Quadrupole Collectivity in 32 , 34 , 36 , 38 Si and the N 5 20 Shell Closure

R. W. Ibbotson,1 T. Glasmacher,1,2 B. A. Brown,1,2 L. Chen,1,2 M. J. Chromik,1,* P. D. Cottle,3 M. Fauerbach,1,2,† K. W. Kemper,3 D. J. Morrissey,1,4 H. Scheit,1,2 and M. Thoennessen1,2 1National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824 2Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 3Department of Physics, Florida State University, Tallahassee, Florida, 32306 4Department of Chemistry, Michigan State University, East Lansing, Michigan 48824 (Received 13 August 1997) The b-unstable nuclei 32,34,36,38Si have been produced by projectile fragmentation and studied by inbeam Coulomb excitation. Excited states at 1399 6 25 keV and 1084 6 20 keV have been identified for the first time in 36Si and 38Si, respectively, and tentatively assigned J ­ 2. The BsE2; 01 ! 21 d values leading to these states and the previously identified 21 states in 32,34Si have been measured, and are compared to shell model calculations. Our results indicate that the 2 1 state in 34Si has a large fp-shell intruder component, and that the 21 states in the N . 20 silicon isotopes can be reproduced assuming an N ­ 20 shell closure. [S0031-9007(98)05530-6]