NIST: Physical Measurement Laboratory:Physical Reference Data

Radionuclide Half Life Measurements Made at NIST
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  Radionuclide     Number of  
Sources
Number of
  Half Lives  
Followed
  Half Life*   Statistical
Standard
  Uncertainty  
Other
Standard
  Uncertainty  
  Reference¤  

152Eu41.6 - 1.8  4947.2 1.1 d  0.70.8§,6
154Eu32.4  3145.2 1.1 d  1.10.0§,6
155Eu23.1 - 4.3  1739.06 0.45 d  0.450.0§,6


*The stated uncertainties are the sum, in quadrature, of the statistical uncertainty (the "external standard deviation" in the weighted mean) and other uncertainties which include those from the Stevenson equation (NBS Special Publication 626) and from the correction for the 210Bi ingrowth in the radium reference sources.

¤The reference for every radionuclide is § unless otherwise noted.