysis. Two such suicide inactivators for monoamine oxidase have been labeled with carbon-11 and used to map the enzyme subtypes in the living human and animal body using PET. By using positron emission tomography to image the distribution of radioactivity produced by the body penetrating radiation emitted by carbon-11, a map of functionally active monoamine oxidase activity is obtained. Clorgyline and L-deprenyl are suicide enzyme inhibitors and irreversibly inhibit monoamine oxidase. When these inhibitors are labeled with carbon-11 they provide selective probes for monoamine oxidase localization and reactivity in vivo using positron emission tomography.

  20. Positron emitter labeled enzyme inhibitors

    DOEpatents

    Fowler, J.S.; MacGregor, R.R.; Wolf, A.P.

    1987-05-22

    This invention involved a new strategy for imaging and mapping enzyme activity in the living human and animal body using positron emitter-labeled suicide enzyme inactivators or inhibitors which become covalently bound to the enzyme as a result of enzymatic catalysis. Two such suicide in activators for monoamine oxidase have been labeled with carbon-11 and used to map the enzyme subtypes in the living human and animal body using PET. By using positron emission tomography to image the distribution of radioactivity produced by the body penetrating radiation emitted by carbon-11, a map of functionally active monoamine oxidase activity is obtained. Clorgyline and L-deprenyl are suicide enzyme inhibitors and irreversibly inhibit monoamine oxidase. When these inhibitors are labeled with carbon-11 they provide selective probes for monoamine oxidase localization and reactivity in vivo using positron emission tomography. 2 figs.

  1. Positron-alkali atom scattering

    NASA Technical Reports Server (NTRS)

    Mceachran, R. P.; Horbatsch, M.; Stauffer, A. D.; Ward, S. J.

    1990-01-01

    Positron-alkali atom scattering was recently investigated both theoretically and experimentally in the energy range from a few eV up to 100 eV. On the theoretical side calculations of the integrated elastic and excitation cross sections as well as total cross sections for Li, Na and K were based upon either the close-coupling method or the modified Glauber approximation. These theoretical results are in good agreement with experimental measurements of the total cross section for both Na and K. Resonance structures were also found in the L = 0, 1 and 2 partial waves for positron scattering from the alkalis. The structure of these resonances appears to be quite complex and, as expected, they occur in conjunction with the atomic excitation thresholds. Currently both theoretical and experimental work is in progress on positron-Rb scattering in the same energy range.

  2. The possibilities of simultaneous detection of gamma rays, cosmic-ray electrons and positrons on the GAMMA-400 space observatory

    NASA Astrophysics Data System (ADS)

    Galper, A. M.; Aptekar, R. L.; Arkhangelskaya, I. V.; Boezio, M.; Bonvicini, V.; Dolgoshein, B. A.; Farber, M. O.; Fradkin, M. I.; Gecha, V. Ya.; Kachanov, V. A.; Kaplin, V. A.; Mazets, E. P.; Menshenin, A. L.; Picozza, P.; Prilutskii, O. F.; Rodin, V. G.; Runtso, M. F.; Spillantini, P.; Suchkov, S. I.; Topchiev, N. P.; Vacchi, A.; Yurkin, Yu. T.; Zampa, N.; Zverev, V. G.

    2011-02-01

    The GAMMA-400 space observatory will provide precise measurements of gamma rays, electrons, and positrons in the energy range 0.1-3000 GeV. The good angular and energy resolutions, as well as identification capabilities (angular resolution ~0.01°, energy resolution ~1%, and proton rejection factor ~106) will allow us to study the main galactic and extragalactic sources, diffuse gamma-ray background, gamma-ray bursts, and to measure electron and positron fluxes. The peculiar characteristics of the experiment is simultaneous detection of gamma rays and cosmic-ray electrons and positrons, which can be connected with annihilation or decay of dark matter particles.

  3. Constraining decaying dark matter with Fermi LAT gamma-rays

    SciTech Connect

    Zhang, Le; Sigl, Günter; Weniger, Christoph; Maccione, Luca; Redondo, Javier E-mail: christoph.weniger@desy.de E-mail: redondo@mppmm.mpg.de

    2010-06-01

    High energy electrons and positrons from decaying dark matter can produce a significant flux of gamma rays by inverse Compton off low energy photons in the interstellar radiation field. This possibility is inevitably related with the dark matter interpretation of the observed PAMELA and FERMI excesses. The aim of this paper is providing a simple and universal method to constrain dark matter models which produce electrons and positrons in their decay by using the Fermi LAT gamma-ray observations in the energy range between 0.5 GeV and 300 GeV. We provide a set of universal response functions that, once convolved with a specific dark matter model produce the desired constraints. Our response functions contain all the astrophysical inputs such as the electron propagation in the galaxy, the dark matter profile, the gamma-ray fluxes of known origin, and the Fermi LAT data. We study the uncertainties in the determination of the response functions and apply them to place constraints on some specific dark matter decay models that can well fit the positron and electron fluxes observed by PAMELA and Fermi LAT. To this end we also take into account prompt radiation from the dark matter decay. We find that with the available data decaying dark matter cannot be excluded as source of the PAMELA positron excess.

  4. High resolution Cerenkov light imaging of induced positron distribution in proton therapy

    SciTech Connect

    Yamamoto, Seiichi Fujii, Kento; Morishita, Yuki; Okumura, Satoshi; Komori, Masataka; Toshito, Toshiyuki

    2014-11-01

    Purpose: In proton therapy, imaging of the positron distribution produced by fragmentation during or soon after proton irradiation is a useful method to monitor the proton range. Although positron emission tomography (PET) is typically used for this imaging, its spatial resolution is limited. Cerenkov light imaging is a new molecular imaging technology that detects the visible photons that are produced from high-speed electrons using a high sensitivity optical camera. Because its inherent spatial resolution is much higher than PET, the authors can measure more precise information of the proton-induced positron distribution with Cerenkov light imaging technology. For this purpose, they conducted Cerenkov light imaging of induced positron distribution in proton therapy. Methods: First, the authors evaluated the spatial resolution of our Cerenkov light imaging system with a {sup 22}Na point source for the actual imaging setup. Then the transparent acrylic phantoms (100 × 100 × 100 mm{sup 3}) were irradiated with two different proton energies using a spot scanning proton therapy system. Cerenkov light imaging of each phantom was conducted using a high sensitivity electron multiplied charge coupled device (EM-CCD) camera. Results: The Cerenkov light’s spatial resolution for the setup was 0.76 ± 0.6 mm FWHM. They obtained high resolution Cerenkov light images of the positron distributions in the phantoms for two different proton energies and made fused images of the reference images and the Cerenkov light images. The depths of the positron distribution in the phantoms from the Cerenkov light images were almost identical to the simulation results. The decay curves derived from the region-of-interests (ROIs) set on the Cerenkov light images revealed that Cerenkov light images can be used for estimating the half-life of the radionuclide components of positrons. Conclusions: High resolution Cerenkov light imaging of proton-induced positron distribution was possible. The

  5. Particle physics. Positrons ride the wave

    SciTech Connect

    Piot, Philippe

    2015-08-26

    Here, experiments reveal that positrons — the antimatter equivalents of electrons — can be rapidly accelerated using a plasma wave. The findings pave the way to high-energy electron–positron particle colliders.

  6. Positron-acoustic shock waves associated with cold viscous positron fluid in superthermal electron-positron-ion plasmas

    SciTech Connect

    Uddin, M. J. Alam, M. S.; Mamun, A. A.

    2015-06-15

    A theoretical investigation is made on the positron-acoustic (PA) shock waves (SHWs) in an unmagnetized electron-positron-ion plasma containing immobile positive ions, cold mobile positrons, and hot positrons and electrons following the kappa (κ) distribution. The cold positron kinematic viscosity is taken into account, and the reductive perturbation method is used to derive the Burgers equation. It is found that the viscous force acting on cold mobile positron fluid is a source of dissipation and is responsible for the formation of the PA SHWs. It is also observed that the fundamental properties of the PA SHWs are significantly modified by the effects of different parameters associated with superthermal (κ distributed) hot positrons and electrons.

  7. Electromagnetic cascade in high-energy electron, positron, and photon interactions with intense laser pulses

    NASA Astrophysics Data System (ADS)

    Bulanov, S. S.; Schroeder, C. B.; Esarey, E.; Leemans, W. P.

    2013-06-01

    The interaction of high-energy electrons, positrons, and photons with intense laser pulses is studied in head-on collision geometry. It is shown that electrons and/or positrons undergo a cascade-type process involving multiple emissions of photons. These photons can consequently convert into electron-positron pairs. As a result charged particles quickly lose their energy developing an exponentially decaying energy distribution, which suppresses the emission of high-energy photons, thus reducing the number of electron-positron pairs being generated. Therefore, this type of interaction suppresses the development of the electromagnetic avalanche-type discharge, i.e., the exponential growth of the number of electrons, positrons, and photons does not occur in the course of interaction. The suppression will occur when three-dimensional effects can be neglected in the transverse particle orbits, i.e., for sufficiently broad laser pulses with intensities that are not too extreme. The final distributions of electrons, positrons, and photons are calculated for the case of a high-energy e-beam interacting with a counterstreaming, short intense laser pulse. The energy loss of the e-beam, which requires a self-consistent quantum description, plays an important role in this process, as well as provides a clear experimental observable for the transition from the classical to quantum regime of interaction.

  8. Investigation of Positron-CO scattering using Positronium Annihilation Ratio Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kauppila, W. E.; Edwards, J. J.; Miller, E. G.; Stein, T. S.; Surdutovich, E.

    2006-05-01

    We are using the technique [1] of positronium annihilation ratio spectroscopy (PsARS) to study the annihilation of 6 - 13 eV positrons colliding with CO. In this method we detect in coincidence (a) two 511 keV annihilation gamma rays, and simultaneously (b) two 300 - 460 keV gamma rays from the three gamma decay of ortho-Ps. The ratio of these signals R3γ/2γ versus positron impact energy reveals anomalous behavior for CO when compared with other gases [1] suggesting that some other mechanism than Ps formation is contributing to positron annihilation at an energy about 1 eV above the Ps formation threshold of 7.2 eV. Recognizing that the threshold for electronic excitation by positron impact is located where the anomalous R3γ/2γ behavior occurs suggests that we may be observing an effect where the positron is electronically exciting CO and temporarily binding to the molecule in a resonance-like state from which the positron can annihilate with an electron producing an enhanced 511 keV coincidence signal consistent with our measurements. [1] W.E. Kauppila, E.G. Miller, H.F.M. Mohamed, K. Pipinos, T.S. Stein and E. Surdutovich, Phys. Rev. Lett. 93, 113401 (2004).

  9. Free Volume Structure of Acrylic-Type Dental Nanocomposites Tested with Annihilating Positrons.

    PubMed

    Shpotyuk, Olha; Ingram, Adam; Shpotyuk, Oleh

    2016-12-01

    Positron annihilation spectroscopy in lifetime measuring mode exploring conventional fast-fast coincidence ORTEC system is employed to characterize free volume structure of commercially available acrylic-type dental restorative composite Charisma® (Heraeus Kulzer GmbH, Germany). The measured lifetime spectra for uncured and light-cured composites are reconstructed from unconstrained x3-term fitting and semi-empirical model exploring x3-x2-coupling decomposition algorithm. The governing channel of positron annihilation in the composites studied is ascribed to mixed positron-Ps trapping, where Ps decaying in the third component is caused entirely by input from free-volume holes in polymer matrix, while the second component is defined by free positron trapping in interfacial free-volume holes between filler nanoparticles and surrounded polymer matrix. Microstructure scenario of the photopolymerization shrinkage includes cross-linking of structural chains in polymer matrix followed by conversion of bound positron-electron (positronium) traps in positron-trapping interfacial free-volume voids in a vicinity of agglomerated filler nanoparticles.

  10. Free Volume Structure of Acrylic-Type Dental Nanocomposites Tested with Annihilating Positrons

    NASA Astrophysics Data System (ADS)

    Shpotyuk, Olha; Ingram, Adam; Shpotyuk, Oleh

    2016-11-01

    Positron annihilation spectroscopy in lifetime measuring mode exploring conventional fast-fast coincidence ORTEC system is employed to characterize free volume structure of commercially available acrylic-type dental restorative composite Charisma® (Heraeus Kulzer GmbH, Germany). The measured lifetime spectra for uncured and light-cured composites are reconstructed from unconstrained x3-term fitting and semi-empirical model exploring x3-x2-coupling decomposition algorithm. The governing channel of positron annihilation in the composites studied is ascribed to mixed positron-Ps trapping, where Ps decaying in the third component is caused entirely by input from free-volume holes in polymer matrix, while the second component is defined by free positron trapping in interfacial free-volume holes between filler nanoparticles and surrounded polymer matrix. Microstructure scenario of the photopolymerization shrinkage includes cross-linking of structural chains in polymer matrix followed by conversion of bound positron-electron (positronium) traps in positron-trapping interfacial free-volume voids in a vicinity of agglomerated filler nanoparticles.

  11. 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

  12. J-PET detector system for studies of the electron-positron annihilations

    NASA Astrophysics Data System (ADS)

    Pawlik-Niedźwiecka, M.; Khreptak, O.; Gajos, A.; Wieczorek, A.; Alfs, D.; Bednarski, T.; Białas, P.; Curceanu, C.; Czerwiński, E.; Dulski, K.; Głowacz, B.; Gupta-Sharma, N.; Gorgol, M.; Hiesmayr, B. C.; Jasińska, B.; Kamińska, D.; Korcyl, G.; Kowalski, P.; Krzmień, W.; Krawczyk, N.; Kubicz, E.; Mohammed, M.; Niedźwiecki, Sz.; Raczyński, L.; Rudy, Z.; Silarski, M.; Wiślicki, W.; Zgardzińska, B.; Zieliński, M.; Moskal, P.

    2016-11-01

    Jagiellonian Positron Emission Tomograph (J-PET) has been recently constructed at the Jagiellonian University as a prototype of a cost-effective scanner for the metabolic imaging of the whole human body. J-PET detector is optimized for the measurement of momentum and polarization of photons from the electron-positron annihilations. It is built out of strips of plastic scintillators, forming three cylindrical layers. As detector of gamma quanta it will be used for studies of discrete symmetries and multiparticle entanglement of photons originating from the decays of ortho-positronium atoms.

  13. Optical imaging of Cerenkov light generation from positron-emitting radiotracers

    PubMed Central

    Robertson, R; Germanos, M S; Li, C; Mitchell, G S; Cherry, S R; Silva, M D

    2009-01-01

    Radiotracers labeled with high-energy positron-emitters, such as those commonly used for positron emission tomography (PET) studies, emit visible light immediately following decay in a medium. This phenomenon, not previously described for these imaging tracers, is consistent with Cerenkov radiation and has several potential applications, especially for in vivo molecular imaging studies. Herein we detail a new molecular imaging tool, Cerenkov Luminescence Imaging, the experiments conducted that support our interpretation of the source of the signal, and proof-of-concept in vivo studies that set the foundation for future application of this new method. PMID:19636082

  14. Testing astrophysical models for the PAMELA positron excess with cosmic ray nuclei.

    PubMed

    Mertsch, Philipp; Sarkar, Subir

    2009-08-21

    The excess in the positron fraction measured by PAMELA has been interpreted as due to annihilation or decay of dark matter in the Galaxy. More prosaically it has been ascribed to direct production of positrons by nearby pulsars or due to pion production during diffusive shock acceleration of hadronic cosmic rays in nearby sources. We point out that measurements of secondary cosmic ray nuclei can discriminate between these possibilities. New data on the titanium-to-iron ratio support the hadronic source model above and enable a prediction for the boron-to-carbon ratio at energies above 100 GeV.

  15. Positron microanalysis with high intensity beams

    SciTech Connect

    Hulett, L.D. Jr.; Donohue, D.L.

    1990-01-01

    One of the more common applications for a high intensity slow positron facility will be microanalysis of solid materials. In the first section of this paper some examples are given of procedures that can be developed. Since most of the attendees of this workshop are experts in positron spectroscopy, comprehensive descriptions will be omitted. With the exception of positron emission microscopy, most of the procedures will be based on those already in common use with broad beams. The utility of the methods have all been demonstrated, but material scientists use very few of them because positron microbeams are not generally available. A high intensity positron facility will make microbeams easier to obtain and partially alleviate this situation. All microanalysis techniques listed below will have a common requirement, which is the ability to locate the microscopic detail or area of interest and to focus the positron beam exclusively on it. The last section of this paper is a suggestion of how a high intensity positron facility might be designed so as to have this capability built in. The method will involve locating the specimen by scanning it with the microbeam of positrons and inducing a secondary electron image that will immediately reveal whether or not the positron beam is striking the proper portion of the specimen. This scanning positron microscope' will be a somewhat prosaic analog of the conventional SEM. It will, however, be an indispensable utility that will enhance the practicality of positron microanalysis techniques. 6 refs., 1 fig.

  16. Positron Anomaly in Galactic Cosmic Rays: Constraining Dark Matter Contribution

    NASA Astrophysics Data System (ADS)

    Sagdeev, Roald; Malkov, Mikhail; Diamond, Patrick

    2016-10-01

    An explanation of the unexpected rise in the positron fraction of the cosmic ray (CR) leptonic energy spectrum, is proposed. It is argued that the e+/- spectra are different because they are accelerated by a charge-sign selective mechanism. This premise was hinted at by a recent result from the AMS-02 spectrometer that revealed a difference between e+ and antiproton spectra, which both are secondary CRs but of the opposite charges. The new mechanism extends the diffusive shock acceleration (DSA) to make it charge-sign selective. The DSA, operating in Galactic supernova remnant (SNR) shocks, is held responsible for the production of the bulk of the CRs. The new mechanism was found to account for the positron data with an excellent agreement, except in a limited energy range between 100-300 GeV. In this range, the data exceed the theoretical prediction systematically, thus opening a window for a contribution from dark matter decay or annihilation as well as nearby pulsars. The charge-sign selectivity of the DSA arises from an electric field induced by the CR protons illuminating the neutral gas clumps in the SNR surroundings. The electric field expels positrons from the clump but traps electrons and secondary antiprotons, thus suppressing their acceleration in such SNRs. Work supported by NASA ATP-program under Grant NNX14AH36G, and by the US Department of Energy under Award No. DE-FG02-04ER54738.

  17. Slow positron beam generator for lifetime studies

    NASA Technical Reports Server (NTRS)

    Singh, Jag J. (Inventor); Eftekhari, Abe (Inventor); St.clair, Terry L. (Inventor)

    1991-01-01

    A slow positron beam generator uses a conductive source residing between two test films. Moderator pieces are placed next to the test film on the opposite side of the conductive source. A voltage potential is applied between the moderator pieces and the conductive source. Incident energetic positrons: (1) are emitted from the conductive source; (2) are passed through test film; and (3) isotropically strike moderator pieces before diffusing out of the moderator pieces as slow positrons, respectively. The slow positrons diffusing out of moderator pieces are attracted to the conductive source which is held at an appropriate potential below the moderator pieces. The slow positrons have to pass through the test films before reaching the conductive source. A voltage is adjusted so that the potential difference between the moderator pieces and the conductive source forces the positrons to stop in the test films. Measurable annihilation radiation is emitted from the test film when positrons annihilate (combine) with electrons in the test film.

  18. Materials analysis using positron beam lifetime spectroscopy

    SciTech Connect

    Hartley, J.; Howell, R. H., Asoka-Kumar, P.; Sterne, P.; Stoeffl, W.

    1998-11-12

    We are using a defect analysis capabilities based on two positron beam lifetime spectrometers: the first is based on a 3 MeV electrostatic accelerator and the second on our high current linac beam. The high energy beam lifetime spectrometer is routinely used to perform positron lifetime analysis with a 3 MeV positron beam on thick sample specimens. It is being used for bulk sample analysis and analysis of samples encapsulated in controlled environments for in situ measurements. A second, low energy, microscopically focused, pulsed positron beam for defect analysis by positron lifetime spectroscopy is under development at the LLNL high current positron source. This beam will enable defect-specific, 3-dimensional maps of defect concentration with sub-micron location resolution. When coupled with first principles calculations of defect specific positron lifetimes it will enable new levels of defect concentration mapping and defect identification.

  19. High intensity positron program at LLNL

    SciTech Connect

    Asoka-Kumar, P.; Howell, R.H.; Stoeffl, W.

    1998-09-23

    Lawrence Livermore National Laboratory (LLNL) is the home of the world's highest current beam of keV positrons. The potential for establishing a national center for materials analysis using positron annihilation techniques around this capability is being actively pursued. The high LLNL beam current will enable investigations in several new areas. We are developing a positron microprobe that will produce a pulsed, focused positron beam for 3-dimensional scans of defect size and concentration with submicron resolution. Below we summarize the important design features of this microprobe. Several experimental end stations will be available that can utilize the high current beam with a time distribution determined by the electron linac pulse structure, quasi-continuous, or bunched at 20 MHz, and can operate in an electrostatic or (and) magnetostatic environment. Some of the planned early experiments are: two-dimensional angular correlation of annihilation radiation of thin films and buried interfaces, positron diffraction holography, positron induced desorption, and positron induced Auger spectra.

  20. RADIOACTIVE POSITRON EMITTER PRODUCTION BY ENERGETIC ALPHA PARTICLES IN SOLAR FLARES

    SciTech Connect

    Murphy, R. J.; Kozlovsky, B.; Share, G. H. E-mail: benz@wise.tau.ac.il

    2015-01-01

    Measurements of the 0.511 MeV positron-annihilation line from solar flares are used to explore the flare process in general and ion acceleration in particular. In flares, positrons are produced primarily by the decay of radioactive positron-emitting isotopes resulting from nuclear interactions of flare-accelerated ions with ambient solar material. Kozlovsky et al. provided ion-energy-dependent production cross sections for 67 positron emitters evaluated from their threshold energies (some <1 MeV nucleon{sup –1}) to a GeV nucleon{sup –1}, incorporating them into a computer code for calculating positron-emitter production. Adequate cross-section measurements were available for proton reactions, but not for α-particle reactions where only crude estimates were possible. Here we re-evaluate the α-particle cross sections using new measurements and nuclear reaction codes. In typical large gamma-ray line flares, proton reactions dominate positron production, but α-particle reactions will dominate for steeper accelerated-ion spectra because of their relatively low threshold energies. With the accelerated-{sup 3}He reactions added previously, the code is now reliable for calculating positron production from any distribution of accelerated-ion energies, not just those of typical flares. We have made the code available in the online version of the Journal. We investigate which reactions, projectiles, and ion energies contribute to positron production. We calculate ratios of the annihilation-line fluence to fluences of other gamma-ray lines. Such ratios can be used in interpreting flare data and in determining which nuclear radiation is most sensitive for revealing acceleration of low-energy ions at the Sun.

  1. Capture and polarization of positrons in a proposed NLC polarized positron source

    SciTech Connect

    Batygin, Yuri K

    2003-05-28

    A proposed NLC polarized positron source utilizes a 150 GeV electron beam passing through a helical undulator. The resulting flux of polarized photons is converted in a thin positron production target. Spin polarized positrons are captured using a high field flux concentrator followed by an accelerator section immersed in a solenoidal field. Positron tracking through the accelerating and focusing systems is done together with integration of spin precession. Optimization of the collection system is performed to insure high positron yield into the 6-dimensional acceptance of the subsequent pre-damping ring while keeping the high value of positron beam polarization.

  2. Positron confinement in embedded lithium nanoclusters

    NASA Astrophysics Data System (ADS)

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

    2002-02-01

    Quantum confinement of positrons in nanoclusters offers the opportunity to obtain detailed information on the electronic structure of nanoclusters by application of positron annihilation spectroscopy techniques. In this work, positron confinement is investigated in lithium nanoclusters embedded in monocrystalline MgO. These nanoclusters were created by means of ion implantation and subsequent annealing. It was found from the results of Doppler broadening positron beam analysis that approximately 92% of the implanted positrons annihilate in lithium nanoclusters rather than in the embedding MgO, while the local fraction of lithium at the implantation depth is only 1.3 at. %. The results of two-dimensional angular correlation of annihilation radiation confirm the presence of crystalline bulk lithium. The confinement of positrons is ascribed to the difference in positron affinity between lithium and MgO. The nanocluster acts as a potential well for positrons, where the depth of the potential well is equal to the difference in the positron affinities of lithium and MgO. These affinities were calculated using the linear muffin-tin orbital atomic sphere approximation method. This yields a positronic potential step at the MgO||Li interface of 1.8 eV using the generalized gradient approximation and 2.8 eV using the insulator model.

  3. High-resolution positron Q-value measurements and nuclear-structure studies far from the stability line. Progress report

    SciTech Connect

    Avignone, F.T. III.

    1981-02-28

    Extensive data analysis and theoretical analysis has been done to complete the extensive decay scheme investigation of /sup 206/ /sup 208/Fr and the level structures of /sup 206/ /sup 208/Rn. A final version of a journal article is presented in preprint form. Extensive Monte Carlo calculations have been made to correct the end point energies of positron spectra taken with intrinsic Ge detectors for annihilation radiation interferences. These calculations were tested using the decay of /sup 82/Sr which has previously measured positron branches. This technique was applied to the positron spectra collected at the on-line UNISOR isotope separator. The reactions used were /sup 60/Ni(/sup 20/Ne;p2n)/sup 77/Rb and /sup 60/Ni(/sup 20/Ne;pn)/sup 78/Rb. Values for 5, ..gamma..-..beta../sup +/ coincidence positron end point energies are given for the decay of /sup 77/Rb. The implied Q-value is 5.075 +- 0.010 MeV. A complete paper on the calculated corrections is presented. A flow chart of a more complete program which accounts for positrons scattering out of the detector and for bremsstralung radiation is also presented. End-point energies of four ..beta../sup +/ branches in /sup 77/Rb are given as well as a proposed energy level scheme of /sup 75/Kr based on ..gamma..-..gamma.. coincidence data taken at UNISOR.

  4. Nonplanar positron-acoustic Gardner solitary waves in electron-positron-ion plasmas with superthermal electrons and positrons

    NASA Astrophysics Data System (ADS)

    Uddin, M. J.; Alam, M. S.; Mamun, A. A.

    2015-02-01

    Nonplanar (cylindrical and spherical) positron-acoustic (PA) Gardner solitary waves (SWs) in an unmagnetized plasma system consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated. The modified Gardner equation is derived by using the reductive perturbation technique. The effects of cylindrical and spherical geometries, superthermal parameter of hot positrons and electrons, relative temperature ratios, and relative number density ratios on the PA Gardner SWs are studied by using the numerical simulations. The implications of our results in various space and laboratory plasma environments are briefly discussed.

  5. Nonplanar positron-acoustic Gardner solitary waves in electron-positron-ion plasmas with superthermal electrons and positrons

    SciTech Connect

    Uddin, M. J. Alam, M. S.; Mamun, A. A.

    2015-02-15

    Nonplanar (cylindrical and spherical) positron-acoustic (PA) Gardner solitary waves (SWs) in an unmagnetized plasma system consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated. The modified Gardner equation is derived by using the reductive perturbation technique. The effects of cylindrical and spherical geometries, superthermal parameter of hot positrons and electrons, relative temperature ratios, and relative number density ratios on the PA Gardner SWs are studied by using the numerical simulations. The implications of our results in various space and laboratory plasma environments are briefly discussed.

  6. 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.

  7. 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.

  8. Positron study of annealing of gallium arsenide

    SciTech Connect

    Rice-Evans, P.C.; Smith, D.L.; Evans, H.E.; Gledhill, G.A. )

    1991-02-01

    A positron beam has been used to investigate the sub-surface changes in semi-insulating gallium arsenide which had been annealed to a range of temperatures. The variations of the Doppler S parameter as a function of positron implantation energy, when subjected to a diffusion analysis, indicate variations in positron trapping at different depths. The results indicate the changes in the type of point defect that accompany the annealing.

  9. Initial results of positron ionization mass spectrometry

    NASA Technical Reports Server (NTRS)

    Donohue, D. L.; Hulett, L. D., Jr.; Mcluckey, S. A.; Glish, G. L.; Eckenrode, B. A.

    1990-01-01

    The use of monoenergetic positrons for the ionization of organic molecules in the gas phase is described. The ionic products are analyzed with a time-of-flight mass spectrometer and detected to produce a mass spectrum. The ionization mechanisms which can be studied in this way include positron impact at energies above the ionization limit of the target molecules, positronium formation in the Ore gap energy range, and positron attachment at energies less than 1eV. The technique of positron ionization mass spectrometry (PIMS) may have analytical utility in that chemical selectivity is observed for one or more of these processes.

  10. Applications and advances of positron beam spectroscopy

    SciTech Connect

    Howell, R., LLNL

    1998-03-18

    Over 50 scientists from DOE-DP, DOE-ER, the national laboratories, academia and industry attended a workshop held on November 5-7, 1997 at Lawrence Livermore National Laboratory. Workshop participants were charged to address two questions: Is there a need for a national center for materials analysis using positron techniques and can the capabilities at Lawrence Livermore National Laboratory serve this need. To demonstrate the need for a national center, the workshop participants discussed the technical advantages enabled by high positron currents and advanced measurement techniques, the role that these techniques would play in materials analysis and the demand for the data. Livermore now leads the world in materials analysis capabilities by positrons due to developments in response to demands of stockpile stewardship. The Livermore facilities now include the world`s highest current beam of keV positrons, a scanning pulsed positron microprobe under development capable of three dimensional maps of defect size and concentration, an MeV positron beam for defect analysis of large samples, and electron momentum spectroscopy by positrons. It was concluded that the positron microprobe under development at LLNL and other new instruments that would be relocated at LLNL at the high current keV source are an exciting step forward in providing results for the positron technique. These new data will impact a wide variety of applications.

  11. On the method of positron lifetime measurement

    NASA Technical Reports Server (NTRS)

    Nishiyama, F.; Shizuma, K.; Nasai, H.; Nishi, M.

    1983-01-01

    A fast-slow coincidence system was constructed for the measurement of positron lifetimes in material. The time resolution of this system was 270 ps for the (60)Co gamma rays. Positron lifetime spectra for 14 kinds of alkali halides were measured with this system. Two lifetime components and their intensities were derived from analyses of the lifetime spectra.

  12. Descriptions of positron defect analysis capabilities

    SciTech Connect

    Howell, R.H.

    1994-10-01

    A series of descriptive papers and graphics appropriate for distribution to potential collaborators has been assembled. These describe the capabilities for defect analysis using positron annihilation spectroscopy. The application of positrons to problems in the polymer and semiconductor industries is addressed.

  13. 21 CFR 892.1110 - Positron camera.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Positron camera. 892.1110 Section 892.1110 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1110 Positron camera. (a) Identification. A...

  14. 21 CFR 892.1110 - Positron camera.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Positron camera. 892.1110 Section 892.1110 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1110 Positron camera. (a) Identification. A...

  15. 21 CFR 892.1110 - Positron camera.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Positron camera. 892.1110 Section 892.1110 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1110 Positron camera. (a) Identification. A...

  16. 21 CFR 892.1110 - Positron camera.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Positron camera. 892.1110 Section 892.1110 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1110 Positron camera. (a) Identification. A...

  17. 21 CFR 892.1110 - Positron camera.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Positron camera. 892.1110 Section 892.1110 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES RADIOLOGY DEVICES Diagnostic Devices § 892.1110 Positron camera. (a) Identification. A...

  18. Ionisation of atomic hydrogen by positron impact

    NASA Technical Reports Server (NTRS)

    Spicher, Gottfried; Olsson, Bjorn; Raith, Wilhelm; Sinapius, Guenther; Sperber, Wolfgang

    1990-01-01

    With the crossed beam apparatus the relative impact-ionization cross section of atomic hydrogen by positron impact was measured. A layout of the scattering region is given. The first measurements on the ionization of atomic hydrogen by positron impact are also given.

  19. Positron collisions with alkali-metal atoms

    NASA Technical Reports Server (NTRS)

    Gien, T. T.

    1990-01-01

    The total cross sections for positron and electron collisions with potassium, sodium, lithium and rubidium are calculated, employing the modified Glauber approximation. The Modified Glauber cross sections for positron collision with potassium and sodium at low intermediate energies are found to agree reasonably well with existing experimental data.

  20. Electron and Positron Stopping Powers of Materials

    National Institute of Standards and Technology Data Gateway

    SRD 7 NIST Electron and Positron Stopping Powers of Materials (PC database for purchase)   The EPSTAR database provides rapid calculations of stopping powers (collisional, radiative, and total), CSDA ranges, radiation yields and density effect corrections for incident electrons or positrons with kinetic energies from 1 keV to 10 GeV, and for any chemically defined target material.

  1. 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.

  2. Positron beam studies of transients in semiconductors

    NASA Astrophysics Data System (ADS)

    Beling, C. D.; Ling, C. C.; Cheung, C. K.; Naik, P. S.; Zhang, J. D.; Fung, S.

    2006-02-01

    Vacancy-sensing positron deep level transient spectroscopy (PDLTS) is a positron beam-based technique that seeks to provide information on the electronic ionization levels of vacancy defects probed by the positron through the monitoring of thermal transients. The experimental discoveries leading to the concept of vacancy-sensing PDLTS are first reviewed. The major problem associated with this technique is discussed, namely the strong electric fields establish in the near surface region of the sample during the thermal transient which tend to sweep positrons into the contact with negligible defect trapping. New simulations are presented which suggest that under certain conditions a sufficient fraction of positrons may be trapped into ionizing defects rendering PDLTS technique workable. Some suggestions are made for techniques that might avoid the problematic electric field problem, such as optical-PDLTS where deep levels are populated using light and the use of high forward bias currents for trap filling.

  3. Design Issues for the ILC Positron Source

    SciTech Connect

    Bharadwaj, V.; Batygin, Yu.K.; Pitthan, R.; Schultz, D.C.; Sheppard, J.; Vincke, H.; Wang, J.W.; Gronberg, J.; Stein, W.; /LLNL, Livermore

    2006-02-15

    A positron source for the International Linear Collider (ILC) can be designed using either a multi-GeV electron beam or a multi-MeV photon beam impinging on a metal target. The major design issues are: choice of drive beam and its generation, choice of target material, the target station, positron capture section, target vault and beam transport to the ILC positron damping ring complex. This paper lists the ILC positron source requirements and their implications for the design of the positron source. A conceptual design for the ILC is expected to be finished in the next two years. With emphasis on this timescale, source design issues and possible solutions are discussed.

  4. Positron emission tomography: physics, instrumentation, and image analysis.

    PubMed

    Porenta, G

    1994-01-01

    Positron emission tomography (PET) is a noninvasive diagnostic technique that permits reconstruction of cross-sectional images of the human body which depict the biodistribution of PET tracer substances. A large variety of physiological PET tracers, mostly based on isotopes of carbon, nitrogen, oxygen, and fluorine is available and allows the in vivo investigation of organ perfusion, metabolic pathways and biomolecular processes in normal and diseased states. PET cameras utilize the physical characteristics of positron decay to derive quantitative measurements of tracer concentrations, a capability that has so far been elusive for conventional SPECT (single photon emission computed tomography) imaging techniques. Due to the short half lives of most PET isotopes, an on-site cyclotron and a radiochemistry unit are necessary to provide an adequate supply of PET tracers. While operating a PET center in the past was a complex procedure restricted to few academic centers with ample resources, PET technology has rapidly advanced in recent years and has entered the commercial nuclear medicine market. To date, the availability of compact cyclotrons with remote computer control, automated synthesis units for PET radiochemistry, high-performance PET cameras, and user-friendly analysis workstations permits installation of a clinical PET center within most nuclear medicine facilities. This review provides simple descriptions of important aspects concerning physics, instrumentation, and image analysis in PET imaging which should be understood by medical personnel involved in the clinical operation of a PET imaging center.

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

  6. EM reconstruction of dual isotope PET using staggered injections and prompt gamma positron emitters

    PubMed Central

    Andreyev, Andriy; Sitek, Arkadiusz; Celler, Anna

    2014-01-01

    Purpose: The aim of dual isotope positron emission tomography (DIPET) is to create two separate images of two coinjected PET radiotracers. DIPET shortens the duration of the study, reduces patient discomfort, and produces perfectly coregistered images compared to the case when two radiotracers would be imaged independently (sequential PET studies). Reconstruction of data from such simultaneous acquisition of two PET radiotracers is difficult because positron decay of any isotope creates only 511 keV photons; therefore, the isotopes cannot be differentiated based on the detected energy. Methods: Recently, the authors have proposed a DIPET technique that uses a combination of radiotracer A which is a pure positron emitter (such as 18F or 11C) and radiotracer B in which positron decay is accompanied by the emission of a high-energy (HE) prompt gamma (such as 38K or 60Cu). Events that are detected as triple coincidences of HE gammas with the corresponding two 511 keV photons allow the authors to identify the lines-of-response (LORs) of isotope B. These LORs are used to separate the two intertwined distributions, using a dedicated image reconstruction algorithm. In this work the authors propose a new version of the DIPET EM-based reconstruction algorithm that allows the authors to include an additional, independent estimate of radiotracer A distribution which may be obtained if radioisotopes are administered using a staggered injections method. In this work the method is tested on simple simulations of static PET acquisitions. Results: The authors’ experiments performed using Monte-Carlo simulations with static acquisitions demonstrate that the combined method provides better results (crosstalk errors decrease by up to 50%) than the positron-gamma DIPET method or staggered injections alone. Conclusions: The authors demonstrate that the authors’ new EM algorithm which combines information from triple coincidences with prompt gammas and staggered injections improves

  7. Positron emission tomography: An overview

    PubMed Central

    Shukla, A. K.; Kumar, Utham

    2006-01-01

    The rate of glucose utilization in tumor cells is significantly enhanced as compared to normal cells and this biochemical characteristic is utilized in PET imaging using FDG as a major workhorse. The PET systems as well as cyclotrons producing positron emitting radiopharmaceuticals have undergone continuous technological refinements. While PET (CT) systems enable fusion images as well as precise attenuation correction, the self-shielded cyclotrons developed provide dedicated systems for in-house production of a large number of PET radiopharmaceuticals. The application of PET images in oncology includes those of pulmonary, colorectal, breast, lymphoma, head & neck, bone, ovarian and GI cancers. The PET has been recognized as promising diagnostic tool to predict biological and physiological changes at the molecular level and hence offer a potential area for future applications including Stem Cell research. PMID:21206635

  8. Positron emission tomography wrist detector

    DOEpatents

    Schlyer, David J.; O'Connor, Paul; Woody, Craig; Junnarkar, Sachin Shrirang; Radeka, Veljko; Vaska, Paul; Pratte, Jean-Francois

    2006-08-15

    A method of serially transferring annihilation information in a compact positron emission tomography (PET) scanner includes generating a time signal representing a time-of-occurrence of an annihilation event, generating an address signal representing a channel detecting the annihilation event, and generating a channel signal including the time and address signals. The method also includes generating a composite signal including the channel signal and another similarly generated channel signal concerning another annihilation event. An apparatus that serially transfers annihilation information includes a time signal generator, address signal generator, channel signal generator, and composite signal generator. The time signal is asynchronous and the address signal is synchronous to a clock signal. A PET scanner includes a scintillation array, detection array, front-end array, and a serial encoder. The serial encoders include the time signal generator, address signal generator, channel signal generator, and composite signal generator.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  10. Time reversal violation in radiative beta decay: experimental plans

    NASA Astrophysics Data System (ADS)

    Behr, J. A.; McNeil, J.; Anholm, M.; Gorelov, A.; Melconian, D.; Ashery, D.

    2017-01-01

    Some explanations for the excess of matter over antimatter in the universe involve sources of time reversal violation (TRV) in addition to the one known in the standard model of particle physics. We plan to search for TRV in a correlation between the momenta of the beta, neutrino, and the radiative gamma sometimes emitted in nuclear beta decay. Correlations involving three (out of four) momenta are sensitive at lowest order to different TRV physics than observables involving spin, such as electric dipole moments and spin-polarized beta decay correlations. Such experiments have been done in radiative kaon decay, but not in systems involving the lightest generation of quarks. An explicit low-energy physics model being tested produces TRV effects in the Fermi beta decay of the neutron, tritium, or some positron-decaying isotopes. We will present plans to measure the TRV asymmetry in radiative beta decay of laser-trapped 38mK at better than 0.01 sensitivity, including suppression of background from positron annihilation. Supported by NSERC, D.O.E., Israel Science Foundation. TRIUMF receives federal funding via a contribution agreement with the National Research Council of Canada.

  11. AMS-02 positron excess: New bounds on dark matter models and hint for primary electron spectrum hardening

    NASA Astrophysics Data System (ADS)

    Feng, Lei; Yang, Rui-Zhi; He, Hao-Ning; Dong, Tie-Kuang; Fan, Yi-Zhong; Chang, Jin

    2014-01-01

    The data collected by ATIC, CREAM and PAMELA all display remarkable cosmic ray nuclei spectrum hardening above the magnetic rigidity ∼240 GV. One natural speculation is that the primary electron spectrum also gets hardened (possibly at ∼80 GV) and the hardening partly accounts for the electron/positron total spectrum excess discovered by ATIC, HESS and Fermi-LAT. If it is the case, the increasing behavior of the subsequent positron-to-electron ratio will get flattened and the spectrum hardening should be taken into account in the joint fit of the electron/positron data otherwise the inferred parameters will be biased. Our joint fits of the latest AMS-02 positron fraction data together with the PAMELA/Fermi-LAT electron/positron spectrum data suggest that the primary electron spectrum hardening is needed in most though not all modelings. The bounds on dark matter models have also been investigated. In the presence of spectrum hardening of primary electrons, the amount of dark-matter-originated electron/positron pairs needed in the modeling is smaller. Even with such a modification, the annihilation channel χχ→μ+μ- has been tightly constrained by the Fermi-LAT Galactic diffuse emission data. The decay channel χ→μ+μ- is found to be viable.

  12. Multimode vibrational couplings in resonant positron annihilation.

    PubMed

    d'A Sanchez, Sergio; Lima, Marco A P; Varella, Márcio T do N

    2011-09-02

    The mechanisms for multimode vibrational couplings in resonant positron annihilation are not well understood. We show that these resonances can arise from positron-induced distortions of the potential energy surface (target response to the positron field). Though these distortions can transfer energy into single- and multiquantum vibrations, they have so far been disregarded as a pathway to resonant annihilation. We also compare the existing annihilation theories and show that the currently accepted model can be cast as a special case of the Feshbach annihilation theory.

  13. Prototyping of the ILC Baseline Positron Target

    SciTech Connect

    Gronberg, J; Brooksby, C; Piggott, T; Abbott, R; Javedani, J; Cook, E

    2012-02-29

    The ILC positron system uses novel helical undulators to create a powerful photon beam from the main electron beam. This beam is passed through a titanium target to convert it into electron-positron pairs. The target is constructed as a 1 m diameter wheel spinning at 2000 RPM to smear the 1 ms ILC pulse train over 10 cm. A pulsed flux concentrating magnet is used to increase the positron capture efficiency. It is cooled to liquid nitrogen temperatures to maximize the flatness of the magnetic field over the 1 ms ILC pulse train. We report on prototyping effort on this system.

  14. The Buffer-Gas Positron Accumulator and Resonances in Positron-Molecule Interactions

    NASA Technical Reports Server (NTRS)

    Surko, C.M.

    2007-01-01

    This is a personal account of the development of our buffer-gas positron trap and the new generation of cold beams that these traps enabled. Dick Drachman provided much appreciated advice to us from the time we started the project. The physics underlying trap operation is related to resonances (or apparent resonances) in positron-molecule interactions. Amusingly, experiments enabled by the trap allowed us to understand these processes. The positron-resonance "box score" to date is one resounding "yes," namely vibrational Feshbach resonances in positron annihilation on hydrocarbons; a "probably" for positron-impact electronic excitation of CO and NZ;an d a "maybe" for vibrational excitation of selected molecules. Two of these processes enabled the efficient operation of the trap, and one almost killed it in infancy. We conclude with a brief overview of further applications of the trapping technology discussed here, such as "massive" positron storage and beams with meV energy resolution.

  15. Semileptonic Decays

    SciTech Connect

    Luth, Vera G.; /SLAC

    2012-10-02

    The following is an overview of the measurements of the CKM matrix elements |V{sub cb}| and |V{sub ub}| that are based on detailed studies of semileptonic B decays by the BABAR and Belle Collaborations and major advances in QCD calculations. In addition, a new and improved measurement of the ratios R(D{sup (*)}) = {Beta}({bar B} {yields} D{sup (*)}{tau}{sup -}{bar {nu}}{sub {tau}})/{Beta}({bar B} {yields} D{sup (*)}{ell}{sup -}{bar {nu}}{sub {ell}}) is presented. Here D{sup (*)} refers to a D or a D* meson and {ell} is either e or {mu}. The results, R(D) = 0.440 {+-} 0.058 {+-} 0.042 and R(D*) = 0.332 {+-} 0.024 {+-} 0.018, exceed the Standard Model expectations by 2.0{sigma} and 2.7{sigma}, respectively. Taken together, they disagree with these expectations at the 3.4{sigma} level. The excess of events cannot be explained by a charged Higgs boson in the type II two-Higgs-doublet model.

  16. Positron annihilation spectroscopy on a beam of positrons the LEPTA facility

    NASA Astrophysics Data System (ADS)

    Ahmanova, E. V.; Eseev, M. K.; Kobets, A. G.; Meshkov, I. N.; Orlov, O. S.; Sidorin, A. A.; Siemek, K.; Horodek, P.

    2016-12-01

    The results and possibilities of the samples surfaces research by the Doppler method of positron annihilation spectroscopy (PAS) for a monochromatic beam of positrons at the LEPTA facility are presented in this paper. Method with high-resolution sensitivity to defects like vacancies and dislocations allows scanning of the surface and near-surface sample layers to a depth of several micrometers by the method of Doppler broadening of annihilation lines. The opportunities for the development of a PAS method based on the measurement of the positron lifetime in the sample irradiated by ordered flow of positrons from the injector of accelerator complex LEPTA at JINR are discussed.

  17. Bulk Materials Analysis Using High-Energy Positron Beams

    SciTech Connect

    Glade, S C; Asoka-Kumar, P; Nieh, T G; Sterne, P A; Wirth, B D; Dauskardt, R H; Flores, K M; Suh, D; Odette, G R

    2002-11-11

    This article reviews some recent materials analysis results using high-energy positron beams at Lawrence Livermore National Laboratory. We are combining positron lifetime and orbital electron momentum spectroscopic methods to provide electron number densities and electron momentum distributions around positron annihilation sites. Topics covered include: correlation of positron annihilation characteristics with structural and mechanical properties of bulk metallic glasses, compositional studies of embrittling features in nuclear reactor pressure vessel steel, pore characterization in Zeolites, and positron annihilation characteristics in alkali halides.

  18. Method of processing positron lifetime spectra

    SciTech Connect

    Valuev, N.P.; Klimov, A.B.; Zhikharev, A.N.

    1985-05-01

    This paper describes a method for the processing of spectra of positron annihilation which permits a much more relaible determination of the lifetime during numerical processing of spectra by computer.

  19. Positron kinetics in an idealized PET environment

    NASA Astrophysics Data System (ADS)

    Robson, R. E.; Brunger, M. J.; Buckman, S. J.; Garcia, G.; Petrović, Z. Lj.; White, R. D.

    2015-08-01

    The kinetic theory of non-relativistic positrons in an idealized positron emission tomography PET environment is developed by solving the Boltzmann equation, allowing for coherent and incoherent elastic, inelastic, ionizing and annihilating collisions through positronium formation. An analytic expression is obtained for the positronium formation rate, as a function of distance from a spherical source, in terms of the solutions of the general kinetic eigenvalue problem. Numerical estimates of the positron range - a fundamental limitation on the accuracy of PET, are given for positrons in a model of liquid water, a surrogate for human tissue. Comparisons are made with the ‘gas-phase’ assumption used in current models in which coherent scattering is suppressed. Our results show that this assumption leads to an error of the order of a factor of approximately 2, emphasizing the need to accurately account for the structure of the medium in PET simulations.

  20. Addiction Studies with Positron Emission Tomography

    ScienceCinema

    Joanna Fowler

    2016-07-12

    Brookhaven scientist Joanna Fowler describes Positron Emission Technology (PET) research at BNL which for the past 30 years has focused in the integration of basic research in radiotracer chemistry with the tools of neuroscience to develop new scientific

  1. Addiction Studies with Positron Emission Tomography

    SciTech Connect

    Joanna Fowler

    2008-10-13

    Brookhaven scientist Joanna Fowler describes Positron Emission Technology (PET) research at BNL which for the past 30 years has focused in the integration of basic research in radiotracer chemistry with the tools of neuroscience to develop new scientific

  2. Electric charges of positrons and antiprotons

    SciTech Connect

    Hughes, R.J. ); Deutch, B.I. )

    1992-07-27

    Tests of the electric charges carried by the positron and antiproton are derived from recent measurements of the cyclotron frequencies of these particles, and from the spectroscopy of exotic atoms in which they are constituents.

  3. Electron and positron induced processes. POSMOL 2013

    NASA Astrophysics Data System (ADS)

    Limão-Vieira, Paulo; Campeanu, Radu; Hoshino, Masamitsu; Ingólfsson, Oddur; Mason, Nigel; Nagashima, Yasuyuki; Tanuma, Hajime

    2014-09-01

    POSMOL 2013, the international meeting on electron and positron induced processes comprising the XVII International Workshop on Low-Energy Positron and Positronium Physics and the XVIII International Symposium on Electron-Molecule Collisions and Swarms, was held at Kanazawa Bunka Hall, Kanazawa, Ishikawa, Japan, from 19-21 July 2013. The XVII Workshop encompassed all aspects of positron, positronium and antiproton interactions with electrons, atoms, molecules and solid surfaces, and topics related to these, whereas the XVIII Symposium encompassed all aspects of electron interactions with molecules in both gaseous and condensed phases. Particular topics include studies of electron interactions with biomolecules, electron induced surface chemistry and the study of plasma processes. Recent research on the study of electron swarms was also highlighted. Contribution to the Topical Issue "Electron and Positron Induced Processes", edited by Michael Brunger, Radu Campeanu, Masamitsu Hoshino, Oddur Ingólfsson, Paulo Limão-Vieira, Nigel Mason, Yasuyuki Nagashima and Hajime Tanuma.

  4. 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.

  5. Thermal positron interactions with alkali covered tungsten

    NASA Astrophysics Data System (ADS)

    Yamashita, Takashi; Iida, Shimpei; Terabe, Hiroki; Nagashima, Yasuyuki

    2016-11-01

    The branching ratios of positron reemission, positronium emission, positronium negative ion emission and capture to the surface state for thermalized positrons at polycrystalline tungsten surfaces coated with Na, K and Cs have been measured. The data shows that the ratios depend on the coverage of the alkali-metal coating. The fraction of the emitted positronium increases with the coverage of the coating up to 90%.

  6. Modulation of a quantum positron acoustic wave

    NASA Astrophysics Data System (ADS)

    Amin, M. R.

