Calculations of the Nuclear Response to Hadronic and Electromagnetic Probes

Proton and electron scattering probes have been critical tools in the study of nuclear structure. Recent scattering experiments using polarized proton beams have shown that nuclear spin excitations in light nuclei are relatively suppressed at low excitation energy but surprisingly enhanced at higher excitation. This thesis will discuss the interpretation of these results in terms of a macroscopic schematic model based on sum rule techniques and in terms of a fully microscopic Random Phase approximation calculation. In particular, it will be seen that an asymmetric width for the states resulting from the coupling to two particle -two hole excitations is responsible, in both the macroscopic and microscopic approaches, for the distribution of the spin strength. Predictions for experimental verification of the theoretical studies have been made for a variety of incident proton energies and momentum transfer values for ^{40}Ca. Similar quenching problems are well known from experimental results using electron probes. The quasielastic peak in the electron scattering spectrum is lower by a factor of two than previous theoretical calculations would indicate. Although the inclusion of two particle-two hole correlations has previously shown moderated success, it is demonstrated in this thesis that the inclusion of many particle correlation effects is significant. This has been demonstrated within the context of the macroscopic Fermi Gas model and has been shown to be successful in accounting for the reduction throughout the period table. A more complete Random Phase Approximation calculation has verified that these correlations continue to account for the reduction in a fully microscopic calculation. Some brief discussion is made regarding the application of this formalism within a relativistic framework.