Pulse tube refrigeration for detectors

High purity germanium (HPGe) gamma-ray detectors are used for nondestructive assay. Liquid nitrogen (LN2), a cryogen, is commonly used to cool these detectors. Cryogen use is associated with several health risks and operational problems. This has prompted the development of cryogen-free refrigeration. A new generation of commercial pulse tube refrigerator (PTR) has been developed during the last decade. A unique feature of the PTR is the absence of cold moving parts. This significantly reduces the generated noise and vibration. In the following report, LN2, a modified Joule-Thompson cooler, and a PTR unit are examined and their cooling effectiveness with HPGe gamma-ray detectors compared. Overall, PTR is an engineering equivalent to LN2 and modified Joule-Thompson cooler systems used in gamma spectroscopy and eliminate the health and physical hazards associated with LN2 systems without adding hazards. (author)