The energy required to break down a nucleus into its component nucleons is called the nuclear binding energy . 63 Cu + Energy 29 p + + 34 n o Nuclear binding energies are usually expressed in terms of kJ/mole of nuclei or MeV's/nucleon. To convert the binding energy to MeV (megaelectron volts) per nucleon we will employ the conversion factor for converting joules into MeV (1 MeV = 1.602 x 10 - 13 J ) and the number of nucleons (protons and neutrons) which make up the nucleus.