Beryllium-7 and Tritium Variations of Rain Water in Korea

Both beryllium-7 and tritium are produced by cosmic ray interactions in the upper atmosphere. Beryllium-7 is produced by the interaction between cosmic rays and oxygen and nitrogen by spallation reaction. Similarly tritium is mostly produced by mostly neutron spallation with upper atmospheric gases. Recently, we have investigated the variations of both beryllium-7 and tritium concentrations of Korean rainwater. Both beryllium-7 and tritium data obtained from September, 2007 to the present time show clear trends associated with rainwater amount, air mixing of the stratosphere in the spring. Both beryllium-7 and tritium peaks appeared during fall season and spring. However, interestingly, the trend of tritium variation is shifted about a month compared to that of beryllium-7 in the atmosphere. This could be due to the different residence time between tritium and beryllium-7. Beryllium-7 exists as a part of aerosol particles in the atmosphere as tritium exists as a part of water molecule in the atmosphere before precipitation and other particles sweep off these nuclides to the ground. The previous published concentrations of beryllium-7 in rainwater for New Zealand and Japan are ranged from (0.8 ~ 4.3) x 10^7 and (0.7 ~ 2.8) x 10^7 (atoms/kg), respectively. The concentrations of beyrillium-7 in Daejeon, Korea of this study are similar to those the published values. We also investigated sodium variation of the rainwater to see the effect of salt movement from the coastal region of Korea. There are not sufficient published data for beryllium-7 in rainwater for Korea. The data of this study will be an important data set of rainwater for future studies associated with rainwater in Korea.