PNNL

Abstract

ABSTRACT Treaty verification, environmental surveillance, and physics experiments continue to require increased sensitivity for detecting and quantifying radionuclides of interest using gamma-ray spectrometry. This can be accomplished by establishing high detection efficiency and reducing instrument backgrounds. A current effort for increased sensitivity in high resolution gamma spectroscopy will produce an intrinsic germanium (HPGe) array designed for high detection efficiency, ultra-low-background performance, and useful coincidence efficiencies. The system design is optimized to accommodate filter paper samples, e.g. samples collected by the Radionuclide Aerosol Sampler/Analyzer (RASA). The system will provide high sensitivity for weak collections on atmospheric filter samples, as well as offering the potential to gather additional information from more active filters using gamma cascade coincidence detection. The instrument will also be capable of making advances in low-dose neutron activation analysis. The first of two ultra-low-background vacuum cryostats has been assembled, with a second in progress. Traditional methods for constructing ultra-low-background detectors were followed, including use of materials known to be low in radioactive contaminants, use of ultra pure reagents, clean room assembly, etc. The cryostat is constructed mainly from copper electroformed into near-final geometry at Pacific Northwest National Laboratory. Details of the detector assembly, vacuum tests, and test measurement results are presented.