Isotopes of actinium

Actinium (Ac) has no stable isotopes. A standard atomic mass cannot be given.

An isotope of actinium occurring within the radioactive disintegration chain of thorium was known as:
* "mesothorium II" : ²²⁸Ac

Naturally occurring actinium is composed of one radioactive isotope; ²²⁷Ac. 36 radioisotopes have been characterized with the most stable being ²²⁷Ac with a half-life of 21.772 y, ²²⁵Ac with a half-life of 10.0 days, and ²²⁶Ac with a half-life of 29.37 h.

All of the remaining radioactive isotopes have half-lifes that are less than 10 hours and the majority of these have half lifes that are less than one minute. The shortest-lived isotope of actinium is ²¹⁷Ac which decays through alpha decay and electron capture. It has a half-life of 69 ns. Actinium also has two meta states.

Purified ²²⁷Ac comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.773-year half-life. 98.62% of ²²⁷Acdecays to thorium (²²⁷Th) through beta decay and 1.38% of ²²⁷Ac decays to francium (²²³Fr) through alpha decayCitation |contribution = Chemical Elements |year = 2005| title = Van Nostrand's Encyclopedia of Chemistry| editor-last = Considine| editor-first = Glenn D.| pages = 332| place= New York| publisher = Wylie-Interscience| id = 0-471-61525-0 ] .

The isotopes of actinium range in atomic weight from 206 u (²⁰⁶Ac) to 236 u (²³⁶Ac).

The shortest lived isotope of Actinium is ²¹⁷Ac.

Table

Notes

* 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.

ee also

*Actinium series

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.