Diffusion heating and cooling of positrons in constrained media

Journal Article · Fri Jun 01 00:00:00 EDT 1979 · Phys. Rev., A; (United States)

DOI:https://doi.org/10.1103/PhysRevA.19.2317· OSTI ID:5985904

Brandt, W; Arista, N R

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 the effective diffusion coefficient pertinent for trapping relative to that in the infinite medium. The effects on the annihilation characteristics are those of a reduced trapping rate and of an apparent initial positron population in sinks, as it is recorded by an instrument with finite time resolution. The results pertain to positronium diffusion in small gas cells, to the escape of positrons or positronium from small solids, and to the trapping of positrons by vacancies or voids in solids. They are compared with experimental results.

• Research Organization: Department of Physics, New York University, New York, New York 10003
• OSTI ID: 5985904
• Journal Information: Phys. Rev., A; (United States), Vol. 19:6
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
74 ATOMIC AND MOLECULAR PHYSICS
POSITRONS
ANNIHILATION
DIFFUSION
CROSS SECTIONS
SOLIDS
TRAPPING
ANTILEPTONS
ANTIMATTER
ANTIPARTICLES
BASIC INTERACTIONS
ELECTROMAGNETIC INTERACTIONS
ELEMENTARY PARTICLES
FERMIONS
INTERACTIONS
LEPTONS
654001* - Radiation & Shielding Physics- Radiation Physics
Shielding Calculations & Experiments
640303 - Atomic
Molecular & Chemical Physics- Positronium
Muonium
& Muonic & Mesic Atoms & Molecules