Alec Neeson said: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 decay is a type of radioactive decay process in which a nucleus emits an electron and an antineutrino to become a nucleus with one less proton. This process was first described by Enrico Fermi in 1934.
In Fermi decay, ∆S=0 means that the spin of the nucleus and the spin of the emitted particle are in the same direction. ∆J=0 means that there is no change in the total angular momentum of the nucleus before and after the decay.
The conservation of spin and angular momentum is important in Fermi decay because it helps determine the possible energy states and emission probabilities of the decay process.
An example of Fermi decay with ∆S=0 and ∆J=0 is the beta decay of a neutron into a proton, electron, and antineutrino.
Yes, other types of decay that follow the ∆S=0 and ∆J=0 rule include beta plus decay (positron emission) and electron capture, both of which involve the emission of a particle and an antineutrino with no change in spin or angular momentum.