Inelastic Electron Scattering in 28Si between 4MeV and 50MeV Excitation Energy.

摘要

91.2 MeV electrons were used to study 28 Si in the excitation range from 4 to 50 MeV. Fragmentation of E2 strength into states below the GQR region was found, with states between 0 and 15 MeV exhausting 35% of the E2 isoscalar EWSR. Available (gamma, abs) data were used to disentangle E1 and E2 strength in the region 15 to 30 MeV and show E2 strength separated into two distinct groups in this region. A cluster of E2 strength centered at 17.5 MeV and believed to be in the oblate ground state well exhausts 22% of the E2 isoscalar EWSR and a broad but clearly separate group of strength from 20 to 30 MeV exhausts 65% of the E2 isovector EWSR. Significant transition strength was found between 30 and 50 MeV which exhausts between 25 and 35% of the total E2 EWSR. Evidence was found for the existence of an E2 giant resonance corresponding to the oblate well of 28Si at 24 MeV. (Author)