Exploring highly-deformed ground states involving the second intruder orbit in Z>50 even-even nuclei

Abstract

We present a systematic survey of even-even nuclei with $Z>50$ to identify where a very large prolate configuration driven by the second intruder orbit emerges. Within the energy density functional theory framework, we find in representative cases a pronounced prolate minimum at quadrupole deformation $β_2\approx$ 0.3--0.4. A characteristic feature of these minima is a local enhancement of the hexadecapole ($β_4$) component relative to nearby deformations, which is a clear fingerprint of the $β_2$--$β_4$ coupling expected for the second intruder orbit. Representative comparisons among three Skyrme interactions show a similar appearance of the highly deformed minimum and a local enhancement of $β_4$ at the prolate minimum, indicating qualitative robustness with respect to the interaction. The resulting maps highlight specific heavy nuclei where highly deformed ground states are anticipated.

Figures (12)

• Figure 1: Quadrupole deformation parameters $|\beta_2|$ of even-even nuclei from proton dripline to $N=126$ of Te ($Z=52$) to Hg ($Z=80$) isotopes as a function of the neutron number. For visibility, the $|\beta_2|$ values of each isotope is shifted by $0.05\times (Z-52)$ and oblate shapes ($\beta_2<0$) are represented by open symbols.
• Figure 2: Hexadecapole deformation parameters $\beta_4$ of even-even nuclei from proton dripline to $N=126$ of Te ($Z=52$) to Hg ($Z=80$) isotopes as a function of the neutron number. For visibility, the $\beta_4$ values of each isotope is shifted by $0.05\times (Z-52)$.
• Figure 3: (a) Proton and (b) neutron single-particle energies (s.p.e) and (c) deformation energies of $^{166}$Nd as a function of quadrupole deformation parameter $\beta_2$. Blue solid and red dashed curves in the panels (a) and (b) present negative and positive parity single-particle levels, respectively. Thick dashed curves denote the proton and neutron chemical potentials. A vertical dotted line indicates the $\beta_2$ value of the ground state for a guide to the eye.
• Figure 4: Same as Fig. \ref{['pec.config.166Nd']} but for $^{138}$Gd.
• Figure 5: Deformation energy curve for $^{272}$No obtained from axial HFB calculations with the HFBTHO solver, using an axially deformed harmonic-oscillator basis truncated at $N_{\max}=14$. Octupole deformation ($\beta_3$) is not included.