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Uranium-232

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Isotope of uranium

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Uranium-232
General

Symbol	²³²U
Names	uranium-232
Protons(Z)	92
Neutrons(N)	140
Nuclide data
Half-life(t_1/2)	68.9 years^[1]
Parent isotopes	²³⁶Pu (α) ²³²Np (β⁺) ²³²Pa (β⁻)
Decay products	²²⁸Th
Decay modes
Decay mode	Decay energy (MeV)
Alpha	5.414^[2]
Isotopes of uranium Complete table of nuclides

Uranium-232 (²³²
U) is anisotope of uranium. It has a half-life of 68.9 years and is a side product in thethorium cycle. It has been cited^{[by whom?]} as an obstacle tonuclear proliferation using²³³U as thefissile material, because the intensegamma radiation emitted by²⁰⁸Tl (a daughter of²³²U, produced relatively quickly) makes the²³³U contaminated with it more difficult to handle.

Production of²³³U (through the neutron irradiation of²³²Th) invariably produces small amounts of²³²U as an impurity, because of parasitic (n,2n) reactions onuranium-233 itself, or onprotactinium-233, or onthorium-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 ofuranium-238:

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

The decay chain of²³²U quickly yields strong gamma radiation emitters:^[3]

²³²U (α, 68.9 years)

²²⁸Th (α, 1.9125 years) (after this, the decay chain is identical to that of²³²Th; 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 evenmass number,²³²U has a significantneutron absorption cross section forfission (thermal neutrons75 barns (b),resonance integral380 b) as well as forneutron capture (thermal73 b, resonance integral280 b). This makes it afissile isotope, though using it alone in a reactor or bomb is not reasonable.