Measurement of radioactive contamination in the high-resistivity silicon CCDs of the DAMIC experiment

AGUILAR-AREVALO, A.; AMIDEI, D.; BERTOU, X.; BOLE, D.; BUTNER, M.; CANCELO, G.; VÁZQUEZ, A. CASTAÑEDA; CHAVARRIA, A.E.; NETO, J.R.T. DE MELLO; DIXON, S.; D'OLIVO, J.C.; ESTRADA, J.; MORONI, G. FERNANDEZ; TORRES, K.P. HERNÁNDEZ; IZRAELEVITCH, F.; KAVNER, A.; KILMINSTER, B.; LAWSON, I.; LIAO, J.; LÓPEZ, M.; MOLINA, J.; MORENO-GRANADOS, G.; PENA, J.; PRIVITERA, P.; SARKIS, Y.; SCARPINE, V.; SCHWARZ, T.; HARO, M. SOFO; TIFFENBERG, J.; MACHADO, D. TORRES; TRILLAUD, F.; YOU, X.; ZHOU, J.

JOURNAL OF INSTRUMENTATION

IOP PUBLISHING LTD

Año: 2015 vol. 10

1748-0221

We present measurements of radioactive contamination in the high-resistivity silicon charge-coupled devices (CCDs) used by the DAMIC experiment to search for dark matter particles. Novel analysis methods, which exploit the unique spatial resolution of CCDs, were developed to identify α and β particles. Uranium and thorium contamination in the CCD bulk was measured through α spectroscopy, with an upper limit on the 238U (232Th) decay rate of 5 (15) kg-1 d-1 at 95% CL. We also searched for pairs of spatially correlated electron tracks separated in time by up to tens of days, as expected from 32Si -32P or 210Pb -210Bi sequences of β decays. The decay rate of 32Si was found to be 80+110 -65 kg-1 d-1 (95% CI). An upper limit of ∼35 kg-1 d-1 (95% CL) on the 210Pb decay rate was obtained independently by α spectroscopy and the β decay sequence search. These levels of radioactive contamination are sufficiently low for the successful operation of CCDs in the forthcoming 100 g DAMIC detector.