¹Farshid Nozarian,²Suzette Timmerman,¹Ingo Leya
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70201]
¹Physics Institute, Space Science and Planetology, University of Bern, Bern, Switzerland
²Institute of Geological Sciences, University of Bern, Bern, Switzerland
Published by arrangement with John Wiley & Sons

The 40K-K cosmic-ray exposure (CRE) dating system offers a promising method for determining exposure ages of iron meteorites by combining the radioactive cosmogenic 40K with the stable cosmogenic isotopes 39K and 41K. However, earlier applications relied on semi-empirical production models and inconsistent analytical data sets, limiting their reliability. This study presents a comprehensive reassessment of the 40K-K and 4He/21Ne system using state-of-the-art model calculations. Production rates of 39K, 40K, and 41K were simulated with the GEANT4–INCL++6 framework, incorporating updated excitation functions and fully considering depth-dependent shielding effects. The resulting model yields physically robust relationships between K isotopes and noble gas shielding proxies, such as 4He/21Ne. In addition to revisiting the classical approach used by Voshage and co-workers, we introduce two new alternative strategies for calculating CRE ages: a two-component mixing model and a native-K correction approach that mitigates contamination effects. Overall, these developments establish a more accurate and physically consistent framework for future applications of the 40K–K system in cosmochemistry and studies of galactic cosmic rays.