Uranium-232
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Uranium-232 (^{232}
_{}U^{}
_{}, U-232) is an isotope of uranium. It has a half-life of around
68.9 years and is a side product in the thorium cycle. It has been cited as an obstacle to nuclear proliferation using ^{233}U as the fissile material, because the intense gamma radiation emitted by ^{208}Tl (a daughter of ^{232}U, produced relatively quickly) makes the ^{233}U contaminated with it more difficult to handle.
General | |
---|---|
Symbol | ^{232}U |
Names | uranium-232, U-232, U-232 |
Protons | 92 |
Neutrons | 140 |
Nuclide data | |
Half-life | 68.9 years |
Parent isotopes | ^{236}Pu (α) ^{232}Np (β^{+}) ^{232}Pa (β^{−}) |
Decay products | ^{228}Th |
Isotopes of uranium Complete table of nuclides |
Production of ^{233}U (through the neutron irradiation of ^{232}Th) invariably produces small amounts of ^{232}U as an impurity, because of parasitic (n,2n) reactions on uranium-233 itself, or on protactinium-233, or on thorium-232:
- ^{232}Th (n,γ) ^{233}Th (β−) ^{233}Pa (β−) ^{233}U (n,2n) ^{232}U
- ^{232}Th (n,γ) ^{233}Th (β−) ^{233}Pa (n,2n) ^{232}Pa (β−) ^{232}U
- ^{232}Th (n,2n) ^{231}Th (β−) ^{231}Pa (n,γ) ^{232}Pa (β−) ^{232}U
Another channel involves neutron capture reaction on small amounts of thorium-230, which is a tiny fraction of natural thorium present due to the decay of uranium-238:
- ^{230}Th (n,γ) ^{231}Th (β−) ^{231}Pa (n,γ) ^{232}Pa (β−) ^{232}U
The decay chain of ^{232}U quickly yields strong gamma radiation emitters:^{[1]}
- ^{232}U (α, 68.9 years)
- ^{228}Th (α, 1.9 year)
- ^{224}Ra (α, 3.6 day, 0.24 MeV) (from this point onwards, the decay chain is identical to that of ^{232}Th; thorium-232 is nevertheless much less dangerous because its extremely long half-life of about 14-15 billion years means that not as much of its dangerous daughters builds up)
- ^{220}Rn (α, 55 s, 0.54 MeV)
- ^{216}Po (α, 0.15 s)
- ^{212}Pb (β−, 10.64 h)
- ^{212}Bi (α, 61 min, 0.78 MeV)
- ^{208}Tl (β−, 3 min, 2.6 MeV) (35.94% branching ratio)
- ^{208}Pb (stable)
This makes manual handling in a glove box with only light shielding (as commonly done with plutonium) too hazardous, (except possibly in a short period immediately following chemical separation of the uranium from thorium-228, radium-224, radon-220, and polonium-216) and instead requiring remote manipulation for fuel fabrication.
Unusually for an isotope with even mass number, ^{232}U has a significant neutron absorption cross section for fission (thermal neutrons 75 barns (b), resonance integral 380 b) as well as for neutron capture (thermal 73 b, resonance integral 280 b).
Lighter: uranium-231 |
Uranium-232 is an isotope of uranium |
Heavier: uranium-233 |
Decay product of: plutonium-236 (α) neptunium-232 (β^{+}) protactinium-232 (β^{−}) |
Decay chain of uranium-232 |
Decays to: thorium-228 (α) |
ReferencesEdit
- ^ Griffin, H. C. Natural Radioactive Decay Chains, Chapter 13 of Handbook of Nuclear Chemistry, Second Edition, Springer 2011, ISBN 978-1-4419-0719-6