Determination of multielements by neutron activation analysis using a coincidence counting method

When gamma -rays are counted using gamma -ray spectrometry for neutron activation analysis (NAA), the Compton continum from high-energy gamma -rays often interfers with the detection of nuclides with lower energy gamma -rays. A coincidence counting of gamma -rays in the cascade series with a coaxial Ge detector and a well-type NaI(Tl) detector can reduce this problem. The coincidence counting method was applied to the determination of Se, Hf, Ba, Cs, Co, Sb and Sc in 3 kinds of certified reference materials (NIES CRM No.16 river sediment, NIES/NIRS typical Japanese diet CRM and NIES/WAMRL fish otolith CRM) and 10 kind of iron remains excavated at the ruins of Kaman-Kalehoyuk in Turkey. These samples and comparative standards were irradiated for 6 h at a thermal neutron flux of 3.7 x 10(12) n cm(-2) s(-1) in the Rikkyo University Research Reactor (TRIGA Mark-II, 100 kW). The irradiated samples were couted by multiparameter MCA (LN-9000, Laboratory Equipment Corporation). A coaxial Ge detector (relative efficiency of 21% and FWHM of 1.8 keV at 1332 keV) was used for the conventional counting method. For the coincidence counting method, the coaxial Ge detector along with a well-type NaI(Tl) detector (6 in.phi x 6 in., well 3 in.phi x 4 in.) was used. Using this method to determine Se, Hf, Ba, Cs, Co, Sb and Sc, the lower limit of the determination was improved by 2 similar to 4 times compared with the conventional counting method using the coaxial Ge detector. The determined values were in good agreement with title certified values.