Nuclear Structure Inferred from Heavy Ion Coulomb Excitation

Abstract

Low-lying nuclear spectra in all nuclei exhibit to some extent, features characteristic of quadrupole collective modes of motion. Thus it is interesting to ascertain to what extent it is possible to describe nuclear properties using phenomenological collective models such as the Interacting Boson Model^l or geometrical models since they can give a clear insight into the structure of a complex many body system. Nuclear E2 properties are a direct and unambiguous measure of the collective shape parameters for quadrupole collectivity. Unfortunately, this sensitivity could not be exploited fully in the past due to the sparseness of the available E2 data. Consequently most collective models have emphasized fits to level energies because of the extensive body of data available. However, the level energies of the collective states are sensitive to both microscopic and collective parameters. As a result the collective parameters extracted from level energies can be ambiguous. Coulomb excitation selectively excites collective states and the excitation cross sections are a direct measure of the strong E2 matrix elements. It is just these enhanced E2 matrix elements that collective models should predict the best. Recent advances in the field of Coulomb excitation makes it feasible, for the first time, to measure essentially all the E2 matrix elements for the low lying nuclear levels. These data should prove to be a stringent test of collective models. In particular it is now practical to use a simple model independent method for extracting collective parameters from E2 data. Application of these techniques to study heavy rotational and shape transitional nuclei and the model implications are discussed in this and the adjoining paper².

Supported by the National Science Foundation.