Optimal HPGe Detector Selection for Gamma-Ray Spectroscopy

This work analyzes the optimal combination between HPGe detectors and sample geometries that result in the lowest Minimum Detectable Activities (MDA) for a given type of shielding. The minimum MDA for a set of nuclides is the criteria to optimize the HPGe detector and the sample geometry. The analysis is made on a large set of detectors of different sizes, p-n junction configuration and aspect ratio available from Canberra Industries Inc., whose response has been characterized with the In-Situ Object Counting System (ISOCS) software. Background spectra in two standard shielding configurations have been acquired and a spectra library has been assembled. This offers the extended capability to establishing the optimal detector for a given application, before purchasing the detector. For each detector, the absolute efficiency is calculated for various sample geometries using ISOCS and an interface that uses the standard Genie2000 spectroscopy software engine. We present two comparisons, one of a coaxial detector and a Broad Energy Ge detector (BEGe) a.k.a planar point contact detector of the same relative efficiency, and comparison of two coaxial detectors of different relative efficiency. The preliminary conclusion is that a larger detector with more efficiency is not always the best choice for the given measurement geometry. Instead, the optimal matching of the detector size with measurement geometry provides the best experimental and economical solution.