COLLECTIVE OBLATE DIPOLE ROTATIONAL BANDS IN PB-198

The nucleus 198Pb was populated via the W-186(O-17, 5n)198Pb reaction at beam energies of 92 and 98 MeV. Five collective rotational cascades of DELTAI = 1 transitions have been found. Four are highly regular, one much more irregular. The structures are incorporated into a level scheme which extends up to approximately spin 32HBAR and an excitation energy of about 10 MeV. Angular correlation measurements confirm the dipole character of the interband transitions. Their M1 multipolarity is inferred, and from this supposition the experimental data are interpreted in terms of oblate high-K two quasiproton configurations coupled to aligned neutron excitations. This interpretation is extended to include other DELTAI = 1 oblate structures observed in 194-201Pb. It is shown that the pattern of observed moments of inertia can be understood in the simple unpaired picture involving neutron i13/2 excitations. The identical bands observed are interpreted in terms of the normal-parity weakly-coupled singlet orbital.