2016 Volume 19 Issue 1 Pages 40-48
Smoking and radon inhalation are the primary causes of lung cancer in many countries. The world average annual dose due to radon inhalation is 1.26 mSv y－1, which is more than half of the annual exposure dose from natural radiation sources, 2.40 mSv y－1. In this study, radon and thoron radioactivity concentrations（ hereafter referred to simply as concentrations） measurements were carried out in the Tokyo Metropolitan University Arakawa Campus building using a pulse type ionization chamber and passive radon and thoron discriminative monitors. The respective average （±σ） radon concentrations （Bq m－3） for each day of the week from Sunday to Saturday were: 21 ± 7, 20 ± 7, 20 ± 8, 22 ± 6, 21 ± 7, 20 ± 6, 23 ± 7. On week days, the radon concentration peaked daily at 8:00 am with a value of 25 ± 6 Bq m－3, it decreased until 7:00 pm reaching a value of 17 ± 7 Bq m－3, and then, showed a rising trend to the next morning’s peak. Radon concentration tended to show a higher value and less fluctuation on weekends. No seasonal change was observed. No correlation was observed between radon concentration and thoron concentration. In Japan, the repor ted arithmetic average radon concentration indoors is 15.5 Bq m－3 and the arithmetic average concentration outdoors is 5.4 Bq m－3. The annual effective dose of radon by inhalation in Japan is 0.64 mSv y－1. The average radon concentration of reinforced concrete buildings tends to be higher, though a radon concentration survey in reinforced concrete buildings in Japan is lacking. Calculated annual average exposure dose in the campus reinforced concrete building was 0.15 mSv y－1. Annual average exposure dose considering an indoor environment other than the Arakawa Campus building was 0.42 mSv y－1.
