High-Spin Three-Particle States inBi207

Abstract

High-spin three-particle levels populated in the decay of a 182±6-μsec isomeric state in ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ have been studied using the pulsed external beam of the Stockholm 225-cm cyclotron. The isomeric state was produced in the ${}_{}{}^{205}{}_{}{}^{}\mathrm{T}1\mathrm{}(28-\mathrm{MeV} \alpha , 2n){}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ reaction. The intensities and energies of the 13 delayed $\gamma$ transitions observed fit consistently into a level scheme of six excited levels having energies (keV) and spins: 2101.5 ($\frac{21}{2}$), 1645.4 ($\frac{15}{2}$), 1357.9 ($\frac{15}{2}$), 1240.5 ($\frac{13}{2}$), 931.8 ($\frac{13}{2}$), and 669.5 ($\frac{11}{2^{-}}$) Shell-model calculations have been performed showing that the observed levels can be interpreted as resulting from the coupling of the two-neutron-hole states in ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ with the odd proton. From the known level structure of ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ and the investigation of the $n-p$ interaction in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Bi}$, the theoretically expected level structure of ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ has been calculated. The average energy difference between theoretically and experimentally determined levels is as low as 18 keV, and the agreement of experimental and theoretical transition probabilities is also satisfactory. The spin assignments are confirmed, and all levels except the $\frac{21}{2}$ are found to have odd parity.