Different stable nuclear spins for the same isotope

[Garlic]

Hello everyone,
When I look at the isotope lists, I always see only one nuclear spin for a specific isotope. (Why) can't an isotope have different nuclear spin types that are stable? I know metastable isotopes exist, but I am asking about the stable isotopes. Can't there be a case where the isotope has two stable nuclear spin types, and one is fissile but the other one is not?

 

[nikkkom]

They exist, they are called "nuclear isomers".

 

[Garlic]

They exist, they are called "nuclear isomers".

But nuclear isomers are usually unstable, there are only a few of them which are observionally stable. It is really interesting that stable nuclear isomers aren't very common, I expected lots of isotopes to have multiple stable nuclear isomers, similar to lots of elements having multiple stable isotopes.
Is it because isomeric transitions happen very rapidly if the decay is allowed, like how rapid electromagnetic decay occurs in hadron resonances?

 

[mfb]

One of the states has to have lower energies than the others, which makes a gamma decay possible.
Nuclear isomers are always excited states. The same particles are there, just in a different arrangement. This is different from nuclear isotopes.

 

[nikkkom]

But nuclear isomers are usually unstable, there are only a few of them which are observionally stable. It is really interesting that stable nuclear isomers aren't very common

It's to be expected: nuclear isomers have different binding energy. Therefore, a more energetic one is allowed to tunnel into a less energetic state. IOW: all isomers (except for one which is ground state) are unstable.

 

[Garlic]

Why is ¹⁸⁰Ta the ground state although it has a half life about 8.1 hours, where the observationally stable ^180m1Ta is a metastable nuclear isomer?

 

[mfb]

Its lifetime is just orders of magnitude larger, it is unstable but with a lifetime above the current experimental limits. The large spin difference between isomer and ground state (and other possible final states) makes the decay so rare.

 

[Garlic]

I understand, thank you.