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

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Sm-150/Sm-149 and Gd-158/Gd-157 isotopic shifts in extraterrestrial materials provide evidence of the occurrence of neutron capture reactions caused by the interaction of cosmic rays with the surface of the materials. The Sm and Gd isotopic shifts of chemical leachates from the Kapoeta meteorite, known as a solar-gas-rich meteorite, show a clear neutron capture record corresponding to the neutron fluence up to 9.0 x 10(15) n cm(-2). The intensities of the neutron fluences of two fractions from Kapoeta significantly exceed what is expected from the time for cosmic ray irradiation during the transit to Earth. Furthermore, the combination of Sm and Gd isotopic shifts, defined as epsilon(Sm)/epsilon(Gd) to understand the neutron energy spectrum, shows a different neutron irradiation environment for certain components of Kapoeta (epsilon(Sm)/epsilon(Gd) = 1.9 +/- 0.5, and 1.9 +/- 0.7) from those of other meteorites and lunar samples (epsilon(Sm)/epsilon(Gd) = 0.4-0.9). The isotopic data of Sm and Gd from Kapoeta suggest the irradiation of non-thermalized neutrons with the energies over 1 eV from the early Sun.
2009-07-30