Protactinium-234 half-life

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>





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> So which one is it?
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Both! Proactinium-234 exhibits **[nuclear isomerism](http://en.wikipedia.org/wiki/Nuclear_isomer)**. 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.


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