nuclear fusion

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nuclear fusion

a reaction in which two nuclei combine to form a nucleus with the release of energy

Nuclear fusion

One of the primary nuclear reactions, the name usually designating an energy-releasing rearrangement collision which can occur between various isotopes of low atomic number. See Nuclear reaction

Interest in the nuclear fusion reaction arises from the expectation that it may someday be used to produce useful power, from its role in energy generation in stars, and from its use in the fusion bomb. Since a primary fusion fuel, deuterium, occurs naturally and is therefore obtainable in virtually inexhaustible supply, solution of the fusion power problem would permanently solve the problem of the present rapid depletion of chemically valuable fossil fuels. As a power source, the lack of radioactive waste products from the fusion reaction is another argument in its favor as opposed to the fission of uranium. See Nuclear fission

In a nuclear fusion reaction the close collision of two energy-rich nuclei results in a mutual rearrangement of their nucleons (protons and neutrons) to produce two or more reaction products, together with a release of energy. The energy usually appears in the form of kinetic energy of the reaction products, although when energetically allowed, part may be taken up as energy of an excited state of a product nucleus. In contrast to neutron-produced nuclear reactions, colliding nuclei, because they are positively charged, require a substantial initial relative kinetic energy to overcome their mutual electrostatic repulsion so that reaction can occur. This required relative energy increases with the nuclear charge Z, so that reactions between low-Z nuclei are the easiest to produce. The best known of these are the reactions between the heavy isotopes of hydrogen, deuterium, and tritium.

Nuclear fusion reactions can be self-sustaining if they are carried out at a very high temperature. That is to say, if the fusion fuel exists in the form of a very hot ionized gas of stripped nuclei and free electrons termed a plasma, the agitation energy of the nuclei can overcome their mutual repulsion, causing reactions to occur. This is the mechanism of energy generation in the stars and in the fusion bomb. It is also the method envisaged for the controlled generation of fusion energy.

The cross sections (effective collisional areas) for many of the simple nuclear fusion reactions have been measured with high precision. It is found that the cross sections generally show broad maxima as a function of energy and have peak values in the general range of 0.01 barn (1 barn = 10-24 cm2) to a maximum value of 5 barns, for the deuterium-tritium (D-T) reaction. The energy releases of these reactions can be readily calculated from the mass difference between the initial and final nuclei or determined by direct measurement.

Some of the important simple fusion reactions, their reaction products, and their energy releases are:

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If it is remembered that the energy release in the chemical reaction in which hydrogen and oxygen combine to produce a water molecule is about 1 eV per reaction, it will be seen that, gram for gram, fusion fuel releases more than 1,000,000 times as much energy as typical chemical fuels.

nuclear fusion

A process in which two light nuclei join to yield a heavier nucleus. An example is the fusion of two hydrogen nuclei to give a deuterium nucleus plus a positron plus a neutrino; this reaction occurs in the Sun. Such processes take place at very high temperatures (millions of kelvin) and are consequently called thermonuclear reactions. With light elements, fusion releases immense amounts of energy: fusion is the energy-producing process in stars.

The lighter chemical elements evolve energy in fusion reactions whereas heavier elements (those with a mass number above 56) require an input of energy to maintain the reaction. Thus although most elements up to iron can be formed by fusion reactions in stars (see nucleosynthesis), heavier elements must be synthesized by other nuclear reactions. See also carbon cycle; proton-proton chain reaction.

nuclear fusion

[′nü·klē·ər ′fyü·zhən]
(nuclear physics)

Nuclear fusion

One of the primary nuclear reactions, the name usually designating an energy-releasing rearrangement collision which can occur between various isotopes of low atomic number.

