Physics
Induced Fission
Induced fission refers to the process of splitting an atomic nucleus into two or more smaller nuclei by bombarding it with a neutron. This process releases a large amount of energy and additional neutrons, which can then induce further fission reactions in nearby nuclei. Induced fission is a key principle behind nuclear power and nuclear weapons.
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12 Key excerpts on "Induced Fission"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter-4 Nuclear Fission An Induced Fission reaction. A slow-moving neutron is absorbed by the nucleus of a uranium-235 atom, which in turn splits into fast-moving lighter elements (fission products) and releases three free neutrons. In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free ____________________ WORLD TECHNOLOGIES ____________________ neutrons and photons (in the form of gamma rays), as well. Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as elec-tromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). For fission to produce energy, the total binding energy of the resulting elements has to be lower than that of the starting element. Fission is a form of nuclear transmutation because the resulting fragments are not the same element as the original atom. Nuclear fission produces energy for nuclear power and to drive the explosion of nuclear weapons. Both uses are made possible because certain substances called nuclear fuels undergo fission when struck by free neutrons and in turn generate neutrons when they break apart. This makes possible a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon. The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very tempting source of energy. The products of nuclear fission, however, are on average far more radioactive than the heavy elements which are normally fissioned as fuel, and remain so for significant amounts of time, giving rise to a nuclear waste problem.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 4 Nuclear Fission An Induced Fission reaction. A slow-moving neutron is absorbed by the nucleus of a uranium-235 atom, which in turn splits into fast-moving lighter elements (fission products) and releases three free neutrons. In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free neutrons and photons (in the form of gamma rays), as well. Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electro- ________________________ WORLD TECHNOLOGIES ________________________ magnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). For fission to produce energy, the total binding energy of the resulting elements has to be lower than that of the starting element. Fission is a form of nuclear transmutation because the resulting fragments are not the same element as the original atom. Nuclear fission produces energy for nuclear power and to drive the explosion of nuclear weapons. Both uses are made possible because certain substances called nuclear fuels undergo fission when struck by free neutrons and in turn generate neutrons when they break apart. This makes possible a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon. The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very tempting source of energy. The products of nuclear fission, however, are on average far more radioactive than the heavy elements which are normally fissioned as fuel, and remain so for significant amounts of time, giving rise to a nuclear waste problem.
eBook - ePub- Robert E. Masterson(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
billions of times more energy each day than fission does in the universe as a whole. Nuclear fusion is also the process that is responsible for creating the heat and light that are produced in stars such as our Sun.Nuclear fission is based on the concept of inducing a heavy element (such as Uranium-233, Uranium-235, or Plutonium-239) to split apart into two or more parts. Practically speaking, this can be done by allowing one of these isotopes to absorb a slow-moving neutron and to transform themselves into an agitated state. The nucleus can only become stable again by releasing some of its excess energy and several photons and neutrons in the process. The difference between the mass of the nucleus before it splits apart and the mass of the nucleus after it splits apart (plus its by-products), when multiplied by the square of the speed of light c, is equal to the amount of kinetic energy E that is released. This kinetic energy is then converted into heat, which allows the blades of a steam turbine to spin, and for electrical energy to be produced. The key to all of this happening is to create what is known as acontrolled nuclear chain reactionand to allow this chain reaction to occur for as long as possible without getting out of control. The length of time that this is possible is roughly proportional to the enrichment of the fuel. Commercial power reactors need to be partially refueled every 18 or 24 months, while military reactors can run for many years without the need for refueling. In this chapter, we would like to present the physical principles that allow the nuclear chain reaction to occur (see Figure 7.1 ).FIGURE 7.1 Two universal symbols of the nuclear power industry in the world today. (a) A 3-meter tall sculpture of Einstein’s famous equation E = mc2
eBook - ePubNuclear Engineering Fundamentals
A Practical Perspective
- Robert E. Masterson(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
