Design, construction, and assessment of a neutron shield for CDMS test facilities.

Abstract

The Cryogenic Dark Matter Search (CDMS) experiment is an effort to detect dark matter in the form of weakly interacting massive particles (WIMPs). CDMS utilizes cryogenic semiconductor detectors in order to accomplish this. At the University of Minnesota the testing and characterization of these detectors is one of the main responsibilities. To further improve characterization of the detectors, it is important to reduce the number of background events from reaching the detector as best as possible. This is especially significant in the case of neutrons since they produce nuclear recoils in the crystal similar to what is expected of a WIMP; these signals would be indistinguishable from each other in the data. Thus, the project was to build a neutron shield made of high-density polyethylene which would surround the dilution refrigerator where the detector was operated. Data was taken with the detector exposed to a Cf- 252 (neutron) source with and without the shield in order to determine the shielding capability of the polyethylene. The data was analyzed and the results demonstrated a consistent shielding effect on events appearing as nuclear recoils, suggesting that the neutron shield is fulfilling its desired purpose.