Atmospheric concentrations of 210Pb and 7Be observed in Okinawa Islands

Atmospheric measurements of naturally occurring radionuclides 210Pb and 7Be were conducted at ground level in the Okinawa Islands. Weekly data collected from Okinawa-jima over a seven-year period from 2004 to 2011 and Kume-jima and Minamidaito-jima over a two-year period from 2008 to 2010 are presented and discussed. The monthly averaged activity concentrations of 210Pb at three sites showed a 'one-peak' seasonal variation - the maximum peak appeared from autumn to spring - and 7Be showed a pattern similar to that of 210Pb. Activity concentrations of 210Pb and 7Be at Okinawa Islands ranged from 0.06 to 1.98 mBq/m3 with a mean of 0.80 mBq/m3 and from 1.45 to 15.1 mBq/m3 with a mean of 8.47 mBq/m3, respectively. Activity concentrations of both radionuclides at Kume-jima and Minamidaito-jima were almost the same as at Okinawa-jima. It is suggested that the relatively higher activity concentrations of both radionuclides in winter observed at the present three sites are affected by the air mass from the inland area of the Asian Continent. (author)