What does mean by mass defect? Establish relation between mass defect and nuclear binding energy. And hence write the expression for binding energy per nucleon.
Mass defect: It is found that the mass of a stable nucleus is always less than the sum of masses of its constituent protons and neutrons in their free state.
Consider the Nucleus AZX.
Expression for binding energy: The nucleus AZX contains Z protons and (A−Z) neutrons.
Its mass defect is
Δm=Zmp+(A−Z)mn−mN
Where mN→ mass of nucleus
The binding energy Eb of the nucleus is given by,
ΔEb=Δm×c2=[Zmp+(A−Z)mn−mN]c2
The binding between the constituents of the nucleus is the binding energy per nucleon, Ebn, which is the ratio of the binding energy Eb of a nucleus to the number of the nucleons, A, in that nucleus:
Ebn=EbA.