Masses of neutron-rich Ni and Cu isotopes and the shell closure at Z = 28 , N = 40 S. Rahaman, J. Hakala, V. -V. Elomaa, T. Eronen, U. Hager, A. Jokinen, A. Kankainen, I. D. Moore, H. Penttilä, S. Rinta-Antila et al. (4 more) Eur. Phys. J. A, 34 1 (2007) 5-9 Published online: 19 October 2007 DOI: 10.1140/epja/i2007-10489-y