Neutron particle-hole structure of states in ²⁰⁸Pb determined from the proton decay of the d_5/2 isobaric analog resonance in ²⁰⁹Bi

Abstract.

Proton scattering on ²⁰⁸Pb via isobaric analog resonances (IARs) in ²⁰⁹Bi generates neutron particle-hole configurations in excited states of ²⁰⁸Pb . The spin and parity of the neutron particle correspond to the spin and parity of the resonance. We performed experiments on the ²⁰⁸Pb (p, p’) reaction via all known isobaric analog resonances in ²⁰⁹Bi with the Q3D magnetic spectrograph in München. We observed more than 130 levels in the range of excitation energies E _x < 6.4 MeV. In the proton decay of the d _5/2 resonance, 29 levels have cross-sections larger than 5% of the maximum cross-section of any level. Six levels in the range 4.6 < E _x < 5.2 MeV correspond to states with known spins and major $\ensuremath \nu(d_{5/2}^{+1} p_{1/2}^{-1})$ strength. Six levels in the range 5.7 < E _x < 6.4 MeV contain most of the $\ensuremath \nu(d_{5/2}^{+1} p_{3/2}^{-1})$ strength. At least one level originates from an unresolved doublet. Among the states with a major $\ensuremath \nu(d_{5/2}^{+1} p_{3/2}^{-1})$ component, only states with spins 1^- and 3^- are firmly identified. The comparison to previous data taken with semiconductor detectors reveals details of the structure of at least 18 states in the range 4.6 < E _x < 6.4 MeV.