What is "nuclear fusion"

nuclear fusion \nuclear fusion\ n. A type of nuclear reaction in which atomic nuclei combine to form more massive nuclei with the simultaneous release of energy.

Syn: fusion, nuclear fusion reaction.

n. (context physics English) The combining of the nuclei of small atoms to form the nuclei of larger ones, with a resulting release of large quantities of energy; the process that makes the sun shine, and hydrogen bomb explode.

n. a nuclear reaction in which nuclei combine to form more massive nuclei with the simultaneous release of energy [syn: fusion, nuclear fusion reaction]

In nuclear physics, nuclear fusion is a nuclear reaction in which two or more atomic nuclei come close enough to react and form one or more different atomic nuclei and subatomic particles (neutrons and/or protons). The difference in mass between the products and reactants leads to the release of large amounts of energy. This difference in mass arises due to the difference in atomic " binding energy" between the atomic nuclei before and after the reaction. Fusion is the process that powers active or " main sequence" stars, or other high magnitude stars.

The fusion of two nuclei with lower masses than iron-56 (which, along with nickel-62, has the largest binding energy per nucleon) generally releases energy, while the fusion of nuclei heavier than iron requires energy input. The opposite is true for the reverse process, nuclear fission. This means that only lighter elements are fusable, such as hydrogen and helium, and likewise, that only heavier elements are fissionable, such as uranium and plutonium. There are, however, extreme astrophysical events that can lead to short periods of fusion with heavier nuclei. This is the process that gives rise to the creation of the heavy elements during events such as a supernova.

Following the discovery of quantum tunneling by physicist Friedrich Hund, in 1929 Robert Atkinson and Fritz Houtermans used the measured masses of light elements to predict that large amounts of energy could be released by fusing small nuclei. Building upon the nuclear transmutation experiments by Ernest Rutherford, carried out several years earlier, the laboratory fusion of hydrogen isotopes was first accomplished by Mark Oliphant in 1932. During the remainder of that decade the steps of the main cycle of nuclear fusion in stars were worked out by Hans Bethe. Research into fusion for military purposes began in the early 1940s as part of the Manhattan Project. Fusion was accomplished in 1951 with the Greenhouse Item nuclear test. Nuclear fusion on a large scale in an explosion was first carried out on November 1, 1952, in the Ivy Mike hydrogen bomb test.

Research into developing controlled thermonuclear fusion for civil purposes also began in earnest in the 1950s, and it continues to this day.