Studies on the adjustment of the oxidation states of Pu oxidation states for the analysis of Pu isotopes in soil samples

The major oxidation states of Pu in acidic solutions are Pu(III), Pu(IV), Pu(V) and Pu(VI). Reducing and oxidizing reagents such as H2O2, NaNO2, Na2SO3 and N2H5OH have been used to adjust the Pu oxidation state. Nuclear counting methods can be applied for determining the amounts of Pu isotopes in very low level Pu concentrations with a high sensitivity. For micro molar concentration (> 10-6 M) of Pu, absorption spectroscopic techniques can be used for a quantitative determination of the oxidation states of Pu in an aqueous solution. Each oxidation state shows a completely distinctive absorption spectrum composed of characteristic, narrow and intense bands. Several investigations have been performed for a determination of the Pu oxidation states in a nitric acid media by the absorption spectroscopic method. However, there have been very few studies on the spectroscopic properties of the Pu oxidation states in a hydrochloric acid medium. Over the years, the redox states of plutonium have been stabilized by a complexation with various ligands. Among these, a nitrate anion has played a historically critical role in the processing and purification of plutonium. Also, a chloride anion has played a significant part in the separation and purification of plutonium for a very low level of Pu in environmental samples. The objective of this work is to measure various oxidation states of plutonium and to investigate the stability of the plutonium oxidation states with a laps of time in a HCl medium by using a UV-Vis-NIR spectrophotometer. Also, the adjustment method for the Pu oxidation states to Pu(IV) and Pu(VI) in a HCl medium was applied for determining the Pu isotopes in IAEA reference soils