Cosmogenic Activation and Background Mitigation Studies for the DarkSide-20k Liquid Argon Detector

Mitigating cosmogenic backgrounds is crucial for achieving the ultra-low background requirements of the DarkSide-20k liquid argon time projection chamber (TPC). We present a detailed study of isotope production and activation in the TPC argon and structural materials induced by cosmic-ray secondaries using the FLUKA Monte Carlo transport code. Particular emphasis is placed on the production of ³⁹Ar from ⁴⁰Ar, for which activation rates obtained from FLUKA are compared with independent cross-section predictions from TALYS, INCL and IAEA dataset, using cosmic-ray flux spectra parameterized by Mei and Hime. The induced activities of several β–n emitting isotopes are also evaluated, and event-selection cuts are developed to suppress their contributions to the low-energy background. We further estimate activation rates expected at the LNGS site and during argon storage and transport, quantifying their potential impact on the initial detector background budget. These results provide a validated framework for background control and input for pre-operation purification strategies in DarkSide-20k.