Why is radioactivity considered a nuclear phenomenon?

(N/A) Radioactivity is considered a nuclear phenomenon because it involves the spontaneous disintegration of an unstable atomic nucleus.
$1$. The process originates from within the nucleus,where the ratio of neutrons to protons is not optimal for stability.
$2$. The emission of alpha particles,beta particles,or gamma rays occurs due to the rearrangement of nucleons (protons and neutrons) inside the nucleus to reach a more stable state.
$3$. External factors such as temperature,pressure,chemical state,or electromagnetic fields do not affect the rate of radioactive decay,proving that the process is independent of the electronic structure of the atom and is entirely confined to the nucleus.