[18p-E312-1~7] 2.4 Accelerator Mass Spectrometry, Accelerator Beam Analysis

[18p-E312-4] Distribution of the cosmogenic ¹⁰Be in the atmosphere.

〇Takeyasu Yamagata^1,2, Hisao Nagai², Hiroyuki Matsuzaki¹ (1.The Univ. of Tokyo, 2.Nihon Univ.)

Keywords:Accelerator mass spectrometry, Cosmogenic nuclide

The concentrations of ⁷Be and ¹⁰Be were investigated at Dazaifu, Fukuoka (1999-2002) and Tokyo (2002-2014) during 1998 to 2014. The seasonal variations were same in each year; high concentrations and high isotopic ratios of ¹⁰Be/⁷Be caused by strong stratosphere-troposphere exchange (STE) were appeared in February to June, and the high concentrations but constant ¹⁰Be/⁷Be by vertical convection in troposphere were appeared in July to December. The concentrations were reconstructed by the box model formula. The parameters of the mean residence time and STE intensities, and period, were constant. The amplitudes of production rate were higher than the amplitude of cosmic ray neutron flux observed at Moscow near earth’s surface by a factor of 4. Since the neutron flux amplitude at polar region that was little influenced by geomagnetic field was only 10% higher than Moscow, the high amplitudes of production rate were assumed that caused by changing of energy spectrum of galactic cosmic ray.