Thorium-208

Properties and data of the isotope ²⁰⁸Th.

Content

Thorium-208 is a radioisotope of the chemical element thorium, which, in addition to the element-specific 90 protons, has 118 neutrons in the atomic nucleus, resulting in the mass number 208. The very short-lived, only artificially producible, unstable and therefore radioactive nuclide has no practical significance; dealing with ²⁰⁸Th is for academic purposes only.

About the neutron-poor isotope ²⁰⁸Th and its production by the complete fusion reaction ⁶⁴Ni + ¹⁴⁷Sm → ²⁰⁸Th + 3n was first reported in 2010 [1].

General data

Name of the isotope:Thorium-208; Th-208Symbol:²⁰⁸Th or 20890ThMass number A:208 (= number of nucleons)Atomic number Z:90 (= number of protons)Neutrons N:118Isotopic mass:208.01791(4) u (atomic weight of Thorium-208)Nuclide mass:207.9685442 u (calculated nuclear mass without electrons)Mass excess:16.68306 MeVMass defect:1.708802968 u (per nucleus)Nuclear binding energy:1591.73971187 MeV (per nucleus)
7.65259477 MeV (average binding energy per nucleon)Separation energy:
S_P = 1.75(6) MeV (first proton)Half-life:1.7 msDecay constant λ:407.7336356235 s^-1Specific activity α:1.180494897624 × 10⁺²⁴ Bq g^-1
31905267503362 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Year of discovery:2010

Radioactive Decay

Half-life T_½ = 1.7 ms respectively 1.7 × 10^-3 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²⁰⁴Ra	100 %	8.20(3) MeV

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 118) and isobaric (same nucleon number A = 208) with Thorium-208. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 118	Isobar A = 208
72	¹⁹⁰Hf
73	¹⁹¹Ta
74	¹⁹²W
75	¹⁹³Re
76	¹⁹⁴Os
77	¹⁹⁵Ir
78	¹⁹⁶Pt	²⁰⁸Pt
79	¹⁹⁷Au	²⁰⁸Au
80	¹⁹⁸Hg	²⁰⁸Hg
81	¹⁹⁹Tl	²⁰⁸Tl
82	²⁰⁰Pb	²⁰⁸Pb
83	²⁰¹Bi	²⁰⁸Bi
84	²⁰²Po	²⁰⁸Po
85	²⁰³At	²⁰⁸At
86	²⁰⁴Rn	²⁰⁸Rn
87	²⁰⁵Fr	²⁰⁸Fr
88	²⁰⁶Ra	²⁰⁸Ra
89	²⁰⁷Ac	²⁰⁸Ac
90	²⁰⁸Th	²⁰⁸Th

External data and identifiers

Adopted Levels, Gammas:NuDat 208Th

Literature and References

[1] - J. A. Heredia, A. N. Andreyev, S. Antalic et al.:
The new isotope ²⁰⁸Th.
In: The European Physical Journal A, (2010), DOI 10.1140/epja/i2010-11058-1.