Thorium-229m

Properties and data of the isotope ²²⁹Th.

Content

General data

Name of the isotope:Thorium-229m; Th-229mSymbol:²²⁹Th or 22990ThMass number A:229 (= number of nucleons)Atomic number Z:90 (= number of protons)Neutrons N:139Isotopic mass:229.0317614(26) u (atomic weight of Thorium-229m)
Excitation energy: 0.00810(17) keVNuclide mass:228.9823956 u (calculated nuclear mass without electrons)Mass excess:29.58555 MeVMass defect:1.876914804 u (per nucleus)Nuclear binding energy:1748.33487844 MeV (per nucleus)
7.63465012 MeV (average binding energy per nucleon)Half-life:7(1) μsDecay constant λ:99021.025794278 s^-1Specific activity α:2.604011202744 × 10⁺²⁶ Bq g^-1
7.037868115526 × 10⁺¹⁵ Ci g^-1Spin and parity:
(nuclear angular momentum)3/2+Year of discovery:1976

Radioactive Decay

Half-life T_½ = 7(1) μs respectively 7 × 10^-6 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
Iso	²²⁹Th

Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear Isomer	Excitation Energy	Half-life	Spin
²²⁹Th		7880(120) a	5/2+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 139) and isobaric (same nucleon number A = 229) with Thorium-229m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

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

Literature and References

[1] - NN:
Entwicklung einer Thoriumkern-Uhr Th-229.
In: Internetchemie News, (2015/2019).

[2] - Benedict Seiferle, Lars von der Wense, Peter G. Thirolf:
Lifetime Measurement of the ²²⁹Th Nuclear Isomer.
In: Physical Review Letters, (2016), DOI 10.1103/PhysRevLett.118.042501.

[3] - Tomas Sikorsky, Jeschua Geist, Daniel Hengstler et al.:
Measurement of the ²²⁹Th Isomer Energy with a Magnetic Microcalorimeter.
In: Physical Review Letters, (2020), DOI 10.1103/PhysRevLett.125.142503.