Determination of Strategic Metals in Graphitic Formations by the Methods of Neutron Activation Analysis with a Californium Source

The content of a number of strategic metals (Au, Sc, La, Sm, Eu, Dy) was determined by the method of instrumental neutron activation analysis (INAA) at the original device with a radionuclide neutron source based on ²⁵²Cf at a level comparable to their clarks in graphite-bearing rocks of the south of the Russian Far East. The key advantage of INAA in the analysis of difficult to dissolve carbon-containing materials is the non-destructive nature of the method. The proposed methodological approach avoids the complex procedure of sample decomposition, analyte separation and associated problems (dissolution, contamination and losses). Introduction into the activation zone up to 300 cm³ of a carbonaceous sample with at least 87 wt % carbon content was not shown significant influence of the carbon on the INAA results. The detection limits were calculated for analyzed elements. The possibility to determine in natural high-carbon objects the contents of Sc, La, Sm, Eu, Dy at the level below Clark level was confirmed. No significant dependence of INAA results on the density and coarseness of the tested samples was revealed. The results of determination of strategic metals in graphite-bearing metamorphic rocks of the south of the Russian Far East for two different INAA variants (reactor and with ²⁵²Cf radionuclide source) were compared. The comparison shows that our data obtained at the device with the ²⁵²Cf radionuclide source for most of the studied elements well agree with the results obtained earlier at the WWR-M reactor at the St. Petersburg Institute of Nuclear Physics named after B.P. Konstantinov. At the same time, the possibility to irradiate samples with volume of 50–100 cm³ provides high representativeness of the INAA method at ²⁵²Cf activation. It was shown that INAA method with radionuclide source ²⁵²Cf is suitable for effective determination of trace elements content in carbon-containing samples of mineral raw materials.