The atomic number of a nucleus is the number of protons contained in the nucleus.

(K-capture) An unstable atom with too many protons in the nucleus, and not enough energy to emit a positron, reaches a stable state in the way, that one proton captured an electron from the atom's inner shell (K-shell) and change to a neutron. A neutrino is emitted from the atoms nucleus by this process. The atomic mass of the atom is unchanged, but the decreased number of protons transformed the atom to a different element.

Atomic or nuclear fission is the process of splitting a heavy nucleus into two lighter nuclei. Some nuclides split up spontaneous as a type of radioactive decay. In other elements, fission is induced through the reaction of an incident radiation with the nucleus. High energy rates are released during the fission reaction (difference between the binding energies); this energy is used to produce heat and electricity e.g. in nuclear power plants.

In the internal conversion process the multipole electric field of the nucleus of an atom, in an electromagnetically excited state, react with an orbit electron. With enough energy the electron is ejected (internal conversion electron). The energy of the conversion electron depends on the energy transferred from the nucleus reduced by the shell specific binding energy. This process competes with gamma emission. The refilling for the vacancy left by the internal conversion electron occurs through the Auger effect, a higher orbit electron take place and x-ray or an Auger electron will be emitted.
The atomic number of the atom gets not changed by internal conversion.

See also Conversion Electron, Auger Effect and Auger Electron.

If a nucleus still has excess energy after attempts of stabilization, it can emit energy without changing the number of protons or neutrons. This process is named isomeric transition. One way of isomeric transition is the emission of a gamma rays, the other competing way is internal conversion, where the excess energy of the nucleus must exceed the binding energy of an electron, which then will be ejected from the atom.

See also Decay, Gamma Radiation and Internal Conversion.