Radon Gas or rado (formerly called niton or nito) is the chemical element represented in the periodic table by the symbol Rn and atomic number 86.

Discovered in 1899 by Robert B. Owens and Ernest Rutherford, it is a noble and radioactive gas  formed from the decay of radium, which in turn is generated by the α decay of uranium. Polonium and bismuth are the extremely toxic products of the radioactive decay of radon.

Radon is a very heavy gas, dangerous for human health if inhaled in significant quantities.

One of the main risk factors of radon is linked to the accumulation in closed places where it permeates from the subsoil; it is the second cause of lung cancer, especially among smokers.

Outdoors, however, the concentration of radon is very limited, thanks to its high specific weight which hinders its exit from the ground and to the dilution in the atmosphere of the exhalation part (about 1000 times lower than the potential concentration indoors).