# It is said that atoms of elements of high atomic mass are unstable. So they emit alpha, beta or gamma rays. Suppose an atom emits alpha rays. The binding energy of alpha particle is about 27 MeV(million electron volt). It is said that as a result of this emission, the binding energy per nucleon of the parent atom increases. Could anyone please explain why? Is it because of the removal of 2 protons whose repulsive forces are responsible for the decreasing stability of the nucleus?