Cs contamination from Chernobyl of soils in Piemonte (North-West Italy): spatial distribution and deposition model

137Caesium was measured in soils sampled from 101 locations distributed across the Piemonte Region (North-West of Italy). The contamination levels found ranged from a few kBq m-2 to about 60 kBq m-2, the regional average being of the order of 15 kBq m-2. The data obtained were interpolated with geostatistical functions in order to obtain a detailed map of radio-active contamination for the whole region. A second map, representing the rainfall for the period of Chernobyl atmospheric contamination, weighted with the estimated values of air contamination, was produced. The comparison of the two maps and a statistical analysis of the data show that 84% of the 137Cs global inventory is due to wet deposition, associated with 9% pre-Chernobyl fallout and a 7% attributed to Chernobyl dry deposition. A deposition model based on a linear relationship between wet deposition (Dw) and 'weighted rainfall' (Rw) is proposed, applied and tested with available data. On this basis the following parameters were estimated: scavenging factor, washout ratio, cloud height, dry deposition velocity, median diameter of the particles.