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This is going to seem like a rather daft question, but what is the definitive half-live for protactinium-234 (234Pa)? I'm seeing lots of different answers in various academic papers etc.

For instance, in Bonotto & Andrews (2000) the half-life of protactinium-234 (234Pa) is given as 1.18 minutes, but in Edwards et al. (2003) they report the 234Pa half-life as 6.67 hours. So which one is it?

Bonotto, D.M. & Andrews, J.N. The transfer of uranium isotopes 234U and 238U to the waters interacting with carbonates from Mendip Hills area (England). Applied Radiation and Isotopes. 52, 965-983. 2000. DOI: http://dx.doi.org/10.1016/S0969-8043(99)00151-7

Edwards, R.L., Gallup, C.D. & C Uranium-series Dating of Marine and Lacustrine Carbonates. Reviews in Mineralogy & Geochemistry. 52, 363-406 . 2003. URL: http://www.minsocam.org/msa/rim/Rim52.html

tschoppi
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cjms85
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1 Answers1

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So which one is it?

Both! Proactinium-234 exhibits nuclear isomerism. The metastable form $\ce{^{234m}Pa}$ has a half-life time in the range of 1 min, whereas $\ce{^{234}Pa}$ shows a half-life time around 6 hrs.

Ben Norris
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Klaus-Dieter Warzecha
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    In fact, if you check out the Wikipedia article on nuclear isomers, the $\ce{^{234}Pa}/ \ce{^{234m}Pa}$ pair is the oldest known example of nuclear isomerism. – Ben Norris Feb 17 '14 at 13:22
  • Okay. So the half-life length depends on the state of the nuclear spin. With 234Pa having a 4+ state and 234mPa having a 0- state. So out of the two, which half-life is more common? Is it similar to branched decay, in that one pathway, in this case half-life rather than decay mode, is more common than the other? – cjms85 Feb 17 '14 at 13:49