Three recent Letters have presented Dirac-equation optical-model calculations for intermediate-energy nucleon-nucleus scattering based upon a relativistic impulse approximation. In these works the relativistic impulse approximation is shown to be capable of explaining certain features of the experimental data that resist all attempts at a nonrelativistic impulse-approximation description. The reasons for the success of these relativistic impulse-approximation calculations are analyzed in the present work.

• Received 5 July 1983

DOI:https://doi.org/10.1103/PhysRevLett.51.1733