Uranium and thorium mixed oxides are being prepared using natural U and Th for studies on fuels for Advanced Heavy Water Reactors,
wherein composition of U and Th is specific and requires strict control in terms their contents and homogeneity. Chemical
quality control necessitates accurate and precise compositional characterization of the fuel material by a suitable analytical
method. Among various analytical methods for U and Th, instrumental neutron activation analysis (INAA) is one of the best
methods for their simultaneous determination without chemical dissolution and separation. INAA methods using reactor neutrons
namely thermal NAA and epithermal NAA were standardized for the determination of U and Th in their mixed oxides. Standards,
synthetic samples and U–Th mixed oxide samples, prepared in cellulose matrix, were irradiated at pneumatic carrier facility
of Dhruva reactor as well as at self serve facility of CIRUS reactor under cadmium cover (0.5 mm). Radioactive assay was carried
out using a 40% relative efficiency HPGe detector. Both activation and daughter products of 238U (239U and 239Np) and 232Th (233Th and 233Pa) were used for their concentration determination. The method was validated by analyzing synthetic samples of 6–48%U–Th
mixed oxides. The standardized method was used for the concentration determination of U and Th in 4–30%U–Th mixed oxide samples.
Results of U and Th concentrations including associated uncertainties obtained from the INAA methods are presented in this
Elemental analysis of some Nigerian grains for cobalt, zinc, iron, and chromium, was done by thermal NAA. The concentration of these essential trace elements were found as follows: rice /0.18–0.98 ppm Cr, 27–307 ppm Fe, 0.133–0.237 ppm Co, 12.4–17.8 ppm Zn/; soyabean /0.32–0.59 ppm Cr, 67–81 ppm Fe, 0.244–0.358 ppm Co, 42–45 ppm Zn/; maize /0.05–0.75 ppm Cr, 22.7–47.6 ppm Fe, 0.20–0.65 ppm Co, 15.8–33.4 ppm Zn/; ground-nut /0.22–2.02 ppm Cr, 27.2–34.8 ppm Fe, 0.08–1.73 ppm Co, 24.3–38.2 ppm Zn/. No pattern was established for the elemental concentration in the grain samples. The result obtained suggest that an average diet of these grains will provide an adequate concentration of these essential elements.
As part of an ongoing Great Lakes deposition study, we have determined a series of heavy metals in air filter samples collected near Lake Ontario. To decrease our detection limits for key elements used in our receptor modeling, we have employed instrumental epithermal neutron activation analysis (NAA) and Compton suppression techniques. Our detection limits were much better than those with thermal NAA, typically, 0.3 ng for Sb, 0.7 ng for As, 8 ng for Cd, 0.2 ng for In, 14 ng for I, 5 ng for Mo and 2 ng for U. Silicon, which is usually not reported in conventional NAA results for air filters, was routinely determined at the 60 g level. Accuracy was corroborated by analyzing the certified reference material concurrently.
Aerosol samples were collected on Whatman 41 filters at two sites near Lake Huron and one site near Lake Ontario. These samples were then analyzed by instrumental neutron activation analysis (NAA) at the University of Illinois. The detection limits for certain trace elements were enhanced by irradiation with both thermal and epithermal neutrons and also by counting with Compton suppression techniques. The sample was divided in half to allow for four irradiations. Short-lived thermal NAA resulted in the determination of Al, Br, Ca, Cl, Cu, K, Mn, Na, Ti, and V. A short epithermal irradiation was used to determine Cu, I, In, Si, Sn and U. A one and one-half hour epithermal irradiation was utilized for the determination of As, Au, Br, Sm, Sb, and W. The elements Cr, Cs, Fe, Hf, Ni, Sc, Se, Th. Zn, and several rare earths were determined with a long thermal irradiation. Utilizing a Compton suppression gamma-ray counting system reduced the background and enhanced the detection of several isotopes which primarily emit only a single gamma-ray upon decay. Counting was simultaneously performed with a normal counting mode so that the detection of isotopes with multiple decay gamma-rays was not impaired.
Authors:S. Ohde, M. Hossain, H. Ozaki, and T. Masuzawa
A simple and non-destructive method has been proposed for the routine determination of uranium by epithermal neutron activation analysis in coral skeletons. Using a cadmium capsule, about 0.1-0.2 g samples were irradiated for 6 hours in the Triga Mark II Reactor. Measurements of -ray (239Np via 239U) were performed with each sample and standard after cooling for about three days. Compared with a non-destructive thermal NAA, the present method was found to improve the sensitivity because it reduced the intense Compton background induced by 24Na. We determined uranium in coral standards within 2% of analytical precision. The data obtained for the carbonate standards are mostly consistent with reported values. The present method could be usefully applied to determine uranium contents in fossil corals from the Funafuti Atoll in the Pacific. The distribution of uranium between seawater and coral skeletons is also discussed in order to understand the environmental media in which the coral grew.