Lifetimes of Energy Levels in ${\mathrm{Al}}^{28}$, ${\mathrm{Mn}}^{56}$, ${\mathrm{Cu}}^{64}$, ${\mathrm{Rh}}^{104}$, and ${\mathrm{I}}^{128}$ Excited by Slow Neutron Capture

Measurements of delayed coincidences between $\gamma$ rays were used to determine the half-lives of states excited by slow-neutron capture in various nuclei. The half-lives found were: ${\mathrm{Mn}}^{56}$, first excited level ${11.4}_{-3\mathrm{}}^{+2\mathrm{}}$ nsec, second excited level 5.1±0.5 nsec; ${\mathrm{Rh}}^{104}$, first excited level 2.6±0.2 nsec, 96-kev transition ≤0.6 nsec; ${\mathrm{Cu}}^{64}$, first excited level ≤0.3 nsec, second excited level ≤0.3 nsec; ${\mathrm{Al}}^{28}$, first excited level 2.3±0.2 nsec; ${\mathrm{I}}^{128}$, 30-kev level 8.8±1.0 nsec, 137-kev level 8.0±0.6 nsec, 90-kev transition ≤0.7 nsec. Measurements of pulse-height spectra satisfying the condition of prompt and delayed coincidence and measurements at neutron resonances of iodine were used to establish the presence of excited states at 30 and 137 kev in ${\mathrm{I}}^{128}$. A previously unreported neutron resonance was observed in ${\mathrm{I}}^{127}$ at a neutron energy of 10.7 ev.