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

A new isomeric state in Zn-78 has been identified and studied in the fragme ntation of a 60.5 AMeV Kr-86 beam on a Ni-nat target. The measured energies of the transitions and the half-life, T-1/2 = 319(9) ns, of the isomeric d ecay suggest a spin and parity assignment I-pi = 8(+). The deduced B(E2,8() --> 6(+)) value equals 1.21(5) W.u. is well reproduced in large scale she ll 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 charg es of 0.5e for both protons and neutrons were used. This result consists th e first experimental evidence of the persistance of the N = 50 shell gap in the 78 vicinity of Ni-78(28)50. (C) 2000 Elsevier Science B.V. All rights reserved.