ABSTRACT

Gamma-spectrometry is a powerful technique for making low-level nuclear measurements in support of research studies as varied as environmental monitoring to the nature of meteorites. Recent advancements in the functionality of detector electronics and computer performance are redefining the possibilities for radionuclide detection. Advanced multidimensional gamma-spectrometry systems capable of coincidence, anti-coincidence and delayed coincidence and coupled with other forms of radiation detection (α, β, X-ray) are becoming a viable option for modestly equipped radiometrology laboratories. Powerful multichannel analyzers (MCAs) that can provide precise nanosecond logging of detector events are enabling this transition. The simplest systems include surrounding a germanium (Ge) gamma-spectrometer with plastic scintillators to detect and reject cosmic background radiation. This can provide a mean background reduction of almost 80% and improvements in the minimum detectable activity (MDA) of 40-50%. Similar improvements are achievable using Compton suppression systems that surround the Ge with a sodium iodide (NaI) shield. More advanced systems combine detectors into arrays for radionuclide measurement based upon unique coincidence radiation signatures, and are capable of background reductions exceeding 99%. At Pacific Northwest National Laboratory (PNNL) an ultra-sensitive multidimensional gamma-spectrometer is being developed in an underground laboratory that combines these technologies to provide a world-class detection capability. Its ability to measure multiple radiation signatures will provide unprecedented detection possibilities and the opportunity for exploration of the gamma landscape.