Cosmogenic nuclides 7Be and 10Be in rains collected in Tokyo

Concentrations of cosmogenic nuclides 7Be and 10Be in rains collected in Tokyo during the last 20 years were determined by γ-ray spectrometry and accelerator mass spectrometry. For the seasonal variation, the highest values for 10Be flux and 10Be/7Be ratio were observed in spring, February to April, and they decreased till the lowest values in autumn. On the other hand, there were not so clear feature for 7Be flux. These feature were caused by the transport of stratospheric air with high 10Be concentration into the troposphere. The annual fluxes for 7Be and 10Be change cyclic, and the average for 7Be and 10Be were ∼3 and ∼10 (x10-2 atom cm-2 s-1) with ±50% and ±30% deviation, respectively. Comparing to the sunspot number as the index of cosmic ray intensity, the annual 7Be flux was anti-correlated, and also the annual 10Be flux was anti-correlated with two years delay. This imply that the most part of 7Be atoms deposited in Tokyo were produced in the troposphere, and the fairly large part of 10Be atoms deposited in Tokyo were produced in the stratosphere. (author)