Nuclear binding energy

nuclear binding energy
(Science: physics) The difference between the total energy (= mc^2) of the bound nucleus, and the energies of the individual constituent particles (= sum of masses c^2). The nuclear binding energy per nucleon is a maximum for iron. Fusion releases energy because light nuclei are less tightly bound than medium–weight nuclei, and thus energy is liberated when they become more tightly bound after fusing. Fission releases energy for the same reason – heavy nuclei are also less tightly bound than medium-weight nuclei, and energy is liberated when heavy nuclei split into lighter nuclei.