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