Plutonium Oxidation States in Corals and in Synthetic Calcium Carbonates

Annual growth bands from the coral Montastrea annularis preserve a record of fallout plutonium concentrations which is simply related to the known history of fallout 90-Sr deposition. The relationship between the plutonium concentration in an annual band and in coeval seawater is clouded by ignorance of mechanisms of plutonium uptake by corals and in synthetic calcium carbonates. The coral plutonium oxidation-state signature will be recovered through application to corals of techniques (solvent extraction, coprecipitation, selective adsorption) previously applied to homogeneous aqueous solutions. Comparisons will be made within (by ages of annual bands) and between corals (over taxonomy and geography). Coprecipitaiton experiments will provide models of the physicochemical control of plutonium uptake in calcium carbonate. Coprecipitation of plutonium oxidation states in aragonite will be emphasized, but coprecipitations with calcite and aragonite will be compared. In all cases rate of precipitation will be controlled. Results for plutonium coprecipitation will be compared with those obtained for actinide analog (Th, U, Np, Am) for the plutonium oxidation states.