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 the DAMIC at SNOLAB experiment. We utilize the exquisite spatial resolution of CCDs to discriminate between $\alpha$ and $\beta$ decays, and to search with high efficiency for the spatially-correlated decays of various radioisotope sequences. Using spatially-correlated $\beta$ decays, we measure a bulk radioactive contamination of ${}^{32}$Si in the CCDs of $140\pm 30$ $\mu$Bq/kg, and place an upper limit on bulk ${}^{210}$Pb of $<160\mu$Bq/kg. Using similar analyses of spatially-correlated bulk $\alpha$ decays, we set limits of $<11$ $\mu$Bq/kg (0.9 ppt) on ${}^{238}$U and of $<7.3$ $\mu$Bq/kg (1.8 ppt) on ${}^{232}$Th. The ability of DAMIC CCDs to identify and reject spatially-coincident backgrounds, particularly from ${}^{32}$Si, has significant implications for the next generation of silicon-based dark matter experiments, where $\beta$'s from ${}^{32}$Si decay will likely be a dominant background. This capability demonstrates the readiness of the CCD technology to achieve kg-scale dark matter sensitivity.

arXiv comment7 pages, 2 figures

References in corpus (9)

• Supersymmetric Dark Matter
• A History of Dark Matter
• Projected Sensitivity of the SuperCDMS SNOLAB experiment
• SENSEI: First Direct-Detection Constraints on sub-GeV Dark Matter from a Surface Run
• 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
• Measurement of radioactive contamination in the high-resistivity silicon CCDs of the DAMIC experiment
• Plasma effect in Silicon Charge Coupled Devices (CCDs)
• Naturally occurring ${}^{32}$Si and low-background silicon dark matter detectors

Cited by in corpus (7)

• Precision measurement of Compton scattering in silicon with a skipper CCD for dark matter detection
• Abatement of Ionizing Radiation for Superconducting Quantum Devices
• The DAMIC-M Low Background Chamber
• Multi-Amplifier Sensing Charge-coupled Devices for Next Generation Spectroscopy
• Characterization of the background spectrum in DAMIC at SNOLAB
• Spontaneous damage annealing reactions as a possible source of low energy excess in semiconductor detectors
• Removal of spallation-induced tritium from silicon through diffusion