Neutron activation analysis of molybdenum, tin, tantalum and tungsten in silicates

The simultaneous determination of microgram to submicrogram amounts of molybdenum, tin, tantalum and tungsten in silicate rocks was arrived at using the Japanese neutron reactor JRR-1. A sample and comparative standard were irradiated simultaneously with a neutron flux of about 3‧10¹¹n‧cm^-2‧sec^-1 for 3 days (intermittently, 5 hr each day). After cooling for a day, the sample was decomposed with sulfuric and hydrofluoric acids in the presence of carriers and lanthanum hold-back carrier. Following the removal of lanthanide activities as fluorides, the fluoride complex of tantalum was extracted by isopropylacetone. Tin and molybdenum was precipitated with hydrogen sulfide from the remaining activities in the aqueous phase, to which boric and tartaric acids were added to mask hydrofluoric acid and tungstate ions, respectively. The α-benzoinoxime precipitation method was then applied for the recovery of bulk of tungsten in the filtrate from the sulfides. Further decontamination chemistry was carried out for each element. The amount of the elements was estimated by comparing ⁹⁹Mo(67 hr), ¹²¹Sn(27.5 hr), ¹⁸²Ta(111d) and ¹⁸⁷W(23.9 hr) β-activities isolated from the sample with those from the comparative standard. Sensitivities of the method were ∼1 ppm for Mo and Sn, ∼0.1 ppm for Ta and ∼0.01 ppm for W. (author)