The b-unstable nuclei 32,34,36,38 Si 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 36 Si and 38 Si, respectively, and tentatively assigned J p 2 1 . The B͑E2; 0 1 1 ! 2 1 1 ͒ values leading to these states and the previously identified 2 1 1 states in 32,34 Si have been measured, and are compared to shell model calculations. Our results indicate that the 2 1 1 state in 34 Si has a large fp-shell intruder component, and that the 2 1 1 states in the N . 20 silicon isotopes can be reproduced assuming an N 20 shell closure. [S0031-9007(98)

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Recent experiments performed using the S800 spectrograph at the National Superconducting Cyclotron Laboratory have shed a new light on techniques to measure the valence wave function of halo nuclei. The momentum of the heavy fragment resulting from the stripping of the halo particle is measured by the spectrograph, and its final excited state is measured by means of a NaI g-detector array located around the target. The large angular and momentum acceptances of the S800 provide a measurement of the full momentum vector. The analysis of the shape of the momentum distributions corresponding to different core fragment final states distinguishes between core excitations coming from reactions where a particle from the core-rather than the halo-is removed in the reaction, and components of the halo wave function where the halo particle is coupled to an excited state of the core.