\begin{definition}[Definition:Radioactive Decay]
'''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.
\end{definition}