Nuclear fusion is a type of nuclear reaction where two light nuclei collide together to form a single, heavier nucleus. Fusion results in a release of energy because the mass of the new nucleus is less than the sum of the original masses. Based on the principle of mass-energy equivalence, this mass difference means that some mass that was "lost" has been converted into energy.[2] For elements lighter than iron, fusion often releases energy. For elements heavier than iron, it takes energy to cause fusion to happen. In order to make elements heavier than iron either a high energy particle beam is required, or a supernova. Show Although the fusion of small atoms gives off a lot of energy, initiating this process requires a significant amount of energy. This energy is needed to overcome the Coulomb repulsion that exists between the protons the two different nuclei. Hydrogen atoms must be pushed close enough together so that the strong nuclear force can overcome the coulomb repulsion. The initial energy needed is a major factor which makes fusion difficult to achieve.[2] Types of Fusion ReactionsThere are several different types of fusion reactions, but most involve two isotopes of hydrogen known as deuterium and tritium. Some fusion reactions include:[3]
Figure 1. An animation showing deuterium-tritium fusion.[4] Use in Energy GenerationCurrently, there are no large-scale fusion reactor that could provide energy for commercial use. This is because it has been difficult for scientists to create a controllable, non-destructive way of harnessing the energy released during fusion.[3] The process of fusion is difficult to control largely because of the extreme conditions necessary for the reactions to take place. First, fusion requires both extremely high temperatures to give hydrogen atoms enough energy to overcome repulsion between the protons. Energy from microwaves or lasers must be used to heat hydrogen atoms to the necessary temperatures. At these temperatures, hydrogen is a plasma, and this plasma must be sufficiently contained for fusion to continue, and safety.[3] Second, high pressures are needed to squeeze hydrogen atoms close enough to fuse. This process is done by using intense magnetic fields, lasers, or ion beams.[3] For potential nuclear energy sources, the deuterium-tritium fusion reaction is most likely because the conditions are less extreme.[2] Currently, the largest fusion effort is the International Thermonuclear Experimental Reactor or ITER in France. This reactor began construction in 2013 and uses a confinement method known as a Tokamak. This Tokamak provides a way to magnetically confine the hot plasma required for fusion. The experimental phase of ITER is expected to begin in 2027.[5] For more information on this project, click here. While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Select Citation Style Copy CitationShare Share Share to social media Facebook Twitter URL Give Feedback External Websites Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Your Feedback Submit FeedbackThank you for your feedback Our editors will review what you’ve submitted and determine whether to revise the article. External Websites
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Alternate titles: atomic fusion, fusion, thermonuclear fusion By Robert W. Conn Last Updated: Dec 9, 2022 Article History Table of Contents laser-activated fusion See all media Key People:Yevgeny Konstantinovich Zavoysky Hans Bethe Igor Vasilyevich Kurchatov Lyman Spitzer Gersh Itskovich Budker...(Show more)Related Topics:fusion reactor nuclear energy proton-proton chain nucleosynthesis CNO cycle...(Show more) See all related content → Summary Read a brief summary of this topicnuclear fusion, process by which nuclear reactions between light elements form heavier elements (up to iron). In cases where the interacting nuclei belong to elements with low atomic numbers (e.g., hydrogen [atomic number 1] or its isotopes deuterium and tritium), substantial amounts of energy are released. The vast energy potential of nuclear fusion was first exploited in thermonuclear weapons, or hydrogen bombs, which were developed in the decade immediately following World War II. For a detailed history of this development, see nuclear weapon. Meanwhile, the potential peaceful applications of nuclear fusion, especially in view of the essentially limitless supply of fusion fuel on Earth, have encouraged an immense effort to harness this process for the production of power. For more detailed information on this effort, see fusion reactor. This article focuses on the physics of the fusion reaction and on the principles of achieving sustained energy-producing fusion reactions. The fusion reactionFusion reactions constitute the fundamental energy source of stars, including the Sun. The evolution of stars can be viewed as a passage through various stages as thermonuclear reactions and nucleosynthesis cause compositional changes over long time spans. Hydrogen (H) “burning” initiates the fusion energy source of stars and leads to the formation of helium (He). Generation of fusion energy for practical use also relies on fusion reactions between the lightest elements that burn to form helium. In fact, the heavy isotopes of hydrogen—deuterium (D) and tritium (T)—react more efficiently with each other, and, when they do undergo fusion, they yield more energy per reaction than do two hydrogen nuclei. (The hydrogen nucleus consists of a single proton. The deuterium nucleus has one proton and one neutron, while tritium has one proton and two neutrons.) Fusion reactions between light elements, like fission reactions that split heavy elements, release energy because of a key feature of nuclear matter called the binding energy, which can be released through fusion or fission. The binding energy of the nucleus is a measure of the efficiency with which its constituent nucleons are bound together. Take, for example, an element with Z protons and N neutrons in its nucleus. The element’s atomic weight A is Z + N, and its atomic number is Z. The binding energy B is the energy associated with the mass difference between the Z protons and N neutrons considered separately and the nucleons bound together (Z + N) in a nucleus of mass M. The formula is B = (Zmp + Nmn − M)c2, where mp and mn are the proton and neutron masses and c is the speed of light. It has been determined experimentally that the binding energy per nucleon is a maximum of about 1.4 10−12 joule at an atomic mass number of approximately 60—that is, approximately the atomic mass number of iron. Accordingly, the fusion of elements lighter than iron or the splitting of heavier ones generally leads to a net release of energy. Two types of fusion reactionsFusion reactions are of two basic types: (1) those that preserve the number of protons and neutrons and (2) those that involve a conversion between protons and neutrons. Reactions of the first type are most important for practical fusion energy production, whereas those of the second type are crucial to the initiation of star burning. An arbitrary element is indicated by the notation AZX, where Z is the charge of the nucleus and A is the atomic weight. An important fusion reaction for practical energy generation is that between deuterium and tritium (the D-T fusion reaction). It produces helium (He) and a neutron (n) and is written D + T → He + n. To the left of the arrow (before the reaction) there are two protons and three neutrons. The same is true on the right. Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now The other reaction, that which initiates star burning, involves the fusion of two hydrogen nuclei to form deuterium (the H-H fusion reaction): H + H → D + β + + ν, where β + represents a positron and ν stands for a neutrino. Before the reaction there are two hydrogen nuclei (that is, two protons). Afterward there are one proton and one neutron (bound together as the nucleus of deuterium) plus a positron and a neutrino (produced as a consequence of the conversion of one proton to a neutron). Both of these fusion reactions are exoergic and so yield energy. The German-born physicist Hans Bethe proposed in the 1930s that the H-H fusion reaction could occur with a net release of energy and provide, along with subsequent reactions, the fundamental energy source sustaining the stars. However, practical energy generation requires the D-T reaction for two reasons: first, the rate of reactions between deuterium and tritium is much higher than that between protons; second, the net energy release from the D-T reaction is 40 times greater than that from the H-H reaction. What is a heavy nucleus?The so-called 'heavy nuclei' are the nuclei of ordinary atoms of high atomic number whose electrons have been stripped away yielding a very heavy, highly charged particle. Energy from a heavy ion is deposited along the core of the track, where the ionization events produced in glancing collisions are quite dense.
Does nuclear fusion create heavier elements?nuclear fusion, process by which nuclear reactions between light elements form heavier elements (up to iron). In cases where the interacting nuclei belong to elements with low atomic numbers (e.g., hydrogen [atomic number 1] or its isotopes deuterium and tritium), substantial amounts of energy are released.
What nuclei are used in fusion?The main fuels used in nuclear fusion are deuterium and tritium, both heavy isotopes of hydrogen. Deuterium constitutes a tiny fraction of natural hydrogen, only 0,0153%, and can be extracted inexpensively from seawater. Tritium can be made from lithium, which is also abundant in nature.
Which heavy element is used in nuclear fission?The fuel that nuclear reactors use to produce nuclear fission is pellets of the element uranium. In a nuclear reactor, atoms of uranium are forced to break apart. As they split, the atoms release tiny particles called fission products. Fission products cause other uranium atoms to split, starting a chain reaction.
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What is the heavier nucleus that is created in fusion?
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