Determination of lanthanum in large steel samples by the neutron activation method

In view of the inhomogeneous distribution of lanthanum in steel, large samples should be used for the determination of this element. The method elaborated consists in the preparation of an average samople by dissolving 50 g steel and analysing an aliquot of the obtained solution corresponding to 0.5 g of steel. In order to reduce the activity of the sample, iron and some other elements are separated from the steel solution by electrolysis prior to irradiation. The amount of lanthanum contamination introduced during the pre-irradiation treatment of the sample is relatively low (10^?10–10^?9 g) if the treatment is carried out under suitable conditions. The post-irradiation treatment consists in the separation of²⁴Na by shaking the sample solution with Sb₂O₅. The¹⁴⁰La-activity is measured by means of a γ-spectrometer (1.6 MeV photopeak).