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The D-T fusion reaction, is the most efficient reaction known in terms of energy released.
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Image courtesy of Plasma Physics Laboratory

Fusion Reactions

Nuclear fusion is a process where two or more nuclei combine to form an element with a higher atomic number (more protons in the nucleus). Fusion is the reverse process of nuclear fission. Fusion of light elements (the reactants) into heavier elements (the products) releases energy, (as does fission of heavy elements into lighter elements). For fusion, the energy release occurs when the mass of the fusion products is smaller than the reactants. The difference between the total masses of all the protons and neutrons of a nucleus and the mass of the nucleus itself can be expressed in terms of the binding energy. The energy released is proportional to the difference in the masses as predicted by Einstein's famous equation, E=mc2. Fusion reactions power the Sun and other stars.

For a fusion reaction to occur it is necessary to bring the reactants so close together that nuclear forces become important and "glue" the reactants together. However, the range of interaction of the nuclear force is very small (10-15 meters), and the reactants (positively charged nuclei) repel each other because of the electrostatic force. For these reasons fusion most easily occurs in a high density, high temperature environment.

On Earth, nuclear fusion was reached first in the explosion of the Hydrogen bomb. In a non-desctructive manner, fusion has also been reached in different experimental devices aimed at studying the possibility of producing energy in a controlled fashion (similar to what is presently done in nuclear power plants using fission). The D-T reaction is presently the best candidate for implementing a controlled fusion power station in the near future.

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The atomic number of an atom tells us how many protons are in the nucleus of that atom. Why is that important? The chemical properties of an element are determined by the number of electrons in its atoms,...more

Element (Chemical Element)

An element (also called a "chemical element") is a substance made up entirely of atoms having the same atomic number; that is, all of the atoms have the same number of protons. Hydrogen, helium, oxygen,...more

Binding Energy

A plot of the binding energy per nucleon vs. atomic mass shows a peak atomic number 56 (Iron). Elements with atomic mass less then 56 release energy if formed as a result of a fusion reaction. Above this...more

Fundamental Forces

The interactions in the Universe are governed by four forces (strong, weak, electromagnetic and gravitational). Physicists are trying to derive a unified theory that would describe all the forces in nature...more

The Hydrogen Bomb

In the Hydrogen bomb the explosion of a nuclear fission charge (atomic bomb) produces the temperature and density necessary for the fusion of Deuterium and Tritium (isotopes of Hydrogen), resulting in...more

Fusion Experiments

There are several experiments worldwide where the conditions for nuclear fusion reactions have been achieved in a controlled manner. The two main approaches that are being explored are magnetic confinement...more

The Solar Core

The solar core is made up of an extremely hot and dense gas (in the plasma state). Despite a density of 160,000 Kg/m3, the temperature of 15 million kelvins (27 million degrees Faranheit) prevents the...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA