Lithium isotopic analysis by optical emission spectroscopy

Optical emission spectroscopy has been used to discriminate isotopic composition differences in the range of 92.6% (natural isotopic mixture) to 99.7% of /sup 7/Li. A desmountable hollow-cathode lamp was employed as an emission source for the lines /sup 2/S/sub 1/2/ - /sup 2/P/sub 1/2,3/2/ (670.8 nm), the isotopic displacement (15 pm) being of the same magnitude as the fine structure. The lines were resolved with a 3.4 m Ebert-Fastie spectrograph employed in a high dispersion mode (second order of a 1180 grooves/mm grating; theoretical resolution power: 360.000;linear reciprocal dispersion:77 pm/mm). The emission characteristics of the lamp (current intensity and argon gas pressure) were previously studied with a low resolution monochromator with photoelectric detection. In the spectrograph, the resolved doublets were photographied with a 1 N emulsion; the line transmittances were measured with a recording microphotometer. A plot of the line exposure ratio vs. isotopic composition of [/sup 2/S/sub 1/2/ -/sup 2/P/sub 3/2/ (/sup 7/Li)] relative to ([/sup 2/S/sub 1/2/ - /sup 2/P/sub 1/2/ (/sup 7/Li)] + [/sup 2/S/sub 1/2/ -/sup 2/P/sub 3/2/ (/sup 6/Li)]) gave a linear analytical curve (correlation coefficient = 0.992 for N = 4) over the tested range. (M.E.L.)