Solar and galactic cosmic-ray records of the Fermo (H) chondrite regolith breccia

We demonstrate the presence of solar flare as well as neutron capture effects in the isotopic composition of rare gases in the Fermo regolith breccia acquired on its parent body based on the measurements of tracks, rare gases and radionuclides. The track density along a 3.2 cm long core decreases by a factor of about 6 and by more than a factor of 13 within the meteorite, indicating small (2-9 cm) and asymmetrical ablation. Rare gases show a large trapped component; the isotopic ratios, particularly Ne-20/Ne-22 similar or equal to 11 and Ne-20/Ar-36 = 10 are indicative of a solar component. The galactic cosmic-ray exposure age is determined to be 8.8 Ma. Activities of a dozen radionuclides ranging in half-life from 16 day V-48 to 0.73 Ma Al-26 are consistent with their expected production rates. Track, rare gas and radionuclide data show that the meteoroid was a small body (less than or equal to 120 kg) and had a simple, one-stage exposure history to cosmic rays in the interplanetary space. However, Kr-82 and Xe-128 show an excess due to neutron irradiation on the parent body of the meteorite. The presence of solar gases and the neutron capture effects indicate several stages of irradiation on the parent asteroid. The chemical composition of Fermo confirms that it belongs to the H group of ordinary chondrites with lithic clasts having varying compositions. delta N-15 is found to be 8.3 +/-1.2%, close to the typical values observed in H chondrites.