Hi can any body help me on this I really need it. The nuclide Sn has a filled proton shell, 50 being on one of the magic nucleon number. Sb has an extra proton outside this shell to make 51. According to the shell model, extra proton should be easier to remove than a proton from the filled shell. Verify this by calculating the required energy in each case. Sn mass 121 Atomic Mass (u) 119.902199 Sb mass 120 Atomic Mass (u) 120.903821 Mass of hydrogen atom is 1.007825u.