= Unique forbidden beta decay
{title2=$\Delta J=l+1,\quad\pi_f/\pi_i=(-1)^l$}
An $l$th-forbidden <beta decay transition> with the maximal leading angular-momentum transfer $l+1$. Only the spin-dependent $S=1$ coupling can attain that transfer at this orbital order. Thus a $0^+\to2^-$ transition is first-forbidden unique, whereas a same-parity $\Delta J=2$ transition is second-forbidden nonunique. Unique refers to the leading weak multipole structure, not a claim that every correction to the decay vanishes.
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