Humidity-dependent radon retention in zeolite and non-zeolite sorbents for ²²⁵Ac production facilities

Efficient mitigation of ²²²Rn releases is essential for the safe handling of ²²⁶Ra and related α-emitters used in targeted radiotherapy. We evaluated a suite of sorbent materials, including silver-exchanged zeolites and activated carbon, under controlled laboratory conditions. Breakthrough experiments were conducted at defined dew points, and ²²²Rn retention was quantified using retention time (RT), adsorption coefficient (K), and radon retention capacity (RRC). Across all materials, K values decreased systematically with increasing dew point, confirming the strong competitive effect of water vapor. Silver-exchanged Ag-ETS-10 zeolite exhibited the highest initial performance (K up to ∼120m³/kg at low humidity), whereas activated carbon and Ag-MOR-2 showed lower but more humidity-tolerant behavior. Regeneration studies demonstrated that several Ag-zeolites retained a substantial fraction of their capacity after reuse. These findings highlight both the potential and the limitations of silver-based zeolites, particularly Ag-ETS-10, and underscore the importance of humidity control and regeneration protocols in the design of radon traps for isotope production facilities.