Daily Variation of Cosmogenic Nuclide Be-7 Concentration in the Atmosphere and Solar Activities

Concentrations of cosmogenic radioisotop e Be-7 in air were daily observed at Yamagata University during 2000 and 2002. From the power spectral analysis, the periodicity of the period of 26 days is shown for the daily Be-7 concentrations. The folding analysis shows that the phase delay of the Be-7 concentration was roughly 8 days to the sunspot number. These results indicate that the Be-7 concentrations in the air at ground level have 26-day periodicity as a component of time variations and it is caused by the solar modulation of galactic cosmic rays.