    2015-09-01

    Amplitude modulation of a positron acoustic wave is considered in a four-component electron-positron plasma in the quantum magnetohydrodynamic regime. The important ingredients of this study are the inclusion of the particle exchange-correlation potential, quantum diffraction effects via the Bohm potential, and dissipative effect due to viscosity in the momentum balance equation of the charged carriers. A modified nonlinear Schrödinger equation is derived for the evolution of the slowly varying amplitude of the quantum positron acoustic wave by employing the standard reductive perturbation technique. Detailed analysis of the linear and nonlinear dispersions of the quantum positron acoustic wave is presented. For a typical parameter range, relevant to some dense astrophysical objects, it is found that the quantum positron acoustic wave is modulationally unstable above a certain critical wavenumber. Effects of the exchange-correlation potential and the Bohm potential in the wave dynamics are also studied. It is found that the quantum effect due to the particle exchange-correlation potential is significant in comparison to the effect due to the Bohm potential for smaller values of the carrier wavenumber. However, for comparatively larger values of the carrier wavenumber, the Bohm potential effect overtakes the effect of the exchange-correlation potential. It is found that the critical wavenumber for the modulation instability depends on the ratio of the equilibrium hot electron number density and the cold positron number density and on the ratio of the equilibrium hot positron number density and the cold positron number density. A numerical result on the growth rate of the modulation instability is also presented.

  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. Cerenkov radiation allows in vivo optical imaging of positron emitting radiotracers

    NASA Astrophysics Data System (ADS)

    Spinelli, Antonello E.; D'Ambrosio, Daniela; Calderan, Laura; Marengo, Mario; Sbarbati, Andrea; Boschi, Federico

    2010-01-01

    In this paper, we showed that Cerenkov radiation (CR) escaping from the surface of small living animals injected with 18F-FDG can be detected with optical imaging techniques. 18F decays by emitting positrons with a maximum energy of 0.635 MeV; such positrons, when travelling into tissues faster than the speed of light in the same medium, are responsible of CR emission. A detailed model of the CR spectrum considering the positron energy spectrum was developed in order to quantify the amount of light emission. The results presented in this work were obtained using a commercial optical imager equipped with charged coupled detectors (CCD). Our data open the door to optical imaging (OI) in vivo of the glucose metabolism, at least in pre-clinical research. We found that the heart and bladder can be clearly identified in the animal body reflecting the accumulation of the 18F-FDG. Moreover, we describe two different methods based on the spectral analysis of the CR that can be used to estimate the depth of the source inside the animal. We conclude that 18F-FDG can be employed as it is as a bimodal tracer for positron emission tomography (PET) and OI techniques. Our results are encouraging, suggesting that it could be possible to apply the proposed approach not only to β+ but also to pure β- emitters.

  9. On the neutrinoless double β{sup +}/EC decays

    SciTech Connect

    Suhonen, Jouni

    2013-12-30

    The neutrinoless double positron-emission/electron-capture (0νβ{sup +}/EC) decays are studied for the magnitudes of the involved nuclear matrix elements (NMEs). Decays to the ground state, 0{sub gs}{sup +}, and excited 0{sup +} states are discussed. The participant many-body wave functions are evaluated in the framework of the quasiparticle random-phase approximation (QRPA). Effective, G-matrix-derived nuclear forces are used in realistic single-particle model spaces. The channels β{sup +}β{sup +}, β{sup +}EC, and the resonant neutrinoless double electron capture (R0νECEC) are discussed.

  10. Intense low energy positron beams

    SciTech Connect

    Lynn, K.G.; Jacobsen, F.M.

    1993-12-31

    Intense positron beams are under development or being considered at several laboratories. Already today a few accelerator based high intensity, low brightness e{sup +} beams exist producing of the order of 10{sup 8} {minus} 10{sup 9} e{sup +}/sec. Several laboratories are aiming at high intensity, high brightness e{sup +} beams with intensities greater than 10{sup 9} e{sup +}/sec and current densities of the order of 10{sup 13} {minus} 10{sup 14} e{sup +} sec{sup {minus}} {sup 1}cm{sup {minus}2}. Intense e{sup +} beams can be realized in two ways (or in a combination thereof) either through a development of more efficient B{sup +} moderators or by increasing the available activity of B{sup +} particles. In this review we shall mainly concentrate on the latter approach. In atomic physics the main trust for these developments is to be able to measure differential and high energy cross-sections in e{sup +} collisions with atoms and molecules. Within solid state physics high intensity, high brightness e{sup +} beams are in demand in areas such as the re-emission e{sup +} microscope, two dimensional angular correlation of annihilation radiation, low energy e{sup +} diffraction and other fields. Intense e{sup +} beams are also important for the development of positronium beams, as well as exotic experiments such as Bose condensation and Ps liquid studies.

  11. Amplitude analysis of the charmed decay D0 to KKpipi

    NASA Astrophysics Data System (ADS)

    Skidmore, Nicola

    2017-01-01

    An amplitude analysis of the 4-body charmed decay D0 -> KKππ is presented using data collected from electron-positron collisions at the CLEO experiment. Both flavour tagged and CP tagged data are utilized in the analysis making it unique from amplitude analyses performed at other colliders and providing extra sensitivity to the phases of the amplitude components. The amplitude model is used to search for CP violation in the D0 decay by analysing D0 and D0 decays separately. The model is also crucial input for a model-dependent measurement of the CP-violating phase γ using B+/- ->D0(-> KKππ) K+/- decays, which remains one of the least constrained parameters of the Standard Model. Forum on International Physics Distinguished Student Seminar Program, and European Research Council

  12. Track structure simulation for positron emitters of physical interest. Part III: The case of the non-standard radionuclides

    NASA Astrophysics Data System (ADS)

    Le Loirec, C.; Champion, C.

    2007-11-01

    With the growth of clinical Positron Emission Tomography (PET) utilizations, new molecular tracers, able to aid in the assessment, therapy planning and monitoring of cancer patients, are synthesized. As suggested by some works reported in the literature, these newcomers may be positron emitting isotopes of lanthanium, 134La, iodine, 120I, 121I and 124I, arsenic, 72As and 74As, oxygen, 14O, and neon, 19Ne. In this work, we present an inter comparison of these eight radiopharmaceuticals which may be used in PET. To do that we have used a Monte Carlo simulation of positron following-up in water that we have adapted to the beta decay of radionuclides. We have also access to accurate spatial and energetic distributions of the potential PET radiopharmaceuticals under investigation here. The results are given in an analytical way and have been compared, when possible, with theoretical and experimental values available in the literature.

  13. Dynamics of the positron acoustic waves in electron-positron-ion magnetoplasmas

    NASA Astrophysics Data System (ADS)

    Ali, Rustam; Saha, Asit; Chatterjee, Prasanta

    2017-01-01

    Dynamics of the positron acoustic waves in electron-positron-ion (e-p-i) magnetoplasmas with κ-distributed hot electrons and positrons is investigated in the frameworks of the Kadomtsev-Petviashili (KP) and modified Kadomtsev-Petviashili (mKP) equations. Employing the reductive perturbation technique, the KP and mKP equations are derived. Using the bifurcation theory of planar dynamical systems, the positron acoustic solitary wave solutions, the kink and anti-kink wave solutions are obtained. Considering an external periodic perturbation in the electron-positron-ion magnetoplasmas, the perturbed KP and mKP equations are studied via some qualitative and quantitative approaches. To corroborate in the fact that the perturbed KP and mKP equations can indeed give rise to the quasiperiodic and chaotic motions, the phase plane plots, time series plots, and the Poincaré section are used. The quasiperiodic and developed chaos can be observed for the perturbed positron acoustic waves. The frequency (ω ) of the external periodic perturbation plays the role of the switching parameter in chaotic motions of the perturbed positron acoustic waves through quasiperiodic route to chaos. This work can be useful to understand the dynamics of nonlinear electromagnetic perturbations in space and laboratory plasmas consisting of κ-distributed hot electrons and positrons.

  14. Rare And Radiative B Meson Decays From the BaBar Experiment

    SciTech Connect

    Stelzer, J.; /SLAC

    2006-08-28

    Since its start in 1999 the BABAR experiment has collected a vast amount of data. Electron-positron collisions at the energy of the {Upsilon}(4S) resonance have produced about 240 million coherent B{sup 0}{bar B}{sup 0} and B{sup +}B{sup -} pairs, opening the doors for exploration of rare B meson decays. An overview of the electroweak penguin physics program of BABAR is given, the analysis of two specific decays is presented in detail.

  15. Cosmic ray positron excess: is the dark matter solution a good bet?

    NASA Astrophysics Data System (ADS)

    Lavalle, Julien

    2010-06-01

    The recent observation by the PAMELA satellite of a rising positron fraction up to ~100 GeV has triggered a considerable amount of putative interpretations in terms of dark matter (DM) annihilation or decay. Here, we make a critical reassessment of such a possibility, recalling the elementary conditions with respect to the standard astrophysical background that would make it likely, showing that they are not fulfilled. Likewise, we argue that, as now well accepted, DM would need somewhat contrived properties to contribute significantly to the observed positron signal, even when including e.g. clumpiness effects. This means that most of natural DM candidates arising in particle physics beyond the standard model are not expected to be observed in the cosmic antimatter spectrum, unfortunately. However, this does not prevent them from remaining excellent DM candidates, this only points towards the crucial need of developing much more complex detection strategies (multimessenger, multiwavelength, multiscale searches).

  16. Elastic and inelastic scattering of positrons in gases and solids

    NASA Technical Reports Server (NTRS)

    Mcgowan, J. W.

    1972-01-01

    Three apparatuses were designed and built: The first, which is now operative, was designed to study the details of positron thermalization in solids and the subsequent emission of the low energy positrons from moderating foils; The second apparatus now under test is a positron bottle similar in design to an electron trap. It was built to store positrons at a fixed energy and to look at the number of stored positrons (storage time) as a function of a scattering gas in the vacuum chamber. The third apparatus is a crossed beam apparatus where positron-, alkali scattering will be studied. Much of the apparatus is now under test with electrons.

  17. Analysis of positron annihilation lifetime data by numerical laplace inversion with the program CONTIN

    NASA Astrophysics Data System (ADS)

    Gregory, Roger B.; Zhu, Yongkang

    1990-05-01

    The performance of the program CONTIN [Stephen W. Provencher, Comput. Phys. Commun. 27 (1982) 229], modified to solve Fredholm integral equations with convoluted kernels of the type that occur in the deconvolution and analysis of positron annihilation lifetime data, is investigated with computer-simulated test data. The method avoids direct determination of the instrument resolution function by employing the decay curve of a reference material with a well-known single lifetime. CONTIN employs a constrained, regularized least-squares analysis to calculate a continuous annihilation-rate probability density function (pdf) which is the most parsimonious solution that is consistent with the experimental data and prior knowledge. The performance of the algorithm for extracting positron annihilation lifetime information was evaluated by using several measures of the information content of the data described by Schrader and Usmar [in: Positron Annihilation Studies of Fluids, ed. S. Sharma (World Scientific, Singapore, 1988) p. 215]. The quality of the CONTIN reconstruction of the annihilation-rate pdf is strongly dependent on the information content of the data and is greatly improved as the total number of counts in the data set is increased. Nevertheless, the method provides excellent estimates of the intensities and mean lifetimes of peaks in the annihilation-rate pdf, even when the total counts in the data set are relatively low (10 5-10 6). The sensitivity of the algorithm to systematic errors in the data, including errors in the instrument resolution function, shifts in the positron of the zero-time channel of the sample and reference data and contamination of the reference decay by additional lifetime components was also evaluated. Errors in the FWHM of the instrument resolution function and shifts in the zero time channel as small as {1}/{10}to{1}/{5} of the channel width of the instrument generate additional spurious peaks in the annihilation-rate pdf and

  18. Evidence of Positron Annihilation at Electronic Excitation Threshold for N2 ^*

    NASA Astrophysics Data System (ADS)

    Miller, E. G.; Edwards, J. J.; Kauppila, W. E.; Stein, T. S.; Surdutovich, E.

    2006-05-01

    We are investigating Positronium (Ps) formation for < 20 eV positrons interacting with N2 in a gas scattering cell. The technique [1] of Ps annihilation ratio spectroscopy (PsARS) is used to obtain the ratios of coincidence signals for two of the three gamma rays (S3γ) in the photon energy window 300 to 460 keV resulting from ortho-Ps decay to that for two 511 keV gamma rays (S2γ) arising from para-Ps decay and other processes. By comparing these ratios of S3 γ/S2γ for N2 to those for Ar it is found that N2 exhibits strikingly anomalous behavior near and below the Ps formation threshold. Typically, this ratio remains constant within 2 eV above the Ps threshold. For N2, this ratio decreases to zero at the threshold and an S2 γ signal remains for an energy of ˜0.3 eV below. Since N2 has an electronic excitation threshold for positron impact that opens up at ˜0.3 eV below the Ps threshold, the present results strongly suggest that the incident positron is electronically exciting N2 and then binding to the excited N2 in a temporary resonance-like state from which the bound positron annihilates with a molecular electron. ^*Research supported by NSF Grant PHY 99-88093.[1] W.E. Kauppila, E.G. Miller, H. F.M. Mohamed, K. Pipinos, T. S. Stein, and E. Surdutovich, Phys. Rev. Lett. 93, 113401 (2004).

  19. Electron capture from solids by positrons

    SciTech Connect

    Howell, R.

    1987-08-01

    The capture of electrons in solids is modified from that in gasses by several factors. The most important is the collective interaction of the electrons which results in a density of electron states in the solid in wide bands. Also the high density of electrons in many solids gives a high frequency of interaction as compared to gasses, and quickly destroys any electron-positron states in the metal matrix. Consequently, most positrons implanted in a metal will rapidly thermalize, and unless they reach the surface will annihilate with an electron in an uncorrelated state. Positronium formation from positrons scattered at a metal surface is analogous to ion neutralization however, most of the positronium comes from positrons passing through the surface from the bulk. The dominant motivation for studying positronium formation has been the hope that the distribution of the electrons at the surface would be obtained through the annihilation properties of positrons trapped at the surface or through analysis of the energy and angular distributions of the positronium emitted into the vacuum. These distributions have been measured and are included in this paper. 17 refs.

  20. Cosmic ray electron and positron excesses from a fourth generation heavy Majorana neutrino

    SciTech Connect

    Masina, Isabella; Sannino, Francesco E-mail: sannino@cp3-origins.net

    2011-08-01

    Unexpected features in the energy spectra of cosmic rays electrons and positrons have been recently observed by PAMELA and Fermi-LAT satellite experiments, opening to the exciting possibility of an indirect manifestation of new physics. A TeV-scale fourth lepton family is a natural extension of the Standard Model leptonic sector (also linked to the hierarchy problem in Minimal Walking Technicolor models). The heavy Majorana neutrino of this setup mixes with Standard Model charged leptons through a weak charged current interaction. Here, we first study analytically the energy spectrum of the electrons and positrons originated in the heavy Majorana neutrino decay modes, also including polarization effects. We then compare the prediction of this model with the experimental data, exploiting both the standard direct method and our recently proposed Sum Rules method. We find that the decay modes involving the tau and/or the muon charged leptons as primary decay products fit well the PAMELA and Fermi-LAT lepton excesses while there is tension with respect to the antiproton to proton fraction constrained by PAMELA.

  1. Unthermalized positrons in gamma ray burst sources

    NASA Technical Reports Server (NTRS)

    Tkaczyk, W.; Karakula, S.

    1992-01-01

    The spectra of the broadening 0.511 MeV annihilation line produced by high temperatures was calculated in the case of unthermalized plasma; i.e., T sub e(+) is not = T sub e(-). The flattening in the spectrum of the annihilation lines for large differences of electron and positron temperatures is a strong indication that the observed features of the hard tailed spectrum of the gamma bursts can be well described by annihilation of unthermalized positrons. It is proposed that the charge separation occurring in Eddington limited accretion onto a neutron star or the one photon pair production in strong magnetic fields as a mechanism for the production of unthermalized positrons in the sources of gamma bursts. From the best fit of experimental spectra by the model, the parameters of sources for which the regions with different plasma temperatures can exist is evaluated.

  2. Positron transport: The plasma-gas interface

    SciTech Connect

    Marler, J. P.; Petrovic, Z. Lj.; Bankovic, A.; Dujko, S.; Suvakov, M.; Malovic, G.; Buckman, S. J.

    2009-05-15

    Motivated by an increasing number of applications, new techniques in the analysis of electron transport have been developed over the past 30 years or so, but similar methods had yet to be applied to positrons. Recently, an in-depth look at positron transport in pure argon gas has been performed using a recently established comprehensive set of cross sections and well-established Monte Carlo simulations. The key novelty as compared to electron transport is the effect of positronium formation which changes the number of particles and has a strong energy dependence. This coupled with spatial separation by energy of the positron swarm leads to counterintuitive behavior of some of the transport coefficients. Finally new results in how the presence of an applied magnetic field affects the transport coefficients are presented.

  3. 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.

  4. Trapped positrons observed by PAMELA experiment

    NASA Astrophysics Data System (ADS)

    Mikhailov, V. V.; Adriani, O.; Barbarino, G.; Bazilevskaya, G. A.; Bellotti, R.; Boezio, M.; Bogomolov, E. A.; Bongi, M.; Bonvicini, V.; Bottai, S.; Bruno, A.; Cafagna, F. S.; Campana, D.; Carbone, R.; Carlson, P.; Casolino, M.; Castellini, G.; Consiglio, L.; De Santis, C.; De Simone, N.; Di Felice, V.; Galper, A. M.; Karelin, A. V.; Koldashov, S. V.; Koldobsky, S.; Krutkov, S. Yu; Kvashnin, A. N.; Leonov, A. A.; Malakhov, V. V.; Marcelli, L.; Martucci, M.; Mayorov, A. G.; Menn, W.; Merge, M.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Papini, P.; Palma, F.; Panico, B.; Pearce, M.; Picozza, P.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Yu I.; Vacchi, A.; Vannuccini, E.; Vasiliev, G. I.; Voronov, S. A.; Yurkin, Yu T.; Zampa, G.; Zampa, N.

    2016-02-01

    Measurements of electron and positron spatial distributions in energy range from 80 MeV to several GeV below the geomagnetic cutoff rigidity were carried out using the PAMELA magnetic spectrometer. The instrument is installed on board the Resurs-DK satellite which was launched June 15th 2006 on an elliptical orbit with the inclination 70 degrees and the altitude 350-600 km. The procedure of trajectories calculations in the geomagnetic filed gives a way to separate stably trapped and short lived albedo components produced in interactions of cosmic ray protons with the residual atmosphere. The work presents spatial distributions of trapped, quasitrapped and short-lived albedo electrons and positrons in the near Earth space. Electron to positron ratio points out on different production mechanism of trapped and quasitrapped particles.

  5. Positron annihilation in solid and liquid Ni

    SciTech Connect

    Fluss, M.J.; Smedskjaer, L.C.; Chakraborty, B.; Chason, M.K.

    1982-03-01

    New techniques have been developed for the study of metals via positron annihilation which provide for the in-situ melting of the samples and subsequent measurements via Doppler broadening of positron-annihilation radiation. Here we report these metods currently in use at our laboratory; ion implantation of /sup 58/Co and the use of Al/sub 2/O/sub 3/ crucibles for in-situ melting followed by the decomposition of the Doppler-broadened spectrum into a parabolic and a Gaussian component. Our earliest results obtained for pure Ni in the polycrystalline solid and in the liquid state are compared. An interesting similarity is reported for the distributions of the high-momentum (Gaussian) component for positrons annihilating in vacancies at high temperatures and those annihilating in liquid Ni.

  6. Positron states and annihilation characteristics of surface-trapped positrons at the oxidized Cu(110) surface

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    The process by which oxide layers are formed on metal surfaces is still not well understood. In this work we present the results of theoretical studies of positron states and annihilation characteristics of surface-trapped positrons at the oxidized Cu(110) surface. An ab-initio investigation of stability and associated electronic properties of different adsorption phases of oxygen on Cu(110) has been performed on the basis of density functional theory and using DMOl3 code. The changes in the positron work function and the surface dipole moment when oxygen atoms occupy on-surface and sub-surface sites have been attributed to charge redistribution within the first two layers, buckling effects within each layer and interlayer expansion. The computed positron binding energy, positron surface state wave function, and annihilation probabilities of surface trapped positrons with relevant core electrons demonstrate their sensitivity to oxygen coverage, elemental content, atomic structure of the topmost layers of surfaces, and charge transfer effects. Theoretical results are compared with experimental data obtained from studies of oxidized transition metal surfaces using positron annihilation induced Auger electron spectroscopy. This work was supported in part by the National Science Foundation Grant DMR-0907679.

  7. Nonlinear excitations for the positron acoustic shock waves in dissipative nonextensive electron-positron-ion plasmas

    NASA Astrophysics Data System (ADS)

    Saha, Asit

    2017-03-01

    Positron acoustic shock waves (PASHWs) in unmagnetized electron-positron-ion (e-p-i) plasmas consisting of mobile cold positrons, immobile positive ions, q-nonextensive distributed electrons, and hot positrons are studied. The cold positron kinematic viscosity is considered and the reductive perturbation technique is used to derive the Burgers equation. Applying traveling wave transformation, the Burgers equation is transformed to a one dimensional dynamical system. All possible vector fields corresponding to the dynamical system are presented. We have analyzed the dynamical system with the help of potential energy, which helps to identify the stability and instability of the equilibrium points. It is found that the viscous force acting on cold mobile positron fluid is a source of dissipation and is responsible for the formation of the PASHWs. Furthermore, fully nonlinear arbitrary amplitude positron acoustic waves are also studied applying the theory of planar dynamical systems. It is also observed that the fundamental features of the small amplitude and arbitrary amplitude PASHWs are significantly affected by the effect of the physical parameters q e , q h , μ e , μ h , σ , η , and U. This work can be useful to understand the qualitative changes in the dynamics of nonlinear small amplitude and fully nonlinear arbitrary amplitude PASHWs in solar wind, ionosphere, lower part of magnetosphere, and auroral acceleration regions.

  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. Monoenergetic positron beam at the reactor based positron source at FRM-II

    NASA Astrophysics Data System (ADS)

    Hugenschmidt, C.; Kögel, G.; Repper, R.; Schreckenbach, K.; Sperr, P.; Straßer, B.; Triftshäuser, W.

    2002-05-01

    The principle of the in-pile positron source at the Munich research reactor FRM-II is based on absorption of high energy prompt γ-rays from thermal neutron capture in 113Cd. For this purpose, a cadmium cap is placed inside the tip of the inclined beam tube SR-11 in the moderator tank of the reactor, where an undisturbed thermal neutron flux up to 2×10 14n cm-2 s-1 is expected. Inside the cadmium cap a structure of platinum foils is placed for converting high energy γ-radiation into positron-electron pairs. Due to the negative positron work function, moderation in annealed platinum leads to emission of monoenergetic positrons. Therefore, platinum will also be used as moderator, since its moderation property seems to yield long-term stability under reactor conditions and it is much easier to handle than tungsten. Model calculations were performed with SIMION-7.0w to optimise geometry and potential of Pt-foils and electrical lenses. It could be shown that the potentials between the Pt-foils must be chosen in the range of 1-10 V to extract moderated positrons. After successive acceleration to 5 keV by four electrical lenses the beam is magnetically guided in a solenoid field of 7.5 mT resulting in a beam diameter of about 25 mm. An intensity of about 10 10 slow positrons per second is expected in the primary positron beam. Outside of the reactor shield a W(1 0 0) single crystal remoderation stage will lead to an improvement of the positron beam brilliance before the positrons are guided to the experimental facilities.

  10. 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.

  11. NLC Positron Target Heating(LCC-0065)

    SciTech Connect

    Schultz, D

    2003-10-07

    The NLC requires an intense beam with a large number of positrons. These positrons are produced by a high energy electron beam impinging on a solid tungsten-rhenium alloy target. The particle shower that develops in the solid target deposits significant energy in the material, leading to target stresses and potentially to target damage. The stresses can be analyzed once the magnitude and extent of the energy deposition is known. This note details the modeling of the energy deposition using EGS, performed for the NLC and the SLC targets and for possible NLC targets made of copper or nickel instead of WRe.

  12. Preferential positron heating and acceleration by synchrotron maser instabilities in relativistic positron-electron-proton plasmas

    NASA Technical Reports Server (NTRS)

    Hoshino, Masahiro; Arons, Jonathan

    1991-01-01

    A new process of the preferential strong heating of positrons through the ion synchrotron maser instability in positron-electron-proton magnetized plasmas is investigated using particle-in-cell simulations. It is shown that the positrons form a nonthermal power-law-like energy distribution via their gyroresonant interaction with the extraordinary modes emitted by the ions. It is noted that this process may be of significance in connection with the shock excitation of nonthermal synchrotron radiation from astrophysical systems powered by relativistic outflows from compact central objects, e.g., supernova remnants powered by pulsars and jets from active galactic nuclei.

  13. Role of vibrational dynamics in resonant positron annihilation on molecules.

    PubMed

    Jones, A C L; Danielson, J R; Natisin, M R; Surko, C M

    2013-05-31

    Vibrational Feshbach resonances are dominant features of positron annihilation for incident positron energies in the range of the molecular vibrations. Studies in relatively small molecules are described that elucidate the role of intramolecular vibrational energy redistribution into near-resonant multimode states, and the subsequent coupling of these modes to the positron continuum, in suppressing or enhancing these resonances. The implications for annihilation in other molecular species, and the necessary ingredients of a more complete theory of resonant positron annihilation, are discussed.

  14. Positron studies of metal-oxide-semiconductor structures

    SciTech Connect

    Au, H.L.; Asoka-Kumar, P.; Nielsen, B.; Lynn, K.G. )

    1993-03-15

    Positron annihilation spectroscopy provides a new probe to study the properties of interface traps in metal-oxide semiconductors (MOS). Using positrons, we have examined the behavior of the interface traps as a function of gate bias. We propose a simple model to explain the positron annihilation spectra from the interface region of a MOS capacitor.

  15. Physics perspectives at JLab with a polarized positron beam

    SciTech Connect

    Voutier, Eric J.-M.

    2014-06-01

    Polarized positron beams are in some respect mandatory complements to polarized electron beams. The advent of the PEPPo concept for polarized positron production opens the possibility for the developement at the Jefferson Laboratory of a continuous polarized positron beam. The benefits of such a beam for hadronic structure studies are discussed, together with the technical and technological challenges to face.

  16. Positron emission tomography - a new approach to brain chemistry

    SciTech Connect

    Jacobson, H.G.

    1988-11-11

    Positron emission tomography permits examination of the chemistry of the brain in living beings. Until recently, positron emission tomography had been considered a research tool, but it is rapidly moving into clinical practice. This report describes the uses and applications of positron emission tomography in examinations of patients with strokes, epilepsy, malignancies, dementias, and schizophrenia and in basic studies of synaptic neurotransmission.

  17. The multilayer Fe/Hf studied with slow positron beam

    NASA Astrophysics Data System (ADS)

    Murashige, Y.; Tashiro, M.; Nakajyo, T.; Koizumi, T.; Kanazawa, I.; Komori, F.; Ito, Y.

    1997-04-01

    The positron annihilation parameter versus the incident positron energy is measured in the thin Fe films and the Fe/Hf bilayer on silica substrate, by means of the variable energetic slow-positron beam technique. We have analyzed the change in open-volume spaces and vacancy-type defects among the Fe microcrystals in these thin films with the deposition temperature.

  18. Baryonic B Decays

    NASA Astrophysics Data System (ADS)

    Chistov, R.

    2016-02-01

    In this talk the decays of B-mesons into baryons are discussed. Large mass of B-meson makes possible the decays of the type B → baryon (+mesons). Experimental observations and measurements of these decays at B-factories Belle and BaBar have stimulate the development of theoretical models in this field. We briefly review the experimental results together with the current theoretical models which describe baryonic B decays.

  19. Propagation of solitary waves in relativistic electron-positron-ion plasmas with kappa distributed electrons and positrons

    SciTech Connect

    Shah, Asif; Mahmood, S.; Haque, Q.

    2011-11-15

    Electrostatic ion acoustic solitary waves are studied in a plasma system comprising of relativistic ions, kappa distributed electrons, and positrons. The increase in the relativistic streaming factor and positron and electron kappa parameters cause the soliton amplitude to thrive. However, the soliton amplitude diminishes as the positron concentration is increased in the system. Our results are general and may be helpful, in understanding nonlinear phenomena in the presence of kappa distibuted electrons, positrons, and relativistically streaming ions.

  20. Positron Interactions with Atoms and Ions

    NASA Technical Reports Server (NTRS)

    Bhatia, Anand K.

    2012-01-01

    Dirac, in 1928, combining the ideas of quantum mechanics and the ideas of relativity invented the well-known relativistic wave equation. In his formulation, he predicted an antiparticle of the electron of spin n-bar/2. He thought that this particle must be a proton. Dirac published his interpretation in a paper 'A theory of electrons and protons.' It was shown later by the mathematician Hermann Weyl that the Dirac theory was completely symmetric between negative and positive particles and the positive particle must have the same mass as that of the electron. In his J. Robert Oppenheimer Memorial Prize Acceptance Speech, Dirac notes that 'Blackett was really the first person to obtain hard evidence for the existence of a positron but he was afraid to publish it. He wanted confirmation, he was really over cautious.' Positron, produced by the collision of cosmic rays in a cloud chamber, was detected experimentally by Anderson in 1932. His paper was published in Physical Review in 1933. The concept of the positron and its detection were the important discoveries of the 20th century. I have tried to discuss various processes involving interactions of positrons with atoms and ions. This includes scattering, bound states and resonances. It has not been possible to include the enormous work which has been carried out during the last 40 or 50 years in theory and measurements.

  1. Positron elastic scattering from alkaline earth targets

    NASA Astrophysics Data System (ADS)

    Poveda, Luis A.; Assafrão, Denise; Mohallem, José R.

    2016-07-01

    A previously reported model potential approach [Poveda et al., Phys. Rev. A 87, 052702 (2013)] was extended to study low energy positron elastic scattering from beryllium and magnesium. The cross sections were computed for energies ranging from 10-5 eV up to well above the positronium formation threshold. The present results are in good agreement with previous reports, including the prediction of a p-wave resonance in the cross section for magnesium. The emergence of this shape resonance is connected to a trend observed in the evolution of the partial wave cross section in going from Be to Mg target. This trend lead us to speculate that a sharp d-wave resonance should be observed in positron elastic scattering from calcium. The positron-target binding energies are investigated in detail, both using the scattering information and by direct computation of the bound state energies using the model potentials. Contribution to the Topical Issue "Advances in Positron and Electron Scattering", edited by Paulo Limao-Vieira, Gustavo Garcia, E. Krishnakumar, James Sullivan, Hajime Tanuma and Zoran Petrovic.Supplementary material in the form of one pdf file available from the Journal web page at http://dx.doi.org/10.1140/epjd/e2016-70120-y

  2. Resonances in Positron-molecule Interactions

    NASA Astrophysics Data System (ADS)

    Surko, C. M.

    2006-05-01

    The development of cold, trap-based beams has enabled high-resolution, energy-resolved studies of positron scattering and annihilation processes [1]. This talk focuses on three topics in this area. For hydrocarbon molecules such as alkanes (CnH2n+2), giant enhancements in annihilation rates are observed due to vibrational Feshbach resonances. The dependence of the rates on positron energy provides evidence that positrons bind to these molecules and a measure of the binding energies [1]. Recent results include evidence for a second, ``positronically excited'' bound state and new data for the methane series, CH3X, where X is a halogen. Other ``resonance-like features'' are sharp increases in the near-threshold electronic excitation cross sections for CO and N2 [2], and in the vibrational excitation cross sections for CO, CO2 and CH4 [3, 4]. Outstanding questions and the relationship of these observations to available theoretical predictions will be discussed.1. C. M. Surko, G. F. Gribakin, and S. J. Buckman, J. Phys. B 38, R57 (2005).2. J. P. Marler and C. M. Surko, Phys. Rev. A 72, 062713 (2005).3. J. P. Marler and C. M. Surko, Phys. Rev. A 72, 062702 (2005).4. J. P. Marler, G. F. Gribakin and C. M. Surko, Nuclear Instrum. and Meth. B, in press (2006).

  3. Positrons observed to originate from thunderstorms

    NASA Astrophysics Data System (ADS)

    Fishman, Gerald J.

    2011-05-01

    Thunderstorms are the result of warm, moist air moving rapidly upward, then cooling and condensing. Electrification occurs within thunderstorms (as noted by Benjamin Franklin), produced primarily by frictional processes among ice particles. This leads to lightning discharges; the types, intensities, and rates of these discharges vary greatly among thunderstorms. Even though scientists have been studying lightning since Franklin's time, new phenomena associated with thunderstorms are still being discovered. In particular, a recent finding by Briggs et al. [2011], based on observations by the Gamma-Ray Burst Monitor (GBM) instrument on NASA's satellite-based Fermi Gamma-ray Space Telescope (Fermi), shows that positrons are also generated by thunderstorms. Positrons are the antimatter form of electrons—they have the same mass and charge as an electron but are of positive rather than negative charge; hence the name positron. Observations of positrons from thunderstorms may lead to a new tool for understanding the electrification and high-energy processes occurring within thunderstorms. New theories, along with new observational techniques, are rapidly evolving in this field.

  4. 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.

  5. Excitation of helium ion by positron impact

    SciTech Connect

    Khan, P.; Ghosh, A.S.

    1986-01-01

    Three (1s,2s,2p) and five (1s,2s,2p,3s-bar,3p-bar) -state close-coupling methods have been employed to calculate the n = 2 excitation cross sections of helium ion by positron impact. The effect of pseudostate is found to be very pronounced in the case of 1s-2s excitation.

  6. Progress Towards a Practical Multicell Positron Trap

    NASA Astrophysics Data System (ADS)

    Danielson, J. R.

    2013-10-01

    The physics and technology of positron confinement is central to a range of applications at the forefront of antimatter science. Progress in this area has been driven by the development of a suite of novel non-neutral plasma techniques whereby up to 4 ×109 positrons have now been trapped and stored. However the next generation of experiments will require orders of magnitude more positrons. This talk describes techniques to increase storage capacity to >=1012 using a novel multi-cell trap architecture. Plasmas will be stored in separate Penning-Malmberg traps (``cells'') arranged in parallel off the magnetic axis to maximize use of the magnetic field volume while minimizing the required confinement voltages. Experiments with electrons in a test structure will be described to explore the basic physics and technology of the multicell concept and to set the design of a 21-cell trap for 1012 positrons. Over 50% of a trapped plasma has been injected into an off-axis cell, and hour-long confinement of 2 ×108 particles has been achieved using rotating electric fields. Experiments are under way to identify the limits of the injection process and demonstrate confinement >1010 particles in a single off-axis cell using kilovolt confinement potentials. In collaboration with N. C. Hurst, C. J. Baker, and C. M. Surko. This work is supported by U.S. DTRA and the U.S. DOE/NSF plasma partnership.

  7. Positron Spectroscopy of Hydrothermally Grown Actinide Oxides

    DTIC Science & Technology

    2014-03-27

    In this method, the powdered material is placed in a solution which contains extremely powerful mineralizers, such as cesium fluoride for actinide...the isotope that acts as a positron source is sodium -22, which has a relatively short half-life (2.6 y) and emits a characteristic gamma photon (at

  8. Positron source position sensing detector and electronics

    DOEpatents

    Burnham, Charles A.; Bradshaw, Jr., John F.; Kaufman, David E.; Chesler, David A.; Brownell, Gordon L.

    1985-01-01

    A positron source, position sensing device, particularly with medical applications, in which positron induced gamma radiation is detected using a ring of stacked, individual scintillation crystals, a plurality of photodetectors, separated from the scintillation crystals by a light guide, and high resolution position interpolation electronics. Preferably the scintillation crystals are several times more numerous than the photodetectors with each crystal being responsible for a single scintillation event from a received gamma ray. The light guide will disperse the light emitted from gamma ray absorption over several photodetectors. Processing electronics for the output of the photodetectors resolves the location of the scintillation event to a fraction of the dimension of each photodetector. Because each positron absorption results in two 180.degree. oppositely traveling gamma rays, the detection of scintillation in pairs permits location of the positron source in a manner useful for diagnostic purposes. The processing electronics simultaneously responds to the outputs of the photodetectors to locate the scintillations to the source crystal. While it is preferable that the scintillation crystal include a plurality of stacked crystal elements, the resolving power of the processing electronics is also applicable to continuous crystal scintillators.

  9. Advanced Instrumentation for Positron Emission Tomography [PET

    DOE R&D Accomplishments Database

    Derenzo, S. E.; Budinger, T. F.

    1985-04-01

    This paper summarizes the physical processes and medical science goals that underlay modern instrumentation design for Positron Emission Tomography. The paper discusses design factors such as detector material, crystalphototube coupling, shielding geometry, sampling motion, electronics design, time-of-flight, and the interrelationships with quantitative accuracy, spatial resolution, temporal resolution, maximum data rates, and cost.

  10. Advanced instrumentation for Positron Emission Tomography

    SciTech Connect

    Derenzo, S.E.; Budinger, T.F.

    1985-04-01

    This paper summarizes the physical processes and medical science goals that underly modern instrumentation design for Positron Emission Tomography. The paper discusses design factors such as detector material, crystalphototube coupling, shielding geometry, sampling motion, electronics design, time-of-flight, and the interrelationships with quantitative accuracy, spatial resolution, temporal resolution, maximum data rates, and cost. 71 refs., 3 figs., 3 tabs.

  11. Double β-decay nuclear matrix elements for the A=48 and A=58 systems

    NASA Astrophysics Data System (ADS)

    Skouras, L. D.; Vergados, J. D.

    1983-11-01

    The nuclear matrix elements entering the double β decays of the 48Ca-48Ti and 58Ni-58Fe systems have been calculated using a realistic two nucleon interaction and realistic shell model spaces. Effective transition operators corresponding to a variety of gauge theory models have been considered. The stability of such matrix elements against variations of the nuclear parameters is examined. Appropriate lepton violating parameters are extracted from the A=48 data and predictions are made for the lifetimes of the positron decays of the A=58 system. RADIOACTIVITY Double β decay. Gauge theories. Lepton nonconservation. Neutrino mass. Shell model calculations.

  12. Constraints on decaying dark matter from Fermi observations of nearby galaxies and clusters

    SciTech Connect

    Dugger, Leanna; Profumo, Stefano; Jeltema, Tesla E. E-mail: tesla@ucolick.org

    2010-12-01

    We analyze the impact of Fermi gamma-ray observations (primarily non-detections) of selected nearby galaxies, including dwarf spheroidals, and of clusters of galaxies on decaying dark matter models. We show that the fact that galaxy clusters do not shine in gamma rays puts the most stringent limits available to-date on the lifetime of dark matter particles for a wide range of particle masses and decay final states. In particular, our results put strong constraints on the possibility of ascribing to decaying dark matter both the increasing positron fraction reported by PAMELA and the high-energy feature in the electron-positron spectrum measured by Fermi. Observations of nearby dwarf galaxies and of the Andromeda Galaxy (M31) do not provide as strong limits as those from galaxy clusters, while still improving on previous constraints in some cases.

  13. Positron and positronium interactions with Cu

    SciTech Connect

    Bromley, M.W.J.; Mitroy, J.

    2002-12-01

    The configuration-interaction (CI) method is used to investigate the interactions of positrons and positronium with copper at low energies. The calculations were performed within the framework of the fixed-core approximation with semiempirical polarization potentials used to model dynamical interactions between the active particles and the (1s-3d) core. Initially, calculations upon the e{sup +}Li system were used to refine the numerical procedures and highlighted the extreme difficulties of using an orthodox CI calculation to describe the e{sup +} Li system. The positron binding energy of e{sup +}Cu derived from a CI calculation which included electron and positron orbitals with l{<=}18 was 0.005 12 hartree while the spin-averaged annihilation rate was 0.507x10{sup 9} s{sup -1}. The configuration basis used for the bound-state calculation was also used as a part of the trial wave function for a Kohn variational calculation of positron-copper scattering. The positron-copper system has a scattering length of about 13.1a{sub 0} and the annihilation parameter Z{sub eff} at threshold was 72.9. The dipole polarizability of the neutral copper ground state was computed and found to be 41.6a{sub 0}{sup 3}. The structure of CuPs was also studied with the CI method and it was found to have a binding energy of 0.0143 hartree and an annihilation rate of {approx}2x10{sup 9} s{sup -1}.

  14. Positron annihilation studies of moisture in graphite-reinforced composites

    NASA Technical Reports Server (NTRS)

    Singh, J. J.; Holt, W. H.; Mock, W., Jr.; Buckingham, R. D.

    1980-01-01

    The positron lifetime technique of monitoring absorbed moisture is applied to several composites, including graphite/polymides which are candidates for high-temperature (over 260 C) applications. The experimental setup is a conventional fast-slow coincidence system wherein the positron lifetime is measured with respect to a reference time determined by the detection of a nuclear gamma ray emitted simultaneously with the positron. From the experiments, a rate of change of positron mean lifetime per unit mass of water can be determined for each type of specimen. Positron lifetime spectra are presented for a graphite/polyimide composite and for a pure polyimide.

  15. Relativistic Positron Creation Using Ultra-Intense Short Pulse Lasers

    SciTech Connect

    Chen, H; Wilks, S; Bonlie, J; Liang, E; Myatt, J; Price, D; Meyerhofer, D; Beiersdorfer, P

    2008-08-25

    We measure up to 2 x 10{sup 10} positrons per steradian ejected out the back of {approx}mm thick gold targets when illuminated with short ({approx} 1 ps) ultra-intense ({approx} 1 x 10{sup 20} W/cm{sup 2}) laser pulses. Positrons produced predominately by the Bethe-Heitler process and have an effective temperature of 2-4 MeV, with the distribution peaking at 4-7 MeV. The angular distribution of the positrons is anisotropic. The measurements indicate the laser produced, relativistic positron densities ({approx} 10{sup 16} positrons/cm{sup 3}) are the highest ever created in the laboratory.

  16. Relativistic Positron Creation Using Ultraintense Short Pulse Lasers

    SciTech Connect

    Chen Hui; Wilks, Scott C.; Bonlie, James D.; Price, Dwight F.; Beiersdorfer, Peter; Liang, Edison P.; Myatt, Jason; Meyerhofer, David D.

    2009-03-13

    We measure up to 2x10{sup 10} positrons per steradian ejected out the back of {approx}mm thick gold targets when illuminated with short ({approx}1 ps) ultraintense ({approx}1x10{sup 20} W/cm{sup 2}) laser pulses. Positrons are produced predominately by the Bethe-Heitler process and have an effective temperature of 2-4 MeV, with the distribution peaking at 4-7 MeV. The angular distribution of the positrons is anisotropic. Modeling based on the measurements indicate the positron density to be {approx}10{sup 16} positrons/cm{sup 3}, the highest ever created in the laboratory.

  17. First platinum moderated positron beam based on neutron capture

    NASA Astrophysics Data System (ADS)

    Hugenschmidt, C.; Kögel, G.; Repper, R.; Schreckenbach, K.; Sperr, P.; Triftshäuser, W.

    2002-12-01

    A positron beam based on absorption of high energy prompt γ-rays from thermal neutron capture in 113Cd was installed at a neutron guide of the high flux reactor at the ILL in Grenoble. Measurements were performed for various source geometries, dependent on converter mass, moderator surface and extraction voltages. The results lead to an optimised design of the in-pile positron source which will be implemented at the Munich research reactor FRM-II. The positron source consists of platinum foils acting as γ-e +e --converter and positron moderator. Due to the negative positron work function moderation in heated platinum leads to emission of monoenergetic positrons. The positron work function of polycrystalline platinum was determined to 1.95(5) eV. After acceleration to several keV by four electrical lenses the beam was magnetically guided in a solenoid field of 7.5 mT leading to a NaI-detector in order to detect the 511 keV γ-radiation of the annihilating positrons. The positron beam with a diameter of less than 20 mm yielded an intensity of 3.1×10 4 moderated positrons per second. The total moderation efficiency of the positron source was about ɛ=1.06(16)×10 -4. Within the first 20 h of operation a degradation of the moderation efficiency of 30% was observed. An annealing procedure at 873 K in air recovers the platinum moderator.

  18. On-ground detection of an electron-positron annihilation line from thunderclouds

    NASA Astrophysics Data System (ADS)

    Umemoto, D.; Tsuchiya, H.; Enoto, T.; Yamada, S.; Yuasa, T.; Kawaharada, M.; Kitaguchi, T.; Nakazawa, K.; Kokubun, M.; Kato, H.; Okano, M.; Tamagawa, T.; Makishima, K.

    2016-02-01

    Thunderclouds can produce bremsstrahlung gamma-ray emission, and sometimes even positrons. At 00:27:00 (UT) on 13 January 2012, an intense burst of gamma rays from a thundercloud was detected by the GROWTH experiment, located in Japan, facing the Sea of Japan. The event started with a sharp gamma-ray flash with a duration of <300 ms coincident with an intracloud discharge, followed by a decaying longer gamma-ray emission lasting for ˜60 s. The spectrum of this prolonged emission reached ˜10 MeV, and contained a distinct line emission at 508 ±3 (stat .)±5 (sys .) keV, to be identified with an electron-positron annihilation line. The line was narrow within the instrumental energy resolution (˜80 keV) , and contained 520 ±50 photons which amounted to ˜10 % of the total signal photons of 5340 ±190 detected over 0.1-10 MeV. As a result, the line equivalent width reached 280 ±40 keV, which implies a nontrivial result. The result suggests that a downward positron beam produced both the continuum and the line photons.

  19. On-ground detection of an electron-positron annihilation line from thunderclouds.

    PubMed

    Umemoto, D; Tsuchiya, H; Enoto, T; Yamada, S; Yuasa, T; Kawaharada, M; Kitaguchi, T; Nakazawa, K; Kokubun, M; Kato, H; Okano, M; Tamagawa, T; Makishima, K

    2016-02-01

    Thunderclouds can produce bremsstrahlung gamma-ray emission, and sometimes even positrons. At 00:27:00 (UT) on 13 January 2012, an intense burst of gamma rays from a thundercloud was detected by the GROWTH experiment, located in Japan, facing the Sea of Japan. The event started with a sharp gamma-ray flash with a duration of <300 ms coincident with an intracloud discharge, followed by a decaying longer gamma-ray emission lasting for ∼60 s. The spectrum of this prolonged emission reached ∼10 MeV, and contained a distinct line emission at 508±3(stat.)±5(sys.) keV, to be identified with an electron-positron annihilation line. The line was narrow within the instrumental energy resolution (∼80keV), and contained 520±50 photons which amounted to ∼10% of the total signal photons of 5340±190 detected over 0.1-10 MeV. As a result, the line equivalent width reached 280±40 keV, which implies a nontrivial result. The result suggests that a downward positron beam produced both the continuum and the line photons.

  20. Methods and apparatus for producing and storing positrons and protons

    DOEpatents

    Akers, Douglas W.

    2010-07-06

    Apparatus for producing and storing positrons may include a trap that defines an interior chamber therein and that contains an electric field and a magnetic field. The trap may further include a source material that includes atoms that, when activated by photon bombardment, become positron emitters to produce positrons. The trap may also include a moderator positioned adjacent the source material. A photon source is positioned adjacent the trap so that photons produced by the photon source bombard the source material to produce the positron emitters. Positrons from the positron emitters and moderated positrons from the moderator are confined within the interior chamber of the trap by the electric and magnetic fields. Apparatus for producing and storing protons are also disclosed.

  1. Optimization of positrons generation based on laser wakefield electron acceleration

    NASA Astrophysics Data System (ADS)

    Wu, Yuchi; Han, Dan; Zhang, Tiankui; Dong, Kegong; Zhu, Bin; Yan, Yonghong; Gu, Yuqiu

    2016-08-01

    Laser based positron represents a new particle source with short pulse duration and high charge density. Positron production based on laser wakefield electron acceleration (LWFA) has been investigated theoretically in this paper. Analytical expressions for positron spectra and yield have been obtained through a combination of LWFA and cascade shower theories. The maximum positron yield and corresponding converter thickness have been optimized as a function of driven laser power. Under the optimal condition, high energy (>100 MeV ) positron yield up to 5 ×1011 can be produced by high power femtosecond lasers at ELI-NP. The percentage of positrons shows that a quasineutral electron-positron jet can be generated by setting the converter thickness greater than 5 radiation lengths.

  2. Positron annihilation lifetime spectroscopy at a superconducting electron accelerator

    NASA Astrophysics Data System (ADS)

    Wagner, A.; Anwand, W.; Attallah, A. G.; Dornberg, G.; Elsayed, M.; Enke, D.; Hussein, A. E. M.; Krause-Rehberg, R.; Liedke, M. O.; Potzger, K.; Trinh, T. T.

    2017-01-01

    The Helmholtz-Zentrum Dresden-Rossendorf operates a superconducting linear accelerator for electrons with energies up to 35 MeV and average beam currents up to 1.6 mA. The electron beam is employed for production of several secondary beams including X-rays from bremsstrahlung production, neutrons, and positrons. The secondary positron beam after moderation feeds the Monoenergetic Positron Source (MePS) where positron annihilation lifetime (PALS) and positron annihilation Doppler-broadening experiments in materials science are performed in parallel. The adjustable repetition rate of the continuous-wave electron beams allows matching of the pulse separation to the positron lifetime in the sample under study. The energy of the positron beam can be set between 0.5 keV and 20 keV to perform depth resolved defect spectroscopy and porosity studies especially for thin films.

  3. High-yield positron systems for linear colliders

    SciTech Connect

    Clendenin, J.E.

    1989-04-01

    Linear colliders, such as the SLC, are among those accelerators for which a high-yield positron source operating at the repetition rate of the accelerator is desired. The SLC, having electron energies up to 50 GeV, presents the possibility of generating positron bunches with useful charge even exceeding that of the initial electron bunch. The exact positron yield to be obtained depends on the particular capture, transport and damping system employed. Using 31 GeV electrons impinging on a W-type converter phase-space at the target to the acceptance of the capture rf section, the SLC source is capable of producing, for every electron, up to two positrons within the acceptance of the positron damping ring. The design of this source and the performance of the positron system as built are described. Also, future prospects and limitations for high-yield positron systems are discussed. 11 refs., 5 figs., 3 tabs.

  4. Beta decay and the origins of biological chirality - Experimental results

    NASA Technical Reports Server (NTRS)

    Gidley, D. W.; Rich, A.; Van House, J.; Zitzewitz, P. W.

    1982-01-01

    Preliminary experimental results are presented of an investigation of the possible role of preferential radiolysis by electrons emitted in the beta decay of radionuclides, a parity-nonconserving process, in the universal causation of the optical activity of biological compounds. Experiments were designed to measure the asymmetry in the production of triplet positronium upon the bombardment of an amino acid powder target by a collimated beam of positrons as positron helicity or target chirality is reversed. No asymmetry down to a level of 0.0007 is found in experiments on the D and L forms of cystine and tryptophan, indicating an asymmetry in positronium formation cross section of less than 0.01, while an asymmetry of 0.0031 is found for leucine, corresponding to a formation cross section asymmetry of about 0.04

  5. Performance Characteristics of a Positron Projection Imager For Mouse Whole-body Imaging

    PubMed Central

    Seidel, Jurgen; Xi, Wenze; Kakareka, John W.; Pohida, Thomas J.; Jagoda, Elaine M.; Green, Michael V.; Choyke, Peter L.

