The 222Rn activity concentration, external radiation dose and air ion production rates in a boreal forest in Finland between March 2000 and June 2006

We measured the 222 Rn content of the air by continuously collecting particle-bound daughter nuclides 214 Pb and 214 Bi onto glass-fibre filters and counting their beta particle emissions with Geiger-Muller tubes. A scintillation gamma spectrometer system measured external radiation, which main components are gamma and cosmic radiation. Our purpose was to detect long-term, seasonal and diurnal variations in 222 Rn activity concentration and external radiation dose rate in a Finnish boreal forest during the years 2000-2006. The long-term variations in activity concentration and dose rate were small, whereas the annual variations were more pronounced. In late summer and autumn, the diurnal cycle of 222 Rn activity concentration was strongest, whereas the diurnal cycle of external radiation dose rate was practically non-existing throughout the year. We utilised the 222 Rn and external radiation measurements also when calculating air ion production rate in the lower boundary layer. Based on our results, the total ion production rate varied in the range 4.2-17.6 ion pairs cm -3 s -1 . The fraction of 222 Rn contribution in the ion production varied in the range 0-0.43, with average fraction 0.11 ± 0.07. These results indicate that ion production was typically dominated by the external radiation on our measurement site.