What characteristics of radioactivity show it to be nuclear in origin and not atomic?

The phenomenon of radioactivity is the spontaneous breakdown of energetically unstable atomic nuclei into more stable atomic nuclei.

The spontaneous emission of \({\rm{\alpha }}\)- particles, \({\rm{\beta }}\) particles or \({\rm{\gamma - }}\)radiation from the nuclei of some elements is called radioactivity. This phenomenon was discovered by Becquerel. The emitted radiations are called nuclear radiation and the element emitting these radiations is called radioactive element.

Radioactivity is not affected by any chemical or physical property. Naturally occurring radioactive nuclides are heavy elements like uranium,thorium,radium etc. They are independent of temperature or ionization of atom. Also the energy poses by these radiations is more than the atomic energy. These are some of the experimental evidences shows that radioactivity is nuclear in origin.

Therefore, Radioactivity is not affected by any chemical or physical property.so its practical origin in nuclear not atomic