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

Atmosphere-sourced argon contains traces of ⁴²Ar, whose β⁻-decaying progeny ⁴²K 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 ⁴²K behavior and suppression techniques, ⁴²Ar was produced by irradiating natural argon with 34 MeV ⁷Li³⁺ 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 ∼1×10⁶ atoms s⁻¹. The activated argon was injected into the one-ton SCARF cryostat, where two HPGe detectors monitored the subsequent ⁴²K activity build-up. A time-dependent model describing ⁴²Ar mixing and ⁴²K 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 ⁴²K background studies, essential for developing and validating suppression strategies for next-generation LAr-based rare-event experiments such as LEGEND-1000.