Photon-activation analysis of standard rocks using an automatic γ-ray counting system with a micro-robot

Abstract

Nondestructive multi-element photon-activation analysis has been used to determine the abundance of thirteen trace elements: Ba, Ce, Co, Cr, Cs, Nb, Ni, Rb, Sc, Sr, Y, Zn and Zr in nine GSJ standard rocks (JR-1, JR-2, JG-1, JA-1, JB-1, JB-2, JB-3, JGb-1 and JP-1) and four USGS standard rocks (G-2, GSP-1, AGV-1 and BCR-1). Rock samples and multi-element standards were irradiated simultaneously with 30 MeV bremsstrahlung. The (γ, n) and (γ, p) reaction products were measured with an automatic γ-ray counting system with a micro-robot. In a typical measurement, the counting statistics error is lower than 5% for concentrations>2ppm for Nb, 5ppm for Ce, 10ppm for Co, Rb, Sr, and Y, and for Zr at concentrations>20ppm. The abundance of elements in the rock standards obtained with the present facility are in good agreement with the reported data in most cases. Precision is better than ±5% (lσ) for concentrations>10ppm for Nb and Y, >50ppm for Sr, and for Co, Rb, and Zr at concentra-tions>25 to 40ppm, depending on the element. It is important for volcanic geochemistry in island arcs to determine Nb, Y, and Zr together with Rb and Sr accurately.