Low Background Measurements of Radioisotope Contamination via Gamma Spectroscopy

Abstract

Astronomical observations have shown that most of the universe is made up of dark matter and dark energy rather than the normal matter and energy we observe every day. The Cryogenic Dark Matter Search, CDMS, is working to detect dark matter particles with very pure, super-cooled germanium crystals. In order to be sensitive enough to discover weakly interacting dark matter the germanium detectors must be well shielded by placing them deep underground and surrounding them with lead in addition to many other means. In this research project the low level contamination of materials used in the construction of current and planned detector assemblies was measured in order to reduce the background of future CDMS detectors. The isotopes investigated included U-238, Th-232, K-40, Co-60 and Cs-137. The contamination measurements were done via gamma spectroscopy in a low background detector, named Gopher, located in the Soudan mine. A selection of the analyzed samples are presented here, as well as the results of a shielding upgrade to Gopher that improved its measurement capabilities considerably. The results obtained in Gopher are very important to improving the CDMS experiment in the future and it's new shield design can be used in upgrading similar detectors elsewhere.