Determination of uranium, thorium, and 20 other elements in high-purity tungsten by radiochemical neutron activation analysis

A radiochemical neutron activation analysis method for the determination of 22 elements in high-purity tungsten has been developed. For the assay of indicator radionuclides with long half-lives, the radiochemical separation was performed from HF/H2O2, HF/NH4F and HCl/H2SO4 media by a combination of cation and anion exchange on a Dowex 50 W x 8 and Dowex 1 x 8 column. An effective removal of the matrix-produced radionuclides of W and Re was achieved. U was determined via 140La, the daughter nuclide of the fission product 140Ba. Limits of detection of 2 ng/g for U and 0.02 ng/g for Th can be achieved. For the other elements, the limits of detection are between 0.004 ng/g (Sc) and 200 ng/g (Sr). The elements Hf, Ta and Sb could be determined by instrumental neutron activation analysis. This method was applied to the analysis of two tungsten powder samples of different purity grade. The results and limits of detection are compared with those of other methods. (orig.)