Detection limits of the NaI(Tl) shielded HPGe spectrometer

The results of a detailed study of the low-level performance of a NaI(Tl) shield added to an iron shielded HPGe spectrometer are presented. Both the “slow” and the “fast” anticoincidence gating modes were tested, the “slow” mode being found better suited for general low-level spectroscopy applications. In long runs the stability of the system in this mode is satisfactory. The anticoincidence action of the NaI(T1) shield lowers the integral background of the iron shielded HPGe detector in the energy range from 30 keV to 2 MeV by a factor of 6.5, and suppresses the continuum above 150 keV by a factor larger than 10.