Isotopic evidence of non-thermalized neutron irradiation in solar-gas-rich meteorites:Possibility of the interaction with solar neutrons and activity from the early S

摘要

150sm/149Sm and 158Gd/ 157Gd isotopic shifts in extraterrestrial materials provide evidence of the occurrenceof neutron capture reactions caused by the interaction of cosmic rays with the surface of the materials. TheSm and Gd isotopic shifts of chemical leachates from the Kapoeta meteorite, known as a solar-gas-richmeteorite, show a clear neutron capture record corresponding to the neutron fluence up to 9.0 x 1015n cm-2.The intensities of the neutron fluences of two fractions from Kapoeta significantly exceed what is expectedfrom the time for cosmic ray irradiation during the transit to Earth. Furthermore, the combination of Sm andGd isotopic shifts, defined as csm/ccd to understand the neutron energy spectrum, shows a different neutronirradiation environment for certain components of Kapoeta (Esm/E =1.9 ± 0.5, and 1.9 ± 0.7) from those ofother meteorites and lunar samples (ESmigGd = 0.4-0.9). The isotopic data of Sm and Gd from Kapoetasuggest the irradiation of non-thermalized neutrons with the energies over 1 eV from the early Sun.