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Plutonium-240

Plutonium-240 (240
Pu
or Pu-240) is an isotope of plutonium formed when plutonium-239 captures a neutron. The detection of its spontaneous fission led to its discovery in 1944 at Los Alamos and had important consequences for the Manhattan Project.[3]

Plutonium-240, 240Pu
General
Symbol240Pu
Namesplutonium-240, 240Pu, Pu-240
Protons (Z)94
Neutrons (N)146
Nuclide data
Natural abundanceTrace
Half-life (t1/2)6561(7) years[1]
Isotope mass240.0538135(20)[2] Da
Decay modes
Decay modeDecay energy (MeV)
Alpha decay5.25575(14)[2]
Isotopes of plutonium
Complete table of nuclides

240Pu undergoes spontaneous fission as a secondary decay mode at a small but significant rate. The presence of 240Pu limits plutonium's use in a nuclear bomb, because the neutron flux from spontaneous fission initiates the chain reaction prematurely, causing an early release of energy that physically disperses the core before full implosion is reached.[4][5] It decays by alpha emission to uranium-236.

Nuclear properties edit

About 62% to 73% of the time when 239Pu captures a neutron, it undergoes fission; the remainder of the time, it forms 240Pu. The longer a nuclear fuel element remains in a nuclear reactor, the greater the relative percentage of 240Pu in the fuel becomes.

The isotope 240Pu has about the same thermal neutron capture cross section as 239Pu (289.5±1.4 vs. 269.3±2.9 barns),[6][7] but only a tiny thermal neutron fission cross section (0.064 barns). When the isotope 240Pu captures a neutron, it is about 4500 times more likely to become plutonium-241 than to fission. In general, isotopes of odd mass numbers are more likely to absorb a neutron, and can undergo fission upon neutron absorption more easily than isotopes of even mass number. Thus, even mass isotopes tend to accumulate, especially in a thermal reactor.

Nuclear weapons edit

The inevitable presence of some 240Pu in a plutonium-based nuclear warhead core complicates its design, and pure 239Pu is considered optimal.[8] This is for a few reasons:

  • 240Pu has a high rate of spontaneous fission. A single stray neutron that is introduced while the core is supercritical will cause it to detonate almost immediately, even before it has been crushed to an optimal configuration. The presence of 240Pu would thus randomly cause fizzles, with an explosive yield well below the potential yield.[8][5]
  • Isotopes besides 239Pu release significantly more radiation, which complicates its handling by workers.[8]
  • Isotopes besides 239Pu produce more decay heat, which can cause phase change distortions of the precision core if allowed to build up.[8]

The spontaneous fission problem was extensively studied by the scientists of the Manhattan Project during World War II.[9] It blocked the use of plutonium in gun-type nuclear weapons in which the assembly of fissile material into its optimal supercritical mass configuration can take up to a millisecond to complete, and made it necessary to develop implosion-style weapons where the assembly occurs in a few microseconds.[10] Even with this design, it was estimated in advance of the Trinity test that 240Pu impurity would cause a 12% chance of the explosion failing to reach its maximum yield.[8]

The minimization of the amount of 240
Pu
, as in weapons-grade plutonium (less than 7% 240Pu) is achieved by reprocessing the fuel after just 90 days of use. Such rapid fuel cycles are highly impractical for civilian power reactors and are normally only carried out with dedicated weapons plutonium production reactors. Plutonium from spent civilian power reactor fuel typically has under 70% 239Pu and around 26% 240
Pu
, the rest being made up of other plutonium isotopes, making it more difficult to use it for the manufacturing of nuclear weapons.[4][8][11][12] For nuclear weapon designs introduced after the 1940s, however, there has been considerable debate over the degree to which 240
Pu
poses a barrier for weapons construction; see the article Reactor-grade plutonium.

