Utilization of research reactors for instrumental neutron activation analysis of geological material in REE exploration activities of Atomic Minerals Directorate, Hyderabad, India

The Instrumental Neutron Activation Analysis (INAA) technique is extensively used for determination of the REE elements (La, Ce, Nd, Sm, Eu, Tb, Tm, Yb, Lu), other trace elements (Sc, Cr, Co, Zn, Ga, As, Rb, Sb, Cs, Ba, Hf, W, Ta, Au, Ag, U, Th) and major elements (Na, Ca, Fe and K) for more than four decades in AMD on variety of geological material and from different geological domains to support the geochemical studies in the Directorate. The nondestructive technique along with other analytical techniques is capable of yielding the elemental concentrations with high sensitivity and low detection limits (ppm to ppb) making good interpretation of the data. The REE patterns obtained are critical in the interpretation of the physico-chemical and redox conditions prevalent at the time of minerals crystallisation and rock emplacement. In the present studies the irradiation of eight Ultramafic samples from Um Sohryngkew river area, Jaintia Hills, Meghalaya has been done in DHRUVA Reactors in BARC, Mumbai with a thermal flux of 10¹³ n cm^-2 s^-1. Samples and certified reference standards are packed in aluminium foil of high purity. The irradiated samples and standards spectrums were analysed at RSA Laboratory, Hyderabad using a p-type (PGC-3018) High Pure Germanium (HPGe) coaxial semiconductor detector- RE 30%, DSG detector systems, GmbH which is coupled to the target dMCApro- digital MCA. WinTMCA32 software was used for the analyses of the spectrums. The Chondrite normalised REE pattern studied, indicate negative Eu anamolies with Eu/Eu* ranging from 0.41 to 0.58 which indicates oxidising conditions prevalent at the time of formation of the rock. The REE content (Σ REE from 176.7 to 252.5, n=8) point towards mineralised nature of the ultramafic rocks. (author)