Unitary Modifications of the Impulse Approximation

Unitary modifications of the impulse approximation, proposed by Rosenberg and Queen, are investigated, and the connection between them established. It is shown that Queen's approximation does not in fact ensure elastic unitarity, and that if Queen's approximation is modified so as to retain the unitarity constraint, then Rosenberg's approximation is obtained. In preliminary elastic-scattering calculations on a soluble three-body model, it is found that unitarity is violated strongly by the impulse approximation, and to a smaller extent by Queen's approximation. Both of the unitary modifications substantially reduce the impulse-approximation differential cross sections, and yield improved results in the forward hemisphere.