Probing core polarization around ⁷⁸Ni: intermediate energy Coulomb excitation of ⁷⁴Ni

¹ INFN Legnaro National Laboratories, Legnaro (Pd), Italy
² Department of Physics, Padua University, Padua, Italy
³ NSCL, Michigan State University, East Lansing, Michigan 48824-1421, USA
⁴ INFN Pisa, Pisa, Italy
⁵ Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
⁶ INFN Naples, Naples, Italy
⁷ Physics Department, Naples University Federico II, Italy
⁸ Physics Department, Deenbandhu Chhoturam University, Murthal, Sonepat, Haryana 131039, India
⁹ Ionizing Radiations Laboratory, University of Salamanca, Spain
¹⁰ INFN Padua, Padua, Italy
¹¹ CSIC-IFIC, Valencia, Spain

^a e-mail: tommaso.marchi@lnl.infn.it

Published online: 19 December 2013

Abstract

The study of the evolution of nuclear shells far from stability provides fundamental information about the shape and symmetry of the nuclear mean field. Nuclei with large neutron/proton ratio allow to probe the density dependence of the effective interaction. Indeed, it was recently shown that tensor and three-body forces play an important role in breaking and creating magic numbers. Of particular interest is the region of ⁷⁸Ni where the large neutron excess coincides with a double shell closure.

We have recently measured the B(E2; 0⁺ → 2⁺) of the ⁷⁴Ni nucleus in an intermediate-energy Coulomb excitation experiment performed at the National Superconducting Cyclotron Laboratory of the Michigan State University. The ⁷⁴Ni secondary beam has been produced by fragmentation of ⁸⁶Kr at 140 AMeV on a thick Be target. Selected radioactive fragments impinged on a secondary ¹⁹⁷Au target where the measurement of the emitted γ-rays allows to extract the Coulomb excitation cross section and related structure information. Preliminary B(E2) values do not point towards an enhancement of the transition matrix element and the comparison to what was already measured by Aoi and co-workers in [1] opens new scenarios in the interpretation of the shell evolution of the Z=28 isotopes.