Positron and Positronium Annihilation in Liquid Helium at the Lambda Point

Abstract

This paper is a result from an experiment that counted and analyzed positron and positronium annihilation events as close as possible above and below the lambda point 2.186 o K in liquid helium. The theory of annihilation, modes of annihilation, and positronium formation is presented as typical in much of the literature available on the subject today. A very recent theory is proposed to offer a mechanism to compensate for the discrepancy between experimental results and theoretical expectations for triplet to singlet conversion of triplet positronium in liquid helium. The mechanism is a bubble which protects the positronium atom from contact with the medium.