Define and discuss mass deficit. A helium nucleus contains 2 protons and 2 neutrons. Using the established mass of the proton and neutron determine what the assembled mass should be. Compare this with the actual mass measured and determine the mass deficit, the difference between the actual and the measured. Use the figures to determine the energy in joules. Discuss the binding energy/nucleus with iron-56 as the nuclei most stable. Discuss how the transmutation occurring for nuclei greater than 56 lead to a greater stability as the nuclei.