Study of alpha background in a dark matter detector

Abstract

Alpha background, specifically from radon and its progeny in the uranium and thorium chains, has been a major issue in dark matter detectors. This work focuses on alpha background presence in the DMTPC experiment by examining the energy distribution and the rate of alpha tracks in detector's fiducial volume. It was found that the rate and the energy distribution of alpha tracks are inconsistent with radon buildup in the detector. This was verified by replacing stainless steel materials with copper that is known to have lower uranium concentration. The alpha background was reduced 5 fold confirming that the origin of alphas is from early uranium decay chain, not radon buildup in the detector.