ABSTRACT
Since the discovery of the atomic nucleus, it has been a unique test system for an understanding of the quantal many-body phenomena. It has been clear that in different mass regimes, nuclei show different varieties of characteristics, strongly dependent on the interplay of individual particle motion and the collective dynamics. These two contrasting properties led to the introduction of nuclear shell model by Goeppert-Mayer and Jensen [1] and collective or geometric models by Bohr and Mottelson [2]. Starting from the mid-1970s, extensive experimental studies of exotic nuclei, such as those far from stability, in the mass range A=60-100 (see Figure 1.1) have led to exciting discoveries of large deformations, coexistence of nearly spherical and deformed shapes, rapid variations of structure with changes in neutron and proton numbers and so on. Studies of heavy ion fusion evaporation reactions and techniques of in-beam gamma-ray spectroscopy have revealed the existence of a variety of rotational bands up to high values of angular momentum, band crossings, shape changes, back bending, and many other properties [3]. For example, shape coexistence was discovered in 72Se in 1974 [4, 5] almost simultaneously with its discovery in mercury isotopes. Such a property was totally unexpected since, for a long time, the nuclei in the A=60-100 region were considered to be nearly spherical, perhaps somewhat an-harmonic vibrators, in the ground state. All the properties of these nuclei gave new insights into the role of nuclear configurations and forces and new structural information.
