A method for determining the 2π-counting efficiency of beta-particle sources

This paper is concerned with the efficiency of large-area beta-particle sources. Attention is focussed on sources in which the radioactivity is distributed in a surface layer of an anodized aluminum foil. The efficiency takes into account the reflection and absorption of particles in the aluminum foil, and is defined as the ratio of the number of particles emerging from the foil to the number of particles emitted. A method of estimating the efficiency is proposed which combines measurements and transport calculations. The experimental part of the method consists of measuring the thickness of the layer of mylar which, when inserted between source and detector, cuts the counting rate in half. The theoretical part consists of calculations of beta-particle transport in a two-layer aluminum-mylar medium, which relate the efficiency of the source to the thickness of the measured half-value layer. (orig.)