Nanosize radon short-lived decay products in the air of the Postojna Cave.

At two points in the Postojna Cave, short-term monitoring in summer and in winter of air concentrations of radon and radon decay products, equilibrium factor, unattached fraction of radon decay products (f(un)), barometric pressure, relative air humidity in the cave and air temperature in the cave and outdoor has been carried out, with the emphasis on f(un). Dose conversion factors, calculated on the basis of f(un) values obtained (ranging from 0.09 to 0.65) exceed 5 mSv WLM(-1), by a factor of 11.5-14.0 in summer and of 3.0-4.0 in winter for mouth breathing, and 3.1-3.5 in summer and 1.5-1.7 in winter for nasal breathing.