Effects of near-source photon scattering at the energy of 60 keV

Compton scattering on electrons in materials in the vicinity of low-energy photon-emitting atoms and in the vicinity of the detector sensitive volume causes a continuous distribution below the full-energy peak (the “shoulder”). To study effects of the near-source Compton scattering, a collimator was used in front of a planar germanium detector to reduce the near-detector scattering. The measurements show that even a small mass in vicinity of emitting atoms, such as that of a standard calibration source plate (0.59 g), results in a considerable shoulder, whose shape depends very much on the orientation of the source plate. Additional mass near the source causes a strong enlargement of the shoulder, while the shape depends very much on its position. Calculations of single-Compton scattering on electrons in the vicinity of emitting atoms reproduce reasonably well the numbers of pulses and the shapes of the observed shoulders.