Lifetime measurements in Nb 99 and Zr 99: Investigation of shape coexistence

Abstract

The A≈100 mass region is of special interest due to a rapid shape transition, observed by going from neutron number 58 to 60, especially pronounced in the Zr isotopes, where Zr98 is weakly and Zr100 is strongly deformed. To further examine this intricate phenomenon, in this work lifetimes of low-lying excited states in the nuclei Zr99 and Nb99 were determined using fast-timing techniques and an experimental setup consisting of four LaBr3(Ce) detectors. Neutron rich A=99 fragments were produced in neutron induced fission and separated by the spectrometer LOHENGRIN at the Institut Laue-Langevin in Grenoble, France. Experimental values are compared to two different calculations in the framework of the interacting boson-fermion model and discussed in the context of shape coexistence. © 2023 American Physical Society.