Abstract: Based on the respiratory tract biodynamic model in ICRP 66 report, this paper established the clearance model of human respiratory tract by using Simulink simulation tool in MATLAB software. The variation of pulmonary effective dose conversion coefficient (mSv/WLM) under different parameters was calculated by using the clearance model. The results showed that the particle size of inhaled radon progeny had the greatest influence on the lung effective dose conversion coefficient. The lung effective dose conversion coefficient could change more than 10 times when the particle size range was between 0.7 nm and 10,000 nm. The second factor is respiration rate, which directly determines the number of radon daughter particles inhaled. The lung effective dose conversion coefficient of a male under heavy working state is 4.2 times that of a male under sleep state. The effect of unbound state fraction on dose conversion coefficient will change with the size of inhaled radon daughters. When the unbound state fraction changes from 0 to 0.08, the lung effective dose conversion coefficient can increase by 79% at most. In contrast, absorbed blood rate only affects the pulmonary effective dose conversion coefficient by less than 4%.

Key words: simulink, radon progeny, internal irradiation, respiratory tract clearance model