High-Purity Germanium Crystals for Low Background Counting Arrays

The next generation of DOE low-background user facilities will require suitable germanium crystal production capabilities. These crystal-growth techniques must accommodate the handling of highly enriched germanium in a manner consistent with low background counting. In this project, germanium crystal growth techniques will be experimentally developed specifically for the growth of crystals for low-background counting arrays. The approach will include the development of (1) inexpensive and modular crystal pullers that are suitable for installation in low-background facilities, and (2) crystal-growth techniques that minimize the contamination of highly enriched germanium. In Phase I, an inexpensive and modular prototype germanium crystal puller was developed. Using this puller, germanium crystals were successfully grown and demonstrated to have properties well suited to the fabrication of low-background germanium detectors. During the Phase II, the crystal growth techniques will be refined to grow large high-purity germanium crystals suitable for the fabrication of large low-background germanium detectors. Commercial Applications and other Benefits as described by the awardee: The germanium crystal growth technique should greatly decrease the cost of large arrays of low background germanium detectors. These detector arrays are at the forefront of physics in the search for rare processes such as neutrinoless double-beta decay. Such detector arrays also could be used for low-level counting facilities to characterize radioactive materials.