1. The problem statement, all variables and given/known data Two isotopes of a certain element have binding energies that differ by 5.03 MeV. The isotope with the larger binding energy contains one more neutron than the other isotope. Find the difference in atomic mass between the two isotopes. 2. Relevant equations 1u=931.5MeV 3. The attempt at a solution mass defect = m c = speed of light binding energy= mc^2 5.03 MeV = binding energy 1 - binding energy 2 I don't know where to go from here. The solution manual says if you convert 5.03MeV to atomic mass unit (u) and then subtract that from the atomic mass unit of a neutron (1.008665u-0.00540u), then that will be your answer. I guess the real question here is that I can't relate how you get the difference in atomic mass by just subtracting from the neutron.