The isotope spectrum shift in the 6707.8A resonance line of lithium has been used for the assay of the isotopes Li 6 and Li 7. A hollow cathode source loaded with 4 mg of Li2SO4 is excited at 35 ma using purified helium at about 2- to 3-mm pressure as support gas. Characteristics, such as tube geometry, pressure, sample life, flow rate of gas, current, and anode-cathode spacing have been studied to give reproducible line intensity ratios. Precision of the method based on a 95 percent confidence interval is about 6 percent of the Li 6 content or, by difference, about 0.5 percent of the Li 7 content in natural material.
Spectra are obtained with a 21-foot, 30,000 lines per inch grating spectrograph using first order for which the Li 6–Li 7 isotope shift of 0.159A is readily separated. A multiplier phototube (1P28) set on the 4603A lithium line is used in an integrating circuit as an exposure meter.
© 1952 Optical Society of AmericaFull Article | PDF Article
James K. Brody
J. Opt. Soc. Am. 42(6) 408-415 (1952)
G. K. Werner, D. D. Smith, S. J. Ovenshine, O. B. Rudolph, and J. R. McNally
J. Opt. Soc. Am. 45(3) 202-205 (1955)
H. M. Crosswhite, G. H. Dieke, and C. Salmon Legagneur
J. Opt. Soc. Am. 45(4) 270-280 (1955)