From the ground into the lungs
The gaseous radon which comes out of the ground transforms within an hour into lead 210. During this hour an atom of radon will first transmute into several intermediate elements, some of which can deposit on tiny particles and enter the lungs if inhaled. Two of these radioelements, polonium 218 and polonium 214, emit alpha rays: the most dangerous form of radiations on direct contact with living matter.
IRES/IN2P3