HADRON EXCITATION OF GIANT RESONANCES

Abstract

This chapter reviews the giant resonance studies in heavy nuclei using scattering of different hadronic probes. From detailed studies of α scattering described in the chapter, the distributions of isoscalar strengths of multipolarity were obtained. In addition to more detailed information on the isoscalar giant quadrupole resonance (GQR), the most important points are the study of compressional modes of excitation and higher multipolarity giant resonances. The chapter gives a brief description of different isoscalar excitation modes, compressional modes, and higher multipole resonances. It discusses the recent aspects of heavy-ion excitation of giant resonances, which are related to the question of multi-phonon excitation in heavy-ion collisions. Compressional modes of excitation are of great importance because they are directly related to the compressibility of nuclear matter. Knowledge of two such modes is provided in the chapter: (1) the giant monopole resonance (GMR) and (2) the isoscalar dipole resonance. The isoscalar dipole resonance is difficult to study experimentally. Nuclear compressibilities were derived from microscopic and macroscopic models. In a detailed picture of the monopole compression presented in the chapter, the volume and surface effects, which may be in phase (scaling mode) or out of phase (anti-scaling), were obtained. Concerning the second compression mode—the isoscalar dipole resonance—data from 160 MeV π scattering and 800 MeV ρ scattering from 208 Pb indicate a structure consistent in excitation energy and width with α scattering results. Quite differently, there are Saclay data at higher α energy from which an isoscalar dipole excitation has also been extracted but is too high in excitation energy for 208 Pb.