Thorough investigations on indoor radon in Băiţa radon-prone area (Romania)

► The annual average of indoor radon concentration for Băiţa area was 241 ± 178 Bq m− 3. ► A large variability among rooms within surveyed dwellings was clearly evidenced. ► The radon concentrations in bedrooms without cellar were higher than above the cellar. ► The ratio between radon concentration at ground floor and cellar was calculated. ► A wide variation range between ground floor rooms and cellar was reported.