MEASUREMENT OF THE LITHIUM ISOTOPIC CONCENTRATION

A method for determining the atomic proportions of Li-6 and Li-7 isotopes in enriched (LiF)-Li-6, (LiF)-Li-7 and lithium metallic samples is presented. This study is based on measuring the energy spectra of alpha particles from proton-induced Li-7(p,alpha)He-4 and F-19(p,alpha)O-16 nuclear reactions and those of backscattered protons. The enriched LiF targets were obtained by thermal evaporation of thermoluminescent dosimetry chips, TLD-700 ((LiF)-Li-7) and TLD-600 ((LiF)-Li6)), onto self-supporting carbon substrates. Targets of metallic lithium were prepared in the same way. The Li-6 enriched TLD-600 sample was found to contain 4.78 at.% of Li-7; however, no significant amount of Li-6 was found in the TLD-700 sample. A 7.57 at.% concentration of Li-6 in lithium metallic target was determined by using the TLD-700 as a Li-7 isotope content standard. This value is consistent with the reported 7.5 at.% natural abundance of Li-6.