Mass Defect

The difference between the sum of the masses of the nucleons constituting a nucleus and the rest mass of the nucleus is known as mass defect. It is denoted by m.

Let us calculate the mass defect in case of the nucleus of an atom The nucleus of the atom contains Z protons and (A-Z) neutrons. Therefore, if () is mass of the nucleus of the atom , then the mass defect is given by

'

The binding energy of a nucleus may be defined as the energy equivalent to the mass defect of the nucleus. It may be measured as the work required to be done to separate the nucleon an infinite distance apart, so that very no longer intract with each other.

If is mass defect of a nucleus, then according to Einstein’s Mass-energy relation, binding energy of the nucleus = (in joule).

Here, mass defect has to be measured in kilogram. In case, Mass defect is measured in a.m.u., then

Binding energy of the nucleus = (in MeV)