Study of Solids by Use of Nonthermalized Positrons

Nielsen, B.; Lynn, Kelvin G.; Chen, Yen C.

doi:10.1103/physrevlett.57.1789

Cited by 61 publications

(10 citation statements)

References 13 publications

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“…The value of n depends on the energy and varies from 1.16 at 3 MeV to 1.68 at 10 keV. 25,26 From Monte Carlo simulations 21 and from studies of multilayer structures, 26,27 it was found that nϷ1.6 for positrons, but there are indications that this value depends on the material. 28 The shaping parameter m is close to 2 as shown from fits to Monte Carlo simulations 21 and from studies of multilayer structures.…”

Section: A Diffusion Of Thermal Positronsmentioning

confidence: 99%

“…In lifetime measurements, 29,30 nonthermal trapping of positrons was proposed to explain a drop with temperature in f , the annihilation rate of untrapped positrons. Nonthermal positron trapping in vacancies was observed only recently 25,31 and was shown to affect the analysis of the diffusion length of positrons. These experiments also showed that trapping is very efficient and can occur faster than 10 Ϫ15 s. A recent theoretical model 32 showed resonances in the trapping rate at energies of about 1-2 eV that can only enhance nonthermal trapping.…”

Section: B Nonthermal Positronsmentioning

confidence: 99%

“…The energy loss process of charged particles in a solid or liquid recently has received much attention [66][67][68][69][70] because the analysis of the S and F parameter data strongly depends on a knowledge of the positron implantation profile. 70 The energy analysis of the reemitted positrons was performed with two parallel grids in front of the sample.…”

Section: Nonthermal-positron Effectsmentioning

confidence: 99%

“…70 The energy analysis of the reemitted positrons was performed with two parallel grids in front of the sample. The sample was maintained at 30 V, and the grid bias varied from 10 to 50 V. Nonthermal positrons that leave the sample having the normal component of the kinetic energy less than the grid potential return to the metal where they annihilate.…”

Section: Nonthermal-positron Effectsmentioning

confidence: 99%

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Positron diffusion in solid and liquid metals

et al. 1999

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We made a systematic study of the diffusion of positrons in several liquid and solid metals with a vertical positron beam. Several interesting effects have been observed by studying the line shape parameter S, the fraction of positronium formed at the surface, and the diffusion length of positrons in liquids. The S parameter and the fraction of positronium created and released at the surface ͑F parameter͒ were measured as a function of temperature in the solid and liquid phases of Ga, Bi, Na, Sn, In, and Pb. An appreciable change just below or across the melting point in the S parameter was measured in metals where positron trapping has not been observed ͑Ga, Bi, and Sn͒. In metals where positron trapping occurs in the solid phase, there is a small change or none in the S parameter ͑Pb and In͒, which indicates that there is only a small change in the nature of the traps. Positron trapping was seen in all the liquid metals, indicating that they have a high density of defectlike sites that trap positrons. The diffusion length of positrons in the liquid was extracted from the experimental data. In Ga, Bi, and Sn, there is a large drop in the diffusion length upon melting; in Pb and In, only a small change or none is seen. In all liquid metals the diffusion length increases as the temperature increases, suggesting that diffusion is related to trapping in temporary fluctuations in the liquid's structure. The positron moves from fluctuation to fluctuation. The size of the traps strongly depends on temperature, and so when it increases, the positron's hopping motion increases. We also measured the reemitted energy spectra of positrons from liquid and solid surfaces. No appreciable change was seen with increasing temperature or when the metals melted.

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Section: A Diffusion Of Thermal Positronsmentioning

confidence: 99%

Section: B Nonthermal Positronsmentioning

confidence: 99%

Section: Nonthermal-positron Effectsmentioning

confidence: 99%

Section: Nonthermal-positron Effectsmentioning

confidence: 99%

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Positron diffusion in solid and liquid metals

et al. 1999

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“…This peak is due to the resonant p-wave scattering, which causes a considerable enhancement of the delocalized wave function a t the defect and thereby the increase of the energy lev) - vacancies are shown matrix element (19). McMullen and Stott [19] realized that the appearance of the resonance explains in a natural way the depletion of the flux of positrons reemitted from A1 samples in the slow positron beam experiments [30]. This kind of phenomena is not possible in the old model calculations [17,18, 291 based on approximative positron wave functions.…”

Section: Defects In Setrricoiiductorsmentioning

confidence: 99%

Theoretical Aspects of Positrons in Imperfect Solids

Puska

1987

Phys. Stat. Sol. (a)

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New high precision lifetime measurements in pure copper and a 0.3 at.% AgSb alloy with a BaF₂ lifetime spectrometer

Ederhof

Luhr-Tanck

Sager

et al. 1987

Cryst. Res. Technol.

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The temperature dependence of positron annihilation in copper and a 0.3 at. "/b AgSb alloy has been investigated by measuring the positron lifetime. I n both cases the vacancy lifetime is nearly independent on temperature while the bulk lifetime shows a rapid increase after the onset of detectable vacancies. This increase can be explained by trapping during thernialization with a n enhanced trapping rate.

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Study of Solids by Use of Nonthermalized Positrons

Cited by 61 publications

References 13 publications

Positron diffusion in solid and liquid metals

Positron diffusion in solid and liquid metals

Theoretical Aspects of Positrons in Imperfect Solids

New high precision lifetime measurements in pure copper and a 0.3 at.% AgSb alloy with a BaF₂ lifetime spectrometer

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Study of Solids by Use of Nonthermalized Positrons

Cited by 61 publications

References 13 publications

Positron diffusion in solid and liquid metals

Positron diffusion in solid and liquid metals

Theoretical Aspects of Positrons in Imperfect Solids

New high precision lifetime measurements in pure copper and a 0.3 at.% AgSb alloy with a BaF2 lifetime spectrometer

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New high precision lifetime measurements in pure copper and a 0.3 at.% AgSb alloy with a BaF₂ lifetime spectrometer