Nature of continua in inelastic α- and⁶Li-scattering at 26 MeV/A

The continua excited by inelastic scattering of 26 MeV/A α- and⁶Li-particles from²⁸Si have been studied at forward angles by coincident detection of γ-rays in final nuclei after particle decay. While the coincident γ-ray spectra in⁶Li-induced reactions show only transitions in mass A=24, 27 and 28 nuclei, in the α-induced reactions γ-transitions in mass 20 to 28 nuclei were observed. Inelastic⁶Li-scattering with energy losses between 30 and 80 MeV predominantly leads to γ-transitions in²⁷Si and²⁷Al. We interpret this as due to a dominant direct one-nucleon removal process producing the characteristic "triangular" shapes of the inclusive inelastic⁶Li spectra.⁶Li-induced reactions on²⁷Al show a corresponding behaviour. The typical flat α-spectra result from additional truly inelastic processes which lead to highly excited states in the target nuclei and subsequent evaporation of nucleons and α-particles. This is supported by the measured γ-multiplicities and by means of Hauser-Feshbach calculations which allow to deduce that part of the inelastic α-continuum which decays by particle evaporation.