Energy

Beta decay takes place between isobars. The beta decays are determined by the mass differences. Various modes of beta decay are possible.

decay

This is for . The decay can be written as

Note that the masses we deal with are atomic masses; in increasing the atomic number, the atom acquires another electron; this is `provided' by the beta decay process. Thus the overall atomic process is

The neutrino is massless. The energy released as kinetic energy is then

decay

This is for . The decay can be written as

However, the reduction in atomic number has liberated an atomic electron; in terms of atoms

The energy released as kinetic energy is then

Electron capture

The above process cannot occur if the mass difference is less than twice the electrom mass ( MeV). The competing process of electron capture then becomes important. The s electrons in particular have a non-vanishing density within the nuclear volume. An atomic electron can then be `captured' by a proton to yield

Electron numbers are now balanced and the energy release is

where is the binding energy of the captured electron.