Half-lives of self-purification for various isotopes in soils of the Chernobyl Exclusion Zone

Abstract

During 2001-2002 we investigated current contamination of soils in several places in the Chornobyl zone. We have measured the content of alpha emitting isotopes Pu, 241 Am, 154,155 Eu, 90 Sr, and 137 Cs in layers of soil up to the depth of 30cm. By including the two mechanisms of migration: convection and diffusion in our model, we were able to estimate the ecological and effective half-lives of self-purification processes for these layers of soil. Effective half-lives vary from 20 to 400 years dependent upon the type of soil and the isotopes. Understanding the rates of migration and dissipation of radioisotopes in the environment is essential for predicting the effectiveness of natural remediation processes, or self-purification. The rate of radionuclide migration in the different soil types can differ markedly. As a result, the ecological half-life (T1/2,ecol) of self-purification processes for upper layers of soil may exceed, or be considerably shorter than, the physical half-life (T1/2) of the radionuclide. The effective half-life (T1/2,eff )i s a measure of self-purification and includes both ecological and physical losses in accordance with the formula: 1/T1/2,eff = 1/T1/2,ecol + 1/T1/2. We have evaluated the effective half-lives for Pu, 241 Am, 154,155 Eu, 90 Sr, and 137 Cs using measurements of contaminated soil profiles from research sites in the Red Forest and Glyboky Lake inside the Chornobyl Exclusion Zone.