Inhalation of the short-lived radon and thoron decay products in homes, at work places and in the outdoor atmosphere, yield the greatest amount of the natural radiation exposure of man. Radon is known to present a risk of lung cancer when it, or rather its decay products are inhaled. For this reason, it is of great importance to determine concentrations of radon, thoron and their progeny in a room. For that purpose extended Jacobi's room model for...