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

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 $\mathrm{\hslash }$ 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.