nuclear fusion

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Related to Thermonuclear fusion: thermonuclear bomb, Thermonuclear fission

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:

() 

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 ?
3) Free-floating objects in young stellar clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not 'planets' but are 'sub-brown dwarfs' (or whatever name is most appropriate).
More than 40 years of intensive research has already been devoted to developing controlled thermonuclear fusion. Most difficult of all the obstacles still to be overcome in developing thermonuclear technology is attainment of the extraordinarily high temperatures and pressures necessary to break the nucleus of hydrogen--100 million degrees Celsius for heavy hydrogen (deuterium-tritium) reactions.
The scope of the workshop includes accelerators for high energy physics, plasma heating and current drive in controlled thermonuclear fusion research, and radar and directed energy/high power microwave systems.
A technique that some scientists claim generates thermonuclear fusion in a benchtop apparatus works even without its controversial neutron trigger.
He was awarded the 1995 Edward Teller Medal for his pioneering research and leadership in the use of lasers for controlled thermonuclear fusion. He has served on the Director's Advisory Committee for Lawrence Livermore National Laboratory and as a consultant to the Los Alamos National Laboratory.
Because it is a religion, after all: we believe' in nuclear energy, in clean coal from carbon storage, in large-scale renewable energy, in controlled thermonuclear fusion within 50 years, in an abundance in oil for many years to come, and even in a secure gas supply.
Fourth-generation thermonuclear fusion and fission reactors have also been criticised as impediments to adeveloping "more viable and applicable" energy solutions.
Depending on how rapidly a black hole spins, the energy released by a given amount of mass can be 10 to several hundred times the energy released in thermonuclear fusion.
Some scientists even claim that thermonuclear fusion can occur in the implosions.
During the seminar, schoolchildren learned about discoveries in the field of astronomy, bioengineering, thermonuclear fusion and archeology.
His main research focus is on the properties of magnetically confined plasmas for thermonuclear fusion energy applications.
And the signing of the international thermonuclear fusion experimental reactor (ITER) agreement earlier this year gives Europe an unrivalled leadership in research into future energy sources, within a seven-party international cooperation effort.