Nuclear magnetic and quadrupole moments for nuclear structure research on exotic nuclei

Abstract

One of the key issues in current nuclear physics research is to investigate the properties of so-called `exotic nuclei' and of `exotic nuclear structures'. Exotic nuclei are nuclei with a proton-to-neutron ratio that is very different from the proton-to-neutron ratio in stable nuclei (a technical term related to this ratio is the `isospin'). We define exotic nuclear structures as excitation modes of nuclei that have a very different structure than the structure (or shape) of the nuclear ground state. By putting the nucleons in a nucleus to extreme conditions of isospin and excitation energy one can investigate details of one of the four basic forces in nature: the strong force which binds the nucleons together to form a bound nucleus. While the basic properties of the strong nucleon–nucleon interaction are known from investigating the properties of nuclei near the `valley of stability', recent developments in the study of exotic nuclei have demonstrated that specific properties of the strong interaction, such as the influence of the spin-orbit term, are not yet understood. Because the nucleus forms a complex many-body system, it is impossible to describe it by ab initio calculations (except for a few very light nuclei, for which such calculations have become possible in the last few years) and therefore approximations need to be introduced. Several theoretical models have been developed in order to describe the properties of nuclei all over the nuclear chart. It is by measuring the basic nuclear properties such as masses, binding energies, lifetimes, excitation schemes, static and dynamic moments, and by comparing these properties to the predictions from the nuclear models, that these models can be tested and effective interactions can be improved. Furthermore, the measured nuclear properties can be a guide in understanding the changes, which the nuclear force undergoes in extreme conditions.In this report, we focus on the electric and magnetic properties of a nuclear state, namely on what the static magnetic dipole and electric quadrupole moments can teach us about the nucleus as a system of independently moving particles in a central potential or as a system of collectively moving nucleons. We give an overview of some techniques to measure nuclear moments for a variety of nuclear states and we discuss how the recent developments in the production of exotic nuclei have influenced the development of new experimental tools for nuclear moment studies.