Production Rate Measurement of Tritium and Other Cosmogenic Isotopes in Germanium with CDMSlite

Abstract

Future direct searches for low-mass dark matter particles with germanium detectors, such as SuperCDMS SNOLAB, are expected to be limited by backgrounds from radioactive isotopes activated by cosmogenic radiation inside the germanium. There are limited experimental data available to constrain production rates and a large spread of theoretical predictions. We examine the calculation of expected production rates, and analyze data from the second run of the CDMS low ionization threshold experiment (CDMSlite) to estimate the rates for several isotopes. We model the measured CDMSlite spectrum and fit for contributions from tritium and other isotopes. Using the knowledge of the detector history, these results are converted to cosmogenic production rates at sea level. The production rates in atoms/(kg•day) are 74 ± 9 for 3 H, 1.5 ± 0.7 for 55 Fe, 17 ± 5 for 65 Zn, and 30 ± 18 for 68 Ge.

Search for Low-Mass Dark Matter with CDMSlite Using a Profile Likelihood Fit

“…These can generally be ignored. The isotopes that undergo EC give discrete lines in the detectors below ∼10 keV and were observed in the CDMSlite Run 2 spectrum [37]. We describe analytic models for the tritium beta-decay spectrum and the EC lines.…”