Vertical migration of ¹³⁷Cs in the South Caspian soil

¹ Faculty of Sciences, University of Guilan, PO Box 3489, Rasht, Iran
² Faculty of Physics, Damghan University, PO Box 41167, Damghan, Iran

Received: 30 December 2011
Accepted: 9 May 2012

Abstract

In order to study the vertical migration of anthropogenic ¹³⁷Cs, soil inventories of this radionuclide were measured in two regions selected on the basis of a previous comprehensive survey in the northern Iranian province of Guilan located in the South Caspian region. Ten sampl ing stations were randomly chosen in these regions and split-level sampling was carried out to a depth of 30 cm. Sample analysis was performed using a HPGe detector system. In situ gamma measurements in both regions were als o carried out with the aid of a portable germanium spectrometer. The experimental data were then compared with the solution of the convection-dispersion equation (CDE) with the proper initial and boundary conditions to evaluate initial deposition as well as transport parameter values. The solution, including the effects of both considered sources, i.e. global fallout and Chernobyl releases, fits the measured data well. The effective convection velocity and dispersion coefficients of ¹³⁷Cs lie in the range of 0-0.25 cm·y^-1 and 0.32-0.75 cm²·y^-1, respectively, indicating a very slow migrat ion rate in the area. Most of the deposited ¹³⁷Cs still remained in the top 10-cm layer. Moreover, the fitted depth profiles were then employed to correct the surface activities of ¹³⁷Cs estimated by in situ measurements.