What is the mass loss of the nucleus, in u, upon emission of this gamma ray? - g?

Suppose that the energy of the emitted gamma ray photon is given the symbol "e" in units of Kev

Now, we use Einstein's equation (E = mc²) where c is the speed of light (3 x 10^8 m/sec)

substituting in this equation, we find that:

e = mass x c²

mass = e / c²

Now to get the corresponding value in atomic mass unit:

1 eV/c² = 1 / (931.46 * 10^6) amu

Therefore,

The mass in amu = e x 1 / (931.46 * 10^6) atomic mass unit