Ambient dose rate measured at the official reference point in a building at a few km distance from the village from 1997 to 2016. Each dot represents the monthly or the quarterly mean dose rate. Closed circles: indoor ambient dose rate; open circle: outdoor dose rate. The lines represent the non-linear regression of each dataset. Adjusted regression squares are, r² = 0.4759 for Indoor data and r² = 0.8967 for outdoor data. The apparent half-life for outdoor dose rate is 18.15 years.