d
\(1\, a.m.u\) is defined as \(1 / 12^{\text {th }}\) of the mass of an atom of \(6^{ C ^{12}}\) isotope.

It can be shown that

1 a.m.u \(=1.66 \times 10^{27}\,kg\).

According to Einstein, mass energy equivalence

\(E = mc ^2\)

Where \(m =1.66 \times 10^{-27}\, kg\)

\(C =3 \times 10^8\, m / sec\), we get

\(E =1.49 \times 10^{-10}\, J \left(1 Mev =1.6 \times 10^{-13}\, J \right)\)

\(E =\frac{1.49 \times 10^{-10}\, J }{1.6 \times 10^{-13}}\,Mev\)

\(E =931.25\,Mev\)

Hence a change in mass of \(1\,a. m.u\) (called mass defect) releases an energy equal to \(931 \,Mev\).

\(1\,amu =931\,Mev\) is used as a standard conversion.