First observation of collective dipole rotational bands in the neutron-deficient bismuth nuclei

The nucleus 202Bi was populated via the 196Pt(11B,5n)202Bi reaction at a beam energy of 75 MeV. Three regular sequences of magnetic dipole transitions have been found. A comparison is made with the known Delta I=1 rotational bands seen in the neighbouring Pb nuclei. An interpretation in terms of collective oblate configurations involving high-K proton and alignable neutron orbitals is suggested

First observation of a collective dipole rotational band in the A∼200 mass region

The nucleus 198Pb was populated via the 186W(17O,5n)198Pb reaction at beam energies of 92 and 98 MeV. A highly regular rotational ΔI=1 band has been found. Angular correlation measurements confirm the transitions to be dipoles. Assuming M1 multipolarity for these transitions the experimental data are interpreted in terms of a configuration of oblate shape. This is the first such collective oblate structure identified in the A∼200 mass region

Collective dipole rotational bands in197Pb

The nucleus197Pb was populated via the186W(17O,6n)197Pb reaction at beam energies of 98 and 110 MeV. Two regular ΔI=1 bands of magnetic dipole transitions have been found. Possible interpretations in terms of collective oblate configurations involving high-K proton orbitals coupled to three i13/2neutrons are discussed. The similarities between several of the bands discovered in197–200pbnuclei are emphasized

Collective oblate dipole rotational bands in 198^{198}pb

The nucleus 198Pb was populated via the 186W(17O, 5n)198Pb reaction at beam energies of 92 and 98 MeV. Five collective rotational cascades of ΔI = 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 32ħ 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 ΔI= 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 excitations. The identical bands observed are interpreted in terms of the normal-parity weakly-coupled singlet orbital

Coexistence of collective oblate and superdeformed prolate shapes in 196Pb

The 196Pb nucleus was populated via the 184W(16O,4n)196Pb and 186W(16O,6n)196Pb reactions at beam energies of 98 MeV and 120 MeV, respectively. A new Delta I=1 magnetic dipole band has been observed. This band is believed to be built on a collective oblate configuration involving high-K proton orbitals coupled to two rotationally aligned i13/2 neutrons. The previously observed 196Pb superdeformed band was also populated in these reactions