Definition:Radioactive Decay

Definition
Radioactive decay is a first-order reaction in which the atoms of a substance may spontaneously break apart, thereby turning into atoms of a different substance. The probability of an individual atom decaying is an intrinsic property of the given chemical element.

Having decayed, that atom is now transformed into an atom of a different type, and so is not subject to any further occurrences of that particular decay process.

However, the new atom may have its own particular (different) mode of decay itself.