Alpha recoil separation of a large number of ${}_{}{}^{221}{}_{}{}^{}\mathrm{Fr}$ sources from a pure almost massless source of ${}_{}{}^{225}{}_{}{}^{}\mathrm{Ac}$ made possible the study of the level structure of ${}_{}{}^{217}{}_{}{}^{}\mathrm{At}$ following alpha decay from ${}_{}{}^{221}{}_{}{}^{}\mathrm{Fr}$. Alphas in coincidence with all gammas and gammas and electrons in coincidence with ${}_{}{}^{221}{}_{}{}^{}\mathrm{Fr}$ alphas were used in this study. The levels in ${}_{}{}^{217}{}_{}{}^{}\mathrm{At}$ can be interpreted in terms of the π(${\mathit{h}}_{9/2}$${)}^3$ ν(${\mathit{g}}_{9/2}$${)}^{\mathrm{-}4}$, π(${\mathit{h}}_{9/2}$${)}^2$ ${\mathrm{f}}_{7/2}$ ν(${\mathit{g}}_{9/2}$${)}^{\mathrm{-}4}$, and π(${\mathit{h}}_{9/2}$${)}^2$ ${\mathit{i}}_{13/2}$ ν(${\mathit{g}}_{9/2}$${)}^{\mathrm{-}4}$ shell-model configurations. Considerable similarity in the configurations and energies of the states of ${}_{}{}^{217}{}_{}{}^{}\mathrm{At}$ and ${}_{}{}^{215}{}_{}{}^{}\mathrm{At}$ is observed. The only change is in the neutron part of the configurations where the ‘‘particle’’ partial configuration in ${}_{}{}^{215}{}_{}{}^{}\mathrm{At}$ (...ν(${\mathit{g}}_{9/2}$${)}^4$) is replaced by the ‘‘hole’’ partial configuration in ${}_{}{}^{217}{}_{}{}^{}\mathrm{At}$ (...ν(${\mathit{g}}_{9/2}$${)}^{\mathrm{-}4}$). No evidence for parity doublets is found in ${}_{}{}^{217}{}_{}{}^{}\mathrm{At}$.

• Received 25 October 1994

DOI:https://doi.org/10.1103/PhysRevC.51.1192