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Germanium detector arrays are needed for low-level counting facilities. The applications in such user facilities include the characterization of low-level radioactive samples. In addition, the same detector arrays can perform important fundamental physics measurements, including the search for rare-events like neutrino-less double-beta decay. Recently, relatively large detectors (approximately 700 g) having relatively small (approximately few mm) p+ contacts are being investigated as a possible detector basis for these detector arrays. A detector having a small, relatively low capacitance, p+ contact has been fabricated as a demonstration. The development and properties of the detector system are discussed., Published in Proceedings of Monitoring Research Review (30th): Ground-Based Nuclear Explosion Monitoring Technologies, Portsmouth, VA, 23-25 Sep 2008, p768-771, sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). Prepared in collaboration with Pacific Northwest National Laboratory. The original document contains color images.

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 Sampler/Analyzer (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., Published in Proceedings of Monitoring Research Review (30th): Ground-Based Nuclear Explosion Monitoring Technologies, Portsmouth, VA, 23-25 Sep 2008, p772-777, sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). Prepared in collaboration with the Pacific Northwest National Laboratory, and Air Force Technical Applications Center. The original document contains color images.

Compact maintenance-free mechanical cooling systems are being developed to operate large volume (approx. 570 cm(3), approx. 3 kg, 140 % or larger) germanium detectors for field applications. A new generation of domestically produced Stirling-cycle mechanical coolers provide the basis for this evolution. When properly instrumented, these systems can cool the very largest volume germanium detectors with no maintenance or liquid nitrogen requirements. The user can leave these systems unplugged on the shelf until needed. The maintenance-free operating lifetime of these detector systems will exceed 5 years. These features are necessary for remote long-duration liquid-nitrogen free deployment of large-volume germanium gamma-ray detector systems for nuclear explosion monitoring. The Radionuclide Aerosol Sampler/Analyzer (RASA) will greatly benefit from the availability of such detector systems by eliminating the need for liquid nitrogen at RASA sites while still allowing the very largest available germanium detectors to be utilized for the highest sensitivity measurements. To reliably provide such systems, the basic technical fundamentals are being investigated: temperature, vacuum, and vibration. A RASA cryostat and detector have been developed and fabricated. The cryostat has been tested and verified to cool a very large (as large as 10-cm long by 10-cm diameter) detector to temperatures as low as 50 degrees Kelvin. The system is free of microphonic noise with the cooler operating at full power. The lower detector operating temperature, coupled with robust detector fabrication technology, provides a detector system that will operate reliably for a very long time (5+ years)., Presented at the Monitoring Research Review (29th): Ground-Based Nuclear Explosion Monitoring Technologies, held in Denver, CO on 25-27 September 2007. Published in the Proceedings of the Monitoring Research Review (29th): Ground-Based Nuclear Explosion Monitoring Technologies, p770-778, 2007. Sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). The original document contains color images.

Germanium detector arrays are needed for low-level counting facilities. The applications of such user facilities include characterization of low-level radioactive samples. In addition, the same detector arrays can perform important fundamental physics measurements including the search for rare-events like neutrinoless double-beta decay. Germanium coaxial detectors having segmented outer contacts can provide sensitivity improvement in low-background measurements. The segmented outer detector contact allows pulse-shape analysis measurements that provide additional background reduction. Currently, n-type (reverse electrode) germanium coaxial detectors are used whenever a segmented coaxial detector is needed because the outer boron (electron barrier) contact is thin and can be relatively easily segmented. Coaxial detectors fabricated from p-type germanium cost less, usually have better energy resolution, and can be larger than n-type coaxial detectors. However, it is difficult to reliably segment p-type coaxial detectors because thick (tilde 1 mm) lithium-diffused (hole barrier) contacts are the standard outside contact for p-type coaxial detectors. During this Phase II small business innovation research grant (SBIR), we are developing thinner, segmented, and stable lithium-diffused contacts. Many small planar test detectors have been fabricated with segmented lithium-diffused contacts. Center contact and guard-ring structures have been fabricated on the detectors to study the rectification and segmentation properties of lithium-diffused contacts. Fabrication techniques have been established that successfully produce repeatable rectification and segmentation. The rectification and segmentation appear to be stable with respect to modest temperature cycles. These results are fundamental steps toward developing segmented lithium-diffused contacts for p-type coaxial detectors., Presented at the Monitoring Research Review (29th): Ground-Based Nuclear Explosion Monitoring Technologies, held in Denver, CO on 25-27 September 2007. Published in the Proceedings of the Monitoring Research Review (29th): Ground-Based Nuclear Explosion Monitoring Technologies, p764-769, 2007. Sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). The original document contains color images.