Radon-220 decay chain

²²⁰Rn is a decay product of the long-lived ²³²Th isotope. The half life of ²³²Th is 14 billion year. Thorium occurs in thorite and in thorianite and is thought to be about three times as abundant as uranium and about as abundant as lead. However, in ordinary soil and in building materials made from soil usually more ²³⁸U than ²³²Th occurs. A striking feature of the decay series of ²²⁰Rn is its branching after the ²¹²Bi isotope. It is not uncommon that a nuclide has two different decay types, but one decay type usually dominates over the other(s) in such a way that the nuclide can be considered to have only one daughter.

Radon-220 decay chain