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, o ne much more irregular. The structures are incorporated into a level s cheme which extends up to approximately spin 32HBAR and an excitation energy of about 10 MeV. Angular correlation measurements confirm the d ipole character of the interband transitions. Their M1 multipolarity i s inferred, and from this supposition the experimental data are interp reted in terms of oblate high-K two quasiproton configurations coupled to aligned neutron excitations. This interpretation is extended to in clude other DELTAI = 1 oblate structures observed in 194-201Pb. It is shown that the pattern of observed moments of inertia can be understoo d in the simple unpaired picture involving neutron i13/2 excitations. The identical bands observed are interpreted in terms of the normal-pa rity weakly-coupled singlet orbital.