    2013-01-01

    Introduction We describe a prototype positron projection imager (PPI) for visualizing the whole-body biodistribution of positron-emitting compounds in mouse-size animals. The final version of the PPI will be integrated into the MONICA portable dual-gamma camera system to allow the user to interchangeably image either single photon or positron-emitting compounds in a shared software and hardware environment. Methods A mouse is placed in the mid-plane between two identical, opposed, pixelated LYSO arrays separated by 21.8-cm and in time coincidence. An image of the distribution of positron decays in the animal is formed on this mid-plane by coincidence events that fall within a small cone angle to the perpendicular to the two detectors and within a user-specified energy window. We measured the imaging performance of this device with phantoms and in tests performed in mice injected with various compounds labeled with positron-emitting isotopes. Results Representative performance measurements yielded the following results (energy window 250–650 keV, cone angle 3.5-degrees): resolution in the image mid-plane, 1.66-mm (FWHM), resolution ±1.5-cm above and below the image plane, 2.2-mm (FWHM), sensitivity: 0.237-cps/kBq (8.76-cps/μCi) 18F (0.024% absolute). Energy resolution was 15.9% with a linear-count-rate operating range of 0–14.8 MBq (0–400 μCi) and a corrected sensitivity variation across the field-of-view of <3%. Whole-body distributions of [18F] FDG and [18F] fluoride were well visualized in mice of typical size. Conclusion Performance measurements and field studies indicate that the PPI is well suited to whole-body positron projection imaging of mice. When integrated into the MONICA gamma camera system, the PPI may be particularly useful early in the drug development cycle where, like MONICA, basic whole-body biodistribution data can direct future development of the agent under study and where logistical factors (e.g., available imaging space, non

  6. Addendum to Radiative corrections to the Dalitz plot of semileptonic decays of neutral baryons with light or charm quarks''

    SciTech Connect

    Martinez, A.; Tun, D.M.; Garcia, A.; Sanchez-Colon, G. Coordinacion de Dinamica Orbital, Telecomunicaciones de Mexico, Av. de las Telecomunicaciones s/n, C.P. 09300, Mexico, Distrito Federal Departamento de Fisica, Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional, Apartado Postal 14-740, C.P. 07000, Mexico, Distrito Federal )

    1994-08-01

    We show that the radiative corrections containing terms up to order [alpha][ital q]/[pi][ital M][sub 1] for unpolarized semileptonic decays of baryons with positron emission can be obtained by simply reversing the sign of the axial-vector form factors in the corresponding final expressions of such decays with electron emission. This rule is valid regardless of the final kinematical variables chosen and of the particular Lorentz frame in which the final results are required.

  7. Studies of discrete symmetries in a purely leptonic system using the Jagiellonian Positron Emission Tomograph

    NASA Astrophysics Data System (ADS)

    Moskal, P.; Alfs, D.; Bednarski, T.; Białas, P.; Curceanu, C.; Czerwiński, E.; Dulski, K.; Gajos, A.; Głowacz, B.; Gupta-Sharma, N.; Gorgol, M.; Hiesmayr, B. C.; Jasińska, B.; Kamińska, D.; Khreptak, O.; Korcyl, G.; Kowalski, P.; Krzemień, W.; Krawczyk, N.; Kubicz, E.; Mohammed, M.; Niedźwiecki, Sz.; Pawlik-Niedńwiecka, M.; Raczyński, L.; Rudy, Z.; Silarski, M.; Smyrski, J.; Wieczorek, A.; Wiślicki, W.; Zgardzińska, B.; Zieliński, M.

    2016-11-01

    Discrete symmetries such as parity (P), charge-conjugation (C) and time reversal (T) are of fundamental importance in physics and cosmology. Breaking of charge conjugation symmetry (C) and its combination with parity (CP) constitute necessary conditions for the existence of the asymmetry between matter and antimatter in the observed Universe. The presently known sources of discrete symmetries violations can account for only a tiny fraction of the excess of matter over antimatter. So far CP and T symmetries violations were observed only for systems involving quarks and they were never reported for the purely leptonic objects. In this article we describe briefly an experimental proposal for the test of discrete symmetries in the decays of positronium atom which is made exclusively of leptons. The experiments are conducted by means of the Jagiellonian Positron Emission Tomograph (J-PET) which is constructed from strips of plastic scintillators enabling registration of photons from the positronium annihilation. J-PET tomograph together with the positronium target system enable to measure expectation values for the discrete symmetries odd operators constructed from (i) spin vector of the ortho-positronium atom, (ii) momentum vectors of photons originating from the decay of positronium, and (iii) linear polarization direction of annihilation photons. Linearly polarized positronium will be produced in the highly porous aerogel or polymer targets, exploiting longitudinally polarized positrons emitted by the sodium 22Na isotope. Information about the polarization vector of orthopositronium will be available on the event by event basis and will be reconstructed from the known position of the positron source and the reconstructed position of the orthopositronium annihilation. In 2016 the first tests and calibration runs are planned, and the data collection with high statistics will commence in the year 2017.

  8. 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.

  9. Experimental study of a crystal positron source

    NASA Astrophysics Data System (ADS)

    Chehab, R.; Cizeron, R.; Sylvia, C.; Baier, V.; Beloborodov, K.; Bukin, A.; Burdin, S.; Dimova, T.; Drozdetsky, A.; Druzhinin, V.; Dubrovin, M.; Golubev, V.; Serednyakov, S.; Shary, V.; Strakhovenko, V.; Artru, X.; Chevallier, M.; Dauvergne, D.; Kirsch, R.; Lautesse, Ph.; Poizat, J.-C.; Remillieux, J.; Jejcic, A.; Keppler, P.; Major, J.; Gatignon, L.; Bochek, G.; Kulibaba, V.; Maslov, N.; Bogdanov, A.; Potylitsin, A.; Vnukov, I.

    2002-01-01

    Tungsten crystals oriented on their <111> axis, were submitted to 6 and 10 GeV electron beams on the SPS-CERN transfer lines. The crystals, 4 and 8 mm thick, used alone or associated to 4 mm thick amorphous disk, were studied as positron sources. The emerging positrons were detected by a Drift Chamber partially immersed in a magnetic field, where their trajectories were reconstructed providing the energy spectrum and the angular distribution. Significant enhancements were observed for the crystal source when compared to the amorphous one of the same thickness. The gain was larger than 3 and 2 for the 4 mm and 8 mm targets, respectively. The presented results look very promising for e+e- linear colliders.

  10. Positron Emission Tomography Imaging of Hypoxia

    PubMed Central

    Lapi, Suzanne E.; Voller, Thomas F.; Welch, Michael J.

    2009-01-01

    Synopsis Hypoxia imaging has applications in functional recovery in ischemic events such as stroke and myocardial ischemia, but especially in tumors in which hypoxia can be predictive of treatment response and overall prognosis. Recently there has been development of imaging agents utilizing positron emission tomography for non-invasive imaging of hypoxia. Many of these PET agents have come to the forefront of hypoxia imaging. Halogenated PET nitroimidazole imaging agents labeled with 18F (t1/2 = 110 m) and 124I (t1/2 = 110 m) have been under investigation for the last 25 years, with radiometal agents (64Cu-ATSM) being developed more recently. This review focuses on these positron emission tomography imaging agents for hypoxia. PMID:20046923

  11. 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.

  12. Positron spectroscopy of 2D materials using an advanced high intensity positron beam

    NASA Astrophysics Data System (ADS)

    McDonald, A.; Chirayath, V.; Lim, Z.; Gladen, R.; Chrysler, M.; Fairchild, A.; Koymen, A.; Weiss, A.

    An advanced high intensity variable energy positron beam(~1eV to 20keV) has been designed, tested and utilized for the first coincidence Doppler broadening (CDB) measurements on 6-8 layers graphene on polycrystalline Cu sample. The system is capable of simultaneous Positron annihilation induced Auger electron Spectroscopy (PAES) and CDB measurements giving it unparalleled sensitivity to chemical structure at external surfaces, interfaces and internal pore surfaces. The system has a 3m flight path up to a micro channel plate (MCP) for the Auger electrons emitted from the sample. This gives a superior energy resolution for PAES. A solid rare gas(Neon) moderator was used for the generation of the monoenergetic positron beam. The positrons were successfully transported to the sample chamber using axial magnetic field generated with a series of Helmholtz coils. We will discuss the PAES and coincidence Doppler broadening measurements on graphene -Cu sample and present an analysis of the gamma spectra which indicates that a fraction of the positrons implanted at energies 7-60eV can become trapped at the graphene/metal interface. This work was supported by NSF Grant No. DMR 1508719 and DMR 1338130.

  13. Dipole configuration for confinement of positrons and electron-positron plasma

    NASA Astrophysics Data System (ADS)

    Stenson, E. V.; Saitoh, H.; Horn-Stanja, J.; Hergenhahn, U.; Paschkowski, N.; Sunn Pedersen, T.; Stoneking, M. R.; Dickmann, M.; Singer, M.; Vohburger, S.; Hugenschmidt, C.; Schweikhard, L.; Danielson, J. R.; Surko, C. M.

    2016-10-01

    Laboratory creation and confinement of electron-positron plasmas, which are expected to exhibit atypical plasma physics characteristics, would enable tests of many theory and simulation predictions (e.g., the stabilization of anomalous transport mechanisms). This is the goal of APEX/PAX (A Positron-Electron eXperiment/Positron Accumulation eXperiment). Following demonstration of efficient (38%) E ×B injection and subsequent confinement (τ = 3-5 ms) of cold positrons in a dipole magnetic field, the system is undergoing upgrades from a supported permanent magnet to a supported HTSC (high-temperature superconductor) coil, then to a levitated HTSC coil suitable for the simultaneous confinement of electrons and positrons. This contribution will report on the design and testing of the new systems and subsystems (e.g., for cooling, excitation, and levitation) and, if available, on results of upcoming experiments using a ``rotating wall'' to generate inward particle flux deeper into the confinement region. on behalf of the APEX/PAX team and collaborators.

  14. Positrons for Antihydrogen with ATRAP: efficient transfer of large positron numbers

    NASA Astrophysics Data System (ADS)

    Storry, Cody; Comeau, Daniel; Dror, Asaf; Fitzakerley, Daniel; George, Matthew; Hessels, Eric; Weel, Matthew

    2012-06-01

    Positrons accumulated in a room-temperature buffer-gas-cooled positron accumulator are efficiently transferred into a superconducting solenoid which houses the ATRAP cryogenic Penning trap for antihydrogen research. The positrons are guided along a 9-meter-long magnetic guide which connects the central field lines of the 0.15-tesla field in the positron accumulator to central magnetic field lines of the superconducting solenoid. Seventy independently-controllable electromagnets are required to overcome the fringing field of the large-bore superconducting solenoid. The guide includes both a 15 degree upward bend and a 105 degree downward bend to account for the orthogonal orientation of the accumulator with respect to the cryogenic Penning trap. Low-energy positrons ejected from the accumulator follow the magnetic field lines within the guide and are transferred into the superconducting solenoid with nearly 100% efficiency. 7 meters of 5-cm-diameter stainless-steel tube, and a 20-mm-long, 1.5-mm-diameter cryogenic pumping restriction ensure that the 10-2 mbar pressure in the accumulator is well isolated from the extreme vacuum required in the Penning trap to allow long antimatter storage times.

  15. Positron-inert gas differential elastic scattering

    NASA Technical Reports Server (NTRS)

    Kauppila, W. E.; Smith, Steven J.; Kwan, C. K.; Stein, T. S.

    1990-01-01

    Measurements are being made in a crossed beam experiment of the relative elastic differential cross section (DCS) for 5 to 300 eV positrons scattering from inert gas atoms (He, Ne, Ar, Kr, and Xe) in the angular range from 30 to 134 deg. Results obtained at energies around the positronium (Ps) formation threshold provide evidence that Ps formation and possibly other inelastic channels have an effect on the elastic scattering channel.

  16. Imaging Prostate Cancer with Positron Emission Tomography

    DTIC Science & Technology

    2014-07-01

    AD_________________ Award Number: W81XWH-13-1-0125 TITLE: Imaging Prostate Cancer with Positron Emission Tomography...ABOVE ADDRESS. 1. REPORT DATE 2014 2. REPORT TYPE Annual 3. DATES COVERED 01 Sept 2013-31 Aug 2014 4. TITLE AND SUBTITLE Imaging Prostate Cancer ...proposal is to develop peptide based radiopharmaceuticals and evaluate them as PET imaging agents in preclinical animal models of prostate cancer

  17. Positron studies of defected metals, metallic surfaces

    SciTech Connect

    Bansil, A.

    1991-01-01

    Specific problems proposed under this project included the treatment of electronic structure and momentum density in various disordered and defected systems. Since 1987, when the new high-temperature superconductors were discovered, the project focused extensively on questions concerning the electronic structure and Fermiology of high-[Tc] superconductors, in particular, (i) momentum density and positron experiments, (ii) angle-resolved photoemission intensities, (iii) effects of disorder and substitutions in the high-[Tc]'s.

  18. Cosmic-ray Positrons from Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Venter, C.; Kopp, A.; Harding, A. K.; Gonthier, P. L.; Büsching, I.

    2015-07-01

    Observations by the Fermi Large Area Telescope of γ-ray millisecond pulsar (MSP) light curves imply copious pair production in their magnetospheres, and not exclusively in those of younger pulsars. Such pair cascades may be a primary source of Galactic electrons and positrons, contributing to the observed enhancement in positron flux above ∼10 GeV. Fermi has also uncovered many new MSPs, impacting Galactic stellar population models. We investigate the contribution of Galactic MSPs to the flux of terrestrial cosmic-ray electrons and positrons. Our population synthesis code predicts the source properties of present-day MSPs. We simulate their pair spectra invoking an offset-dipole magnetic field. We also consider positrons and electrons that have been further accelerated to energies of several TeV by strong intrabinary shocks in black widow (BW) and redback (RB) systems. Since MSPs are not surrounded by pulsar wind nebulae or supernova shells, we assume that the pairs freely escape and undergo losses only in the intergalactic medium. We compute the transported pair spectra at Earth, following their diffusion and energy loss through the Galaxy. The predicted particle flux increases for non-zero offsets of the magnetic polar caps. Pair cascades from the magnetospheres of MSPs are only modest contributors around a few tens of GeV to the lepton fluxes measured by the Alpha Magnetic Spectrometer, PAMELA, and Fermi, after which this component cuts off. The contribution by BWs and RBs may, however, reach levels of a few tens of percent at tens of TeV, depending on model parameters.

  19. COSMIC-RAY POSITRONS FROM MILLISECOND PULSARS

    SciTech Connect

    Venter, C.; Kopp, A.; Büsching, I.; Harding, A. K.; Gonthier, P. L.

    2015-07-10

    Observations by the Fermi Large Area Telescope of γ-ray millisecond pulsar (MSP) light curves imply copious pair production in their magnetospheres, and not exclusively in those of younger pulsars. Such pair cascades may be a primary source of Galactic electrons and positrons, contributing to the observed enhancement in positron flux above ∼10 GeV. Fermi has also uncovered many new MSPs, impacting Galactic stellar population models. We investigate the contribution of Galactic MSPs to the flux of terrestrial cosmic-ray electrons and positrons. Our population synthesis code predicts the source properties of present-day MSPs. We simulate their pair spectra invoking an offset-dipole magnetic field. We also consider positrons and electrons that have been further accelerated to energies of several TeV by strong intrabinary shocks in black widow (BW) and redback (RB) systems. Since MSPs are not surrounded by pulsar wind nebulae or supernova shells, we assume that the pairs freely escape and undergo losses only in the intergalactic medium. We compute the transported pair spectra at Earth, following their diffusion and energy loss through the Galaxy. The predicted particle flux increases for non-zero offsets of the magnetic polar caps. Pair cascades from the magnetospheres of MSPs are only modest contributors around a few tens of GeV to the lepton fluxes measured by the Alpha Magnetic Spectrometer, PAMELA, and Fermi, after which this component cuts off. The contribution by BWs and RBs may, however, reach levels of a few tens of percent at tens of TeV, depending on model parameters.

  20. Positron annihilation study of P implanted Si

    SciTech Connect

    Asoka-Kumar, P.; Au, H.L.; Lynn, K.G. ); Sferlazzo, P. . SED Division)

    1992-01-01

    High-energy ion implantation (above 200 keV) is now commonly used in a variety of VLSI processes. The high energy required for these implants is often achieved by implanting multiply charged ions, which inevitably brings in the problem of low-energy ion contamination. The low-energy contamination is difficult to diagnose and detect. Positron annihilation spectroscopy is used to examine the defect distributions in these high energy implants with varying degrees of contamination.

  1. Positron annihilation study of P implanted Si

    SciTech Connect

    Asoka-Kumar, P.; Au, H.L.; Lynn, K.G.; Sferlazzo, P.

    1992-12-01

    High-energy ion implantation (above 200 keV) is now commonly used in a variety of VLSI processes. The high energy required for these implants is often achieved by implanting multiply charged ions, which inevitably brings in the problem of low-energy ion contamination. The low-energy contamination is difficult to diagnose and detect. Positron annihilation spectroscopy is used to examine the defect distributions in these high energy implants with varying degrees of contamination.

  2. The Clic Electron and Positron Polarized Sources

    NASA Astrophysics Data System (ADS)

    Rinolfi, L.

    2011-01-01

    The CLIC polarized electron source is based on a DC gun where the photocathode is illuminated by a laser beam. Each micro-bunch has a charge of 6 × 109 e-, a width of 100 ps and a repetition rate of 2 GHz. A peak current of 10 A in the micro-bunch is a challenge for the surface charge limit of the photo-cathode. Two options are feasible to generate the 2 GHz e- bunch train: 100 ps micro-bunches can be extracted from the photo-cathode either by a 2 GHz laser system or by generating a macro-bunch using a ~200 ns laser pulse and a subsequent RF bunching system to produce the appropriate micro-bunch structure. Recent results obtained by SLAC, for the latter case, are presented. The polarized positron source is based on a positron production scheme in which polarized photons are produced by a laser Compton scattering process. The resulting circularly-polarized gamma photons are sent onto a target, producing pairs of longitudinally polarized electrons and positrons. The Compton backscattering process occurs either in a Compton ring, where a 1 GeV electron beam interacts with circularly-polarized photons in an optical resonator or in a 1.8 GeV Compton Energy Recovery Linac (ERL) or in a 6 GeV Linac with several optical cavities. The undulator scheme is also studied. The nominal CLIC e+ bunch population is 6.7 × 109 particles per bunch at 200 MeV. The tradeoff between e+ yield and level of polarization is an important topic. The overall scheme for both polarized electron and positron beams is described.

  3. Measurement and verification of positron emitter nuclei generated at each treatment site by target nuclear fragment reactions in proton therapy

    SciTech Connect

    Miyatake, Aya; Nishio, Teiji; Ogino, Takashi; Saijo, Nagahiro; Esumi, Hiroyasu; Uesaka, Mitsuru

    2010-08-15

    Purpose: The purpose of this study is to verify the characteristics of the positron emitter nuclei generated at each treatment site by proton irradiation. Methods: Proton therapy using a beam on-line PET system mounted on a rotating gantry port (BOLPs-RGp), which the authors developed, is provided at the National Cancer Center Kashiwa, Japan. BOLPs-RGp is a monitoring system that can confirm the activity distribution of the proton irradiated volume by detection of a pair of annihilation gamma rays coincidentally from positron emitter nuclei generated by the target nuclear fragment reactions between irradiated proton nuclei and nuclei in the human body. Activity is measured from a start of proton irradiation to a period of 200 s after the end of the irradiation. The characteristics of the positron emitter nuclei generated in a patient's body were verified by the measurement of the activity distribution at each treatment site using BOLPs-RGp. Results: The decay curves for measured activity were able to be approximated using two or three half-life values regardless of the treatment site. The activity of half-life value of about 2 min was important for a confirmation of the proton irradiated volume. Conclusions: In each proton treatment site, verification of the characteristics of the generated positron emitter nuclei was performed by using BOLPs-RGp. For the monitoring of the proton irradiated volume, the detection of {sup 15}O generated in a human body was important.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

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

    PubMed Central

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

    2016-01-01

    The luminescence and scintillation properties of ZnO single crystals were studied by photoluminescence and X-ray-induced luminescence (XRIL) techniques. XRIL allowed a direct comparison to be made between the near-band emission (NBE) and trap emissions providing insight into the carrier recombination efficiency in the ZnO crystals. It also provided bulk luminescence measurements that were not affected by surface states. The origin of a green emission, the dominant trap emission in ZnO, was then investigated by gamma-induced positron spectroscopy (GIPS) - a unique defect spectroscopy method that enables positron lifetime measurements to be made for a sample without contributions from positron annihilation in the source materials. The measurements showed a single positron decay curve with a 175 ps lifetime component that was attributed to Zn vacancies passivated by hydrogen. Both oxygen vacancies and hydrogen-decorated Zn vacancies were suggested to contribute to the green emission. By combining scintillation measurements with XRIL, the fast scintillation in ZnO crystals was found to be strongly correlated with the ratio between the defect luminescence and NBE. This study reports the first application of GIPS to semiconductors, and it reveals the great benefits of the XRIL technique for the study of emission and scintillation properties of materials. PMID:27550235

  6. Positron follow-up in liquid water: II. Spatial and energetic study for the most important radioisotopes used in PET.

    PubMed

    Champion, C; Le Loirec, C

    2007-11-21

    With the increasing development of positron emission tomography (PET), beta(+)-emitters are more and more regularly used in nuclear medicine. Therefore, today it is of prime importance to have a reliable description of their behavior in living matter in order to quantify the full spectra of the molecular damages potentially radio-induced and then to access a cellular dosimetry. In this work, we present a detailed inter-comparison of the main isotopes commonly used in PET: (18)F, (11)C, (13)N, (15)O, (68)Ga and (82)Rb. We have used an event-by-event Monte Carlo code recently developed for positron tracking in water (Champion and Le Loirec 2006 Phys. Med. Biol. 51 1707-23) which consists in simulating step-by-step, interaction after interaction, the history of each ionizing particle created during the irradiation of the biological matter. This simulation has been finally adapted for describing the decays of medically important positron emitters. Quantitative information about positron penetrations, Positronium formation, annihilation event distributions, energy deposit patterns and dose profiles is then accessible and compared to published measurements and/or calculations.

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

    PubMed

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

    2016-08-23

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

  8. Radiative decays at LHCb

    NASA Astrophysics Data System (ADS)

    Giubega, L. E.

    2016-12-01

    Precise measurements on rare radiative B decays are performed with the LHCb experiment at LHC. The LHCb results regarding the ratio of branching fractions for two radiative decays, B 0 → K *0 γ and B s → ϕ γ, the direct CP asymmetry in B 0 → K *0 γ decay channel and the observation of the photon polarization in the B ± → K ±π∓π± γ decay, are included. The first two measurements were performed in 1 fb-1 of pp collisions data and the third one in 3 fb-1 of data, respectively.

  9. Positron annihilation in superconducting 123 compounds

    SciTech Connect

    Peter, M.; Manuel, A.A.; Erb, A. . Dept. of Physics of Condensed Matter)

    1998-12-20

    After a brief review of the theory of angular correlation of positron annihilation radiation (ACAR), the authors illustrate experimental principles and give examples of successful determination of electron momentum density (EMD) and of positron lifetime in solids. The central question which the authors try to answer concerns the contribution of positron spectroscopy to the knowledge and understanding of the new high temperature superconducting oxides. They find that in these oxides also, partially filled bands exist and they can observe parts of their Fermi surface and measure lifetimes in accordance with band theoretical calculations. There are characteristic differences, however. The intensity of the anisotropy of the ACAR signal is below theoretical expectation and signals depend on sample preparation. Recent studies by the Geneva group have concerned dependence of the signals on impurities, on oxygen content and on the thermal history of preparation. Of particular interest are correlations between the variations of these signals and between the variations of structural and transport properties in these substances. Besides deliberate additions of impurities, the Geneva group also reports progress in the preparations of samples of highest purity (barium zirconate crucibles). The alloy series Pr[sub x]Y[sub 1[minus]x]Ba[sub 2]Cu[sub 3]O[sub 7[minus][delta

  10. Feasibility study for positron emission mammography.

    PubMed

    Thompson, C J; Murthy, K; Weinberg, I N; Mako, F

    1994-04-01

    A feasibility study is presented for a small, low-cost, dedicated device for positron emission mammography. Two detector arrays above and below the breast would be placed in a conventional mammography unit. These detectors are sensitive to positron annihilation radiation, and are connected to a coincidence circuit and a multiplane image memory. Images of the distribution of positron-emitting isotope are obtained in real time by incrementing the memory location at the intersection of each line of response. Monte Carlo simulations of a breast phantom are compared with actual scans of this phantom in a conventional PET scanner. The simulations and experimental data are used to predict the performance of the proposed system. Spatial resolution experiments using very narrow bismuth germanate BGO crystals suggest that spatial resolutions of about 2 mm should be possible. The efficiency of the proposed device is about ten times that of a conventional brain scanner. The scatter fraction is greater, but the scattered radiation has a very flat distribution. By designing the device to fit in an existing mammography unit, conventional mammograms can be taken after the injection of the radio-pharmaceutical allowing exact registration of the emission and conventional mammographic images.

  11. New generation electron-positron factories

    NASA Astrophysics Data System (ADS)

    Zobov, Mikhail

    2011-09-01

    In 2010 we celebrate 50 years since commissioning of the first particle storage ring ADA in Frascati (Italy) that also became the first electron-positron collider in 1964. After that date the particle colliders have increased their intensity, luminosity and energy by several orders of magnitude. Namely, because of the high stored beam currents and high rate of useful physics events (luminosity) the modern electron-positron colliders are called "factories". However, the fundamental physics has required luminosities by 1-2 orders of magnitudes higher with respect to those presently achieved. This task can be accomplished by designing a new generation of factories exploiting the potential of a new collision scheme based on the Crab Waist (CW) collision concept recently proposed and successfully tested at Frascati. In this paper we discuss the performance and limitations of the present generation electron-positron factories and give a brief overview of new ideas and collision schemes proposed for further collider luminosity increase. In more detail we describe the CW collision concept and the results of the crab waist collision tests in DAϕNE, the Italian ϕ-factory. Finally, we briefly describe most advanced projects of the next generation factories based on the CW concept: SuperB in Italy, SuperKEKB in Japan and SuperC-Tau in Russia.

  12. Advances in positron and electron scattering*

    NASA Astrophysics Data System (ADS)

    Limão-Vieira, Paulo; García, Gustavo; Krishnakumar, E.; Petrović, Zoran; Sullivan, James; Tanuma, Hajime

    2016-10-01

    The topical issue on Advances in Positron and Electron Scattering" combines contributions from POSMOL 2015 together with others devoted to celebrate the unprecedented scientific careers of our loyal colleagues and trusted friends Steve Buckman (Australian National University, Australia) and Michael Allan (University of Fribourg, Switzerland) on the occasion of their retirements. POSMOL 2015, the XVIII International Workshop on Low-Energy Positron and Positronium Physics and the XIX International Symposium on Electron-Molecule Collisions and Swarms, was held at Universidade NOVA de Lisboa, Lisboa, Portugal, from 17-20 July 2015. The international workshop and symposium allowed to achieve a very privileged forum of sharing and developing our scientific expertise on current aspects of positron, positronium and antiproton interactions with electrons, atoms, molecules and solid surfaces, and related topics, as well as electron interactions with molecules in both gaseous and condensed phases. Particular topics include studies of electron interactions with biomolecules, electron induced surface chemistry and the study of plasma processes. Recent developments in the study of swarms are also fully addressed.

  13. Search for decays Bs -> etaprime eta and Bs -> etaprime pi0 in Belle data

    NASA Astrophysics Data System (ADS)

    Zummo, Anthony; Savinov, Vladimir; Belle Collaboration

    2017-01-01

    We search for the decays Bs ->η' η and Bs ->η'π0 using 121 . 4fb-1 of data collected at the ϒ(5 S) resonance with the Belle detector at the KEKB asymmetric-energy electron-positron collider. These decays are suppressed in the Standard Model of particle physics and proceed through b -> u and b -> s transitions, which are sensitive to new physics. The expected branching fractions in the Standard Model are 33 . 5 ×10-6 for Bs ->η' η and 0 . 12 ×10-6 for Bs ->η'π0 . Neither decay has been observed yet. We use Monte Carlo simulation to study Belle sensitivity to these decays. We report the current status of our investigations to provide the best sensitivity to discovering these decays in the existing data.

  14. Measurements of Cabibbo-suppressed hadronic decay fractions of charmed D^0 and D^+ mesons [rapid communication

    NASA Astrophysics Data System (ADS)

    BES Collaboration; Ablikim, M.; Bai, J. Z.; Ban, Y.; Bian, J. G.; Cai, X.; Chang, J. F.; Chen, H. F.; Chen, H. S.; Chen, H. X.; Chen, J. C.; Chen, Jin; Chen, Jun; Chen, M. L.; Chen, Y. B.; Chi, S. P.; Chu, Y. P.; Cui, X. Z.; Dai, H. L.; Dai, Y. S.; Deng, Z. Y.; Dong, L. Y.; Dong, Q. F.; Du, S. X.; Du, Z. Z.; Fang, J.; Fang, S. S.; Fu, C. D.; Fu, H. Y.; Gao, C. S.; Gao, Y. N.; Gong, M. Y.; Gong, W. X.; Gu, S. D.; Guo, Y. N.; Guo, Y. Q.; He, K. L.; He, M.; He, X.; Heng, Y. K.; Hu, H. M.; Hu, T.; Huang, X. P.; Huang, X. T.; Ji, X. B.; Jiang, C. H.; Jiang, X. S.; Jin, D. P.; Jin, S.; Jin, Y.; Jin, Yi; Lai, Y. F.; Li, F.; Li, G.; Li, H. H.; Li, J.; Li, J. C.; Li, Q. J.; Li, R. Y.; Li, S. M.; Li, W. D.; Li, W. G.; Li, X. L.; Li, X. Q.; Li, Y. L.; Liang, Y. F.; Liao, H. B.; Liu, C. X.; Liu, F.; Liu, Fang; Liu, H. H.; Liu, H. M.; Liu, J.; Liu, J. B.; Liu, J. P.; Liu, R. G.; Liu, Z. A.; Liu, Z. X.; Lu, F.; Lu, G. R.; Lu, H. J.; Lu, J. G.; Luo, C. L.; Luo, L. X.; Luo, X. L.; Ma, F. C.; Ma, H. L.; Ma, J. M.; Ma, L. L.; Ma, Q. M.; Ma, X. B.; Ma, X. Y.; Mao, Z. P.; Mo, X. H.; Nie, J.; Nie, Z. D.; Peng, H. P.; Qi, N. D.; Qian, C. D.; Qin, H.; Qiu, J. F.; Ren, Z. Y.; Rong, G.; Shan, L. Y.; Shang, L.; Shen, D. L.; Shen, X. Y.; Sheng, H. Y.; Shi, F.; Shi, X.; Sun, H. S.; Sun, J. F.; Sun, S. S.; Sun, Y. Z.; Sun, Z. J.; Tang, X.; Tao, N.; Tian, Y. R.; Tong, G. L.; Wang, D. Y.; Wang, J. Z.; Wang, K.; Wang, L.; Wang, L. S.; Wang, M.; Wang, P.; Wang, P. L.; Wang, S. Z.; Wang, W. F.; Wang, Y. F.; Wang, Z.; Wang, Z. Y.; Wang, Zhe; Wang, Zheng; Wei, C. L.; Wei, D. H.; Wu, N.; Wu, Y. M.; Xia, X. M.; Xie, X. X.; Xin, B.; Xu, G. F.; Xu, H.; Xue, S. T.; Yan, M. L.; Yang, F.; Yang, H. X.; Yang, J.; Yang, Y. X.; Ye, M.; Ye, M. H.; Ye, Y. X.; Yi, L. H.; Yi, Z. Y.; Yu, C. S.; Yu, G. W.; Yuan, C. Z.; Yuan, J. M.; Yuan, Y.; Zang, S. L.; Zeng, Y.; Zeng, Yu; Zhang, B. X.; Zhang, B. Y.; Zhang, C. C.; Zhang, D. H.; Zhang, H. Y.; Zhang, J.; Zhang, J. W.; Zhang, J. Y.; Zhang, Q. J.; Zhang, S. Q.; Zhang, X. M.; Zhang, X. Y.; Zhang, Y. Y.; Zhang, Yiyun; Zhang, Z. P.; Zhang, Z. Q.; Zhao, D. X.; Zhao, J. B.; Zhao, J. W.; Zhao, M. G.; Zhao, P. P.; Zhao, W. R.; Zhao, X. J.; Zhao, Y. B.; Zheng, H. Q.; Zheng, J. P.; Zheng, L. S.; Zheng, Z. P.; Zhong, X. C.; Zhou, B. Q.; Zhou, G. M.; Zhou, L.; Zhou, N. F.; Zhu, K. J.; Zhu, Q. M.; Zhu, Y. C.; Zhu, Y. S.; Zhu, Yingchun; Zhu, Z. A.; Zhuang, B. A.; Zhuang, X. A.; Zou, B. S.

    2005-08-01

    Using data collected with the BESII detector at Beijing Electron Positron Collider, the measurements of relative branching fractions for seven Cabibbo-suppressed hadronic weak decays D→KK, ππ, KKππ and ππππ, D→KK, KKπ and πππ are presented.

  15. High-field capture section for SLC positron source

    SciTech Connect

    Hoag, H.A.; Deruyter, H.; Kramer, J.; Yao, C.G.

    1986-05-01

    The positron source for SLC is being installed at the two-thirds point on the SLAC linac. Electron bunches at 33 GeV impinge upon a Tantalum/Tungsten target, producing showers of positrons with energies extending from approximately 2 to 20 MeV, with most positrons at the low end of this range. Positrons with low energies and finite transverse momenta slip phase during the processes of reacceleration and reinjection into the SLC system, increasing the energy spread and reducing the overall yield of the positron source. This reduction in yield has to be minimized by ''capturing'' the positrons with a high-field accelerator section placed as soon after the target as possible. The design, fabrication and RF testing of this accelerator section are described.

  16. Search for monenergetic gamma rays from psi /3684/ decay

    NASA Technical Reports Server (NTRS)

    Simpson, J. W.; Beron, B. L.; Ford, R. L.; Hofstadter, R.; Howell, R. L.; Hughes, E. B.; Liberman, A. D.; Martin, T. W.; Oneill, L. H.; Hilger, E.

    1975-01-01

    Results are reported of a search for monoenergetic gamma rays with energies above 50 MeV arising from psi (3684) decay. The measurements were made by operating an electron-positron storage ring at a center-of-mass energy of 3684 MeV and detecting the secondary gamma rays with large-crystal NaI(T1) spectrometers. No significant evidence is found for the emission of such radiation, and upper limits are placed on such emissions for energies above 50 MeV.

  17. Values of the phase space factors for double beta decay

    SciTech Connect

    Stoica, Sabin Mirea, Mihai

    2015-10-28

    We report an up-date list of the experimentally most interesting phase space factors for double beta decay (DBD). The electron/positron wave functions are obtained by solving the Dirac equations with a Coulomb potential derived from a realistic proton density distribution in nucleus and with inclusion of the finite nuclear size (FNS) and electron screening (ES) effects. We build up new numerical routines which allow us a good control of the accuracy of calculations. We found several notable differences as compared with previous results reported in literature and possible sources of these discrepancies are discussed.

  18. Radioactive Decay - An Analog.

    ERIC Educational Resources Information Center

    McGeachy, Frank

    1988-01-01

    Presents an analog of radioactive decay that allows the student to grasp the concept of half life and the exponential nature of the decay process. The analog is devised to use small, colored, plastic poker chips or counters. Provides the typical data and a graph which supports the analog. (YP)

  19. A General Quantum Mechanical Method to Predict Positron Spectroscopy

    DTIC Science & Technology

    2007-06-01

    70 6.2.3 Positronic Systems for Modeling and Experiment 71 Appendix A. Electron-Positron Annihilation Observables from NEO-HF and NEO-MP2...spectroscopy (PAS) experiments are widely used to study materials defects, including point defects in semiconductors and voids in composite materials...addition to traditional PAS techniques, experiments involving VFRs are also discussed. In Section 2.2, methods for modeling positron interaction with

  20. Positron Annihilation Studies In Polymer Nano-Composites

    SciTech Connect

    Chen, H. M.; Awad, Somia; Jean, Y. C.; Yang, J.; Lee, L. James

    2011-06-01

    Positron annihilation spectroscopy coupled with a variable mono-energy positron beam has been applied to study nanoscale polymeric nanocomposites. New information about multilayer depth profiles and structures, interfacial free-volume and open space properties have been obtained in polystyrene/carbon nano fiber composites. The S parameter in Doppler Broadening Energy Spectra combined slow positron beam is used to quantitatively represent the free volume, open spaces, and interactions in the interface between polystyrene matrix and carbon nanofibers.

  1. Detecting positron-atom bound states through resonant annihilation.

    PubMed

    Dzuba, V A; Flambaum, V V; Gribakin, G F

    2010-11-12

    A method is proposed for detecting positron-atom bound states by observing enhanced positron annihilation due to electronic Feshbach resonances at electron-volt energies. The method is applicable to a range of open-shell transition-metal atoms which are likely to bind the positron: Fe, Co, Ni, Tc, Ru, Rh, Sn, Sb, Ta, W, Os, Ir, and Pt. Estimates of their binding energies are provided.

  2. Beta decay and the origin of biologial chirality - New experimental results

    NASA Technical Reports Server (NTRS)

    Van House, J.; Rich, A.; Zitzewitz, P. W.

    1984-01-01

    The hypothetical connection developed by Vester and Ulbricht (1959), between the handedness of beta particles in radioactive decay and the (L) sign of biologial chirality is investigated in a radiolysis experiment. The experiment measured the predicted asymmetry in the formation triplet or 'ortho-' positronium (oPs) in amino acid enantiomers by low energy positrons under conditions of helicity reversal. The positrons were focused on amino acid powder samples. By measuring the time between positron arrival and emission of gamma rays, long-lived oPs were separated from other species. It is found that the asymmetry in leucine (0.8 x 10 to the -4th) is consistent with the theoretical prediction of 10 to the -6th. Neither the experimental limits nor the theoretical estimates are found to rule out a mechanism like that described by Vester and Ulbricht as the cause of the sign of the observed chiral polarization.

  3. On the localization of positrons in metal vacancies

    NASA Astrophysics Data System (ADS)

    Babich, A. V.; Pogosov, V. V.; Reva, V. I.

    2015-11-01

    The probability of localization of positrons in single vacancies of Al, Cu, and Zn as a function of temperature has been calculated. Vacancy has been simulated by a cavity with a radius of the Wigner-Seitz cell in the stabilized jellium model. A formula for the rate of trapping of a positron by a vacancy as a function of the positron energy has been obtained using the "golden" rule for transitions under the assumption that the positron energy is spent on excitation of electron-hole pairs. The temperature dependence of the localization rate has been calculated for thermalized positrons. It has been found that, in the vicinity of the triple point, the localization rate is close in order of magnitude to the annihilation rate. Based on the results reported in our previous publications devoted to the evaluation of the influence of vacancies on the work function of free positrons, it has been assumed that, near the surface of the metal, there are vacancies charged by positrons. In the approximation of a two-dimensional superlattice, the near-surface vacancy barrier has been estimated. The experimentally revealed shift of the energy distribution of re-emitted positrons has been assumed to be caused by the reflection of low-energy positrons from the vacancy barrier back into the bulk of the metal where they annihilate.

  4. Sensitivity of positron annihilation to hydrogen in Zr

    SciTech Connect

    Hood, G.M.; Schultz, R.J.

    1982-01-01

    Positron annihilation spectroscopy has been applied to the quantitative determination of hydrogen in zirconium. The sensitivity of the positron annihilation was noted to be influenced not only by the presence of hydrogen but also by the heat treatment of the hydrided samples. The positron is attracted to the relatively negative, or ion-core-deficient regions of the metal, F regions commonly associated with vacancies, voids and dislocations. It was found to be very difficult to gauge the relative effects which hydrides and dislocations might have on the positron annihilation in zirconium. (BLM)

  5. Positron-molecule bound states and positive ion production

    NASA Technical Reports Server (NTRS)

    Leventhal, M.; Passner, A.; Surko, C. M.

    1990-01-01

    The interaction was studied of low energy positrons with large molecules such as alkanes. These data provide evidencce for the existence of long lived resonances and bound states of positrons with neutral molecules. The formation process and the nature of these resonances are discussed. The positive ions produced when a positron annihilates with an electron in one of these resonances were observed and this positive ion formation process is discussed. A review is presented of the current state of the understanding of these positron-molecule resonances and the resulting positive ion formation. A number of outstanding issues in this area is also discussed.

  6. What is the fate of runaway positrons in tokamaks?

    DOE PAGES

    Liu, Jian; Qin, Hong; Fisch, Nathaniel J.; ...

    2014-06-19

    In this study, massive runaway positrons are generated by runaway electrons in tokamaks. The fate of these positrons encodes valuable information about the runaway dynamics. The phase space dynamics of a runaway position is investigated using a Lagrangian that incorporates the tokamak geometry, loop voltage, radiation and collisional effects. It is found numerically that runaway positrons will drift out of the plasma to annihilate on the first wall, with an in-plasma annihilation possibility less than 0.1%. The dynamics of runaway positrons provides signatures that can be observed as diagnostic tools.

  7. Search for a positron anisotropy with PAMELA experiment

    NASA Astrophysics Data System (ADS)

    Panico, B.; Adriani, O.; Barbarino, G. C.; Bazilevskaya, G. A.; Bellotti, R.; Boezio, M.; Bogomolov, E. A.; Bongi, M.; Bonvicini, V.; Bottai, S.; Bruno, A.; Cafagna, F.; Campana, D.; Carlson, P.; Casolino, M.; Castellini, G.; De Donato, C.; De Santis, C.; De Simone, N.; Di Felice, V.; Formato, V.; Galper, A. M.; Giaccari, U.; Karelin, A. V.; Koldashov, S. V.; Koldobskiy, S.; Krutkov, S. Y.; Kvashnin, A. N.; Leonov, A.; Malakhov, V.; Marcelli, L.; Martucci, M.; Mayorov, A. G.; Menn, W.; Mergé, M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Palma, F.; Pearce, M.; Picozza, P.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Y. I.; Vacchi, A.; Vannuccini, E.; Vasilyev, G. I.; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.

    2015-09-01

    The PAMELA experiment has been collecting data since 2006; its results indicate a rise in the positron fraction with respect to the sum of electrons and positrons in the cosmic-ray (CR) spectrum above 10 GeV. This excess can be due to additional sources, as SNRs or pulsars, which can lead to an anisotropy in the local CR positron, detectable from current experiments. We report on the analysis on spatial distributions of positron events collected by PAMELA, taking into account also the geomagnetic field effects. No significant deviation from the isotropy has been observed.

  8. Recent Developments in the Design of the NLC Positron Source

    SciTech Connect

    Kotseroglou, T.; Bharadwaj, V.; Clendenin, J.E.; Ecklund, S,; Frisch, J.; Krejcik, P,; Kukikov, A.V.; Liu, J.; Maruyama, T.; Millage, K.K.; Mulhollan, G.; Nelson, W.R.; Schultz, D.C.; Sheppard, J.C.; Turner, J.; Van Bibber, K.; Flottmann, K.; Namito, Y.

    1999-11-05

    Recent developments in the design of the Next Linear Collider (NLC) positron source based on updated beam parameters are described. The unpolarized NLC positron source [1,2] consists of a dedicated 6.2 GeV S-band electron accelerator, a high-Z positron production target, a capture system and an L-band positron linac. The 1998 failure of the SLC target, which is currently under investigation, may lead to a variation of the target design. Progress towards a polarized positron source is also presented. A moderately polarized positron beam colliding with a highly polarized electron beam results in an effective polarization large enough to explore new physics at NLC. One of the schemes towards a polarized positron source incorporates a polarized electron source, a 50 MeV electron accelerator, a thin target for positron production and a new capture system optimized for high-energy, small angular-divergence positrons. The yield for such a process, checked using the EGS4 code, is of the order of 10{sup -3}. The EGS4 code has being enhanced to include the effect of polarization in bremsstrahlung and pair-production process.

  9. Production of a_1 in heavy meson decays

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Zhao, Zhen-Xing

    2016-02-01

    In this work, we study various decays of heavy B / D mesons into the a_1(1260), based on the form factors derived in different nonperturbative or factorization approaches. These decay modes are helpful to explore the dynamics in the heavy to light transitions. Meanwhile they can also provide insights to a newly discovered state, the a_1(1420) with I^G(J^{PC})= 1^-(1^{++}) observed in the π ^+ f_0(980) final state in the π ^-p→ π ^+π ^-π ^- p process. Available theoretical explanations include tetraquark or rescattering effects due to a_1(1260) decays. If the a_1(1420) were induced by the rescattering, its production rates are completely determined by those of the a_1(1260). Our numerical results for decays into the a_1(1260) indicate that there is a promising prospect to study these decays on experiments including BES-III, LHCb, Babar, Belle, and CLEO-c, the forthcoming Super-KEKB factory and the under-design Circular Electron-Positron Collider.

  10. Probing the positron moderation process using high-intensity, highly polarized slow-positron beams

    NASA Technical Reports Server (NTRS)

    Van House, J.; Zitzewitz, P. W.

    1984-01-01

    A highly polarized (P = 0.48 + or - 0.02) intense (500,000/sec) beam of 'slow' (Delta E = about 2 eV) positrons (e+) is generated, and it is shown that it is possible to achieve polarization as high as P = 0.69 + or - 0.04 with reduced intensity. The measured polarization of the slow e+ emitted by five different positron moderators showed no dependence on the moderator atomic number (Z). It is concluded that only source positrons with final kinetic energy below 17 keV contribute to the slow-e+ beam, in disagreement with recent yield functions derived from low-energy measurements. Measurements of polarization and yield with absorbers of different Z between the source and moderator show the effects of the energy and angular distributions of the source positrons on P. The depolarization of fast e+ transmitted through high-Z absorbers has been measured. Applications of polarized slow-e+ beams are discussed.

  11. Internal Pair Decay of Giant Resonances in Hot LEAD-200.

    NASA Astrophysics Data System (ADS)

    Adami, Susan

    Electron-positron pairs emitted during the de -excitation of the hot ^{200}Pb were detected with the Stony Brook pair detector, a phoswich array, in order to observe the internal pair decay of giant resonances (GR) built on excited states. These collective excitations are particularly well defined in heavy nuclei, and the full GR sum rule had been found in the ground state excitations of both the giant dipole resonance and the isoscalar monopole resonance. The excited compound nucleus was formed by bombarding a ^{181} Ta target with a 95 MeV pulsed ^ {19}F beam. While the gamma-decay from giant resonances of multipolarities L >=q 1 results in cross-sections 3-4 orders of magnitudes bigger than the internal pair decay, the decay of giant monopole resonances via a collective E0 transition can only be observed in the e^+ - e^ --decay channel. Another advantage of investigating electro-magnetic transitions via the pair decay channel is the fact that the correlation angle (and also the energy sharing) between the electron and the positron provides insight in the multipolarity of the observed transition. Especially the angular correlation distribution of an L = 0 transition is easily distinguished from the L >=q 1 cases. In the data analysis, the pair spectra were compared to calculations using the statistical model code CASCADE, which was modified to include the internal pair decay of giant resonances from the compound nucleus as well as from the fission fragments. In addition, gamma measurements from the same reaction at a comparable excitation energy (93 MeV) were available. The extracted pair spectra confirmed the CASCADE prediction that the giant dipole resonance dominates the pair decay from a hot, heavy nucleus. Superior statistics would be necessary in order to extract weaker modes like the monopole or quadrupole resonances and due to the lack in statistics this work can only offer a rough estimate for the width and position of the isoscalar giant monopole

  12. Positron impact ionization of atomic hydrogen

    SciTech Connect

    Acacia, P.; Campeanu, R.I.; Horbatsch, M.

    1993-05-01

    We will present integrated cross sections for ionization of atomic hydrogen by positrons. These have been calculated in a distorted-wave approximation using energy-dependent effective charges in the final channel as well as static and polarization potentials in the initial channel. We present two models for calculating the energy-dependent effective charges both of which produce results in good agreement with the recent experimental measurements of Spicher et al. This is in contrast to previous distorted-wave calculations which used fixed effective charges as well as classical trajectory calculations. Both of these latter methods produced results which were substantially below ours and the experimental data.

  13. Possible resonance in positron-lithium scattering

    NASA Astrophysics Data System (ADS)

    Abdel-Raouf, M. A.; Wood, R. F.

    1990-09-01

    The possible appearance of resonances in the partial cross sections of the inelastic collisions of positrons with lithium atoms at energies below 5 eV is investigated. It is assumed that only elastic and rearrangement channels are open, while excitation channels are closed. A coupled static formalism, in which the polarization potentials of the lithium and positronium are switched on, is employed. The basis set of Clementi and Roetti [At. Data Nucl. Data Tables 14, 177 (1974)] is used for describing the target model. Comparison between the resulting total cross sections and those obtained by other authors is presented.

  14. Positron autoradiography for intravascular imaging: feasibility evaluation.

    PubMed

    Shikhaliev, Polad M; Xu, Tong; Ducote, Justin L; Easwaramoorthy, Balasubramaniam; Mukherjee, Jogeshwar; Molloi, Sabee

    2006-02-21

    Approximately 70% of acute coronary artery disease is caused by unstable (vulnerable) plaques with an inflammation of the overlying cap and high lipid content. A rupturing of the inflamed cap of the plaque results in propagation of the thrombus into the lumen, blockage of the artery and acute ischaemic syndrome or sudden death. Morphological imaging such as angiography or intravascular ultrasound cannot determine inflammation status of the plaque. A radiotracer such as 18F-FDG is accumulated in vulnerable plaques due to higher metabolic activity of the inflamed cap and could be used to detect a vulnerable plaque. However, positron emission tomography (PET) cannot detect the FDG-labelled plaques because of respiratory and heart motions, small size and low activity of the plaques. Plaques can be detected using a miniature particle (positron) detector inserted into the artery. In this work, a new detector concept is investigated for intravascular imaging of the plaques. The detector consists of a storage phosphor tip bound to the end of an intravascular catheter. It can be inserted into an artery, absorb the 18F-FDG positrons from the plaques, withdrawn from the artery and read out. Length and diameter of the storage phosphor tip can be matched to the length and the diameter of the artery. Monte Carlo simulations and experimental evaluations of coronary plaque imaging with the proposed detector were performed. It was shown that the sensitivity of the storage phosphor detector to the positrons of 18F-FDG is sufficient to detect coronary plaques with 1 mm and 2 mm sizes and 590 Bq and 1180 Bq activities in the arteries with 2 mm and 3 mm diameters, respectively. An experimental study was performed using plastic tubes with 2 mm diameter filled with an FDG solution, which simulates blood. FDG spots simulating plaques were placed over the surface of the tube. A phosphor tip was inserted into the tube and imaged the plaques. Exposure time was 1 min in all simulations and

  15. Positron emission tomography (PET) for cholangiocarcinoma

    PubMed Central

    Breitenstein, S.; Apestegui, C.

