Curium isotopes in Chernobyl fallout

Abstract

In nuclear reactors plutonium and transplutonium isotopes are produced by multiple neutron capture of uranium and plutonium and are important for the energy production and their composition reflects the core burnout. Under normal operation these elements are not released to the environment in significant amounts. There are accordingly very few areas or source terms where exotic transplutonium elements, such as curium isotopes, can be studied in the environment. The Chernobyl accident provided a complex spectrum of fission and activation products in fallout while the relative amounts, compared to the core inventory, of refractory elements such as transuranium and transplutonium elements were small. The major alpha-activity consisted of Cm-242 (T-1/2=163 d) that would have decayed after a few years. In this study we have demonstrated the presence of so called "supported Cm-242" from the long-lived Am-242(m) (T-1/2=141 a) in environmental samples, following fallout from the Chernobyl accident. It has also been possible to assess the core bum up by using the data obtained for the Cm isotopes. The curium isotopes Cm-243 (T-1/2=29.1 a) and Cm-244 (T-1/2=18.1 a) cannot be resolved by conventional alpha-spectrometry. The assessment of these isotopes in environmental samples contaminated from the Chernobyl accident has been made by studying the effective half-life of the mixture of the isotopes. The data are compared with those previously obtained by high-resolution alpha-spectrometry and spectral deconvolution.