Temporal reduction of the external gamma dose rate due to 137Cs mobility in sandy beaches

In the present paper the contribution to the external gamma dose rate due to 137Cs in soil as a function of time is presented. Sampling sites were selected along the Calabria and Basilicata Regions coastal beaches (southern part of Italy) to assess the external gamma dose rate in air, 1 m above the ground level. A convection-dispersion model, with constant parameters was used to approximate the radiocesium soil vertical migration. The model was calibrated using the initial 137Cs activity deposition in this region (Chernobyl fallout) and 137Cs activity concentration down the soil profile, measured 10 years later. The dispersion coefficient and the advection velocity values, were respectively: 2.17 cm2 y−1 and 0.32 cm y−1. The Radionuclide Software Package (RSP), which uses a Monte Carlo simulation code, was used to determine the primary 137Cs gamma dose contribution in air 1 m above the ground surface. The resulting 137Cs external dose rate ranged from 0.42 nGy h−1 in 1986, to 0.05 nGy h−1 in 2007.