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.

Cosmogenic Activation in Double Beta Decay Experiments

“…[28], production rates specifically for tritium were deduced for common target materials in dark matter detectors, including germanium, following a selection of excitation functions including mainly those from TENDL and HEAD-2009 libraries at low and high energies, respectively. The result for natural germanium is in very good agreement with the measured production rates by EDELWEISS [100] and CDMSlite [101]. As it can be seen from Tables 1 and 2, the measured production rate by MAJORANA for enriched germanium is higher than for natural germanium; the explanation could be that cross sections increase with the mass number of the germanium isotope, following TENDL-2013 and HEAD-2009 data [28].…”

“…The obtained production rates were compared with ACTIVIA calculations using the Gordon et al parameterization for the neutron spectrum. • Measurements of the production rates of tritium and other cosmogenic isotopes were carried out also with the CDMS low ionization threshold experiment (CDMSlite) [101], from the analysis of data from the second run. The measured spectrum was modeled and fit considering contributions from different isotopes including tritium.…”

Constraints on dark photons and axionlike particles from the SuperCDMS Soudan experiment

“…In the iZIP analysis the considered masses range from 3 to 500 keV=c 2 , where the lower limit is chosen to avoid the rapidly dropping efficiency at lower energies. For CDMSlite we use the same selection criteria used for the Run 2 and Run 3 WIMP searches, for which the resolution model and detection efficiencies are already published [48,49,52]. Section IVA summarizes these results.…”

“…The original WIMP search analyses of CDMSlite Run 2 and 3 extended up to 2 keV and the efficiency curves that were only derived up to this energy do not cover the full range needed for this analysis. For CDMSlite Run 2, the efficiency curve was extended up to 30 keV for a background study [52]. This was accomplished by linearly interpolating the efficiency between the values measured at 2 keV and the 71 Ge peak at 10.37 keV; above this energy, electron recoils from 133 Ba calibration data were compared to Monte Carlo simulations, showing a drop in efficiency starting at ∼20 keV, which is attributed to saturation in one of the phonon sensors (see Ref.…”

“…This was accomplished by linearly interpolating the efficiency between the values measured at 2 keV and the 71 Ge peak at 10.37 keV; above this energy, electron recoils from 133 Ba calibration data were compared to Monte Carlo simulations, showing a drop in efficiency starting at ∼20 keV, which is attributed to saturation in one of the phonon sensors (see Ref. [52] for details). For this analysis, the efficiency for Run 3 was extended in the same manner.…”