Thorium-228

Properties and data of the isotope ²²⁸Th.

Content

General data

Name of the isotope:Thorium-228; Th-228Other names:RadiothoriumSymbol:²²⁸Th or 22890ThMass number A:228 (= number of nucleons)Atomic number Z:90 (= number of protons)Neutrons N:138Isotopic mass:228.0287398(19) u (atomic weight of Thorium-228)Nuclide mass:227.979374 u (calculated nuclear mass without electrons)Mass excess:26.77095 MeVMass defect:1.871271488 u (per nucleus)Nuclear binding energy:1743.07816344 MeV (per nucleus)
7.64507966 MeV (average binding energy per nucleon)Separation energy:S_N = 7.1052(23) MeV (first neutron)
S_P = 6.3676(21) MeV (first proton)Cross section:σ(n.γ) = 120(20) barn (thermal neutron capture cross-section)
σ(n.f) < 0.3 b (gap cross-section)Half-life:1.9116(16) aDecay constant λ:1.149011755130 × 10^-8 s^-1Specific activity α:30348730873317 Bq g^-1
820.23596954911 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Year of discovery:1905

Radioactive Decay

Half-life T_½ = 1.9116(16) a respectively 6.03255082 × 10⁷ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²²⁴Ra	100 %	5.52015(22) MeV

Parent Nuclides

Direct parent isotopes are: ²³²U, ²²⁸Ac, ²²⁸Pa.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 138) and isobaric (same nucleon number A = 228) with Thorium-228. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 138	Isobar A = 228
82	²²⁰Pb
83	²²¹Bi
84	²²²Po
85	²²³At	²²⁸At
86	²²⁴Rn	²²⁸Rn
87	²²⁵Fr	²²⁸Fr
88	²²⁶Ra	²²⁸Ra
89	²²⁷Ac	²²⁸Ac
90	²²⁸Th	²²⁸Th
91	²²⁹Pa	²²⁸Pa
92	²³⁰U	²²⁸U
93	²³¹Np	²²⁸Np
94	²³²Pu	²²⁸Pu
95	²³³Am
96	²³⁴Cm
97	²³⁵Bk