Effects of near-source Compton scattering in low-energy γ-ray spectra

An extension of the previous study of germanium-detector response function for 59.537 keV γ-rays has been made. The continua adjacent to the full-energy peaks, which are due to Compton scattering in atoms in vicinity of the γ-ray emitting atoms (the “shoulders”), were measured with 26.345, 79.623, 80.999, 88.032, 86.554 and 105.338 keV γ-rays for various orientations of the source plates. The changes in the shoulder spectra clearly indicate the importance of the near-source Compton scattering. Previous calculations, that included only single Compton scattering (assuming stationary electrons) and broadening due to the detector resolution, have been improved by including also the broadening due to momentum distributions of atomic electrons, and double Compton scattering. Also, a spectrum has been obtained by a the Monte Carlo calculation. Better fits to the previously reported spectra measured with the 59.537 keV γ-rays have been obtained. The shoulders in the newly measured spectra are also well explained. The calculated ratios of the numbers of pulses in the shoulders and in the corresponding full-energy peaks are in a reasonable agreement with the experimental ratios.