Why does radioactivity take place?

When mass differences are small and the change in particles can only take place with the "weak" interaction, the rate of radioactive decay is slow. When mass differences are relatively large and the change takes place through the "strong" (or more fundamentally "color") interaction, the decay rate is fast. read more

In the case of radioactive decay, instability occurs when there is an imbalance in the number of protons and neutrons in the atomic nucleus. Basically, there is too much energy inside the nucleus to hold all the nucleons together. read more

Gamma radiation is emitted after the alpha or beta decay when the nucleus is in a “metastable” (excited) condition - it removes this excitation energy. Finally - to a physicist, the difference between x-ray and gamma radiation is the amount of energy a photon contains; gammas are higher-energy than x-rays. read more