Interplay between single-particle and collective effects in the in the Odd-A Cu Isotopes beyond N=40

Abstract

Collective properties of the low-lying levels in the odd-A neutron-rich nuclei 67,73Cu were inves- tigated by Coulomb excitation with radioactive beams. The beams were produced at the ISOLDE facility at CERN and post-accelerated by REX-ISOLDE up to 2.99 MeV/u. Gamma-rays were iden- tified with the MINIBALL array. In 67,69Cu, low-lying 1/2-, 5/2- and 7/2- states were populated. In 71,73Cu, besides the known transitions deexciting the single-particle-like 5/2- and core-coupled 7/2- levels, gamma-rays of 454 and 135 keV, respectively, were observed for the first time. Based on a re-analysis of beta-decay work and comparison with the systematics, a spin 1/2- is suggested for these excited states. Three B(E2) values were determined in each of the four isotopes. The re- sults indicate a significant change in the structure of the odd-A Cu isotopes beyond N=40 where single-particle-like and collective levels are suggested to coexist at very low excitation energies.