Levels of airborne radionuclides at Hegura Island, Japan

摘要

Activity concentrations of airborne ~(222)Rn, ~(210)Pb,~7Bb, ~(137)Cs and ~(22)Na have been measured at Hegura Island (37.8°N, 136.9°E) located 50 km from Noto Peninsula, and their variations have been studied and compared with those found at Tatsunokuchi, Ishikawa Prefecture, Japan. Activity concentrations of ~(210)Pb and ~7Be varied hourly even in calm weather, and predominantly during drastic changes in meteorological conditions such as the passage of a typhoon or cold front. Activity concentrations and seasonal variations of both~(210)Pb and ~7Be at Hegura Island were found to be similar to those measured at Tatsunokuchi, with decreasing levels from late spring to summer and increasing levels from autumn to winter season. These variations are opposite to those obtained for ~(222) in the corresponding areas. Activity concentrations of airborne ~(137)Cs and ~(22)Na at Hegura Island varied from 0.1 to ～1.5 μBq m~(-3) and showed seasonal variations similar to those of ~(210)Pb and ~7Be.