Bulk environmental samples analyzed with anticosmic-shielded ultralow-background germanium detector systems

A low-level gamma-ray counting system has been developed which reduces system background (relative or other typical low-background systems) by a factor of ten in the zero to one MeV energy region, and by as much as a factor of forty at higher energies. This germanium-diode gamma-ray spectrometer was constructed for a modest investment over that required for a conventional germanium detector. The techniques involved use: (1) materials of known radiopurity to surround the diode, (2) an active external anticosmic shield to reduce the background continuum due to interactions of cosmic particles with the detector and passive lead shielding, and (3) nitrogen exhausted from the cryogenic dewar to minimize the introduction of ubiquitous radon decay nuclei into sample counting chamber. A novel method for handling samples prior to counting is presented. Also, some of the difficulties encountered in calibrating a system intended for bulk samples are discussed