    2008-01-01

    The combination of positron emission tomography (PET) with computed tomography (PET-CT) provides simultaneous metabolic and anatomic information on tumors in the same imaging session. Sensitivity of PET/PET-CT is higher for intrahepatic (>90%) than for extrahepatic cholangiocarcinoma (CCA) (about 60%). The detection rate of distant metastasis is 100%. PET, and particularly PET-CT, improves the results and impacts on the oncological management in CCA compared with other imaging modalities. Therefore, PET-CT is recommended in the preoperative staging of intrahepatic (strength of recommendation: moderate) and extrahepatic (strength of recommendation: low) CCA. PMID:18773069

  16. DHCAL with minimal absorber: measurements with positrons

    NASA Astrophysics Data System (ADS)

    Freund, B.; Neubüser, C.; Repond, J.; Schlereth, J.; Xia, L.; Dotti, A.; Grefe, C.; Ivantchenko, V.; Berenguer Antequera, J.; Calvo Alamillo, E.; Fouz, M.-C.; Marin, J.; Puerta-Pelayo, J.; Verdugo, A.; Brianne, E.; Ebrahimi, A.; Gadow, K.; Göttlicher, P.; Günter, C.; Hartbrich, O.; Hermberg, B.; Irles, A.; Krivan, F.; Krüger, K.; Kvasnicka, J.; Lu, S.; Lutz, B.; Morgunov, V.; Provenza, A.; Reinecke, M.; Sefkow, F.; Schuwalow, S.; Tran, H. L.; Garutti, E.; Laurien, S.; Matysek, M.; Ramilli, M.; Schroeder, S.; Bilki, B.; Norbeck, E.; Northacker, D.; Onel, Y.; Cvach, J.; Gallus, P.; Havranek, M.; Janata, M.; Kovalcuk, M.; Kvasnicka, J.; Lednicky, D.; Marcisovsky, M.; Polak, I.; Popule, J.; Tomasek, L.; Tomasek, M.; Sicho, P.; Smolik, J.; Vrba, V.; Zalesak, J.; van Doren, B.; Wilson, G. W.; Kawagoe, K.; Hirai, H.; Sudo, Y.; Suehara, T.; Sumida, H.; Takada, S.; Tomita, T.; Yoshioka, T.; Bilokin, S.; Bonis, J.; Cornebise, P.; Pöschl, R.; Richard, F.; Thiebault, A.; Zerwas, D.; Hostachy, J.-Y.; Morin, L.; Besson, D.; Chadeeva, M.; Danilov, M.; Markin, O.; Popova, E.; Gabriel, M.; Goecke, P.; Kiesling, C.; van der Kolk, N.; Simon, F.; Szalay, M.; Corriveau, F.; Blazey, G. C.; Dyshkant, A.; Francis, K.; Zutshi, V.; Kotera, K.; Ono, H.; Takeshita, T.; Ieki, S.; Kamiya, Y.; Ootani, W.; Shibata, N.; Jeans, D.; Komamiya, S.; Nakanishi, H.

    2016-05-01

    In special tests, the active layers of the CALICE Digital Hadron Calorimeter prototype, the DHCAL, were exposed to low energy particle beams, without being interleaved by absorber plates. The thickness of each layer corresponded approximately to 0.29 radiation lengths or 0.034 nuclear interaction lengths, defined mostly by the copper and steel skins of the detector cassettes. This paper reports on measurements performed with this device in the Fermilab test beam with positrons in the energy range of 1 to 10 GeV. The measurements are compared to simulations based on GEANT4 and a standalone program to emulate the detailed response of the active elements.

  17. Positron Scanner for Locating Brain Tumors

    DOE R&D Accomplishments Database

    Rankowitz, S.; Robertson, J. S.; Higinbotham, W. A.; Rosenblum, M. J.

    1962-03-01

    A system is described that makes use of positron emitting isotopes for locating brain tumors. This system inherently provides more information about the distribution of radioactivity in the head in less time than existing scanners which use one or two detectors. A stationary circular array of 32 scintillation detectors scans a horizontal layer of the head from many directions simultaneously. The data, consisting of the number of counts in all possible coincidence pairs, are coded and stored in the memory of a Two-Dimensional Pulse-Height Analyzer. A unique method of displaying and interpreting the data is described that enables rapid approximate analysis of complex source distribution patterns. (auth)

  18. Positron autoradiography for intravascular imaging: feasibility evaluation

    NASA Astrophysics Data System (ADS)

    Shikhaliev, Polad M.; Xu, Tong; Ducote, Justin L.; Easwaramoorthy, Balasubramaniam; Mukherjee, Jogeshwar; Molloi, Sabee

    2006-02-01

    Approximately 70% of acute coronary artery disease is caused by unstable (vulnerable) plaques with an inflammation of the overlying cap and high lipid content. A rupturing of the inflamed cap of the plaque results in propagation of the thrombus into the lumen, blockage of the artery and acute ischaemic syndrome or sudden death. Morphological imaging such as angiography or intravascular ultrasound cannot determine inflammation status of the plaque. A radiotracer such as 18F-FDG is accumulated in vulnerable plaques due to higher metabolic activity of the inflamed cap and could be used to detect a vulnerable plaque. However, positron emission tomography (PET) cannot detect the FDG-labelled plaques because of respiratory and heart motions, small size and low activity of the plaques. Plaques can be detected using a miniature particle (positron) detector inserted into the artery. In this work, a new detector concept is investigated for intravascular imaging of the plaques. The detector consists of a storage phosphor tip bound to the end of an intravascular catheter. It can be inserted into an artery, absorb the 18F-FDG positrons from the plaques, withdrawn from the artery and read out. Length and diameter of the storage phosphor tip can be matched to the length and the diameter of the artery. Monte Carlo simulations and experimental evaluations of coronary plaque imaging with the proposed detector were performed. It was shown that the sensitivity of the storage phosphor detector to the positrons of 18F-FDG is sufficient to detect coronary plaques with 1 mm and 2 mm sizes and 590 Bq and 1180 Bq activities in the arteries with 2 mm and 3 mm diameters, respectively. An experimental study was performed using plastic tubes with 2 mm diameter filled with an FDG solution, which simulates blood. FDG spots simulating plaques were placed over the surface of the tube. A phosphor tip was inserted into the tube and imaged the plaques. Exposure time was 1 min in all simulations and

  19. Liquid Metal Target for NLC Positron Source

    SciTech Connect

    Sheppard, John C.

    2002-08-19

    Possibility of creating the liquid lead target with parameters, optimum for the NLC positron source, is investigated. Target has a form of titanium vessel, filled with liquid lead, pumped through. The energy deposition in target is characterized by 35 kW average power and up to 250 J/g specific energy at optimum beam sigma 0.6 mm. The use of pumped through liquid lead as target material solves both the problems of power evacuation and target survival. The window for beam exit is made of both temperature and pressure resistive material--the diamond-like ceramic BN.

  20. Positron Emission Tomography: Its 65 years

    NASA Astrophysics Data System (ADS)

    Del Guerra, A.; Belcari, N.; Bisogni, M.

    2016-04-01

    Positron Emission Tomography (PET) is a well-established imaging technique for in vivo molecular imaging. In this review after a brief history of PET there are presented its physical principles and the technology that has been developed for bringing PET from a bench experiment to a clinical indispensable instrument. The limitations and performance of the PET tomographs are discussed, both as for the hardware and software aspects. The status of art of clinical, pre-clinical and hybrid scanners (, PET/CT and PET/MR) is reported. Finally the actual trend and the recent and future technological developments are fully illustrated.

  1. Recovering the triple coincidence of non-pure positron emitters in preclinical PET

    NASA Astrophysics Data System (ADS)

    Lin, Hsin-Hon; Chuang, Keh-Shih; Chen, Szu-Yu; Jan, Meei-Ling

    2016-03-01

    Non-pure positron emitters, with their long half-lives, allow for the tracing of slow biochemical processes which cannot be adequately examined by the commonly used short-lived positron emitters. Most of these isotopes emit high-energy cascade gamma rays in addition to positron decay that can be detected and create a triple coincidence with annihilation photons. Triple coincidence is discarded in most scanners, however, the majority of the triple coincidence contains true photon pairs that can be recovered. In this study, we propose a strategy for recovering triple coincidence events to raise the sensitivity of PET imaging for non-pure positron emitters. To identify the true line of response (LOR) from a triple coincidence, a framework utilizing geometrical, energy and temporal information is proposed. The geometrical criterion is based on the assumption that the LOR with the largest radial offset among the three sub pairs of triple coincidences is least likely to be a true LOR. Then, a confidence time window is used to test the valid LOR among those within triple coincidence. Finally, a likelihood ratio discriminant rule based on the energy probability density distribution of cascade and annihilation gammas is established to identify the true LOR. An Inveon preclinical PET scanner was modeled with GATE (GEANT4 application for tomographic emission) Monte Carlo software. We evaluated the performance of the proposed method in terms of identification fraction, noise equivalent count rates (NECR), and image quality on various phantoms. With the inclusion of triple coincidence events using the proposed method, the NECR was found to increase from 11% to 26% and 19% to 29% for I-124 and Br-76, respectively, when 7.4-185 MBq of activity was used. Compared to the reconstructed images using double coincidence, this technique increased the SNR by 5.1-7.3% for I-124 and 9.3-10.3% for Br-76 within the activity range of 9.25-74 MBq, without compromising the spatial resolution or

  2. Recovering the triple coincidence of non-pure positron emitters in preclinical PET.

    PubMed

    Lin, Hsin-Hon; Chuang, Keh-Shih; Chen, Szu-Yu; Jan, Meei-Ling

    2016-03-07

    Non-pure positron emitters, with their long half-lives, allow for the tracing of slow biochemical processes which cannot be adequately examined by the commonly used short-lived positron emitters. Most of these isotopes emit high-energy cascade gamma rays in addition to positron decay that can be detected and create a triple coincidence with annihilation photons. Triple coincidence is discarded in most scanners, however, the majority of the triple coincidence contains true photon pairs that can be recovered. In this study, we propose a strategy for recovering triple coincidence events to raise the sensitivity of PET imaging for non-pure positron emitters. To identify the true line of response (LOR) from a triple coincidence, a framework utilizing geometrical, energy and temporal information is proposed. The geometrical criterion is based on the assumption that the LOR with the largest radial offset among the three sub pairs of triple coincidences is least likely to be a true LOR. Then, a confidence time window is used to test the valid LOR among those within triple coincidence. Finally, a likelihood ratio discriminant rule based on the energy probability density distribution of cascade and annihilation gammas is established to identify the true LOR. An Inveon preclinical PET scanner was modeled with GATE (GEANT4 application for tomographic emission) Monte Carlo software. We evaluated the performance of the proposed method in terms of identification fraction, noise equivalent count rates (NECR), and image quality on various phantoms. With the inclusion of triple coincidence events using the proposed method, the NECR was found to increase from 11% to 26% and 19% to 29% for I-124 and Br-76, respectively, when 7.4-185 MBq of activity was used. Compared to the reconstructed images using double coincidence, this technique increased the SNR by 5.1-7.3% for I-124 and 9.3-10.3% for Br-76 within the activity range of 9.25-74 MBq, without compromising the spatial resolution or

  3. A feasibility study of ortho-positronium decays measurement with the J-PET scanner based on plastic scintillators

    NASA Astrophysics Data System (ADS)

    Kamińska, D.; Gajos, A.; Czerwiński, E.; Alfs, D.; Bednarski, T.; Białas, P.; Curceanu, C.; Dulski, K.; Głowacz, B.; Gupta-Sharma, N.; Gorgol, M.; Hiesmayr, B. C.; Jasińska, B.; Korcyl, G.; Kowalski, P.; Krzemień, W.; Krawczyk, N.; Kubicz, E.; Mohammed, M.; Niedźwiecki, Sz.; Pawlik-Niedźwiecka, M.; Raczyński, L.; Rudy, Z.; Silarski, M.; Wieczorek, A.; Wiślicki, W.; Zgardzińska, B.; Zieliński, M.; Moskal, P.

    2016-08-01

    We present a study of the application of the Jagiellonian positron emission tomograph (J-PET) for the registration of gamma quanta from decays of ortho-positronium (o-Ps). The J-PET is the first positron emission tomography scanner based on organic scintillators in contrast to all current PET scanners based on inorganic crystals. Monte Carlo simulations show that the J-PET as an axially symmetric and high acceptance scanner can be used as a multi-purpose detector well suited to pursue research including e.g. tests of discrete symmetries in decays of ortho-positronium in addition to the medical imaging. The gamma quanta originating from o-Ps decay interact in the plastic scintillators predominantly via the Compton effect, making the direct measurement of their energy impossible. Nevertheless, it is shown in this paper that the J-PET scanner will enable studies of the { o-Ps }→ 3γ decays with angular and energy resolution equal to σ (θ ) ≈ {0.4°} and σ (E) ≈ 4.1 {keV}, respectively. An order of magnitude shorter decay time of signals from plastic scintillators with respect to the inorganic crystals results not only in better timing properties crucial for the reduction of physical and instrumental background, but also suppresses significantly the pile-ups, thus enabling compensation of the lower efficiency of the plastic scintillators by performing measurements with higher positron source activities.

  4. Alpha-decay properties of /sup 205-208/Fr: Identification of /sup 206/Fr/sup m/

    SciTech Connect

    Ritchie, B.G.; Toth, K.S.; Carter, H.K.; Mlekodaj, R.L.; Spejewski, E.H.

    1981-05-01

    Alpha-particle and ..gamma..-ray spectral measurements were made for /sup 205-208/Fr. A new a emitter (T/sub 1/2/ = 0.7 +- 0.1 sec and E/sub a/ = 6.930 +- 0.005 MeV) was observed and identified with the decay of a previously unknown isomer in /sup 206/Fr. From the a particle and g ray intensities, a decay branching ratios were deduced for /sup 205-208/Fr utilizing available information concerning the nuclides' (electron capture+positron) decay properties. Reduced widths were calculated and compared with those of neighboring nuclei.

  5. Monte Carlo calculations of positron emitter yields in proton radiotherapy.

    PubMed

    Seravalli, E; Robert, C; Bauer, J; Stichelbaut, F; Kurz, C; Smeets, J; Van Ngoc Ty, C; Schaart, D R; Buvat, I; Parodi, K; Verhaegen, F

    2012-03-21

    Positron emission tomography (PET) is a promising tool for monitoring the three-dimensional dose distribution in charged particle radiotherapy. PET imaging during or shortly after proton treatment is based on the detection of annihilation photons following the ß(+)-decay of radionuclides resulting from nuclear reactions in the irradiated tissue. Therapy monitoring is achieved by comparing the measured spatial distribution of irradiation-induced ß(+)-activity with the predicted distribution based on the treatment plan. The accuracy of the calculated distribution depends on the correctness of the computational models, implemented in the employed Monte Carlo (MC) codes that describe the interactions of the charged particle beam with matter and the production of radionuclides and secondary particles. However, no well-established theoretical models exist for predicting the nuclear interactions and so phenomenological models are typically used based on parameters derived from experimental data. Unfortunately, the experimental data presently available are insufficient to validate such phenomenological hadronic interaction models. Hence, a comparison among the models used by the different MC packages is desirable. In this work, starting from a common geometry, we compare the performances of MCNPX, GATE and PHITS MC codes in predicting the amount and spatial distribution of proton-induced activity, at therapeutic energies, to the already experimentally validated PET modelling based on the FLUKA MC code. In particular, we show how the amount of ß(+)-emitters produced in tissue-like media depends on the physics model and cross-sectional data used to describe the proton nuclear interactions, thus calling for future experimental campaigns aiming at supporting improvements of MC modelling for clinical application of PET monitoring.

  6. RARE KAON DECAYS.

    SciTech Connect

    LITTENBERG, L.

    2005-07-19

    Lepton flavor violation (LFV) experiments have probed sensitivities corresponding to mass scales of well over 100 TeV, making life difficult for models predicting accessible LFV in kaon decay and discouraging new dedicated experiments of this type.

  7. Charmless B Decays

    SciTech Connect

    Gradl, Wolfgang; /Edinburgh U.

    2007-03-06

    Rare charmless hadronic B decays are a good testing ground for the standard model. The dominant amplitudes contributing to this class of B decays are CKM suppressed tree diagrams and b {yields} s or b {yields} d loop diagrams (''penguins''). These decays can be used to study interfering standard model (SM) amplitudes and CP violation. They are sensitive to the presence of new particles in the loops, and they provide valuable information to constrain theoretical models of B decays. The B factories BABAR at SLAC and Belle at KEK produce B mesons in the reaction e{sup +}e{sup -} {yields} {Upsilon}(4S) {yields} B{bar B}. So far they have collected integrated luminosities of about 406 fb{sup -1} and 600 fb{sup -1}, respectively. The results presented here are based on subsets of about 200-500 fb{sup -1} and are preliminary unless a journal reference is given.

  8. Radiative B Decays

    SciTech Connect

    Bard, D.; /Imperial Coll., London

    2011-11-23

    I discuss recent results in radiative B decays from the Belle and BaBar collaborations. I report new measurements of the decay rate and CP asymmetries in b {yields} s{gamma} and b {yields} d{gamma} decays, and measurements of the photon spectrum in b {yields} s{gamma}. Radiative penguin decays are flavour changing neutral currents which do not occur at tree level in the standard model (SM), but must proceed via one loop or higher order diagrams. These transitions are therefore suppressed in the SM, but offer access to poorlyknown SM parameters and are also a sensitive probe of new physics. In the SM, the rate is dominated by the top quark contribution to the loop, but non-SM particles could also contribute with a size comparable to leading SM contributions. The new physics effects are potentially large which makes them theoretically very interesting, but due to their small branching fractions they are typically experimentally challenging.

  9. 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.

  10. Towards laboratory produced relativistic electron–positron pair plasmas

    SciTech Connect

    Chen, Hui; Meyerhofer, D. D.; Wilks, S. C.; Cauble, R.; Dollar, F.; Falk, K.; Gregori, G.; Hazi, A.; Moses, E. I.; Murphy, C. D.; Myatt, J.; Park, J.; Seely, J.; Shepherd, R.; Spitkovsky, A.; Stoeckl, C.; Szabo, C. I.; Tommasini, R.; Zulick, C.; Beiersdorfer, P.

    2011-12-01

    We review recent experimental results on the path to producing electron–positron pair plasmas using lasers. Relativistic pair-plasmas and jets are believed to exist in many astrophysical objects and are often invoked to explain energetic phenomena related to Gamma Ray Bursts and Black Holes. On earth, positrons from radioactive isotopes or accelerators are used extensively at low energies (sub-MeV) in areas related to surface science positron emission tomography and basic antimatter science. Experimental platforms capable of producing the high-temperature pair-plasma and high-flux jets required to simulate astrophysical positron conditions have so far been absent. In the past few years, we performed extensive experiments generating positrons with intense lasers where we found that relativistic electron and positron jets are produced by irradiating a solid gold target with an intense picosecond laser pulse. The positron temperatures in directions parallel and transverse to the beam both exceeded 0.5 MeV, and the density of electrons and positrons in these jets are of order 1016 cm-3 and 1013 cm-3, respectively. With the increasing performance of high-energy ultra-short laser pulses, we expect that a high-density, up to 1018 cm-3, relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter.

  11. Recent Developments in Positron Emission Tomography (PET) Instrumentation

    DOE R&D Accomplishments Database

    Derenzo, S. E.; Budinger, T. F.

    1986-04-01

    This paper presents recent detector developments and perspectives for positron emission tomography (PET) instrumentation used for medical research, as well as the physical processes in positron annihilation, photon scattering and detection, tomograph design considerations, and the potentials for new advances in detectors.

  12. Positron-annihilation study of radiation defects in sodium azide

    SciTech Connect

    Etin, G.I.; Ryabykh, S.M.

    1987-07-01

    Annihilation-photon angular correlation has been used to examine radiation defects in sodium azide capable of trapping positrons. The calculated and measured characteristics have been determined for various defects, including micropores filled by radiolytic nitrogen. The positron annihilation rates have been determined for the regions around radiation defects.

  13. Moisture determination in composite materials using positron lifetime techniques

    NASA Technical Reports Server (NTRS)

    Singh, J. J.; Holt, W. R.; Mock, W., Jr.

    1980-01-01

    A technique was developed which has the potential of providing information on the moisture content as well as its depth in the specimen. This technique was based on the dependence of positron lifetime on the moisture content of the composite specimen. The positron lifetime technique of moisture determination and the results of the initial studies are described.

  14. Formation of a high intensity low energy positron string

    NASA Astrophysics Data System (ADS)

    Donets, E. D.; Donets, E. E.; Syresin, E. M.; Itahashi, T.; Dubinov, A. E.

    2004-05-01

    The possibility of a high intensity low energy positron beam production is discussed. The proposed Positron String Trap (PST) is based on the principles and technology of the Electron String Ion Source (ESIS) developed in JINR during the last decade. A linear version of ESIS has been used successfully for the production of intense highly charged ion beams of various elements. Now the Tubular Electron String Ion Source (TESIS) concept is under study and this opens really new promising possibilities in physics and technology. In this report, we discuss the application of the tubular-type trap for the storage of positrons cooled to the cryogenic temperatures of 0.05 meV. It is intended that the positron flux at the energy of 1-5 eV, produced by the external source, is injected into the Tubular Positron Trap which has a similar construction as the TESIS. Then the low energy positrons are captured in the PST Penning trap and are cooled down because of their synchrotron radiation in the strong (5-10 T) applied magnetic field. It is expected that the proposed PST should permit storing and cooling to cryogenic temperature of up to 5×109 positrons. The accumulated cooled positrons can be used further for various physics applications, for example, antihydrogen production.

  15. A Simple Estimate of the Mass of the Positron.

    ERIC Educational Resources Information Center

    Jones, Goronwy Tudor

    1993-01-01

    Discusses a small part of the final state of a high-energy neutrino interaction: a head-on collision of a positron and a stationary electron. Provides a bubble chamber picture and describes the resulting particle effects. Uses momentum to determine the mass of the positron. (MVL)

  16. Monte Carlo modelling of positron transport in real world applications

    NASA Astrophysics Data System (ADS)

    Marjanović, S.; Banković, A.; Šuvakov, M.; Petrović, Z. Lj

    2014-05-01

    Due to the unstable nature of positrons and their short lifetime, it is difficult to obtain high positron particle densities. This is why the Monte Carlo simulation technique, as a swarm method, is very suitable for modelling most of the current positron applications involving gaseous and liquid media. The ongoing work on the measurements of cross-sections for positron interactions with atoms and molecules and swarm calculations for positrons in gasses led to the establishment of good cross-section sets for positron interaction with gasses commonly used in real-world applications. Using the standard Monte Carlo technique and codes that can follow both low- (down to thermal energy) and high- (up to keV) energy particles, we are able to model different systems directly applicable to existing experimental setups and techniques. This paper reviews the results on modelling Surko-type positron buffer gas traps, application of the rotating wall technique and simulation of positron tracks in water vapor as a substitute for human tissue, and pinpoints the challenges in and advantages of applying Monte Carlo simulations to these systems.

  17. Electrons and positrons from expanding supernova envelopes in dense clouds

    NASA Technical Reports Server (NTRS)

    Stephens, S. A.

    1985-01-01

    If antiprotons in cosmic rays are produced as secondary particles in sources, it is expected that positrons are also created by the same process. The interstellar spectra of positrons and electrons are calculated by taking into account such sources. Spectra are then compared with observations.

  18. Recent developments in positron emission tomography (PET) instrumentation

    SciTech Connect

    Derenzo, S.E.; Budinger, T.F.

    1986-04-01

    This paper presents recent detector developments and perspectives for positron emission tomography (PET) instrumentation used for medical research, as well as the physical processes in positron annihilation, photon scattering and detection, tomograph design considerations, and the potentials for new advances in detectors. 117 refs., 4 figs., 4 tabs.

  19. Analysis of positron lifetime spectra in polymers

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.; Mall, Gerald H.; Sprinkle, Danny R.

    1988-01-01

    A new procedure for analyzing multicomponent positron lifetime spectra in polymers was developed. It requires initial estimates of the lifetimes and the intensities of various components, which are readily obtainable by a standard spectrum stripping process. These initial estimates, after convolution with the timing system resolution function, are then used as the inputs for a nonlinear least squares analysis to compute the estimates that conform to a global error minimization criterion. The convolution integral uses the full experimental resolution function, in contrast to the previous studies where analytical approximations of it were utilized. These concepts were incorporated into a generalized Computer Program for Analyzing Positron Lifetime Spectra (PAPLS) in polymers. Its validity was tested using several artificially generated data sets. These data sets were also analyzed using the widely used POSITRONFIT program. In almost all cases, the PAPLS program gives closer fit to the input values. The new procedure was applied to the analysis of several lifetime spectra measured in metal ion containing Epon-828 samples. The results are described.

  20. Electron-Positron Flows around Magnetars

    NASA Astrophysics Data System (ADS)

    Beloborodov, Andrei M.

    2013-11-01

    The twisted magnetospheres of magnetars must sustain a persistent flow of electron-positron plasma. The flow dynamics is controlled by the radiation field around the hot neutron star. The problem of plasma motion in the self-consistent radiation field is solved using the method of virtual beams. The plasma and radiation exchange momentum via resonant scattering and self-organize into the "radiatively locked" outflow with a well-defined, decreasing Lorentz factor. There is an extended zone around the magnetar where the plasma flow is ultra-relativistic; its Lorentz factor is self-regulated so that it can marginally scatter thermal photons. The flow becomes slow and opaque in an outer equatorial zone, where the decelerated plasma accumulates and annihilates; this region serves as a reflector for the thermal photons emitted by the neutron star. The e ± flow carries electric current, which is sustained by a moderate induced electric field. The electric field maintains a separation between the electron and positron velocities, against the will of the radiation field. The two-stream instability is then inevitable, and the induced turbulence can generate low-frequency emission. In particular, radio emission may escape around the magnetic dipole axis of the star. Most of the flow energy is converted to hard X-ray emission, which is examined in an accompanying paper.

  1. ELECTRON-POSITRON FLOWS AROUND MAGNETARS

    SciTech Connect

    Beloborodov, Andrei M.

    2013-11-10

    The twisted magnetospheres of magnetars must sustain a persistent flow of electron-positron plasma. The flow dynamics is controlled by the radiation field around the hot neutron star. The problem of plasma motion in the self-consistent radiation field is solved using the method of virtual beams. The plasma and radiation exchange momentum via resonant scattering and self-organize into the 'radiatively locked' outflow with a well-defined, decreasing Lorentz factor. There is an extended zone around the magnetar where the plasma flow is ultra-relativistic; its Lorentz factor is self-regulated so that it can marginally scatter thermal photons. The flow becomes slow and opaque in an outer equatorial zone, where the decelerated plasma accumulates and annihilates; this region serves as a reflector for the thermal photons emitted by the neutron star. The e {sup ±} flow carries electric current, which is sustained by a moderate induced electric field. The electric field maintains a separation between the electron and positron velocities, against the will of the radiation field. The two-stream instability is then inevitable, and the induced turbulence can generate low-frequency emission. In particular, radio emission may escape around the magnetic dipole axis of the star. Most of the flow energy is converted to hard X-ray emission, which is examined in an accompanying paper.

  2. Development of a Positron Source for JLab at the IAC

    SciTech Connect

    Forest, Tony

    2013-10-12

    We report on the research performed towards the development of a positron sour for Jefferson Lab's (JLab) Continuous Electron Beam Accelerator Facility (CEBAF) in Newport News, VA. The first year of work was used to benchmark the predictions of our current simulation with positron production efficiency measurements at the IAC. The second year used the benchmarked simulation to design a beam line configuration which optimized positron production efficiency while minimizing radioactive waste as well as design and construct a positron converter target. The final year quantified the performance of the positron source. This joint research and development project brought together the experiences of both electron accelerator facilities. Our intention is to use the project as a spring board towards developing a program of accelerator based research and education which will train students to meet the needs of both facilities as well as provide a pool of trained scientists.

  3. Positron beam lifetime spectroscopy at Lawrence Livermore National Laboratory

    SciTech Connect

    Howell, R.H.; Cowan, T.E.; Hartley, J.H.; Stern, P.A. |

    1996-10-01

    Defect analysis is needed for samples ranging in thickness from thin films to large engineering parts. We are meeting that need with two positron beam lifetime spectrometers: on on a 3 MeV electrostatic accelerator and the second on our high current linac beam. The high energy beam spectrometer performs positron lifetime analysis on thick samples which can be encapsulated for containment or for in situ measurements in controlled environments. At our high current beam, we are developing a low energy, microscopically focused, pulsed positron beam to enable positron annihilation lifetime spectroscopy for defect specific, 3-D maps with sub-micron location resolution. The data from these instruments with the aid of first principles calculations of defect specific positron lifetimes.

  4. A compact and high sensitivity positron detector using dual-layer thin GSO scintillators for a small animal PET blood sampling system

    NASA Astrophysics Data System (ADS)

    Yamamoto, Seiichi; Imaizumi, Masao; Shimosegawa, Eku; Kanai, Yasukazu; Sakamoto, Yusuke; Minato, Kotaro; Shimizu, Keiji; Senda, Michio; Hatazawa, Jun

    2010-07-01

    For quantitative measurements of small animals such as mice or rats, a compact and high sensitivity continuous blood sampling detector is required because their blood sampling volume is limited. For this purpose we have developed and tested a new positron detector. The positron detector uses a pair of dual-layer thin gadolinium orthosilicate (GSO) scintillators with different decay times. The front layer detects the positron and the background gamma photons, and the back layer detects the background gamma photons. By subtracting the count rate of the latter from that of the former, the count rate of the positrons can be estimated. The GSO for the front layer has a Ce concentration of 1.5 mol% (decay time of 35 ns), and that for the back layer has a Ce concentration of 0.5 mol% (decay time of 60 ns). By using the pulse shape analysis, the count rate of these two GSOs can be discriminated. The thickness is 0.5 mm, which is thick enough to detect positrons while minimizing the detection of the background gamma photons. These two types of thin GSOs were optically coupled to each other and connected to a metal photomultiplier tube (PMT) through triangular light guides. The signal from the PMT was digitized by 100 MHz free-running A-D converters in the data acquisition system and digitally integrated at two different integration times for the pulse shape analysis. We obtained good separation of the pulse shape distributions of these two GSOs. The energy threshold level was decreased to 80 keV, increasing the sensitivity of the detector. The sensitivity of a small diameter plastic tube was 8.6% and 24% for the F-18 and C-11 positrons, respectively. The count rate performance was linear up to ~50 kcps. The background counts from the gamma photons could be precisely corrected. The time-activity curve (TAC) of the rat artery blood was successfully obtained and showed a good correlation with that measured using a well counter. With these results, we confirmed that the

  5. Experimental Constraints on Left-Right Symmetric Models from Muon Decay

    SciTech Connect

    Bayes, R.; Hillairet, A.; Davydov, Yu. I.; Faszer, W.; Gill, D. R.; Grossheim, A.; Gumplinger, P.; Henderson, R. S.; Hu, J.; Marshall, G. M.; Mischke, R. E.; Olchanski, K.; Olin, A.; Openshaw, R.; Poutissou, J.-M.; Poutissou, R.; Sheffer, G.; Shin, B.; Bueno, J. F.; Hasinoff, M. D.

    2011-01-28

    The TWIST Collaboration has completed a new measurement of the energy-angle spectrum of positrons from the decay of highly polarized muons. A simultaneous measurement of the muon decay parameters {rho}, {delta}, and P{sub {mu}}{sup {pi}{xi}} tests the standard model in a purely leptonic process and provides improved limits for relevant extensions to the standard model. Specifically, for the generalized left-right symmetric model |(g{sub R}/g{sub L}){zeta}|<0.020 and (g{sub L}/g{sub R})m{sub 2}>578 GeV/c{sup 2}, both 90% C.L.

  6. Decaying neutralino dark matter in anomalous U(1){sub H} models

    SciTech Connect

    Sierra, D. Aristizabal; Restrepo, D.; Zapata, Oscar

    2009-09-01

    In supersymmetric models extended with an anomalous U(1){sub H} different R-parity violating couplings can yield an unstable neutralino. We show that in this context astrophysical and cosmological constraints on neutralino decaying dark matter forbid bilinear R-parity breaking neutralino decays and lead to a class of purely trilinear R-parity violating scenarios in which the neutralino is stable on cosmological scales. We have found that among the resulting models some of them become suitable to explain the observed anomalies in cosmic-ray electron/positron fluxes.

  7. Progress of the Hypernuclear Decay Pion Spectroscopy Program at MAMI-C

    NASA Astrophysics Data System (ADS)

    Nagao, Sho; Achenbach, Patrick; Arai, Naoki; Ayerbe Gayoso, Carlos; Böhm, Ralph; Borodina, Olga; Bosnar, Damir; Bozsurt, Vakkas; Devenjak, Luka; Distler, Michael O.; Esser, Anselm; Fujita, Manami; Friščič, Ivica; Fujii, Yuu; Gogami, Toshiyuki; Gómez Rodríguez, Mar; Hirose, Satoshi; Kanda, Hiroki; Kaneta, Masashi; Kim, Eunhee; Kusaka, Junichiro; Margaryan, Amur; Merkel, Harald; Müller, Ulrich; Nakamura, Satoshi N.; Pochodzalla, Josef; Rappold, Christophe; Reinhold, Joerg; Saito, Takehiko R.; Sanchez Lorente, Alicia; Sánchez Majos, Salvador; Sören Schlimme, Björn; Schoth, Matthias; Schulz, Florian; Sfienti, Concettina; Širca, Simon; Takahashi, Yuta; Tang, Liguang; Thiel, Michaela; Tsukada, Kyo; Uchiyama, Daisuke

    We have performed high resolution spectroscopies for binding energies of light Λ hypernuclei with newly established experimental technique "hypernuclear decay pion spectroscopy using electro-photo production". We identified successfully a first decay pion peak from Λ 4H in 2012 experiment. A spectrometer Kaos for K+ tagger was upgraded and suppressed large positron background using a lead wall in the experiment. We performed the next generation experiment with higher statistics in 2014. In this experiment, we achieved twice higher beam intensity and doubled the length of the beam-time with a lower background rate thanks to improvements for the lead wall and a trigger system.

  8. The multi-scattering model for calculations of positron spatial distribution in the multilayer stacks, useful for conventional positron measurements

    SciTech Connect

    Dryzek, Jerzy; Siemek, Krzysztof

    2013-08-21

    The spatial distribution of positrons emitted from radioactive isotopes into stacks or layered samples is a subject of the presented report. It was found that Monte Carlo (MC) simulations using GEANT4 code are not able to describe correctly the experimental data of the positron fractions in stacks. The mathematical model was proposed for calculations of the implantation profile or positron fractions in separated layers or foils being components of a stack. The model takes into account only two processes, i.e., the positron absorption and backscattering at interfaces. The mathematical formulas were applied in the computer program called LYS-1 (layers profile analysis). The theoretical predictions of the model were in the good agreement with the results of the MC simulations for the semi infinite sample. The experimental verifications of the model were performed on the symmetrical and non-symmetrical stacks of different foils. The good agreement between the experimental and calculated fractions of positrons in components of a stack was achieved. Also the experimental implantation profile obtained using the depth scanning of positron implantation technique is very well described by the theoretical profile obtained within the proposed model. The LYS-1 program allows us also to calculate the fraction of positrons which annihilate in the source, which can be useful in the positron spectroscopy.

  9. Quantitative imaging of I-124 using positron emission tomography with applications to radioimmunodiagnosis and radioimmunotherapy

    SciTech Connect

    Pentlow, K.S.; Graham, M.C.; Lambrecht, R.M.; Cheung, N.K.; Larson, S.M. )

    1991-05-01

    Positron emission tomography (PET) is potentially useful for the quantitative imaging of radiolabeled antibodies, leading in turn to improved dosimetry in radioimmunotherapy. Iodine-124 is a positron-emitting nuclide with appropriate chemical properties and half-life (4.2 days) for such studies since the radiolabeling of antibodies with iodine is well understood and the half-life permits measurements over several days. Unfortunately, I-124 has a complex decay scheme with many high-energy gamma rays and a positron abundance of only 25%. It has therefore been largely ignored as a PET-imaging nuclide. However, measurements made with phantoms and animals under realistic conditions using a BGO-based PET scanner have shown that satisfactory imaging and quantitation can be achieved. Investigations of spatial resolution, the linearity of regional observed count rate versus activity in the presence of other activity, and the visualization and quantitation of activity in spheres with different surrounding background activities were carried out with phantoms up to 22 cm in diameter. Compared with F-18, spatial resolution was only slightly degraded (13.5 mm FWHM vs 12 mm FWHM) while linearity was the same over a 10:1 activity range (0.015 to 0.15 MBq/ml for I-124). The visualization and quantitation of spheres was also slightly degraded when using similar imaging times. Increasing the imaging time for I-124 reduced the difference. To verify that the technique would work in vivo, measurements were made of human neuroblastoma tumors in rats which had been injected with I-124 labeled 3F8 antibody. Although the number of samples was small, good agreement was achieved between image-based measurements and direct measurements of excised 4-g tumors. Thus quantitative imaging of I-124 labeled antibodies appears to be possible under realistic conditions.

  10. Roles of superthermal electrons and positrons on positron-acoustic solitary waves and double layers in electron-positron-ion plasmas.

    PubMed

    Alam, M S; Uddin, M J; Masud, M M; Mamun, A A

    2014-09-01

    Positron-acoustic (PA) solitary waves (SWs) and double layers (DLs) in four-component plasmas consisting of immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated both numerically and analytically by deriving Korteweg-de Vries (K-dV), modified K-dV (mK-dV), and Gardner equations along with their DLs solutions using the reductive perturbation method. It is examined that depending on the plasma parameters, the K-dV SWs, Gardner SWs, and DLs support either compressive or rarefactive structures, whereas mK-dV SWs support only compressive structure. It is also found that the presence of superthermal (kappa distributed) hot positrons and hot electrons significantly modify the basic features of PA SWs as well as PA DLs. Besides, the critical number density ratio of hot positrons and cold positrons play an important role in the polarity of PA SWs and DLs. The implications of our results in different space as well as laboratory plasma environments are briefly discussed.

  11. The impact of positrons beam on the propagation of super freak waves in electron-positron-ion plasmas

    NASA Astrophysics Data System (ADS)

    Ali Shan, S.; El-Tantawy, S. A.

    2016-07-01

    In this work, we examine the nonlinear propagation of planar ion-acoustic freak waves in an unmagnetized plasma consisting of cold positive ions and superthermal electrons subjected to cold positrons beam. For this purpose, the reductive perturbation method is used to derive a nonlinear Schrödinger equation (NLSE) for the evolution of electrostatic potential wave. We determine the domain of the plasma parameters where the rogue waves exist. The effect of the positron beam on the modulational instability of the ion-acoustic rogue waves is discussed. It is found that the region of the modulational stability is enhanced with the increase of positron beam speed and positron population. Second as positrons beam increases the nonlinearities of the plasma system, large amplitude ion acoustic rogue waves are pointed out. The present results will be helpful in providing a good fit between the theoretical analysis and real applications in future laboratory plasma experiments.

  12. Applicability of modified effective-range theory to positron-atom and positron-molecule scattering

    SciTech Connect

    Idziaszek, Zbigniew; Karwasz, Grzegorz

    2006-06-15

    We analyze low-energy scattering of positrons on Ar atoms and N{sub 2} molecules using the modified effective-range theory (MERT) developed by O'Malley, et al. [J. Math. Phys. 2, 491 (1961)]. We use the formulation of MERT based on exact solutions of the Schroedinger equation with polarization potential rather than low-energy expansions of phase shifts into momentum series. We show that MERT describes the experimental data well, provided that effective-range expansion is performed both for s- and p-wave scattering, which dominate in the considered regime of positron energies (0.4-2 eV). We estimate the values of the s-wave scattering length and the effective range for e{sup +}-Ar and e{sup +}-N{sub 2} collisions.

  13. Single-photon transmission measurements in positron tomography using 137Cs.

    PubMed

    Yu, S K; Nahmias, C

    1995-07-01

    Transmission measurements are an essential step in the quantification of radioisotope distributions in vivo using positron tomographic techniques. The development of a new technique for measuring transmission data that relies on the detection of photons in 'singles' mode rather than 'coincidence' mode no longer restricts the choice of transmission sources to those that decay by positron emission. The motivation for using the 'singles' mode of operation is the substantial increase in count rate that can be achieved. This corresponds to a great increase in the statistical accuracy of the transmission data. We propose 137Cs as a suitable isotope for this purpose. 137Cs is more economical than 68Ge, the traditional source used for transmission measurements, in terms of longer half-life and lower financial cost. 137Cs can be used for transmission measurements without any recalibration of the tomograph, and the estimated spatial resolution is comparable to that obtained using annihilation photons. A simple extrapolation method is developed, which allows extrapolation of the attenuation coefficients measured at 662 keV to 511 keV. A dual-energy-window technique, whereby correction can be made on-the-fly during acquisition, is used for scatter correction. The measured linear attenuation coefficients agree with predicted values.

  14. Calculations of the interference of annihilation radiations with positron spectra in a Ge detector

    NASA Astrophysics Data System (ADS)

    Avignone, F. T.; Noma, H.; Moltz, D. M.; Toth, K. S.

    1981-10-01

    The distortion of the Kurie plots of allowed positron spectra due to annihilation radiations was calculated by a simple Monte-Carlo technique for a small intrinsic Ge detector. The experimentally observed non-linearity near the end point is accurately reproduced by the calculations. Corrections were calculated for 15 theoretical allowed spectra with end-point energies ranging from 2.5 to 10 MeV for one small detector 1.6 cm in diameter and 0.7 cm thick and one larger detector 4.0 cm in diameter and 1.0 cm thick. The major effect of this interference is to shift the end-point up in energy from 182 keV at 2.5 MeV and to 204 keV at 9 MeV in the small detector and from 279 keV at 2.5 MeV and to 321 keV at 9 MeV in the larger detector. The method was used to correct the end-point energies of the two positron branches in the decay of 82Sr. The corrected data give values of (3.19 ± 0.02) and (2.42 ± 0.02) MeV. The resulting Q-value is (4.21 ± 0.02) MeV.

  15. Receptor-specific positron emission tomography radiopharmaceuticals: /sup 75/Br-labeled butyrophenone neuroleptics

    SciTech Connect

    Moerlein, S.M.; Stoecklin, G.; Weinhard, K.; Pawlik, G.; Heiss, W.D.

    1985-11-01

    Cerebral dopaminergic D/sub 2/ receptors are involved in several common disease states, such as schizophrenia, Parkinson's disease, and Huntington's chorea. The use of radiolabeled D/sub 2/ receptor-binding ligands with positron emission tomography (PET) to noninvasively quantitate D/sub 2/ receptor densities thus has potential application in medicine. Butyrophenone neuroleptics have a high in vitro and in vivo binding affinity for cerebral D/sub 2/ receptors, and due to the useful chemical and nuclear decay properties of /sup 74/Br (76% ..beta../sup +/, half-life = 1.6 h), the authors have evaluated radiobrominated bromospiperone (BSP), brombenperidol (BBP), and bromperidol (BP) as radiopharmaceuticals for use with PET.

  16. Positron annihilation study on free volume of amino acid modified, starch-grafted acrylamide copolymer

    NASA Astrophysics Data System (ADS)

    Mahmoud, K. R.; Al-Sigeny, S.; Sharshar, T.; El-Hamshary, H.

    2006-05-01

    Free volume measurements using positron annihilation lifetime spectroscopy was performed for uncrosslinked and crosslinked starch-grafted polyacrylamide, and their modified amino acid samples including some of their iron(III) complexes. The measurements were performed at room temperature. The analysis of lifetime spectra yielded mostly three lifetime components. It was observed that the values of the short lifetime component τ1 are slightly higher than the lifetime associated with the self-decay of para-positronium atoms in polymers. The free volume was probed using ortho-positronium pick-off annihilation lifetime parameters. The mean free volume has also been calculated from the lifetime data. The avrage value of this parameter of the crosslinked polymer were found to be higher than those of the uncrosslinked polymer.

  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. Na-22 decay gamma rays from classical novae

    NASA Technical Reports Server (NTRS)

    Truran, James W.

    1993-01-01

    NASA Grant NAG 5-1565 has provided support for a program of theoretical research in nuclear astrophysics and related areas, focusing upon the possibility of detecting gamma rays from nearby novae. Particular attention has been given to the evaluation of the theoretical expectations for gamma ray emission from four possible sources: (1) the positron decays of the unstable CNO and fluorine isotopes that are transported to the surface regions of the envelope in the earliest stages of the outbursts; (2) Be-7 decay gamma rays, (3) Na-22 decay gamma rays released in the later stages of the outbursts; and (4) Al-26 decay gamma rays from novae and their possible contribution to Galactic emission. The critical questions of (1) the frequency of occurrence of ONeMg-enriched novae; (2) the expected Galactic distribution of the novae that produce 26Al; and (3) the nature of the observed soft X-ray emission from classical novae, have also been addressed. Considerable progress in research has been achieved on many of these fronts. Brief summaries of the results of several research projects are presented.

  19. Faking ordinary photons by displaced dark photon decays

    NASA Astrophysics Data System (ADS)

    Tsai, Yuhsin; Wang, Lian-Tao; Zhao, Yue

    2017-01-01

    A light metastable dark photon decaying into a collimated electron/positron pair can fake a photon, either converted or unconverted, at the LHC. The detailed object identification relies on the specifics of the detector and strategies for the reconstruction. We study the fake rate based on the ATLAS (CMS) detector geometry and show that it can be O(1) with a generic choice of parameters. Especially, the probability of being registered as a photon is angular dependent. Such detector effects can induce bias to measurements on certain properties of new physics. In this paper, we consider the scenario where dark photons in final states are from a heavy resonance decay. Consequently, the detector effects can dramatically affect the results when determining the spin of a resonance. Further, if the decay products from the heavy resonance are one photon and one dark photon, which has a large probability to fake a diphoton event, the resonance is allowed to be a vector. Because of the difference in detectors, the cross sections measured in ATLAS and CMS do not necessarily match. Furthermore, if the diphoton signal is given by the dark photons, the standard model Z γ and Z Z final states do not necessarily come with the γ γ channel, which is a unique signature in our scenario. The issue studied here is relevant also for any future new physics searches with photon(s) in the final state. We discuss possible ways of distinguishing dark photon decay and a real photon in the future.

  20. Positron Emission Tomography of the Heart

    DOE R&D Accomplishments Database

    Schelbert, H. R.; Phelps, M. E.; Kuhl, D. E.

    1979-01-01

    Positron emission computed tomography (PCT) represents an important new tool for the noninvasive evaluation and, more importantly, quantification of myocardial performance. Most currently available techniques permit assessment of only one aspect of cardiac function, i.e., myocardial perfusion by gamma scintillation camera imaging with Thallium-201 or left ventricular function by echocardiography or radionuclide angiocardiography. With PCT it may become possible to study all three major segments of myocardial performance, i.e., regional blood flow, mechanical function and, most importantly, myocardial metabolism. Each of these segments can either be evaluated separately or in combination. This report briefly describes the principles and technological advantages of the imaging device, reviews currently available radioactive tracers and how they can be employed for the assessment of flow, function and metabolism; and, lastly, discusses possible applications of PCT for the study of cardiac physiology or its potential role in the diagnosis of cardiac disease.

  1. Compact conscious animal positron emission tomography scanner

    DOEpatents

    Schyler, David J.; O'Connor, Paul; Woody, Craig; Junnarkar, Sachin Shrirang; Radeka, Veljko; Vaska, Paul; Pratte, Jean-Francois; Volkow, Nora

    2006-10-24

    A method of serially transferring annihilation information in a compact positron emission tomography (PET) scanner includes generating a time signal for an event, generating an address signal representing a detecting channel, generating a detector channel signal including the time and address signals, and generating a composite signal including the channel signal and similarly generated signals. The composite signal includes events from detectors in a block and is serially output. An apparatus that serially transfers annihilation information from a block includes time signal generators for detectors in a block and an address and channel signal generator. The PET scanner includes a ring tomograph that mounts onto a portion of an animal, which includes opposing block pairs. Each of the blocks in a block pair includes a scintillator layer, detection array, front-end array, and a serial encoder. The serial encoder includes time signal generators and an address signal and channel signal generator.

  2. Tumor Quantification in Clinical Positron Emission Tomography

    PubMed Central

    Bai, Bing; Bading, James; Conti, Peter S

    2013-01-01

    Positron emission tomography (PET) is used extensively in clinical oncology for tumor detection, staging and therapy response assessment. Quantitative measurements of tumor uptake, usually in the form of standardized uptake values (SUVs), have enhanced or replaced qualitative interpretation. In this paper we review the current status of tumor quantification methods and their applications to clinical oncology. Factors that impede quantitative assessment and limit its accuracy and reproducibility are summarized, with special emphasis on SUV analysis. We describe current efforts to improve the accuracy of tumor uptake measurements, characterize overall metabolic tumor burden and heterogeneity of tumor uptake, and account for the effects of image noise. We also summarize recent developments in PET instrumentation and image reconstruction and their impact on tumor quantification. Finally, we offer our assessment of the current development needs in PET tumor quantification, including practical techniques for fully quantitative, pharmacokinetic measurements. PMID:24312151

  3. Positron Emission Tomography with improved spatial resolution

    SciTech Connect

    Drukier, A.K.

    1990-04-01

    Applied Research Corporation (ARC) proposed the development of a new class of solid state detectors called Superconducting Granular Detectors (SGD). These new detectors permit considerable improvements in medical imaging, e.g. Positron Emission Tomography (PET). The biggest impact of this technique will be in imaging of the brain. It should permit better clinical diagnosis of such important diseases as Altzheimer's or schizophrenia. More specifically, we will develop an improved PET-imager; a spatial resolution 2 mm may be achievable with SGD. A time-of-flight capability(t {approx} 100 psec) will permit better contrast and facilitate 3D imaging. In the following, we describe the results of the first 9 months of the development.

  4. Instrumentation optimization for positron emission mammography

    SciTech Connect

    Moses, William W.; Qi, Jinyi

    2003-06-05

    The past several years have seen designs for PET cameras optimized to image the breast, commonly known as Positron Emission Mammography or PEM cameras. The guiding principal behind PEM instrumentation is that a camera whose field of view is restricted to a single breast has higher performance and lower cost than a conventional PET camera. The most common geometry is a pair of parallel planes of detector modules, although geometries that encircle the breast have also been proposed. The ability of the detector modules to measure the depth of interaction (DOI) is also a relevant feature. This paper finds that while both the additional solid angle coverage afforded by encircling the breast and the decreased blurring afforded by the DOI measurement improve performance, the ability to measure DOI is more important than the ability to encircle the breast.

