NONRELATIVISTIC AND RELATIVISTIC DESCRIPTIONS OF PROTON-NUCLEUS SCATTERING

Historically, work in medium energy nucleon-nucleus scattering physics started in the 1950s and has continued since. During the past ten years exciting new developments have occurred, and this work reviews these developments. Two distinct theoretical approaches tor describing the medium energy scattering process are discussed. The first is nonrelativistic and is based on approximate solutions to the many-body Schrodinger equation. The second is relativistic and is based on covariant meson exchange theory and the Dirac equation. A pedagogical discussion of nonrelativistic multiple scattering formalisms is presented, followed by a description of the approximation schemes used in numerical applications of the theory. Recent theoretical developments in the nonrelativistic approach, including medium corrections to the effective projectile-target nucleon interaction, off-shell contributions, and full integration ("full-folding") of the nucleon-nucleus optical potential are discussed in detail. The historical development of the relativistic scattering models for the nucleon-nucleus system is reviewed and each of the principal models developed during the past ten years is explained, starting with the original relativistic impulse approximation model. We show direct comparisons, some previously unpublished, between the predictions of the best available nonrelativistic and relativistic scattering models and the data. A number of specific proton-nucleus elastic scattering cases are considered, including p + O-16, Ca-40 and Pb-208 at incident proton laboratory energies of 200, 500 and 800 MeV. Both relativistic and nonrelativistic approaches provide surprisingly similar and fairly good overall descriptions of the data. Finally, possible areas of further theoretical work in this field are discussed.