Physics & Astronomy ETDs

Publication Date

1-31-1966

Abstract

A systematic study is made of the interaction of 22-MeV He3 ions with several medium-weight nuclei. The central purpose of this study is to compare the interactions induced by this strongly absorbed, spin-­one-half projectile to those induced by the more commonly used nuclear probes: neutrons, protons, and alpha particles. The target nuclei are restricted to three cases, Fe56,58 and Ni58, but the scope of the experimental studies is as extensive as the variety of experimental equipment available would allow. These studies then include the elastic and inelastic scattering as well as the neutron spectra in the region above 0.5 MeV. In general, conventional techniques are used for the measurements and these are described in the text. A solid-state dE/dx x E counter telescope was used to measure the differential cross section for elastic and inelastic scattering. The neutron spectra were obtained using nuclear emulsions at low energies, a liquid hydrogen bubble chamber at medium energies, and a special neutron-counter telescope at the highest energies. Because this latter instrument is not of a conventional design, it is described in greater detail than the other detection systems. It is possible to interpret the experimental results with existing theoretical analysis, which permits an immediate comparison of these results to those obtained by utilizing other nuclear probes. In several cases this comparison indicates rather unique features of He3-induced reactions. The elastic data are analyzed both in terms of an optical model and a strong-absorption model. The results of these two theoretical approaches are compared and their differences discussed. A strong­-absorption model code was written specifically for the present purpose and its structure is closely examined. The inelastic scattering calculations are made using distorted-wave-Born-approximation (DWBA) methods, and it is in these calculations that the most significant departures from nucleon and alpha-particle results are obtained. It is shown that the He3 nucleus excites collective states through the absorptive (imaginary) potential rather than through the real potential as in the case of the other projectiles. Finally, the low-energy neutron data are examined from a compound-nucleus viewpoint by means of an evaporation model and nuclear temperatures are extracted. In this analysis it is found that shell effects are absent at high excitation energies and the level density depends primarily on A. The high-energy portion of the spectra is treated as direct interaction and the ground-state distributions in particular are compared to DWBA predictions for a double-stripping mechanism. The immediate consequence of this comparison is an indication that the pairing model fails to yield adequate spectroscopic factors; the shell model provides better agreement with the data. The distinctive features of the He3 interaction are summarized and possible unique applications are discussed.

Degree Name

Physics

Level of Degree

Doctoral

Department Name

Physics & Astronomy

First Committee Member (Chair)

Christopher Pratt Leavitt

Second Committee Member

Louis Rosen

Third Committee Member

Howard Carnes Bryant

Project Sponsors

The U.S. Atomic Energy Commision

Language

English

Document Type

Dissertation

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