Quadrupole collectivity in neutron-rich Fe and Cr isotopes

Intermediate-energy Coulomb excitation measurements are performed on the N≥40 neutron-rich nuclei Fe66,68 and Cr64. The reduced transition matrix elements providing a direct measure of the quadrupole collectivity B(E2;2+1→0+1) are determined for the first time in Fe4268 and Cr4064 and confirm a previous recoil distance method lifetime measurement in Fe4066. The results are compared to state-of-the-art large-scale shell-model calculations within the full fpgd neutron orbital model space using the Lenzi-Nowacki-Poves-Sieja effective interaction and confirm the results of the calculations that show these nuclei are well deformed
This work was supported by the National Science Foundation under Grant No. PHY11-02511 (NSCL), and by the U.S. Department of Energy under Awards No. DEAC02- 05CH11231 (LBNL), No. DE-FG02-08ER41556 (NSCL), No. DE-FG52-06NA26206, and No. DE-FG02- 05ER41379 (University of Richmond). Part of this work was performed under the auspices of the U.S. Department of Energy Lawrence Livermore National Laboratory (LLNL) under Award No. DE-AC52-07NA27344. A. P. recognizes MICINN (Spain) (Grant No. FPA2011-29854) and Comunidad de Madrid (Spain) (Project No. HEPHACOS S2009-ESP-147) for support. We would also like to thank the operations staff at NSCL for their outstanding work in beam delivery