Isotopes of thorium

Although thorium (Th) has multiple isotopes, none of these isotopes are stable; however, one isotope is "relatively" stable (²³²Th). As such, thorium is considered to be mononuclidic. It has a characteristic terrestrial isotopic composition and thus an atomic mass can be given.:Standard atomic mass: 232.03806(2) u

Isotopes of thorium occurring within the radioactive disintegration chains of actinium, thorium, and uranium were known as
* "radio-actinium": ²²⁷Th
* "radio-thorium": ²²⁸Th
* "ionium": ²³⁰Th
* "uranium Y": ²³¹Th
* "uranium X₁": ²³⁴Th

Twenty-seven radioisotopes have been characterized, with the most abundant and/or stable being ²³²Th with a half-life of 14.05 billion years, ²³⁰Th with a half-life of 75,380 years, ²²⁹Th with a half-life of 7340 years, and ²²⁸Th with a half-life of 1.92 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,cite journal|author=E. Ruchowska et al. |title=Nuclear structure of ²²⁹Th" |journal=Phys. Rev. C|volume= 73|pages=044326|date=2006| url=http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRVCAN000073000004044326000001 |doi=10.1103/PhysRevC.73.044326 ] recently measured to be 7.6 0.5 eV. cite journal|author=B. R. Beck et al. |title=Energy splitting in the ground state doublet in the nucleus ²²⁹Th" |journal=Physical Review Letters|volume= 98|pages=142501|date=2007-04-06| url=http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000098000014142501000001 |doi=10.1103/PhysRevLett.98.142501 ]

The known isotopes of thorium range in atomic weight from 209 u (²⁰⁹Th)cite journal|author=H. Ikezoe et al. |title=alpha decay of a new isotope of ²⁰⁹Th" |journal=Phys. Rev. C|volume= 54|pages=2043|date=1996| url=http://prola.aps.org/pdf/PRC/v54/i4/p2043_1 |format=subscription required |doi=10.1103/PhysRevC.54.2043 ] to 238 u (²³⁸Th).

Table

Notes

* Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
* Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
* Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

References

* Isotope masses from [http://www.nndc.bnl.gov/amdc/index.html Ame2003 Atomic Mass Evaluation] by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in "Nuclear Physics" A729 (2003).
* Isotopic compositions and standard atomic masses from [http://www.iupac.org/publications/pac/2003/7506/7506x0683.html Atomic weights of the elements. Review 2000 (IUPAC Technical Report)] . "Pure Appl. Chem." Vol. 75, No. 6, pp. 683-800, (2003) and [http://www.iupac.org/news/archives/2005/atomic-weights_revised05.html Atomic Weights Revised (2005)] .
* Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
** Audi, Bersillon, Blachot, Wapstra. [http://amdc.in2p3.fr/web/nubase_en.html The Nubase2003 evaluation of nuclear and decay properties] , Nuc. Phys. A 729, pp. 3-128 (2003).
** National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the [http://www.nndc.bnl.gov/nudat2/ NuDat 2.1 database] (retrieved Sept. 2005).
** David R. Lide (ed.), Norman E. Holden in "CRC Handbook of Chemistry and Physics, 85th Edition", online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.