Different stable nuclear spins for the same isotope

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Discussion Overview

The discussion centers around the concept of nuclear spins in isotopes, specifically questioning whether stable isotopes can have multiple stable nuclear spin types. Participants explore the existence of nuclear isomers and the conditions under which they may be stable or unstable.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why isotopes typically have only one nuclear spin and whether it is possible for an isotope to have two stable nuclear spin types, one fissile and the other not.
  • Another participant asserts that nuclear isomers do exist, but they are usually unstable, with only a few being observably stable.
  • It is noted that stable nuclear isomers are uncommon, and one participant expresses surprise at this, suggesting that rapid isomeric transitions may contribute to their rarity.
  • A participant explains that nuclear isomers are always excited states and that one state must have lower energy than others to allow for gamma decay.
  • Another participant emphasizes that all isomers, except for the ground state, are unstable due to differences in binding energy, allowing more energetic isomers to transition to less energetic states.
  • A question is raised regarding the ground state of 180Ta and its half-life in comparison to the metastable isomer 180m1Ta.
  • A response clarifies that the ground state has a significantly longer lifetime, making its decay rare due to a large spin difference between the isomer and ground state.

Areas of Agreement / Disagreement

Participants generally agree that nuclear isomers exist but disagree on the prevalence of stable nuclear isomers and the implications of their stability. The discussion remains unresolved regarding the conditions that lead to the stability of nuclear isomers.

Contextual Notes

Participants mention the rapidity of isomeric transitions and the relationship between energy states, but these points are not fully resolved or quantified. The discussion also touches on the definitions of stability and the observational limits of isotopes.

Garlic
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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?
 
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They exist, they are called "nuclear isomers".
 
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nikkkom said:
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?
 
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.
 
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Garlic said:
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.
 
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?
 
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.
 
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I understand, thank you.
 

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