Dipole bands and multi-quasiparticle excitations in 193Pb

The nucleus 193Pb was populated via the 168Er(30Si,5n) reaction at a beam energy of 159 MeV and studied with the EUROGAM II spectrometer. Five new dipole Δ I = 1 cascades have been found. These structures have been connected to the level scheme which has been considerably extended up to a spin of ħ and an excitation energy of about 8 MeV. Angular distribution coefficients, a2, 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. The 193Pb 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]9/2t? ⊗ [606]13/2+)K=11t -, coupled to one or three rotation aligned quasineutrons involving the i13/2, p 3/2, f5/2 and/or h{9/2} subshells. The main difference, compared with the heavier lead isotopes, is the presence of large Ω orbitals from the ν (i13/2) shell near the Fermi surface which are responsible for the increasing band-head spin as A decreases.