The 24-sec isomeric state ${\mathrm{Nb}}^{90m}$ is found to decay more slowly in superconducting metal than in the normal metal. Superconductivity was quenched with a magnetic field, and all measurements were taken at 4.2°K. The result was ${\lambda }_{\mathrm{superconductive}}-{\lambda }_{\mathrm{normal}}=(-19.5\mathrm{}\pm 5.5)\times {10}^{-4\mathrm{}}{\lambda }_{\mathrm{normal}}$. Sources of error and the statistical consistency of the data are discussed.

• Received 28 October 1968

DOI:https://doi.org/10.1103/PhysRev.179.450