Shape coexistence in ⁹⁴Zr studied via Coulomb excitation

In recent years, a number of both theoretical and experimental investigations have been performed focusing on the zirconium isotopic chain. In particular, state-of-the-art Monte Carlo shell-model calculations predict shape coexistence in these isotopes. In this context, the ⁹⁴Zr nucleus, which is believed to possess a nearly spherical ground state, is particularly interesting since the purported deformed structure is basedon the low-lying 0₂⁺ state, making it amenable for detailed study. In order to provide definitive conclusionson the shapes of the low-lying states, two complementary experiments to study ⁹⁴Zr by means of low-energy Coulomb excitation were performed. This data will allow the quadrupole moments of the 2_1,2⁺ levels to be extracted as well as for the deformation parameters of the 0_1,2⁺ states to be determined and, thus, definitive conclusions to be drawn on the role of shape coexistence in this nucleus for the first time.

The first experiment was performed at the INFN Legnaro National Laboratory with the GALILEO-SPIDER setup, which, for the first time, was coupled with 6 lanthanum bromide scintillators (LaBr3:Ce) in order to maximize the γ-ray detection effciency. The second experiment was performed at the Maier-Leibnitz Laboratory (MLL) in Munich and used a Q3D magnetic spectrograph to detect the scattered ¹²C ions following Coulomb excitation of ⁹⁴Zr targets.