See also edit

References edit

  1. ^ Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (December 2003). "The Nubase evaluation of nuclear and decay properties". Nuclear Physics A. 729 (1): 3–128. Bibcode:2003NuPhA.729....3A. CiteSeerX 10.1.1.692.8504. doi:10.1016/j.nuclphysa.2003.11.001.
  2. ^ a b Audi, Georges; Wapstra, Aaldert Hendrik; Thibault, Catherine (December 2003). "The Ame2003 atomic mass evaluation". Nuclear Physics A. 729 (1): 337–676. Bibcode:2003NuPhA.729..337A. doi:10.1016/j.nuclphysa.2003.11.003.
  3. ^ Farwell, G. W. (1990). "Emilio Segre, Enrico Fermi, Pu-240, and the atomic bomb". Symposium to Commemorate the 50th Anniversary of the Discovery of Transuranium Elements.
  4. ^ a b Şahin, Sümer (1981). "Remarks On The Plutonium-240 Induced Pre-Ignition Problem In A Nuclear Device". Nuclear Technology. 54 (1): 431–432. doi:10.13182/NT81-A32795. The energy yield of a nuclear explosive decreases by one and two orders of magnitude if the 240 Pu content increases from 5 (nearly weapons-grade plutonium) to 15 and 25%, respectively
  5. ^ a b Bodansky, David (2007). "Nuclear Bombs, Nuclear Energy, and Terrorism". Nuclear Energy: Principles, Practices, and Prospects. Springer Science & Business Media. ISBN 978-0-387-26931-3.
  6. ^ Mughabghab, S. F. (2006). Atlas of neutron resonances : resonance parameters and thermal cross sections Z=1-100. Amsterdam: Elsevier. ISBN 978-0-08-046106-9.
  7. ^ "Actinide data: Thermal neutron cross sections, resonance integrals, and Westcott factors". Nuclear Data for Safeguards. International Atomic Energy Agency. Retrieved 2016-09-11.
  8. ^ a b c d e f Mark, J. Carson; Hippel, Frank von; Lyman, Edward (2009-10-30). "Explosive Properties of Reactor-Grade Plutonium" (PDF). Science & Global Security. 17 (2–3): 170–185. Bibcode:2009S&GS...17..170M. doi:10.1080/08929880903368690. ISSN 0892-9882. S2CID 219716695.
  9. ^ Chamberlain, O.; Farwell, G. W.; Segrè, E. (1954). "Pu-240 and Its Spontaneous Fission". Physical Review. 94 (1): 156. Bibcode:1954PhRv...94..156C. doi:10.1103/PhysRev.94.156.
  10. ^ Hoddeson, Lillian (1993). "The Discovery of Spontaneous Fission in Plutonium during World War II". Historical Studies in the Physical and Biological Sciences. 23 (2): 279–300. doi:10.2307/27757700. JSTOR 27757700.
  11. ^ Şahin, Sümer; Ligou, Jacques (1980). "The Effect of the Spontaneous Fission of Plutonium-240 on the Energy Release in a Nuclear Explosive". Nuclear Technology. 50 (1): 88. doi:10.13182/NT80-A17072.
  12. ^ Şahi̇n, Sümer (1978). "The effect of Pu-240 on neutron lifetime in nuclear explosives". Annals of Nuclear Energy. 5 (2): 55–58. doi:10.1016/0306-4549(78)90104-4.

External links edit

  • NLM Hazardous Substances Databank – Plutonium, Radioactive


Lighter:
plutonium-239
Plutonium-240 is an
isotope of plutonium
Heavier:
plutonium-241
Decay product of:
curium-244 (α)
neptunium-240
(β)
Decay chain
of plutonium-240
Decays to:
uranium-236 (α)

