<P> Surface energy . A nucleon at the surface of a nucleus interacts with fewer other nucleons than one in the interior of the nucleus and hence its binding energy is less . This surface energy term takes that into account and is therefore negative and is proportional to the surface area . </P> <P> Coulomb Energy . The electric repulsion between each pair of protons in a nucleus contributes toward decreasing its binding energy . </P> <P> Asymmetry energy (also called Pauli Energy). An energy associated with the Pauli exclusion principle . Were it not for the Coulomb energy, the most stable form of nuclear matter would have the same number of neutrons as protons, since unequal numbers of neutrons and protons imply filling higher energy levels for one type of particle, while leaving lower energy levels vacant for the other type . </P> <P> Pairing energy . An energy which is a correction term that arises from the tendency of proton pairs and neutron pairs to occur . An even number of particles is more stable than an odd number . </P>

What is located between the nucleus and the electrons