${}^{42}$Ar Production and Injection to a Liquid Argon Environment for Background Mitigation Studies

Abstract

Atmosphere-sourced argon contains traces of ${}^{42}$Ar, whose ${\beta }^{-}$-decaying progeny ${}^{42}$K represents a significant intrinsic background for rare-event experiments using liquid argon (LAr) as detector or shielding medium. Understanding and mitigating this background is crucial for current and future large-scale detectors in neutrino and dark-matter physics. To enable controlled studies of ${}^{42}$K behavior and suppression techniques, ${}^{42}$Ar was produced by irradiating natural argon with 34 MeV ${}^7$Li${}^{3+}$ ions at the Maier-Leibnitz-Laboratorium tandem accelerator, using beam currents of $101\pm 5$ nA and $140\pm 5$ nA, yielding $476\pm 9$ Bq within two weeks, corresponding to a production rate of $\sim 1\times 10^6$ atomss${}^{-1}$. The activated argon was injected into the one-ton SCARF cryostat, where two HPGe detectors monitored the subsequent ${}^{42}$K activity build-up. A time-dependent model describing ${}^{42}$Ar mixing and ${}^{42}$K equilibration in LAr yielded characteristic mixing time constants between one and two days. The established production and injection capability provides a reproducible platform for high-statistics ${}^{42}$K background studies, essential for developing and validating suppression strategies for next-generation LAr-based rare-event experiments such as LEGEND-1000.

arXiv comment8 pages, 8 figures