Coincidence gamma-ray spectrometry

Gamma-ray spectrometry with high-purity germanium (HPGe) detectors is often the technique of choice in an environmental radioactivity laboratory. When measuring environmental samples associated activities are usually low so an important parameter that describes the performance of the spectrometer for a nuclide of interest is the minimum detectable activity (MDA).

There are many ways for lowering the MDAs in gamma spectrometry. Recently, developments of fast and compact digital acquisition systems have led to growing number of multiple HPGe detector spectrometers. In these applications all detected events are recorded in a list mode file with their timestamp and energy, enabling coincidence identification and spectrum manipulation in post-processing.

When coincidence gamma-spectrometry is used for cascade emitting nuclides, coincident signals can be extracted thus significantly reducing the background, as random coincidences are unlikely. This is especially evident when there is high activity of other nuclides present in the sample contributing to high Compton background.

When the nuclide of interest is a single-gamma emitter, coincidence signal can be subtracted from the total to lower the background. In this work, we present a new coincidence spectrometer operated at the Gamma Laboratory of the Radioecology Section at Center for Nuclear Technologies (Nutech). NUCLeGeS consists of two HPGe detectors equipped with a digital acquisition system enabling timestamped list mode data acquisition with 10 ns time resolution.

Post-processing software enables coincidence identification and produces spectra ready for use with GENIE2000 analysis software.