Radioactive decay is the process in which a nucleus of an unstable atom loses energy by releasing radiation. The history of radioactive decay dates all the way back to 1896. Discovered by a French scientist named Henri Becquerel, radiation was thought to be similar to X-rays, instead is was much more complicated. The loss of energy from the nucleus happens when the parent radionuclide transforms into an atom with a nucleus in a different form, containing a different number of protons and neutrons
radioactive decay process wherein an excited nucleus interacts electromagnetically with one the orbital electrons of the atom. This causes the electron to be emitted (ejected) from the atom. Thus, in an internal conversion process, a high-energy electron is emitted from the radioactive atom, not from the nucleus. For this reason, the high-speed electrons resulting from internal conversion are not beta particles, since the latter come from beta decay, where they are newly created in the nuclear decay process