Development of protocol for determination of silicon and phosphorus in geologic materials using fast neutron activation analysis (FNAA)

Abstract

Silicon and phosphorus are important constituents of many geological materials and critically influence petrogenesis, mineral stability, element partitioning, and the geochemical cycling of nutrients and metals. Precise quantification of Si and P in rocks, soils, and sediments is therefore vital across fields from igneous and metamorphic petrology to environmental geochemistry and soil fertility mapping. Determination of these elements by traditional techniques- wet chemistry, XRF and ICP-MS is particularly problematic because these methods are time consuming, contamination due to sample handling, matrix effects etc. Si and P have very low thermal neutron cross section making NAA ineffective for their measurement. Threshold reactions induced by fast neutron offers a promising alternative. In this study the protocol for the FNAA was carefully developed and validated. Samples were irradiated for 5 minutes and allowed to cool for one minute before being counted. The results show that at close geometry of 2.20cm the concentration of these is comparable with those of the certificate. Upon validation with U-score test the validity of FNAA as a method for analysis of Si and P was further upheld.