Determination Of The Coulomb Correction And Isovector Terms Of The Nucleon Nucleus Optical Model Potential From Neutron Elastic Scattering At 303 And 40 Mev

Differential elastic- and inelastic-scattering cross sections, measured from approx. 1.5 to 10.0 MeV, are interpreted in terms of spherical-optical-statistical (OM) and coupled-channels models. A successful description of the differential elastic scattering below 10 MeV and the total cross section to 20.0 MeV is achieved using the spherical OM with energy-dependent strengths and geometries. These energy dependencies are large below approx. 7.0 MeV, but become smaller and similar to those reported for /open quotes/global/close quotes/ potentials at higher energies. This change in the energy dependence of the parameters probably marks the onset of the Fermi surface anomaly approx. 19 MeV above the Fermi energy. Inelastic scattering to the levels below 1.8 MeV displays a forward-peaked behavior. This nonstatistical component is interpreted using the weak-coupling model in which the f--2 proton hole is coupled to the 2/sup /plus// state in 6°Ni. This model provides an explanation of the unusual energy dependence and relatively small radius found for the imaginary OM potential. The coupling also contributes to the large value of this potential. The real spherical OM potential derived from the neutron-scattering results is extrapolated to bound energies by using the dispersion relationship and the method of moments. The resulting real-potential strength and radius peak at approx.-10.0 MeV, whereas the real diffuseness is at a minimum at this energy. The extrapolated potential is approx. 8% larger than that implied by reported particle-state energies, and approx. 13% smaller than indicated by hole-state energies. 42 refs., 8 figs.

Direct Nuclear Reactions deals with the theory of direct nuclear reactions, their microscopic aspects, and their effect on the motions of the individual nucleons. The principal results of the theory are described, with emphasis on the approximations involved to understand how well the theory can be expected to hold under specific experimental conditions. Applications to the analysis of experiments are also considered. This book consists of 19 chapters and begins by explaining the difference between direct and compound nuclear reactions. The reader is then introduced to the theory of plane waves, some results of scattering theory, and the phenomenological optical potential. The following chapters focus on form factors and their nuclear structure content; the basis of the optical potential as an effective interaction; reactions such as inelastic single- and two-nucleon transfer reactions; the effect of nuclear correlations; and the role of multiple-step reactions. The theory of inelastic scattering and the relationship between the effective and free interactions are also discussed, along with reactions between heavy ions and the polarizability of nuclear wave functions during a heavy-ion reaction. This monograph will be of interest to nuclear physicists.

Ratios of the cross sections for elastic scattering of 8 MeV neutrons from adjacent nuclei are measured over the angular range (almost equal to)20° - 160° for the target pairs 51V/Cr, 59Co/58Ni, Cu/Zn, 89Y/93Nb, 89Y/Zr, 93Nb/Zr, In/Cd and 2°9Bi/Pb. The observed ratios vary from unity by as much as a factor of (almost equal to)2 at some angles for the lighter target pairs. Approximately half the measured ratios are reasonably explained by a simple spherical optical model, including size and isospin contributions. In all cases, the geometry of the real optical--model potential is essentially the same for neighboring nuclei, and the real--potential strengths are consistent with the Lane model. In contrast, it is found that the imaginary potential may be quite different for adjacent nuclei, and the nature of this difference is examined. It is shown that the spin--spin interaction has a negligible effect on the calculation of the elastic--scattering ratios, but that channel coupling, leading to a large reorientation of the target ground state, can be a consideration, particularly in the 59Co/58Ni case. In the A (almost equal to) 50--60 region the calculated ratios are sensitive to spin--orbit effects, but the exact nature of this interaction must await more definitive polarization measurements. The measured and calculated results suggest that the concept of a conventional global'' or even regional'' optical potential provides no more than a qualitative representation of the physical reality for a number of cases. 48 refs., 14 figs., 3 tabs.

Atomic and Molecular Physics : Atomic Physics (1001--1122) - Molecular Physics (1123--1142) - Nuclear Physics : Basic Nuclear Properties (2001--2023) - Nuclear Binding Energy, Fission and Fusion (2024--2047) - The Deuteron and Nuclear forces (2048--2058) - Nuclear Models (2059--2075) - Nuclear Decays (2076--2107) - Nuclear Reactions (2108--2120) - Particle Physics : Interactions and Symmetries (3001--3037) - Weak and Electroweak Interactions, Grand Unification Theories (3038--3071) - Structure of Hadros and the Quark Model (3072--3090) - Experimental Methods and Miscellaneous Topics : Kinematics of High-Energy Particles (4001--4061) - Interactions between Radiation and Matter (4062--4085) - Detection Techniques and Experimental Methods (4086--4105) - Error Estimation and Statistics (4106--4118) - Particle Beams and Accelerators (4119--4131).