Measurement of $\gamma$-ray distributions from the reaction ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}(\alpha ,n\gamma ){}_{}{}^{26}{}_{}{}^{}\mathrm{Al}$ confirms spin $J=5\mathrm{}$ for the 3404-keV level and gives an unambiguous spin assignment of $J=6\mathrm{}$ for the 3508-keV level. Measurement of lifetimes and mixing ratios show that both states have positive parity. The excitation energy and the enhanced $E2\mathrm{}$ strength of > 11 Weisskopf units for the $6^{+}$ to $5^{+}$ ground-state transition identify the level at 3508 keV as the $6^{+}$ member of a $K=5^{+}$ rotational band based on the ground state.

• Received 12 October 1971

DOI:https://doi.org/10.1103/PhysRevLett.27.1463