Rotational motion in nuclei.

The exploration of nuclear structure over the last quarter century has been a rich experience for those who have had the privilege to participate. As the nucleus has been subjected to more and more penetrating probes, it has continued to reveal unexpected facets and to open new perspectives. The preparation of our talks today has been an occasion for Ben Mottelson and myself to relive the excitement of this period and to recall the interplay of so many ideas and discoveries coming from the worldwide community of nuclear physicists, as well as the warmth of the personal relations that have been involved. In this development, the study of rotational motion has had a special role. Because of the simplicity of this mode of excitation and the many quantitative relations it implies, it has been an important testing ground for many of the general ideas on nuclear dynamics. Indeed, the response to rotational motion has played a prominent role in the development of dynamical concepts ranging from celestial mechanics to the spectra of elementary particles.