Proton single particle energies next to 78Ni: Spectroscopy of 77Cu via single proton knock-out reaction

Excited states of ⁷⁷Cu have been investigated by use of single proton knock-out reaction at the Radioactive Isotope Beam Factory in RIKEN in order to reveal the main components of the proton single-particle states. Three excited states were observed at 271, 902 and 2068 keV in ⁷⁷Cu. The lowest-energy excited state follows the trend predicted for the crossing of the $3/2_1^{-}$ and $5/{2_1}^{-}$ states. Comparing the excitation energies of the $3/2^{-}$, $5/2^{-}$ and $7/2^{-}$ levels from ⁶⁹Cu to ⁷⁷Cu one can see that the $Z=28$ shell gap between the $p_{3/2}$ and $f_{7/2}$ states is rather stable, while the $f_{5/2}-f_{7/2}$ spin–orbit splitting decreases by ∼1.5 MeV in agreement with shell model calculations using the tensor force.