A study of fast neutron interactions in high-purity germanium detectors

The interaction properties of fast neutrons in a closed-end coaxial and a planar high-purity germanium detector (HPGe) have been studied. Digitized waveforms of HPGe preamplifier signals were recorded for time-of-flight separated neutrons and γ -rays emitted by a 252Cf source. The experimental results were compared to simulations of pulse shapes and to GEANT4 simulations of the interactions of the neutrons and γ -rays in the detectors. In the analysis, special emphasis was given to elastically scattered neutrons, which for HPGe energy thresholds below about 50 keV give the largest contribution to the interaction probability, and which may be an important effect to take into account in future γ -ray spectrometers based on γ -ray tracking. No differences between the pulse shapes of detected neutrons and γ -rays were observed. The general agreement between the experimental and simulated results was found to be good.