Two-Particle Separation Energy Trends in the Superdeformed Well

A measurement of the energy and spin of superdeformed states in ${}^{190}\mathrm{Hg}$, obtained through the observation of transitions directly linking superdeformed and normal states, expands the number of isotopes in which binding energies at superdeformation are known. Comparison with neighboring nuclei shows that two-proton separation energies are higher in the superdeformed state than in the normal state, despite the lower Coulomb barrier and lower total binding energy. This unexpected result provides a critical test for nuclear models.

Figure 1

(a) and (b) Spectrum obtained by triple-gating on the SD quasivacuum band in ${}^{190}\mathrm{Hg}$. (c) Spectrum in coincidence with at least two SD transitions (marked with closed triangles) and the 2717 keV transition.

Figure 2

Partial decay scheme.

Figure 3

(a) and (b) Known energies of SD quasivacuum states in even-even Hg and Pb nuclei compared with the results of static (SLy4 Skyrme [17] and D1S Gogny [18]) and dynamic (GCM [18]) mean-field calculations. (c) Binding energies per nucleon in the SD and ND systems.

Figure 4

Two-neutron ($S_{2n}$) and two-proton ($S_{2p}$) separation energies as a function of neutron number (left-hand panels) and proton number (right-hand panels). Open (closed) symbols indicate ground-state (SD) separation energies.