  5. Making Relativistic Positrons Using Ultra-Intense Short Pulse Lasers

    SciTech Connect

    Chen, H; Wilks, S; Bonlie, J; Chen, C; Chen, S; Cone, K; Elberson, L; Gregori, G; Liang, E; Price, D; Van Maren, R; Meyerhofer, D D; Mithen, J; Murphy, C V; Myatt, J; Schneider, M; Shepherd, R; Stafford, D; Tommasini, R; Beiersdorfer, P

    2009-08-24

    This paper describes a new positron source produced using ultra-intense short pulse lasers. Although it has been studied in theory since as early as the 1970s, the use of lasers as a valuable new positron source was not demonstrated experimentally until recent years, when the petawatt-class short pulse lasers were developed. In 2008 and 2009, in a series of experiments performed at Lawrence Livermore National Laboratory, a large number of positrons were observed after shooting a millimeter thick solid gold target. Up to 2 x 10{sup 10} positrons per steradian ejected out the back of {approx}mm thick gold targets were detected. The targets were illuminated with short ({approx}1 ps) ultra-intense ({approx}1 x 10{sup 20} W/cm{sup 2}) laser pulses. These positrons are produced predominantly by the Bethe-Heitler process, and have an effective temperature of 2-4 MeV, with the distribution peaking at 4-7 MeV. The angular distribution of the positrons is anisotropic. For a wide range of applications, this new laser based positron source with its unique characteristics may complements the existing sources using radioactive isotopes and accelerators.

  6. The Calibration of the PEPPo Polarimeter for Electrons and Positrons

    SciTech Connect

    Adeyemi, Adeleke Hakeem; Voutier, Eric J-.M.

    2013-06-01

    The PEPPo (Polarized Electrons for Polarized Positrons) experiment at Jefferson Laboratory investigated the polarization transfer from longitudinally polarized electrons to longitudinally polarized positrons, with the aim of developing this technology for a low energy (~MeV) polarized positron source. Polarization of the positrons was measured by means of a Compton transmission polarimeter where incoming positrons transfer their polarization into circularly polarized photons that were subsequently analyzed by a thick polarized iron target. The measurement of the transmitted photon flux with respect to the orientation of the target polarization (+-) or the helicity (+-) of the incoming leptons provided the measurement of their polarization. Similar measurements with a known electron beam were also performed for calibration purposes. This presentation will describe the apparatus and calibrations performed at the injector at the Jefferson Laboratory to measure positron polarization in the momentum range 3.2-6.2 MeV/c, specifically to quantify the positron analyzing power from electron experimental data measured over a comparable momentum range.

  7. Positron scattering measurements for application to medical physics

    NASA Astrophysics Data System (ADS)

    Sullivan, James

    2015-09-01

    While the use of positrons in medical imaging is now well established, there is still much to learn regarding the transport of positrons through the body, and the subsequent damage induced. Current models of dosimetry use only a crude approximation of the collision physics involved, and at low energies misrepresent the thermalisation process to a considerable degree. Recently, collaborative work has commenced to attempt to refine these models, incorporating a better representation of the underlying physics and trying to gain a better understanding of the damage done after the emission of a positron from a medical radioisotope. This problem is being attacked from several different angles, with new models being developed based upon established techniques in plasma and swarm physics. For all these models, a realistic representation of the collision processes of positrons with relevant molecular species is required. At the Australian National University, we have undertaken a program of measurements of positron scattering from a range of molecules that are important in biological systems, with a focus on analogs to DNA. This talk will present measurements of positron scattering from a range of these molecules, as well as describing the experimental techniques employed to make such measurements. Targets have been measured that are both liquid and solid at room temperature, and new approaches have been developed to get absolute cross section data. The application of the data to various models of positron thermalisation will also be described.

  8. Making relativistic positrons using ultraintense short pulse lasers

    SciTech Connect

    Chen Hui; Wilks, S. C.; Bonlie, J. D.; Chen, S. N.; Cone, K. V.; Elberson, L. N.; Price, D. F.; Schneider, M. B.; Shepherd, R.; Stafford, D. C.; Tommasini, R.; Van Maren, R.; Beiersdorfer, P.; Gregori, G.; Meyerhofer, D. D.; Myatt, J.

    2009-12-15

    This paper describes a new positron source using ultraintense short pulse lasers. Although it has been theoretically studied since the 1970s, the use of lasers as a valuable new positron source was not demonstrated experimentally until recent years, when the petawatt-class short pulse lasers were developed. In 2008 and 2009, in a series of experiments performed at the Lawrence Livermore National Laboratory, a large number of positrons were observed after shooting a millimeter thick solid gold target. Up to 2x10{sup 10} positrons/s ejected at the back of approximately millimeter thick gold targets were detected. The targets were illuminated with short (approx1 ps) ultraintense (approx1x10{sup 20} W/cm{sup 2}) laser pulses. These positrons are produced predominantly by the Bethe-Heitler process and have an effective temperature of 2-4 MeV, with the distribution peaking at 4-7 MeV. The angular distribution of the positrons is anisotropic. For a wide range of applications, this new laser-based positron source with its unique characteristics may complement the existing sources based on radioactive isotopes and accelerators.

  9. Data for modeling of positron collisions and transport in gases

    NASA Astrophysics Data System (ADS)

    Petrović, Z. Lj.; Banković, A.; Dujko, S.; Marjanović, S.; Malović, G.; Sullivan, J. P.; Buckman, S. J.

    2013-07-01

    We review the current status of positron cross sections for collisions with atoms and molecules from the viewpoint of their use in studies of positron transport processes in gases, liquids and human tissue. The data include cross sections for positron scattering in rare gases, molecular gases (eg., for N2, H2, CO2, CF4) and in particular for organic molecules and those relevant for applications in medicine (e.g. formic acid and water vapor). The cross sections were taken from an assessment of previously published positron-target cross sections. All of the cross sections are based on binary collision measurements and theoretical calculations, and they were not explicitly modified according to the standard swarm analysis. The main reason for this is systematic lack of experimental data for positron transport properties in gases. However, we believe that our compiled sets of cross sections are at level of sophistication, and of sufficient accuracy, to provide correct interpretation of future positron-based experiments. Using these cross sections as an input in our Monte Carlo simulations and Boltzmann equation treatment, we review some interesting points observed in the profiles of various transport coefficients for positrons in gases. Particular emphasis is placed upon the analysis of kinetic phenomena generated by the explicit influence of Ps formation.

  10. A combined matrix isolation spectroscopy and cryosolid positron moderation apparatus

    SciTech Connect

    Molek, Christopher D.; Michael Lindsay, C.; Fajardo, Mario E.

    2013-03-15

    We describe the design, construction, and operation of a novel apparatus for investigating efficiency improvements in thin-film cryogenic solid positron moderators. We report results from solid neon, argon, krypton, and xenon positron moderators which illustrate the capabilities and limitations of our apparatus. We integrate a matrix isolation spectroscopy diagnostic within a reflection-geometry positron moderation system. We report the optical thickness, impurity content, and impurity trapping site structures within our moderators determined from infrared absorption spectra. We use a retarding potential analyzer to modulate the flow of slow positrons, and report positron currents vs. retarding potential for the different moderators. We identify vacuum ultraviolet emissions from irradiated Ne moderators as the source of spurious signals in our channel electron multiplier slow positron detection channel. Our design is also unusual in that it employs a sealed radioactive Na-22 positron source which can be translated relative to, and isolated from, the cryogenic moderator deposition substrate. This allows us to separate the influences on moderator efficiency of surface contamination by residual gases from those of accumulated radiation damage.

  11. Scattering of positrons and electrons by alkali atoms

    NASA Technical Reports Server (NTRS)

    Stein, T. S.; Kauppila, W. E.; Kwan, C. K.; Lukaszew, R. A.; Parikh, S. P.; Wan, Y. J.; Zhou, S.; Dababneh, M. S.

    1990-01-01

    Absolute total scattering cross sections (Q sub T's) were measured for positrons and electrons colliding with sodium, potassium, and rubidium in the 1 to 102 eV range, using the same apparatus and experimental approach (a beam transmission technique) for both projectiles. The present results for positron-sodium and -rubidium collisions represent the first Q sub T measurements reported for these collision systems. Features which distinguish the present comparisons between positron- and electron-alkali atom Q sub T's from those for other atoms and molecules (room-temperature gases) which have been used as targets for positrons and electrons are the proximity of the corresponding positron- and electron-alkali atom Q sub T's over the entire energy range of overlap, with an indication of a merging or near-merging of the corresponding positron and electron Q sub T's near (and above) the relatively low energy of about 40 eV, and a general tendency for the positron-alkali atom Q sub T's to be higher than the corresponding electron values as the projectile energy is decreased below about 40 eV.

  12. Applications and advances of positron beam spectroscopy: appendix a

    SciTech Connect

    Howell, R. H., LLNL

    1997-11-05

    Over 50 scientists from DOE-DP, DOE-ER, the national laboratories, academia and industry attended a workshop held on November 5-7, 1997 at Lawrence Livermore National Laboratory jointly sponsored by the DOE-Division of Materials Science, The Materials Research Institute at LLNL and the University of California Presidents Office. Workshop participants were charged to address two questions: Is there a need for a national center for materials analysis using positron techniques and can the capabilities at Lawrence Livermore National Laboratory serve this need. To demonstrate the need for a national center the workshop participants discussed the technical advantages enabled by high positron currents and advanced measurement techniques, the role that these techniques will play in materials analysis and the demand for the data. There were general discussions lead by review talks on positron analysis techniques, and their applications to problems in semiconductors, polymers and composites, metals and engineering materials, surface analysis and advanced techniques. These were followed by focus sessions on positron analysis opportunities in these same areas. Livermore now leads the world in materials analysis capabilities by positrons due to developments in response to demands of science based stockpile stewardship. There was a detailed discussion of the LLNL capabilities and a tour of the facilities. The Livermore facilities now include the worlds highest current beam of keV positrons, a scanning pulsed positron microprobe under development capable of three dimensional maps of defect size and concentration, an MeV positron beam for defect analysis of large samples, and electron momentum spectroscopy by positrons. This document is a supplement to the written summary report. It contains a complete schedule, list of attendees and the vuegraphs for the presentations in the review and focus sessions.

  13. Decay of superdeformed bands

    SciTech Connect

    Carpenter, M.P.; Khoo, T.L.; Lauritsen, T.

    1995-12-31

    One of the major challenges in the study of superdeformation is to directly connect the large number of superdeformed bands now known to the yrast states. In this way, excitation energies, spins and parities can be assigned to the levels in the second well which is essential to establish the collective and single-particle components of these bands. This paper will review some of the progress which has been made to understand the decay of superdeformed bands using the new arrays including the measurement of the total decay spectrum and the establishment of direct one-step decays from the superdeformed band to the yrast line in {sup 194}Hg. 42 refs., 5 figs.

  14. Suppressed Charmed B Decay

    SciTech Connect

    Snoek, Hella Leonie

    2009-06-02

    This thesis describes the measurement of the branching fractions of the suppressed charmed B0 → D*- a0+ decays and the non-resonant B0 → D*- ηπ+ decays in approximately 230 million Υ(4S) → B$\\bar{B}$ events. The data have been collected with the BABAR detector at the PEP-II B factory at the Stanford Linear Accelerator Center in California. Theoretical predictions of the branching fraction of the B0 → D*- a{sub 0}+ decays show large QCD model dependent uncertainties. Non-factorizing terms, in the naive factorization model, that can be calculated by QCD factorizing models have a large impact on the branching fraction of these decay modes. The predictions of the branching fractions are of the order of 10-6. The measurement of the branching fraction gives more insight into the theoretical models. In general a better understanding of QCD models will be necessary to conduct weak interaction physics at the next level. The presence of CP violation in electroweak interactions allows the differentiation between matter and antimatter in the laws of physics. In the Standard Model, CP violation is incorporated in the CKM matrix that describes the weak interaction between quarks. Relations amongst the CKM matrix elements are used to present the two relevant parameters as the apex of a triangle (Unitarity Triangle) in a complex plane. The over-constraining of the CKM triangle by experimental measurements is an important test of the Standard Model. At this moment no stringent direct measurements of the CKM angle γ, one of the interior angles of the Unitarity Triangle, are available. The measurement of the angle γ can be performed using the decays of neutral B mesons. The B0 → D*- a0+ decay is sensitive to the angle γ and, in comparison to the current decays that are being employed, could significantly

  15. Implications of the first AMS-02 measurement for dark matter annihilation and decay

    SciTech Connect

    Jin, Hong-Bo; Wu, Yue-Liang; Zhou, Yu-Feng E-mail: ylwu@itp.ac.cn

    2013-11-01

    In light of the first measurement of the positron fraction by the AMS-02 experiment, we perform a detailed global analysis on the interpretation of the latest data of PAMELA, Fermi-LAT, and AMS-02 in terms of dark matter (DM) annihilation and decay in various propagation models. The allowed regions for the DM particle mass and annihilation cross section or decay life-time are obtained for channels with leptonic final states: 2e, 2μ, 2τ, 4e, 4μ and 4τ. We show that for the conventional astrophysical background the AMS-02 positron fraction data alone favour a DM particle mass ∼ 500(800) GeV if DM particles annihilate dominantly into 2μ(4μ) final states, which is significantly lower than that favoured by the Fermi-LAT data of the total flux of electrons and positrons. The allowed regions by the two experiments do not overlap at a high confidence level (99.99999%C.L.). We consider a number of propagation models with different halo height Z{sub h}, diffusion parameters D{sub 0} and δ{sub 1/2}, and power indices of primary nucleon sources γ{sub p1/p2}. The normalization and the slope of the electron background are also allowed to vary. We find that the tension between the two experiments can be only slightly reduced in the propagation model with large Z{sub h} and D{sub 0}. The consistency of fit is improved for annihilation channels with 2τ and 4τ final states which favour TeV scale DM particle with large cross sections above ∼ 10{sup −23} cm{sup 3}s{sup −1}. In all the considered leptonic channels, the current data favour the scenario of DM annihilation over DM decay. In the decay scenario, the charge asymmetric DM decay is slightly favoured.

  16. Positron production using a 1.7 MV pelletron accelerator

    SciTech Connect

    Alcantara, K. F.; Santos, A. C. F.; Crivelli, P.

    2013-04-19

    We report the foremost phase of a fourth generation positron source, being constructed at the Federal University of Rio de Janeiro. Positron yields are reported by making use of the {sup 19}F(p,{alpha}e{sup +}e{sup -}){sup 16}O reaction, where the fluorine target is in the form of a CaF{sub 2} pellet. Positron production has been observed by detecting 511 keV annihilation gamma rays emerging from the irradiated CaF{sub 2} target.

  17. Bulk defect analysis with a high-energy positron beam

    SciTech Connect

    Hartley, J. H.; Howell, R. H.; Sterne, P. A.

    1998-09-23

    A program using a positron beam to probe defects in bulk materials has been developed at Lawrence Livermore National Laboratory. Positron annihilation lifetime spectroscopy (PALS) provides non-destructive analysis of average defect size and concentration. A 3 MeV positron beam is supplied by Sodium-22 at the terminal of a Pelletron accelerator. The high-energy beam allows large (greater than or equal to 1 cm2) engineering samples to be measured in air or even sealed in an independent environment. A description of the beam-PALS system will be presented along with a summary of recent measuremen

  18. High intensity positron beam and angular correlation experiments at Livermore

    SciTech Connect

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

    1985-03-01

    A positron beam apparatus that produces a variable energy positron beam with sufficient intensity to perform new positron experiments in an ultrahigh vacuum environment has been installed at the Lawrence Livermore 100 MeV electron linac. We have installed two large area position sensitive gamma-ray detectors to measure angular correlations in two dimensions and a separate highly collimated detector to measure positronium energy distributions by time-of-flight velocity determination. Data from measurements on single crystals of Cu will be described.

  19. Progress toward positron-electron pair plasma experiments

    SciTech Connect

    Stenson, E. V.; Stanja, J.; Hergenhahn, U.; Saitoh, H.; Niemann, H.; Pedersen, T. Sunn; Marx, G. H.; Schweikhard, L.; Danielson, J. R.; Surko, C. M.; Hugenschmidt, C.

    2015-06-29

    Electron-positron plasmas have been of theoretical interest for decades, due to the unique plasma physics that arises from all charged particles having precisely identical mass. It is only recently, though, that developments in non-neutral plasma physics (both in linear and toroidal geometries) and in the flux of sources for cold positrons have brought the goal of conducting electron-positron pair plasma experiments within reach. The APEX/PAX collaboration is working on a number of projects in parallel toward that goal; this paper provides an overview of recent, current, and upcoming activities.

  20. Anti-hydrogen production with positron beam ion trap

    SciTech Connect

    Itahashi, Takahisa

    2008-08-08

    In low-energy antiproton physics, it is advantageous to be able to manipulate anti-particles as freely as normal particles. A robust production and storage system for high-quality positrons and antiprotons would be a substantial advance for the development of anti-matter science. The idea of electron beam ion trap could be applied for storage of anti-particle when the electron beam could be replaced by the positron beam. The bright positron beam would be brought about using synchrotron radiation source with a superconducting wiggler. The new scheme for production of anti-particles is proposed by using new accelerator technologies.

  1. Positrons in the Galaxy: Their Births, Marriages and Deaths

    NASA Technical Reports Server (NTRS)

    Skinner, Gerald K.

    2010-01-01

    High energy (approximately GeV) positrons are seen within cosmic rays and observation of a narrow line at 511 keV shows that positrons are annihilating in the galaxy after slowing down to approximately keV energies or less. Our state of knowledge of the origin of these positrons, of the formation of positronium 'atoms', and of the circumstances of their annihilation or escape from the galaxy are reviewed and the question of whether the two phenomena are linked is discussed.

  2. Positronic molecule calculations using Monte Carlo configuration interaction

    NASA Astrophysics Data System (ADS)

    Coe, Jeremy P.; Paterson, Martin J.

    2016-02-01

    We modify the Monte Carlo configuration interaction procedure to model atoms and molecules combined with a positron. We test this method with standard quantum chemistry basis sets on a number of positronic systems and compare results with the literature and full configuration interaction when appropriate. We consider positronium hydride, positronium hydroxide, lithium positride and a positron interacting with lithium, magnesium or lithium hydride. We demonstrate that we can capture much of the full configuration interaction results, but often require less than 10% of the configurations of these multireference wavefunctions. The effect of the number of frozen orbitals is also discussed.

  3. Methods and applications of positron-based medical imaging

    NASA Astrophysics Data System (ADS)

    Herzog, H.

    2007-02-01

    Positron emission tomography (PET) is a diagnostic imaging method to examine metabolic functions and their disorders. Dedicated ring systems of scintillation detectors measure the 511 keV γ-radiation produced in the course of the positron emission from radiolabelled metabolically active molecules. A great number of radiopharmaceuticals labelled with 11C, 13N, 15O, or 18F positron emitters have been applied both for research and clinical purposes in neurology, cardiology and oncology. The recent success of PET with rapidly increasing installations is mainly based on the use of [ 18F]fluorodeoxyglucose (FDG) in oncology where it is most useful to localize primary tumours and their metastases.

  4. Theoretical survey on positronium formation and ionisation in positron atom scattering

    NASA Technical Reports Server (NTRS)

    Basu, Madhumita; Ghosh, A. S.

    1990-01-01

    The recent theoretical studies are surveyed and reported on the formation of exotic atoms in positron-hydrogen, positron-helium and positron-lithium scattering specially at intermediate energy region. The ionizations of these targets by positron impact was also considered. Theoretical predictions for both the processes are compared with existing measured values.

  5. Flavor changing nucleon decay

    NASA Astrophysics Data System (ADS)

    Maekawa, Nobuhiro; Muramatsu, Yu

    2017-04-01

    Recent discovery of neutrino large mixings implies the large mixings in the diagonalizing matrices of 5 bar fields in SU (5) grand unified theory (GUT), while the diagonalizing matrices of 10 fields of SU (5) are expected to have small mixings like Cabibbo-Kobayashi-Maskawa matrix. We calculate the predictions of flavor changing nucleon decays (FCND) in SU (5), SO (10), and E6 GUT models which have the above features for mixings. We found that FCND can be the main decay mode and play an important role to test GUT models.

  6. Search for the decay

    NASA Astrophysics Data System (ADS)

    Aaij, R.; Adeva, B.; Adinolfi, M.; Affolder, A.; Ajaltouni, Z.; Akar, S.; Albrecht, J.; Alessio, F.; Alexander, M.; Ali, S.; Alkhazov, G.; Alvarez Cartelle, P.; Alves, A. A.; Amato, S.; Amerio, S.; Amhis, Y.; An, L.; Anderlini, L.; Anderson, J.; Andreotti, M.; Andrews, J. E.; Appleby, R. B.; Aquines Gutierrez, O.; Archilli, F.; d'Argent, P.; Artamonov, A.; Artuso, M.; Aslanides, E.; Auriemma, G.; Baalouch, M.; Bachmann, S.; Back, J. J.; Badalov, A.; Baesso, C.; Baldini, W.; Barlow, R. J.; Barschel, C.; Barsuk, S.; Barter, W.; Batozskaya, V.; Battista, V.; Bay, A.; Beaucourt, L.; Beddow, J.; Bedeschi, F.; Bediaga, I.; Bel, L. J.; Belyaev, I.; Ben-Haim, E.; Bencivenni, G.; Benson, S.; Benton, J.; Berezhnoy, A.; Bernet, R.; Bertolin, A.; Bettler, M.-O.; van Beuzekom, M.; Bien, A.; Bifani, S.; Bird, T.; Birnkraut, A.; Bizzeti, A.; Blake, T.; Blanc, F.; Blouw, J.; Blusk, S.; Bocci, V.; Bondar, A.; Bondar, N.; Bonivento, W.; Borghi, S.; Borsato, M.; Bowcock, T. J. V.; Bowen, E.; Bozzi, C.; Braun, S.; Brett, D.; Britsch, M.; Britton, T.; Brodzicka, J.; Brook, N. H.; Bursche, A.; Buytaert, J.; Cadeddu, S.; Calabrese, R.; Calvi, M.; Calvo Gomez, M.; Campana, P.; Campora Perez, D.; Capriotti, L.; Carbone, A.; Carboni, G.; Cardinale, R.; Cardini, A.; Carniti, P.; Carson, L.; Carvalho Akiba, K.; Casanova Mohr, R.; Casse, G.; Cassina, L.; Castillo Garcia, L.; Cattaneo, M.; Cauet, Ch.; Cavallero, G.; Cenci, R.; Charles, M.; Charpentier, Ph.; Chefdeville, M.; Chen, S.; Cheung, S.-F.; Chiapolini, N.; Chrzaszcz, M.; Cid Vidal, X.; Ciezarek, G.; Clarke, P. E. L.; Clemencic, M.; Cliff, H. V.; Closier, J.; Coco, V.; Cogan, J.; Cogneras, E.; Cogoni, V.; Cojocariu, L.; Collazuol, G.; Collins, P.; Comerma-Montells, A.; Contu, A.; Cook, A.; Coombes, M.; Coquereau, S.; Corti, G.; Corvo, M.; Couturier, B.; Cowan, G. A.; Craik, D. C.; Crocombe, A.; Cruz Torres, M.; Cunliffe, S.; Currie, R.; D'Ambrosio, C.; Dalseno, J.; David, P. N. Y.; Davis, A.; De Bruyn, K.; De Capua, S.; De Cian, M.; De Miranda, J. M.; De Paula, L.; De Silva, W.; De Simone, P.; Dean, C.-T.; Decamp, D.; Deckenhoff, M.; Del Buono, L.; Déléage, N.; Derkach, D.; Deschamps, O.; Dettori, F.; Dey, B.; Di Canto, A.; Di Ruscio, F.; Dijkstra, H.; Donleavy, S.; Dordei, F.; Dorigo, M.; Dosil Suárez, A.; Dossett, D.; Dovbnya, A.; Dreimanis, K.; Dujany, G.; Dupertuis, F.; Durante, P.; Dzhelyadin, R.; Dziurda, A.; Dzyuba, A.; Easo, S.; Egede, U.; Egorychev, V.; Eidelman, S.; Eisenhardt, S.; Eitschberger, U.; Ekelhof, R.; Eklund, L.; El Rifai, I.; Elsasser, Ch.; Ely, S.; Esen, S.; Evans, H. M.; Evans, T.; Falabella, A.; Färber, C.; Farinelli, C.; Farley, N.; Farry, S.; Fay, R.; Ferguson, D.; Fernandez Albor, V.; Ferrari, F.; Ferreira Rodrigues, F.; Ferro-Luzzi, M.; Filippov, S.; Fiore, M.; Fiorini, M.; Firlej, M.; Fitzpatrick, C.; Fiutowski, T.; Fol, P.; Fontana, M.; Fontanelli, F.; Forty, R.; Francisco, O.; Frank, M.; Frei, C.; Frosini, M.; Fu, J.; Furfaro, E.; Gallas Torreira, A.; Galli, D.; Gallorini, S.; Gambetta, S.; Gandelman, M.; Gandini, P.; Gao, Y.; García Pardiñas, J.; Garofoli, J.; Garra Tico, J.; Garrido, L.; Gascon, D.; Gaspar, C.; Gastaldi, U.; Gauld, R.; Gavardi, L.; Gazzoni, G.; Geraci, A.; Gerick, D.; Gersabeck, E.; Gersabeck, M.; Gershon, T.; Ghez, Ph.; Gianelle, A.; Gianì, S.; Gibson, V.; Giubega, L.; Gligorov, V. V.; Göbel, C.; Golubkov, D.; Golutvin, A.; Gomes, A.; Gotti, C.; Grabalosa Gándara, M.; Graciani Diaz, R.; Granado Cardoso, L. A.; Graugés, E.; Graverini, E.; Graziani, G.; Grecu, A.; Greening, E.; Gregson, S.; Griffith, P.; Grillo, L.; Grünberg, O.; Gui, B.; Gushchin, E.; Guz, Yu.; Gys, T.; Hadjivasiliou, C.; Haefeli, G.; Haen, C.; Haines, S. C.; Hall, S.; Hamilton, B.; Hampson, T.; Han, X.; Hansmann-Menzemer, S.; Harnew, N.; Harnew, S. T.; Harrison, J.; He, J.; Head, T.; Heijne, V.; Hennessy, K.; Henrard, P.; Henry, L.; Hernando Morata, J. A.; van Herwijnen, E.; Heß, M.; Hicheur, A.; Hill, D.; Hoballah, M.; Hombach, C.; Hulsbergen, W.; Humair, T.; Hussain, N.; Hutchcroft, D.; Hynds, D.; Idzik, M.; Ilten, P.; Jacobsson, R.; Jaeger, A.; Jalocha, J.; Jans, E.; Jawahery, A.; Jing, F.; John, M.; Johnson, D.; Jones, C. R.; Joram, C.; Jost, B.; Jurik, N.; Kandybei, S.; Kanso, W.; Karacson, M.; Karbach, T. M.; Karodia, S.; Kelsey, M.; Kenyon, I. R.; Kenzie, M.; Ketel, T.; Khanji, B.; Khurewathanakul, C.; Klaver, S.; Klimaszewski, K.; Kochebina, O.; Kolpin, M.; Komarov, I.; Koopman, R. F.; Koppenburg, P.; Korolev, M.; Kravchuk, L.; Kreplin, K.; Kreps, M.; Krocker, G.; Krokovny, P.; Kruse, F.; Kucewicz, W.; Kucharczyk, M.; Kudryavtsev, V.; Kurek, K.; Kvaratskheliya, T.; La Thi, V. N.; Lacarrere, D.; Lafferty, G.; Lai, A.; Lambert, D.; Lambert, R. W.; Lanfranchi, G.; Langenbruch, C.; Langhans, B.; Latham, T.; Lazzeroni, C.; Le Gac, R.; van Leerdam, J.; Lees, J.-P.; Lefèvre, R.; Leflat, A.; Lefrançois, J.; Leroy, O.; Lesiak, T.; Leverington, B.; Li, Y.; Likhomanenko, T.; Liles, M.; Lindner, R.; Linn, C.; Lionetto, F.; Liu, B.; Lohn, S.; Longstaff, I.; Lopes, J. H.; Lucchesi, D.; Lucio Martinez, M.; Luo, H.; Lupato, A.; Luppi, E.; Lupton, O.; Machefert, F.; Maciuc, F.; Maev, O.; Malde, S.; Malinin, A.; Manca, G.; Mancinelli, G.; Manning, P.; Mapelli, A.; Maratas, J.; Marchand, J. F.; Marconi, U.; Marin Benito, C.; Marino, P.; Märki, R.; Marks, J.; Martellotti, G.; Martinelli, M.; Martinez Santos, D.; Martinez Vidal, F.; Martins Tostes, D.; Massafferri, A.; Matev, R.; Mathad, A.; Mathe, Z.; Matteuzzi, C.; Matthieu, K.; Mauri, A.; Maurin, B.; Mazurov, A.; McCann, M.; McCarthy, J.; McNab, A.; McNulty, R.; Meadows, B.; Meier, F.; Meissner, M.; Merk, M.; Milanes, D. A.; Minard, M.-N.; Mitzel, D. S.; Molina Rodriguez, J.; Monteil, S.; Morandin, M.; Morawski, P.; Mordà, A.; Morello, M. J.; Moron, J.; Morris, A. B.; Mountain, R.; Muheim, F.; Müller, J.; Müller, K.; Müller, V.; Mussini, M.; Muster, B.; Naik, P.; Nakada, T.; Nandakumar, R.; Nasteva, I.; Needham, M.; Neri, N.; Neubert, S.; Neufeld, N.; Neuner, M.; Nguyen, A. D.; Nguyen, T. D.; Nguyen-Mau, C.; Niess, V.; Niet, R.; Nikitin, N.; Nikodem, T.; Ninci, D.; Novoselov, A.; O'Hanlon, D. P.; Oblakowska-Mucha, A.; Obraztsov, V.; Ogilvy, S.; Okhrimenko, O.; Oldeman, R.; Onderwater, C. J. G.; Osorio Rodrigues, B.; Otalora Goicochea, J. M.; Otto, A.; Owen, P.; Oyanguren, A.; Palano, A.; Palombo, F.; Palutan, M.; Panman, J.; Papanestis, A.; Pappagallo, M.; Pappalardo, L. L.; Parkes, C.; Passaleva, G.; Patel, G. D.; Patel, M.; Patrignani, C.; Pearce, A.; Pellegrino, A.; Penso, G.; Pepe Altarelli, M.; Perazzini, S.; Perret, P.; Pescatore, L.; Petridis, K.; Petrolini, A.; Petruzzo, M.; Picatoste Olloqui, E.; Pietrzyk, B.; Pilař, T.; Pinci, D.; Pistone, A.; Playfer, S.; Plo Casasus, M.; Poikela, T.; Polci, F.; Poluektov, A.; Polyakov, I.; Polycarpo, E.; Popov, A.; Popov, D.; Popovici, B.; Potterat, C.; Price, E.; Price, J. D.; Prisciandaro, J.; Pritchard, A.; Prouve, C.; Pugatch, V.; Puig Navarro, A.; Punzi, G.; Qian, W.; Quagliani, R.; Rachwal, B.; Rademacker, J. H.; Rakotomiaramanana, B.; Rama, M.; Rangel, M. S.; Raniuk, I.; Rauschmayr, N.; Raven, G.; Redi, F.; Reichert, S.; Reid, M. M.; dos Reis, A. C.; Ricciardi, S.; Richards, S.; Rihl, M.; Rinnert, K.; Rives Molina, V.; Robbe, P.; Rodrigues, A. B.; Rodrigues, E.; Rodriguez Lopez, J. A.; Rodriguez Perez, P.; Roiser, S.; Romanovsky, V.; Romero Vidal, A.; Rotondo, M.; Rouvinet, J.; Ruf, T.; Ruiz, H.; Ruiz Valls, P.; Saborido Silva, J. J.; Sagidova, N.; Sail, P.; Saitta, B.; Salustino Guimaraes, V.; Sanchez Mayordomo, C.; Sanmartin Sedes, B.; Santacesaria, R.; Santamarina Rios, C.; Santovetti, E.; Sarti, A.; Satriano, C.; Satta, A.; Saunders, D. M.; Savrina, D.; Schiller, M.; Schindler, H.; Schlupp, M.; Schmelling, M.; Schmelzer, T.; Schmidt, B.; Schneider, O.; Schopper, A.; Schune, M.-H.; Schwemmer, R.; Sciascia, B.; Sciubba, A.; Semennikov, A.; Sepp, I.; Serra, N.; Serrano, J.; Sestini, L.; Seyfert, P.; Shapkin, M.; Shapoval, I.; Shcheglov, Y.; Shears, T.; Shekhtman, L.; Shevchenko, V.; Shires, A.; Silva Coutinho, R.; Simi, G.; Sirendi, M.; Skidmore, N.; Skillicorn, I.; Skwarnicki, T.; Smith, E.; Smith, E.; Smith, J.; Smith, M.; Snoek, H.; Sokoloff, M. D.; Soler, F. J. P.; Soomro, F.; Souza, D.; Souza De Paula, B.; Spaan, B.; Spradlin, P.; Sridharan, S.; Stagni, F.; Stahl, M.; Stahl, S.; Steinkamp, O.; Stenyakin, O.; Sterpka, F.; Stevenson, S.; Stoica, S.; Stone, S.; Storaci, B.; Stracka, S.; Straticiuc, M.; Straumann, U.; Stroili, R.; Sun, L.; Sutcliffe, W.; Swientek, K.; Swientek, S.; Syropoulos, V.; Szczekowski, M.; Szczypka, P.; Szumlak, T.; T'Jampens, S.; Tekampe, T.; Teklishyn, M.; Tellarini, G.; Teubert, F.; Thomas, C.; Thomas, E.; van Tilburg, J.; Tisserand, V.; Tobin, M.; Todd, J.; Tolk, S.; Tomassetti, L.; Tonelli, D.; Topp-Joergensen, S.; Torr, N.; Tournefier, E.; Tourneur, S.; Trabelsi, K.; Tran, M. T.; Tresch, M.; Trisovic, A.; Tsaregorodtsev, A.; Tsopelas, P.; Tuning, N.; Ukleja, A.; Ustyuzhanin, A.; Uwer, U.; Vacca, C.; Vagnoni, V.; Valenti, G.; Vallier, A.; Vazquez Gomez, R.; Vazquez Regueiro, P.; Vázquez Sierra, C.; Vecchi, S.; Velthuis, J. J.; Veltri, M.; Veneziano, G.; Vesterinen, M.; Viaud, B.; Vieira, D.; Vieites Diaz, M.; Vilasis-Cardona, X.; Vollhardt, A.; Volyanskyy, D.; Voong, D.; Vorobyev, A.; Vorobyev, V.; Voß, C.; de Vries, J. A.; Waldi, R.; Wallace, C.; Wallace, R.; Walsh, J.; Wandernoth, S.; Wang, J.; Ward, D. R.; Watson, N. K.; Websdale, D.; Weiden, A.; Whitehead, M.; Wiedner, D.; Wilkinson, G.; Wilkinson, M.; Williams, M.; Williams, M. P.; Williams, M.; Wilson, F. F.; Wimberley, J.; Wishahi, J.; Wislicki, W.; Witek, M.; Wormser, G.; Wotton, S. A.; Wright, S.; Wyllie, K.; Xie, Y.; Xu, Z.; Yang, Z.; Yuan, X.; Yushchenko, O.; Zangoli, M.; Zavertyaev, M.; Zhang, L.; Zhang, Y.; Zhelezov, A.; Zhokhov, A.; Zhong, L.

    2015-08-01

    A search for decays is performed using 3 .0 fb1- of pp collision data recorded by the LHCb experiment during 2011 and 2012. The f 0(980) meson is reconstructed through its decay to the π + π - final state in the mass window 900 MeV /c 2 < m( π + π -) < 1080 MeV /c 2. No significant signal is observed. The first upper limits on the branching fraction of are set at 90 % (95 %) confidence level. [Figure not available: see fulltext.

  7. Structure and decay in the QED vacuum

    NASA Astrophysics Data System (ADS)

    Labun, Lance Andrew

    This thesis is a guide to a selection of the author's published work that connect and contribute to understanding the vacuum of quantum electrodynamics in strong, prescribed electromagnetic fields. This theme is elaborated over the course of two chapters: The first chapter sets the context, defining the relevant objects and conditions of the study and reviewing established knowledge upon which this study builds. The second chapter organizes and explains important results appearing in the published work. The papers 1. (Labun and Rafelski, 2009) "Vacuum Decay Time in Strong External Fields" 2. (Labun and Rafelski, 2010a) "Dark Energy Simulacrum in Nonlinear Electrodynamics" 3. (Labun and Rafelski, 2010b) "QED Energy-Momentum Trace as a Force in Astrophysics" 4. (Labun and Rafelski, 2010c) "Strong Field Physics: Probing Critical Acceleration and Inertia with Laser Pulses and Quark-Gluon Plasma" 5. (Labun and Rafelski, 2010d) "Vacuum Structure and Dark Energy" 6. (Labun and Rafelski, 2011) "Spectra of Particles from Laser-Induced Vacuum Decay" are presented in their published format as appendices. Related literature is cited throughout the body where it directly supports the content of this overview; more extensive references are found within the attached papers. This study begins with the first non-perturbative result in quantum electrodynamics, a result obtained by Heisenberg and Euler (1936) for the energy of a zero-particle state in a prescribed, long-wavelength electromagnetic field. The resulting Euler-Heisenberg effective potential generates a nonlinear theory of electromagnetism and exhibits the ability of the electrical fields to decay into electron-positron pairs. Context for phenomena arising from the Euler-Heisenberg effective potential is established by considering the energy-momentum tensor of a general nonlinear electromagnetic theory. The mass of a field configuration is defined, and I discuss two of its consequences pertinent to efforts to observe

  8. Positron acceleration in plasma bubble wakefield driven by an ultraintense laser

    SciTech Connect

    Hou, Ya-Juan; Wan, Feng; Sang, Hai-Bo Xie, Bai-Song

    2016-01-15

    The dynamics of positrons accelerating in electron-positron-ion plasma bubble fields driven by an ultraintense laser is investigated. The bubble wakefield is obtained theoretically when laser pulses are propagating in the electron-positron-ion plasma. To restrict the positrons transversely, an electron beam is injected. Acceleration regions and non-acceleration ones of positrons are obtained by the numerical simulation. It is found that the ponderomotive force causes the fluctuation of the positrons momenta, which results in the trapping of them at a lower ion density. The energy gaining of the accelerated positrons is demonstrated, which is helpful for practical applications.

  9. Enhanced positron trapping by Ag nanoclusters at low temperatures: A challenge of positron sensitivity to quantum dots

    NASA Astrophysics Data System (ADS)

    Zou, B.; Qi, N.; Liu, Z. W.; Chen, Z. Q.; Liu, H. Q.; Yi, D. Q.; Tang, Z.

    2017-03-01

    Microstructure evolution of three Al-Ag alloys with different Ag contents (1 wt. % Ag, 5 wt. % Ag, and 15 wt. % Ag) was studied by positron annihilation spectroscopy during the aging process. In situ measurements of the positron lifetime and Doppler broadening of annihilation radiation indicate the fast formation of Ag-rich clusters during natural aging of the alloys. The formation of Ag-rich clusters was further confirmed by coincidence Doppler broadening measurements. The Ag signal reflected by the Coincidence Doppler broadening spectrum increases with increasing Ag content and is further enhanced after subsequent artificial aging at 140 °C. This might be due to the increase in the size of Ag clusters. The temperature dependence of the Doppler broadening spectra between 10 K and 290 K was measured for the Al-Ag alloys after natural and artificial aging. Detrapping of positrons from Ag clusters with increasing temperature was observed for all the three Al-Ag alloys after natural aging and for the Al-1 wt. % Ag after artificial aging. This indicates that Ag clusters act as shallow positron trapping centers. The thermal detrapping of positrons becomes ambiguous with increasing Ag content in the alloy and is nearly invisible in the artificially aged Al-5 wt. % Ag and Al-15 wt. % Ag. The positron binding energy of the Ag cluster is roughly estimated to be about 18.8 meV and 50 meV in the Al-1 wt. % Ag sample after natural aging and artificial aging at 140 °C, respectively, which suggests that the confinement of positrons in the quantum-dot like state depends on the size or chemical composition of clusters. Theoretical calculations confirm positron trapping by Ag nanoclusters, and the confinement of positrons is enhanced with increasing Ag cluster size.

  10. Decay Time of Cathodoluminescence

    ERIC Educational Resources Information Center

    Kraftmakher, Yaakov

    2009-01-01

    Simple measurements of the decay time of cathodoluminescence are described. Cathodoluminescence is used in many devices, including computer monitors, oscilloscopes, radar displays and television tubes. The experimental setup is simple and easy to build. Two oscilloscopes, a function generator, and a fast photodiode are needed for the experiments.…

  11. Positron lifetime calculation for the elements of the periodic table.

    PubMed

    Campillo Robles, J M; Ogando, E; Plazaola, F

    2007-04-30

    Theoretical positron lifetime values have been calculated systematically for most of the elements of the periodic table. Self-consistent and non-self-consistent schemes have been used for the calculation of the electronic structure in the solid, as well as different parametrizations for the positron enhancement factor and correlation energy. The results obtained have been studied and compared with experimental data, confirming the theoretical trends. As is known, positron lifetimes in bulk show a periodic behaviour with atomic number. These calculations also confirm that monovacancy lifetimes follow the same behaviour. The effects of enhancement factors used in calculations have been commented upon. Finally, we have analysed the effects that f and d electrons have on positron lifetimes.

  12. Positron annihilation characteristics in mesostructural silica films with various porosities

    SciTech Connect

    Xiong, Bangyun; Mao, Wenfeng; Tang, Xiuqin; He, Chunqing

    2014-03-07

    Porous silica films with various porosities were prepared via a sol-gel method using a nonionic amphiphilic triblock copolymer F127 as the structure-directing agent. Doppler broadening of positron annihilation radiation (DBAR) spectra were collected for the prepared films using a variable energy slow positron beam. Different linear relationships between positron annihilation line shape parameters S and W are found for the as-deposited films and calcined ones, indicative of the decomposition of the copolymer porogen in the as-deposited films upon calcination. This also reveals the variation of positron annihilation sites as a function of F127 loading or porosity. Strong correlations between positronium 3γ annihilation fraction, S parameter and porosity of the mesoporous silica films with isolated pores are obtained, which may provide a complementary method to determine closed porosities of mesoporous silica films by DBAR.

  13. Improved generalized gradient approximation for positron states in solids

    NASA Astrophysics Data System (ADS)

    Kuriplach, Jan; Barbiellini, Bernardo

    2014-04-01

    Several first-principles calculations of positron-annihilation characteristics in solids have added gradient corrections to the local-density approximation within the theory by Arponen and Pajanne [Ann. Phys. (NY) 121, 343 (1979), 10.1016/0003-4916(79)90101-5] since this theory systematically overestimates the annihilation rates. As a further remedy, we propose to use gradient corrections for other local-density approximation schemes based on perturbed hypernetted chain and on quantum Monte Carlo results. Our calculations for various metals and semiconductors show that the proposed schemes generally improve the positron lifetimes when they are confronted with experiment. We also compare the resulting positron affinities in solids with data from slow-positron measurements.

  14. 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.

  15. Positron Computed Tomography: Current State, Clinical Results and Future Trends

    DOE R&D Accomplishments Database

    Schelbert, H. R.; Phelps, M. E.; Kuhl, D. E.

    1980-09-01

    An overview is presented of positron computed tomography: its advantages over single photon emission tomography, its use in metabolic studies of the heart and chemical investigation of the brain, and future trends. (ACR)

  16. Probing of Unembedded Metallic Quantum Dots with Positrons

    SciTech Connect

    Fischer, C G; Denison, A B; Weber, M H; Wilcoxon, J P; Woessner, S; Lynn, K G

    2003-08-01

    We employed the two detector coincident Doppler Broadening Technique (coPAS) to investigate Ag, Au and Ag/Au alloy quantum dots of varying sizes which were deposited in thin layers on glass slides. The Ag quantum dots range from 2 to 3 nm in diameter, while the Ag/Au alloy quantum dots exhibit Ag cores of 2 nm and 3 nm and Au shells of varying thickness. We investigate the possibility of positron confinement in the Ag core due to positron affinity differences between Ag and Au. We describe the results and their significance to resolving the issue of whether positrons annihilate within the quantum dot itself or whether surface and positron escape effects play an important role.

  17. Cosmic-ray positron energy spectrum measured by PAMELA.

    PubMed

    Adriani, O; Barbarino, G C; Bazilevskaya, G A; Bellotti, R; Bianco, A; Boezio, M; Bogomolov, E A; Bongi, M; Bonvicini, V; Bottai, S; Bruno, A; Cafagna, F; Campana, D; Carbone, R; Carlson, P; Casolino, M; Castellini, G; De Donato, C; De Santis, C; De Simone, N; Di Felice, V; Formato, V; Galper, A M; Karelin, A V; Koldashov, S V; Koldobskiy, S A; Krutkov, S Y; Kvashnin, A N; Leonov, A; Malakhov, V; Marcelli, L; Martucci, M; Mayorov, A G; Menn, W; Mergé, M; Mikhailov, V V; Mocchiutti, E; Monaco, A; Mori, N; Munini, R; Osteria, G; Palma, F; Papini, P; Pearce, M; Picozza, P; Pizzolotto, C; Ricci, M; Ricciarini, S B; Rossetto, L; Sarkar, R; Scotti, V; Simon, M; Sparvoli, R; Spillantini, P; Stochaj, S J; Stockton, J C; Stozhkov, Y I; Vacchi, A; Vannuccini, E; Vasilyev, G I; Voronov, S A; Yurkin, Y T; Zampa, G; Zampa, N; Zverev, V G

    2013-08-23

    Precision measurements of the positron component in the cosmic radiation provide important information about the propagation of cosmic rays and the nature of particle sources in our Galaxy. The satellite-borne experiment PAMELA has been used to make a new measurement of the cosmic-ray positron flux and fraction that extends previously published measurements up to 300 GeV in kinetic energy. The combined measurements of the cosmic-ray positron energy spectrum and fraction provide a unique tool to constrain interpretation models. During the recent solar minimum activity period from July 2006 to December 2009, approximately 24,500 positrons were observed. The results cannot be easily reconciled with purely secondary production, and additional sources of either astrophysical or exotic origin may be required.

  18. Positron annihilation characteristics in mesostructural silica films with various porosities

    NASA Astrophysics Data System (ADS)

    Xiong, Bangyun; Mao, Wenfeng; Tang, Xiuqin; He, Chunqing

    2014-03-01

    Porous silica films with various porosities were prepared via a sol-gel method using a nonionic amphiphilic triblock copolymer F127 as the structure-directing agent. Doppler broadening of positron annihilation radiation (DBAR) spectra were collected for the prepared films using a variable energy slow positron beam. Different linear relationships between positron annihilation line shape parameters S and W are found for the as-deposited films and calcined ones, indicative of the decomposition of the copolymer porogen in the as-deposited films upon calcination. This also reveals the variation of positron annihilation sites as a function of F127 loading or porosity. Strong correlations between positronium 3γ annihilation fraction, S parameter and porosity of the mesoporous silica films with isolated pores are obtained, which may provide a complementary method to determine closed porosities of mesoporous silica films by DBAR.

  19. Positron computed tomography: current state, clinical results and future trends

    SciTech Connect

    Schelbert, H.R.; Phelps, M.E.; Kuhl, D.E.

    1980-09-01

    An overview is presented of positron computed tomography: its advantages over single photon emission tomography, its use in metabolic studies of the heart and chemical investigation of the brain, and future trends. (ACR)

  20. Multiple-ionization of xenon atoms by positron impact

    NASA Technical Reports Server (NTRS)

    Kruse, Georg; Quermann, Andreas; Raith, Wilhelm; Sinapius, Guenther

    1990-01-01

    Previously the cross sections were measured for positronium formation and single ionization by positron impact for He and H2. With the same apparatus, slightly modified, the single and multiple ionization of xenon is now investigated. The principle of the method is the detection of ion and positron in time correlation which allows the discrimination of positronium formation (whereby the positron vanishes) and the destinction of single, double and triple impact ionization (which lead to different ion flight times from the gas target to the ion detector). By using secondary electrons from the positron moderator, similar measurements were performed on electron impact ionization. By comparing with literature values for electron multiple ionization cross sections, the detection-probability ratios were determined for the differently charged ions.

  1. The Role of Chemistry in Positron Emission Tomography.

    ERIC Educational Resources Information Center

    Feliu, Anthony L.

    1988-01-01

    Investigates use of positron emission tomography (PET) to study in-vivo metabolic processes. Discusses methodology of PET and medical uses. Outlines the production of different radioisotopes used in PET radiotracers. Includes selected bibliography. (ML)

  2. An Undulator Based Polarized Positron Source for CLIC

    SciTech Connect

    Liu, Wanming; Gai, Wei; Rinolfi, Louis; Sheppard, John; /SLAC

    2012-07-02

    A viable positron source scheme is proposed that uses circularly polarized gamma rays generated from the main 250 GeV electron beam. The beam passes through a helical superconducting undulator with a magnetic field of {approx} 1 Tesla and a period of 1.15 cm. The gamma-rays produced in the undulator in the energy range between {approx} 3 MeV - 100 MeV will be directed to a titanium target and produce polarized positrons. The positrons are then captured, accelerated and transported to a Pre-Damping Ring (PDR). Detailed parameter studies of this scheme including positron yield, and undulator parameter dependence are presented. Effects on the 250 GeV CLIC main beam, including emittance growth and energy loss from the beam passing through the undulator are also discussed.

  3. Magnetoacoustic solitons in dense astrophysical electron-positron-ion plasmas

    NASA Astrophysics Data System (ADS)

    Hussain, S.; Mahmood, S.; Mushtaq, A.

    2013-08-01

    Nonlinear magnetoacoustic waves in dense electron-positron-ion plasmas are investigated by using three fluid quantum magnetohydrodynamic model. The quantum mechanical effects of electrons and positrons are taken into account due to their Fermionic nature (to obey Fermi statistics) and quantum diffraction effects (Bohm diffusion term) in the model. The reductive perturbation method is employed to derive the Korteweg-de Vries (KdV) equation for low amplitude magnetoacoustic soliton in dense electron-positron-ion plasmas. It is found that positron concentration has significant impact on the phase velocity of magnetoacoustic wave and on the formation of single pulse nonlinear structure. The numerical results are also illustrated by taking into account the plasma parameters of the outside layers of white dwarfs and neutron stars/pulsars.

