Isotopes of thorium

Isotopes of thorium (90Th)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
227Th trace 18.693 d α 223Ra
228Th trace 1.9125 y α 224Ra
229Th trace 7916 y α 225Ra
230Th 0.02% 75400 y α 226Ra
231Th trace 25.52 h β− 231Pa
232Th 100.0% 1.40×1010 y α 228Ra
233Th trace 21.83 min β− 233Pa
234Th trace 24.11 d β− 234Pa
Standard atomic weight Ar°(Th)

Thorium (90Th) has seven naturally occurring isotopes but none are stable. One isotope, 232Th, is relatively stable, with a half-life of 1.40×1010 years, considerably longer than the age of the Earth, and even slightly longer than the generally accepted age of the universe. This isotope makes up nearly all natural thorium, so thorium was considered to be mononuclidic. However, in 2013, IUPAC reclassified thorium as binuclidic, due to large amounts of 230Th in deep seawater. Thorium has a characteristic terrestrial isotopic composition and thus a standard atomic weight can be given.

Thirty-one radioisotopes have been characterized, with the most stable being 232Th, 230Th with a half-life of 75,400 years, 229Th with a half-life of 7,916 years, and 228Th with a half-life of 1.91 years. All of the remaining radioactive isotopes have half-lives that are less than thirty days and the majority of these have half-lives that are less than ten minutes. One isotope, 229Th, has a nuclear isomer (or metastable state) with a remarkably low excitation energy,[4] recently measured to be 8.355733554021(8) eV[5][6] It has been proposed to perform laser spectroscopy of the 229Th nucleus and use the low-energy transition for the development of a nuclear clock of extremely high accuracy.[7][8][9]

The known isotopes of thorium range in mass number from 207[10] to 238.

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  2. ^ "Standard Atomic Weights: Thorium". CIAAW. 2013.
  3. ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  4. ^ E. Ruchowska (2006). "Nuclear structure of 229Th" (PDF). Physical Review C. 73 (4): 044326. Bibcode:2006PhRvC..73d4326R. doi:10.1103/PhysRevC.73.044326. hdl:10261/12130.
  5. ^ Cite error: The named reference Tiedau2024 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Zhang2024 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference PR-Tiedau2024 was invoked but never defined (see the help page).
  8. ^ Peik, E.; Tamm, Chr. (2003-01-15). "Nuclear laser spectroscopy of the 3.5 eV transition in 229Th" (PDF). Europhysics Letters. 61 (2): 181–186. Bibcode:2003EL.....61..181P. doi:10.1209/epl/i2003-00210-x. S2CID 250818523. Archived (PDF) from the original on 2024-04-14. Retrieved 2024-04-30.
  9. ^ Campbell, C.J.; Radnaev, A.G.; Kuzmich, A.; Dzuba, V.A.; Flambaum, V.V.; Derevianko, A. (2012). "A single ion nuclear clock for metrology at the 19th decimal place" (PDF). Physical Review Letters. 108 (12) 120802: 120802. arXiv:1110.2490. Bibcode:2012PhRvL.108l0802C. doi:10.1103/PhysRevLett.108.120802. PMID 22540568. S2CID 40863227. Retrieved 2024-04-30.
  10. ^ Cite error: The named reference Yang207 was invoked but never defined (see the help page).
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