The properties of high-spin states in ${}_{}{}^{205}{}_{}{}^{}\mathrm{At}$ have been studied with the ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ (${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, $4n$) ${}_{}{}^{205}{}_{}{}^{}\mathrm{At}$ reaction. In-beam measurements [with Ge(Li) detectors] of $\gamma -\gamma$ coincidences, $\gamma$-ray angular distributions, and pulsed-beam $\gamma$ timing were made to determine the decay scheme, level energies, $\gamma$-ray multipolarities, spin-parity assignments, and isomeric lifetimes. High-spin states up to $\frac{29}{2}\hslash$ were identified as either proton excitations of the ($N=126\mathrm{}$) ${}_{}{}^{211}{}_{}{}^{}\mathrm{At}$ nucleus coupled to the ${}_{}{}^{202}{}_{}{}^{}\mathrm{Pb}$ ($Z=82\mathrm{}$) ground state or neutron excitations of ${}_{}{}^{202}{}_{}{}^{}\mathrm{Pb}$ coupled to the ${\left(\pi h_{\frac{9}{2}}\right)}^3{\frac{9}{2}}^{-}$ ground state of ${}_{}{}^{211}{}_{}{}^{}\mathrm{At}$. The lifetime measurements of the ${\frac{25}{2}}^{+}$ 2062-keV state and the unobserved isomeric state (${\frac{29}{2}}^{+}$) above 2339 keV yielded mean lifetimes of 92(3) nsec and ∼3 μsec, respectively.

NUCLEAR REACTIONS ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ (${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, $4n\gamma$)${}_{}{}^{205}{}_{}{}^{}\mathrm{At}$, $E_{{}_{}{}^{12}{}_{}{}^{}\mathrm{C}}=77\mathrm{}$ MeV, measured $\gamma -\gamma$ coincidence, $\gamma -W\left(\theta \right)$, pulsed-beam $\gamma$ timing; deduced levels, $\gamma$ multipolarities, $J^{\pi }$, $T_{\frac{1}{2}}$, $B\left(E1\right)$.

• Received 9 July 1981

DOI:https://doi.org/10.1103/PhysRevC.25.889