Mitigation effects of radon decay products by air cleaner

Comparison measurement of unattached radon progeny concentration in three different environments

Accurate measurement of unattached radon progeny is important for dose evaluation of radon exposure. For quality control of field surveys, a series of comparison measurements were carried out using three commercial unattached radon progeny monitors in real environments as well as in a radon chamber. The results show that the radon equilibrium equivalent concentrations (EECs) of different monitors agree very well, mostly within ±3.0% where there is no thoron progeny interference in the radon chamber. However, the unattached fraction of radon progeny is not so consistent, and the relative difference is 3.3% ~ 39.5% in different environments. The unattached fraction of radon progeny is affected by aerosol concentration. Anomalously high unattached fraction was found in the environment with extremely high humidity and low aerosol concentration. For accurate measurement of unattached radon progeny, specific attention should be paid to the collection efficiency of unattached radon progeny and the interference of attached radon progeny on a wire screen.

Japanese population dose from natural radiation

The radiation doses from natural radiation sources in Japan are reviewed using the latest knowledge. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the Nuclear Safety Research Association report the annual effective doses from cosmic rays, terrestrial radiation, inhalation, and ingestion as natural sources. In this paper, the total annual effective dose from cosmic-ray exposure is evaluated as 0.29 mSv. The arithmetic mean of the annual effective dose from external exposure to terrestrial radiation is 0.33 mSv for the Japanese population using the data of nationwide surveys by the National Institute of Radiological Sciences. Previously in Japan, although three different groups have conducted nationwide indoor radon surveys using passive-type radon monitors, to date only the Japan Chemical Analysis Center (JCAC) has performed a nationwide radon survey using a unified method for radon measurements conducted indoor, outdoor, and in the workplace. Consequently, the JCAC results are used for the annual effective dose from radon and that for radon inhalation is estimated as 0.50 mSv using a current dose conversion factor. In this paper, UNSCEAR values are used for the mean indoor and outdoor thoron-progeny concentrations, and the annual effective dose from thoron is reported as 0.09 mSv. Thus, the annual effective dose from radon and thoron inhalation is 0.59 mSv. From a JCAC large-scale survey of foodstuffs, the committed effective dose from the main radionuclides in dietary intake is 0.99 mSv. Finally, the Japanese population dose from natural radiation is given as 2.2 mSv, which is similar to the reported global average of 2.4 mSv.

Characteristics of indoor radon and its progeny in a Japanese dwelling while using air appliances

Characteristics of radon and its progeny were investigated in different air conditions by turning four types of indoor air appliances on and off in a two-story concrete Japanese dwelling. The four appliances were air conditioner, air cleaner, gas heater and cooker hood. The measurements were done using two devices: (1) a Si-based semiconductor detector for continuous measurement of indoor radon concentration and (2) a ZnS(Ag) scintillation counting system for equilibrium-equivalent radon concentration. Throughout the entire experiment, the cooker hood was the most effective in decreasing indoor radon concentration over a long period of time and the less effective was the air conditioner, while the air cleaner and gas heater did not affect the concentration of radon. However, the results measured in each air condition will differ according to the lifestyles and activities of the inhabitants. In this study, indoor radon and its progeny in a Japanese dwelling will be characterised by the different air conditions.