Isotopic selectivity and ionization efficiency are discussed in the isotope separation processes of Gd based on polarization selection rules and based on isotope shift. Enrichment of ^157Gd to 90% was experimentally demonstrated using both methods together. The features of the absorption spectra of Gd in yellow-red and blue regions were summarized. Absorption spectra that are suitable for separation process using isotope shift were examined and an obtainable selectivity and efficiency are quantitatively calculated

Isotopic selectivity and ionization efficiency are discussed in the isotope separation processes of Gd based on polarization selection rules and based on isotope shift. Enrichment of 157 Gd to 90% was experimentally demonstrated using both methods together. The features of the absorption spectra of Gd in yellow-red and blue regions were summarized. Absorption spectra that are suitable for separation process using isotope shift were examined and an obtainable selectivity and efficiency are quantitatively calculated.