42Ar production and injection to a liquid argon environment for background mitigation studies

Atmosphere-sourced argon contains traces of 42 Ar, whose β − -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(5) nA and 140(5) nA, yielding ( 477 ± 9 ) Bq during two weeks, corresponding to a production rate of ∼ 1 × 1 0 6 atoms s −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 .