Decay ofTh234to thePa234isomers

The low-energy portion of the photon spectrum for the $\beta$ decay of ${}_{}{}^{234}{}_{}{}^{}\mathrm{Th}$ has been investigated with a carefully calibrated Ge(Li) detection system because of the excessive photon intensity of the $M1\mathrm{}$ 73.7-keV transition reported previously. The new photon intensity obtained for this transition relative to other strong transitions is consistent with the most recent conversion electron measurements in the two-step ${}_{}{}^{234}{}_{}{}^{}\mathrm{Pa}_{}^m{}_{}{}^{}$ isomeric transition. The upper energy limit of the unobserved $E3\mathrm{}$ isomeric transition is discussed in terms of total converion coefficients, hindrance factors, and the detection limit of the recent conversion electron measurements.