The rate of decay of a nuclear isomer has been demonstrated to be influenced by its electronic environment. This effect has been utilized to detect environmental changes of ${\mathrm{Tc}}^{99m}$ in its metallic lattice at low temperatures. The effect of low temperature on the decay constant of ${\mathrm{Tc}}^{99m}$ in technetium metal was measured. Measurements were made at 77°K and 4.2°K. Since the metal is superconducting at 4.2°K, a measurement was made at 4.2°K in a magnetic field sufficient to destroy superconductivity. Results of the experiments indicate a negligible change in the decay constant for the metal at 77°K, whereas a noticeable change in the decay constant was observed for the superconducting metal at 4.2°K: $\lambda \left(4.2\mathrm{}°\mathrm{K} \mathrm{superconducting}\right)-\lambda \left(293\mathrm{}°\mathrm{K}\right)=(6.4\mathrm{}\pm 0.4)\times {10}^{-4\mathrm{}}\lambda \left(293\mathrm{}°\mathrm{K}\right).\mathrm{}$ Measurements on the low-temperature normal-state metal indicate a gross removal of this influence: $\lambda \left(4.2\mathrm{}°\mathrm{K} \mathrm{normal}\right)-\lambda \left(293\mathrm{}°\mathrm{K}\right)=(1.3\mathrm{}\pm 0.4)\times {10}^{-4\mathrm{}}\lambda \left(293\mathrm{}°\mathrm{K}\right).\mathrm{}$

• Received 2 June 1958

DOI:https://doi.org/10.1103/PhysRev.112.77