  4. Positron beam facility at Kyoto University Research Reactor

    NASA Astrophysics Data System (ADS)

    Xu, Q.; Sato, K.; Yoshiie, T.; Sano, T.; Kawabe, H.; Nagai, Y.; Nagumo, K.; Inoue, K.; Toyama, T.; Oshima, N.; Kinomura, A.; Shirai, Y.

    2014-04-01

    A positron beam facility is presently under construction at the Kyoto University Research Reactor (KUR), which is a light-water moderated tank-type reactor operated at a rated thermal power of 5 MW. A cadmium (Cd) - tungsten (W) source similar to that used in NEPOMUC was chosen in the KUR because Cd is very efficient at producing γ-rays when exposed to thermal neutron flux, and W is a widely used in converter and moderator materials. High-energy positrons are moderated by a W moderator with a mesh structure. Electrical lenses and a solenoid magnetic field are used to extract the moderated positrons and guide them to a platform outside of the reactor, respectively. Since Japan is an earthquake-prone country, a special attention is paid for the design of the in-pile positron source so as not to damage the reactor in the severe earthquake.

  5. Anatomy of decays

    NASA Astrophysics Data System (ADS)

    Bel, Lennaert; De Bruyn, Kristof; Fleischer, Robert; Mulder, Mick; Tuning, Niels

    2015-07-01

    The decays B {/d 0} → D {/d -} D {/d +} and B {/s 0} → D {/s -} D {/s +} probe the CP-violating mixing phases ϕ d and ϕ s , respectively. The theoretical uncertainty of the corresponding determinations is limited by contributions from penguin topologies, which can be included with the help of the U-spin symmetry of the strong interaction. We analyse the currently available data for B {/d, s 0} → D {/d, s -} D {/d, s +} decays and those with similar dynamics to constrain the involved non-perturbative parameters. Using further information from semileptonic B {/d 0} → D {/d -} ℓ + ν ℓ decays, we perform a test of the factorisation approximation and take non-factorisable SU(3)-breaking corrections into account. The branching ratios of the B {/d 0} → D {/d -} D {/d +}, B {/s 0} → D {/s -} D {/d +} and B {/s 0} → D {/s -} D {/s +}, B {/d 0} → D {/d -} D {/s +} decays show an interesting pattern which can be accommodated through significantly enhanced exchange and penguin annihilation topologies. This feature is also supported by data for the B {/s 0} → D {/d -} D {/d +} channel. Moreover, there are indications of potentially enhanced penguin contributions in the B {/d 0} → D {/d -} D {/d +} and B {/s 0} → D {/s -} D {/s +} decays, which would make it mandatory to control these effects in the future measurements of ϕ d and ϕ s . We discuss scenarios for high-precision measurements in the era of Belle II and the LHCb upgrade.

  6. A method to detect positron anisotropies with Pamela data

    NASA Astrophysics Data System (ADS)

    Panico, B.; Adriani, O.; Barbarino, G. C.; Bazilevskaya, G. A.; Bellotti, R.; Boezio, M.; Bogomolov, E. A.; Bongi, M.; Bonvicini, V.; Bottai, S.; Bruno, A.; Cafagna, F.; Campana, D.; Carbone, R.; Carlson, P.; Casolino, M.; Castellini, G.; De Donato, C.; De Santis, C.; De Simone, N.; Di Felice, V.; Formato, V.; Galper, A. M.; Giaccari, U.; Karelin, A. V.; Koldashov, S. V.; Koldobskiy, S.; Krutkov, S. Y.; Kvashnin, A. N.; Leonov, A.; Malakhov, V.; Marcelli, L.; Martucci, M.; Mayorov, A. G.; Menn, W.; Merge, M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Palma, F.; Papini, P.; Pearce, M.; Picozza, P.; Pizzolotto, C.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Y. I.; Vacchi, A.; Vannuccini, E.; Vasilyev, G. I.; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.; Zverev, V. G.

    2014-11-01

    The PAMELA experiment is collecting data since 2006; its results indicate the presence of a large flux of positron with respect to electrons in the CR spectrum above 10 GeV. This excess might also be originated in objects such as pulsars and microquasars or through dark matter annihilation. Here the electrons and positrons events collected by PAMELA have been analized searching for anisotropies. The analysis is performed at different angular scales and results will be presented at the conference.

  7. Antihydrogen formation in laser-assisted positron-antiproton scattering

    NASA Astrophysics Data System (ADS)

    Li, Shu-Min; Miao, Yan-Gang; Zhou, Zi-Fang; Chen, Ji; Liu, Yao-Yang

    1998-09-01

    Antihydrogen formation in the laser-assisted positron-antiproton (nonrelativistic) radiative recombination is investigated. The state of incident positron is given by the Coulomb-Volkov wave function. The perturbative dressed wave function of the atom is obtained in the soft-photon approximation. Our calculation shows that for a geometry of laser polarization parallel to the incident direction, the formation cross section of antihydrogen is greatly reduced. Especially at high impact energy, the reduction is remarkable.

  8. A Multicell Trap for Positron Accumulation and Storage

    DTIC Science & Technology

    2006-04-21

    device to accumulate N >_ 1012 positrons (i.e., an increase of a factor of 1000 over current performance) and to store this collection of antimatter ...would be an important step toward the development of even more flexible, portable reservoirs of antimatter with few logistic requirements. The first...N > 1012 positrons (i.e., an increase of a factor of 1000 over current performance) and to store this collection of antimatter as a plasma for times

  9. Positronium formation from positron impact on hydrogen and helium targets

    NASA Astrophysics Data System (ADS)

    Naginey, T. C.; Stacy, Eric W.; Pollock, B. B.; Walters, H. R. J.; Whelan, Colm T.

    2014-06-01

    Charge-exchange cross sections are presented for collisions of positrons with hydrogen and neutral and singly ionized helium targets using a variant of the classical trajectory Monte Carlo approach. As a check on the method a comparison is made with the corresponding proton results. An extended error analysis is presented. Reasonable agreement with available experimental data is found, and the charge-exchange cross section for positrons on He+ is predicted.

  10. Electron positron pair production at RHIC and LHC

    SciTech Connect

    Cem Gueclue, M.

    2008-11-11

    The STAR Collaboration at the Relativistic Heavy Ion Collider present data on electron-positron pair production accompanied by nuclear breakup at small impact parameters where the simultaneous excitation of the two ions, mainly the giant dipole resonance GDR, can occur. We calculate the electron-positron pair production cross section relevant for the STAR experimental setup, and compare our results with the other calculations. We have also predictions for the LHC energies.

  11. Positron emission tomographic imaging of tumors using monoclonal antibodies

    SciTech Connect

    Zalutsky, M.R.

    1992-08-01

    This research project is developing methods for utilizing positron emission tomography (PET) to increase the clinical potential of radiolabeled monoclonal antibodies (MAbs). This report describes the development of methods for labeling MAbs and their fragments with positron-emitting halogen nuclides, fluorine-18 and iodine-124. These nulides were selected because of the widespread availability of F-18 and because of our extensive experience in the development of new protein radiohalogenation methods.

  12. Positron transport and thermalization - the plasma-gas interface

    NASA Astrophysics Data System (ADS)

    Marler, Joan

    2008-11-01

    Low energy positrons are now used in many fields including atomic physics, material science and medicine [1]. Plasma physics is providing new tools for this research, including Penning-Malmberg buffer-gas traps to accumulate positrons and the use of rotating electric fields (the ``rotating wall'' technique) to compress positrons radially and create tailored beams [1]. These devices (now available commercially), which rely in key instances on positron-neutral interactions, are a convenient way to create plasmas and beams for a variety of applications. A deeper understanding of the relevant cooling and loss mechanisms is required to take full advantage of this technology. This talk focuses on a recent study of positrons in such a tenuous gaseous environment in the presence of an applied electric field [2]. Energy-resolved collision cross sections and a Monte Carlo code modified to include positrionium (Ps) formation are used to obtain transport coefficients and the thermalization and Ps-formation rates. A markedly different type of negative differential conductivity is observed (i.e., not seen in electron systems), due to the non-conservative nature of the Ps-formation process. It is particularly prominent in gases with large, highly energy dependent Ps-formation cross sections. The relevance of these calculations to other positron applications will also be discussed, including a currently planned study of positrons in gaseous water. It is hoped that these calculations will inspire a new generation of positron transport experiments.*Work done in collaboration with Z.Lj. Petrovi'c, A. Bankovi'c, M. Suvakov, G. Malovi'c, S. Dujko, S.J. Buckman. 1. C. M. Surko and R. G. Greaves, Phys. Plasmas 11, 2333-2348 (2004).2. A. Bankovi'c, J. P. Marler, M. Suvakov, G. Malovi'c, and Z. Lj. Petrovi'c, Nucl. Instrum. and Meth. in Phys. Res. B 266, 462-465 (2008).

  13. Short-lived positron emitter labeled radiotracers - present status

    SciTech Connect

    Fowler, J.S.; Wolf, A.P.

    1982-01-01

    The preparation of labelled compounds is important for the application of positron emission transaxial tomography (PETT) in biomedical sciences. This paper describes problems and progress in the synthesis of short-lived positron emitter (/sup 11/C, /sup 18/F, /sup 13/N) labelled tracers for PETT. Synthesis of labelled sugars, amino acids, and neurotransmitter receptors (pimozide and spiroperidol tagged with /sup 11/C) is discussed in particular. (DLC)

  14. Resonances in low-energy positron-alkali scattering

    NASA Technical Reports Server (NTRS)

    Horbatsch, M.; Ward, S. J.; Mceachran, R. P.; Stauffer, A. D.

    1990-01-01

    Close-coupling calculations were performed with up to five target states at energies in the excitation threshold region for positron scattering from Li, Na and K. Resonances were discovered in the L = 0, 1 and 2 channels in the vicinity of the atomic excitation thresholds. The widths of these resonances vary between 0.2 and 130 MeV. Evidence was found for the existence of positron-alkali bound states in all cases.

  15. Positron annihilation in TiBe/sub 2/

    SciTech Connect

    Manuel, A.A.; Hoffmann, L.; Singh, A.K.; Jarlborg, T.; Peter, M.; Smith, J.L.; Fisk, Z.; Pecora, L.M.; Ehrlich, A.C.

    1988-01-01

    We report positron annihilation measurements on TiBe/sub 2/. Calculations using LMTO band structure method are also presented. The good agreement with the experimental data leads to the conclusion that the unusual magnetic properties of this compound can be well explained in terms of its electronic structure. A reconstruction of the electron-positron momentum distribution from calculated and measured 2D-ACPAR is discussed. 10 refs., 3 figs.

  16. Constraints on decaying dark matter from the extragalactic gamma-ray background

    SciTech Connect

    Ando, Shin'ichiro; Ishiwata, Koji E-mail: koji.ishiwata@desy.de

    2015-05-01

    If dark matter is unstable and the mass is within GeV–TeV regime, its decays produce high-energy photons that give contribution to the extragalactic gamma-ray background (EGRB). We constrain dark matter decay by analyzing the 50-month EGRB data measured with Fermi satellite, for different decay channels motivated with several supersymmetric scenarios featuring R-parity violation. We adopt the latest astrophysical models for various source classes such as active galactic nuclei and star-forming galaxies, and take associated uncertainties properly into account. The lower limits for the lifetime are very stringent for a wide range of dark matter mass, excluding the lifetime shorter than 10{sup 28} s for mass between a few hundred GeV and ∼1 TeV, e.g., for b b-bar decay channel. Furthermore, most dark matter models that explain the anomalous positron excess are also excluded. These constraints are robust, being little dependent on astrophysical uncertainties, unlike other probes such as Galactic positrons or anti-protons.

  17. A slow positron beam generator for lifetime studies

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.; Eftekhari, Abe; St.clair, Terry L.

    1989-01-01

    A slow positron beam generator using well-annealed polycrystalline tungsten moderators and a Na-22 positron source was developed. A 250 micro c source, deposited on a 2.54 micron thick aluminized mylar, is sandwiched between two (2.54 cm x 2.54 cm x 0.0127 cm) tungsten pieces. Two (2.54 cm x 2.54 cm x t cm) test polymer films insulate the two tungsten moderator pieces from the aluminized mylar source holder (t=0.00127 to 0.0127). A potential difference of 10 to 100 volts--depending on the test polymer film thickness (t)--is applied between the tungsten pieces and the source foil. Thermalized positrons diffusing out of the moderator pieces are attracted to the source foil held at an appropriate potential below the moderator pieces. These positrons have to pass through the test polymer films before they can reach the source foil. The potential difference between the moderator pieces and the aluminized mylar is so adjusted as to force the positrons to stop in the test polymer films. Thus the new generator becomes an effective source of positrons for assaying thin polymer films for their molecular morphology.

  18. Si nanocrystals and nanocrystal interfaces studied by positron annihilation

    NASA Astrophysics Data System (ADS)

    Kujala, J.; Slotte, J.; Tuomisto, F.; Hiller, D.; Zacharias, M.

    2016-10-01

    Si nanocrystals embedded in a SiO 2 matrix were studied with positron annihilation and photoluminescence spectroscopies. Analysis of the S- and W-parameters for the sample annealed at 800 °C reveals a positron trap at the interface between the amorphous nanodots and the surrounding matrix. Another trap state is observed in the 1150 °C heat treated samples where nanodots are in a crystalline form. Positrons are most likely trapped to defects related to dangling bonds at the surface of the nanocrystals. Passivation of the samples results on one hand in the decrease of the S-parameter implying a decrease in the open volume of the interface state and, on the other hand, in the strengthening of the positron annihilation signal from the interface. The intensity of the photoluminescence signal increases with the formation of the nanocrystals. Passivation of samples strengthens the photoluminescence signal, further indicating a successful deactivation of luminescence quenching at the nanocrystal surface. Strengthening of the positron annihilation signal and an increase in the photoluminescence intensity in passivated silicon nanocrystals suggests that the positron trap at the interface does not contribute to a significant extent to the exciton recombination in the nanocrystals.

  19. Positron sensing of distribution of defects in depth materials

    NASA Astrophysics Data System (ADS)

    Kupchishin, A. I.; Kupchishin, A. A.; Voronova, N. A.; Kirdyashkin, V. I.

    2016-02-01

    It was developed a non-destructive method of positron sensing, which allows to determine the distribution of defects in the depth of the material. From the analysis we can conclude that the angular distribution curves of annihilation photons (well as and on the characteristics in experiments on the lifetime, 3γ - angular correlation, Doppler effect) is influenced by three main factors: a) The distribution of defects in the depth of the material, their dimensions as well as parameters of the interaction of positrons with defects. With increasing the concentration of defects the intensity Jγ(a, ξ) varies more; b) Modification of the energy spectrum of slow positrons due to the influence of defects, wherein the spectrum of positrons becomes softer, and the average energy of the positron annihilation is reduced; c) Deformation of the momentum distribution of the electrons in the region of defect. The energy spectrum of electrons is also becomes softer, and the average energy of the electrons (on which positrons annihilate) is less. The experimentally were measured spectra of photons in the zone of annihilation and were calculated the distribution of defects in depth for a number of metals.

  20. Positron annihilation study on hafnium metals given various treatments

    SciTech Connect

    Min, Duck Ki; Kang, Myung Soo ); Yoon, Young Ku )

    1993-08-01

    The positron annihilation technique that enables measurements of positron lifetime, two-photon angular correlation and Doppler broadening due to annihilation radiation has been established for studies of the electronic configuration and defect properties in solids. In metals, positrons can be trapped at vacancies and their agglomerates as well as at dislocations, but not at interstitials. Because of these interactions, the positron annihilation method can be applied to studies of the behavior of dislocations during annealing of plastically deformed metals. Furthermore, it is possible by measurements of annihilation characteristics to identify defects such as vacancies, dislocations and vacancy-clusters, and to determine spatial dimensions of defects. In this work, positron annihilation measurements for annealed, cold worked, annealed and then quenched, and cold worked and then cathodically hydrogen charged hafnium specimens were made to obtain information on (a) positron annihilation characteristics of hafnium metal, (b) role of vacancy-type defects on hydrogen charging, (c) defects produced during hydrogen charging and (d) recovery of lattice defects in hafnium and effects of hydrogen on defects recovery upon annealing.

  1. PhytoBeta imager: a positron imager for plant biology

    SciTech Connect

    Weisenberger, Andrew G; Lee, Seungjoon; McKisson, John; McKisson, J E; Xi, Wenze; Zorn, Carl; Reid, Chantal D; Howell, Calvin R; Crowell, Alexander S; Cumberbatch, Laurie; Fallin, Brent; Stolin, Alexander; Smith, Mark F

    2012-06-01

    Several positron emitting radioisotopes such as 11C and 13N can be used in plant biology research. The 11CO2 tracer is used to facilitate plant biology research toward optimization of plant productivity, biofuel development and carbon sequestration in biomass. Positron emission tomography (PET) imaging has been used to study carbon transport in live plants using 11CO2. Because plants typically have very thin leaves, little medium is present for the emitted positrons to undergo an annihilation event. The emitted positrons from 11C (maximum energy 960 keV) could require up to approximately 4 mm of water equivalent material for positron annihilation. Thus many of the positrons do not annihilate inside the leaf, resulting in limited sensitivity for PET imaging. To address this problem we have developed a compact beta-positive, beta-minus particle imager (PhytoBeta imager) for 11CO2 leaf imaging. The detector is based on a Hamamatsu H8500 position sensitive photomultiplier tube optically coupled via optical grease to a 0.5 mm thick Eljen EJ-212 plastic scintillator. The detector is equipped with a flexible arm to allow its placement and orientation over or under the leaf to be studied while maintaining the leaf's original orientation. To test the utility of the system the detector was used to measure carbon translocation in a leaf of the spicebush (Lindera benzoin) under two transient light conditions.

  2. Positron Injector Accelerator and RF System for the ILC

    SciTech Connect

    Wang, J.W.; Adolphsen, C.; Bharadwaj, V.; Bowden, G.; Jongewaard, E.; Li, Z.; Miller, R.; Sheppard, J.C.; /SLAC

    2007-03-28

    Due to the extremely high energy deposition from positrons, electrons, photons and neutrons behind the positron target, and because a solenoid is required to focus the large emittance positron beam, the 1.3 GHz preaccelerator has to use normal conducting structures up to energy of 400 MeV. There are many challenges in the design of the normal-conducting portion of the ILC positron injector system such as obtaining high positron yield with required emittance, achieving adequate cooling with the high RF and particle loss heating, and sustaining high accelerator gradients during millisecond-long pulses in a strong magnetic field. Considering issues of feasibility, reliability and cost savings for the ILC, the proposed design for the positron injector contains both standing-wave (SW) and traveling-wave (TW) L-band accelerator structures. A short version of the new type of the SW section is under fabrication and testing. An updated status report is given. This paper also covers acceleration vs. deceleration for pre-accelerator sections, SW vs. TW structures, as well as longitudinal matching from target to linac and linac to damping ring.

  3. Positron dynamics in surface-charged solid argon

    SciTech Connect

    Jorgensen, L.V.; Merrison, J.P.; Deutch, B.I.; Charlton, M.; Jones, G.O.

    1995-10-15

    Studies have been made of the reemission of positrons incident at low energies upon solid argon to which electric fields were applied by charging an overlayer of molecular oxygen. An enhancement in positron reemission was observed which reached a maximum for an applied field of around 7 kV mm{sup {minus}1}. At this field strength the same yield was observed for implantation energies ranging from 1 to 10 keV, consistent with enhancement due to field-induced positron drift to the exit surface. At higher electric fields, the observed gradual decrease in enhancement was attributed to the heating of the positron energy distribution above the positronium formation threshold. Quantitative agreement with our experimental results has been obtained using a Monte Carlo simulation from which estimates for the positron diffusion length and mobility of 1.7(+2.0,{minus}0.4) {mu}m and 4.7(+2.9,{minus}0.4){times}10{sup {minus}3} m{sup 2} V{sup {minus}1} s{sup {minus}1}, respectively, have been derived. This model was also able to successfully reproduce previous results obtained using surface-charged argon {beta}{sup +} moderators. An abrupt and almost complete reduction in positron reemission was observed for applied surface potentials above a value which showed a weak dependence on film thickness.

  4. PEPPo: Using a Polarized Electron Beam to Produce Polarized Positrons

    SciTech Connect

    Adeyemi, Adeleke H.

    2015-09-01

    Polarized positron beams have been identified as either an essential or a significant ingredient for the experimental program of both the present and next generation of lepton accelerators (JLab, Super KEK B, ILC, CLIC). An experiment demonstrating a new method for producing polarized positrons has been performed at the Continuous Electron Beam Accelerator Facility at Jefferson Lab. The PEPPo (Polarized Electrons for Polarized Positrons) concept relies on the production of polarized e⁻/e⁺ pairs from the bremsstrahlung radiation of a longitudinally polarized electron beam interacting within a high-Z conversion target. PEPPo demonstrated the effective transfer of spin-polarization of an 8.2 MeV/c polarized (P~85%) electron beam to positrons produced in varying thickness tungsten production targets, and collected and measured in the range of 3.1 to 6.2 MeV/c. In comparison to other methods this technique reveals a new pathway for producing either high-energy or thermal polarized positron beams using a relatively low polarized electron beam energy (~10MeV) .This presentation will describe the PEPPo concept, the motivations of the experiment and high positron polarization achieved.

  5. Symmetry relations in nucleon decay

    NASA Astrophysics Data System (ADS)

    Hurlbert, Anya; Wilczek, Frank

    1980-05-01

    Some experimental consequences of the structure of the effective hamiltonian for nucleon decay are presented. New results concern relations among inclusive decay rates, a striking test of the kinship hypothesis involving μ+ polarization, and soft π theorems.

  6. Positron-attachment to small molecules: Vibrational enhancement of positron affinities with configuration interaction level of multi-component molecular orbital approach

    SciTech Connect

    Tachikawa, Masanori

    2015-12-31

    To theoretically demonstrate the binding of a positron to small polarized molecules, we have calculated the vibrational averaged positron affinity (PA) values along the local vibrational contribution with the configuration interaction level of multi-component molecular orbital method. This method can take the electron-positron correlation contribution into account through single electronic - single positronic excitation configurations. The PA values are enhanced by including the local vibrational contribution from vertical PA values due to the anharmonicity of the potential.

  7. Hypoxia imaging agents labeled with positron emitters.

    PubMed

    Hoigebazar, Lathika; Jeong, Jae Min

    2013-01-01

    Imaging hypoxia using positron emission tomography (PET) is of great importance for therapy of cancer. [(18)F]Fluoromisonidazole (FMISO) was the first PET agent for hypoxia imaging, and various radiolabeled nitroimidazole derivatives such as [(18)F]fluoroerythronitroimidazole (FETNIM), [(18)F]1-α-D: -(2-deoxy-2-fluoroarabinofuranosyl)-2-nitroimidazole (FAZA), [(18)F]2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide (EF-5), and [(18)F]fluoroetanidazole (FETA) have been developed successively. To overcome the high cost of cyclotron installation, (68)Ga-labeled nitroimidazole derivatives also have been developed. Another important hypoxia imaging agent is (64)Cu-diacetyl-bis(N (4)-methylthiosemicarbazone) ((64)Cu-ATSM), which can distribute in cancer tissue rapidly due to high lipophilicity. However, its application is limited due to high cost of radionuclide production. Although various hypoxia imaging agents have been reported and tested, hypoxia PET images still have to be improved, because of the low blood flow in hypoxic tissues and resulting low uptake of the agents.

  8. SLC positron damping ring optics design

    SciTech Connect

    Delahaye, J.P.; Rivkin, L.

    1984-12-01

    The basic SLAC Linear Collider operation scheme assumes the use of two damping rings, one for the e/sup -/, one for the e/sup +/, in order to reduce the colliding beam normalized emittances to 30..pi.. ..mu..radm hence raising the corresponding luminosity by a factor 170. The e/sup -/ damping ring which optics was designed by H. Wiedemann, has been extensively studied and modelled since it's completion at the end of 1982. The e/sup +/ damping ring to be built soon will be based on the same design except for some modifications resulting from the studies on the e/sup -/ damping ring which clearly pointed out two major optics weak points: the extracted normalized emittances are 30 to 60% bigger than the design values, which already left no margin for unavoidable blow-up between the damping rings and the SLC interaction point, and the chromaticity correction based on distributed sextupole components provided by shaping the ends of the bending magnet poles was insufficient. Moreover the QDI quadrupoles introduce a strong coupling between transverse planes due to an undesirable skew component. The present note describes the basic modifications of the ring lattice and main equipment positions in order to improve the first two points in the Positron Damping Ring. The QDI quadrupole design has already been modified and magnets of a new type will be implemented in both damping rings.

  9. Low-energy positron scattering by pyrimidine

    SciTech Connect

    Barbosa, Alessandra Souza; Pastega, Diego F.; Bettega, Márcio H. F.

    2015-12-28

    This work reports elastic integral and differential cross sections for positron collisions with pyrimidine, for energies up to 20 eV. The cross sections were computed with the Schwinger multichannel method in the static plus polarization approximation. We also employed the Born closure procedure to account for the long range potential due to the permanent dipole moment of the molecule. Our results are compared with the experimental total cross section of Zecca et al. [J. Phys. B 43, 215204 (2010)], the experimental grand-total, quasi-elastic integral and differential cross section of Palihawadana et al. [Phys. Rev. A 88, 12717 (2013)]. We also compare our results with theoretical integral and differential cross sections obtained by Sanz et al. [Phys. Rev. A 88, 62704 (2013)] with the R-matrix and the independent atom model with screening-corrected additivity rule methods, and with the results computed by Franz and Gianturco [Phys. Rev. A 88, 042711 (2013)] using model correlation-polarization potentials. The agreement between the theory and the experiment is encouraging.

  10. Data acquisition with a positron emission tomograph

    SciTech Connect

    Freifelder, R.; Karp, J.S.

    1997-12-31

    Positron Emission Tomography (PET) is a clinical imaging modality used in Nuclear Medicine. PET measures functionality rather than anatomical features and is therefore invaluable in the treatment of diseases which are characterized by functional changes in organs rather than anatomical changes. Typical diseases for which PET is used are cancer, epilepsy, and heart disease. While the scanners are not very complex, the performance demands on the devices are high. Excellent spatial resolution, 4-5 mm, and high sensitivity are key to maintaining high image quality. Compensation or suppression of scattered radiation is also necessary for good image quality. The ability to acquire data under high counting rates is also necessary in order to minimize the injected dose to the patient, minimize the patient`s time in the scanner, and finally to minimize blurring due to patient motion. We have adapted various techniques in our data acquisition system which will be reported on in this talk. These include pulse clipping using lumped delay lines, flash ADCs with short sampling time, the use of a local positioning algorithm to limit the number of data words being used in subsequent second level software triggers and calculations, and finally the use of high speed dedicated calculator boards for on-line rebinning and reduction of the data. Modifications to the system to allow for transmission scanning will also be discussed.

  11. Positron emission tomography in generalized seizures

    SciTech Connect

    Theodore, W.H.; Brooks, R.; Margolin, R.; Patronas, N.; Sato, S.; Porter, R.J.; Mansi, L.; Bairamian, D.; DiChiro, G.

    1985-05-01

    The authors used /sup 18/F-fluorodeoxyglucose (FDG) positron emission tomography (PET) to study nine patients with clinical absence or generalized seizures. One patient had only absence seizures, two had only generalized tonic-clonic seizures, and six had both seizure types. Interictal scans in eight failed to reveal focal or lateralized hypometabolism. No apparent abnormalities were noted. Two patients had PET scans after isotope injection during hyperventilation-induced generalized spike-wave discharges. Diffusely increased metabolic rates were found in one compared with an interictal scan, and in another compared with control values. Another patient had FDG injected during absence status: EEG showed generalized spike-wave discharges (during which she was unresponsive) intermixed with slow activity accompanied by confusion. Metabolic rates were decreased, compared with the interictal scan, throughout both cortical and subcortical structures. Interictal PET did not detect specific anatomic regions responsible for absence seizure onset in any patient, but the results of the ictal scans did suggest that pathophysiologic differences exist between absence status and single absence attacks.

  12. Amorphous silicon detectors in positron emission tomography

    SciTech Connect

    Conti, M. Lawrence Berkeley Lab., CA ); Perez-Mendez, V. )

    1989-12-01

    The physics of the detection process is studied and the performances of different Positron Emission Tomography (PET) system are evaluated by theoretical calculation and/or Monte Carlo Simulation (using the EGS code) in this paper, whose table of contents can be summarized as follows: a brief introduction to amorphous silicon detectors and some useful equation is presented; a Tantalum/Amorphous Silicon PET project is studied and the efficiency of the systems is studied by Monte Carlo Simulation; two similar CsI/Amorphous Silicon PET projects are presented and their efficiency and spatial resolution are studied by Monte Carlo Simulation, light yield and time characteristics of the scintillation light are discussed for different scintillators; some experimental result on light yield measurements are presented; a Xenon/Amorphous Silicon PET is presented, the physical mechanism of scintillation in Xenon is explained, a theoretical estimation of total light yield in Xenon and the resulting efficiency is discussed altogether with some consideration of the time resolution of the system; the amorphous silicon integrated electronics is presented, total noise and time resolution are evaluated in each of our applications; the merit parameters {epsilon}{sup 2}{tau}'s are evaluated and compared with other PET systems and conclusions are drawn; and a complete reference list for Xenon scintillation light physics and its applications is presented altogether with the listing of the developed simulation programs.

  13. Theory of weak hypernuclear decay

    SciTech Connect

    Dubach, J.F.; Feldman, G.B.; Holstein, B.R. |; de la Torre, L.

    1996-07-01

    The weak nomesonic decay of {Lambda}-hypernuclei is studied in the context of a one-meson-exchange model. Predictions are made for the decay rate, the {ital p}/{ital n} stimulation ratio and the asymmetry in polarized hypernuclear decay. Copyright {copyright} 1996 Academic Press, Inc.

  14. B Decays Involving Light Mesons

    SciTech Connect

    Eschrich, Ivo Gough; /UC, Irvine

    2007-01-09

    Recent BABAR results for decays of B-mesons to combinations of non-charm mesons are presented. This includes B decays to two vector mesons, B {yields} {eta}{prime}({pi}, K, {rho}) modes, and a comprehensive Dalitz Plot analysis of B {yields} KKK decays.

  15. Precision measurement of the positron asymmetry of laser-cooled, spin-polarized 37K

    NASA Astrophysics Data System (ADS)

    Melconian, Dan; Fenker, B.; Behr, J. A.; Anholm, M.; Ashery, D.; Behling, R. S.; Cohen, I.; Craiciu, I.; Gorelov, A.; Gwinner, G.; McNeil, J.; Mehlman, M.; Smale, S.; Warner, C. L.

    2017-01-01

    Precision low-energy measurements in nuclear β decay can be used to provide constraints on possible physics beyond the standard model, complementing searches at high-energy colliders. The short-lived isotope 37K was produced at ISAC-TRIUMF and confined in an alternating magneto-optical trap before being spin-polarized to 99.13(9)% via optical pumping. Our system allows for an exceptionally open geometry with the decay products escaping with their momenta unperturbed by the shallow trapping potential. The emitted positrons are detected in a pair of symmetric detectors placed along the polarization axis to measure the β asymmetry. The analysis was performed blind and considers β-scattering as well as other systematic effects. The results place limits on the mass of a hypothetical W boson coupling to right-handed neutrinos as well as contribute to an independent determination of the Vud element of the CKM matrix. The β asymmetry result as well as improvements and future plans will be described. This work is supported in part by the U.S. Department of Energy, the Natural Sciences and Engineering Research Council of Canada, and the Israel Science Foundation.

  16. An Alternative Approach to Understanding the Observed Positron Fraction

    NASA Astrophysics Data System (ADS)

    Israel, Martin H.

    2014-10-01

    Space-based observations by PAMELA (Adriani et al., Nature 458, 607, 2009), Fermi-LAT (Ackerman et al., Phys. Rev. Lett. 105, 01103, 2012), and AMS (Aguilar et al., Phys. Rev. Lett. 110, 141102, 2013) have demonstrated that the positron fraction (e+/total-e) increases with increasing energy above about 10 GeV. According to the propagation model for Galactic cosmic rays in widespread use (Moskalenko & Strong, Astrophys. J. 493, 693, 1998), the production of secondary positrons from interaction of cosmic-ray protons and heavier nuclei with the interstellar medium gives a generally falling positron fraction between 10 and 100 GeV, with secondary positrons accounting for only ˜20 % of the observed positron fraction at 100 GeV; so some other physical phenomena have been proposed to explain the data. An alternative approach to interpreting the positron observations is to consider these data as presenting an opportunity for re-examining models of Galactic cosmic-ray propagation. Following release of the PAMELA data, three groups published propagation models (Shaviv, et al., Phys. Rev. Lett. 103, 111302, 2009, Cowsik and Burch, Phys. Rev. D. 82, 023009, 2010, Katz et al., Mon. Not. R. Aston. Soc. 405, 1458 2010) in which the observed positron fraction is explained entirely by secondary positrons produced in the interstellar medium. In May of this year, stimulated by the AMS extension of the positron data to higher energy with excellent statistics, two of those groups presented further development of their calculations (Cowsik et al. 2013, Blum et al. 2013), again concluding that the observed positrons can be understood as secondaries. None of the authors of these five papers was registered for the 33rd International Cosmic Ray Conference (ICRC). Although I am not an author of any of these papers, I have some close familiarity with one of these recent papers, so the conference organizers invited me to bring this alternative approach to the attention of the conference. The

  17. Superallowed Fermi beta decay

    SciTech Connect

    Hardy, J. C.; Towner, I. S.

    1998-12-21

    Superallowed 0{sup +}{yields}0{sup +} nuclear beta decay provides a direct measure of the weak vector coupling constant, G{sub V}. We survey current world data on the nine accurately determined transitions of this type, which range from the decay of {sup 10}C to that of {sup 54}Co, and demonstrate that the results confirm conservation of the weak vector current (CVC) but differ at the 98% confidence level from the unitarity condition for the Cabibbo-Kobayashi-Maskawa (CKM) matrix. We examine the reliability of the small calculated corrections that have been applied to the data, and assess the likelihood of even higher quality nuclear data becoming available to confirm or deny the discrepancy. Some of the required experiments depend upon the availability of intense radioactive beams. Others are possible today.

  18. Decay Dynamics of Tumors

    PubMed Central

    2016-01-01

    The fractional cell kill is a mathematical expression describing the rate at which a certain population of cells is reduced to a fraction of itself. We investigate the mathematical function that governs the rate at which a solid tumor is lysed by a cell population of cytotoxic lymphocytes. We do it in the context of enzyme kinetics, using geometrical and analytical arguments. We derive the equations governing the decay of a tumor in the limit in which it is plainly surrounded by immune cells. A cellular automaton is used to test such decay, confirming its validity. Finally, we introduce a modification in the fractional cell kill so that the expected dynamics is attained in the mentioned limit. We also discuss the potential of this new function for non-solid and solid tumors which are infiltrated with lymphocytes. PMID:27310010

  19. Exotic Decays of the 125 GeV Higgs Boson at Future $e^+e^-$ Lepton Colliders

    SciTech Connect

    Liu, Zhen; Wang, Lian-Tao; Zhang, Hao

    2016-12-29

    Discovery of unexpected properties of the Higgs boson offers an intriguing opportunity of shedding light on some of the most profound puzzles in particle physics. The Beyond Standard Model (BSM) decays of the Higgs boson could reveal new physics in a direct manner. Future electron-positron lepton colliders operating as Higgs factories, including CEPC, FCC-ee and ILC, with the advantages of a clean collider environment and large statistics, could greatly enhance the sensitivity in searching for these BSM decays. In this work, we perform a general study of Higgs exotic decays at future $e^+e^-$ lepton colliders, focusing on the Higgs decays with hadronic final states and/or missing energy, which are very challenging for the High-Luminosity program of the Large Hadron Collider (HL-LHC). We show that with simple selection cuts, $O(10^{-3}\\sim10^{-5})$ limits on the Higgs exotic decay branching fractions can be achieved using the leptonic decaying spectator $Z$ boson in the associated production mode $e^+e^-\\rightarrow Z H$. We further discuss the interplay between the detector performance and Higgs exotic decay, and other possibilities of exotic decays. Our work is a first step in a comprehensive study of Higgs exotic decays at future lepton colliders, which is a key ingredient of Higgs physics that deserves further investigation.

  20. Radioactive decay data tables

    SciTech Connect

    Kocher, D.C.

    1981-01-01

    The estimation of radiation dose to man from either external or internal exposure to radionuclides requires a knowledge of the energies and intensities of the atomic and nuclear radiations emitted during the radioactive decay process. The availability of evaluated decay data for the large number of radionuclides of interest is thus of fundamental importance for radiation dosimetry. This handbook contains a compilation of decay data for approximately 500 radionuclides. These data constitute an evaluated data file constructed for use in the radiological assessment activities of the Technology Assessments Section of the Health and Safety Research Division at Oak Ridge National Laboratory. The radionuclides selected for this handbook include those occurring naturally in the environment, those of potential importance in routine or accidental releases from the nuclear fuel cycle, those of current interest in nuclear medicine and fusion reactor technology, and some of those of interest to Committee 2 of the International Commission on Radiological Protection for the estimation of annual limits on intake via inhalation and ingestion for occupationally exposed individuals.

  1. RADIATIVE PENGUIN DECAYS FROM BABAR

    SciTech Connect

    Eigen, Gerald

    2003-08-28

    Electroweak penguin decays provide a promising hunting ground for Physics beyond the Standard Model (SM). The decay B {yields} X{sub s}{gamma}, which proceeds through an electromagnetic penguin loop, already provides stringent constraints on the supersymmetric (SUSY) parameter space. The present data samples of {approx}1 x 10{sup 8} B{bar B} events allow to explore radiative penguin decays with branching fractions of the order of 10{sup -6} or less. In this brief report they discuss a study of B {yields} K*{ell}{sup +}{ell}{sup -} decay modes and a search for B {yields} {rho}({omega}){gamma} decays.

  2. Charmless b decays at CDF

    SciTech Connect

    Donega, Mauro; /Geneva U.

    2005-07-01

    The authors report on the charmless B decays measurements performed on 180 pb{sup -1} of data collected with the CDF II detector at the Fermilab Tevatron collider. This paper describes: the first observation of the decay mode B{sub s} {yields} K{sup +}K{sup -} and the measurement of the direct Cp asymmetry in the ({bar B}){sub d} {yields} K{sup {+-}}{pi}{sup {-+}} decay; the first evidence of the decay mode B{sub s} {yields} {phi}{phi} and the branching ratio and Cp asymmetry for the B{sup {+-}} {yields} {phi}K{sup {+-}} decay.

  3. Plasma and trap-based techniques for science with positrons

    NASA Astrophysics Data System (ADS)

    Danielson, J. R.; Dubin, D. H. E.; Greaves, R. G.; Surko, C. M.

    2015-01-01

    In recent years, there has been a wealth of new science involving low-energy antimatter (i.e., positrons and antiprotons) at energies ranging from 102 to less than 10-3 eV . Much of this progress has been driven by the development of new plasma-based techniques to accumulate, manipulate, and deliver antiparticles for specific applications. This article focuses on the advances made in this area using positrons. However, many of the resulting techniques are relevant to antiprotons as well. An overview is presented of relevant theory of single-component plasmas in electromagnetic traps. Methods are described to produce intense sources of positrons and to efficiently slow the typically energetic particles thus produced. Techniques are described to trap positrons efficiently and to cool and compress the resulting positron gases and plasmas. Finally, the procedures developed to deliver tailored pulses and beams (e.g., in intense, short bursts, or as quasimonoenergetic continuous beams) for specific applications are reviewed. The status of development in specific application areas is also reviewed. One example is the formation of antihydrogen atoms for fundamental physics [e.g., tests of invariance under charge conjugation, parity inversion, and time reversal (the CPT theorem), and studies of the interaction of gravity with antimatter]. Other applications discussed include atomic and materials physics studies and the study of the electron-positron many-body system, including both classical electron-positron plasmas and the complementary quantum system in the form of Bose-condensed gases of positronium atoms. Areas of future promise are also discussed. The review concludes with a brief summary and a list of outstanding challenges.

  4. Determination of elemental tissue composition following proton treatment using positron emission tomography

    NASA Astrophysics Data System (ADS)

    Cho, Jongmin; Ibbott, Geoffrey; Gillin, Michael; Gonzalez-Lepera, Carlos; Min, Chul Hee; Zhu, Xuping; El Fakhri, Georges; Paganetti, Harald; Mawlawi, Osama

    2013-06-01

    Positron emission tomography (PET) has been suggested as an imaging technique for in vivo proton dose and range verification after proton induced-tissue activation. During proton treatment, irradiated tissue is activated and decays while emitting positrons. In this paper, we assessed the feasibility of using PET imaging after proton treatment to determine tissue elemental composition by evaluating the resultant composite decay curve of activated tissue. A phantom consisting of sections composed of different combinations of 1H, 12C, 14N, and 16O was irradiated using a pristine Bragg peak and a 6 cm spread-out Bragg-peak (SOBP) proton beam. The beam ranges defined at 90% distal dose were 10 cm the delivered dose was 1.6 Gy for the near monoenergetic beam and 2 Gy for the SOBP beam. After irradiation, activated phantom decay was measured using an in-room PET scanner for 30 min in list mode. Decay curves from the activated 12C and 16O sections were first decomposed into multiple simple exponential decay curves, each curve corresponding to a constituent radioisotope, using a least-squares method. The relative radioisotope fractions from each section were determined. These fractions were used to guide the decay curve decomposition from the section consisting mainly of 12C + 16O and calculate the relative elemental composition of 12C and 16O. A Monte Carlo simulation was also used to determine the elemental composition of the 12C + 16O section. The calculated compositions of the 12C + 16O section using both approaches (PET and Monte Carlo) were compared with the true known phantom composition. Finally, two patients were imaged using an in-room PET scanner after proton therapy of the head. Their PET data and the technique described above were used to construct elemental composition (12C and 16O) maps that corresponded to the proton-activated regions. We compared the 12C and 16O compositions of seven ROIs that corresponded to the vitreous humor, adipose/face mask, adipose

  5. Positron Emission Mammography with Multiple Angle Acquisition

    SciTech Connect

    Mark F. Smith; Stan Majewski; Raymond R. Raylman

    2002-11-01

    Positron emission mammography (PEM) of F-18 fluorodeoxyglucose (FDG) uptake in breast tumors with dedicated detectors typically has been accomplished with two planar detectors in a fixed position with the breast under compression. The potential use of PEM imaging at two detector positions to guide stereotactic breast biopsy has motivated us to use PEM coincidence data acquired at two or more detector positions together in a single image reconstruction. Multiple angle PEM acquisition and iterative image reconstruction were investigated using point source and compressed breast phantom acquisitions with 5, 9, 12 and 15 mm diameter spheres and a simulated tumor:background activity concentration ratio of 6:1. Image reconstruction was performed with an iterative MLEM algorithm that used coincidence events between any two detector pixels on opposed detector heads at each detector position. This present study compared two acquisition protocols: 2 angle acquisition with detector angular positions of -15 and +15 degrees and 11 angle acquisition with detector positions spaced at 3 degree increments over the range -15 to +15 degrees. Three- dimensional image resolution was assessed for the point source acquisitions, and contrast and signal-to-noise metrics were evaluated for the compressed breast phantom with different simulated tumor sizes. Radial and tangential resolutions were similar for the two protocols, while normal resolution was better for the 2 angle acquisition. Analysis is complicated by the asymmetric point spread functions. Signal- to-noise vs. contrast tradeoffs were better for 11 angle acquisition for the smallest visible 9 mm sphere, while tradeoff results were mixed for the larger and more easily visible 12 mm and 15 mm diameter spheres. Additional study is needed to better understand the performance of limited angle tomography for PEM. PEM tomography experiments with complete angular sampling are planned.

  6. Positron Emission Mammography with Multiple Angle Acquisition

    SciTech Connect

    Mark F. Smith; Stan Majewski; Raymond R. Raylman

    2002-11-01

    Positron emission mammography (PEM) of F-18 fluorodeoxyglucose (FbG) uptake in breast tumors with dedicated detectors typically has been accomplished with two planar detectors in a fixed position with the breast under compression. The potential use of PEM imaging at two detector positions to guide stereotactic breast biopsy has motivated us to use PEM coincidence data acquired at two or more detector positions together in a single image reconstruction. Multiple angle PEM acquisition and iterative image reconstruction were investigated using point source and compressed breast phantom acquisitions with 5, 9, 12 and 15 mm diameter spheres and a simulated tumor:background activity concentration ratio of 6:1. Image reconstruction was performed with an iterative MLEM algorithm that used coincidence events between any two detector pixels on opposed detector heads at each detector position. This present study compared two acquisition protocols: 2 angle acquisition with detector angular positions of -15 and +15 degrees and 11 angle acquisition with detector positions spaced at 3 degree increments over the range -15 to +15 degrees. Three-dimensional image resolution was assessed for the point source acquisitions, and contrast and signal-to-noise metrics were evaluated for the compressed breast phantom with different simulated tumor sizes. Radial and tangential resolutions were similar for the two protocols, while normal resolution was better for the 2 angle acquisition. Analysis is complicated by the asymmetric point spread functions. Signal- to-noise vs. contrast tradeoffs were better for 11 angle acquisition for the smallest visible 9 mm sphere, while tradeoff results were mixed for the larger and more easily visible 12 mm and 15 mm diameter spheres. Additional study is needed to better understand the performance of limited angle tomography for PEM. PEM tomography experiments with complete angular sampling are planned.

  7. Effect of positron range on spatial resolution.

    PubMed

    Phelps, M E; Hoffman, E J; Huang, S C; Ter-Pogossian, M M

    1975-07-01

    The effect of beta+ range on spatial resolution of imaging systems employing the detection of 511-keV annihilation radiation was determined by measuring the variation in the line-spread functions (LSFs) of positron-emitting radionuclides of 64Cu, 11C, and 15O as compared with the 514-keV gamma-ray emitter 85Sr. These radionuclides have maximum beta+ energies of 0.656, 0.960, and 1.72 MeV, respectively. The LSFs were measured in a tissue-equivalent phantom with high-resolution (approximately 2.4 mm FWHM) and low-resolution (approximately 8.8 mm FWHM) straightbore collimators coupled to a NaI(Tl) detector. Theoretical LSFs for the beta+ ranges were also calculated and convolved with the 85Sr LSF to yield the predicted LSFs for 11C and 15O. The high-resolution study showed a 0% and 2.3% increase in the full-width half-maximum (FWHM) and full-width tenth-maximum (FWO.1M) for the low-energy beta+ of 64Cu and a 37% (FWHM) and 52% (FWO.1M) increase for the high energy beta+ of 15O as compared with 85Sr. However, when the system resolution was decreased to 8.8 mm FWHM, the 64Cu showed no change at FWHM or FWO.1M and the 15O showed a 2.3% (FWHM) and 7.8% (FWO.1M) relative to 85Sr. The predicted LSFs were in good agreement with the experimental. These data indicate that the effect of beta+ range on spatial resolution is minimal unless the beta+ energy is larger than or equal to 1.5 MeV and the system resolution is on the order of a few millimeters.

  8. Acceleration of positrons in supernova shocks

    NASA Technical Reports Server (NTRS)

    Ellison, Donald C.

    1992-01-01

    During this project we investigated the acceleration of leptons (electrons and positrons) in collisionless shock waves. In particular, we were interested in how leptons are accelerated in the blast waves existing in the remnants of supernova explosions. Supernova remnants (SNRs) have long been considered as the most likely source of galactic cosmic rays but no definite connection between SNRs and the cosmic rays seen at earth can be made. Only by understanding lepton acceleration in shocks can the rich SNR data base be properly used to understand cosmic ray origins. Our project was directed at the neglected aspects of lepton acceleration. We showed that the efficiency of lepton acceleration depended critically on the lepton injection energy. We showed that, even when infection effects are not important, that proton and lepton distribution functions produced by shocks are quite different in the critical energy range for producing the observed synchrotron emission. We also showed that transrelativistic effects produced proton spectra that were not in agreement with standard results from radio observations, but that the lepton spectra were, in fact, consistent with observations. We performed simulations of relativistic shocks (shocks where the flow speed is a sizable fraction of the speed of light) and discovered some interesting effects. We first demonstrated the power of the Monte Carlo technique by determining the shock jump conditions in relativistic shocks. We then proceeded to determine how relativistic shocks accelerate particles. We found that nonlinear relativistic shocks treat protons and leptons even more differently than nonrelativistic shocks. The transrelativistic effects on the shock structure from the heavy ion component reduces the lepton acceleration to a tiny fraction of the ion acceleration. This effect is dramatic even if high energy leptons (many times thermal energy) are injected, and was totally unexpected. Our results have important

  9. A new look at the cosmic ray positron fraction

    NASA Astrophysics Data System (ADS)

    Boudaud, M.; Aupetit, S.; Caroff, S.; Putze, A.; Belanger, G.; Genolini, Y.; Goy, C.; Poireau, V.; Poulin, V.; Rosier, S.; Salati, P.; Tao, L.; Vecchi, M.

    2015-03-01

    Context. The positron fraction in cosmic rays has recently been measured with improved accuracy up to 500 GeV, and it was found to be a steadily increasing function of energy above ~10 GeV. This behaviour contrasts with standard astrophysical mechanisms, in which positrons are secondary particles, produced in the interactions of primary cosmic rays during their propagation in the interstellar medium. The observed anomaly in the positron fraction triggered a lot of excitement, as it could be interpreted as an indirect signature of the presence of dark matter species in the Galaxy, the so-called weakly interacting massive particles (WIMPs). Alternatively, it could be produced by nearby sources, such as pulsars. Aims: These hypotheses are probed in light of the latest AMS-02 positron fraction measurements. As regards dark matter candidates, regions in the annihilation cross section to mass plane, which best fit the most recent data, are delineated and compared to previous measurements. The explanation of the anomaly in terms of a single nearby pulsar is also explored. Methods: The cosmic ray positron transport in the Galaxy is described using a semi-analytic two-zone model. Propagation is described with Green functions as well as with Bessel expansions. For consistency, the secondary and primary components of the positron flux are calculated together with the same propagation model. The above mentioned explanations of the positron anomaly are tested using χ2 fits. The numerical package MicrOMEGAs is used to model the positron flux generated by dark matter species. The description of the positron fraction from conventional astrophysical sources is based on the pulsar observations included in the Australia Telescope National Facility (ATNF) catalogue. Results: The masses of the favoured dark matter candidates are always larger than 500 GeV, even though the results are very sensitive to the lepton flux. The Fermi measurements point systematically to much heavier

  10. Positron emission tomography imaging of braintumors with Cobalt-55 and L-[1-C11]-tyrosine

    SciTech Connect

    Jansen, H.M.L.; Pruim J.; Willemsen, A.T.M.

