Determination of trace elements in coal and fly ash by neutron activation analysis

Concentration of 49 elements in NBS coal standard reference materials (SRM 1632 a and SRM 1635) and coal fly ash standard reference material (SRM 1633 a) were determined by instrumental neutron activation analysis (INAA). Each sample (ca. (25 -- 150) mg) was irradiated for short time (2 min) at thermal neutron flux 1.5 x 1012 n cm-2 s-1 and for long time (5 h) at thermal neutron flux 3.2 x 1012 n cm2 s-1 in Musashi Institute of Technology Research Reactor (MITRR). Gamma-ray spectra from short time irradiation samples were taken for 4 min after (2 -- 15) min after irradiation and for 15 min after (8 -- 70) min after irradiation using a Ge(Li) detector coupled to an 8192 multi-channel analyzer and a mini-computer (GAMA system). Gamma-ray spectra from long time irradiation samples were taken for about 2 h after (3 -- 12) d after irradiation and for about 10 h after (15 -- 60) d after irradiation. The analyzed values were in good agreement with NBS certified values except for a few elements. In order to improve the sensitivity of detection of some elements, long time irradiation samples were also counted by means of an anticoincidence counting method or a coincidence counting method with a Ge(Li) detector and a well-type NaI(Tl) detector. Concentrations of 12 elements (Pr, Nd, Rb, Th, Cr, Ce, Fe, Hg, Zr, Sr, Ni, Zn) were determined by the anticoincidence counting method and concentrations of 3 elements (Ba, Hf, Se) were determined by the coincidence counting method. (author)