Nuclear fusion
Nuclear fusion combines nuclei, releasing energy that powers stars and weapons.
Nuclear fusion is a reaction in which two or more atomic nuclei combine to form a larger nucleus. The difference in mass between the reactants and products is manifested as either the release or the absorption of energy, a difference that arises from changes in nuclear binding energy. Active stellar cores are powered by fusion, and nucleosynthesis via fusion—both in the Big Bang and within stars—creates all elements lighter than nickel. Fusion typically occurs through thermonuclear fusion, an isotropic process requiring a triple product of extremely high temperature (in the kiloelectronvolt or hundred million Kelvin range), high density, and sufficient confinement time. These conditions are found only in thermonuclear weapons, boosted fission weapons, and experimental fusion power devices. A fusion process that produces nuclei lighter than nickel-62 is generally exothermic, due to the positive gradient of the binding energy curve; the most fusible nuclei are among the lightest, especially deuterium, tritium, and helium-3. The opposite process, nuclear fission, is most energetic for very heavy nuclei, particularly the actinides. Fusion power research aims to harness this energy, with tokamaks and stellarators being the dominant magnetic confinement designs. Fusion devices also serve as neutron sources and in superheavy element production. The concept of nuclear fusion was first proposed by American chemist William Draper Harkins in 1915. Francis William Aston’s 1919 invention of the mass spectrometer revealed that four hydrogen atoms are heavier than one helium atom, leading Arthur Eddington in 1920 to correctly predict that hydrogen fusion into helium could power stars. Quantum tunneling, discovered by Friedrich Hund in 1927, was applied to the nucleus by George Gamow in 1928, first to alpha decay and then to fusion. In 1929, Robert Atkinson and Fritz Houtermans made the first stellar fusion rate estimates. Hans Bethe and Charles Critchfield enumerated the proton–proton chain in 1938, and in 1939 Bethe published the CNO cycle for higher-mass stars. Early experiments included John Cockcroft and Ernest Walton’s 1932 reaction of a proton with lithium, producing two alpha particles, often considered the first artificial fusion. In 1933, Ernest Lawrence’s cyclotron experiments accidentally produced deuterium–deuterium fusion, though misinterpreted. In 1934, Mark
- field
- Nuclear physics
- known_for
- Powering stars, thermonuclear weapons, and potential energy source
- key_reactions
- Deuterium–tritium (DT) fusion, deuterium–deuterium (DD) fusion
Lore & Background
Nuclear fusion is a reaction where atomic nuclei combine to form a larger nucleus, with the mass difference between reactants and products released or absorbed as energy due to changes in nuclear binding energy. This process powers active stellar cores and, through nucleosynthesis in the Big Bang and stars, creates all elements lighter than nickel. Fusion typically occurs as thermonuclear fusion, an isotropic process requiring an extreme triple product of very high temperature—in the kiloelectronvolt or hundred million Kelvin range—density, and confinement time. Such conditions exist only in thermonuclear weapons, boosted fission weapons, and fusion power experiments. Fusion producing nuclei lighter than nickel-62 is generally exothermic due to the positive slope of the binding energy curve; the most fusible nuclei are the lightest, especially deuterium, tritium, and helium-3. In contrast, nuclear fission is most energetic for very heavy nuclei like the actinides. Fusion power research aims to harness this energy, with tokamaks and stellarators as dominant magnetic confinement designs; fusion devices also serve as neutron sources and in superheavy element production.
Reader's Guide
Nuclear fusion is fundamental to understanding stellar energy production and the synthesis of light elements. Its theoretical foundation was laid in the early 20th century by scientists like Harkins, Eddington, Gamow, and Bethe, who explained how stars fuse hydrogen into helium. Experimental milestones in the 1930s—from Cockcroft and Walton's first artificial fusion to Oliphant's demonstration of deuterium fusion and Ruhlig's discovery of the DT reaction—established the key reactions. The weaponization of fusion during the Manhattan Project and Cold War led to the development of thermonuclear weapons, including the Teller-Ulam design and boosted fission weapons. These advances also demonstrated the extreme conditions required for fusion. Controlled fusion for energy remains a major scientific and engineering challenge, pursued in devices like tokamaks and stellarators. Fusion's significance extends to its role as a neutron source and in superheavy element production, while its potential as a nearly limitless energy source continues to drive research.
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