The properties of high-spin states in ${}_{}{}^{207}{}_{}{}^{}\mathrm{At}$ have been studied with the ${}_{}{}^{204}{}_{}{}^{}\mathrm{Pb}({}_{}{}^6{}_{}{}^{}\mathrm{Li},3n){}_{}{}^{207}{}_{}{}^{}\mathrm{At}$ reaction. In-beam measurements with Ge(Li) and intrinsic Ge detectors of $\gamma -\gamma$ coincidences, $\gamma$-ray angular distributions, pulsed-beam $\gamma$ timing, and perturbed angular distributions with an applied magnetic field were made to determine a decay scheme, level energies, $\gamma$-ray multipolarities, spin-parity assignments, an isomeric lifetime, and a $g$ factor. High-spin states up to $\frac{25}{2\hslash }$ were identified as either proton excitations of the ($N=126\mathrm{}$) ${}_{}{}^{207}{}_{}{}^{}\mathrm{At}$ nucleus coupled to the ${}_{}{}^{204}{}_{}{}^{}\mathrm{Pb}$ $Z=82\mathrm{}$ ground state or neutron excitations of ${}_{}{}^{204}{}_{}{}^{}\mathrm{Pb}$ coupled to the ${\left(\pi h_{\frac{9}{2}}\right)}^3{\frac{9}{2}}^{-}$ ground state of ${}_{}{}^{211}{}_{}{}^{}\mathrm{At}$. Lifetime and $g$-factor measurements of the ${25/2}^{+}$ 2117-keV isomer, which yielded values of $\tau =156\mathrm{}\left(3\right)\mathrm{}$ nsec and $g=0.30\mathrm{}\left(1\right)\mathrm{}$, respectively, strongly support a $|{\left(\pi h_{\frac{9}{2}}\right)}^3{\frac{9}{2}}^{-},{\left(\nu f_{\frac{5}{2}}\right)}^{-1\mathrm{}}{\left(\nu i_{\frac{13}{2}}\right)}^{-1\mathrm{}}{9}^{-};{\frac{25}{2}}^{+}〉$ configuration for this level.

NUCLEAR REACTIONS ${}_{}{}^{204}{}_{}{}^{}\mathrm{Pb}({}_{}{}^6{}_{}{}^{}\mathrm{Li},3n\gamma )$, $E_{\mathrm{Li}}=34\mathrm{}$ MeV; measured $\gamma -\gamma$ coin, $\gamma -W\left(\theta \right)$, pulsed-beam $\gamma$ timing, perturbed angular distributions; deduced levels, $\gamma$ multipolarities, $J^{\pi }$, $T_{\frac{1}{2}}$, $B\left(E1\mathrm{}\right)\mathrm{}$, $g$.

• Received 20 June 1980

DOI:https://doi.org/10.1103/PhysRevC.23.272