Despite the considerable effort that has been devoted to the study of atomic nuclei, there are still many open questions. We do not have a standard model of the nucleus that describes the observed nuclear properties in terms of fundamental forces. Basic facts, such as which combinations of neutrons and protons can form a nucleus, are not known. Nevertheless, considerable progress has been made using effective interactions and various many body techniques. For example, the nuclear shell model has been very effective in describing nuclear properties in certain regions. However, even here we are now finding, based on our first glimpses with the current rare isotope generation facilities, that as the neutron to proton ratio in nuclei is varied the normal shell structure of nuclei changes. Other well accepted tenants, such as the behavior of the nuclear radius with mass number, are also being challenged. A key to the future progress toward a nuclear standard model will be the ability to vary the neutron to proton ratio in nuclei. The proposed Rare Isotope Accelerator, RIA, would provide experiments with this capability. This talk will discuss the question of why RIA is critical for the future understanding of nuclear structure and point out how RIA will address issues in nuclear science.

ANL Physics Division Colloquium Schedule