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.