Efficiency for close geometries and extended sources of a p-type germanium detector with low-energy sensitivity

Typically, germanium detectors designed to have good sensitivity to low-energy photons and good efficiency at high energies are constructed from n-type crystals with a boron-implanted outer contact. These detectors usually exhibit inferior resolution and peak shape compared to ones made from p-type crystals. To overcome the resolution and peak-shape deficiencies, a new method of construction of a germanium detector element was developed. This has resulted in a gamma-ray detector with high sensitivity to photon energies from 14 keV to 2 MeV, while maintaining good resolution and peak shape over this energy range. Efficiency measurements, done according to the draft IEEE 325-2004 standard, show efficiencies typical of a GMX or n-type detector at low energies. The detectors are of large diameter suitable for counting extended samples such as filter papers. The Gaussian peak shape and good resolution typical of a GEM or p-type are maintained for the high count rates and peak separation needed for activation analysis.