Study of subshell closure at N = 40 by Coulomb excitation

Summary A Coulomb excitation experiment has been performed in order to study the subshell closure at N = 40 for neutron-rich nuclei. This subshell effect is thought to be enhanced when large N/Z ratios are encountered. Therefore, the Z = 28 68 Ni is of particular interest in order to test this behaviour. Some experimental information is already available for 68 Ni at low excitation energy: a 0 + 2 isomer, a 2 + state and a long-lived 5 - state. The high energy of the 2 + state suggests the shell closure though its reduced transition probability B ( E 2) has never been mesured. The nuclei 68 Ni, 70,72 Zn, 76 Ge have been produced in the fragmentation of a 86 Kr beam at 60 MeV/A. The selection of these secondary beams has been performed by LISE3 spectrometer at GANIL. Performances of the detector system “Château de Cristal” and preliminary results on reduced transition probabilities B ( E 2) are presented and discussed.