Advances in large-diameter, low-energy HPGe detectors

The preparation of large diameter germanium crystals of both P- and N-types has made possible the construction of coaxial detectors of relative efficiency exceeding 100% for commercial exploitation. A new development involves large diameter (70 mm) N-type coaxial detectors of low length-to-diameter ratio (''LO-AX'' detectors). These new detectors have similar resolution to available 50 and 60 mm diameter crystals; thus the low-energy photon efficiency of a 70 mm device is nearly twice that of a standard 50 mm detector. Spectra are presented and discussed from the monitoring of plutonium and americium lung phantoms and the study of mining samples as examples of two cases where the larger diameter detectors have advantages over the smaller detectors. (orig.)