Determination of fluorine in coral skeletons by instrumental neutron activation analysis

A systematic and non-destructive technique is proposed for the determination of fluorine in coral samples by instrumental neutron activation analysis using the 19F(n,γ)20F reaction. About 50 to 80-mg samples in polypropylene capsules were irradiated for 15 seconds in the pneumatic transfer tube system (PN-3) of JRR-3M reactor. After the irradiation at a thermal neutron flux of 1.5 x 1013 n x cm-2 x s-1, the coral samples and standards were cooled for 6 seconds and the γ-rays emitted were measured for 15 seconds with a Ge detector. The sequence from sample irradiation to γ-ray counting was performed under a computer-control mode. The analytical precision was ∼5% for the JCp-1 coral standard. The present method was applied to the determination of fluorine in corals from Thailand, Okinawa and the Philippines. The advantage of one method over destructive techniques is discussed by comparing the analytical results obtained for the JCp-1 coral standard using INAA, ion chromatography and spectrophotometry. Factors that may control the levels of fluorine in corals are also discussed. (author)