Uranium-232
Uranium-232 (232
92U
140, 232
U
, 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 emitted by 232U's daughters as they decay (especially 208Tl in particular) 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, or on thorium-232:
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:
The decay chain of 232U quickly yields strong gamma radiation emitters:
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, 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).
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