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

Abstract

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 $\alpha$ and $\beta$ particles. Uranium and thorium contamination in the CCD bulk was measured through $\alpha$ spectroscopy, with an upper limit on the ${}^{238}$U (${}^{232}$Th) 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 ${}^{32}$Si-${}^{32}$P or ${}^{210}$Pb-${}^{210}$Bi sequences of $\beta$ decays. The decay rate of ${}^{32}$Si was found to be $80_{-65}^{+110}$ kg${}^{-1}$ d${}^{-1}$ (95% CI). An upper limit of $\sim$35 kg${}^{-1}$ d${}^{-1}$ (95% CL) on the ${}^{210}$Pb decay rate was obtained independently by $\alpha$ spectroscopy and the $\beta$ decay sequence search. These levels of radioactive contamination are sufficiently low for the successful operation of CCDs in the forthcoming 100 g DAMIC detector.

18 pages, 20 figures

References in corpus (2)

• Asymmetric Dark Matter: Theories, Signatures, and Constraints
• CDMSlite: A Search for Low-Mass WIMPs using Voltage-Assisted Calorimetric Ionization Detection in the SuperCDMS Experiment

Cited by in corpus (19)

• DarkSide-20k: A 20 Tonne Two-Phase LAr TPC for Direct Dark Matter Detection at LNGS
• Projected Sensitivity of the SuperCDMS SNOLAB experiment
• Search for low-mass WIMPs in a 0.6 kg day exposure of the DAMIC experiment at SNOLAB
• Results on Low-Mass Weakly Interacting Massive Particles from an 11 kg-day Target Exposure of DAMIC at SNOLAB
• First Direct-Detection Constraints on eV-Scale Hidden-Photon Dark Matter with DAMIC at SNOLAB
• Measurement of the ionization produced by sub-keV silicon nuclear recoils in a CCD dark matter detector
• Directional recoil detection
• Model-independent determination of the Migdal effect via photoabsorption
• Cosmogenic activation of materials
• Cosmogenic activation of silicon
• Zwicky Transient Facility constraints on the optical emission from the nearby repeating FRB 180916.J0158+65
• Measurement of the bulk radioactive contamination of detector-grade silicon with DAMIC at SNOLAB
• Naturally occurring ${}^{32}$Si and low-background silicon dark matter detectors
• A high-resolution CMOS imaging detector for the search of neutrinoless double $\beta$ decay in ${}^{82}$Se
• Abatement of Ionizing Radiation for Superconducting Quantum Devices
• Particle detection and tracking with DNA
• A boron-coated CCD camera for direct detection of Ultracold Neutrons (UCN)
• Characterization of the background spectrum in DAMIC at SNOLAB
• PSF-like Alpha-Particle Events in LSST Images