Thorium-231

Properties and data of the isotope ²³¹Th.

Content

General data

Name of the isotope:Thorium-231; Th-231Other names:Uran Y. Uranium YSymbol:²³¹Th or 23190ThMass number A:231 (= number of nucleons)Atomic number Z:90 (= number of protons)Neutrons N:141Isotopic mass:231.0363028(13) u (atomic weight of Thorium-231)Nuclide mass:230.986937 u (calculated nuclear mass without electrons)Mass excess:33.81584 MeVMass defect:1.889703236 u (per nucleus)Nuclear binding energy:1760.24722611 MeV (per nucleus)
7.62011786 MeV (average binding energy per nucleon)Separation energy:S_N = 5.11802(20) MeV (first neutron)
S_P = 7.312(16) MeV (first proton)Half-life:25.57(8) hDecay constant λ:7.529952424281 × 10^-6 s^-1Specific activity α:1.963049098166 × 10⁺¹⁶ Bq g^-1
530553.81031524 Ci g^-1Spin and parity:
(nuclear angular momentum)5/2+Year of discovery:1911

Radioactive Decay

Half-life T_½ = 25.57(8) h (hours) respectively 9.2052 × 10⁴ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	²³¹Pa	100 %	3.915(15) MeV

Parent Nuclides

Direct parent isotopes are: ²³⁵U, ²³¹Ac.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 141) and isobaric (same nucleon number A = 231) with Thorium-231. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 141	Isobar A = 231
83	²²⁴Bi
84	²²⁵Po
85	²²⁶At
86	²²⁷Rn
87	²²⁸Fr	²³¹Fr
88	²²⁹Ra	²³¹Ra
89	²³⁰Ac	²³¹Ac
90	²³¹Th	²³¹Th
91	²³²Pa	²³¹Pa
92	²³³U	²³¹U
93	²³⁴Np	²³¹Np
94	²³⁵Pu	²³¹Pu
95	²³⁶Am	²³¹Am
96	²³⁷Cm
97	²³⁸Bk
98	²³⁹Cf
99	²⁴⁰Es
100	²⁴¹Fm