Plutonium-242
| General | |
|---|---|
| Symbol | 242Pu |
| Names | plutonium-242 |
| Protons (Z) | 94 |
| Neutrons (N) | 148 |
| Nuclide data | |
| Half-life (t1/2) | 375000 years[1] |
| Isotope mass | 242.059741[2] Da |
| Decay products | 238U |
| Decay modes | |
| Decay mode | Decay energy (MeV) |
| alpha decay | 4.984[3] |
| Isotopes of plutonium Complete table of nuclides | |
Plutonium-242 (242Pu or Pu-242) is the second longest-lived isotope of plutonium, with a half-life of 375,000 years. The half-life of 242Pu is about 15 times that of 239Pu; so it is one-fifteenth as radioactive, and not one of the larger contributors to nuclear waste radioactivity. 242Pu's gamma ray emissions are also weaker than those of the other isotopes.[4] As the direct parent of uranium-238 it is part of the uranium series decay chain.
It is not fissile (but it is fissionable by fast neutrons), and its neutron capture cross section is low. Like the other even isotopes of plutonium it has a significant rate of spontaneous fission.
In the nuclear fuel cycle
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Plutonium-242 is produced by successive neutron capture on 239Pu, 240Pu, and 241Pu. The odd-mass isotopes 239Pu and 241Pu have about a 3/4 chance of undergoing fission on capture of a thermal neutron and about a 1/4 chance of retaining the neutron and becoming the following isotope. The proportion of 242Pu is low at low burnup but increases faster than linearly due to the intermediate isotopes' buildup.
242Pu has a particularly low cross section for thermal neutron capture; and it takes three neutron absorptions to become another fissile isotope (curium-245) and then one more neutron to undergo fission. Even then, there is a chance of the fourth neutron being absorbed instead of fissioning, leading to curium-246 (with again only a small neutron cross-section), so the mean number of neutrons absorbed until fission is even higher than 4. Therefore, 242Pu is particularly unsuited to recycling in a thermal reactor and would be better used in a fast reactor where it can be fissioned directly. However, 242Pu's low cross section means that relatively little of it is transmuted during one cycle in a thermal reactor.
References
[edit]- ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3) 030001. doi:10.1088/1674-1137/abddae.
- ^ Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3) 030003. doi:10.1088/1674-1137/abddaf.
- ^ National Nuclear Data Center. "NuDat 3.0 database". Brookhaven National Laboratory.
- ^ "PLUTONIUM ISOTOPIC RESULTS OF KNOWN SAMPLES USING THE SNAP GAMMA SPECTROSCOPY ANALYSIS CODE AND THE ROBWIN SPECTRUM FITTING ROUTINE" (PDF). Archived from the original (PDF) on 2017-08-13. Retrieved 2013-03-15.