Variation of 7Be concentration in Tokushima

The atmospheric 7Be radioactive nuclide in the environmental radioactivities has been used as a radio tracer to elucidate the degree of horizontal mixing of global atmosphere migration within the surface air layer. The 7Be nuclide has been produced by a spallation-reaction between cosmic ray and gas fractions in a stratosphere where is located upon a surface air layer. The 7Be nuclides are attached to aerosol particles in the stratosphere, and they are transported to the surface air layer with taking a few months. In addition, the another atmospheric radioactive nuclide of 214Pb in the environmental radioactivities is one of the progenies of 222Rn which is emitted from the ground surface into the atmosphere, and also exists in the atmosphere with the same as form attached in aerosol particles. The correlations between the 7Be and 214Pb atmospheric concentrations in the surface air layer at Tokushima (eastern Shikoku island) are examined. Samples of atmospheric aerosol particles were collected on glass fiber filters with a high volume air samples at a height of about 15 m. Radioactivities of 7Be and 214Pb were measured using an HPGe detector. For seasonal variation during April 2001 and 2002, the mean radioactive concentration of 7Be measured in Tokushima was 2.5 mBq/m3. It was confirmed that the concentrations of 7Be and 214Pb were lower in summer and higher in winter and spring. For daily variations, the atmospheric concentrations of 7Be and 214Pb were decreasing toward the early morning and also increasing with the temperature rise. (M. Suetake)