Odd-even, symmetry and shell effects in pre-equilibrium emission

The energy spectra and angular distributions of 55Mn, 58Ni(α,p) reactions at E/sub α/ = 27 MeV have been measured. The theory of exciton model can be used to reproduce the experimental results quite well. The probabilities of pre-equilibrium emission of (α,p) and (α,n) reactions for a series of nuclei have been analyzed systematically. It was found that at the lower excitation energies odd-even, symmetry and shell effects should exist in the probabilities of pre-equilibrium emission. As the incident energy increases, the odd-even, symmetry and shell effects of pre-equilibrium emission should become weaker. The reasons for these phenomena are the characteristics of related binding energies and pairing correction energies. The parameter K in the average transition matrix element has to be changed a little with the incident energy when fitting the data, and has also been discussed