Uranium-232

{{Short description|Isotope of uranium}} {{more citations needed|date=November 2015}} {{Infobox isotope | alternate_names = | symbol = U | mass_number = 232 | mass = | num_neutrons = 140 | num_protons = 92 | abundance = | halflife = {{val|68.9|u=years}}<ref>{{NUBASE2020}}</ref> | image =Uranium-232.svg | image_caption = | decay_product = Thorium-228 | decay_symbol = Th | decay_mass = 228 | decay_mode1 = Alpha | decay_energy1 = 5.414<ref>{{NNDC}}</ref> | decay_mode2 = | decay_energy2 = | decay_mode3 = | decay_energy3 = | decay_mode4 = | decay_energy4 = | parent = Plutonium-236 | parent_symbol = Pu | parent_mass = 236 | parent_decay = a | parent2 = Neptunium-232 | parent2_symbol = Np | parent2_mass = 232 | parent2_decay = b+ | parent3 = Protactinium-232 | parent3_symbol = Pa | parent3_mass = 232 | parent3_decay = b- | spin = | excess_energy = | binding_energy = }}

'''Uranium-232''' ('''{{SimpleNuclide|Uranium|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{{by whom|date=August 2025}} as an obstacle to nuclear proliferation using ²³³U as the fissile material, because the intense gamma radiation emitted by ²⁰⁸Tl (a daughter of ²³²U, produced relatively quickly) 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:

:²³²Th (n,γ) ²³³Th (β⁻) ²³³Pa (β⁻) ²³³U (n,2n) ²³²U :²³²Th (n,γ) ²³³Th (β⁻) ²³³Pa (n,2n) ²³²Pa (β⁻) ²³²U :²³²Th (n,2n) ²³¹Th (β⁻) ²³¹Pa (n,γ) ²³²Pa (β⁻) ²³²U

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:

:²³⁰Th (n,γ) ²³¹Th (β⁻) ²³¹Pa (n,γ) ²³²Pa (β⁻) ²³²U

The decay chain of ²³²U quickly yields strong gamma radiation emitters:<ref>Griffin, H. C. ''Natural Radioactive Decay Chains'', Chapter 13 of ''Handbook of Nuclear Chemistry'', Second Edition, Springer 2011, {{ISBN|978-1-4419-0719-6}}</ref>

:²³²U (α, 68.9 years) :²²⁸Th (α, 1.9125 years) (after this, the decay chain is identical to that of ²³²Th; thorium-232 is nevertheless much less dangerous because its much longer half-life, 14 billion years or 200 million times that of uranium-232, means the build-up of daughters is that much less for equal mass) :²²⁴Ra (α, 3.632 days) :²²⁰Rn (α, 55.6 s) :²¹⁶Po (α, 0.144 s) :²¹²Pb (β⁻, 10.627 h) :²¹²Bi (α, 60.55 min, 0.78 MeV), with 35.94% branching ratio to :²⁰⁸Tl (β⁻, 3.053 min), 99.75% chance to emit 2.6 MeV gamma ray :²⁰⁸Pb (stable)

This makes manual handling in a glove box with only light shielding (as commonly done with plutonium) too hazardous, except in a period short compared to the Th-228 half-life just after chemical separation of the uranium, 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 {{val|75|u=barns (b)}}, resonance integral {{val|380|u=b}}) as well as for neutron capture (thermal {{val|73|u=b}}, resonance integral {{val|280|u=b}}). This makes it a fissile isotope, though using it alone in a reactor or bomb is not reasonable.

{{Isotope sequence |element=uranium |lighter=uranium-231 |heavier=uranium-233 |before=plutonium-236 '''(α)''' <br /> neptunium-232 '''(β⁺)''' <br /> protactinium-232 '''(β⁻)'''<nowiki/> |after=thorium-228 '''(α)'''<nowiki/> }}

==References== {{Reflist}}

{{Isotopes of uranium}}

Category:Isotopes of uranium Category:Nuclear materials Category:Fissile materials