NAA of rare earth elements in fluoride glass and its raw materials containing gadolinium by dual comparator method

Scandium and terbium have excellent features as comparator elements for NAA, for example the half lives of their radionuclides produced by (n, γ) reaction are resemble each other. The neutron activation cross sections of scandium and terbium and of lanthanum, europium, gadolinium and dysprosium were re-estimated using the experimental holes of JRR-3 HP-3 and of JRR-4 pneumatic tube with cadmium filter. And the optimum values were chosen among the reported nuclear data. So that europium, terbium, dysprosium and lanthanum could be determined within 10% in error by using a pair of scandium and terbium as a comparator. This method was applied to the determination of those four rare earth elements in the raw materials of fluoride glass for optical fiber. The self shielding effect of neutrons was not ignored in the sample containing gadolinium. The glass, which was produced by melting the mixture of 60 mol% zirconium fluoride, 32 mol% barium fluoride, 4 mol% gadolinium fluoride and 4 mol% aluminium fluoride, was irradiated together with a pair of scandium and terbium comparator at JRR-3 HP-3. At first apparent content of gadolinium in the glass was determined and the self shielding factor defined as the ratio of apparent weight to irradiated one of gadolinium was estimated. Then the concentrations of europium, terbium, dysprosium and lanthanum were corrected by the factor and could be determined within 10% in error.