Time dependent diffusion and annihilation of positrons

Britton, D T

Title: Time dependent diffusion and annihilation of positrons

Full Record
Other Related Research

Abstract

The time-dependent diffusion equation of positrons implanted epithermally in a semi-infinite solid has been solved using a Green's function method. Subsequent lifetime spectra, deriving from the annihilation of free thermal and surface trapped positrons, and from para-Ps, have been modeled. The resulting curves resemble a sum of two exponential components. Because of the very short times involved, the contribution due to non-thermal positrons reaching the surface is much less significant than for steady-state models. At room temperature reflection of thermal positrons at the surface has very little effect on the solution to the diffusion equation. For strongly reflecting surfaces the sink and annihilation rates are qualitatively similar to those for a transparent surface, although strongly reduced.

Authors:

Britton, D T ^[1]

Institut fuer Nukleare Festkoerperphysik, Universitaet der Bundeswehr, Muenchen, D-8014 Neubiberg (Germany)

Publication Date:: Fri Feb 01 00:00:00 EST 1991

OSTI Identifier:: 5020882

Report Number(s):: CONF-900798-
Journal ID: ISSN 0094-243X; CODEN: APCPC

Resource Type:: Conference

Journal Name:: AIP Conference Proceedings (American Institute of Physics); (United States)

Additional Journal Information:: Journal Volume: 218:1; Conference: 4. international workshop on slow-positron beam techniques for solids and surfaces, London (Canada), 3-6 Jul 1990; Journal ID: ISSN 0094-243X

Country of Publication:: United States

Language:: English

Subject:: 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; POSITRONS; ANNIHILATION; DIFFUSION; SOLIDS; POSITRON COLLISIONS; GREEN FUNCTION; LIFETIME; POSITRONIUM; SURFACE PROPERTIES; TIME DEPENDENCE; TRAPPING; ANTILEPTONS; ANTIMATTER; ANTIPARTICLES; BASIC INTERACTIONS; COLLISIONS; ELECTROMAGNETIC INTERACTIONS; ELEMENTARY PARTICLES; FERMIONS; FUNCTIONS; INTERACTIONS; LEPTONS; MATTER; PARTICLE INTERACTIONS; 656002* - Condensed Matter Physics- General Techniques in Condensed Matter- (1987-); 654001 - Radiation & Shielding Physics- Radiation Physics, Shielding Calculations & Experiments; 656003 - Condensed Matter Physics- Interactions between Beams & Condensed Matter- (1987-)

Citation Formats


                    Britton, D T. Time dependent diffusion and annihilation of positrons.  United States: N. p., 1991. 
        Web.

Copy to clipboard


                    Britton, D T. Time dependent diffusion and annihilation of positrons.  United States.

Copy to clipboard


                    Britton, D T. 1991.  
        "Time dependent diffusion and annihilation of positrons".  United States.

Copy to clipboard


                    
@article{osti_5020882,

  title        = {Time dependent diffusion and annihilation of positrons},

  author       = {Britton, D T},

  abstractNote = {The time-dependent diffusion equation of positrons implanted epithermally in a semi-infinite solid has been solved using a Green's function method. Subsequent lifetime spectra, deriving from the annihilation of free thermal and surface trapped positrons, and from para-Ps, have been modeled. The resulting curves resemble a sum of two exponential components. Because of the very short times involved, the contribution due to non-thermal positrons reaching the surface is much less significant than for steady-state models. At room temperature reflection of thermal positrons at the surface has very little effect on the solution to the diffusion equation. For strongly reflecting surfaces the sink and annihilation rates are qualitatively similar to those for a transparent surface, although strongly reduced.},

  doi          = {},

  url          = {https://www.osti.gov/biblio/5020882},
  journal      = {AIP Conference Proceedings (American Institute of Physics); (United States)},

  issn         = {0094-243X},

  number       = ,

  volume       = 218:1,

  place        = {United States},

  year         = {Fri Feb 01 00:00:00 EST 1991},

  month        = {Fri Feb 01 00:00:00 EST 1991}

}

Copy to clipboard

Conference:

Other availability

Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share:

Export Metadata

Save to My Library

Similar records in OSTI.GOV collections:

Diffusion heating and cooling of positrons in constrained media

Journal Article Brandt, W; Arista, N - Phys. Rev., A; (United States)

Thermalized positrons in media with spatial constraints can be trapped by sinks, and annihilate with electrons into ..gamma.. quanta with characteristics that are discernibly different from those of positrons annihilating in the bulk. The dependence of the cross sections for scattering in the medium on positron velocity determines whether the fastest or the slowest particles in the velocity distribution disappear preferentially from the volume. This causes the cooling or heating of the positrons remaining in the medium. The diffusion equation is solved to derive the annihilation characteristics of positrons, with the result that diffusion heating and cooling always reduce themore »« less
https://doi.org/10.1103/PhysRevA.19.2317
Two-dimensional angular correlation of annihilation radiation study of positron interactions with surfaces of aluminum

Journal Article Chen, D; Berko, S; Canter, K; ... - Phys. Rev. B: Condens. Matter; (United States)

Studies were made of the interactions of positrons with three low index surfaces of aluminum ((100), (110), and (111)) at room temperature with the aluminum surface at elevated temperatures and with oxygen adsorption on the aluminum surface. Our measurements using the improved two-dimensional angular correlation of annihilation radiation technique on surfaces support three established processes: spontaneous positronium (Ps) formation and emission, positrons bound in a surface state, and surface-state positrons thermally desorbed as Ps atoms. A method has been developed to accurately separate these components. The positron surface-state annihilation spectra are nearly isotropic for all three Al surfaces, which indicatesmore »« less
https://doi.org/10.1103/PhysRevB.39.3966
Photon correlations in positron annihilation

Journal Article Gauthier, Isabelle; Hawton, Margaret - Physical Review. A

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)].
https://doi.org/10.1103/PHYSREVA.81.062121
Positron transport in solids and the interaction of positrons with surfaces

Miscellaneous Kong, Yuan

In studying positron transport in solids, a two-stream model is proposed to account for the epithermal positrons. Thus positron implantation, thermalization, and diffusion processes are completely modeled. Experimentally, positron mobility in thermally grown SiO[sub 2] is measured in a sandwiched structure by using the Doppler broadening technique. Positron drift motion and the electric field configuration in a Si surface buried under overlayers are measured with the positron annihilation [gamma]-ray centroid shift technique. These studies are not only important in measuring positron transport and other properties in complicated systems, they are also of practical significance for material characterizations. In studying positronmore »« less
Positron annihilation in low-temperature rare gases. II. Argon and neon

Journal Article Canter, K; Roellig, L - Phys. Rev., A, v. 12, no. 2, pp. 386-395

Lifetime measurements of slow-positron and ortho-positronium (o-Ps) annihilation were made in argon and neon gases at room temperature and below. The argon experiments cover the temperature range 115 to 300$sup 0$K and the density range 0.0356 to 0.0726 g/cm$sup 3$ (approximately equal to 20 to 40 amagat). The slow-positron spectra in argon exhibit a departure from free- positron annihilation below 200$sup 0$K. The departure becomes more marked as the temperature is lowered. No deviation from free o-Ps pickoff annihilation is observed in argon at low temperatures. The neon measurements cover the temperature range 30 to 300$sup 0$K and the densitymore »« less
https://doi.org/10.1103/PhysRevA.12.386

Similar Records