nuclear fusion


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nuclear fusion

a reaction in which two nuclei combine to form a nucleus with the release of energy
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

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.

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

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.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

nuclear fusion

[′nü·klē·ər ′fyü·zhən]
(nuclear physics)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

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.

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.

nuclear fusion

Emulating the energy source of the sun and other stars to create energy on earth. What makes nuclear fusion unusual, is that it generates more energy than the energy it takes to operate it. The largest fusion project is the International Thermonuclear Experimental Reactor (ITER) in France, a collaboration of 35 countries that is building a nuclear reactor using the Tokamak design. The Tokamak is a doughnut-shaped vacuum chamber that creates the environment for nuclear fusion.

Comprising millions of parts and costing more than USD $20 billion, the Tokamak weighs more than 20 thousand tons and requires millions of amps of electricity to drive deuterium and tritium isotopes into each other at 270 million degrees Fahrenheit. Designed to generate 500 megawatts of electricity, the first test is scheduled for 2025, and the reactor is expected to be operational by 2035.

Implosion Rather Than Explosion
Nuclear fusion works the opposite of nuclear fission, which is the nuclear power plant technology in use today. Nuclear fission splits atoms apart, whereas fusion "fuses" atoms together and generates more energy than fission and a million times more than coal, oil or gas.

Considered the Only Hope for the Future
Many scientists consider fusion the only real hope for solving energy production in the future. Countries around the world are always striving for greater productivity. Proponents predict that nuclear fusion is the only way to generate the energy required to support the increased consumption resulting from making more things for an ever-increasing population. Eventually, fossil fuels will run out, and in the meantime, they pollute the atmosphere. Although many people have great hopes in renewable energy, solar and wind cannot meet future energy requirements according to Michael Moore in his 2020 documentary "Planet of the Humans" on YouTube.
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References in periodicals archive ?
What if a 'miracle' technology came along to make nuclear fusion possible on much shorter timescales, and at far lower cost?
Therefore, these technological issues needed to be solved to allow for its application to nuclear fusion reactors requiring further enrichment from highly-concentrated tritiated water.
The problem seems to be that even though all this research is going on we haven't gotten any closer to power-generating nuclear fusion than Farnsworth did.
Ali Akbar Salehi, the Iranian atomic chief, announced on Saturday that an eight million dollar fund had been set up to conduct "serious" research in the area of nuclear fusion.
The European Union (EU) is facing a funding battle for an experiment to commercialise nuclear fusion - the process that powers the sun.
Nuclear fusion occurs when two nuclei are joined to form a heavier element, releasing enormous amounts of energy.
Seoul, May 12 (BNA) North Korea said Wednesday it succeeded in producing a nuclear fusion reaction, a claim that appeared to be aimed at increasing its bargaining power before the communist state rejoins stalled six nation talks on its nuclear ambitions.
succeeded in producing a nuclear fusion reaction, but South Korean experts
SCIENTISTS have cleared a major hurdle to producing nuclear fusion in the laboratory - allowing a possible source of clean cheap energy.
Away from the glare of arc lights focused on climate change negotiations, a dedicated band of scientists is working to make this unlimited source of energy -- nuclear fusion -- a reality.
Korea will grow into one of the world's top five countries in nuclear fusion energy technology by 2021 and start commercial generation of electricity from nuclear fusion by 2040 said South Korean President Rob Moo-hyun, according to a September 14 news report in the Korean independent newspaper The Hankyoreh.
One pamphlet covers its Euro 287 million budgets for nuclear fission and radiation protection research; the other the Euro 1.9 billion earmarked for nuclear fusion and Euro 517 million for Joint Research Centre nuclear studies.

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