Elementary Modes Of Excitation Research Articles

Elementary modes of excitation in the nucleus

In the field of nuclear dynamics a central theme has been the struggle to find the proper place for the complementary concepts referring to the independent motion of the individual nucleons and the collective behaviour of the nuccleus as a whole. This development has been a continuing process involving the interplay of ideas and discoveries relating to all different aspects of nuclear phenomena. The multi-dimensionality of this development makes it tempting to go directly to a description of our present understanding and to the problems and perspectives as they appear today. However, an attempt to follow the evolution of some of the principal ideas may be instructive in illustrating the struggle for understanding of many-body systems, which have continued to inspire the development of fundamental new concepts, even in cases where the basic equations of motion are well established. Concepts appropriate for describing the wealth of nuclear phenomena have been derived from a combination of many different approaches, including the exploration of general relations following from considerations of symmetry, the study of model systems, sometimes of a grossly oversimplified nature, and, of course, the clues provided by the experimental discoveries which have again and again given the development entirely new directions.

Elementary excitations in vibrational nuclei

We propose to describe the entire collective spectrum of vibrational nuclei in terms of few enteracting elementary excitation modes. We discuss in detail the case in which only two elementary modes are important (the quadrupole d and the octupole f-bosons). We give explicit expressions for the energy levels and transition matrix elements.

Theory of Collective Excitations in Spherical Odd-Mass Nuclei. III: Electromagnetic Properties of the Anomalous Coupling States

Various electromagnetic properties of the anomalous coupling states with spin (j-1) are shown to be well explained by the new viewpoint of the dressed n-quasi-particle modes proposed in a previous paper. In this point of view, the anomalous coupling collective states with spin (j -1) are considered as the dressed three-quasi-particle modes, which are regarded as a kind of elementary excitation modes in odd-mass nuclei. The effects of couplings between dressed three-quasi-particle modes and one-quasi-particle mode~ are also discussed in this connection, including those with spin j, (j-1) and (j-2).

Some Current Themes in Nuclear Research

The topics covered include: (a) Elementary modes of excitation with special emphasis on the isoscalar highfrequency quadrupole vibrations. (b) Conditions for shell structure in both spherical and deformed potentials. (c) Modifications in nuclear structure produced by large angular momentum, including a discussion of stability conditions as well as of the spectrum of quantum states in the yrast region for very large angular momentum.

The Many Facets of Nuclear Structure

The review of nuclear structure covers early developments, the nucleus as a quantal many-body system, the interplay of shell structure and nuclear deformations, interaction of nuclear matter in bulk (heavy ion reactions), elementary modes of excitation in a unified description of nuclear dynamics, the fine-grain structure of nuclear matter (high energy probes), and statistics of quantal states for the compound nucleus. Also covered are the strength function for direct interactions, isobaric analog resonance, collective modes in the nuclear pair field (two-particle transfer reactions) rotational spectra, generalized rotational motion, phase transitions induced by rotational perturbation in the Yrast region, and connections to other fields. (auth) reduction of isospin mixing in filled subshells was indicated. (2 tables) (tr- auth)