Fundamentals: Atomic mass unit , u

The mass of proton and neutron are taken to be 1.007825 u and 1.008665 u in nuclear physics where calculations of E = mc2 is used . If proton and neutron are involved in collisions then there are taken to be 1.0 u. Electrons having 0.000548 u normally does not come into the picture in nuclear collisions due to its small mass. It mass cannnot be ignored in nuclear reactions involving binding energy.