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

Abstract

A new isomeric state in 78Zn has been identified and studied in the fragmentation of a 60.5 AMeV 86Kr beam on a natNi 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 28Ni 50.