Plutonium-240

Source: Wikipedia, the free encyclopedia.
Plutonium-240, 240Pu
General
Decay mode
Decay energy (MeV)
Alpha decay5.25575(14)[2]
Isotopes of plutonium
Complete table of nuclides

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]

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

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

thermal reactor
.

Nuclear weapons

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:

The spontaneous fission problem was extensively studied by the scientists 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

References

  1. doi:10.1016/j.nuclphysa.2003.11.001
    .
  2. ^
    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. ^
    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. ^
    ISBN 978-0-387-26931-3
    .
  6. 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. ^
    S2CID 219716695
    .
  9. doi:10.1103/PhysRev.94.156
    .
  10. JSTOR 27757700
    .
  11. doi:10.13182/NT80-A17072
    .
  12. doi:10.1016/0306-4549(78)90104-4
    .

External links


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