Studies of Detection Efficiencies and Operating Characteristics of Ge(Li) Detectors

The rapidly expanding use of Ge(Li) detectors in all fields of gamma-ray spectroscopy has led to a need for information from which experimenters may effectively select the best detector for their special needs. This is necessitated because of the large variety of detector sizes and configurations which are currently available and the lack of standardization of sizes. Several criteria should be considered in the selection of a detector for a specific application. Among these are: 1) detection efficiency, 2) charge collection efficiency, which gives rise to abnormal peak broadening as a function of gamma-ray energy as well as to asymmetric peak shapes, 3) timing characteristics for coincidence applications, and 4) energy resolution which is one of the measures of the ability to identify a weak gamma-ray in the presence of strong higher-energy gamma rays. We have measured these characteristics for several planar and open-ended and five-sided coaxial detectors. Absolute full-energy peak, double-escape peak and single-escape peak efficiencies were obtained for gamma-ray energies from 30 keV to 11 MeV. For planar devices, the effects of thickness and cross-sectional area of the depleted volume have been investigated. Some studies have been made of the problems involved in measuring gamma-ray intensities. These include measurements of the counter "edge effects" by a comparison of the efficiency curves obtained at different source-detector distances. Other studies involve random and real coincidence summing effects which are countingrate and geometry-dependent effects.