Spatial variability of soil 137Cs in the South Caspian region

In a comprehensive program of environmental radioactivity survey in South Caspian region,137Cs inventories in soil has been measured at more than 50 sites in the Iranian northern province of Guilan. This has been the first wide-range survey of soil radionuclide inventories in the narrow band sensitive ecosystem of south Caspian shore. Radioactivity measurements were carried out using HPGe gamma-spectrometry system. The activity concentration of 137Cs in surface soil exhibits a mean value of 17.6 ± 9.4 Bq kg−1, with a range of 2.3–41.7 Bq kg−1. In many sites, split-level sampling method has been applied down to a depth of 20 cm. There were found generally two profiles. Most profiles exhibit a negative exponential distribution, while others revealed a clear subsurface peak in 5–10-cm layer. Cesium deposition in the study area has been estimated to be in the range of 0.38–2.9 kBq m−2 with a mean value of 1.7 kBq m−2. Distribution patterns of 137Cs concentration levels and deposition values have been estimated using Kriging interpolation method. Observed hotspots in deposition pattern coincide with areas of higher precipitation.