Thorium-229

Thorium-229 is a radioactive isotope of Thorium that decays by alpha emission with a half life of 7340 years.²²⁹Th is produced by the decay of uranium-233, and its principal use is for the production of the medical isotopes actinium-225 and bismuth-213. [ [http://www.ne.doe.gov/pdfFiles/U233RptConMarch2001.pdf Report to Congress on the extraction of medical isotopes from U-233] . U.S. Department of Energy. March 2001]

Gamma ray spectroscopy has indicated that ²²⁹Th has a nuclear isomer with a remarkably low excitation energy. Recent measurements of higher-energy gamma rays give 7.6 eV as the energy of the 3/2+ state, with an uncertainty of 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 ] This would make it the lowest-energy nuclear isomer known, and it might be possible to excite this nuclear state using lasers with wavelengths in the vacuum ultraviolet. [cite journal|author=E. Peik and C. Tamm|journal=Europhysics Letters|volume=61|title=Nuclear laser spesctroscopy of the 3.5 eV transition in ²²⁹Th| pages=181–186|date=2003-01-15| url=http://www.iop.org/EJ/abstract/0295-5075/61/2/181|doi=10.1209/epl/i2003-00210-x] The half life of this excited state is not known, though it is estimated at 5 hours.

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