Fusion, nuclear

Fusion, the joining of light nuclei to form heavier nuclei, is favorable for the very light atoms. In both fission and fusion, the energy liberated is equivalent to the loss of mass that accompanies the reactions. Much greater amounts of energy per unit mass of reaaing atoms are produced in fusion than in fission. 

Spectroscopic evidence indicates that the sun is a tremendous fusion reactor consisting of 73% H, 26% He, and 1% other elements. Its major fusion reaction is thought to involve the combination of a deuteron, jH, and a triton, jH, at tremendously high temperatures to form a helium nucleus and a neutron with the release of a huge amount of energy. 

solar energy is actually a form of fusion energy. A fusion reaction releases a tremendous amount of energy. Compare the energy of the deuteron/triton fusion reaction with that released by the burning of the methane in natural gas (see Section 15-1). 

Fusion reactions are accompanied by even greater energy production per unit mass of reacting atoms than are fission reactions. They can be initiated only by extremely high temperatures, however. This is why fusion reactions are often referred to as thermonuclear reactions. The fusion of jH and jH occurs at the lowest temperature of any fusion reaction known, but even this is 40,000,000 K Such temperatures exist in the sun and 

The explosion of a thermonuclear (hydrogen) homh releases tremendous amounts of energy. If we could learn how to control this process, we wouid have neariy iimitiess amounts of energy. 

The fusion reaction easiest to bring about is between a deuterium ion (hydrogen of mass 2) and a tritium ion (hydrogen of mass 3), to produce a helium ion of mass 4 and a neutron  

This reaction is favored because it occurs at an appreciable rate at a lower temperature (20,000,000 K) than other possible fusion reactions. Tritium is a radioactive isotope of hydrogen, with a half-Ufe of 12 years, which does not occur significantly in nature. For use in this fusion reaction tritium must be made by reaction of the lithium isotope of mass 6 with a neutron  

The energy released in these two reactions may be calculated from the decrease in mass between the reactants and the products  

With the conversion factor 931.480 MeV/amu, this fusion reaction releases 17.6 MeV per pair of atoms fused. 

Absorption of the neutron in D thus releases The overall reaction is 

The fusion of a deuterium nucleus and a tritium nucleus releases a lot of energy as shown in Equation 17.5, where Mev stands for million electron volts, a unit of energy  

Nuclear fusion reactions occur naturally in the sun for about five billion years. These reactions are the only source of energy sustaining life on our planet. 

The Tokamak device was invented in 1960, and several nuclear fusion experiments have been carried out in it. Tokamaks are containers which have a very high quality vacuum and within which there are the strongest known magnetic fields. 

The combination of two or more lighter nuclei to form a heavier nucleus is called nuclear fusion. The amount of energy released in fusion reactions is greater than the amount of energy released in fission reactions. However, a huge amount of activation energy (such as an atomic bomb explosion) is needed to initiate nuclear fusion reactions. 

The simplest nuclear fusion reaction is the combination of the isotopes of hydrogen (deuterium and tritium) to form the heavier nucleus of helium. 

In nuclear fusion, two very small atoms, usually isotopes of hydrogen, combine to make a larger atom. A common example is the fusion of deuterium ( H) and tritium (j H) to make helium, as shown  

The energy released in fusion per gram of hydrogen is roughly 10 times more than the amount of energy released in fission per gram of uranium. 

A commercial nuclear fusion power plant would be an excellent source of energy. The supply of deuterium in the world s oceans would last many thousands of years. Tritium can be produced artificially. The helium that is produced is harmless there are no radioactive waste products produced by fusion. Fusion is a very clean form of energy. Unfortunately, even after more than half a century of research, the technology necessary to build and operate a fusion power plant has eluded researchers. Whether or not fusion plants will ever be built is an unanswered question. 

Nuclear fusion is a process in which light nuclei (usually isotopes of hydrogen) combine to form a heavier nucleus, resulting in the release energy. 

Research into the development of nuclear fusion reactors began in the late 1950s with high hopes of reactors going online by the 1980s. The technological difficulties, however, have proven to be insurmountable. 

A few of the more promising fusion reaction systems are shown in Equations 

Note that these reactions involve deuterium and tritium. Deuterium can be derived in great quantities from seawater by techniques discussed in Section 10.3, and tritium can be prepared in nuclear fission reactors as shown in Equation (10.21) and described in Section 10.4. 

