Half-Lives of the First Excited States in ${\mathrm{Sn}}^{117}$, ${\mathrm{Te}}^{121}$, ${\mathrm{Te}}^{123}$, and ${\mathrm{Sb}}^{123}$

Half-lives of the first excited states of ${\mathrm{Sn}}^{117}$ [161 keV, (0.31±0.03) nsec], ${\mathrm{Te}}^{121}$ [214 keV, (0.062±0.015) nsec], ${\mathrm{Te}}^{123}$ [159 keV, (0.186±0.020) nsec], and ${\mathrm{Sb}}^{123}$ [161 keV, (0.64±0.05) nsec] were measured by the delayed coincidence method. The transitions are predominantly $M1\mathrm{}$ and are retarded by a factor of between 30 and 140 relative to the Weisskopf estimate. The $E2\mathrm{}$ speeds of these transitions are also inferred from published data and vary from 0.1 to 30 times single-particle speed.