Plutonium and americium monazite materials: Solid state synthesis and X-ray diffraction study

Abstract

High-temperature solid state syntheses of monazite powders containing plutonium (III), plutonium (IV) and americium (III) were performed. Resulting powders were characterized by X-ray diffraction. Pu 3+PO 4 was readily obtained as a single phase by heating a Pu 4+O 2–NH 4H 2PO 4 mixture under argon atmosphere. Traces of tetravalent plutonium phosphate Pu 4+P 2O 7 were detected when synthesized under air atmosphere. The incorporation of (Pu 4+, Ca 2+) in the monazite structure was investigated under air and argon atmosphere. We showed that Pu 4+ is fully reduced in Pu 3+ under argon atmosphere whereas, under air, the compound with the formula Pu 0.4 3 + Pu 0.3 4 + Ca 0.3 2 + PO 4 was obtained. Pure Am 3+PO 4 was also synthesized under argon atmosphere. X-ray patterns revealed a complete amorphisation of the monazite structure at a relatively low cumulative alpha dose for 241AmPO 4.