billions of times more energy each day than fission does in the universe as a whole. Nuclear fusion is also the process that is responsible for creating the heat and light that are produced in stars such as our sun.Nuclear fission is based on the concept of inducing a heavy element (such as Uranium-233, Uranium-235, or Plutonium-239) to split apart into two or more parts . Practically speaking, this can be done by allowing one of these isotopes to absorb a slow-moving neutron and to transform themselves into an agitated state. The nucleus can only become stable again by releasing some of its excess energy and several photons and neutrons in the process. The difference between the mass of the nucleus before it splits apart and the mass of the nucleus after it splits apart (plus its by-products), when multiplied by the square of the speed of light c, is equal to the amount of kinetic energy E that is released. This kinetic energy is then converted into heat, which allows the blades of a steam turbine to spin, and for electrical energy to be produced. The key to all of this happening is to create what is known as a controlled nuclear chain reaction and to allow this chain reaction to occur for as long as possible without getting out of control. The length of time that this is possible is roughly proportional to the enrichment of the fuel. Commercial power reactors need to be partially refueled every 18 or 24 months, while military reactors can run for many years without the need for refueling. In this chapter, we would like to present the physical principles that allow the nuclear chain reaction to occur (see Figure 7.1
eBook - PDFNuclear Reactions in Heavy Elements
A Data Handbook
- V. M. Gorbachev, Y. S. Zamyatnin, A. A. Lbov(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
PART II NUCLEAR FISSION CHAPTER 4 GENERAL CHARACTERISTICS OF THE FISSION PROCESS Fission of a nucleus means its disintegration into two (less frequently three or four) fragments accompanied by the liberation of a considerable amount of energy and the emission of secondary fission neutrons and -rays. Nuclei of heavy elements can fission either spontaneously (spontaneous fission) or due to bombardment of neutrons, charged particles and -rays (forced or Induced Fission). Most important in practice is fission caused by neutrons. Some isotopes (e.g. 2 3 3 U, 2 3 5 U, 2 3 9 Pu) can be fissioned by neutrons with arbitrary energies, others (e.g. 2 3 2 Th, 2 3 6 U, 238 U) only by neutrons having energies which exceed the fission threshold. The lifetime of a nucleus with regard to spontaneous fission is determined by the fission barrier penetration and will be dealt with in Chapter 5. In the case of forced fission, excitation of the nucleus is caused by a particle or photon, usually with the formation of a compound nucleus. Fission can then be considered as one of the possible competing processes of disintegration of the compound nucleus, the probability of which is described by the ratio of the fission width ry to the total width . The lifetime of the compound nucleus can be evaluated if the value of the total width is known; then r c =h/r where h is Planck's constant. For instance, to a value of ~ 1 eV corresponds r c ~ 10 15 sec. However, values of are known only for low excitation energies (since in this case discrete resonance levels of the compound nucleus are excited). At higher excitation energies the total width becomes comparable to the distance between levels and resonance effects disappear. A very effective experimental method for determining r c is the shadow method developed by A. F. Tulinov et al. [1-4]. In this method use is made of the effect of motion of the compound nucleus caused by the momentum of the incident particle.
eBook - PDF- Richard F. Wilson(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
The reasons are too complex to go into here; all that matters, for our purposes, is that it is an experimental fact. [See Worksheet 5-2.] 147 Nuclear fission, often called splitting the atom, refers to dividing the nucleus into two or more parts. It is the process used in the atomic bomb and nuclear reactors. Let us assume that we can split the nucleus A = 238 into two other nuclei, say, A = 148 and A = 90. From the graph, we compare the binding energy per particle for each of these three nuclei. We start with a binding energy of 7.6 MeV/particle and end with a net of 8.5 MeV/particle. The energy liberated in this splitting is 238 (particles) x [8.5 - 7.6] (MeV/particle) = 215 MeV In summary, the heavy nucleus splits and gives off two lighter nuclei (fission fragments), each of which binds its nucleons more tightly than the uranium. The energy then becomes available, some directly, and some from decay products. A listing of the energy in the fission of U 2 35 is given in Table 5-1. 5 . Nuclear Fission and Fusion We shall look at two such nuclei, uranium (A = 236) and plutonium (A = 240). The shorthand notation for these nuclei are 92U 2 36 and gi+Pu 240 . We must first form these unstable nuclei, as because of their short lifetimes they are not found in nature. TECHNICAL NOTE 5 -3 Notation for Nuclear Reactions An atomic nucleus can be characterized by two numbers: Ζ is the atomic number, or the number of protons in the nucleus. The total charge of the nucleus is exactly Ζ multiplied by the proton charge. A is the mass number. This is defined as the number of protons in the nucleus plus the number of neutrons. The total mass of the atom is approximately A multiplied by the mass of a proton. It is actually a little less than this because of the binding of the nuclei. An atom that is electrically uncharged (neutral) will have exactly Ζ electrons to balance the charge of the protons.
