Semimicroscopic description of the giant dipole resonance
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mimicroscopic Description of the Giant Dipole Resonance B. S. Ishkhanov and V. N. Orlin Skobel’tsyn Institute of Nuclear Physics, Moscow State University, