The role of neutron activation with radiochemistry in geoanalysis

Abstract

This is a review of the current status of radiochemical neutron activation analysis (RNAA) in geoanalysis. It begins with an evaluation of the importance of RNAA now that instrumental neutron activation analysis (INAA) is capable of measuring up to forty elements simultaneously. Radiochemical separations are no longer used to prepare single element sources, except in the case of pure beta emitters such as Bi and T1 which cannot be measured with INAA. In general RNAA is applied to those elements with concentrations below the detection limits for INAA, such as the platinum group elements (PGEs), the halides, Sn, Rb, Sr, Nb, and to low concentrations of the rare earth elements (REEs). Group separations are described for measuring up to 42 elements, particularly where sample size is limited and examples are given where RNAA is combined with INAA to give maximum information. Radiochemical separations have several advantages over other analytical techniques, in particular the lack of contamination and the ability to add carrier to monitor and correct for losses. Therefore RNAA is used to measure sub-μg g−1 (ppm) concentrations of many elements in preference to other techniques. Radiochemical separation schemes are described for the following elements, or groups of elements: As; Bi, Tl, Cd and Hg; Cl and Br; Re; Rh, Ag and In; Rb, Cs, Cr and P; Te; Sn and Mo; Zr and Hf; the PGEs; and the REEs. The review concludes that RNAA has a future in specialised areas for elements below μg g−1 concentrations, in particular where they are below the detection limit for INAA and where other techniques suffer from contamination and losses during decomposition and digestion for analysis. It is unlikely that RNAA will expand significantly but with recent developments in separation procedures there may be new applications in the study of REEs and PGEs.