Equilibrium factor high radon concentration

It is to be noted that the conversion factor of 20 mSv effective dose equivalent per 200 Bq m 3 equilibrium equivalent radon concentration, considered by the ICRP (ICRP, 1984) in recommending an Action Level for remedying high indoor radon concentrations, corresponds to a dose rate of about 40 pGy per y per Bq m 3 radon gas concentration. 

Two types of track-etch monitor occur, open and closed types. In the open type, the SSNTD is not contained in a volume and is exposed to the air as a bare foil. This detector will register the alpha radiation from the Rn and RnD in the air, and the track density on the foil represents the sum of these activities. However, the Rn signal will be much larger than the signal from the RnD, except at very high levels of RnD (high F factor), and the track density has to be interpreted in terms of this ratio, which is typically unknown. In close monitors the SSNTD is enclosed in a closed container into which Rn diffuses through a filter. This prevents the entry of RnD and dust particles into the chamber, and the foil is then sensitive only to the alpha radiation from Rn and RnD formed in the container. There is a repeatable equilibrium between the isotopes in the container, and calibration provides the relationship between the Rn concentration and the track density on the foil. A typical track-etch radon monitor of the closed type is shown in Fig. 9.27. 

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