Spatial profiles of positrons injected at low energies into water: influence of cross section models

Tattersall, Wade J., Cocks, Daniel G., Boyle, Gregory J., Brunger, Michael J., Buckman, Stephen J., Garcia, Gustavo, Petrovic, Zoran Lj, Sullivan, James P., and White, Ronald D. (2017) Spatial profiles of positrons injected at low energies into water: influence of cross section models. Plasma Sources Science and Technology, 26 (4). 045010.

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We present a collated set of interaction cross sections for positrons in water, and study how the choice of ionisation energy sharing and of anisotropy in elastic cross sections influences lowenergy spatial transport. A Monte Carlo code has been developed to model the transport of a beam of positrons injected at 60. eV into water, in which we compare several ionisation energy sharing models, and also vary the anisotropic scattering behaviour for elastic collisions. While the cross sections are primarily applicable to water vapour, we have investigated the inclusion of coherent elastic scattering which is present in liquid water. We present comparative profiles of positron number density, energy deposition, positronium formation, and secondary electron generation. Anisotropic scattering can increase radial diffusion by a factor of two, and a similar effect occurs as a result of coherent elastic scattering, though only at energies below the positronium formation threshold. The results emphasise the need for detailed knowledge of scattering cross sections that are differential in both scattering angles and energy transfer.

Item ID: 50361
Item Type: Article (Research - C1)
ISSN: 1361-6595
Keywords: positron, water, spatial, cross sections, transport, Monte Carlo
Funders: Australian Research Council (ARC), Spanish Ministerio de Economia, Industria y Competitividad (SM)
Projects and Grants: ARC Centres of Excellence and Discovery programmes, SM project FIS2016-80440
Date Deposited: 20 Sep 2017 08:15
FoR Codes: 51 PHYSICAL SCIENCES > 5102 Atomic, molecular and optical physics > 510201 Atomic and molecular physics @ 60%
51 PHYSICAL SCIENCES > 5106 Nuclear and plasma physics > 510602 Plasma physics; fusion plasmas; electrical discharges @ 40%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970102 Expanding Knowledge in the Physical Sciences @ 100%
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