Isotopic compositions of calcium, barium, neodymium and xenon in meteorites

The isotopic compositions of Ca, Ba and Nd in the Allende inclusion EK 1-4-1 resemble those of the terrestrial Ca, Ba and Nd exposed to neutron flux. The values of thermal neutron-capture cross-section were used previously to calculate the variations of the isotopic ratios. Much improved agreement between the calculated and observed isotopic ratios can be obtained if the 15 keV cross-section values for the neutron-capture processes are used. The results from the calculations of the isotopic anomalies observed for Ca, Xe, Ba and Nd are described. The isotopic anomalies of Ca, Ba, Nd and Xe observed in meteorites are explained as those due to the alteration of the isotopic ratios by the combined effect of mass fractionation, neutron-capture and cosmic-ray irradiation processes, which took place prior to and during the period of formation of the solar system. The neutron-capture process appears to have occurred at a temperature higher than that on the earth surface. (J.P.N.)