Positron Transmission and Scattering Measurements Using Superposition of Annihilation Line Shapes: Backscatter Coefficients

Abstract

Backscatter coefficients have been measured for positron spectra emitted by radioactive sources and incident on 20 elements ranging from Li to U. The technique, based on recording the annihilation-$\ensuremath{\gamma}$-ray spectrum in a Ge (Li) detector, eliminates uncertainties encountered in methods where the positrons themselves are detected. The coefficient $R$ for backscatter into $2\ensuremath{\pi}$ is found to vary with atomic number $Z$ according to the relationship $R=0.342 \mathrm{ln}Z\ensuremath{-}0.146$.