Relation between daily variation of cosmogenic nuclide be-7 concentration in atmosphere and solar activities

Daily concentration of Be-7 in air at a ground level has been continuously observing since 1993. As Be-7 is a radioisotope with the half-life of 53 days, which is prod uced by nuclear interactions between cosmic rays and atmosphere, it might be responsible to short time variations of the solar activities such as the rotation period of the sun 27 days. The Be-7 produced at troposphere falls into the ground as aerosol and hence the concentration of it in air is affected by the weather conditions. Although the anti-correlation between the production of cosmogenic nuclides and sunspots numbers in the 11 -yaer solar cycles is evident, the main factor of daily variation of Be-7 concentration in atmosphere is not clear. The Be 7 samples in a- day are collected in a glass filter with a high volume air sampler with the sampling rate of 1000 Litter/min. The radioactivity of Be-7 in the filter is measured with a high -purity germanium gamma ray detector. The time variations of the concentration of Be-7 are analyzed for 730 days at the solar maximum from 2000 to 2002. The power spectral analysis shows that the periodicities of 18 days and 28 days. The folding analysis, also, shows that the Be-7 is anti-correlated to the modulation of the sunspots number. Since the periodicity of 27 days for sunspots indicates the rotation of the sun , the periodicity of 28 days for Be-7 implies a relationship between the concentration of Be-7 in air and the sunspots number. We will describe the relationship between the Be-7 concentration and the sunspots number considering the weather conditions in the ground in detail.