Dipole bands and multi-quasiparticle excitations in193Pb

The nucleus¹⁹³Pb was populated via the¹⁶⁸Er(³⁰Si,5n) reaction at a beam energy of 159 MeV and studied with the EUROGAM II spectrometer. Five new dipoleΔI=1 cascades have been found. These structures have been connected to the level scheme which has been considerably extended up to a spin of 61/2? and an excitation energy of about 8 MeV. Angular distribution coefficients,α ₂, have been measured and confirm the dipole character of the in-band transitions. B(M1)/B(E2) ratios have been extracted for the two most intense cascades. The¹⁹³Pb dipole bands are discussed in comparison with those known in odd lead isotopic series and the structure of the band heads is analyzed in terms of microscopic HF-BCS calculations. The proposed configurations are based on a high-K two quasiproton excitation,π(505]9/2^??606]13/2⁺) _K =11^?, coupled to one or three rotation aligned quasineutrons involving thei _13/2,p _3/2,f _5/2 and/orh _9/2 subshells. The main difference, compared with the heavier lead isotopes, is the presence of largeΩ orbitals from theν (i _13/2) shell near the Fermi surface which are responsible for the increasing band-head spin as A decreases.