Characterization of the Natural Gamma Ray Background Emission at the CDMS Detector Testing Facility

Andrew Emerick and Karley Weir

University of Minnesota

Methods of Experimental Physics Spring 2012

Abstract

We employed a high-purity germanium (HPGe) detector to characterize the natural gamma ray background in the Cryogenic Dark Matter Search (CDMS) Detector Testing Facility. We were concerned primarily with a strong 40K source of unknown origin which has been interfering with the detector testing. In order to properly shield against the background and the 40K source, a proper understanding of the background is necessary. To this end, we constructed a lead enclosure around the HPGe to determine how effective lead shielding would be at attenuating the background gamma rays. Using this lead enclosure, we determined what, if any, directional component existed to the 40K background, and observed other non-homogeneous characteristics to the natural background.