Second generation ultralow background germanium gamma-ray spectrometer using super clean materials and improved multilayered cosimis ray anticoincidence and passive shielding

Large high resolution germanium gamma-ray detectors which are very nearly free of radioactivity are currently being produced. The background previously inherent to the cryostat assembly can now be virtually eliminated, and radioactivity from the environment adequately reduced by means of suitable shielding materials leaving cosmic ray induced activity as the major background component. Our efforts to measure the double beta decay of 76Ge as predicted by Grand Unified Theories have resulted in the development of a shielding system which reduces the continuum from this cosmic ray component by more than two orders of magnitude. This technique was published last year in the proceedings of the IEEE Nuclear Science Symposium. Our current paper describes the development of a low cost shielding system using liquid scintillator for the cosmic ray detector-neutron moderator which accounts for a fortyfold reduction in the cosmic continuum