Incorporation of intruder-sector nucleons in the pseudo-SU(3) model

Extend the pseudo-SU(3) shell-model calculations for the ytterbium isotopes $^{174-178}$Yb to include nucleons in the intruder sector, in order to assess whether their absence explains the predicted loss of collectivity.

Background

The pseudo-SU(3) calculations retain only normal-parity active nucleons and treat abnormal-parity nucleons as renormalizing the dynamics through effective charges. In the heavier isotopes 174−178^{174-178}Yb, the model requires an additional rotor term to reproduce the observed moment of inertia, and the authors identify the omission of intruder-sector nucleons as a possible explanation for the predicted loss of collectivity. They explicitly state that the present calculations cannot yet include this sector, leaving its incorporation as an unresolved challenge for subsequent model development.

References

It should be pointed out that the absence of nucleons in the intruder sector could help to explain the loss of collectivity in ${174-178}$Yb, but at this stage of calculations we are not able to include the intruder sector, presenting a challenge for future works with the model.

— Microscopic study of low-lying energy levels and electromagnetic properties in even-even $^{168-178}$Yb nuclei  (2609.28763 - Vargas et al., 23 Sep 2026) in Section 3, Low-lying energy spectra