Proton Emission
Proton emission is a type of nuclear decay in which an unstable atomic nucleus ejects a single proton.
Proton emission occurs in proton-rich isotopes. It does not occur in any naturally-occurring isotopes – such proton-rich isotopes must be made, usually in a particle accelerator.
An Example of Proton Emission
Cobalt-48 is an isotope of cobalt that decays via proton emission to iron-47. The nuclear equation below represents this process.
$$_{27}^{48}\textrm{Co} \, \rightarrow \, _{26}^{47}\textrm{Fe} + p$$
Since one proton is lost, the atomic number of the original nucleus decreases by 1, and the mass number of the original nucleus also decreases by 1.