Why is the half-life of 178m2 Hafnium isotope 31 years? Maybe it is somehow related to its nuclear spin (16+)?

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    $\begingroup$ I'm voting to close this question as off-topic because this shows absolutely no research effort. $\endgroup$ Sep 14 '16 at 11:22
  • $\begingroup$ Given the answer below gives a reference to a Lawrence Livermore National Lab report, I don't think you will find that level of information on Wikipedia. And, searching is polluted with the 'Hafnium controversy' which is policy, not physics (mainly). $\endgroup$
    – Jon Custer
    Sep 14 '16 at 16:14
  • $\begingroup$ @heather Fortunately M. J. Steil could answer it without any major problems. $\endgroup$
    – peterh
    Sep 14 '16 at 18:33
  • $\begingroup$ Isomer not Isotope. An isomer is an isotope whose nucleus is excited to a higher quantum energy state than its ground state. An isotope can have more than 1 metastable isomers. The isomer tends to stay in the metastable excited quantum state if there are multiple lower quantum steps to fall through. This is the case with said isomer. A few nucleons will always tunnel all the way down, but this is statistically low, thus the long half-life. $\endgroup$ Jan 14 '18 at 0:11

I know next to nothing about nuclear isomers but I found this paper: Theoretical Assessment of 178m2Hf De-Excitation. It's third section describes the physics of hafnium isomers and on page 13 the authors write:

The decay of the $16^+$ state is highly suppressed (with a 31 yr half-life) not only because a change of $K$ by at least 8 units is required, but also because the transition has to have a high multipolarity $λ$, due to large angular-momentum differences between the initial ($J= 16^+$) and energetically feasible final states.

To understand this in detail I would recommend reading the entire third section.


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