Interest in the nuclear fusion reaction arises from the expectation that it may someday be used to produce useful power, from its role in energy generation in stars, and from its use in the fusion bomb. Since a primary fusion fuel, deuterium, occurs naturally and is therefore obtainable in virtually inexhaustible supply, solution of the fusion power problem would permanently solve the problem of the present rapid depletion of chemically valuable fossil fuels. As a power source, the lack of radioactive waste products from the fusion reaction is another argument in its favor as opposed to the fission of uranium.

In a nuclear fusion reaction the close collision of two energy-rich nuclei results in a mutual rearrangement of their nucleons (protons and neutrons) to produce two or more reaction products, together with a release of energy. The energy usually appears in the form of kinetic energy of the reaction products, although when energetically allowed, part may be taken up as energy of an excited state of a product nucleus. In contrast to neutron-produced nuclear reactions, colliding nuclei, because they are positively charged, require a substantial initial relative kinetic energy to overcome their mutual electrostatic repulsion so that reaction can occur. This required relative energy increases with the nuclear charge Z, so that reactions between low-Z nuclei are the easiest to produce. The best known of these are the reactions between the heavy isotopes of hydrogen, deuterium, and tritium.

Nuclear fusion reactions can be self-sustaining if they are carried out at a very high temperature. That is to say, if the fusion fuel exists in the form of a very hot ionized gas of stripped nuclei and free electrons termed a plasma, the agitation energy of the nuclei can overcome their mutual repulsion, causing reactions to occur. This is the mechanism of energy generation in the stars and in the fusion bomb. It is also the method envisaged for the controlled generation of fusion energy.

The cross sections (effective collisional areas) for many of the simple nuclear fusion reactions have been measured with high precision. It is found that the cross sections generally show broad maxima as a function of energy and have peak values in the general range of 0.01 barn (1 barn = 10-24 cm2) to a maximum value of 5 barns, for the deuterium-tritium (D-T) reaction. The energy releases of these reactions can be readily calculated from the mass difference between the initial and final nuclei or determined by direct measurement.

Some of the important simple fusion reactions, their reaction products, and their energy releases are:

() 

If it is remembered that the energy release in the chemical reaction in which hydrogen and oxygen combine to produce a water molecule is about 1 eV per reaction, it will be seen that, gram for gram, fusion fuel releases more than 1,000,000 times as much energy as typical chemical fuels.

References in periodicals archive ?
This fusion reaction is similar to what powers the sun and other stars.
Fusion reaction results in a thermonuclear explosion, such as one generated by a hydrogen bomb, which is far more powerful than a fission atomic device.
In a 1998 recap of cold fusion work to date, Wired magazine reported that in 1994 the Electric Power Research Institute (EPRI), a reputable research organization, had announced results that seemed to confirm the existence of a desktop fusion reaction in experiments.
Indeed, the first test to produce a fusion reaction took place on 9 May 1951.
Unfortunately, however, there is no guarantee that the fusion reaction will take place as planned.
Said McBride's manager Dan Sinars, "When Magnetized Liner Inertial Fusion was first proposed, our biggest concern was whether the instabilities would disrupt the target before fusion reactions could occur.
Thermonuclear fusion occurs in high temperature deuterium-tritium plasma at the order of 100 million degrees Centigrade, and the heat produced by the fusion reaction is used to generate electricity.
Had NIF achieved that milestone, known as ignition, it would have marked the first time a controlled fusion reaction generated more energy than it took to get started.
But to pay for ITER--which aims to produce a self-sustaining fusion reaction, or "burning plasma," and prove that fusion is a viable energy source--the United States is sacrificing the very community of researchers who would apply the results from the ITER experiments.
North Korea claimed Wednesday that its scientist succeeded in creating a controlled nuclear fusion reaction, a feat that would make one of the world's poorest countries the world's most technologically advanced.
They reveal that the ship would have been fired by a controlled thermo- nuclear fusion reaction ignited by laser beams.
The beryllium will be used for inner wall plasma facing components that will line the inside of the reactor as part of a major recommissioning project to prepare JET for fusion reaction testing.