Daily variation of I-131, Cs-134 and Cs-137 activity concentrations in the atmosphere in Osaka during the early phase after the FDNPP accident

To investigate the time variations of radionuclides discharged from the Fukushima Daiichi nuclear power plants accident, we started collecting aerosol samples in Osaka, Japan, using a high-volume sampler from March 15 to May 1, 2011. Atmospheric radioactivity concentrations of I-131, Cs-134 and Cs-137 were measured with germanium semi-conductor detectors. Only I-131 was detected in the early phase and two Cs-134.137 peaks were found in Osaka in April. Using the HYSPLIT model, we concluded that direct transportation of the air mass from the Fukushima area was responsible for such events.