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Mechanically Cooled Large-Volume Germanium Detector Systems for Nuclear Explosion Monitoring
PACIFIC NORTHWEST NATIONAL LAB RICHLAND WA
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Compact maintenance-free mechanical cooling detector systems are being developed to operate large-volume approximately 570 cubic cm, approximately 3 kg, 140 or larger germanium detectors for field applications. These detector systems are necessary for remote long-duration liquid-nitrogen free deployment of large-volume germanium gamma-ray detector systems. The Radionuclide Aerosol SamplerAnalyzer RASA nuclear explosion monitoring systems will benefit from the availability of such detector systems by allowing the very largest available germanium detectors to be utilized for the highest sensitivity measurements. To reliably provide such detector systems, three fundamental technical issues are being investigated temperature, vacuum, and vibration. Two prototype detector systems RASA 1 and RASA 2 have been developed, fabricated, and tested. The cryostats have been demonstrated to cool very large slightly greater than 10-cm long and 10-cm diameter detectors to temperatures as low as 50 K. The vacuum design has been demonstrated to show no measurable degradation over long time periods. The detector systems have been demonstrated to successfully instrument high-purity germanium detectors. Microphonic noise from the vibrating cooler has been completely eliminated in one case, serving as a demonstration of the total detector system viability. Microphonic noise remains the largest technical issue for these detector systems. The third generation, RASA 3, design incorporates mechanical changes to eliminate microphonic noise issues.
APPROVED FOR PUBLIC RELEASE