Nanosecond isomers in neutron-rich ⁶⁷Cu and ⁶⁴Co and a fast E3 transition in ⁶⁷Cu

Gamma-ray cascades from nanosecond isomers in neutron-rich nuclei ₆₇Cu and ⁶⁴Co have been observed through heavy-ion deep-inelastic collisions of ¹⁹⁸Pt+ ⁷⁶Ge (8 MeV/nucleon) using an isomer-scope. In ⁶⁷Cu, an isomeric state at 3464 keV and its decay scheme have been established. The isomeric transition is a hindered M 1 transition between the 15/2⁺ and the 13/2⁺ states with main components of (πp_3/2vg_9/2vf^-1_5/2) _15/2+ and (πp_3/2vg_9/2vp_1/2)_13/2+, respectively. A fast E3 transition between the πg_9/2 and the πp_3/2 single-particle states indicates strong particle-octupole vibration coupling in ⁶⁷Cu. An isomeric state at 834 keV with T_1/2 = 6.4(3) ns has been identified in ⁶⁴Co. Proton-neutron configurations of the levels established in ⁶⁴Co are discussed.