Gamma-Ray Widths inC13,Li6, andP31

The width of the 3.68-MeV level of ${\mathrm{C}}^{13}$ has been measured and found to be $\Gamma =0.44\mathrm{}\pm 0.04$ eV. After correction for the $E^3$ dependence, this is 0.59 times as strong as the mirror transition in ${\mathrm{N}}^{13}$, in agreement with Morpurgo's prediction of approximate equality for $M1\mathrm{}$, $\Delta T=0\mathrm{}$ transitions in mirror nuclei. The ${\mathrm{C}}^{13}$ width was obtained from a comparison of the resonant scattering of bremsstrahlung by ${\mathrm{C}}^{13}$ with that by the 3.51-MeV level of ${\mathrm{P}}^{31}$ and the 3.56-MeV level of ${\mathrm{Li}}^6$. The widths of the ${\mathrm{P}}^{31}$ and ${\mathrm{Li}}^6$ levels were measured in self-absorption experiments, and found to be 52±8 meV and 8.1±0.5 eV, respectively. A limit on the energetically allowed but spin- and parity-forbidden decay of the ${\mathrm{Li}}^6$ level to $\alpha +d$ was established as ${\Gamma }_{\alpha d}<1.3\mathrm{}$ eV.