Determination of trace elements in scallop and fish otolith by instrumental neutron activation analysis using anti-coincidence and coincidence counting methods

Trace element concentrations in scallop reference material and fish otolith certified reference materials prepared at the National Institute for Environmental Studies (NIES) of Japan were determined by instrumental neutron activation analysis (INAA). Nine aliquots of scallop sample (ca. 252 similar to 507 mg) and five aliquots of fish otolith sample (ca. 502 similar to 988 mg) and comparafive standards were irradiated for a short time (10 s) at a thermal neutron flux of 1.5 X 10(12) n cm(-2) s(-1) (pneumatic transfer) and for a long time (6 h) at a thermal neutron flux of 3.7 X 10(12) n cm(-2) s(-1) (central thimble) in the Rikkyo University Research Reactor (100 W). The irradiated samples were measured by conventional gamma-ray spectrometry using a coaxial Ge detector, and by anti-coincidence and coincidence gamma-ray spectrometry with a coaxial Ge detector and a well-type NaI(Tl) detector to determine as many trace elements as possible with high sensitivity. The concentrations of 34 elements of the NIES No.15 scallop referrence material and 16 elements of the NIES No.22 fish otolith CRM were determined. Using the coincidence counting method to determine Se, Ba and Hf, the lower limit of the determination was improved by 2 times compared with the conventional counting method.