Abstract
Low-lying states of have been populated by the two-nucleon removal reaction () and studied using in-beam -ray spectroscopy at the Radioactive Isotope Beam Factory at RIKEN. Two new transitions were identified and assigned as decays from a previously unknown state. This state is suggested to be based on a configuration with . The present observation extends the systematics of the excitation energies of the first state in isotones toward . The determined energy of the state in continues a smooth trend along the isotones. The systematics are compared with shell-model calculations in different model spaces. Good agreement is achieved when considering a model space consisting of the ) orbitals. The calculations with a smaller model space omitting the orbitals below the subshell could not reproduce the experimental energy difference between the ground and first states in isotones, because proton excitations across subshell yield a large amount of correlation energy that lowers the ground states.
- Received 30 April 2021
- Accepted 22 July 2021
DOI:https://doi.org/10.1103/PhysRevC.104.024302
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