Be-7 nuclei produced by galactic cosmic rays and solar energetic particles, in the Earth's atmosphere

Be-7 radioactive nuclei with a half-life of 53.3 days result from spallation reactions of galactic cosmic rays (GCR) and solar energetic particles (SEP) with N and 0 nuclei in the Earth's atmosphere. We calculate the average global production of Be-7 in the atmosphere by GCR and SEP. The result indicates that an intense SEP event produces a large amount of Be-7 in the polar stratosphere and part of them could be transported to the surface at lower latitudes. The ground-level measurement of Be-7 in Japan exhibits the possibility of enhancement in the Be-7 radioactivity associated with the intense SEP event on July 14, 2000. In addition, the present experiment shows seasonal variations in the surface Be-7 concentration which peaks in spring and autumn. We discuss the possible air mass mixing between the stratosphere and troposphere to explain the measured seasonal variations. The surface concentration of Pb-210 nuclei indicates a similar trend to that of Be-7 and we suggest two possible explanations. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.