Chemical characterization of the extraterrestrial material returned by future space mission: An application of nuclear activation methods

Assuming an application to the unknown extraterrestrial samples recovered and returned by spacecraft in near future, we propose an analytical scheme to characterize those samples in chemical compositions. The analytical procedure consists of three nuclear analytical methods, i.e., neutron-induced prompt gamma ray analysis (PGA), instrumental neutron activation analysis (INAA) and instrumental photon activation analysis (IPAA). In this scheme, the sample is first analyzed by PGA, which is followed by IPAA and INAA. These methods are methodologically described, with emphasizing their advantages and disadvantages. With applying such an analytical scheme to unknown samples, we evaluated two issues; elemental and isotopic effects left in samples analyzed by PGA and the ordering of INAA and IPAA. Among three analytical methods, PGA is acknowledged to be highly significant for the initial analysis of unknown extraterrestrial samples, because it non-destructively yields sufficient data of elemental compositions to classify them into known groups of meteorites without producing noticeable effects in chemical and isotopic compositions.