Particle Size of Unattached Radon Progeny in Filtered Room Air

The size distribution of the unattached radon progeny in filtered room air was measured with a serial array of wire screens. Nearly all the size distributions 2 to 3 min air, measured with the graded wire screen samplers were unimodal, with a geometric standard deviation averaging 1.8±0.058. The grand average of the geometric mean and standard error of the mean diffusion coefficient was 0.048±0.0004. The results obtained using different combinations of the graded wire screens were consistent. The measured diffusion coefficient predicts a nasal penetration of 9% to 16% for inspiratory flow rates of 31.min-1 to 30 1.min-1, respectively. The results indicate that about 15% of the inhaled unattached radon progeny penetrate beyond the nose into the tracheobronchial region to deliver a radiation dose to the bronchial epithelium.