High-spin transition quadrupole moments in neutron-rich Mo and Ru nuclei: testing $\gamma $ softness?

TL;DR

This study measures transition quadrupole moments in neutron-rich Mo and Ru nuclei at high spins to explore nuclear shape softness and triaxiality, revealing challenges for current theoretical models to accurately describe these properties.

Contribution

It provides new experimental data on quadrupole moments at high spins in neutron-rich Mo and Ru nuclei, testing the limits of mean-field models in describing nuclear shape phenomena.

Findings

Quadrupole moments decrease at moderate spins.

Mean-field models struggle to reproduce the data.

Data suggest complex shape dynamics beyond simple models.

Abstract

The transition quadrupole moments, $Q_{t}$, of rotational bands in the neutron-rich, even-mass $^{102-108}$Mo and $^{108-112}$Ru nuclei were measured in the 8 to 16 $\hbar $ spin range with the Doppler-shift attenuation method. The nuclei were populated as fission fragments from $^{252}$Cf fission. The detector setup consisted of the Gammasphere spectrometer and the HERCULES fast-plastic array. At moderate spin, the $Q_{t}$ moments are found to be reduced with respect to the values near the ground states. Attempts to describe the observations in mean-field-based models, specifically cranked relativistic Hartree-Bogoliubov theory, illustrate the challenge theory faces and the difficulty to infer information on $\gamma $ softness and triaxiality from the data.