First lifetime investigations of iodine isotopes: The quest for collectivity

We report on spectroscopic information and lifetime measurements in the neutron-rich isotopes. This is the first lifetime data on iodine isotopes beyond . Excited states were populated in fast neutron-induced fission of at the ALTO facility of IJCLab with the LICORNE neutron source and detected using the hybrid -ball spectrometer. The level schemes of the isotopes are revised in terms of excited states with up to maximum spin-parity of , populated for the first time in fast neutron-induced fission. We provide first results on the lifetimes of the and states in and , and the state in . In addition, we give upper lifetime limits for the states in , the state in , the state in , and reexamine the state in . The isomeric data in are reinvestigated, such as the previously known and isomers with of 1.64(14) and 4.6(7) ns, respectively, as obtained in this work. The new spectroscopic information is compared to that from spontaneous or thermal-neutron induced fission and discussed in the context of large scale shell-model (LSSM) calculations for the region beyond , indicating the behavior of collectivity for the three valence-proton iodine chain with .