Measurements of outdoor radon concentration over 24-hour periods in different settlements in Bulgaria

This work presents the results of continuous radon measurements in open atmosphere, including measurements of air humidity, temperature, pressure and gamma dose rate, in 11 different settlements of Bulgaria. Using AlphaGuard equipment, measurements were made in mountain, spas, plain, sea level and uranium mining environments in the summer period, in series of 10-min intervals over 24 hours., . The analysis of results showed different daily variation among the outdoor radon measurements in different measuring sites. The outdoor radon concentrations ranged from 22 Bq.m−3 (city in lowland) to 180 Bq.m−3 (uranium mining site Eleshnica). Outdoor radon levels were found to be increasing during the night by a factor of 1.5 (in 9 locations), factor 2 (location at sea level) and factor 1 (location in the plain). The relation between outdoor radon concentrations and meteorological factors as well with gamma dose rate was observed.