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 ? and ? decays, and to search with high efficiency for the spatially-correlated decays of various radioisotope sequences. Using spatially-correlated ? decays, we measure a bulk radioactive contamination of 32Si in the CCDs of 140 ± 30 ?Bq/kg, and place an upper limit on bulk 210Pb of < 160 ?Bq/kg. Using similar analyses of spatially-correlated ? and ? decays, we set upper limits of < 11 ?Bq/kg (0.9 ppt) on 238U and < 7.3 ?Bq/kg (1.8 ppt) on 232Th in the bulk silicon. The ability of DAMIC CCDs to identify and reject spatially-coincident backgrounds, particularly from 32Si, has significant implications for the next generation of silicon-based dark matter experiments, where ?'s from 32Si decay will likely be a dominant background.
