Instrumental neutron activation analysis of environmental reference materials using a high flux reactor

The standard samples of whole rice and tea leaves, supplied from the National Institute of Environmental Sciences, were analyzed with instrumental neutron activation analysis (INAA). The samples were irradiated in the JMTR Reactor, Japan Atomic Energy Research Institute, with average thermal neutron flux 8.1 x 1013 n·cm-2·s-1 for 5 hrs. After 6-7 days of cooling, gamma spectra were measured using normal gamma spectrometry comprising of coaxial Ge detector and 4096-channeled analyzer. The same samples were analyzed after 8-11 and 11-50 days of cooling times. Also the anticoincidence gamma spectrometry with coaxial Ge detector and well type NaI(Tl) detector were performed. The obtained results were compared with those irradiated in Musashi Reactor with lower neutron flux. The results were in good accordance. In tea leaf samples, the elements Cr, As and Rb, where the values are higher in the present analysis. The elements Ag, Nd, Lu, and Au which had not been quantified with the low flux were quantified. In rice samples, some elements including Na were quantified higher in the present analysis. The result of the analysis are presented in detail and the peak sensitivities of gamma-ray for each element are tabulated. (A.Y.)