Results 221 to 230 of about 494,691 (265)

Lifetimes of positrons in alkali halides

Chemical Physics Letters, 1970
Abstract The positron lifetimes in alkali halides are calculated assuming the outer shell electrons of the halide ion to form an ‘electron plasma’ which is capable of concentrating around the positron. The calculated annihilation rates are found to be in good agreement with the experimental results.
J.C. Garg, B.L. Saraf
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Positron lifetime and implantation in Kapton

Journal of Physics D: Applied Physics, 2006
The polyimide material Kapton has been studied by positron annihilation lifetime spectroscopy (PALS) and lifetime results for two grades of Kapton are presented. Positron transmission measurements using stacked Kapton foil, backed with Al, and with Ni, were performed and the model dependent Kapton positron absorption coefficient values are given ...
S McGuire, D J Keeble
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Positron lifetimes for neutron-irradiated C $_{60}$

Applied Physics A: Materials Science & Processing, 1995
The neutron-irradiation effects on C60 fullerite powder were studied by positron lifetime spectroscopy. Below 0.5 ns, a single lifetime of 382±1 ps was found for the unirradiated annealed sample and two components were resolved after neutron irradiation with a dose of 2×1016 n/cm2. Possible origins of these components are briefly discussed.
F. Bečvář, I. Novotný, I. Procházka, D. Rafaja, J. Kern   +4 more
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Characterization of Graphites by Positron Lifetimes

Japanese Journal of Applied Physics, 1981
Positron lifetimes have been measured in different types of graphites such as glassy carbon, nuclear graphite, pyrolytic graphite and natural graphite. An analysis based on the trapping model shows that positrons preferentially monitor structural defects such as the internal surfaces between crystallites and surfaces around pores or voids.
Tadao Iwata, Hiroshi Fukushima, Michio Shimotomai, Masao Doyama   +3 more
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Positron Lifetimes in Deformed Copper

Journal of the Physical Society of Japan, 1976
Positron lifetime measurements were performed for Cu samples with different densities of lattice defects. The lifetime spectra were successfully resolved into two components with the help of the well established analysis program. Obtained results were quite consistent with those expected from the trapping model.
Kenji Hinode, Shoichiro Tanigawa, Masao Doyama   +2 more
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Positron lifetime spectroscopy in copper

Journal of Physics F: Metal Physics, 1986
The temperature dependence of positron annihilation in copper was investigated by measuring the positron lifetime between 20 and 1070 degrees C. A high-resolution lifetime spectrometer (FWHM 170 ps) with a stability better than +or-1.5 ps over a period of four weeks was used.
T Hehenkamp, T Kurschat, W Luhr-Tanck
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Positron lifetimes in lanthanum sesquisulfides

Physics Letters A, 1981
Abstract The lifetime of positrons trapped in cation monovacancies in high vacancy concentration lanthanum sesquisulfide samples has been measured to be 326±6 ps. More than 98% of all positrons in these samples are trapped.
G.D. Loper, G.A. Mohr
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Mining the bulk positron lifetime

physica status solidi (b), 2009
AbstractWe introduce a new approach to investigate the bulk positron lifetimes of new systems based on data‐mining techniques. Through data mining of bulk positron lifetimes, we demonstrate the ability to predict the positron lifetimes of new semiconductors on the basis of available semiconductor data already studied.
H. Aourag, A. Guittom
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Positron lifetimes in molecular crystals

Canadian Journal of Physics, 1996
Positron lifetime measurements were carried out on molecular crystals of C60, TTF-TCNQ, and (BEDT-TTF)2Cu(NCS)2 utilizing a pulsed variable-energy positron beam. Each lifetime spectrum is well described by a single component. Their values are 390, 338, and 357 ps, respectively. In addition, positron lifetimes were calculated theoretically.
Shoji Ishibashi, Madoka Tokumoto, Nobumori Kinoshita, Norio Terada, Hideo Ihara, Ryoichi Suzuki, Toshiyuki Ohdaira, Tomohisa Mikado, Hiroyuki Anzai   +8 more
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The Calculation of Positron Lifetimes

1984
A recent admirable review by Drachman, 1 given on the occasion of the first conference in this series, contains a helpful section on lifetime calculations. Drachman reviews two interesting techniques for improving the accuracy of calculated lifetimes which are based not upon calculating better wave functions but rather upon operator transformations. In
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