Positron annihilation in Ge(Li) detector from line shape of single-escape peak

The line shape of the single-escape peak of high-energy γ rays has been investigated. A 30-cc Ge(Li) detector was irradiated with 2614.5 and 2753.9-keV γ rays from ²⁰⁸Tl and ²⁴Na, respectively. The observed broadening of the single-escape peaks was attributed to the Doppler shift of annihilation radiation, and, by unfolding the instrumental resolution the momentum distribution of the electrons in a germanium crystal was deduced. In addition, an upper limit of 5.4 ×{} 10^-3 for the ratio of the probabilities for positron annihilation with a K-shell electron to that with an electron from other atomic shells was determined.