Comparison of the cosmic-ray exposure conditions of several kinds of planetary materials studied from the Sm and Gd isotopic variations

Abstract

The surficial parts of solar planetary materials without the atmospheric layers have been exposed to cosmic rays, and have been subject to nuclear reactions such as neutron capture by the interactions of cosmic-ray irradiation. Then, the accumulation of neutron capture reactions produces the variations of isotopic compositions of several elements in the planetary materials. The isotopic variations caused by neutron capture effects can be used to characterize solar planetary materials. In particular, some isotopes such as ¹⁴⁹Sm and ¹⁵⁷Gd have very large neutron capture cross sections, their isotopic variations can be used as a natural dosimeter to quantify the neutrons arising in the planetary materials by cosmic-ray irradiation. The isotopic information can be effectively applied with a view to understanding the cosmic-ray exposure (CRE) histories and shielding conditions, which lead to study of the evolution processes of the solar planetary materials in space. This talk reviews the isotopic studies of Sm and Gd in several kinds of solar planetary materials that are caused by neutron capture reactions in space, and their practical applications for understanding the exposure histories and shielding conditions.