TABLE OF CONTENTS In the preceding chapters, we derived an expression for the transition amplitude for a general rearrangement reaction involving two channels. This involves the complete (and therefore unattainable) exact wave function. The foundations for a very useful approximate scheme were then laid, which involved first the optical potential that describes the relative motion in the elastic channel. The direct reactions are regarded as a perturbation on this. The resulting approximate transition amplitude, involving as it does the distortion (from plane waves) of the wave function of relative motion in incident and outgoing channels, is known as the distorted-wave Born approximation amplitude (DWBA). It has proved enormously useful in the interpretation of experimental data. Whereas closed-form expressions for the cross sections can be obtained in the plane-wave approximation, this is not the case for the DWBA amplitude. Its calculation requires a large-scale computational effort that is practicable only on fast electronic computers. Such computations have been possible for many years. The general strategy of the calculation is common to all direct reactions. The elastic scattering data in the initial and final partitions at or near the energy of the direct reaction are needed for the purpose of determining the optical-potential parameters. The distorted waves are the solution to these two optical-model problems. This describes the wave functions of relative motion. The other ingredient of the transition amplitude is a nuclear overlap function whose form depends on the particular reaction under consideration. It was denoted by (? ? V ?
