Excitation Of Giant Resonances Through Inelastic Scattering

Giant resonances are collective excitations of the atomic nucleus, a typical quantum many-body system. The study of these fundamental modes has in many respects contributed to our understanding of the bulk behavior of the nucleus and of the dynamics of non-equilibrium excitations. Although the phenomenon of giant resonances has been known for more than 50 years, a large amount of information has been obtained in the last 10 years. This book gives an up-to-date, comprehensive account of our present knowledge of giant resonances. It presents the experimental facts and the techniques used to obtain that information, describes how these facts fit into theoretical concepts and how this allows to determine various nuclear properties which are otherwise difficult to obtain. Included as an introduction is an overview of the main facts, a short history of how the field has developed in the course of time, and a discussion of future perspectives.

This is the most recent and complete review on giant resonances in nuclei. It includes electric as well as magnetic collective states and a detailed discussion on the excitation mechanisms and the decay properties is given.

Giant resonances in 165Ho were studied with inelastic scattering of electrons with 60 MeV to 105 MeV incident energy at a scattering angle of 75 degrees. From 5 MeV to 30 MeV excitation energy, five multipole resonances were observed of which only the dipole resonances have been previously reported. Reduced transition probabilities and multipolarity assignments have been made. The five resonances were observed at excitation energies of 9.6 (E0 or E2), 11.5 (E2), 12.3 (E1), 15.8 (E1), and 23.5 MeV (E2). The splitting of the dipole resonance observed in photonuclear reaction experiments with prolate spheroid nuclei are confirmed with inelastic electron scattering.

Inelastic scattering of medium energy heavy ions provides very large cross sections and peak-to-continuum ratios for excitation of giant resonances. For energies above about 50 MeV/nucleon, giant resonances are excited primarily through Coulomb excitation, which is indifferent to isospin, thus providing a good probe for the study of isovector giant resonances. The extremely large cross sections available from heavy ion excitation permit the study of rare decay modes of the giant resonances. In particular, recent measurements have been made of the photon decay of giant resonances following excitation by 22 and 84 MeV/nucleon 17O projectiles. The singles results at 84 MeV/nucleon yield peak cross sections for the isoscalar giant quadrupole resonance and the isovector giant dipole resonance of approximately 0.8 and 3 barns/sr, respectively. Data on the ground state decay of the isoscalar giant quadrupole and isovector giant dipole resonances are presented and compared with calculations. Decays to low-lying excited states are also discussed. Preliminary results from an experiment to isolate the 2°8Pb isovector quadrupole resonance using its gamma decay are presented. 22 refs., 19 figs., 1 tab.

The series of volumes, Contemporary Concepts in Physics, is addressed to the professional physicist and to the serious graduate student of physics. The subject of many-body systems constitutes a central chapter in the study of quantum mechanics, with applications ranging from elementary particle and condensed matter physics to the behaviour of compact stellar objects. Quantal size effects is one of the most fascinating facets of many-body physics; this is testified to by the developments taking place in the study of metallic clusters, fullerenes, nanophase materials, and atomic nuclei. This book is divided into two main parts: the study of giant resonances based on the atomic nucleus ground state (zero temperature), and the study of the y-decay of giant resonances from compound (finite temperature) nuclei.

Results are presented for excitation of giant multipole resonances by inelastic scattering of 350 and 500 MeV 16O projectiles from 9°Zr and 2°8Pb. The giant quadrupole resonance is excited with large cross sections and a very large resonance peak to continuum ratio is obtained. Extracted cross sections agree with DWBA calculations which use standard collective model form factors. Using 380 MeV 170 to excite the giant resonances, the .gamma.-ray decay has been measured for the giant quadrupole resonance region of 2°8Pb. 10 references.

Giant multipole resonances and bound states above 6 MeV in Ni 60 were studied with inelastic scattering of electrons at 102 MeV incident energy and scattering angles of 60, 75, 90, and 105 degrees. In the energy interval from 5 MeV to 40 MeV excitation energy, ten states and resonances were observed of which only those below 7 MeV and those at 16.5 and 18.5 had been previously reported. Reduced transition probabilities were calculated, and multipolarity assignments were made. The ten transitions were observed at excitation energies of 6.1 (E3,E2), 7.0 (E3,M2), 7.6 (E2,E3,M2), 8.4 (E2,E0), 9.9 (E1), 11.8 (E2,E0), 12.9 (E3,M2), 15.0 (E4), 16.5 (E2,E0), and 18.5 (E1) MeV. The E4 resonance at 15.0 MeV was previously unreported. The E2 resonance at 16.5 MeV reported in (alpha, alpha primed) work and the E1 resonance at 18.5 MeV from (Gamma, n) were confirmed. (Author).