Improving the Radiation Damage Resistance of Germanium Detectors

Ever larger gamma ray detector arrays made from germanium crystals are being used, and will continue to be used, in nuclear physics research. However, radiation damage limits the time that a germanium detector can be used; for example, an average Gammasphere detector may function in an array for several months before the effects of the radiation damage become intolerable. Mitigating the effects of radiation damage would significantly improve operation of germanium detector arrays and could greatly reduce the need for annealing detectors in radiation damage environments. By far, the operating temperature is the most important parameter affecting the degradation of detectors caused by radiation damage. This project will analyze the effect of temperature reduction well below the ~95K range, where liquid-nitrogen cooled detectors operate, and design viable options to cool complex arrays to much colder temperatures. Phase I addressed the preliminary complexities of designing and fabricating a mechanically-cooled prototype detector system with the size and cryostat geometry of a Gammasphere detector. This system was shown to achieve reliable operating temperatures of approximately 50K. Phase II will develop, fabricate, and test a mechanically-cooled germanium detector system that will be fit into a Gammasphere. The engineering complexities of multiple system arrays will to be addressed. Commercial Applications and Other Benefits as described by the awardee: The integration of mechanically-cooled, multiple detector systems into complex arrays would reduce the physical size of the array, improve efficiency and longevity, and greatly diminish costs and maintenance of large-array diagnostic detector systems. The technology should impact the operation of germanium detectors at nuclear physics user facilities like Gammasphere, many of which are DOE supported.