Following a major nuclear accident it is of great importance to apply rehabilitation actions for the recovery of vast contaminated territories.

In order to achieve this objective, it is essential to know the medium-and long-term evolution of the contamination and to evaluate how the dose equivalent rate (DER) of the gamma-radiation changes with the migration of the radionuclides in the soil.

The aim of this paper is to define the modification of the DER as a result of 137Cs penetration into the soil.

Information is used which is related to the character of the 137Cs distributions in different soil types and to 137Cs vertical migration velocity (cm y-1) as a function of the types of soils.

Indeed, since 1986 when the Chernobyl accident occurred, soil profiles were studied in undisturbed land in the region of Gomel, Belarus.

The 137Cs content of soil was assayed in the laboratory by gamma-spectrometry and the results obtained are classified into groups according to the type of soil and the 137Cs migration velocity.

The average DER was calculated as a function of 137Cs vertical migration for the above groups and for different levels of contamination ranging from 185 to 7400 kBq m-2.

In order to validate the theoretical computations, a comparison between measured in situ and calculated DERs was carried out.

A good correlation was found between measured and calculated DERs. (...)