Title:

Coulomb excitation and break up

Break up processes involving a three body system in the Coulomb field are studied. A method is developed for the realistic treatment of such a system, and is applied to the break up of the nucleus, ^{7}Li. The Simple Cluster Model of ^{7}Li and the Coulomb excitation code COULVAR are used for the calculations. The continuum states of the α + t system are treated as a set of discrete states, by confining the relative motion of the clusters to a spherical box. The infinite set of states is then truncated by imposing an energy cutoff so that only the states below this energy are considered. The density of these states varies according to the box radius and the energy cutoff. The stability of the model is tested by varying these two parameters. The corresponding calculated probability of excitation of ^{7}Li has converged for a box radius of 20 fm and an energy cutoff of 20 MeV. The level energies and the wavefunctions of the continuum states are then easily obtained and are used to calculate the important matrix elements for the electromagnetic transitions between the bound states and the continuum states of ^{7}Li. The method is used to calculate the probability of excitation of ^{7}Li to its first excited state in the inelastic scattering experiments. It successfully reproduces a range of available data. An approximation is then developed to calculate the nuclearCoulomb interference at low energies (well below the Coulomb barrier). The results of its application supports the need for renormalisation of the nuclear potentials suggested by inverse scattering calculations. The method closely reproduces The ^{7}Li data in this region with the refitted nuclear potentials. The application of the three body model to the break up of ^{7}Li on heavy targets at high energies produces very interesting results. It predicts reasonably good cross sections in the regions of pure Coulomb interaction. It also shows that at high energies the nuclear forces become very strong and affect the classical Rutherford orbit of the projectile. These effects are enhanced for heavier targets and the observed small scattering angle should not be taken as the angle of a classical orbit. Finally improvements towards the generalisation of the method are suggested so that it will be capable of coping with any three body system in a strong Coulomb field.