Hydrogen forms three isotopes protium, deuterium, and tritium. Protium and deuterium can be separated by a variety of physical and chemical processes. Ordinary light hydrogen in H-X bonds can be replaced by deuterium, which then provides a means of following the progress of a variety of reactions. Heavy water is used as a moderator in fission reactors. Tritium, produced naturally in the upper atmosphere and artificially in fission reactors, is a mild beta emitter and is used as a tracer and to make luminous paints and self-luminous exit signs. 

The production, storage, transportation, and use of hydrogen may come to power the entire world economy. Nuclear fusion may be the ultimate power source of the future. A knowledge of the chemistry and physics of hydrogen is fundamental to an understanding of the future as well as the past and present. 

4 Besides the reactions that add up to the proton-proton cycle [Equation (10.4)], there are several other possible solar fusion reactions, two of which are shown below. In each case, fill in the missing product and balance the reaction. 

Solar flares such as these are indications of fusion reactions occurring at temperatures of millions of degrees. 

Fusion reactions require temperatures on the order of tens of millions of degrees for initiation. Such temperatures are present in the sun but have been produced only momentarily on Earth. For example, the hydrogen, or fusion, bomb is triggered by the temperature of an exploding fission bomb. Two typical fusion reactions are 

The total mass of the reactants in the second equation is 4.0229 amu, which is 0.0203 amu greater than the mass of the product. This difference in mass is manifested in the great amount of energy liberated. 

A great deal of research in the United States and in other countries, especially the former Soviet Union, has focused on controlled nuclear fusion reactions. The goal of controlled nuclear fusion has not yet been attained, although the required ignition temperature has been reached in several devices. Evidence to date leads us to believe 

Many people, including environmentalists, regard nuclear fission as a highly undesirable method of energy production. Many fission products such as stroiitium-90 are dangerous radioactive isotopes with long half-lives. Plutonium-239, used as a nuclear fuel and produced in breeder reactors, is one of the most toxic substances known. It is an -emitter with a half-life of 24,400 years. 

Because of the hazards, the future of nuclear reactors is clouded. What was once hailed as the ultimate solution to our energy needs in the twenty-first century is now being debated and questioned by both the scientific community and the general public. It seems likely that the controversy will continue for some time. 

In contrast to the nuclear fission process, nuclear fusion, the combining of small nuclei into larger ones, is largely exempt from the waste disposal problem. 

Nuclear fusion occurs constantly in the sun. The sun is made up mostly of hydrogen and helium. In its interior, where temperatures reach about 15 million degrees Celsius, the following fusion reactions are believed to take place  

Because fusion reactions take place only at very high temperatures, they are often called thermonuclear reactions. 

Find Am for the reaction as written by using the nuclear masses in Table 18.3. 

Comparing the answers to (a) and (b), it appears that the fusion reaction produces about seven times as much energy per gram of reactant (57.2 X 10 versus 8.19 X 10 kj) as does the fission reaction. This factor varies from about 3 to 10, depending on the particular reaction chosen to represent the fission and fusion processes. 

As an energy source, nuclear fusion possesses several additional advantages over nuclear fission. In particular, light isotopes suitable for fusion are far more abundant than the heavy isotopes required for fission. You can calculate, for example (Problem 79), that the fusion of only 2 X 10 % of the deuterium ( H) in seawater would meet the total annual energy requirements of the world. 

One fusion reaction currently under study is a two-step process involving deuterium and lithium as the basic starting materials  

In April 1997, the Tokamak fusion reactor at Princeton shut down when government funding was withdrawn. 

In contrast with nuclear fission where a large nucleus is split into two more stable nuclei, fusion relies on the formation of larger stable nuclei from small nuclei. The main difference is that fusion requires an initial high temperature of millions of degrees to overcome the energy repulsion barrier of the nuclei. In the fusion H-bomb, the high temperature (10 K) is achieved by a fission bomb. 

Various systems have been designed and tested to achieve these high temperatures and to initiate the fusion reaction. Such reaction has been maintained for very short time intervals, which is slowly being extended to longer times. 

Some fusion reaction and the corresponding energy liberated are given below  

This reaction can occur at the lowest temperature and produces the highest fusion—power density. The highly energetic neutrons present technical problems regarding material of construction. 

Recent experiments on the electrolysis of LiOD in D2O on a palladium cathode has been claimed to result in cold fusion. The detection of helium, neutrons, and even tritium has been reported. However, there is considerable doubt about the validity of the claims and cold fusion, like polywater will soon be buried and its obituary published. 

