Some Peculiarities of Digital Gamma-ray Spectroscopy with Germanium Detectors Performed in Presence of Neutrons

We measured the time-differentiated spectrum of the 252Cf source as seen by an high-purity germanium detector triggered by the NE213 liquid scintillator detector. The detectors are off-line coincided from the event-by-event list formed with 10 ns resolution by the quad FADC unit of the CAEN N1728B type. The signatures of the processes induced by fast and slow neutrons, both within the detector itself and in its environment, appear completely separated. The processes induced by fast neutrons are found in the prompt part of the time spectrum and those induced by thermal neutrons in the long tail of delayed coincidences. We analyse the time behaviour of spectral structures at 692 keV, which are the signatures of inelastic neutron scattering on Ge-72, and comment on its suitability for determination of the fast neutron flux in general, and in the digital gamma-ray spectroscopy in particular.