Excitation of the ground-state rotational band in 28Si by inelastic scattering of 25.25 MeV polarized protons

Angular distributions of the analyzing power and cross sections have been measured for the elastic and inelastic scattering of 25.25 MeV protons exciting the K = 0 + ground-state band in 28 Si. Good agreement with experiment is obtained in the coupled-channels formalism on the basis of the rotational model with a quadrupole deformation β 2 = −0.40 (oblate) and a hexadecapole deformation β 4 = +0.15. The calculations show the great sensitivity of the experimental results to both the magnitude and sign of the quadrupole and hexadecapole deformations. Equivalent fits of the data were obtained either by keeping the deformation length of the various deformed terms of the optical potential constant (δ 0 = β 0 R 0 = β I R I = β LS R LS ) or by increasing the deformation of the spin–orbit optical potential relative to the central potential by a factor of 1.5 (β LS = 1.5β cent ).