An ultralow background germanium gamma-ray spectrometer

Abstract An ultralow background 135 cm 3 intrinsic Ge detector has been developed providing a new benchmark in low background gamma-ray spectroscopy. The radioactive background from construction materials has been reduced by more than two orders of magnitude over conventional low background gamma-ray spectrometers. The sources of background in standard commercial cryostats have been identified and eliminated. Data taken with this prototype after elimination of most cosmic ray induced background are presented. The first application of the prototype as well as a large, second generation, multicrystal (∼ 1440 cm 3 ) germanium detector will be an ultrasensitive search for neutrinoless and two-neutrino double beta decay of 76 Ge.