Measurement Of Radioactive Contamination In The Ccd'S Of The Damic Experiment

DAMIC (Dark Matter in CCDs) is an experiment searching for dark matter particles employing fully-depleted charge-coupled devices. Using the bulk silicon which composes the detector as target, we expect to observe coherent WIMP-nucleus elastic scattering. Although located in the SNOLAB laboratory, 2 km below the surface, the CCDs are not completely free of radioactive contamination, in particular coming from radon daughters or from the detector itself. We present novel techniques for the measurement of the radioactive contamination in the bulk silicon and on the surface of DAMIC CCDs. Limits on the Uranium and Thorium contamination as well as on the cosmogenic isotope Si-32, intrinsically present on the detector, were performed. We have obtained upper limits on the U-238 (Th-232) decay rate of 5 (15) kg(-1)d(-1) at 95% CL. Pairs of spatially correlated electron tracks expected from Si-32-P-32 and (210)pb-Bi-210 beta decays were also measured. We have found a decay rate of 80(-65)(+110) Kg(-1)d(-1) for Si-32 and an upper limit of similar to 35 kg(-1)d(-1) for Pb-210, both at 95% CL.