There have been two major accidents (Three Mile Island in the United States and Chernobyl in the former Soviet Union) in which control was lost in nuclear power plants, with subsequent rapid increases in fission rates that resulted in steam explosions and releases of radioactivity. The protective shield of reinforced concrete, which surrounded the Three Mile Island Reactor, prevented release of any radioactivity into the environment. In the Russian accident there had been no containment shield, and, when the steam explosion occurred, fission products plus uranium were released to the environment—in the immediate vicinity and then carried over the Northern Hemisphere, in particular over large areas of Eastern Europe. Much was learned from these accidents and the new generations of reactors are being built to be passive safe. In such passive reactors, when the power level increases toward an xmsafe level, the reactor turns off automatically to prevent the high-energy release that would cause the explosive release of radioactivity. Such a design is assumed to remove a major factor of safety concern in reactor operation, see also Bohr, Niels Fermi, Enrico AIan-HATTAN Project Plutonium Radioactivity Uranium. 

Leo Szilard determined that the formation of neutrons occurs during the fission of uranium. This is crucial to sustaining a chain reaction necessary to build an atomic bomb, the first of which he helped to construct in 1942. Shortly thereafter, realizing the destructive power of the atom bomb, Szilard argued for an end to nuclear weapons research. 

A computer simulation of gold (Au) and nickel (Ni) nuclei fusing. 

In stars with very heavy average masses, helium burning may last for only a few million years before it is replaced by carbon fusion. In time this leads to the production of elements such as calcium, titanium, chromium, iron, and nickel fusion partly by helium capture, partly by the direct fusion of heavy nuclides. For example, two Si can combine to form Ni that can decay to Co which then decays to stable Fe. These last steps of production may occur rather rapidly in a few thousand years. When the nuclear fuel for fusion is exhausted, the star collapses and a supernova results. 

Nuclear fusion became important on Earth with the development of hydrogen bombs. A core of uranium or plutonium is used to initiate a fission reaction that raises the core s temperature to approximately 10 K, sufficient to cause fusion reactions between deuterium and tritium. In fusion bombs, LiD is used as Li reacts with fission neutrons to form tritium that then rm-dergoes fusion with deuterium. It is estimated that approximately half the energy of a 50 megaton thermonuclear weapon comes from fusion and the other half from fission. Fusion reactions in these weapons also produce secondary fission since the high energy neutrons released in the fusion reactions make them very efficient in causing the fission of 

90v 39 yttrium-90 64 hours beta, gamma implanted in tumors 

The energy the earth derives from the sun comes from a type of nuclear reaction called nuclear fusion, in which two small nuclei combine to form a larger nucleus. The smaller nuclei are fused together, you might say. The typical fusion reaction believed to be responsible for the energy radiated by the sun is represented by the equation 

Fusion processes are, in general, more energetic than fission reactions. The fusion of one gram of hydrogen in the above reaction yields about four times as much energy as the fission of an equal mass of uranium-235. So far, people have been able to produce only one kind of large-scale fusion reaction, the explosion of a hydrogen bomb. 

Research efforts are being made to develop a nuclear fusion reactor as a source of useful energy. It has several advantages over fission. It yields more energy per given quantity of fuel. The isotopes required for fusion are far more abundant than those needed for fission. Best of all, fusion yields no radioactive waste, removing both the need for extensive disposal systems and the danger of an accidental release of radiation to the atmosphere. 

Strategy This problem is entirely analogous to Example 19.4. First, find Am for the equation as written, and then find Am for one gram of reactant. Finally, calculate A AE = 9.00 X 1010 kj/g X Am. 

This process is attractive because it has a lower activation energy than other fusion reactions. 

Currently, scientists are studying two types of systems to produce the extremely high temperatures required high-powered lasers and heating by electric currents. At present many technical problems remain to be solved, and it is not clear whether either method will prove useful. 

Image not available for electronic use. Please refer to the image in the textbook. 

The scale on which these transmutations is carried out is extremely small, and in some cases has been described as atom-at-a-time chemistry. The target materials in equations 3.22 and 3.23 are actinoid elements (see Chapter 25), which, although artificially prepared, have relatively long half-lives ( 9vBk, fi = 300 days geCm, h = 3.5 x 10 yr). Studying the product nuclides is extremely difficult, not only because of the tiny quantities of materials involved but also because of their short half-lives (losLr, t = 3 min lo Rf, ti = 65 s). 

In forming artificial radioactive isotopes, problems of isolation are often encountered. For example, a product may decay quickly with the result that the initial product is contaminated with the daughter nuclide. 

