The experimental level structure of ${}_{}{}^{223}{}_{}{}^{}\mathrm{Fr}$ has been studied using the 1.4% alpha decay of 21.8 yr ${}_{}{}^{227}{}_{}{}^{}\mathrm{Ac}$ and subsequent gamma rays to extend the level scheme recently observed following the ${\mathrm{\beta }}^{\mathrm{-}}$ decay of ${}_{}{}^{223}{}_{}{}^{}\mathrm{Rn}$. The level structure of ${}_{}{}^{223}{}_{}{}^{}\mathrm{Fr}$ was also studied theoretically by using the quasiparticle model of Soloviev with octupole degrees of freedom. Both experimentally and theoretically there is strong evidence that ${}_{}{}^{223}{}_{}{}^{}\mathrm{Fr}$ is reflection asymmetric. The theoretical study of microscopic structure of several of the positive-parity bands also indicates the presence of important Nilsson configurations arising from the shell below. The comparison of the level structures of ${}_{}{}^{223}{}_{}{}^{}\mathrm{Fr}$, ${}_{}{}^{221}{}_{}{}^{}\mathrm{Fr}$, and ${}_{}{}^{219}{}_{}{}^{}\mathrm{Fr}$ tends to elaborate the mechanism by which the octupole-modified Nilsson orbitals collapse into the more degenerate shell model states as the mass number decreases.

• Received 27 October 1994

DOI:https://doi.org/10.1103/PhysRevC.51.1708