Superdeformed multi-quasiparticle high-$K$ states and possible isomers in Pb and Po isotopes

Configuration-constrained potential-energy-surface calculations have been performed to investigate multi-quasiparticle high-$K$ states built on superdeformed minima in ${}^{192,194,196}$Pb and ${}^{198}$Po. The calculations predict that ${}^{196}$Pb and ${}^{198}$Po would be favorable candidates for the observation of low-lying superdeformed two- and four-quasiparticle high-$K$ states. The possible decay paths and lifetimes that could lead to isomers are evaluated in detail for ${}^{196}$Pb. Comparisons between the predictions and previous observations of octupole-vibrational excitations indicate also that bands built on superdeformed high-$K$ intrinsic states may compete with the octupole-vibrational mode in this mass region. The quadrupole moments of both the collective and intrinsic excitations are analyzed.

Figure 1

Neutron (a) and proton (b) single-particle levels plotted against ${\beta }_2$ deformation (${\beta }_4=0.06$, $\gamma =0^{\circ }$).

Figure 2

Excitation energies relative to the calculated yrast SD band. Experimental data are in black. A variety of multi-qp states are shown for ${}^{192}$Pb [(a)], ${}^{194}$Pb [(b)], ${}^{196}$Pb [(c)], and ${}^{198}$Po [(d)].

Figure 3

Calculated kinematic moment of inertia for the $K^{\pi }={14}_2^{+}$ (see Table ) high-$K$ SD band in ${}^{196}$Pb. The high-$K$ results are in red, and the yrast SD results in black.

Figure 4

Calculated high-$K$ rotational bands relative to the $K=0$ SD band as a function of angular momentum for ${}^{196}$Pb.

Figure 5

Notional decay scheme of calculated high-$K$ SD bands in ${}^{196}$Pb, showing the main decay paths expected between bands. Energies are in keV, relative to the SD minimum.