I understand that some nuclei and their isotopes are not stable and therefore at random intervals bits of the nucleus (i.e. protons & neutrons) break away with differing amounts of energy depending on a few variables. Grossly simplifying things, alpha particles are big and slow, beta are smaller and faster and gamma rays are highly energetic elecromagnetic radiation traveling at the speed of light. The particles seem easy enough to understand on a basic intuitive level, gamma rays less so. While the particles were an "observable" part of the nucleus before they radiated away, the gamma rays were not. However I believe it is correct to say that a by product of the decay is the generation of gamma rays which can also be characterised as photons. X-rays overlap with gamma rays but to be honest I have not spent much time understanding this area.
This is the background that seems logically to lead to my question. These things (alpha, beta, gamma, X-rays) break off from the nucleus. Their energies are such that they are able to knock electrons off other nuclei (hence "ionizing") and – I'm guessing now – there are imbalances in energy levels in the radioactive nuclei which the decay helps resolve.
What's really going on? What is the basic theoretical framework for understanding this phenomenon? And, putting aside the big bang, where does this story start? Is a radioactive nucleus "born" radioactive?
Best Answer
All elements above Iron are created when a star implodes under its own gravity in the form of a supernova. These heavy elements are ejected into space in this process and go on to form parts of planets such as Earth. This includes all their various radioactive isotopes.
From the moment the unstable isotope is created, it wants to radioactively decay so as to attain a more stable configuration. This will continue to happen until the atom reaches a state which has an extremely long half life (such as $\text{Pb}^{82}$). The three most important ways in which an atom can decay are as follows-
1) $\alpha$-Decay: Ejection of Helium$(\text{He}^{2+})$ ion
2) $\beta^-$-Decay: Ejection of electron$(\text{e}^{-}) \text{ and anti-neutrino}(\bar v_e)$
3) $\beta^+$-Decay: Ejection of positron$(\text{e}^{+}) \text{ and neutrino} (v_e)$
These three affect the atomic and mass number in different ways which you can read more about here. All radioactive disintegration follows first order kinetics. The $\gamma$-rays released is just the difference in mass between the two atoms. This happens according to Einstein's famous equation $E=\Delta mc^2$. These are just the basics which should be sufficient for understanding purposes.