Inseparable positron annihilation and positronium formation in positron-atom collisions: Description in terms of an absorption potential

Journal Article · Wed Oct 01 04:00:00 EDT 2003 · Physical Review. A

DOI:https://doi.org/10.1103/PhysRevA.68.042716· OSTI ID:20640342

Igarashi, Akinori; Kimura, Mineo; Shimamura, Isao; Toshima, Nobuyuki ^[1]

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1. Department of Applied Physics, Miyazaki University, Miyazaki 889-2192 (Japan)

Pair annihilation in the elementary process of positron (e{sup +}) collisions with atoms is discussed in terms of an imaginary, absorption potential. This potential represents the QED effect of both direct annihilation during the collision and the indirect one via positronium (Ps) formation in a unified manner. These two mechanisms are inseparable from each other near the threshold for positronium formation, where the collision time becomes comparable to or even longer than the lifetime of the positronium. The theory is applied to the e{sup +}-H collisions. The dominant s-wave annihilation cross section follows the Baz' threshold law near the thresholds E{sub th}(1s {sup 1,3}S) for the formation of Ps(1s {sup 1,3}S). Simple relations between the singlet and triplet cross sections are derived. The spin-averaged annihilation cross section rises sharply but continuously, first across E{sub th}(1s {sup 1}S), and then across E{sub th}(1s {sup 3}S), which lies at 0.841 meV above E{sub th}(1s {sup 1}S). The cross section would diverge at E{sub th}(1s {sup 1}S) and E{sub th}(1s {sup 3}S) in the conventional theory where Ps is assumed to have an infinite lifetime. The change of the annihilation probability as the Ps leaves H{sup +}, is studied by decomposing it into the contributions from direct and indirect annihilation and from the interference between them.

• OSTI ID: 20640342
• Journal Information: Physical Review. A, Journal Name: Physical Review. A Journal Issue: 4 Vol. 68; ISSN 1050-2947; ISSN PLRAAN
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION
ANNIHILATION
ATOMS
CROSS SECTIONS
ELECTRONS
HYDROGEN IONS 1 PLUS
INTERFERENCE
LIFETIME
MEV RANGE
POSITRON-ATOM COLLISIONS
POSITRONIUM
POSITRONS
POTENTIAL ENERGY
POTENTIALS
PROBABILITY
QUANTUM ELECTRODYNAMICS
S WAVES
SPIN
SURFACES
TRIPLETS