eBook - PDF- Yuri A Berezhnoy(Author)
- 2005(Publication Date)
- WSPC(Publisher)
Chapter 6 Fission of Atomic Nuclei 6.1 Nuclear Fission Mechanism When heavy nuclei capture neutrons, it is possible for a nucleus to split into two or more parts. Nuclear fission was discovered by the German physicists Hahn and Strassmann in 1939. Hahn was awarded the Nobel Prize in Chemistry in 1944 for that. The discovery of fission was preceded by the fundamental works of Fermi on the irradiation of uranium nuclei by neutrons. The Nobel Prize in Physics was awarded to Fermi for his demon-strations of the existence of new radioactive elements produced by neutron irradiation in 1938. The phenomenon of nuclear fission was explained by the Austrian physicist Meitner and the English physicist Frisch in 1939. They called this new kind of nuclear reaction nuclear fission due to the seeming similarity with the process of cell fission leading to the reproduction of bacterium. Then, using the analogy between a nucleus and a drop of liquid, in 1939 N. Bohr and the American physicist Wheeler developed the theory of nuclear fission. That year, an analogous theory was independently proposed by the Soviet physicist Frenkel. Neutron Induced Fission is observed in goTh, giPa, and 92U, and also in the transuranium elements with Z > 93. If the nucleus with (Z, A) breaks into parts, then two nuclei with (Z,A{) and (Z2, A 2 ) are formed, provided that Z + Zi = Z. Besides the fission fragments, fission is accompanied by neutrons (fission neutrons), the number v of which per fission event varies between 2 and 5 for different nuclei (Table 6.1). In uranium fission, the mean value of this magnitude is u = 2.3 ±0.3. Fission neutrons do not have the same energy, but are characterized by a certain energy spectrum. Fig. 147 148 The Quantum World of Nuclear Physics F i 10 3 I I 1 I I I I _ 0 4 8 En Fig. 6.1 Energy spectrum of fission neutrons for 239 Pu nuclei (arbitrary units).
- David Halliday, Jearl Walker, Patrick Keleher, Paul Lasky, John Long, Judith Dawes, Julius Orwa, Ajay Mahato, Peter Huf, Warren Stannard, Amanda Edgar, Liam Lyons, Dipesh Bhattarai(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
• Fission can be understood in terms of the collective model, in which a nucleus is likened to a charged liquid drop carrying a certain excitation energy. • A potential barrier must be tunnelled through if fssion is to occur. Fissionability depends on the relationship between the barrier height E b and the excitation energy E n transferred to the nucleus in the neutron capture. Why study physics? For decades, after World War II, Australia, New Zealand and Pacific nations protested against extensive atmospheric nuclear testing conducted by the United States, Britain and France in the Pacific Ocean. Wind and ocean currents spread the radioactive fallout to inhabited islands. Later, underground nuclear testing fractured the base of fragile atolls, leading to contamination of the marine environment. Today, adverse health and environmental impacts are the legacies of these nuclear testing programs. Pdf_Folio:1067 Let’s now turn to a central concern of physics and certain types of engineering: can we get useful energy from nuclear sources, as people have done for thousands of years from atomic sources by burning materials like wood and coal? As you already know, the answer is yes, but there are major differences between the two energy sources. When we get energy from wood and coal by burning them, we are tinkering with atoms of carbon and oxygen, rearranging their outer electrons into more stable combinations. When we get energy from uranium in a nuclear reactor, we are again burning a fuel, but now we are tinkering with the uranium nucleus, rearranging its nucleons into more stable combinations. Electrons are held in atoms by the electromagnetic Coulomb force, and it takes only a few electron-volts to pull one of them out. On the other hand, nucleons are held in nuclei by the strong force, and it takes a few million electron-volts to pull one of them out.
- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
4. Fission can be understood in terms of the collective model, in which a nucleus is likened to a charged liquid drop carrying a certain excitation energy. 5. A potential barrier must be tunneled through if fission is to occur. Fission- ability depends on the relationship between the barrier height E b and the excitation energy E n transferred to the nucleus in the neutron capture. LEARNING OBJECTIVES 1315 What Is Physics? Let’s now turn to a central concern of physics and certain types of engineering: Can we get useful energy from nuclear sources, as people have done for thousands of years from atomic sources by burning materials like wood and coal? As you already know, the answer is yes, but there are major differences between the two energy sources. When we get energy from wood and coal by burning them, we are tinkering with atoms of carbon and oxygen, rearranging their outer electrons into more stable combinations. When we get energy from uranium in a nuclear reactor, we are again burning a fuel, but now we are tinkering with the uranium nucleus, rearranging its nucleons into more stable combinations. Electrons are held in atoms by the electromagnetic Coulomb force, and it takes only a few electron-volts to pull one of them out. On the other hand, nucleons are held in nuclei by the strong force, and it takes a few million electron- volts to pull one of them out. This factor of a few million is reflected in the fact that we can extract a few million times more energy from a kilogram of uranium than we can from a kilogram of coal. In both atomic and nuclear burning, the release of energy is accompanied by a decrease in mass, according to the equation Q = –Δm c 2 . The central differ- ence between burning uranium and burning coal is that, in the former case, a much larger fraction of the available mass (again, by a factor of a few million) is consumed.
