THE NI-56 B(E2,0(1)(-]2(+)(1)) VALUE - A GOOD TEST FOR THE SHELL-MODEL OFF STABILITY())

Elastic and inelastic proton scattering to the first-excited 2(+) stat e in the doubly-magic, unstable Ni-56 nucleus has been investigated in inverse kinematics with a secondary Ni-56 beam. At the SIS heavy ion synchrotron at GSI Darmstadt, the radioactive heavy-ion beam was produ ced via projectile fragmentation of a stable Ni-58 beam and separated inflight, with a Delta E - TOF - B rho-method, by the fragment separat or FRS. For the transition between the 0(+) groundstate and the first 2(+) state a value B(E2) = 600 +/- 120 e(2) fm(4) was derived, which c orresponds to a deformation parameter beta(Ni-56) = 0.173 +/- 0.017. T his result completes the set of experimental data for the first-excite d 2(+) states of nuclei with magic neutron or proton number in the 1f2 p-shell and provides a sensitive test for recent shell-model predictio ns in the region off stability. The Ni-56 -data are well reproduced by these calculations based on 1 particle - 1 hole excitations in a trun cated (1f(7/2))(h) - (2P(3/2) , 1f(5/2) 1p(3/2))P model space.