    1994-05-01

    The applicability of positron emission tomography (PET) with [C-11] tyrosine (TYR) and Cobalt-55 (Co) in patients with known primary brain tumors is reported. We used Co as a Calcium (Ca) marker to study Ca influx in degenerating neural tissue and TYR to indicate incorporation of amino acids into protein. Four patients showing a primary brain tumor with central necrosis on CT/MRI were studied with Co-PET. Additionally, 2 of these patients were consecutively studied with TYR-PET. Diagnostic confirmation was obtained by means of histology and/or cytology shortly after PET. Thirty-seven MBq Co was administered iv. approximately 24 hours before acquisition. The Co-scan was acquired for I hour. Immediately following Co-PET, 2 patients received 370 MBq TYR iv. TYR-PET acquisition was done dynamically for 55 minutes starting from the time of injection. The necrotic center of the tumor revealed no uptake of either Co or TYR. Vital tumor tissue showed intense uptake of TYR, indicating a high protein synthesis rate (PSR). The circumferent zone between necrotic and tumor tissue showed evident uptake of Co, suggesting cell-decay. In conclusion, TYR and Co are both suitable tracers for visualization of different aspects of brain malignancies, ie. PSR and cell-decay. Combining Co and TYR enables differentiation of necrosis vs. tumor growth with clear marking of the border zone. We think these complementary PET-techniques in conjunction with CT and/or MRI allow the visualization of different aspects of tumor tissue: central necrosis (CT/MRI), cell-decay (Co-PET) and vital tumor tissue (TYR-PET).

  11. Time Modulation of the {beta}{sup +}-Decay Rate of H-Like {sup 140}Pr{sup 58+} Ions

    SciTech Connect

    Ivanov, A. N.; Kryshen, E. L.; Pitschmann, M.; Kienle, P.

    2008-10-31

    Recent experimental data at GSI on the rates of the number of daughter ions, produced by the nuclear K-shell electron capture (EC) decays of the H-like ions {sup 140}Pr{sup 58+} and {sup 142}Pm{sup 60+}, suggest that they are modulated in time with periods T{sub EC}{approx_equal}7 sec and amplitudes a{sub EC}{approx_equal}0.20. Since it is known that these ions are unstable also under the nuclear positron ({beta}{sup +}) decays, we study a possible time dependence of the nuclear {beta}{sup +}-decay rate of the H-like {sup 140}Pr{sup 58+} ion. We show that the time dependence of the {beta}{sup +}-decay rate of the H-like {sup 140}Pr{sup 58+} ion as well as any H-like heavy ions cannot be observed.

  12. Resonances and Bound States in Positron Annihilation on Molecules

    NASA Astrophysics Data System (ADS)

    Surko, C. M.

    2007-10-01

    Positron annihilation is important in such diverse areas as study of metabolic processes in the human brain and the characterization of materials. Annihilation on molecules has been a subject of keen interest for decades. In particular, annihilation rates can be orders of magnitude greater than those expected for simple collisions. Recent results put our understanding of many aspects of this long-standing problem on a firm footing. We now understand that the annihilation proceeds by vibrational Feshbach resonances (VFR). A prerequisite for the existence of these VFR is that the positron binds to the target. The annihilation energy spectra provide the best measures to date of positron binding energies. Predictions of a new theory of VFR-enhanced annihilation in small molecules (methyl halides) [1] show excellent, quantitative agreement with experiment. New data and analyses for larger molecules (e.g., hydrocarbons with more than two carbon atoms) show that annihilation rates depend strongly on the number of vibrational degrees of freedom but, surprisingly, only weakly on positron binding energy. This places important constraints on theories of annihilation in these molecules. Results for second bound (i.e., positronically excited) states and overtone and combination-mode VFR, as well as outstanding questions, will also be discussed. This work is done in collaboration with Jason Young. [1] G. F. Gribakin and C. M. R. Lee, Phys. Rev. Lett. 97, 193201 (2006).

  13. The effect of direct positron production on relativistic feedback rates

    NASA Astrophysics Data System (ADS)

    Vodopiyanov, I. B.; Dwyer, J. R.; Lucia, R. J.; Cramer, E. S.; Arabshahi, S.; Rassoul, H.

    2013-12-01

    Relativistic feedback produces a self-sustaining runaway electron discharge via the production of backward propagating positrons and back-scattered x-rays. To date, only positrons created from pair-production by gamma-rays interacting with the air have been considered. In contrast, direct pair-production involves the creation of electron-positron pairs directly from the interaction of energetic runaway electrons with nuclei, and so it does not require the generation of bremsstrahlung gamma-rays. For high electric fields, where the runaway electron avalanche length scales are short, pair-production involving bremsstrahlung gamma-rays makes a smaller contribution to the total relativistic feedback rates than at lower fields, since both the bremsstrahlung interaction and the pair-production need to occur over a short length. On the other hand, for high fields, because direct positron production only involves one interaction, it may make a significant contribution to relativistic feedback rates in some cases. In this poster, we shall present the direct positron production cross-sections and calculate the effects on the relativistic feedback rates due to this process.

  14. Possibilities with pulsed polarized high density slow positrons

    NASA Astrophysics Data System (ADS)

    Mills, A. P., Jr.

    2014-04-01

    A particularly bright and intense polarized slow positron beam could be formed from isotopically enriched 79Kr produced at a reactor. After moderation with solid Ne, accumulation, compression, and bunching, this type of positron beam would enable a number of experiments including: (1) Long term storage of a neutral polarized electron-positron plasma in a cold box; (2) Pulsed e+ ACAR with a pulsed magnet to measure Fermi surfaces of paramagnetic metals; (3) Single shot measurements of positron annihilation in laser-imploding plasmas; (4) Study of a spin-polarized positronium gas at a density around that of ordinary air to produce a Ps Bose-Einstein condensate at room temperature; (5) High energy polarized positron channelling experiments to study polarized electron spatial wave functions in ferromagnets; and (6) Study of supersonic free expansion spin polarized BEC Ps jets formed from, for example, 1011 m=1 triplet Ps atoms created within an open ended 1 μm diameter cylindrical cavity 100 μm in length.

  15. Interpretation of AMS-02 electrons and positrons data

    SciTech Connect

    Mauro, M. Di; Donato, F.; Fornengo, N.; Vittino, A.; Lineros, R. E-mail: donato@to.infn.it E-mail: rlineros@ific.uv.es

    2014-04-01

    We perform a combined analysis of the recent AMS-02 data on electrons, positrons, electrons plus positrons and positron fraction, in a self-consistent framework where we realize a theoretical modeling of all the astrophysical components that can contribute to the observed fluxes in the whole energy range. The primary electron contribution is modeled through the sum of an average flux from distant sources and the fluxes from the local supernova remnants in the Green catalog. The secondary electron and positron fluxes originate from interactions on the interstellar medium of primary cosmic rays, for which we derive a novel determination by using AMS-02 proton and helium data. Primary positrons and electrons from pulsar wind nebulae in the ATNF catalog are included and studied in terms of their most significant (while loosely known) properties and under different assumptions (average contribution from the whole catalog, single dominant pulsar, a few dominant pulsars). We obtain a remarkable agreement between our various modeling and the AMS-02 data for all types of analysis, demonstrating that the whole AMS-02 leptonic data admit a self-consistent interpretation in terms of astrophysical contributions.

  16. Four-dimensional positron age-momentum correlation

    NASA Astrophysics Data System (ADS)

    Ackermann, Ulrich; Löwe, Benjamin; Dickmann, Marcel; Mitteneder, Johannes; Sperr, Peter; Egger, Werner; Reiner, Markus; Dollinger, Günther

    2016-11-01

    We have performed first four-dimensional age-momentum correlation (4D-AMOC) measurements at a pulsed high intensity positron micro beam and determined the absolute value of the three-dimensional momentum of the electrons annihilating with the positrons in coincidence with the positron age in the sample material. We operated two position sensitive detectors in coincidence to measure the annihilation radiation: a pixelated HPGe-detector and a microchannel plate image intensifier with a CeBr3 scintillator pixel array. The transversal momentum resolution of the 4D-AMOC setup was measured to be about 17 × 10-3 {m}0c (FWHM) and was circa 3.5 times larger than the longitudinal momentum resolution. The total time resolution was 540 ps (FWHM). We measured two samples: a gold foil and a carbon tape at a positron implantation energy of 2 keV. For each sample discrete electron momentum states and their respective positron lifetimes were extracted.

  17. High-intensity positron microprobe at Jefferson Lab

    SciTech Connect

    Golge, Serkan; Vlahovic, Branislav; Wojtsekhowski, Bogdan B.

    2014-06-19

    We present a conceptual design for a novel continuous wave electron-linac based high-intensity slow-positron production source with a projected intensity on the order of 1010 e+/s. Reaching this intensity in our design relies on the transport of positrons (T+ below 600 keV) from the electron-positron pair production converter target to a low-radiation and low-temperature area for moderation in a high-efficiency cryogenic rare gas moderator, solid Ne. The performance of the integrated beamline has been verified through computational studies. The computational results include Monte Carlo calculations of the optimized electron/positron beam energies, converter target thickness, synchronized raster system, transport of the beam from the converter target to the moderator, extraction of the beam from the channel, and moderation efficiency calculations. For the extraction of positrons from the magnetic channel a magnetic field terminator plug prototype has been built and experimental data on the effectiveness of this prototype are presented. The dissipation of the heat away from the converter target and radiation protection measures are also discussed.

  18. High-intensity positron microprobe at Jefferson Lab

    DOE PAGES

    Golge, Serkan; Vlahovic, Branislav; Wojtsekhowski, Bogdan B.

    2014-06-19

    We present a conceptual design for a novel continuous wave electron-linac based high-intensity slow-positron production source with a projected intensity on the order of 1010 e+/s. Reaching this intensity in our design relies on the transport of positrons (T+ below 600 keV) from the electron-positron pair production converter target to a low-radiation and low-temperature area for moderation in a high-efficiency cryogenic rare gas moderator, solid Ne. The performance of the integrated beamline has been verified through computational studies. The computational results include Monte Carlo calculations of the optimized electron/positron beam energies, converter target thickness, synchronized raster system, transport of themore » beam from the converter target to the moderator, extraction of the beam from the channel, and moderation efficiency calculations. For the extraction of positrons from the magnetic channel a magnetic field terminator plug prototype has been built and experimental data on the effectiveness of this prototype are presented. The dissipation of the heat away from the converter target and radiation protection measures are also discussed.« less

  19. Measurement of the Michel parameter {rho} in normal muon decay

    SciTech Connect

    Tu, X.; Amann, J.F.; Bolton, R.D.; Chen, Y.; Cooper, M.D.; Cooper, P.S.; Dzemidzic, M.; Foreman, W.; Gagliardi, C.A.; Haim, D.; Harrison, R.; Hart, G.; Hogan, G.E.; Hungerford, E.V. III; Jui, C.C.H.; Knott, J.E.; Koetke, D.D.; Kozlowski, T.; Kroupa, M.A.; Lan, K.; Liu, F.; Manweiler, R.; Mayes, B.W. II; Mischke, R.E.; Otis, J.N.; Piilonen, L.E.

    1995-07-10

    A new measurement of the Michel parameter {rho} in normal muon decay has been performed using the MEGA positron spectrometer. Over 500 million triggers were recorded and the data are currently being analyzed. The previous result has a precision on the value of {rho}{plus_minus}0.0026. The present experiment expects to improve the precision to {plus_minus}0.0008 or better. The improved result will be a precise test of the standard model of electroweak interactions for a purely leptonic process. It also will provide a better constraint on the {ital W}{sub {ital R}}{minus}{ital W}{sub {ital L}} mixing angle in the left-right symmetric models. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  20. Positron Emission Tomography - Computed Tomography (PET/CT)

    MedlinePlus

    ... nuclear medicine department. Through the natural process of radioactive decay, the small amount of radiotracer in your body ... blood sugar or blood insulin levels. Because the radioactive substance decays quickly and is effective for only a short ...

  1. Is radioactive decay really exponential?

    NASA Astrophysics Data System (ADS)

    Aston, P. J.

    2012-03-01

    Radioactive decay of an unstable isotope is widely believed to be exponential. This view is supported by experiments on rapidly decaying isotopes but is more difficult to verify for slowly decaying isotopes. The decay of 14C can be calibrated over a period of 12550 years by comparing radiocarbon dates with dates obtained from dendrochronology. It is well known that this approach shows that radiocarbon dates of over 3000 years are in error, which is generally attributed to past variation in atmospheric levels of 14C. We note that predicted atmospheric variation (assuming exponential decay) does not agree with results from modelling, and that theoretical quantum mechanics does not predict exact exponential decay. We give mathematical arguments that non-exponential decay should be expected for slowly decaying isotopes and explore the consequences of non-exponential decay. We propose an experimental test of this prediction of non-exponential decay for 14C. If confirmed, a foundation stone of current dating methods will have been removed, requiring a radical reappraisal both of radioisotope dating methods and of currently predicted dates obtained using these methods.

  2. E6 Gamma Decay

    SciTech Connect

    Brown, B. Alex; Rae, W. D. M.

    2011-05-06

    Rare electric hexacontatetrapole (E6) transitions are studied in the full (f{sub 7/2},f{sub 5/2},p{sub 3/2},p{sub 1/2}) shell-model basis. Comparison of theory to the results from the gamma decay in {sup 53}Fe and from inelastic electron scattering on {sup 52}Cr provides unique and interesting tests of the valence wavefunctions, the models used for energy density functionals and into the origin of effective charge.

  3. Rare B Decays

    SciTech Connect

    Jackson, P.D.; /Victoria U.

    2006-02-24

    Recent results from Belle and BaBar on rare B decays involving flavor-changing neutral currents or purely leptonic final states are presented. Measurements of the CP asymmetries in B {yields} K*{gamma} and b {yields} s{gamma} are reported. Also reported are updated limits on B{sup +} {yields} K{sup +}{nu}{bar {nu}}, B{sup +} {yields} {tau}{sup +}{nu}, B{sup +} {yields} {mu}{sup +}{nu} and the recent measurement of B {yields} X{sub s}{ell}{sup +}{ell}{sup -}.

  4. Rare decays and CP asymmetries in charged B decays

    SciTech Connect

    Deshpande, N.G.

    1991-01-01

    The theory of loop induced rare decays and the rate asymmetry due to CP violation in charged B Decays in reviewed. After considering b {yields} s{gamma} and b {yields} se{sup +}e{sup {minus}} decays, the asymmetries for pure penguin process are estimated first. A larger asymmetry can result in those modes where a tree diagram and a penguin diagram interfere, however these estimates are necessarily model dependent. Estimates of Cabbibo suppressed penguins are also considered.

  5. Superallowed Gamow-Teller decay of the doubly magic nucleus 100Sn.

    PubMed

    Hinke, C B; Böhmer, M; Boutachkov, P; Faestermann, T; Geissel, H; Gerl, J; Gernhäuser, R; Górska, M; Gottardo, A; Grawe, H; Grębosz, J L; Krücken, R; Kurz, N; Liu, Z; Maier, L; Nowacki, F; Pietri, S; Podolyák, Zs; Sieja, K; Steiger, K; Straub, K; Weick, H; Wollersheim, H-J; Woods, P J; Al-Dahan, N; Alkhomashi, N; Ataç, A; Blazhev, A; Braun, N F; Čeliković, I T; Davinson, T; Dillmann, I; Domingo-Pardo, C; Doornenbal, P C; de France, G; Farrelly, G F; Farinon, F; Goel, N; Habermann, T C; Hoischen, R; Janik, R; Karny, M; Kaşkaş, A; Kojouharov, I M; Kröll, Th; Litvinov, Y; Myalski, S; Nebel, F; Nishimura, S; Nociforo, C; Nyberg, J; Parikh, A R; Procházka, A; Regan, P H; Rigollet, C; Schaffner, H; Scheidenberger, C; Schwertel, S; Söderström, P-A; Steer, S J; Stolz, A; Strmeň, P

    2012-06-20

    The shell structure of atomic nuclei is associated with 'magic numbers' and originates in the nearly independent motion of neutrons and protons in a mean potential generated by all nucleons. During β(+)-decay, a proton transforms into a neutron in a previously not fully occupied orbital, emitting a positron-neutrino pair with either parallel or antiparallel spins, in a Gamow-Teller or Fermi transition, respectively. The transition probability, or strength, of a Gamow-Teller transition depends sensitively on the underlying shell structure and is usually distributed among many states in the neighbouring nucleus. Here we report measurements of the half-life and decay energy for the decay of (100)Sn, the heaviest doubly magic nucleus with equal numbers of protons and neutrons. In the β-decay of (100)Sn, a large fraction of the strength is observable because of the large decay energy. We determine the largest Gamow-Teller strength so far measured in allowed nuclear β-decay, establishing the 'superallowed' nature of this Gamow-Teller transition. The large strength and the low-energy states in the daughter nucleus, (100)In, are well reproduced by modern, large-scale shell model calculations.

  6. Thermonuclear Supernovae: Probing Magnetic Fields by Positrons and Late-time IR Line Profiles

    NASA Astrophysics Data System (ADS)

    Penney, R.; Hoeflich, P.

    2014-11-01

    We show the importance of γ and positron transport for the formation of late-time spectra in Type Ia supernovae (SNe Ia). The goal is to study the imprint of magnetic fields (B) on late-time IR line profiles, particularly the [Fe II] feature at 1.644 μm, which becomes prominent two to three months after the explosion. As a benchmark, we use the explosion of a Chandrasekhar mass (M Ch) white dwarf (WD) and, specifically, a delayed detonation model that can reproduce the light curves and spectra for a Branch-normal SN Ia. We assume WDs with initial magnetic surface fields between 1 and 109 G. We discuss large-scale dipole and small-scale magnetic fields. We show that positron transport effects must be taken into account for the interpretation of emission features starting at about one to two years after maximum light, depending on the size of B. The [Fe II] line profile and its evolution with time can be understood in terms of the overall energy input by radioactive decay and the transition from a γ-ray to a positron-dominated regime. We find that the [Fe II] line at 1.644 μm can be used to analyze the overall chemical and density structure of the exploding WD up to day 200 without considering B. At later times, positron transport and magnetic field effects become important. After about day 300, the line profile allows one to probe the size of the B-field. The profile becomes sensitive to the morphology of B at about day 500. In the presence of a large-scale dipole field, a broad line is produced in M Ch mass explosions that may appear flat-topped or rounded depending on the inclination at which the SN is observed. Small or no directional dependence of the spectra is found for small-scale B. We note that narrow-line profiles require central 56Ni as shown in our previous studies. Persistent broad-line, flat-topped profiles require high-density burning, which is the signature of a WD close to M Ch. Good time coverage is required to separate the effects of optical

  7. Tungsten mesh as positron transmission moderator in a monoenergetic positron beam

    NASA Astrophysics Data System (ADS)

    Weng, H. M.; Ling, C. C.; Beling, C. D.; Fung, S.; Cheung, C. K.; Kwan, P. Y.; Hui, I. P.

    2004-09-01

    The slow positron yield has been measured for various tungsten (W) moderator samples from a 22Na radioactive source. Multi-folded W mesh, W(1 0 0) single crystal foil and W polycrystalline foil samples have been investigated. It is found that the fast to slow conversion efficiency of the W mesh moderator depends on: (1) the annealing pretreatments, (2) the chemical etching duration and (3) the number of the folding layers. With the raw W mesh material having a wire diameter of 20 μm and transmission efficiency of 92.5%, an optimal efficiency of 1.2 × 10 -3 was achieved with 5 min etching duration and a folding number of 12 layers.

  8. Effective dose to staff members in a positron emission tomography/CT facility using zirconium-89

    PubMed Central

    2013-01-01

    Objective: Positron emission tomography (PET) using zirconium-89 (89Zr) is complicated by its complex decay scheme. In this study, we quantified the effective dose from 89Zr and compared it with fluorine-18 fludeoxyglucose (18F-FDG). Methods: Effective dose distribution in a PET/CT facility in Riyadh was calculated by Monte Carlo simulations using MCNPX. The positron bremsstrahlung, the annihilation photons, the delayed gammas from 89Zr and those emissions from 18F-FDG were modelled in the simulations but low-energy characteristic X-rays were ignored. Results: On the basis of injected activity, the dose from 89Zr was higher than that of 18F-FDG. However, the dose per scan from 89Zr became less than that from 18F-FDG near the patient, owing to the difference in injected activities. In the corridor and control rooms, the 89Zr dose was much higher than 18F-FDG, owing to the difference in attenuation by the shielding materials. Conclusion: The presence of the high-energy photons from 89Zr-labelled immuno-PET radiopharmaceuticals causes a significantly higher effective dose than 18F-FDG to the staff outside the patient room. Conversely, despite the low administered activity of 89Zr, it gives rise to a comparable or even lower dose than 18F-FDG to the staff near the patient. This interesting result raises apparently contradictory implications in the radiation protection considerations of a PET/CT facility. Advances in knowledge: To the best of our knowledge, radiation exposure to staff and public in the PET/CT unit using 89Zr has not been investigated. The ultimate output of this study will lead to the optimal design of the facility for routine use of 89Zr. PMID:23934963

  9. A Conway-Maxwell-Poisson (CMP) model to address data dispersion on positron emission tomography.

    PubMed

    Santarelli, Maria Filomena; Della Latta, Daniele; Scipioni, Michele; Positano, Vincenzo; Landini, Luigi

    2016-10-01

    Positron emission tomography (PET) in medicine exploits the properties of positron-emitting unstable nuclei. The pairs of γ- rays emitted after annihilation are revealed by coincidence detectors and stored as projections in a sinogram. It is well known that radioactive decay follows a Poisson distribution; however, deviation from Poisson statistics occurs on PET projection data prior to reconstruction due to physical effects, measurement errors, correction of deadtime, scatter, and random coincidences. A model that describes the statistical behavior of measured and corrected PET data can aid in understanding the statistical nature of the data: it is a prerequisite to develop efficient reconstruction and processing methods and to reduce noise. The deviation from Poisson statistics in PET data could be described by the Conway-Maxwell-Poisson (CMP) distribution model, which is characterized by the centring parameter λ and the dispersion parameter ν, the latter quantifying the deviation from a Poisson distribution model. In particular, the parameter ν allows quantifying over-dispersion (ν<1) or under-dispersion (ν>1) of data. A simple and efficient method for λ and ν parameters estimation is introduced and assessed using Monte Carlo simulation for a wide range of activity values. The application of the method to simulated and experimental PET phantom data demonstrated that the CMP distribution parameters could detect deviation from the Poisson distribution both in raw and corrected PET data. It may be usefully implemented in image reconstruction algorithms and quantitative PET data analysis, especially in low counting emission data, as in dynamic PET data, where the method demonstrated the best accuracy.

  10. A new scheme to accumulate positrons in a Penning-Malmberg trap with a linac-based positron pulsed source

    NASA Astrophysics Data System (ADS)

    Dupré, P.

    2013-03-01

    The Gravitational Behaviour of Antimatter at Rest experiment (GBAR) is designed to perform a direct measurement of the weak equivalence principle on antimatter by measuring the acceleration of anti-hydrogen atoms in the gravitational field of the Earth. The experimental scheme requires a high density positronium (Ps) cloud as a target for antiprotons, provided by the Antiproton Decelerator (AD) - Extra Low Energy Antiproton Ring (ELENA) facility at CERN. The Ps target will be produced by a pulse of few 1010 positrons injected onto a positron-positronium converter. For this purpose, a slow positron source using an electron Linac has been constructed at Saclay. The present flux is comparable with that of 22Na-based sources using solid neon moderator. A new positron accumulation scheme with a Penning-Malmberg trap has been proposed taking advantage of the pulsed time structure of the beam. In the trap, the positrons are cooled by interaction with a dense electron plasma. The overall trapping efficiency has been estimated to be ˜70% by numerical simulations.

  11. Dynamic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas with superthermal electrons and positrons

    SciTech Connect

    Saha, Asit E-mail: prasantachatterjee1@rediffmail.com; Pal, Nikhil; Chatterjee, Prasanta E-mail: prasantachatterjee1@rediffmail.com

    2014-10-15

    The dynamic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas with superthermal electrons and positrons has been investigated in the framework of perturbed and non-perturbed Kadomtsev-Petviashili (KP) equations. Applying the reductive perturbation technique, we have derived the KP equation in electron-positron-ion magnetoplasma with kappa distributed electrons and positrons. Bifurcations of ion acoustic traveling waves of the KP equation are presented. Using the bifurcation theory of planar dynamical systems, the existence of the solitary wave solutions and the periodic traveling wave solutions has been established. Two exact solutions of these waves have been derived depending on the system parameters. Then, using the Hirota's direct method, we have obtained two-soliton and three-soliton solutions of the KP equation. The effect of the spectral index κ on propagations of the two-soliton and the three-soliton has been shown. Considering an external periodic perturbation, we have presented the quasi periodic behavior of ion acoustic waves in electron-positron-ion magnetoplasmas.

  12. Inelastic cross sections for positron scattering from atomic hydrogen

    SciTech Connect

    Weber, M.; Hofmann, A.; Raith, W.; Sperber, W.; Jacobsen, F.; Lynn, K.G.

    1994-12-31

    Positronium formation (Ps) cross sections for positrons impinging on atomic hydrogen were measured in the impact energy range from 13eV to 255eV at the High Intensity Positron (HIP) beam at Brookhaven National Laboratory (BNL). The Ps-formation cross section was found to rise rapidly from the threshold at 6.8eV to a maximum value of (2.98 {plus_minus} 0.18) {times} 10{sup {minus}16} cm{sup 2} for {approx} 15eV positrons. By 75eV it drops below the detection limit of 0.17 {times} 10{sup {minus}16} cm{sup 2} which is the present level of statistical uncertainty. The experiment was modified to enable the measurement of doubly differential scattering cross sections.

  13. Electron- and positron-proton elastic scattering in CLAS

    SciTech Connect

    Weinstein, L. B.

    2009-09-02

    There is a significant disagreement between measurements of the proton electric form factor, G{sup p}{sub E}, using Rosenbluth separations and polarization transfer. This disagreement, if not explained, could pose a fundamental challenge to our understanding of electron scattering or proton structure. Two-photon exchange (TPE) processes, although not fully calculable, are the most likely explanation of this disagreement. We will definitively test this assertion by comparing the electron-proton and positron-proton elastic scattering cross section in the Jefferson Lab CLAS. We will make a mixed identical electron and positron tertiary beam by passing a 5.5 GeV primary electron beam through a radiator to make a photon beam and then passing the photon beam through a converter to make electron-positron pairs. Measuring the elastic cross sections simultaneously using identical lepton beams should significantly reduce systematic uncertainties.

  14. Electron- and positron-proton elastic scattering in CLAS

    SciTech Connect

    L.B. Weinstein

    2009-08-01

    There is a significant disagreement between measurements of the proton electric form factor, G{sup p}{sub E}, using Rosenbluth separations and polarization transfer. This disagreement, if not explained, could pose a fundamental challenge to our understanding of electron scattering or proton structure. Two-photon exchange (TPE) processes, although not fully calculable, are the most likely explanation of this disagreement. We will definitively test this assertion by comparing the electron-proton and positron-proton elastic scattering cross section in the Jefferson Lab CLAS. We will make a mixed identical electron and positron tertiary beam by passing a 5.5 GeV primary electron beam through a radiator to make a photon beam and then passing the photon beam through a converter to make electron-positron pairs. Measuring the elastic cross sections simultaneously using identical lepton beams should significantly reduce systematic uncertainties.

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

    PubMed

    Sebe, István; Szabó, Barnabás; Zelkó, Romána

    2012-01-01

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

  16. Chemical stability of positronic complexes with atoms and atomic ions

    SciTech Connect

    Karl, M.W.; Nakanishi, H.; Schrader, D.M.

    1984-10-01

    A simple theory for establishing the stability or instability of positron-atomic systems against dissociation is presented. The theory consists of assuming that Morse-potential parameters for protonic diatoms are transferrable to the corresponding positronic molecules, and making appropriate reduced-mass modifications in the calculation of binding energies. The surprisingly good reliability of the method is established by appealing to the well-known positronium affinities of atomic hydrogen and fluorine. Positronium (Ps) binding is found for about half of the 42 atoms tested. In addition, instability is indicated for all nine positron-atom systems tested, and stability is indicated for seven of eight negatively charged systems tested; e.g., PsO/sup -/.

  17. An Affordable Concurrent Approach to Positron Polarization Potentials

    NASA Astrophysics Data System (ADS)

    Nichols, Patrick J.; Gibson, Thomas L.

    2000-06-01

    In order to extend our work on low-energy positron-matter collisions to larger target molecules, we are in the process of purchasing and installing a high-performance, parallel computer for less than $15,000. The system will be constructed from commodity PC-class components, such as Intel Celeron Processors with standard memory, hard drives, and fast ethernet cards. The operating system software, compilers, and standard message-passing routines for this system are available for free from the Beowulf Project. Our modified quantum chemistry codes for generating positron-molecule interaction potentials within the Distributed Positron Model are being converted to parallel form and will be made available for download over the internet. We will present details of our work along with some comparative results.

  18. Spectral and spatial characterisation of laser-driven positron beams

    NASA Astrophysics Data System (ADS)

    Sarri, G.; Warwick, J.; Schumaker, W.; Poder, K.; Cole, J.; Doria, D.; Dzelzainis, T.; Krushelnick, K.; Kuschel, S.; Mangles, S. P. D.; Najmudin, Z.; Romagnani, L.; Samarin, G. M.; Symes, D.; Thomas, A. G. R.; Yeung, M.; Zepf, M.

    2017-01-01

    The generation of high-quality relativistic positron beams is a central area of research in experimental physics, due to their potential relevance in a wide range of scientific and engineering areas, ranging from fundamental science to practical applications. There is now growing interest in developing hybrid machines that will combine plasma-based acceleration techniques with more conventional radio-frequency accelerators, in order to minimise the size and cost of these machines. Here we report on recent experiments on laser-driven generation of high-quality positron beams using a relatively low energy and potentially table-top laser system. The results obtained indicate that current technology allows to create, in a compact setup, positron beams suitable for injection in radio-frequency accelerators.

  19. Recent progress in tailoring trap-based positron beams

    SciTech Connect

    Natisin, M. R.; Hurst, N. C.; Danielson, J. R.; Surko, C. M.

    2013-03-19

    Recent progress is described to implement two approaches to specially tailor trap-based positron beams. Experiments and simulations are presented to understand the limits on the energy spread and pulse duration of positron beams extracted from a Penning-Malmberg (PM) trap after the particles have been buffer-gas cooled (or heated) in the range of temperatures 1000 {>=} T {>=} 300 K. These simulations are also used to predict beam performance for cryogenically cooled positrons. Experiments and simulations are also presented to understand the properties of beams formed when plasmas are tailored in a PM trap in a 5 tesla magnetic field, then non-adiabatically extracted from the field using a specially designed high-permeability grid to create a new class of electrostatically guided beams.

  20. Spectral and spatial characterisation of laser-driven positron beams

    DOE PAGES

    Sarri, G.; Warwick, J.; Schumaker, W.; ...

    2016-10-18

    The generation of high-quality relativistic positron beams is a central area of research in experimental physics, due to their potential relevance in a wide range of scientific and engineering areas, ranging from fundamental science to practical applications. There is now growing interest in developing hybrid machines that will combine plasma-based acceleration techniques with more conventional radio-frequency accelerators, in order to minimise the size and cost of these machines. Here we report on recent experiments on laser-driven generation of high-quality positron beams using a relatively low energy and potentially table-top laser system. Lastly, the results obtained indicate that current technology allowsmore » to create, in a compact setup, positron beams suitable for injection in radio-frequency accelerators.« less

  1. Spectral and spatial characterisation of laser-driven positron beams

    SciTech Connect

    Sarri, G.; Warwick, J.; Schumaker, W.; Poder, K.; Cole, J.; Doria, D.; Dzelzainis, T.; Krushelnick, K.; Kuschel, S.; Mangles, S. P. D.; Najmudin, Z.; Romagnani, L.; Samarin, G. M.; Symes, D.; Thomas, A. G. R.; Yeung, M.; Zepf, M.

    2016-10-18

    The generation of high-quality relativistic positron beams is a central area of research in experimental physics, due to their potential relevance in a wide range of scientific and engineering areas, ranging from fundamental science to practical applications. There is now growing interest in developing hybrid machines that will combine plasma-based acceleration techniques with more conventional radio-frequency accelerators, in order to minimise the size and cost of these machines. Here we report on recent experiments on laser-driven generation of high-quality positron beams using a relatively low energy and potentially table-top laser system. Lastly, the results obtained indicate that current technology allows to create, in a compact setup, positron beams suitable for injection in radio-frequency accelerators.

  2. Wood decay at sea

    NASA Astrophysics Data System (ADS)

    Charles, François; Coston-Guarini, Jennifer; Guarini, Jean-Marc; Fanfard, Sandrine

    2016-08-01

    The oceans and seas receive coarse woody debris since the Devonian, but the kinetics of wood degradation remains one of many unanswered questions about the fate of driftwood in the marine environment. A simple gravimetric experiment was carried out at a monitoring station located at the exit of a steep, forested Mediterranean watershed in the Eastern Pyrenees. The objective was to describe and quantify, with standardized logs (in shape, structure and constitution), natural degradation of wood in the sea. Results show that the mass decrease of wood logs over time can be described by a sigmoidal curve. The primary process of wood decay observed at the monitoring station was due to the arrival and installation of wood-boring species that consumed more than half of the total wood mass in six months. Surprisingly, in a region where there is little remaining wood marine infrastructure, "shipworms", i.e. xylophagous bivalves, are responsible for an important part of this wood decay. This suggests that these communities are maintained probably by a frequent supply of a large quantity of riparian wood entering the marine environment adjacent to the watershed. By exploring this direct link between terrestrial and marine ecosystems, our long term objective is to determine how these supplies of terrestrial organic carbon can sustain wood-based marine communities as it is observed in the Mediterranean Sea.

  3. Theoretical calculation of positron affinities of solute clusters in aluminum alloys

    NASA Astrophysics Data System (ADS)

    Mizuno, Masataka; Araki, Hideki; Shirai, Yasuharu

    2016-01-01

    We have performed theoretical calculations of positron states for solute clusters in aluminum alloys to estimate the positron affinity of solute clusters. Positron states of solute clusters in aluminum alloys were calculated under the electronic structures obtained by first- principles molecular orbital calculations using Al158-X13 clusters. We defined the positron affinity of the solute clusters by the difference in the lowest potential sensed by positrons between the solute clusters and Al bulk. With increasing atomic number of 3d metals, the annihilation fraction of the solute clusters rapidly increases at Mn and shows a maximum at Ni. A similar trend is observed for 4d metals. The localization of positron at the solute clusters mainly arises from charge transfer from Al matrix to solute clusters. The positron affinity defined in this work well represents the localization of positron at the solute clusters in aluminum alloys.

  4. 77 FR 71802 - Guidance on Investigational New Drug Applications for Positron Emission Tomography Drugs...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-04

    ... ``Investigational New Drug Applications for Positron Emission Tomography (PET) Drugs.'' The guidance is intended to assist manufacturers of PET drugs in submitting investigational new drug applications (INDs). DATES... guidance entitled ``Investigational New Drug Applications for Positron Emission Tomography (PET)...

  5. Monte carlo simulation of positron induced secondary electrons in thin carbon foils

    NASA Astrophysics Data System (ADS)

    Cai, L. H.; Yang, B.; Ling, C. C.; Beling, C. D.; Fung, S.

    2011-01-01

    Emission of secondary electrons induced by the passage of low energy positrons through thin carbon foils was studied by the Monte Carlo method. The positron and electron elastic cross sections were calculated by partial wave analysis. The inelastic positron-valence-electron was described by the energy loss function obtained from dielectric theory. The positron-core-electron interaction was modelled by the Gryzinski's excitation function. Positron transport inside the carbon foil was simulated in detail. Secondary electrons created by positrons and high energy secondary electrons through inelastic interactions were tracked through the foil. The positron transmission coefficient and secondary electron yielded in forward and backward geometry are calculated and dependences on positron energy and carbon foil thickness are discussed.

  6. Conceptual design of an intense positron source based on an LIA

    NASA Astrophysics Data System (ADS)

    Long, Ji-Dong; Yang, Zhen; Dong, Pan; Shi, Jin-Shui

    2012-04-01

    Accelerator based positron sources are widely used due to their high intensity. Most of these accelerators are RF accelerators. An LIA (linear induction accelerator) is a kind of high current pulsed accelerator used for radiography. A conceptual design of an intense pulsed positron source based on an LIA is presented in the paper. One advantage of an LIA is its pulsed power being higher than conventional accelerators, which means a higher amount of primary electrons for positron generations per pulse. Another advantage of an LIA is that it is very suitable to decelerate the positron bunch generated by bremsstrahlung pair process due to its ability to adjustably shape the voltage pulse. By implementing LIA cavities to decelerate the positron bunch before it is moderated, the positron yield could be greatly increased. These features may make the LIA based positron source become a high intensity pulsed positron source.

  7. Positron emission tomography: the conceptual idea using a multidisciplinary approach.

    PubMed

    Paans, Anne M J; van Waarde, Aren; Elsinga, Philip H; Willemsen, Antoon T M; Vaalburg, Willem

    2002-07-01

    Positron emission tomography (PET) is a method for quantitatively measuring biochemical and physiological processes in vivo by using radiopharmaceuticals labeled with positron-emitting radionuclides such as 11C, 13N, 15O, and 18F and by measuring the annihilation radiation using a coincidence technique. This technique is also used for measurement of the pharmacokinetics of labeled drugs and measurement of the effects of drugs on metabolism. Deviations from normal metabolism can be measured and insight into biological processes responsible for diseases can be obtained.

  8. Positron annihilation spectroscopy of biological tissue in 11C irradiation.

    PubMed

    Sakurai, Hiroshi; Itoh, Fumitake; Hirano, Yoshiyuki; Nitta, Munetaka; Suzuki, Kosuke; Kato, Daisuke; Yoshida, Eiji; Nishikido, Fumihiko; Wakizaka, Hidekatsu; Kanai, Tatsuaki; Yamaya, Taiga

    2014-11-21

    Positron annihilation spectroscopy (PAS) spectra of biological tissue in 11C irradiation are reported and spatial resolution coefficient of positron emission tomography (PET) obtained from the PAS spectrum is discussed for 11C irradiation. A PAS spectrum of the biological tissue with water is the same as that of the water pool phantom in 11C irradiation. However, a PAS spectrum of the biological tissue with less water differs from that of the water pool phantom. The PET spatial resolution coefficient depends on the kind of biological tissue. However, the PET spatial resolution coefficient, 0.00243±0.00014, can be used as a common value of maximum limit.

  9. Bismuth germanate as a potential scintillation detector in positron cameras.

    PubMed

    Cho, Z H; Farukhi, M R

    1977-08-01

    Timing and energy resolutions of the bismuth germanate (Bi4Ge3O12) scintillation crystals were studied, with particular respect to a positron-camera application. In comparison with the NaI(Tl) system, the detection efficiency for annihilation radiation is more than triple, and coincidence detection efficiency is more than ten times as good. This paper explores the properties of the new scintillator material and their bearing on the spatial resolution and the efficiency of coincidence detection in positron cameras with stationary ring detectors.

  10. Positron lifetime studies in thermoplastic polyimide test specimens

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    Positron lifetime measurements were made in two thermoplastic polyimide materials recently developed at Langley. The long component lifetime values in polyimidesulfone samples are 847 + or - 81 Ps (dry) and 764 + or - 91 Ps (saturated). The corresponding values in LARC thermoplastic imides are 1080 + or - 139 Ps (dry) and 711 + or - 96 Ps (saturated). Clearly, the presence of moisture has greater effect on positron lifetime in LARC thermoplastic imides than in the case of polyimidesulfones. This result is consistent with the photomicrographic observations made on frozen water saturated specimens of these materials.

  11. 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.

  12. Positronium formation in positron-rubidium inelastic scattering

    NASA Astrophysics Data System (ADS)

    Abdel-Raouf, M. A.

    1988-04-01

    Eight partial cross sections of positron-rubidium ( 37Rb) inelastic scattering (corresponding to 0 ⩽ l⩽ 7, where l is the total angular momentum) are calculated at 25 values of the incident energy ranging from 0.1 to 1000 eV. The calculations are carried out using Clementi-Roetti's wavefunctions, and a combination of the coupled-static and frozen-core approximations. A comparison between the total positronium formation cross sections of the collisions of positrons with four different alkali atoms (lithium, sodium, potassium and rubidium) is presented.

  13. Observation of Polarized Positrons from an Undulator-Based Source

    SciTech Connect

    Alexander, G; Barley, J.; Batygin, Y.; Berridge, S.; Bharadwaj, V.; Bower, G.; Bugg, W.; Decker, F.-J.; Dollan, R.; Efremenko, Y.; Gharibyan, V.; Hast, C.; Iverson, R.; Kolanoski, H.; Kovermann, J.; Laihem, K.; Lohse, T.; McDonald, K.T.; Mikhailichenko, A.A.; Moortgat-Pick, G.A.; Pahl, P.; /Tel Aviv U. /Cornell U., Phys. Dept. /SLAC /Tennessee U. /Humboldt U., Berlin /DESY /Yerevan Phys. Inst. /Aachen, Tech. Hochsch. /DESY, Zeuthen /Princeton U. /Durham U. /Daresbury

    2008-03-06

    An experiment (E166) at the Stanford Linear Accelerator Center (SLAC) has demonstrated a scheme in which a multi-GeV electron beam passed through a helical undulator to generate multi-MeV, circularly polarized photons which were then converted in a thin target to produce positrons (and electrons) with longitudinal polarization above 80% at 6 MeV. The results are in agreement with Geant4 simulations that include the dominant polarization-dependent interactions of electrons, positrons and photons in matter.

  14. Positron plasma control techniques for the production of cold antihydrogen

    SciTech Connect

    Funakoshi, R.; Hayano, R. S.; Amoretti, M.; Macri, M.; Testera, G.; Variola, A.; Bonomi, G.; Bowe, P. D.; Hangst, J. S.; Madsen, N.; Canali, C.; Carraro, C.; Lagomarsino, V.; Manuzio, G.; Cesar, C. L.; Charlton, M.; Joergensen, L. V.; Mitchard, D.; Werf, D. P. van der; Doser, M.

    2007-07-15

    An observation of a clear dependence of antihydrogen production on positron plasma shapes is reported. For this purpose a plasma control method has been developed combining the plasma rotating-wall technique with a mode diagnostic system. With the help of real-time and nondestructive observations, the rotating-wall parameters have been optimized. The positron plasma can be manipulated into a wide range of shapes (aspect ratio 6.5{<=}{alpha} < or approx. 80) and densities (1.5x10{sup 8}{<=}n < or approx. 7x10{sup 9} cm{sup -3}) within a short duration (25 s) compatible with the ATHENA antihydrogen production cycle.

  15. What can we learn from a sharply falling positron fraction?

    NASA Astrophysics Data System (ADS)

    Delahaye, Timur; Kotera, Kumiko; Silk, Joseph

    2015-12-01

    Recent results from the AMS-02 data have confirmed that the cosmic ray positron fraction increases with energy between 10 and 200 GeV. This quantity should not exceed 50%, and it is hence expected that it will either converge towards 50% or fall. We study the possibility that future data may show the positron fraction dropping down abruptly to the level expected with only secondary production, and forecast the implications of such a feature in term of possible injection mechanisms that include both Dark Matter and pulsars.

  16. Positronics of radiation-induced effects in chalcogenide glassy semiconductors

    SciTech Connect

    Shpotyuk, O.; Kozyukhin, S. A.; Shpotyuk, M.; Ingram, A.; Szatanik, R.

    2015-03-15

    Using As{sub 2}S{sub 3} and AsS{sub 2} glasses as an example, the principal possibility of using positron annihilation spectroscopy methods for studying the evolution of the free volume of hollow nanoobjects in chalcogenide glassy semiconductors exposed to radiation is shown. The results obtained by measurements of the positron annihilation lifetime and Doppler broadening of the annihilation line in reverse chronological order are in full agreement with the optical spectroscopy data in the region of the fundamental absorption edge, being adequately described within coordination defect-formation and physical-aging models.

  17. Positron beam studies of saponite film prepared by precipitation method

    NASA Astrophysics Data System (ADS)

    Numata, K.; Sato, K.; Fujimoto, K.; Ito, K.

    2017-01-01

    Micrometer-sized saponite particles were isolated by means of gravitational sedimentation method applying Stokes’ law. The sample prepared with this method was film-like state with a thickness of ~ 30 μm and was semitransparent, indicating that the particles are homogeneously stacked all together. Positron lifetime spectroscopy using a slow positron beam yielded two components for ortho-positronium with lifetimes of 1.5 ns and 8.4 ns with the respective relative intensities of 13 % and 10 %. The results suggest that the self-assembly of the larger particles toward structural densification is suppressed for the present film in comparison with the smaller nanoparticles.

  18. Measurement of the ground-state asymmetry parameter for the decay of sup 29 P

    SciTech Connect

    Masson, G.S.

    1988-01-01

    The ground state asymmetry parameter, A{sub gs}, was measured for the decay of polarized {sup 29}P. From A{sub gs} and the published value for ft{sub 1/2}, the decay's Fermi and Gamow-Teller strengths were deduced. Polarized {sup 29}P was produced by bombarding {sup 28}Si with 3.0 MeV vector polarized deuterons. A free standing wafer of pure natural abundance silicon crystal served as both target and host for the {sup 29}P. The target was heated to 140{degree}C and placed in a 1.0mT magnetic field to lengthen the polarization relaxation time. Positrons emitted in the decay were recorded by two detector telescopes placed at 0{degree}C and 180{degree} relative to the sample's polarization axis. A NaI detector, placed at 90{degree} was used to record gammas in coincidence with positrons, making it possible to simultaneously measure the asymmetries for both the ground state and excited state branches. The ground state asymmetry parameter, A{sub gs}, was deduced from these two asymmetries. The vector coupling constant, calculated form the measured Fermi strength, agrees with the predictions of CVC and with the accepted value for the Cabibbo angle. The measured Gamow-Teller strength agrees with recent calculations by Brown and Wildenthal, and disagree with earlier results of Azuelos and Kitching.

  19. Rare B Decays at Babar

    SciTech Connect

    Palombo, Fernando; Collaboration, for the BABAR

    2009-01-12

    The author presents some of the most recent BABAR measurements for rare B decays. These include rate asymmetries in the B decays to K{sup (*)}l{sup +}l{sup -} and K{sup +}{pi}{sup -} and branching fractions in the B decays to l{sup +}{nu}{sub l}, K{sub 1}(1270){sup +}{pi}{sup -} and K{sub 1}(1400){sup +}{pi}{sup -}. The author also reports a search for the B{sup +} decay to K{sub S}{sup 0}K{sub S}{sup 0}{pi}{sup +}.

  20. Positron studies in catalysis research. Final report, September 1993-- May 1995

    SciTech Connect

    1996-05-01

    During the past 20 months, we have completed our positron microscope and performed several studies in our nonmicroscopic depth-profiling positron spectrometer which should ultimately be applicable to catalysis. These studies involve using depth-profiled positron spectrometers to observe the growth dynamics of metal silicides on silicon substrates and to observe defects in glassy polymer surfaces and thin films, and the use of bulk positron lifetime measurements to observe pore-size variations in zeolites.

  1. A low energy positron accumulator for the plasma confinement in a compact magnetic mirror trap

    SciTech Connect

    Higaki, Hiroyuki Kaga, Chikato; Nagayasu, Katsushi; Okamoto, Hiromi; Nagata, Yugo; Kanai, Yasuyuki; Yamazaki, Yasunori

    2015-06-29

    A low energy positron accumulator was constructed at RIKEN for the purpose of confining an electron-positron plasma. The use of 5 mCi {sup 22}Na RI source with a standard solid Ne moderator and N{sub 2} buffer gas cooling resulted in a low energy positron yield of ∼ 3 × 10{sup 5} e+/s. So far, 2 × 10{sup 6} positrons have been accumulated in 120s.

  2. The Effects of Surface Reconstruction and Electron-Positron Correlation on the Annihilation Characteristics of Positrons Trapped at Semiconductor Surfaces

    SciTech Connect

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

    2009-03-10

    Experimental positron annihilation induced Auger electron spectroscopy (PAES) data from Ge(100) and Ge(111) surfaces display several strong Auger peaks corresponding to M{sub 4,5}N{sub 1}N{sub 2,3}, M{sub 2,3}M{sub 4,5}M{sub 4,5}, M{sub 2,3}M{sub 4,5}V, and M{sub 1}M{sub 4,5}M{sub 4,5} Auger transitions. The integrated peak intensities of Auger transitions have been used to obtain experimental annihilation probabilities for the Ge 3d and 3p core electrons. The experimental data were analyzed by performing theoretical studies of the effects of surface reconstructions and electron-positron correlations on image potential induced surface states and annihilation characteristics of positrons trapped at the reconstructed Ge(100) and Ge(111) surfaces. Calculations of positron surface states and annihilation characteristics have been performed for Ge(100) surface with (2x1), (2x2), and (4x2) reconstructions, and for Ge(111) surface with c(2x8) reconstruction. Estimates of the positron binding energy and annihilation characteristics reveal their sensitivity to the specific atomic structure of the topmost layers of the semiconductor and to the approximations used to describe electron-positron correlations. The results of these theoretical studies are compared with the ones obtained for the reconstructed Si(100)-(2x1) and Si(111)-(7x7) surfaces.

  3. Measuring positron-atom binding energies through laser-assisted photorecombination

    NASA Astrophysics Data System (ADS)

    Surko, C. M.; Danielson, J. R.; Gribakin, G. F.; Continetti, R. E.

    2012-06-01

    Described here is a proposed experiment to use laser-assisted photorecombination of positrons from a trap-based beam and metal atoms in the gas phase to measure positron-atom binding energies. Signal rates are estimated, based in part upon experience studying resonant annihilation spectra using a trap-based positron beam.

  4. Acceleration of positrons by a relativistic electron beam in the presence of quantum effects

    SciTech Connect

    Niknam, A. R.; Aki, H.; Khorashadizadeh, S. M.

    2013-09-15

    Using the quantum magnetohydrodynamic model and obtaining the dispersion relation of the Cherenkov and cyclotron waves, the acceleration of positrons by a relativistic electron beam is investigated. The Cherenkov and cyclotron acceleration mechanisms of positrons are compared together. It is shown that growth rate and, therefore, the acceleration of positrons can be increased in the presence of quantum effects.

  5. Accelerated Decay of Radioisotopes

    DTIC Science & Technology

    2013-01-01

    00-01 -2013 Technical June20 l l-June 2012 4 . TITLE AND SUBTITLE Sa. CONTRACT NUMBER DTRA MIPR 11-2362M Accelerated Decay of Radioisotopes Sb...268 x E +2 4.788 026 x E -2 6.894 757 4.535 924 x E -1 4.214 011 x E -2 1.601 846 x E +1 1.000 000 x E -2 2.579 760 x E - 4 1.000 000 x E -8...c a y o f R a d i o i s o t o p e s " P r o p o s a l # B R C A L L 0 7 - N - 2 - 0 0 4 7 I l l u s t r a t i o n o f \\ P F R P a s p o

  6. Neutrinoless Double Beta Decay

    NASA Astrophysics Data System (ADS)

    Fiorini, Ettore

    2007-06-01

    The recent results showing the presence of neutrino oscillations clearly indicate that the difference between the squared mass of neutrinos of different flavors is different from zero, but are unable to determine the nature and the absolute value of the neutrino mass. Neutrinoless double beta decay (DBD) is at present the most powerful tool to ascertain if the neutrino is a Majorana particle and to determine under this condition the absolute value of its mass. The results already obtained in this lepton violating process will be reported and the two presently running DBD experiments briefly discussed. The future second generation experiments will be reviewed with special emphasis to those already partially approved. In conclusion the peculiar and interdisciplinary nature of these searches will be stressed in their exciting aim to discover if neutrino is Dirac or Majorana particle.

