Slow positron beam generator for lifetime studies

Abstract

A slow positron beam generator uses a conductive source residing between two test films. Moderator pieces are placed next to the test films on the opposite side of the conductive source. A voltage potential is applied between the moderator pieces and the conductive source. Incident energetic positrons are, first, emitted from the conductive source, second, passed through test film, and then, third, isotropically strike moderator pieces before diffusing out of the moderator pieces as slow positrons. The slow positrons diffusing out of moderator pieces are attracted to the conductive source which is held at an appropriate potential below the moderator pieces. The slow positrons have to pass through the test films before reaching the conductive source. A voltage is adjusted so that the potential difference between the moderator pieces and the conductive source forces the positrons to stop in the test films. Measurable annihilation radiation is emitted from the test film when positrons annihilate (combine) with electrons in the test film.