Chemical reactions occur because atoms strive for stability. Just like the outer electrons require a certain number of electrons to become stable, the nucleus requires a certain number of protons and neutrons to achieve this stability. The decomposition (breaking down) of the nucleus to achieve this stability is what we call Radioactive Decay. An unstable nucleus can be referred to as a Radionuclide.
Why do atoms decay in the first place? Each nucleus contains protons and neutrons. If there are too many or too few of the neutrons, the core of the atom becomes unstable, leading to the decay of the radionuclide.
How do we measure the rate of decay? We measure this by measuring the time it takes for exactly one-half of the radioactive substance’s nucleus to decay. There are three types of decay, and each one is based off the radiation emitted through radioactivity. The three types are: alpha, beta or gamma decay. Our very own sun emits gamma rays, but unlike that of unstable nuclei, its rays are from solar flares.