  7. Double beta decay: Calorimeters

    NASA Astrophysics Data System (ADS)

    Brofferio, Chiara

    2008-11-01

    Calorimeters or, with a more specific definition, low temperature detectors, have been used by now for more than 15 years in Double Beta Decay (DBD) searches, with excellent results: they compete with Ge diodes for the rank of detectors with the highest sensitivity to the effective neutrino mass, which is defined as a linear combination of the neutrino mass eigenvalues. After a brief introduction to the argument, with some notes on DBD and on bolometers, an update on the now closed experiment CUORICINO and on its successor, CUORE, is given. The fundamental role of background is then revealed and commented, introducing in this way the importance of the specific experiment now under construction, CUORE-0, that will precede CUORE to help optimizing the struggle against surface background. The possible future of this technique is then commented, quoting important R&D studies that are going on, for active shielding bolometers and for scintillating bolometers coupled with light detecting bolometers.

  8. Decay of oscillating universes

    NASA Astrophysics Data System (ADS)

    Mithani, Audrey Todhunter

    2016-08-01

    It has been suggested by Ellis et al that the universe could be eternal in the past, without beginning. In their model, the "emergent universe'' exists forever in the past, in an "eternal'' phase before inflation begins. We will show that in general, such an "eternal'' phase is not possible, because of an instability due to quantum tunneling. One candidate model, the "simple harmonic universe'' has been shown by Graham et al to be perturbatively stable; we find that it is unstable with respect to quantum tunneling. We also investigate the stability of a distinct oscillating model in loop quantum cosmology with respect to small perturbations and to quantum collapse. We find that the model has perturbatively stable and unstable solutions, with both types of solutions occupying significant regions of the parameter space. All solutions are unstable with respect to collapse by quantum tunneling to zero size. In addition, we investigate the effect of vacuum corrections, due to the trace anomaly and the Casimir effect, on the stability of an oscillating universe with respect to decay by tunneling to the singularity. We find that these corrections do not generally stabilize an oscillating universe. Finally, we determine the decay rate of the oscillating universe. Although the wave function of the universe lacks explicit time dependence in canonical quantum cosmology, time evolution may be present implicitly through the semiclassical superspace variables, which themselves depend on time in classical dynamics. Here, we apply this approach to the simple harmonic universe, by extending the model to include a massless, minimally coupled scalar field φ which has little effect on the dynamics but can play the role of a "clock''.

  9. SU-E-T-230: Measurement of Proton-Activated Positron Emission with PRESAGE 3-D Dosimeters

    SciTech Connect

    Carroll, M; Mawlawi, O; Ibbott, G; Adamovics, J

    2014-06-01

    Purpose: Measurement of positron emission following proton beam irradiation of a target has been studied as a method of in-vivo dosimetry. Relative dosimetry studies between a phantom and treatment plan are susceptible to range uncertainties from material heterogeneities and setup error. By using the radiochromic polyurethane dosimeter PRESAGE, we can correlate the proton dose distribution to the PET activity measurement within a single detector. The PRESAGE formulation used was developed for high-LET proton radiotherapy, has similar density and RLSP to tissue, and consists of a greater carbon component, which gives it a higher positron signal than many other 3D detectors. Methods: Three cylindrical PRESAGE dosimeters were irradiated semi-uniformly to 500 cGy with 180- MeV protons. The beam was directed along the dosimeter axis and delivered a 2-cm SOBP at the center of the dosimeter. The dosimeters were rushed to a nearby PET/CT where imaging began within 15 minutes, less than a single half-life of 11C. A 3-hr measurement captured the full activation decay. Afterwards, the dose profiles were measured by optical-CT. A direct comparison between the measured dose and the positron emission was performed using CERR software. Results: The correlations between dose distributions and PET activity were consistent with previous studies in that the proximal region of the SOBP displayed the highest activity. The spatial distributions between the dose and activity were similar. Along the central axis of the beam, we found a shift in the distal 80% of 1 cm. The lateral profile showed good agreement between dose and activity. PET imaging times between 30-min and 3-hrs showed <5% discrepancy. Conclusion: PRESAGE dosimeters offer a strong and unique potential to accurately correlate dosimetric and PET activation information. Implementation in an anthropomorphic phantom could be used to study representative treatment plans. NIH grant 5R01CA100835.

  10. SU-C-204-07: The Production of Short-Lived Positron Emitters in Proton Therapy

    SciTech Connect

    Buitenhuis, H J T; Dendooven, P; Biegun, A K; Goethem, M-J van; Graaf, E R van der; Brandenburg, S; Diblen, F

    2015-06-15

    Purpose: To investigate the production and effect of short-lived positron emitters when using PET for in-vivo range verification during a proton therapy irradiation. Methods: The integrated production of short-lived positron emitters in the stopping of 55 MeV protons was measured in water, carbon, phosphorus and calcium targets. The experimental production rates are used to calculate the production on PMMA and a representative set of 4 tissue materials. The number of decays integrated over an irradiation in these materials is calculated as function of the duration of the irradiation, considering irradiations with the same total number of protons. Results: The most copiously produced short-lived nuclides and their production rates relative to the relevant long-lived nuclides are: 12-N (T1/2 = 11 ms) on carbon (9.5% of the 11-C production), 29-P (T1/2 = 4.1 s) on phosphorus (20% of the 30-P production) and 38m-K (T1/2 = 0.92 s) on calcium (113% of the 38g-K production). No short-lived nuclides are produced on water. The most noticeable Result is that for an irradiation in (carbon-rich) adipose tissue, 12-N will dominate the PET image up to an irradiation duration of 70 s. On bone tissue, 15-O dominates over 12-N after 7–15 s (depending on the carbon-to-oxygen ratio). Conclusions: The presence of 12-N needs to be considered in PET imaging during proton beam irradiations as, depending on tissue composition and PET scanning protocol, it may noticeably deteriorate image quality due to the large positron range blurring. The results presented warrant investigations into the energy-dependent production of 12-N, 29-P and 38m-K and their effect on PET imaging during proton irradiations.

  11. Soudan 2 nucleon decay experiment

    SciTech Connect

    Thron, J.L.

    1986-01-01

    The Soudan 2 nucleon decay experiment consists of a 1.1 Kton fine grained iron tracking calorimeter. It has a very isotropic detection structure which along with its flexible trigger will allow detection of multiparticle and neutrino proton decay modes. The detector has now entered its construction stage.

  12. Theoretical understanding of charm decays

    SciTech Connect

    Bigi, I.I.

    1986-08-01

    A detailed description of charm decays has emerged. The various concepts involved are sketched. Although this description is quite successful in reproducing the data the chapter on heavy flavour decays is far from closed. Relevant questions like on th real strength of weak annihilation, Penguin operators, etc. are still unanswered. Important directions in future work, both on the experimental and theoretical side are identified.

  13. Defects in nitride-based semiconductors probed by positron annihilation

    NASA Astrophysics Data System (ADS)

    Uedono, A.; Sumiya, M.; Ishibashi, S.; Oshima, N.; Suzuki, R.

    2014-04-01

    Point defects in InxGa1-xN grown by metal organic chemical vapor deposition were studied by a monoenergetic positron beam. Measurements of Doppler broadening spectra of the annihilation radiation as a function of incident positron energy for InxGa1-xN (x = 0.08 and 0.14) showed that vacancy-type defects were introduced with increasing InN composition. From comparisons between coincidence Doppler broadening spectra and the results calculated using the projector augmented-wave method, the major defect species was identified as the complexes between a cation vacancy and nitride vacancies. The concentration of the defects was found to be suppressed by Mg doping. An effect of Mg-doping on the positron diffusion properties in GaN and InN was also discussed. The momentum distribution of electrons at the InxGa1-xN/GaN interface was close to that in defect-free GaN or InxGa1-xN, which was attributed to the localization of positrons at the interface due to the electric field caused by polarizations.

  14. Advances in defect characterizations of semiconductors using positrons

    SciTech Connect

    Lynn, K.G.; Asoka-Kumar, P.

    1996-12-31

    Positron Annihilation Spectroscopy (PAS) is a sensitive probe for studying the electronic structure of defects in solids. The authors summarize recent developments in defect characterization of semiconductors using depth-resolved PAS. The progress achieved in extending the capabilities of the PAS method is also described.

  15. On positron annihilation in concentrated random alloys and superconducting cuprates

    SciTech Connect

    Szotek, Z.; Temmerman, W.M.; Gyorffy, B.L.; Stocks, G.M.

    1988-01-01

    We discuss an application of a generalisation of the Lock-Crisp-West theorem to concentrated random alloys. Using a theory developed for binary random alloys we explore a possibility of positron localisation in the new high temperature superconductors. 7 refs., 1 fig.

  16. An outline of positron measurements of superconducting oxides

    SciTech Connect

    Howell, R.H.; Fluss, M.J.

    1991-03-01

    Positron measurements on superconducting oxides have gone through an evolution from divergent results of low statistical precision on samples of suspect quality to convergent results of higher statistical precision on high quality samples. We outline the elements affecting the progress of these experiments and questions that can be addressed at our present state of the art. 11 refs.

  17. Industrial positron-based imaging: Principles and applications

    NASA Astrophysics Data System (ADS)

    Parker, D. J.; Hawkesworth, M. R.; Broadbent, C. J.; Fowles, P.; Fryer, T. D.; McNeil, P. A.

    1994-09-01

    Positron Emission Tomography (PET) has great potential as a non-invasive flow imaging technique in engineering, since 511 keV gamma-rays can penetrate a considerable thickness of (e.g.) steel. The RAL/Birmingham multiwire positron camera was constructed in 1984, with the initial goal of observing the lubricant distribution in operating aero-engines, automotive engines and gearboxes, and has since been used in a variety of industrial fields. The major limitation of the camera for conventional tomographic PET studies is its restricted logging rate, which limits the frequency with which images can be acquired. Tracking a single small positron-emitting tracer particle provides a more powerful means of observing high speed motion using such a camera. Following a brief review of the use of conventional PET in engineering, and the capabilities of the Birmingham camera, this paper describes recent developments in the Positron Emission Particle Tracking (PEPT) technique, and compares the results obtainable by PET and PEPT using, as an example, a study of axial diffusion of particles in a rolling cylinder.

  18. Investigational study of iodine-124 with a positron camera

    SciTech Connect

    Lambrecht, R.M.; Woodhouse, N.; Phillips, R.; Wolczak, D.; Qureshi, A.; Reyes, E.D.; Graser, C.; Al-Yanbawi, S.; Al-Rabiah, A.; Meyer, W.

    1988-01-01

    A case is presented where I-124 produced by a clinical cyclotron was used with a positron emission tomography camera for clinical usage. This represents the first report of the utilization of this modality with this radionuclide. We feel the increased spatial resolution of PET should be of value in looking at thyroid disease.

  19. Simulation of tail distributions in electron-positron circular colliders

    SciTech Connect

    Irwin, J.

    1992-02-01

    In addition to the Gaussian shaped core region, particle bunches in electron-positron circular colliders have a rarefied halo region of importance in determining beam lifetimes and backgrounds in particle detectors. A method is described which allows simulation of halo particle distributions.

  20. Theoretical Formalism To Estimate the Positron Scattering Cross Section.

    PubMed

    Singh, Suvam; Dutta, Sangita; Naghma, Rahla; Antony, Bobby

    2016-07-21

    A theoretical formalism is introduced in this article to calculate the total cross sections for positron scattering. This method incorporates positron-target interaction in the spherical complex optical potential formalism. The study of positron collision has been quite subtle until now. However, recently, it has emerged as an interesting area due to its role in atomic and molecular structure physics, astrophysics, and medicine. With the present method, the total cross sections for simple atoms C, N, and O and their diatomic molecules C2, N2, and O2 are obtained and compared with existing data. The total cross section obtained in the present work gives a more consistent shape and magnitude than existing theories. The characteristic dip below 10 eV is identified due to the positronium formation. The deviation of the present cross section with measurements at energies below 10 eV is attributed to the neglect of forward angle-discrimination effects in experiments, the inefficiency of additivity rule for molecules, empirical treatment of positronium formation, and the neglect of annihilation reactions. In spite of these deficiencies, the present results show consistent behavior and reasonable agreement with previous data, wherever available. Besides, this is the first computational model to report positron scattering cross sections over the energy range from 1 to 5000 eV.

  1. Positron lifetime studies in vinyl polymers of medical importance

    NASA Astrophysics Data System (ADS)

    Ferreira Marques, M. F.; Gordo, P. M.; Gil, C. Lopes; Kajcsos, Zs.; Gil, M. H.; Mariz, M. J.; de Lima, A. P.

    2003-10-01

    Vinyl polymers used as artificial lens implants in ophthalmology were investigated by positron lifetime spectroscopy. The structure of these polymers with free volumes offers the possibility of charging them with anti-inflammatory drugs for sustained release. A correlation between the amount of normalised free volume and the ratio of the methyl methacrylate to ethyl-hexyl-acrylate, used as polymerisation monomers, was found.

  2. Initial results on positron confinement in a magnetospheric configuration

    NASA Astrophysics Data System (ADS)

    Saitoh, Haruhiko; Yoshida, Zensho; Yano, Yoshihisa; Morikawa, Junji

    2011-10-01

    Creation of positron-electron plasma in a laboratory is an interesting and challenging subject, which may open many scientific applications. Although single-component plasma is stably confined in linear traps, for example Penning-Malmberg trap, it is not straightforward to simultaneously confine electrons and positrons as plasma. Toroidal geometries have advantages for solving this problem. For this purpose, studies on toroidal non-neutral plasma have been conducted in the levitated magnetospheric configuration, RT-1. Stable confinement and self-organization of toroidal non-neutral plasma was realized in RT-1; rigid-rotating pure electron plasma is confined for more than 300s [Z. Yoshida et al., PRL 104, 235004 (2010)]. As the initial step toward the formation of magnetospheric antimatter plasmas, we installed a 1MBq Na-22 radiation source in RT-1. Annihilation gamma-rays were observed by a NaI(TI) scintillator detector, for the estimation of basic injection and confinement properties of positrons in the magnetospheric configuration. Numerical analysis of positron orbits in RT-1 and the initial experimental results will be presented. Work funded by MEXT of Japan (23224014, 23654201).

  3. A novel design for a variable energy positron lifetime spectrometer

    NASA Astrophysics Data System (ADS)

    Chen, D.; Zhang, J. D.; Cheng, C. C.; Beling, C. D.; Fung, S.

    2008-10-01

    We present computer simulations of a new design of a variable energy positron lifetime beam that uses for a start signal the secondary electron emission from a 25-nm thick carbon foil (C-foil) located in front of the sample. A needle of ˜30 μm diameter is positioned on-axis right behind the foil, creating a radial electric field that deflects the secondary electrons radially outward so as to miss the sample and to hit the micro-channel plate (MCP) detector placed down beam. The MCP signal provides the start signal for the positron lifetime spectrometer. A grid can be further introduced between the sample holder and the MCP to yield a cleaner signal by preventing the positrons with large transmitted scattering angle from hitting the MCP. The cylindrical symmetry of this design reduces the experimental complexity and offers good timing resolution. We show that the design is robust against the transmitted energy and angle of the secondary electrons and positrons.

  4. Design of a pulsed positron system at Trombay

    NASA Astrophysics Data System (ADS)

    Mukherjee, S.; Sharma, S. K.; Maheshwari, Priya; Gupta, S. K.; Pujari, P. K.

    2015-06-01

    We present here the design of a pulsed beam setup to deliver narrow time width positron pulses. The major constituents of the setup include- 22Na radioactive source and moderator assembly, ExB deflector for filtering out high energy positron and gamma rays, chopper-prebuncher-buncher assembly for time bunching of the slow positrons. In the ExB section, crossed electric and magnetic fields guide the slow positrons through an off-centered hole in a tungsten block. The initial beam will then be time bunched by using a reflection type chopper and a double gap prebuncher. The main buncheris designed as a quarter wave resonator with base frequency of 150 MHz.To prevent the sagging of the cantilevered inner tube of the resonator, we will support the inner conductor using an alumina post. There will be provision of tuning the frequency by using a tuner made of conducting material. The incident beam energy will be varied by biasing the sample.

  5. Positron Emission Tomography: Human Brain Function and Biochemistry.

    ERIC Educational Resources Information Center

    Phelps, Michael E.; Mazziotta, John C.

    1985-01-01

    Describes the method, present status, and application of positron emission tomography (PET), an analytical imaging technique for "in vivo" measurements of the anatomical distribution and rates of specific biochemical reactions. Measurements and image dynamic biochemistry link basic and clinical neurosciences with clinical findings…

  6. 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.

  7. Positron annihilation spectroscopy study of materials for reactor vessels

    NASA Astrophysics Data System (ADS)

    Grafutin, V. I.; Prokop'ev, E. P.; Krsjak, V.; Burcl, R.; Hähner, P.; Zeman, A.; Ilyukhina, O. V.; Erak, D.; Mogilevskyi, M. A.; Myasischeva, G. G.; Funtikov, Yu. V.

    2011-02-01

    Steels used in the nuclear industry have been experimentally studied by positron annihilation spectroscopy. Analysis of the experimental results and their comparison with the existing data make it possible to reveal vacancy defects, in particular, those caused by neutron radiation, and to determine their size.

  8. Studies of Positron Generation from Ultraintense Laser-Matter Interactions

    NASA Astrophysics Data System (ADS)

    Williams, Gerald Jackson

    Laser-produced pair jets possess unique characteristics that offer great potential for their use in laboratory-astrophysics experiments to study energetic phenomenon such as relativistic shock accelerations. High-flux, high-energy positron sources may also be used to study relativistic pair plasmas and useful as novel diagnostic tools for high energy density conditions. Copious amounts of positrons are produced with MeV energies from directly irradiating targets with ultraintense lasers where relativistic electrons, accelerated by the laser field, drive positron-electron pair production. Alternatively, laser wakefield accelerated electrons can produce pairs by the same mechanisms inside a secondary converter target. This dissertation describes a series of novel experiments that investigate the characteristics and scaling of pair production from ultraintense lasers, which are designed to establish a robust platform for laboratory-based relativistic pair plasmas. Results include a simple power-law scaling to estimate the effective positron yield for elemental targets for any Maxwellian electron source, typical of direct laser-target interactions. To facilitate these measurements, a solenoid electromagnetic coil was constructed to focus emitted particles, increasing the effective collection angle of the detector and enabling the investigation of pair production from thin targets and low-Z materials. Laser wakefield electron sources were also explored as a compact, high repetition rate platform for the production of high energy pairs with potential applications to the creation of charge-neutral relativistic pair plasmas. Plasma accelerators can produce low-divergence electron beams with energies approaching a GeV at Hz frequencies. It was found that, even for high-energy positrons, energy loss and scattering mechanisms in the target create a fundamental limit to the divergence and energy spectrum of the emitted positrons. The potential future application of laser

  9. Top decays in extended models

    SciTech Connect

    Gaitan, R.; Miranda, O. G.; Cabral-Rosetti, L. G.

    2009-04-20

    Top quark decays are interesting as a mean to test the Standard Model (SM) predictions. The Cabbibo-Kobayashi-Maskawa (CKM)-suppressed process t{yields}cWW, and the rare decays t{yields}cZ, t{yields}H{sup 0}+c, and t{yields}c{gamma} an excellent window to probe the predictions of theories beyond the SM. We evaluate the flavor changing neutral currents (FCNC) decay t{yields}H{sup 0}+c in the context of Alternative Left-Right symmetric Models (ALRM) with extra isosinglet heavy fermions; the FCNC decays may place at tree level and are only supressed by the mixing between ordinary top and charm quarks. We also comment on the decay process t{yields}c+{gamma}, which involves radiative corrections.

  10. The fast method of Cu-porphyrin complex synthesis for potential use in positron emission tomography imaging

    NASA Astrophysics Data System (ADS)

    Kilian, Krzysztof; Pęgier, Maria; Pyrzyńska, Krystyna

    2016-04-01

    Porphyrin based photosensitizers are useful agents for photodynamic therapy and fluorescence imaging of cancer. Additionally, porphyrins are excellent metal chelators, forming stable metalo-complexes and 64Cu isotope can serve as a positron emitter (t1/2 = 12.7 h). The other advantage of 64Cu is its decay characteristics that facilitates the use of 64Cu-porphyrin complex as a therapeutic agent. Thus, 64Cu chelation with porphyrin photosensitizer may become a simple and versatile labeling strategy for clinical positron emission tomography. The present study reports a convenient method for the synthesis of Cu complex with tetrakis(4-carboxyphenyl)porphyrin (TCPP). The experimental conditions for labeling, such as the metal-to-ligand molar ratio, pH and time of reaction were optimized to achieve a high complexation efficiency in a short period of time as possible. In order to accelerate the metallation, the use of substitution reactions of cadmium or lead porphyrin and the presence of reducing agent, such as ascorbic acid, hydroxylamine and flavonoid - morin, were evaluated. The optimum conditions for the synthesis of the copper complex were borate buffer at pH 9 with the addition of 10-fold molar excess, with respect to Cu2 + ions and TCPP and ascorbic acid which resulted in reduction of the reaction time from 30 min to below 1 min.

  11. Use of 18F-2-Fluorodeoxyglucose to Label Antibody Fragments for Immuno-Positron Emission Tomography of Pancreatic Cancer

    PubMed Central

    2015-01-01

    We generated 18F-labeled antibody fragments for positron emission tomography (PET) imaging using a sortase-mediated reaction to install a trans-cyclooctene-functionalized short peptide onto proteins of interest, followed by reaction with a tetrazine-labeled-18F-2-deoxyfluoroglucose (FDG). The method is rapid, robust, and site-specific (radiochemical yields > 25%, not decay corrected). The availability of 18F-2-deoxyfluoroglucose avoids the need for more complicated chemistries used to generate carbon–fluorine bonds. We demonstrate the utility of the method by detecting heterotopic pancreatic tumors in mice by PET, using anti-Class II MHC single domain antibodies. We correlate macroscopic PET images with microscopic two-photon visualization of the tumor. Our approach provides easy access to 18F-labeled antibodies and their fragments at a level of molecular specificity that complements conventional 18F-FDG imaging. PMID:26955657

  12. Construction of a surface positronium lifetime spectroscopy apparatus with a spin-polarized low energy positron beam

    NASA Astrophysics Data System (ADS)

    Maekawa, M.; Wada, K.; Miyashita, A.; Kawasuso, A.

    2017-01-01

    We have developed a surface positronium (Ps) lifetime spectrometer. A spin-polarized slow positron beam is generated by a sodium-22 source and a solid krypton moderator and transported to the sample chamber by electrostatic lenses. The incident energy is adjusted by a retarding potential using a deceleration tube. For the lifetime measurement, the start signal is obtained from a secondary-electron detector installed in front of the sample. The stop signal is detected by a scintillation detector for annihilation gamma rays. As a performance test, Ps lifetime measurements were carried out and clear decay curves derived from ortho-Ps self-annihilation were successfully observed. This system might be used for the estimation of the spin polarization at the surface of ferromagnetic materials.

  13. Charm and bottom semileptonic decays

    NASA Astrophysics Data System (ADS)

    O'donnell, Patrick J.; Turan, Gürsevil

    1997-07-01

    We review the present status of theoretical attempts to calculate the semileptonic charm and bottom decays and then present a calculation of these decays in the light-front frame at the kinematic point q2=0. This allows us to evaluate the form factors at the same value of q2, even though the allowed kinematic ranges for charm and bottom decays are very different. Also, at this kinematic point the decay is given in terms of only one form factor A0(0). For the ratio of the decay rates given by the E653 collaboration we show that the determination of the ratio of the Cabibbo-Kobayashi-Maskawa matrix elements is consistent with that obtained from the unitarity constraint, though a new measurement by the E687 Collaboration is about two standard deviations too high. At present, though, the unitarity method still has greater accuracy. Since comparisons of the semileptonic decays into ρ and either electrons or muons will be available soon from the E791 Fermilab experiment, we also look at the massive muon case. We show that for a range of q2 the SU(3)F symmetry breaking is small even though the contributions of the various helicity amplitudes becomes more complicated. For B decays, the decay B-->K*ll¯ at q2=0 involves an extra form factor coming from the photon contribution and so is not amenable to the same kind of analysis, leaving only the decay B-->K*νν¯ as a possibility. As the mass of the decaying particle increases we note that the SU(3) symmetry becomes badly broken at q2=0.

  14. Monte Carlo modeling and optimization of buffer gas positron traps

    NASA Astrophysics Data System (ADS)

    Marjanović, Srđan; Petrović, Zoran Lj

    2017-02-01

    Buffer gas positron traps have been used for over two decades as the prime source of slow positrons enabling a wide range of experiments. While their performance has been well understood through empirical studies, no theoretical attempt has been made to quantitatively describe their operation. In this paper we apply standard models as developed for physics of low temperature collision dominated plasmas, or physics of swarms to model basic performance and principles of operation of gas filled positron traps. The Monte Carlo model is equipped with the best available set of cross sections that were mostly derived experimentally by using the same type of traps that are being studied. Our model represents in realistic geometry and fields the development of the positron ensemble from the initial beam provided by the solid neon moderator through voltage drops between the stages of the trap and through different pressures of the buffer gas. The first two stages employ excitation of N2 with acceleration of the order of 10 eV so that the trap operates under conditions when excitation of the nitrogen reduces the energy of the initial beam to trap the positrons without giving them a chance to become annihilated following positronium formation. The energy distribution function develops from the assumed distribution leaving the moderator, it is accelerated by the voltage drops and forms beams at several distinct energies. In final stages the low energy loss collisions (vibrational excitation of CF4 and rotational excitation of N2) control the approach of the distribution function to a Maxwellian at room temperature but multiple non-Maxwellian groups persist throughout most of the thermalization. Optimization of the efficiency of the trap may be achieved by changing the pressure and voltage drops and also by selecting to operate in a two stage mode. The model allows quantitative comparisons and test of optimization as well as development of other properties.

  15. Optimisation of the thickness of the moderator for positron annihilation process study in Ar gas

    NASA Astrophysics Data System (ADS)

    Oka, Toshitaka; Sano, Yosuke; Kino, Yasushi; Sekine, Tsutomu

    2014-06-01

    To investigate the deceleration and annihilation processes of positron in noble gas, we attempted to optimise the thickness of the positron moderator. The results of the decreasing trend of free positron intensity and ortho-positronium intensity with the thickness, and the annihilation rate suggest that the energy of almost all the positrons passed through the metal foils was much above the positronium formation threshold of 9 eV. Total thickness of 0.1 g cm-2 of the moderator and the Ar gas was required to stop almost all the positron in Ar gas.

  16. Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies

    SciTech Connect

    Abbott, D.; Adderley, P.; Adeyemi, A.; Aguilera, P.; Ali, M.; Areti, H.; Baylac, M.; Benesch, J.; Bosson, G.; Cade, B.; Camsonne, A.; Cardman, L. S.; Clark, J.; Cole, P.; Covert, S.; Cuevas, C.; Dadoun, O.; Dale, D.; Dong, H.; Dumas, J.; Fanchini, E.; Forest, T.; Forman, E.; Freyberger, A.; Froidefond, E.; Golge, S.; Grames, J.; Guèye, P.; Hansknecht, J.; Harrell, P.; Hoskins, J.; Hyde, C.; Josey, B.; Kazimi, R.; Kim, Y.; Machie, D.; Mahoney, K.; Mammei, R.; Marton, M.; McCarter, J.; McCaughan, M.; McHugh, M.; McNulty, D.; Mesick, K. E.; Michaelides, T.; Michaels, R.; Moffit, B.; Moser, D.; Muñoz Camacho, C.; Muraz, J. -F.; Opper, A.; Poelker, M.; Réal, J. -S.; Richardson, L.; Setiniyaz, S.; Stutzman, M.; Suleiman, R.; Tennant, C.; Tsai, C.; Turner, D.; Ungaro, M.; Variola, A.; Voutier, E.; Wang, Y.; Zhang, Y.

    2016-05-27

    The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19~MeV/c, limited only by the electron beam polarization. We report that this technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.

  17. The “accumulation effect” of positrons in the stack of foils, detected by measurements of the positron implantation profile

    SciTech Connect

    Dryzek, Jerzy; Siemek, Krzysztof

    2013-12-14

    The profiles of positrons implanted from the radioactive source {sup 22}Na into a stack of foils and plates are the subject of our experimental and theoretical studies. The measurements were performed using the depth scanning of positron implantation profile method, and the theoretical calculations using the phenomenological multi-scattering model (MSM). Several stacks consisting of silver, gold and aluminum foils, and titanium and germanium plates were investigated. We notice that the MSM describes well the experimental profiles; however when the stack consisting of silver and gold foils, the backscattering and linear absorption coefficients differ significantly from those reported in the literature. We suggest the energy dependency of the backscattering coefficient for silver and gold. In the stacks which comprise titanium and germanium plates, there were observed the features, which indicate the presence of the “accumulation effect” in the experimental implantation profile. This effect was previously detected in implantation profiles in Monte Carlo simulations using the GEANT4 tool kit, and it consists in higher localization of positrons close the interface. We suppose that this effect can be essential for positron annihilation in any heterogeneous materials.

  18. In vitro positron emission tomography (PET): use of positron emission tracers in functional imaging in living brain slices.

    PubMed

    Matsumura, K; Bergström, M; Onoe, H; Takechi, H; Westerberg, G; Antoni, G; Bjurling, P; Jacobson, G B; Långström, B; Watanabe, Y

    1995-05-01

    Positron-emitting radionuclides have short half-lives and high radiation energies compared with radioisotopes generally used in biomedical research. We examined the possibility of applying positron emitter-labeled compounds to functional imaging in brain slices kept viable in an oxygenated buffer solution. Brain slices (300 microns thick) containing the striatum were incubated with positron emitter-labeled tracers for 30-45 min. The slices were then rinsed and placed on the bottom of a Plexiglas chamber filled with oxygenated Krebs-Ringer solution. The bottom of the chamber consisted of a thin polypropylene film to allow good penetration of beta+ particles from the brain slices. The chamber was placed on a storage phosphor screen, which has a higher sensitivity and a wider dynamic range than X-ray films. After an exposure period of 15-60 min, the screen was scanned by the analyzer and radioactivity images of brain slices were obtained within 20 min. We succeeded in obtaining quantitative images of (1) [18F]fluorodeoxyglucose uptake, (2) dopamine D2 receptor binding, (3) dopa-decarboxylase activity, and (4) release of [11C]dopamine preloaded as L-[11C]DOPA in the brain slice preparation. These results demonstrate that positron emitter-labeled tracers in combination with storage phosphor screens are useful for functional imaging of living brain slices as a novel neuroscience technique.

  19. Quantitative imaging of disease signatures through radioactive decay signal conversion.

    PubMed

    Thorek, Daniel L J; Ogirala, Anuja; Beattie, Bradley J; Grimm, Jan

    2013-10-01

    In the era of personalized medicine, there is an urgent need for in vivo techniques able to sensitively detect and quantify molecular activities. Sensitive imaging of gamma rays is widely used; however, radioactive decay is a physical constant, and its signal is independent of biological interactions. Here, we introduce a framework of previously uncharacterized targeted and activatable probes that are excited by a nuclear decay-derived signal to identify and measure molecular signatures of disease. We accomplished this by using Cerenkov luminescence, the light produced by β-particle-emitting radionuclides such as clinical positron emission tomography (PET) tracers. Disease markers were detected using nanoparticles to produce secondary Cerenkov-induced fluorescence. This approach reduces background signal compared to conventional fluorescence imaging. In addition to tumor identification from a conventional PET scan, we demonstrate the medical utility of our approach by quantitatively determining prognostically relevant enzymatic activity. This technique can be applied to monitor other markers and represents a shift toward activatable nuclear medicine agents.

  20. Decays of 117Xe--> 117I--> 117 Te

    NASA Astrophysics Data System (ADS)

    Lee, R. S.; Hamilton, J. H.; Ramayya, A. V.; de Lima, A. P.; Sastry, D. L.; Sastry, K. S. R.; Spejewski, E. H.; Mlekodaj, R. L.; Carter, H. K.; Schmidt-Ott, W.-D.; Lin, J.; Bingham, C. R.; Riedinger, L. L.; Zganjar, E. F.

    1985-07-01

    Mass separated 117-->117I-->117Te decays were studied on-line by bombarding 104Pd with 86 MeV 16O ions and off-line by bombarding 107,109Ag with 50-70 MeV 12C. From gamma ray and x ray singles, half-life, excitation function, and coincidence measurements, 26 gamma rays are assigned to the deccay of 117Xe and 31 gamma rays are assigned to the 117I decay. The half-lives were measured to be 61+/-2 sec, 2.22+/-0.04 min, 62+/-2 min, and 2.8×0.2 h for 117Xe, 117I, 117Te,, and 117Sb, respectively. Eight new levels are deduced in 117I and seven new levels in 117Te. From the Kurie plot of the positron spectrum, the QEC(117Xe-->117I) was determined to be >=6.27+/-0.30 MeV.

  1. The beta decay asymmetry parameter of /sup 35/Ar

    SciTech Connect

    Garnett, J.D.

    1987-11-01

    The beta decay asymmetry parameter for /sup 35/Ar = /sup 35/Cl + e/sup +/ + nu/sub e/ has been remeasured in order to resolve a long standing puzzle. Previous asymmetry measurements, when combined with the comparative half-life, yield a value for the vector coupling constant, G/sub v/, that is in serious disagreement with the accepted value. We produced polarized /sup 35/Ar by a (p,n) reaction on /sup 35/Cl using the polarized proton beam provided by Lawrence Berkeley Laboratory's 88-Inch Cyclotron. The polarization of the /sup 35/Ar was determined by measuring the asymmetry of the positrons produced in /sup 35/Ar decay to the first excited state in /sup 35/Cl (branching ratio = 1.3%) in coincidence with a 1219.4 keV gamma ray. Our result, A/sub 0/ = 0.49 +- 0.10, combined with the comparative half-life yields a value for G/sub v/ in agreement with the accepted value.

  2. Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS.

    PubMed

    Adamová, D; Agakichiev, G; Appelshäuser, H; Belaga, V; Braun-Munzinger, P; Cherlin, A; Damjanović, S; Dietel, T; Dietrich, L; Drees, A; Esumi, S I; Filimonov, K; Fomenko, K; Fraenkel, Z; Garabatos, C; Glässel, P; Hering, G; Holeczek, J; Kushpil, V; Lenkeit, B; Maas, A; Marín, A; Milosević, J; Milov, A; Miśkowiec, D; Panebrattsev, Yu; Petchenova, O; Petrácek, V; Pfeiffer, A; Rak, J; Ravinovich, I; Rehak, P; Richter, M; Sako, H; Schmitz, W; Sedykh, S; Seipp, W; Sharma, A; Shimansky, S; Slívová, J; Specht, H J; Stachel, J; Sumbera, M; Tilsner, H; Tserruya, I; Wessels, J P; Wienold, T; Windelband, B; Wurm, J P; Xie, W; Yurevich, S; Yurevich, V

    2003-07-25

    We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2decays by a factor of 5.9+/-1.5(stat)+/-1.2(syst data)+/-1.8(syst meson decays), somewhat larger than previously observed at the higher energy of 158 AGeV. The results are discussed with reference to model calculations based on pi(+)pi(-)-->e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.

  3. Semileptonic and leptonic B decays, circa 2016

    NASA Astrophysics Data System (ADS)

    Ricciardi, Giulia

    2017-02-01

    We summarize the status of semileptonic and leptonic B decays, including |Vcb| and |Vub| exclusive and inclusive determinations, decays to excited states of the charm meson spectrum and decays into τ leptons.

  4. Primordial nucleosynthesis with decaying particles. I - Entropy-producing decays. II - Inert decays

    NASA Technical Reports Server (NTRS)

    Scherrer, Robert J.; Turner, Michael S.

    1988-01-01

    The effect of a nonrelativistic particle X, which decays out of equilibrium, on primordial nucleosynthesis is investigated, including both the energy density of the X particle and the electromagnetic entropy production from its decay. The results are parametrized in terms of the X particle lifetime and the density parameter rm(X), where m(X) is the X particle mass and r is the ratio of X number density to photon number density prior to nucleosynthesis. The results rule out particle lifetimes greater than 1-10 s for large values of rm(X). The question of a decaying particle which produces no electromagnetic entropy in the course of its decay is addressed, and particles which produce both entropy and an inert component in their decay are discussed.

  5. Positron beam lifetime spectroscopy of atomic scale defect distributions in bulk and microscopic volumes

    SciTech Connect

    Howell, R.H.; Cowan, T.E.; Hartley, J.; Sterne, P.; Brown, B.

    1996-05-01

    We are developing a defect analysis capability based on two positron beam lifetime spectrometers: the first is based on a 3 MeV electrostatic accelerator and the second on our high current linac beam. The high energy beam lifetime spectrometer is operational and positron lifetime analysis is performed with a 3 MeV positron beam on thick samples. It is being used for bulk sample analysis and analysis of samples encapsulated in controlled environments for {ital in}{ital situ} measurements. A second, low energy, microscopically focused, pulsed positron beam for defect analysis by positron lifetime spectroscopies is under development at the LLNL high current positron source. This beam will enable defect specific, 3-D maps of defect concentration with sub-micron location resolution and when coupled with first principles calculations of defect specific positron lifetimes it will enable new levels of defect concentration mapping and defect identification.

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

    NASA Astrophysics Data System (ADS)

    Hu, Yi-Fan; Beling, D. C.

    2005-11-01

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

  7. Double Beta Decay

    NASA Astrophysics Data System (ADS)

    Fiorini, Ettore

    2010-12-01

    Almost exactly seventy years ago and only one year before his tragic disappearance the ingenious idea of Ettore Majorana is becoming one of the most important step in the development of fundamental physics. The problem of the nature of the neutrino, namely if it is a massless Dirac particle different from its antineutrino or a Majorana particle with finite mass, is discussed. In fact the recent results showing the presence of neutrino oscillations clearly indicates that the difference between the squared mass of neutrinos of different flavours is finite. Neutrinoless double beta decay (DBD) is at present the most powerful tool to determine the effective value of the mass of a Majorana neutrino. The results already obtained in this lepton violating process will be reported and the two presently running DBD experiments briefly discussed. The future second generation experiments will be reviewed with special emphasis to those already at least partially approved. In conclusion the peculiar and interdisciplinary nature of these searches will be stressed in their exciting aim to discover if neutrino is indeed a Majorana particle.

  8. Decay of Solar Active Regions

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.; Choudhary, Debi Prasad

    2005-01-01

    We examine the record of sunspot group areas observed over a period of 100 years to determine the rate of decay of solar active regions. We exclude observations of groups when they are more than 60deg in longitude from the central meridian and only include data when at least three days of observations are available following the date of maximum area for a spot group's disk passage. This leaves data for some 24,000 observations of active region decay. We find that the decay rate is a constant 20 microHem/day for spots smaller than about 200 microHem (about the size of a supergranule). This decay rate increases linearly to about 90 microHem/day for spots with areas of 1000 microHem. We find no evidence for significant variations in active region decay from one solar cycle to another. However, we do find that the decay rate is slower at lower latitudes. This gives a slower decay rate during the declining phase of sunspot cycles.

  9. Nonleptonic Bc→VV decays

    NASA Astrophysics Data System (ADS)

    Kar, Susmita; Dash, P. C.; Priyadarsini, M.; Naimuddin, Sk.; Barik, N.

    2013-11-01

    We study the exclusive nonleptonic Bc→VV decays, within the factorization approximation, in the framework of the relativistic independent quark model, based on a confining potential in the scalar-vector harmonic form. The weak form factors are extracted from the overlap integral of meson wave functions derived in the relativistic independent quark model. The predicted branching ratios for different Bc-meson decays are obtained in a wide range, from a tiny value of O(10-6) for Bc→D*D(s)* to a large value of 24.32% for Bc→Bs*ρ-, in general agreement with other dynamical-quark-model predictions. The decay modes Bc→Bs*ρ- and Bc→B*ρ- with high branching ratios of 24.32% and 1.73%, respectively, obtained in this model should be detectable at the LHC and Tevatron in the near future. The b→c, u induced decays are predicted predominantly in the longitudinal mode, whereas the c¯→s¯, d¯ induced decays are obtained in a slightly higher transverse mode. The CP-odd fractions (R⊥) for different decay modes are predicted and those for color-favored Bc→D*D*, D*Ds* decays indicate significant CP violation in this sector.

  10. Positron States at Li- and O-adsorbed Fe(001) Ferromagnetic Surfaces Studied by Two-Component Density Functional Theory

    NASA Astrophysics Data System (ADS)

    Hagiwara, Satoshi; Watanabe, Kazuyuki

    2016-11-01

    The positron states for Li- and O-adsorbed Fe(001) ferromagnetic surfaces are studied by using two-component density functional theory. Positron surface lifetimes and positron binding energies are found to be sensitive to changes in the surface structure and the dipole barrier induced by adatoms, which can be understood by the positron density distribution and surface potential. Spin-dependent positron lifetime fractions are in excellent agreement with spin-polarization fractions at the topmost surface, because the localized positrons at the surface are sensitive to the surface magnetic state. Therefore, the present results show that spin-polarized positron annihilation spectroscopy can extract the outermost surface magnetic state.

  11. Decays of the b quark

    NASA Astrophysics Data System (ADS)

    Thorndike, Edward H.; Poling, Ronald A.

    1988-01-01

    Recent experimental results on the decay of b-flavored hadrons are reviewed. Substantial progress has been made in the study of exclusive and inclusive B-meson decays, as well as in the theoretical understanding of these processes. The two most prominent developments are the continuing failure to observe evidence of decays of the b quark to a u quark rather than a c quark, and the surprisingly high level of B 0- overlineB0 mi xing which has recently been reported by the ARGUS collaboration. Notwithstanding these results, we conclude that the health of the Standard Model is excellent.

  12. Tensor interactions and τ decays

    NASA Astrophysics Data System (ADS)

    Godina Nava, J. J.; López Castro, G.

    1995-09-01

    We study the effects of charged tensor weak currents on the strangeness-changing decays of the τ lepton. First, we use the available information on the K+e3 form factors to obtain B(τ--->K-π0ντ)~10-4 when the Kπ system is produced in an antisymmetric tensor configuration. Then we propose a mechanism for the direct production of the K*2(1430) in τ decays. Using the current upper limit on this decay we set a bound on the symmetric tensor interactions.

  13. Glueball decay in holographic QCD

    SciTech Connect

    Hashimoto, Koji; Tan, C.-I; Terashima, Seiji

    2008-04-15

    Using holographic QCD based on D4-branes and D8-anti-D8-branes, we have computed couplings of glueballs to light mesons. We describe glueball decay by explicitly calculating its decay widths and branching ratios. Interestingly, while glueballs remain less well understood both theoretically and experimentally, our results are found to be consistent with the experimental data for the scalar glueball candidate f{sub 0}(1500). More generally, holographic QCD predicts that decay of any glueball to 4{pi}{sup 0} is suppressed, and that mixing of the lightest glueball with qq mesons is small.

  14. Justifying the Vacuum as an Electron-Positron Aggregation and Experimental Falsification

    NASA Astrophysics Data System (ADS)

    Guy Grantham, R.; Montgomery, Ian G.

    2013-09-01

    Historical aether models are placed in context with the electron-positron lattice (epola) model of space due to M. Simhony. A brief outline of the model as an aggregation state of matter, intermediate to the nuclear state and the atomic aggregation state, includes reference to its derivation of physical laws and fundamental constants. The broad application of the epola model is appraised for its validation against a range of physical laws, experiments and constants. Simhony declared a specific dependence for the stability of atomic matter upon speed through the epola, suggesting a test for falsification. This theme is further developed by the same logic to suggest practical experimental and theoretical tests of the epola model. A formula for the inverse fine structure constant of space, providing the accepted CODATA value, is derived from Simhony's explanation of the Bohr - de Broglie model of the ground state electron orbital of the hydrogen atom by including a term for speed through the Cosmos. A theoretical solution of the Michelson-Morley experiment is applied as evidence for the concept. The mechanism of motion through the epola is considered further for possible implications of speed including dependency of decay rates by radio nuclides and the results of former and ongoing experiments are considered.

  15. Optimization of a Scintillator for the Measurement of Positrons from Trapped, Polarized 37K

    NASA Astrophysics Data System (ADS)

    France, Erin; Melconian, Dan

    2011-10-01

    Precision beta decay experiments can be used to test the Standard Model via their value of correlation parameters. The TRINAT Collaboration is performing such an experiment using a source of polarized 37K from a magneto optical trap. The momentum of an emitted positron will be detected using a Silicon strip detector backed by a plastic scintillator. The goal of my research was to optimize the readout of the scintillator by testing different experimental setups. The front face and sides of the scintillator and light guide were wrapped with various reflective materials to find which maximized the light output. We found that one layer of Teflon tape on the front face with a loose wrapping of 3M-ESR (Enhanced Spectral Reflector) on the sides was optimal. We then tested the position dependence of this detector by moving a collimated source of betas across the front face, showing only a (5.9 +/- 0.5)% reduction in light collection at the edge compared to the center. The product of this work will be used in the upcoming TRINAT experiment measuring the beta asymmetry of 37K.

  16. High-energy gamma-ray emission from pion decay in a solar flare magnetic loop

    NASA Technical Reports Server (NTRS)

    Mandzhavidze, Natalie; Ramaty, Reuven

    1992-01-01

    The production of high-energy gamma rays resulting from pion decay in a solar flare magnetic loop is investigated. Magnetic mirroring, MHD pitch-angle scattering, and all of the relevant loss processes and photon production mechanisms are taken into account. The transport of both the primary ions and the secondary positrons resulting from the decay of the positive pions, as well as the transport of the produced gamma-ray emission are considered. The distributions of the gamma rays as a function of atmospheric depth, time, emission angle, and photon energy are calculated and the dependence of these distributions on the model parameters are studied. The obtained angular distributions are not sufficiently anisotropic to account for the observed limb brightening of the greater than 10 MeV flare emission, indicating that the bulk of this emission is bremsstrahlung from primary electrons.

  17. Measurement of the shape factor for the β decay of 14O

    NASA Astrophysics Data System (ADS)

    George, E. A.; Voytas, P. A.; Severin, G. W.; Knutson, L. D.

    2014-12-01

    We report results from an experiment designed to test the conserved vector current (CVC) hypothesis by measuring the shape of the β -decay spectrum for the allowed 0+→1+ ground state decay of 14O . Measurements of the spectrum intensity were obtained with a superconducting beta spectrometer and will be reported for positron kinetic energies ranging from 1.9 to 4.0 MeV. After dividing out phase space, Coulomb, and other correction factors, the resulting shape function has a negative slope of several percent per MeV. We define a parameter a', which is essentially a measure of the average slope of the shape function over the energy range of the measurements, and determine its value to be a'=-0.0290 ±0.0008 (stat.) ±0.0006 (syst.). The measured slope parameter is in good agreement with predictions from shell model calculations that respect CVC.

  18. RARE DECAYS INCLUDING PENGUINS

    SciTech Connect

    Eigen, G

    2003-12-04

    The authors present a preliminary measurement of the exclusive charmless semileptonic B decays, B {yields} {rho}{ell}{nu}, and the extraction of the CKM parameters V{sub ub}. IN a data sample of 55 x 10{sup 6} B{bar B} events they measure a branching fraction of {Beta}(B {yields} {rho}{ell}{nu}) = (3.39 {+-} 0.44{sub stat} {+-} 0.52{sub sys} {+-} 0.60{sub th}) x 10{sup -4} yielding |V{sub ub}| = (3.69 {+-} 0.23{sub stat} {+-} 0.27{sub sys -0.59th}{sup +0.40}) x 10{sup -3}. Next, they report on a preliminary study of the radiative penguin modes B {yields} K{ell}{sup +}{ell}{sup -} and B {yields} K*{ell}{sup +}{ell}{sup -}. In a data sample of 84 x 10{sup 6} B{bar B} events they observe a significant signal (4.4{sigma}) in B {yields} K{ell}{sup +}{ell}{sup -}, yielding a branching fraction of {Beta}(B {yields} K{ell}{sup +}{ell}{sup -}) = (0.78{sub -0.20-0.18}{sup +0.24+0.11}) x 10{sup -6}. In B {yields} K*{ell}{sup +}{ell}{sup -} the observed yield is not yet significant (2.8{sigma}), yielding an upper limit of the branching fraction of {Beta}(B {yields} K*{ell}{sup +}{ell}{sup -}) 3.0 x 10{sup -6} {at} 90% confidence level. Finally, they summarize preliminary results of searches for B {yields} {rho}({omega}){gamma}, B{sup +} {yields} K{sup +} {nu}{bar {nu}} and B{sup 0} {yields} {ell}{sup +}{ell}{sup -}.

  19. Radiative Leptonic B Decays

    SciTech Connect

    Chen, Edward Tann

    2007-01-01

    We present the results of a search for B+ meson decays into γℓ+v, where ℓ = e,μ. We use a sample of 232 million B$\\bar{B}$ meson pairs recorded at the Υ(4S) resonance with the BABAR detector at the PEP-II B factory. We measure a partial branching fraction Δβ in a restricted region of phase space that reduces the effect of theoretical uncertainties, requiring the lepton energy to be in the range 1.875 and 2.850 GeV, the photon energy to be in the range 0.45 and 2.35 GeV, and the cosine of the angle between the lepton and photon momenta to be less than -0.36, with all quantities computed in the Υ(4S) center-of-mass frame. We find Δβ(B+ → γℓ+v) = (-0.31.5+1.3(statistical) -0.6+0.6(systematic) ± 0.1(theoretical)) x 10-6, under the assumption of lepton universality. Interpreted as a 90% confidence-level Bayesian upper limit, the result corresponds to 1.7 x 10-6 for a prior at in amplitude, and 2.3 x 10-6 for a prior at in branching fraction.

  20. Centroid shift of. gamma. rays from positron annihilation in the depletion region of metal-oxide-semiconductor structures

    SciTech Connect

    Leung, T.C.; Kong, Y.; Lynn, K.G.; Nielsen, B. ); Weinberg, Z.A.; Rubloff, G.W. )

    1991-01-07

    Using metal-oxide-semiconductor (MOS) structures, the shift of centroid (peak) of {gamma}-ray energy distributions emitted from positron annihilation has been measured as a function of incident positron energy. The Doppler centroid shift was found to be consistent with the positron motion in the MOS depletion region. The results are described by a one-dimensional positron diffusion model, and provide information on effective'' positron diffusion length under applied field.