Radon: characteristics in air and dose conversion factors

The dose conversion factor (DCF) which gives the relationship between effective dose and potential alpha energy concentration of inhaled short-lived radon decay products is calculated with a dosimetric approach. The calculations are based on a lung dose model with a structure that is related to the new recommended ICRP respiratory tract model. The characteristics of the radon decay products concerning the unattached fraction and the activity size distribution of the radon decay products are important input quantities for the calculation of DCF. Experimental data about these parameters obtained from measurements in homes, at working places, and in the free atmosphere at ground level in the last past years are summarized. Taking into account the measured aerosol characteristics the DCF fractions of the unattached (DCFu) and aerosol-attached (DCFae) radon decay products for different places were calculated. Variation of DCF for different places were caused dominantly by the variation of DCFu of the unattached radon clusters (0.3-32 mSv WLM(-1)). Nose inhalation drastically reduced (about a factor 4) the dose contribution by the unattached cluster. The dose fraction by the radon decay product aerosol (DCFae) varies between 4-10 mSv WLM(-1). Taking into account a relative sensitivity distribution between bronchial, bronchiolar and alveolar regions of the thoracic lung with 0.80:0.15:0.05 and nose breathing the DCF of most of the working places (inhalation rate: 1.2 m3 h(-1)) vary between 5.7-6.7 mSv WLM(-1) depending on the number concentration of the aerosol particles. The DCF-value of 4.2 mSv WLM(-1) for the general public in dwellings with higher aerosol concentration (>4 x 10(4) particles cm(-3)) has about the same value as recommended by ICRP 65 (1994b). Significantly higher are the DCF-values for "normal" aerosol conditions indoors (5 x 10(3)-4 x 10(4) particles cm(-3)) and in the open air (7.3 mSv WLM(-1) and 9.7 mSv WLM(-1)).