Inelastic high energy nucleon scattering on light nuclei

Abstract

The excitation of a nucleus bombarded by nucleons of a few hundreds of MeV is considered as the result of individual interactions of the incoming nucleon with the nucleons of the nucleus. A simple two-particle model, in which a bombarding particle excites a particle moving in a potential well, has been calculated in the first Born approximation. It is shown that the resulting angular distributions have a strong forward dip and vanish at large angles. To a certain extent this result still holds for the case of a nucleus consisting of Fermi- particles with common and isobaric spins. In first order only those states can be excited whose wave functions have, in the sense of the independent particle model, a component differing only in the state of one particle from the ground state wave function. In the case of neutron scattering the cross section has a forward dip if the space part of the wave function of the excited particle is orthogonal to the space part of its ground state wave function. If this is not so, for example if the excitation can occur by a pure spin exchange, there may be a forward maximum. In proton scattering the Coulomb interaction could result in a forward peaked angular distribution by didipole excitation as well as in the above mentioned case of monopole transition. In higher approximation two or more particles in the nucleus can be simultaneously excited. The resulting cross sections are expected to be smaller and more isotropic than in the case of a one-particle excitation. The angular distributions for two types of collective excitation have also been calculated, in the first Born approximation, namely for the lowest quadrupole surface vibration and for the dipole vibration of the nuclear charge. The qualitative features of the experimentally measured cross sections of the scattering of 185 MeV protons on C 12 are shown to be in agreement with the theoretical expectations.