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Title: Measurement of Radioactive Contamination in the High-Resistivity Silicon CCDs of the DAMIC Experiment

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 b decays. The decay rate of 32Si was found to be 80+110-65 (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. Furthermore, these levels of radioactive contamination are sufficiently low for the successful operation of CCDs in the forthcoming 100 g DAMIC detector.
Authors:
 [1]
  1. Universidad Nacional Autonoma de Mexico (Mexico). et al.
Publication Date:
OSTI Identifier:
1223218
Report Number(s):
FERMILAB-PUB--15-315-A-CD-E
Journal ID: ISSN 1748-0221; arXiv eprint number arXiv:1506.02562
Grant/Contract Number:
AC02-07CH11359
Type:
Accepted Manuscript
Journal Name:
Journal of Instrumentation
Additional Journal Information:
Journal Volume: 10; Journal Issue: P08014; Journal ID: ISSN 1748-0221
Publisher:
Institute of Physics (IOP)
Research Org:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Contributing Orgs:
DAMIC Collaboration
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY dark matter dectors (WIMPs, axions, etc.); solid state detectors; very low-energy charged particle detectors; search for radioactive and fissile materials