Discussion
An excited nucleus decayed from an energy level having spin and parity of 3+ to another energy level having spin and parity of O+ by emitting a beta particle. The above beta-decay has the prominent decay mode of :
Answer: B
The decay is a second forbidden Gamow-Teller transition.
The spin changes by ΔJ = 3 (from 3 to 0, the paper's O+ being 0+), and the parity does not change (+ to +). The classification is:
- Allowed: ΔJ = 0, ±1, no parity change (Fermi for ΔJ = 0 with no spin flip, Gamow-Teller for ΔJ = 0, ±1).
- First forbidden: parity changes, ΔJ up to 2.
- Second forbidden: no parity change, ΔJ = 2 or 3.
ΔJ = 3 with no parity change needs two units of orbital angular momentum plus the electron and neutrino spins aligned, which is a second forbidden (unique) Gamow-Teller decay. An allowed Fermi or Gamow-Teller decay cannot change J by 3, and a first forbidden decay requires a parity change.
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