Measurement of the bulk radioactive contamination of detector-grade silicon with DAMIC at SNOLAB
A. Aguilar-Arevalo, D. Amidei, D. Baxter, G. Cancelo, B.A. Cervantes Vergara, A.E. Chavarria, E. Darragh-Ford, J.C. D'Olivo, J. Estrada, F. Favela-Perez, R. Gaïor, Y. Guardincerri, T.W. Hossbach, B. Kilminster, I. Lawson, S.J. Lee, A. Letessier-Selvon, A. Matalon, P. Mitra, A. Piers, P. Privitera, K. Ramanathan, J. Da Rocha, Y. Sarkis, M. Settimo, R. Smida, R. Thomas, J. Tiffenberg, M. Traina, R. Vilar, A.L. Virto
Abstract
Abstract We present measurements of bulk radiocontaminants in the high-resistivity silicon CCDs from the DAMIC experiment at SNOLAB. We utilize the exquisite spatial resolution of CCDs to discriminate between α and β decays, and to search with high efficiency for the spatially-correlated decays of various radioisotope sequences. Using spatially-correlated β decays, we measure a bulk radioactive contamination of 32 Si in the CCDs of 140 ± 30 μBq/kg, and place an upper limit on bulk 210 Pb of < 160 μBq/kg. Using similar analyses of spatially-correlated α and β decays, we set upper limits of < 11 μBq/kg (0.9 ppt) on 238 U and < 7.3 μBq/kg (1.8 ppt) on 232 Th in the bulk silicon. The ability of DAMIC CCDs to identify and reject spatially-coincident backgrounds, particularly from 32 Si, has significant implications for the next generation of silicon-based dark matter experiments, where β's from 32 Si decay will likely be a dominant background.