DETERMINATION OF THE ISOTOPIC COMPOSITIONS OF SAMARIUM AND GADOLINIUMBY THERMAL IONIZATION MASS-SPECTROMETRY

Because of the large neutron capture cross sections for Sm-149, Gd-155 and Gd-157, accurate and sensitive isotopic analyses of samarium and gadolinium can be used to investigate natural neutron irradiation expo sure. in this paper, chemical separation procedures and mass spectrome tric methods for the precise determination of samarium and gadolinium isotopic compositions are described. Isotopic ratios other than Sm-144 /Sm-152, Gd-152/Gd-160, and Gd-154/Gd-160 for both samarium and gadoli nium commercial reagents, artificially neutron-irradiated reagents, an d geological reference reeks are quantified within 0.001% precision at the 95% confidence level. The present method can detect effects cause d by time-integrated neutron flux of 1.3 x 10(14) neutrons/cm(2) in th e environmental samples.