Cosmogenic nuclides in the Košice meteorite: Experimental investigations and Monte Carlo simulations

Abstract

AbstractResults of nondestructive gamma‐ray analyses of cosmogenic radionuclides (7Be, 22Na, 26Al, 46Sc, 48V, 54Mn, 56Co, 57Co, 58Co, and 60Co) in 19 fragments of the Košice meteorite are presented and discussed. The activities varied mainly with position of fragments in the meteoroid body, and with fluxes of cosmic‐ray particles in the space affecting radionuclides with different half‐lives. Monte Carlo simulations of the production rates of 60Co and 26Al compared with experimental data indicate that the pre‐atmospheric radius of the meteoroid was 50 ± 5 cm. In two Košice fragments, He, Ne, and Ar concentrations and isotopic compositions were also analyzed. The noble‐gas cosmic‐ray exposure age of the Košice meteorite is 5–7 Myr, consistent with the conspicuous peak (or doublet peak) in the exposure age histogram of H chondrites. One sample likely contains traces of implanted solar wind Ne, suggesting that Košice is a regolith breccia. The agreement between the simulated and observed 26Al activities indicate that the meteoroid was mostly irradiated by a long‐term average flux of galactic cosmic rays of 4.8 particles cm−2 s−1, whereas the short‐lived radionuclide activities are more consistent with a flux of 7.0 protons cm−2 s−1 as a result of the low solar modulation of the galactic cosmic rays during the last few years before the meteorite fall.