Annual cycle of gross beta activities in aerosol around Daya Bay area, China.

In this paper, the monthly gross beta activities in aerosol during 1995-2004 at Daya Bay area are reported. The gross beta activities were observed to vary in the range of 0.22-5.14 mBq m(-3) with an arithmetic average of 1.60+/-1.00 mBq m(-3) and a geometric average about 1.78+/-0.33 mBq m(-3). It is shown an obvious seasonal variation characteristic, which is ascribed to the washout mechanism and the radon-suppressing mechanism from the soil by the seasonal rainfall. The exponential attenuation with the rainfall is verified and an attenuation index is defined, which is deduced as 0.007+/-0.002 mm(-1) by regression analysis. Finally, the correlation between gross beta activities and (210)Pb concentrations is analyzed. It is indicated that the radionuclide (210)Pb contributes about 61+/-9% to the gross beta activities in the aerosol.