The 8+ isomer in 78Zn and the doubly magic character of 78Ni

Abstract A new isomeric state in 78 Zn has been identified and studied in the fragmentation of a 60.5 AMeV 86 Kr beam on a nat Ni target. The measured energies of the transitions and the half-life, T 1/2 =319(9) ns, of the isomeric decay suggest a spin and parity assignment I π =8 + . The deduced B(E2,8 + → 6 + ) value equals 1.21(5) W.u. is well reproduced in large scale shell model calculations using realistic interactions in the proton-neutron 2p 3/2 , 1f 5/2 , 2p 1/2 , 1g 9/2 model space. Standard E2 polarisation charges of 0.5e for both protons and neutrons were used. This result consists the first experimental evidence of the persistance of the N=50 shell gap in the vicinity of 78 28 Ni 50 .