plutonium, isotope, plutonium, formed, when, plutonium, captures, neutron, detection, spontaneous, fission, discovery, 1944, alamos, important, consequences, manhattan, project, 240pugeneralsymbol240punamesplutonium, 240pu, 240protons, 94neutrons, 146nuclide, . Plutonium 240 240 Pu or Pu 240 is an isotope of plutonium formed when plutonium 239 captures a neutron The detection of its spontaneous fission led to its discovery in 1944 at Los Alamos and had important consequences for the Manhattan Project 3 Plutonium 240 240PuGeneralSymbol240PuNamesplutonium 240 240Pu Pu 240Protons Z 94Neutrons N 146Nuclide dataNatural abundanceTraceHalf life t1 2 6561 7 years 1 Isotope mass240 0538135 20 2 DaDecay modesDecay modeDecay energy MeV Alpha decay5 25575 14 2 Isotopes of plutonium Complete table of nuclides 240Pu undergoes spontaneous fission as a secondary decay mode at a small but significant rate The presence of 240Pu limits plutonium s use in a nuclear bomb because the neutron flux from spontaneous fission initiates the chain reaction prematurely causing an early release of energy that physically disperses the core before full implosion is reached 4 5 It decays by alpha emission to uranium 236 Contents 1 Nuclear properties 2 Nuclear weapons 3 See also 4 References 5 External linksNuclear properties editAbout 62 to 73 of the time when 239Pu captures a neutron it undergoes fission the remainder of the time it forms 240Pu The longer a nuclear fuel element remains in a nuclear reactor the greater the relative percentage of 240Pu in the fuel becomes The isotope 240Pu has about the same thermal neutron capture cross section as 239Pu 289 5 1 4 vs 269 3 2 9 barns 6 7 but only a tiny thermal neutron fission cross section 0 064 barns When the isotope 240Pu captures a neutron it is about 4500 times more likely to become plutonium 241 than to fission In general isotopes of odd mass numbers are more likely to absorb a neutron and can undergo fission upon neutron absorption more easily than isotopes of even mass number Thus even mass isotopes tend to accumulate especially in a thermal reactor Nuclear weapons editThe inevitable presence of some 240Pu in a plutonium based nuclear warhead core complicates its design and pure 239Pu is considered optimal 8 This is for a few reasons 240Pu has a high rate of spontaneous fission A single stray neutron that is introduced while the core is supercritical will cause it to detonate almost immediately even before it has been crushed to an optimal configuration The presence of 240Pu would thus randomly cause fizzles with an explosive yield well below the potential yield 8 5 Isotopes besides 239Pu release significantly more radiation which complicates its handling by workers 8 Isotopes besides 239Pu produce more decay heat which can cause phase change distortions of the precision core if allowed to build up 8 The spontaneous fission problem was extensively studied by the scientists of the Manhattan Project during World War II 9 It blocked the use of plutonium in gun type nuclear weapons in which the assembly of fissile material into its optimal supercritical mass configuration can take up to a millisecond to complete and made it necessary to develop implosion style weapons where the assembly occurs in a few microseconds 10 Even with this design it was estimated in advance of the Trinity test that 240Pu impurity would cause a 12 chance of the explosion failing to reach its maximum yield 8 The minimization of the amount of 240 Pu as in weapons grade plutonium less than 7 240Pu is achieved by reprocessing the fuel after just 90 days of use Such rapid fuel cycles are highly impractical for civilian power reactors and are normally only carried out with dedicated weapons plutonium production reactors Plutonium from spent civilian power reactor fuel typically has under 70 239Pu and around 26 240 Pu the rest being made up of other plutonium isotopes making it more difficult to use it for the manufacturing of nuclear weapons 4 8 11 12 For nuclear weapon designs introduced after the 1940s however there has been considerable debate over the degree to which 240 Pu poses a barrier for weapons construction see the article Reactor grade plutonium See also editBurnup Isotopes of plutoniumReferences edit Audi Georges Bersillon Olivier Blachot Jean Wapstra Aaldert Hendrik December 2003 The Nubase evaluation of nuclear and decay properties Nuclear Physics A 729 1 3 128 Bibcode 2003NuPhA 729 3A CiteSeerX 10 1 1 692 8504 doi 10 1016 j nuclphysa 2003 11 001 a b Audi Georges Wapstra Aaldert Hendrik Thibault Catherine December 2003 The Ame2003 atomic mass evaluation Nuclear Physics A 729 1 337 676 Bibcode 2003NuPhA 729 337A doi 10 1016 j nuclphysa 2003 11 003 Farwell G W 1990 Emilio Segre Enrico Fermi Pu 240 and the atomic bomb Symposium to Commemorate the 50th Anniversary of the Discovery of Transuranium Elements a b Sahin Sumer 1981 Remarks On The Plutonium 240 Induced Pre Ignition Problem In A Nuclear Device Nuclear Technology 54 1 431 432 doi 10 13182 NT81 A32795 The energy yield of a nuclear explosive decreases by one and two orders of magnitude if the 240 Pu content increases from 5 nearly weapons grade plutonium to 15 and 25 respectively a b Bodansky David 2007 Nuclear Bombs Nuclear Energy and Terrorism Nuclear Energy Principles Practices and Prospects Springer Science amp Business Media ISBN 978 0 387 26931 3 Mughabghab S F 2006 Atlas of neutron resonances resonance parameters and thermal cross sections Z 1 100 Amsterdam Elsevier ISBN 978 0 08 046106 9 Actinide data Thermal neutron cross sections resonance integrals and Westcott factors Nuclear Data for Safeguards International Atomic Energy Agency Retrieved 2016 09 11 a b c d e f Mark J Carson Hippel Frank von Lyman Edward 2009 10 30 Explosive Properties of Reactor Grade Plutonium PDF Science amp Global Security 17 2 3 170 185 Bibcode 2009S amp GS 17 170M doi 10 1080 08929880903368690 ISSN 0892 9882 S2CID 219716695 Chamberlain O Farwell G W Segre E 1954 Pu 240 and Its Spontaneous Fission Physical Review 94 1 156 Bibcode 1954PhRv 94 156C doi 10 1103 PhysRev 94 156 Hoddeson Lillian 1993 The Discovery of Spontaneous Fission in Plutonium during World War II Historical Studies in the Physical and Biological Sciences 23 2 279 300 doi 10 2307 27757700 JSTOR 27757700 Sahin Sumer Ligou Jacques 1980 The Effect of the Spontaneous Fission of Plutonium 240 on the Energy Release in a Nuclear Explosive Nuclear Technology 50 1 88 doi 10 13182 NT80 A17072 Sahi n Sumer 1978 The effect of Pu 240 on neutron lifetime in nuclear explosives Annals of Nuclear Energy 5 2 55 58 doi 10 1016 0306 4549 78 90104 4 External links editNLM Hazardous Substances Databank Plutonium Radioactive Lighter plutonium 239 Plutonium 240 is an isotope of plutonium Heavier plutonium 241 Decay product of curium 244 a neptunium 240 b Decay chain of plutonium 240 Decays to uranium 236 a Retrieved from https en wikipedia org w index php title Plutonium 240 amp oldid 1204964995, wikipedia, wiki, book, books, library,

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