Mass Defect
The difference between the mass of a nucleus and the sum of the masses of its constituent nucleons.
Formula / equation
Δm = Zm_p + Nm_n − m_nucleus
Unit
u
In depth
The missing mass has been converted into binding energy according to Einstein's mass–energy equivalence. Because the conversion factor c² is so large, a mass defect of only a fraction of a percent corresponds to an enormous energy release.
Examples in the real world
Helium-4 has a mass defect of 0.0304 u, equivalent to 28.3 MeV of binding energy.