Analogue beta-decay branching estimate ($B_X=({\tau }_P/{\tau }_R)(f_X/f_R)(S_X/S_R)$)

Compare an unknown allowed branch of parent $P$ with a reference allowed decay of mean lifetime ${\tau }_R$ and unit branching fraction. Its branching fraction is the parent mean lifetime ${\tau }_P$ times the inferred partial rate. The phase-space ratio $f_X/f_R$ and the total vector-plus-axial strengths $S_X/S_R$ enter separately. Approximating both strengths by their Fermi transition contributions and both phase-space integrals by $Q^5$ gives a useful scale, but does not establish a unique branch fraction if the axial strengths are unknown.