Here's why:

* Radioactive decay is the process where an unstable atomic nucleus loses energy by emitting radiation.

* This process transforms the original atom (the parent nuclide) into a different atom (the daughter nuclide).

For example, in the decay of carbon-14 (parent nuclide) to nitrogen-14 (daughter nuclide), the carbon-14 atom emits a beta particle (an electron) and a neutrino. This changes the identity of the atom, transforming it into nitrogen-14.