Thorium-229.html



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-213.¹

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.² 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.³ The half life of this excited state is not known, though it is estimated at 5 hours.

References

1. ^ Report to Congress on the extraction of medical isotopes from U-233. U.S. Department of Energy. March 2001
2. ^ B. R. Beck et al. (2007-04-06). "Energy splitting in the ground state doublet in the nucleus ²²⁹Th"". Physical Review Letters 98: 142501. doi:10.1103/PhysRevLett.98.142501, http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000098000014142501000001. 
3. ^ E. Peik and C. Tamm (2003-01-15). "Nuclear laser spesctroscopy of the 3.5 eV transition in ²²⁹Th". Europhysics Letters 61: 181–186. doi:10.1209/epl/i2003-00210-x, http://www.iop.org/EJ/abstract/0295-5075/61/2/181. 

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