Why is energy released by nuclear fusion reactions?
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Havy elements (e.g., uranium) have 92 protons tied together in one nucleus by the short-range nuclear strong force and repelled by the Coulombic force. If the nucleus splits, the attractive force is only slightly reduced (because the nucleons only attract close nucleons strongly), but the longer-range repulsive force is cut dramatically. The average binding force for the 235–238 nucleons of uranium is about 7.7 MeV; after the split (e.g., into iron, tho it’s more complex), the average binding force per nucleon increases to about 8.8 MeV. Thus, one uranium fission can yield 260 MeV of energy.
Deuterium (one proton, one neutron) is bound with an energy of 2.4 MeV, or 1.2 MeV per nucleon. When two deuteriums fuse, helium is produced with a binding energy of 28 MeV. The gain is 23.2 MeV. One fusion produces 9% of the energy of one fission. But we should compare equal starting masses: one fission (~235 nucleons) vs 59 fusions of 4 nucleons each. The comparison is then 260 MeV vs 1363 MeV.
The binding energies of the elements rise to a maximum stability at iron, then decrease. The heavy elements are produced in supernovas and “cooled” down before they can equilibrate to form iron. We got some of that star dust on earth. Wikipedia has a good article. Here is a chart of the binding energies.
Deuterium (one proton, one neutron) is bound with an energy of 2.4 MeV, or 1.2 MeV per nucleon. When two deuteriums fuse, helium is produced with a binding energy of 28 MeV. The gain is 23.2 MeV. One fusion produces 9% of the energy of one fission. But we should compare equal starting masses: one fission (~235 nucleons) vs 59 fusions of 4 nucleons each. The comparison is then 260 MeV vs 1363 MeV.
The binding energies of the elements rise to a maximum stability at iron, then decrease. The heavy elements are produced in supernovas and “cooled” down before they can equilibrate to form iron. We got some of that star dust on earth. Wikipedia has a good article. Here is a chart of the binding energies.
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Fusion powers the Sun and stars as hydrogen atoms fuse together to form helium, and matter is converted into energy. ... The nuclei can then fuse, causing a release of energy.
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