⁵³Mn and ⁶⁰Fe in iron meteorites – new data and model calculations

We measured specific activities of the long-lived cosmogenic radionuclides ⁶⁰Fe in 28 and ⁵³Mn in 41 iron meteorites. Accelerator mass spectrometry was applied at the 14-MV Heavy Ion Accelerator Facility at ANU Canberra for all samples but two which were measured at the Maier-Leibnitz Laboratory, Munich. For the large iron meteorite Twannberg (IIG) we measured six samples for ⁵³Mn. This work doubles the number of existing individual ⁶⁰Fe data and quadruples the number of iron meteorites studied for ⁶⁰Fe. We also significantly extended the entire ⁵³Mn database for iron meteorites. The ⁵³Mn data for the iron meteorite Twannberg vary by more than a factor of 30, indicating a significant shielding dependency. In addition, we performed new model calculations for the production of ⁶⁰Fe and ⁵³Mn in iron meteorites. While the new model is based on the same particle spectra as the earlier model, we no longer use experimental cross sections but instead use cross sections that were calculated using the latest version of the nuclear model code INCL. The new model predictions differ substantially from results obtained with the previous model: Predictions for the ⁶⁰Fe activity concentrations are about a factor of two higher and for ⁵³Mn they are ~30% lower compared to the earlier model, which gives a better agreement with experimental data.