An ultralow-energy $K$-capture branch in the decay of ${}_{}{}^{158}{}_{}{}^{}\mathrm{Tb}$ has recently been suggested as a favorable transition for determination of the electron neutrino mass. The present work describes new measurements of several reaction $Q$-value differences which imply that the ${}_{}{}^{158}{}_{}{}^{}\mathrm{Tb}$ decay energy is not large enough for the reported $K$ capture to take place.

• Received 30 January 1984

DOI:https://doi.org/10.1103/PhysRevC.29.2339