eBook - PDF- James E. Martin(Author)
- 2013(Publication Date)
- Wiley-VCH(Publisher)
The neutrinos emitted in beta transformations of the radioactive fission products constitute about 12 MeV per fission; however, these escape completely and their energy is irrevocably lost. 146 5.2 Physics of Sustained Nuclear Fission It can be shown that complete fission of 1 g of 235 U yields about 1 MW of ther- mal energy which probably contributed to the irresistible temptation for pioneer- ing physicists to produce and collect this abundant source of energy. The modern world has chosen to do this by building nuclear reactors to release fission energy at a controlled rate, and also in nuclear weapons that seek to have large instanta- neous releases of fission energy at an uncontrolled but predictable rate. The release of fission energy is governed by a fundamental set of physical prin- ciples that eventually dictate the design and performance of nuclear reactors and other critical assemblies. Radiation protection for these circumstances must also recognize these same principles in the various applications of nuclear fission, ap- plications that range from sustained and controlled chain reactions in nuclear reactors for nuclear research and electricity production to nuclear criticalities for various purposes including nuclear weapons. Radioactive fission products and activation products are byproducts of these reactions, and these represent a num- ber of radiation protection issues for workers, the public, and the environment; nuclear power reactors are particularly challenging because they are designed to operate for 30–40 years. Fission energy is determined by the fission rate, and reactor thermal power, in watts, is an important parameter for calculating fission product inventories in reactor fuel.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
It is also possible to bring about, or induce, the disintegration of a stable nucleus by striking it with another nucleus, an atomic or subatomic particle, or a g-ray pho- ton. A nuclear reaction is said to occur whenever an incident nucleus, particle, or photon causes a change to occur in a target nucleus. In 1919, Ernest Rutherford observed that when an a particle strikes a nitrogen nucleus, an oxygen nucleus and a proton are produced. This nuclear reaction is written as 2 4 He 1 7 14 N ¡ 17 8 O 1 1 1 H Incident a particle u Nitrogen (target) u Oxygen u Proton, p u Because the incident a particle induces the transmutation of nitrogen into oxygen, this reaction is an example of an induced nuclear transmutation. Nuclear reactions are often written in a shorthand form. For example, the reaction above is designated by 14 7 N (a, p) 17 8 O. The first and last symbols represent the initial and final nuclei, respectively. The symbols within the parentheses denote the incident a particle (on the left) and the small emitted particle or proton p (on the right). Some other induced nuclear transmutations are listed below, together with the equivalent shorthand notations: Nuclear Reaction Notation 1 0 n 1 10 5 B B 7 3 Li 1 4 2 He 10 5 B (n, a) 7 3 Li g 1 25 12 Mg B 24 11 Na 1 1 1 H 12 25 Mg (g, p) 11 24 Na 1 1 H 1 13 6 C B 7 14 N 1 g 6 13 C ( p, g) 7 14 N Induced nuclear reactions, like the radioactive decay process discussed in Section 31.4, obey the conservation laws of physics. Each of these laws deals with a property that 908 Chapter 32 | Ionizing Radiation, Nuclear Energy, and Elementary Particles does not change during a process. The following list shows the property with which each law deals: 1. Conservation of energy/mass (Sections 6.8 and 28.6) 2. Conservation of linear momentum (Section 7.2) 3. Conservation of angular momentum (Section 9.6) 4.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
The less massive fission fragments are near the center of the curve and have a binding energy of approximately 8.5 MeV per nucleon. The Pump Water Heat exchanger Water out Cool steam out Turbine Hot steam in Electric generator Condenser Pump Reactor Pressurized water Figure 32.7 Diagram of a nuclear power plant that uses a pressurized water reactor. 10 8 6 4 2 0 10 8 6 4 2 0 Binding energy per nucleon, MeV 0 50 Fusion Fission 100 150 200 250 Nucleon number A Figure 32.8 When fission occurs, a massive nucleus divides into two fragments whose binding energy per nucleon is greater than that of the original nucleus. When fusion occurs, two low-mass nuclei combine to form a more massive nucleus whose binding energy per nucleon is greater than that of the original nuclei. 32.5 | Nuclear Fusion 823 energy released per nucleon by fission is the difference between these two values, or about 0.9 MeV per nucleon. A glance at the far left end of the diagram in Figure 32.8 suggests another means of generating energy. Two nuclei with very low mass and relatively small binding energies per nucleon could be combined or “fused” into a single, more massive nucleus that has a greater binding energy per nucleon. This process is called nuclear fusion. A substantial amount of energy can be released during a fusion reaction, as Example 6 shows for one possible reaction. Because fusion reactions release so much energy, there is considerable interest in fusion reactors, although to date no commercial units have been constructed. The diffi- culties in building a fusion reactor arise mainly because the two low-mass nuclei must be brought sufficiently near each other so that the short-range strong nuclear force can pull them together, leading to fusion. However, each nucleus has a positive charge and repels the other electrically.
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