Measurement of the bulk radioactive contamination of detector-grade silicon with DAMIC at SNOLAB

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