Cosmogenic activation of materials used in rare event search experiments

Abstract

We evaluate the cosmogenic production rates in some materials that are commonly used as targets and shielding/supporting components for detecting rare events. The results from Geant4 simulations and the calculations of ACTIVIA are compared with the available experimental data. We demonstrate that the production rates from the Geant4-based simulations agree with the available data reasonably well. As a result, we report that the cosmogenic production of several isotopes in various materials can generate potential backgrounds for direct detection of dark matter and neutrinoless double-beta decay.

Cosmogenic activation of germanium used for tonne-scale rare event search experiments

“…The Geant4 package (V9.5p02 + Shielding physics list) used for this study is the same as the one used in our previous study [11]. We simulate two detector geometries in this work.…”

“…However, for the production of the other two critical isotopes, 65 Zn and 68 Ge, the difference between ACTIVIA and the EDELWEISS data is a factor of more than 2 depending on the neutron flux used in ACTIVIA. For example, for the production of 68 Ge, the difference between ACTIVIA1 and the EDELWEISS data is at least a factor of 7.2 and the difference between ACTIVIA2 and the EDELWEISS data is at least a factor of 3 since ACTIVIA2 used a more accurate neutron spectrum based on the fit to the data [11].…”

“…The energy spectra of surface muons, slow neutrons and fast neutrons come from the modified Gaisser's formula [14,15], the air shower simulation results using MCNPX package [16] and the measurements by Gordon [17], respectively. Our previous work [11] has detailed the energy spectrum, energy range, flux and distribution for surface muons and neutrons. For surface protons, the energy spectrum from the work by Hagmann et al [18] is used to sample protons right above the simulation geometry.…”

“…Compared with ACTIVIA [8], which is a popular C ++ computer package used in the field of low-background experiments for calculating the cross-section, production rates and decay yields of cosmogenic isotopes based on data tables and semi-empirical formulae, Geant4-based Monte Carlo simulations [9,10] have been proven to be a more reliable evaluation tool for estimating the cosmogenic production rates in various materials used for xenon-based rare event search experiments [11]. This motivates us to estimate the production rates of cosmogenic isotopes in germanium by using Geant4 simulations and ACTIVIA to evaluate which package is more reliable for germanium-based experiments exploring rare event physics by comparing with the available experimental data.…”

Identification of radiopure titanium for the LZ dark matter experiment and future rare event searches

“…This is significant since radioactive isotopes can be produced by neutron-induced spallation reactions whilst the material is still above ground. Stainless steel contains isotopes of iron, nickel and chromium that can be activated to form radioisotopes such as 56 Co, 58 Co, 54 Mn and 48 V [5], whilst in titanium, only the production of 46 Sc is a concern [6]. Although the LUX experiment [7][8][9][10], LZ's most recent predecessor, successfully manufactured and deployed a cryostat constructed from low-activity titanium to contain 350 kg of LXe [11], securing similarly radiopure material has proved non-trivial across the field of rare-event search experiments.…”