Full Length Research Paper

Evaluation of the ¹³⁷Cs activity-depth profiles by the diffusion-convection model

 I. R. Ajayi¹* and A. T. Raji²

¹Deparment of Physics and Electronics, Adekunle Ajasin University Akungba-Akoko, Ondo State, Nigeria.

²Department of Physics, University of Cape Town, South Africa.

*Corresponding author. E-mail: isajayi@yahoo.com.

Accepted 12 November, 2009.

   Abstract

The diffusion-convection model of ¹³⁷Cs transport has been used to evaluate the activity-depth profiles of soils in southwestern Nigeria in this study. The experimentally determined depth profiles were fitted into the diffusion-convection equation to obtain the diffusion coefficient D and the convective velocity υ. Results obtained showed that the range of the diffusion coefficient was 0.72 – 1.02 cm² per year while that of the convective velocity was from 0.07 to 0.16 cm per year. It was observed that the diffusion coefficient is higher than the convective velocity in all the sampling points. The low convective velocities obtained in all the locations may imply that convective rates of the radionuclide within the soil layers are insignificant compared to the diffusion rates.

Key words: ¹³⁷Cs activity, diffusion coefficient, convective velocity, soil depth, radionuclide.