Uranium-231

Properties and data of the isotope ²³¹U.

Content

Uranium-231 is the short-lived radioisotope of the element Uranium, whose atomic nucleus has 139 neutrons in addition to the element-specific 92 protons, resulting in a mass number of 231: ²³¹U.

General data

Name of the isotope:Uranium-231; U-231Symbol:²³¹U or 23192UMass number A:231 (= number of nucleons)Atomic number Z:92 (= number of protons)Neutrons N:139Isotopic mass:231.0362923(29) u (atomic weight of Uranium-231)Nuclide mass:230.9858296 u (calculated nuclear mass without electrons)Mass excess:33.80606 MeVMass defect:1.888033968 u (per nucleus)Nuclear binding energy:1758.69231299 MeV (per nucleus)
7.61338664 MeV (average binding energy per nucleon)Separation energy:S_N = 5.880(5) MeV (first neutron)
S_P = 5.657(4) MeV (first proton)Half-life:4.2(1) dDecay constant λ:1.910127812389 × 10^-6 s^-1Specific activity α:4.979679111122 × 10⁺¹⁵ Bq g^-1
134585.92192223 Ci g^-1Spin and parity:
(nuclear angular momentum)(5/2-)Year of discovery:1949

Radioactive Decay

Half-life T_½ = 4.2(1) d respectively 3.62880 × 10⁵ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²²⁷Th	0.004(1) %	5.5763(17) MeV
EE	²³¹Pa	ca. 100 %	0.382(3) MeV

Parent Nuclides

Direct parent isotopes are: ²³⁵Pu, ²³¹Np.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 139) and isobaric (same nucleon number A = 231) with Uranium-231. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 139	Isobar A = 231
83	²²²Bi
84	²²³Po
85	²²⁴At
86	²²⁵Rn
87	²²⁶Fr	²³¹Fr
88	²²⁷Ra	²³¹Ra
89	²²⁸Ac	²³¹Ac
90	²²⁹Th	²³¹Th
91	²³⁰Pa	²³¹Pa
92	²³¹U	²³¹U
93	²³²Np	²³¹Np
94	²³³Pu	²³¹Pu
95	²³⁴Am	²³¹Am
96	²³⁵Cm
97	²³⁶Bk
98	²³⁷Cf