Uranium-232

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Uranium-232
General
Name, symbol U-232,232U
Neutrons 140
Protons 92
Nuclide data
Half-life 68.9 years
Parent isotopes 236Pu (α)
232Np (β+)
232Pa (β)
Decay products 228Th

Uranium 232 (232
92
U
140
, 232U, U-232) is an isotope of uranium. It has a half-life of 68.9 years and is a side product in the thorium cycle. It has been cited as an obstacle to nuclear proliferation using 233U as the fissile material, because the intense gamma radiation of 232U's decay products makes the 233U contaminated with it more difficult to handle.

Production of 233U (through the neutron irradiation of 232Th) invariably produces small amounts of 232U as an impurity, because of parasitic (n,2n) reactions on uranium-233 itself, or on protactinium-233:

232Th (n,γ) 233Th (β−) 233Pa (β−) 233U (n,2n) 232U
232Th (n,γ) 233Th (β−) 233Pa (n,2n) 232Pa (β−) 232U

The decay chain of 232U quickly yields strong gamma radiation emitters:

232U (α, 68.9 years)
228Th (α, 1.9 year)
224Ra (α, 3.6 day, 0.24 MeV) (at this point, the decay chain is identical to that of 232Th)
220Rn (α, 55 s, 0.54 MeV)
216Po (α, 0.15 s)
212Pb (β−, 10.64 h)
212Bi (α, 61 m, 0.78 MeV)
208Tl (β−, 3 m, 2.6 MeV) (35.94% branching ratio)
208Pb (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) and instead requiring remote manipulation for fuel fabrication.

Unusually for an isotope with even mass number, 232U 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)