The methods used to separate a desired isotope depend on whether or not the starting material and the product are isotopes of the same element (e.g. equation 3.14). If they are not, the problem is essentially one of chemical separation of a small amount of one element from large amounts of one or more others. Methods of separation include volatilization, electrodeposition, solvent extraction, ion-exchange or precipitation on a carrier . For example, in the process foZn(n,p) Cu, the target (after bombardment with fast neutrons) is dissolved in dilute HNO3 and the Cu is deposited electrolytically. This method is successful because of the significant difference between the reduction potentials °(Cu /Cu) = -I-0.34V and (Zn +/Zn) = -0.76 V (see Chapter 8). 

For this method to be useful, there must be no rapid exchange reaction between target and product (equation 3.25) and hence a covalently bonded alkyl halide rather than an ionic alkali metal halide is chosen for the irradiation. 

The uses of radioisotopes in medicine are extremely important. Certain elements are readily absorbed by particular organs or by the bone in the human body. This is the basis for their use in radiopharmaceuticals (introduced by food or drug intake) to probe the function of human organs diagnostic imaging) or to destroy cancerous cells radiotherapy). An advantage of these techniques is that they are non-invasive. 

Another fertile isotope is ioTh- Upon capturing slow neutrons, thorium is transmuted to uranium-233, which, like uranium-235, is a fissionable isotope  

Uranium-233 (fv = 1.6 X 10 years) is stable enough for long-term storage. 

Although the amounts of uranium-238 and thorium-232 in Earth s erust are relatively plentiful (4 ppm and 12 ppm by mass, respectively), the development of breeder reactors has been very slow. To date, the United States does not have a single operating breeder reactor, and only a few have been built in other countries, such as France and Russia. One problem is economics breeder reactors are more expensive to build than conventional reactors. There are also more technical difficulties associated with the constraction of such reactors. As a result, the future of breeder reactors, in the United States at least, is rather uncertain. 

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Ditmire T, Zweiback J, Yanovsky V P, Cowan T E, Hays G and Wharton K B 1999 Nuclear fusion from explosions of femtosecond laser-heated deuterium clusters Nature 389 489-92... 

Gott Y V, Ioffe M S and Telkovsky V G 1962 Nuclear Fusion Suppl. part 3 (Vienna International Atomio Energy Agenoy) p 1045... 

The ordinary isotope of hydrogen, H, is known as Protium, the other two isotopes are Deuterium (a proton and a neutron) and Tritium (a protron and two neutrons). Hydrogen is the only element whose isotopes have been given different names. Deuterium and Tritium are both used as fuel in nuclear fusion reactors. One atom of Deuterium is found in about 6000 ordinary hydrogen atoms. 

In the spring of 1989, it was announced that electrochemists at the University of Utah had produced a sustained nuclear fusion reaction at room temperature, using simple equipment available in any high school laboratory. The process, referred to as cold fusion, consists of loading deuterium into pieces of palladium metal by electrolysis of heavy water, E)20, thereby developing a sufficiently large density of deuterium nuclei in the metal lattice to cause fusion between these nuclei to occur. These results have proven extremely difficult to confirm (20,21). Neutrons usually have not been detected in cold fusion experiments, so that the D-D fusion reaction familiar to nuclear physicists does not seem to be the explanation for the experimental results, which typically involve the release of heat and sometimes gamma rays. 

Helium-3 [14762-55-1], He, has been known as a stable isotope since the middle 1930s and it was suspected that its properties were markedly different from the common isotope, helium-4. The development of nuclear fusion devices in the 1950s yielded workable quantities of pure helium-3 as a decay product from the large tritium inventory implicit in maintaining an arsenal of fusion weapons (see Deuterium AND TRITIUM) Helium-3 is one of the very few stable materials where the only practical source is nuclear transmutation. The chronology of the isolation of the other stable isotopes of the hehum-group gases has been summarized (4). 

Helium, plentiful in the cosmos, is a product of the nuclear fusion reactions that are the prime source of stellar energy. The other members of the hehum-group gases are thought to have been created like other heavier elements by further nuclear condensation reactions occurring at the extreme temperatures and densities found deep within stars and in supernovas. 

Tritium is produced in heavy-water-moderated reactors and sometimes must be separated isotopicaHy from hydrogen and deuterium for disposal. Ultimately, the tritium could be used as fuel in thermonuclear reactors (see Fusionenergy). Nuclear fusion reactions that involve tritium occur at the lowest known temperatures for such reactions. One possible reaction using deuterium produces neutrons that can be used to react with a lithium blanket to breed more tritium. 

Most schemes that have been proposed to propel starships involve plasmas. Schemes differ both in the selection of matter for propulsion and the way it is energi2ed for ejection. Some proposals involve onboard storage of mass to be ejected, as in modem rockets, and others consider acquisition of matter from space or the picking up of pellets, and their momentum, which are accelerated from within the solar system (184,185). Energy acquisition from earth-based lasers also has been considered, but most interstellar propulsion ideas involve nuclear fusion energy both magnetic, ie, mirror and toroidal, and inertial, ie, laser and ion-beam, fusion schemes have been considered (186—190). 

