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Properties and data of the isotope 232U.


Uranium-232 is the radioisotope of the element Uranium, whose atomic nucleus has 140 neutrons in addition to the element-specific 92 protons, resulting in a mass number of 232.

See also: list of Uranium isotopes.


General data

Name of the isotope:Uranium-232; U-232Symbol:232UMass number A:232Atomic number Z:92 (= number of protons)Neutrons N:140Isotopic mass:232.0371549(1) u (atomic weight of Uranium-232)Nuclide mass:231.9866922 u (calculated nuclear mass without electrons)Mass excess:34.60957 MeVMass defect:1.895836284 u (per nucleus)Nuclear binding energy:1765.96012353 MeV (per nucleus)
7.61189708 MeV (average binding energy per nucleon)
Separation energy:SN = 7.2678(28) MeV (first neutron)
SP = 6.1038(19) MeV (first proton)
Half-life:68.9(4) aDecay constant λ:3.190110367083 × 10-10 s-1Spin and parity:0+Year of discovery:1949


Radioactive Decay

Half-life T½ = 68.9(4) a respectively 2.1728 × 109 seconds s.

Decay modeDaughterProbabilityDecay energyγ energy
α228Thca. 100 %5,41363(9) MeV


Uranium-232 radioactive decay chain


Parent Nuclides

Direct parent isotopes are: 236Pu, 232Np, 232Pa.



Uranium-232 occurs in the thorium cycle and is used as a tracer in nuclear fuel. The U-232 decay chain produces a penetrating gamma radiation that is difficult to shield. With regard to thorium fuel, the presence of highly radiotoxic 232U means that the spent fuel must be handled using remote techniques in heavily shielded containment chambers.


Radiation Protection

The German Radiation Protection Ordinance, for example, specifies the following limit values for the isotope Uranium-232 (exemption limits, clearance values and other values as a radioactive or highly radioactive source of radiation (HASS)):

Isotope:U-232+Exemption level:103 BqExemption level per gram:0,1 Bq/g
Unrestricted handling of solids and liquids.
Activity HASS:0,06 TBqSurface contamination:0,1 Bq cm-2Half-life:68.9 a


Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 140) and isobaric (same nucleon number A = 232) with Uranium-232. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.


OZIsotone N = 140Isobar A = 232


External data and identifiers

Adopted Levels, Gammas:NuDat 232U


Literature and References

[1] - Stephen F. Ashley, Geoffrey T. Parks, William J. Nuttall, Colin Boxall, Robin W. Grimes :
Thorium fuel has risks.
In: Nature, (2012), DOI 10.1038/492031a.

[2] - Andrzej Wojciechowski:
The U-232 production in thorium cycle.
In: Progress in Nuclear Energy, (2018), DOI 10.1016/j.pnucene.2018.03.011.

[3] - Joshua Rhodes, G. Ivan Maldonado:
Exploration of producing Uranium-232 for use as a tracer in uranium fuels.
In: Applied Radiation and Isotopes, (2022), DOI 10.1016/j.apradiso.2022.110275.


Category: Isotopes

Last update: 03.12.2022

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