For which decay class is only Fermi decay mode possible?

[Alec Neeson]

I think that this is a relatively easy question (no equations) however I cannot seem to find anything on it. "For which specific class of decay is only the Fermi decay mode possible?" I know Fermi decay is ∆S=0 and therefore ∆J=0 type of decay

 

[eys_physics]

I think that this is a relatively easy question (no equations) however I cannot seem to find anything on it. "For which specific class of decay is only the Fermi decay mode possible?" I know Fermi decay is ∆S=0 and therefore ∆J=0 type of decay

Fermi beta decay is the only possible mode for transitions where both the initial and final state, has angular momentum zero and the same parities. I'm here referring to the limit of vanishing momentum transfer. For finite momentum transfer there are others, but for beta decay their contribution are negligible.

 

[leader]

Isospin conservation is essential in all particle reactions. This is the origin for the discovery of neutrinos and anti-neutrinos in beta decays/