High-spin states and neutron-hole influence inAt209

Abstract

The properties of high-spin states in $^{209}\mathrm{At}$ have been studied with the $^{206}\mathrm{Pb}(^{6}\mathrm{Li},3n\ensuremath{\gamma})^{209}\mathrm{At}$ At reaction. In-beam measurements with Ge(Li) detectors of $\ensuremath{\gamma}$-ray excitation functions, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences, $\ensuremath{\gamma}$-ray angular distributions, and pulsed beam-$\ensuremath{\gamma}$ timing were made to establish decay schemes, level energies, spin-parity assignments, isomeric lifetimes, and magnetic moments. High-spin states involving three valence protons in the $1{h}_{\frac{9}{2}}$, $2{f}_{\frac{7}{2}}$, or $1{i}_{\frac{13}{2}}$ orbitals were identified. The electromagnetic properties observed in $^{209}\mathrm{At}$ were compared with those in the closed-neutron core nucleus $^{211}\mathrm{At}$ to examine the influence of the two neutron holes on the proton structure; microscopic calculations of this influence were carried out in perturbation theory.NUCLEAR REACTIONS $^{206}\mathrm{Pb}(^{6}\mathrm{Li}, 3n\ensuremath{\gamma})$, ${E}_{\mathrm{Li}}=29\ensuremath{-}34$ MeV; measured $\ensuremath{\gamma}$-excitations, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences, $\ensuremath{\gamma}\ensuremath{-}W(\ensuremath{\theta})$, pulsed beam-$\ensuremath{\gamma}$ timing, perturbed angular distributions; deduced level scheme, $\ensuremath{\gamma}$ multipolarities, ${J}^{\ensuremath{\pi}}$, ${T}_{\frac{1}{2}}$, $B(E2)$, $g$ factor; perturbation calculations.