Moderation and diffusion of positrons in tungsten meshes and foils.

Williams, I.A. and Murtagh, D.J. and Fayer, S.E. and Andersen, S.L. and Chevallier, J. and Kövér, Ákos and Van Reeth, P and Humberston, J.W. and Laricchia, G. (2015) Moderation and diffusion of positrons in tungsten meshes and foils. JOURNAL OF APPLIED PHYSICS, 118. pp. 1-6. ISSN 0021-8979

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Abstract

The efficiency of tungsten meshes and thin foils for moderation of fast positrons from 22Na has been investigated in transmission geometry and a fair agreement has been found with previous experimental results where directly comparable. For foils, the dependence on material thickness is found to be similar to the prediction of the Vehanen-M€akinen diffusion model; however, the magnitude is 5–10 times lower. A broad consensus is observed between experiment and the results of a three-dimensional model developed in this work. For a given thickness, meshes are found to be generally better than foils by around a factor of 10 with a maximum efficiency (�10�3) comparable to that achieved with thin single crystal foils, in accord with previous measurements and the results of the present model.

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