Use of low-background germanium detectors to preselect high-radiopurity materials intended for constructing advanced ultralow-level detectors

The use of ultra-low-background germanium-diode gamma-ray spectrometers to measure the concentrations of radionuclides in a variety of materials is described. Bulk shielding materials that were examined included contemporary lead, 150-year-old lead, 400-year-old lead, pre-1945 battleship steel, and electrorefined copper. Typically, the samples were constructed such that a thickness of 5 cm or more of material completely surrounded the detector except for the end connected to the liquid nitrogen dewar. Several experiments were performed to gauge the effects of shielding materials on the observed cosmogenic neutron flux. Another experiment was performed at ground level using one of the germanium diodes fabricated with superclean materials (copper can and cryostat, custom solder, indium o-ring, etc.) and 5-, 10-, and 15-cm-thick low-activity passive Pb shielding to determine the effects of bulk shielding on the observed background. The results are presented and discussed.<>