Discovery of Radiocesium-bearing Particles in Masks Worn by Members of the Public in Fukushima in Spring 2013

摘要

To investigate the publics' internal exposure by inhalation of radiocesium from the Fukushima Daiichi nuclear disaster in 2011, we examined the activity of radiocesium and radiocesium-bearing particles adhering to nonwoven fabric masks worn daily by members of the public in spring 2013 and 2014. We found a maximum cumulative Cs-137 activity of 4.58 +/- 0.15 Bq in 4 wk of spring 2013, which is 20.8% of the activity measured for the same subject in spring 2012 using the same method. This decrease was faster than the physical decay of radiocesium. Radiocesium was detected in 21 of 722 masks in 2013; three of these included type A radiocesium-bearing particles. The activity ratio of the radiocesium-bearing particles on the mask to the total radiocesium was at most approximately 20%. The two radiocesium sources, radiocesium-bearing particles and fugitive dust, are both insoluble particles. The largest internal dose from inhalation was 7.6 mu Sv in spring 2013, which is negligible compared to the dose limit recommended for members of the public by the International Commission on Radiological Protection.