東京における雨水中の宇宙線生成核種Be-7、 Be-10

Abstract

Concentrations of cosmogenic nuclides Be-7 and Be-10 in rains collected in Tokyo during the last 20 years were determined by gamma-ray spectrometry and accelerator mass spectrometry. For the seasonal variation, the highest values for Be-10 flux and (10)Be/(7)Be 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 Be-7 flux. These feature were caused by the transport of stratospheric air with high Be-10 concentration into the troposphere. The annual fluxes for Be-7 and Be-10 change cyclic, and the average for Be-7 and Be-10 were about 3 and about 10 (x 10(exp -2) atom cm(exp -2)s(exp -1)) with +/- 50 percent and +/- 30 percent deviation, respectively. Comparing to the sunspot number as the index of cosmic ray intensity, the annual Be-7 flux was anti-correlated, and also the annual Be-10 flux was anti-correlated with two years delay. This implies that the most part of Be-7 atoms deposited in Tokyo were produced in the troposphere, and the fairly large part of Be-10 atoms deposited in Tokyo were produced in the stratosphere.