Development and use of a thin-film transmission positron moderator

Lynn, K. G.; Nielsen, B.; Quateman, J. H.
August 1985
Applied Physics Letters;8/1/1985, Vol. 47 Issue 3, p239
Academic Journal
A narrow energy beam of slow positrons can be generated by moderating the beta-decay spectrum of a radioactive β[sup +] source. We report here the development and use of the first moderator in which the low-energy positrons are not extracted from the surface facing the β[sup +] emitter but from the opposite surface, i.e., the transmission moderator. An advantage is that such a configuration eliminates the problem of moderated positrons passing by the radioactive source. This is an essential problem when the source is physically large such as the present commerically available Na[sup 22] sources. This moderator is a 5000-Å self-supporting W (100) film. The growth and treatment of the film were found to provide a high-quality positron moderator. The slow to fast positron conversion efficiency, using a Na[sup 22] source, was found to be 4 × 10[sup -4].


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