Applicability of prompt gamma-ray analysis to the initial analysis of the extraterrestrial materials for chemical composition

Abstract

When extraterrestrial materials are returned to the earth by future space missions, these materials are to be subjected to the initial examination. For such purposes, measurements are desired to be done non-destructively. In this study, we investigated the applicability of non-destructive prompt gamma-ray analysis (PGA) for determining chemical composition of the returned materials, focusing on levels of induced radioactivities and the effect on isotopic composition by PGA. Under current conditions applied for the PGA facility at the Japan Atomic Energy Research Institute, essentially no residual radioactivities remain after appropriate cooling, making the same specimen analyzed by PGA usable for further research without any restriction. The effect on isotopic composition by PGA was examined both for neutron-induced reactions and for neutron-induced nuclear fission of 235U. No significant effect can be brought by neutron-induced reactions even for some noble gas nuclides such as 80Kr and 128I, which can be augmented by (n, γ) reactions on neighboring halogens. Neutron-induced nuclear fission reactions of 235U yield essentially no effect on isotopic composition. In addition, PGA has several advantages over other nondestructive analytical methods such as instrumental neutron activation analysis (INAA) and synchrotron radiation x-ray fluorescence (SR-XRF); INAA leaves a significant level of induced-radioactivities and SR-XRF yields less reliable and less accurate values for elemental composition. Judging from these features and characteristics, it is concluded that PGA can be one of the most suitable analytical methods potentially applicable for initial analysis of returned samples from space.