Indoor 222Rn concentrations in radioisotope use, uranium use, and general use laboratories

Indoor 222Rn concentration was measured using an electrostatic radon monitor of PMT-TEL (Pylon Co.). The variation of radon concentration was compared among three kinds of laboratories: Radioisotope (RI) use, Uranium-use and general use laboratories. The 222Rn concentration observed in RI Center under air conditioning was about 3 Bq/m3 close to the outside 222Rn level. The indoor radon level increased up to about 30 Bq/m3 after the air conditioning was off. Radon exhalation rate was evaluated from increasing rate of radon concentrations after the air conditioning was stopped. In uranium use laboratories, the radon concentration was 40-70 Bq/m3 due to the storage of uranium compounds (about 12 kg). The negative correlation between radon concentration and atmospheric pressure was obtained when the variations of indoor temperature and relative humidity were small. On the other hand, the radon concentration was 5-15 Bq/m3 in general use laboratories of old 2nd building of Engineering, which had not so well shielded windows. In conclusion, indoor radon concentration in uranium use laboratories and RI center became high after air conditioning was off, and so it is recommended that the ventilation should be operated before entering the uranium use laboratories and RI center with well shielded facilities. (author)