Competing shape evolution, crossing configurations and single particle levels in nuclei

Abstract

The evolution of shape in the even-even zirconium (Zr) isotopes has been the subject of study for many years. However, the odd-mass isotopes have not been investigated as extensively due to limited experimental accessibility and computational challenges. This work, employing the interacting boson-fermion model with configuration mixing, examines the effect of rapid shape evolution and normal-intruder configuration crossing -- both identified as quantum phase transitions -- alongside evolution in single particle energies, on the positive-parity spectrum of odd-mass $^\text{93-103}$Zr isotopes. Calculated energy levels, magnetic moments, $B(E2)$ values, and quadrupole moments are compared to experimental data, showing good agreement. The special case of $^{99}$Zr, which lies near the critical point of both quantum phase transitions, is also addressed, offering a new interpretation to the $7/2^+_1$ isomeric state and the occurrence of the type II shell evolution, in light of recent debates.