Theoretical Nuclear Structure Physics

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0070858Barrett Our goal is to understand the structure of atomic nuclei from first principles---namely, in terms of the free nucleon-nucleon (strong) interaction and many-body quantum mechanics. Toward this end, we havedeveloped a new "ab initio" shell-model approach, in which we treat all. A nucleons as active particles in an extremely large basis (model) space. We now have computer codes, which allow us to perform such calculations for nuclei up to A=16, i.e., 16 active nucleons, and have obtained reasonable and encouraging results for the light nuclei studied so far. We are presently performing detailed calculations for A=6 and 7 to study the rate of convergence of the binding energies, spectra, radii, etc., as the size of the model space is increased. A new computer code is now being tested to do calculations for 12C up to 10 million configuration space states, so that we can perform similar calculations for A=12 as we are now doing for A=6 and 7. One of our major accomplishments, to date, is the development of a technique for computing exactly the effective two-body shell-model interaction, which we have employed to solve the A=3 and 4 nucleon systems. From these exact solutions for A=3 and 4, we can extract the effective three-body and four-body interactions. We plan to utilize these effective three- and four-body interactions to construct an expansion for the effective A-nucleon shell-model interaction, which will greatly improve the convergence rate for our calculations. In the near future we will also include a real three-body interaction in our shell-model investigations.