Backangle anomaly in scattering of α-particles from 28Si at low energies

In order to resolve the differences in time literature on the existence of quasi-molecular states in the alpha-Si-28 system, excitation functions were measured for the scattering of alpha-particles from Si-28 in the incident energy range E-lab = 3-7.8 MeV. An angular distribution measurement was carried out in the angular range theta(lab) = 30 degrees-174.5 degrees for every potential resonance observed in the excitation functions. Data was analysed using a Regge-pole formalism by coherently adding specific resonances to an underlying diffraction term calculated by a strong absorption model. Furthermore, the usual compound elastic contribution was incoherently added to the direct interaction part of the cross section. The 6.8 MeV resonance was confirmed with J = 3 and some evidence was observed for a J = 1 resonance around 6.0 MeV. (C) 2000 Elsevier Science B.V. All rights reserved.