The neutron activation determination of lithium in the presence of alkali metals and magnesium

A neutron activation method for lithium in the presence of alkali metals or magnesium has been developed, utilizing the ⁶Li(n,α)³H and ¹⁶O(t,n)¹⁸F nuclear reactions. After a short thermal neutron irradiation with a. lithium standard, 112-min fluorine-18 is separated by a lead chlorofluoridc precipitation. The annihilation photons from the separated fluorine-18 are counted using 2 sodium iodide detectors, a fast-slow coincidence system and a multichannel analyzer. Precision in a synthetic l% lithium-in-sodium matrix was found to be ± 2.0% standard deviation, whereas the accuracy of the method is estimated to be ± 3% or better. The ultimate sensitivity in pure solution is estimated to be about 0.2 p.p.b. and in a sodium matrix about 0.5 p.p.m. The only interferences are several positron emitters, easily discriminated from by chemical separation, decay or by means of other nuclear parameters. Three hours are required for a duplicate determination, following initial sample preparation and dilution. To use the method, the lithium isotopic abundance must be known or determined by mass spectrometry because of the prevalence of depleted litliium in metal and salts.