K. Miyamoto, Plasma Physicsfor Nuclear Fusion, MlT Press, Cambridge, Mass., 1979. 

Deuterium Fusion. At sufficiently high temperatures, deuterium undergoes nuclear fusion with the production of large amounts of energy ... 

It has been claimed that the D-D fusion reaction occurs when D2O is electroly2ed with a metal cathode, preferably palladium, at ambient temperatures. This claim for a cold nuclear fusion reaction that evolves heat has created great interest, and has engendered a voluminous titerature filled with claims for and against. The proponents of cold fusion report the formation of tritium and neutrons by electrolysis of D2O, the expected stigmata of a nuclear reaction. Some workers have even claimed to observe cold fusion by electrolysis of ordinary water (see, for example. Ref. 91). The claim has also been made for the formation of tritium by electrolysis of water (92). On the other hand, there are many experimental results that cast serious doubts on the reahty of cold fusion (93—96). Theoretical calculations indicate that cold fusions of D may indeed occur, but at the vanishingly small rate of 10 events per second (97). As of this writing the cold fusion controversy has not been entirely resolved. 

Nuclear Fusion Reactions. Tritium reacts with deuterium or protons (at sufftciendy high temperatures) to undergo nuclear fusion ... 

The confinement region in which nuclear fusion proceeds is surrounded by a blanket in which the neutrons produced by the fusion reaction are captured to produce tritium. Because of its favorable cross section for neutron capture, lithium is the favored blanket material. Various lithium blanket... 

Applied Sciences, Inc. has, in the past few years, used the fixed catalyst fiber to fabricate and analyze VGCF-reinforced composites which could be candidate materials for thermal management substrates in high density, high power electronic devices and space power system radiator fins and high performance applications such as plasma facing components in experimental nuclear fusion reactors. These composites include carbon/carbon (CC) composites, polymer matrix composites, and metal matrix composites (MMC). Measurements have been made of thermal conductivity, coefficient of thermal expansion (CTE), tensile strength, and tensile modulus. Representative results are described below. 

Burchell, T.D., and Oku, T., Material properties data for fusion reactor plasma facing carbon-carbon composites. Nuclear Fusion, 1994, 5(Suppl.), 77 128. 

J. Roth, E. Vietzke, and A.A. Haasz, Erosion of Graphite Due to Particle Impact. In Supplement of the Journal of Nuclear Fusion, 1991, IAEA. 

Kem-umwandlung, /. nuclear transformation, transmutation, -verknlipfung,/. linkage to a nucleus, -verschmelzimg, /. nuclear fusion, -weehselwirkung, /. nuclear interaction, -werkstoff, m. core material. -woUe,/. prime wool, -zahl, /. number of nuclei, -zelle, /. nuclear cell, -zerfall, m. nuclear disintegration. -zerplatzen, n. nuclear explosion or disintegration. 

See also Nuclear Energy Nuclear Energy, Historical Evolution of the Use of Nuclear Fission Nuclear Fusion. 

Resource pessimists counter that this process cannot proceed forever because the eternal persistence of demand for any given commodity that is destroyed by use must inevitably lead to its depletion. I lowever, the eternal persistence assumption is not necessarily correct. The life of a solar system apparently is long but finite. Energy sources such as nuclear fusion and solar energy in time could replace more limited resources such as oil and natural gas. Already, oil, gas, nuclear power, and coal from better sources have displaced traditional sources of coal in, for example, Britain, Germany, Japan, and France. 

The fear of accidents like Chernobyl, and the high cost of nuclear waste disposal, halted nuclear power plant construction in the United States m the 1980s, and in most ol the rest ol the world by the 1990s. Because nuclear fusion does not present the waste disposal problem of fission reactors, there is hope that fusion will be the primary energy source late in the twenty-first centuiy as the supplies of natural gas and petroleum dwindle. 

See also Acid Rain Air Pollution Atmosphere Carson, Rachel Climatic Effects Disasters Environmental Economics Fossil Fuels Gasoline and Additives Gasoline Engines Government and the Energy Marketplace Nuclear Fission Nuclear Fusion Nuclear Waste. 

See also Nuclear Energy Nuclear Fission Nuclear Fusion. 

Lasers are focused on a small pellet of fuel. This is an attempt to create a nuclear fusion reaction for the purpose of producing energy. (Corbis-Bettmann)... 

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