Application of NAA for chemical characterization of geological materials

Neutron Activation Analysis (NAA) is a nuclear analytical technique, suitable for simultaneous multielemental determination in variety of geological matrices. Geological matrices being complex in nature, involves tedious sample dissolution procedures for complete compositional characterization. For last five decades, Analytical Chemistry Division at BARC, Mumbai is routinely involved in analysis of various geological samples such as rocks, ores, minerals, sediments, soils, employing non-destructive techniques such as NAA. Research reactors at BARC, namely Apsara, CIRUS, Dhruva, Critical facility and KAMINI reactor at Kalpakkam were used for those analyses. In this work, soil samples were analysed for major, minor and trace elements. The samples were homogenized and representative aliquots were irradiated along with reference standards (CRM's). The duration of irradiation and flux were chosen judiciously, to encompass the complete characterization of soil. The irradiation facilities used were: graphite reflector position in the critical facility (CF) reactor (~10⁷ n cm^-2 s^-1), the pneumatic carrier facility (PCF) and tray rod facility of Dhruva reactor (~5x10¹³ n cm^-2 s^-1). After sufficient cooling, gamma ray measurements were carried out using high purity germanium detector. Quantification of the analytes was done using relative method of NAA and the validation was using IAEA CRM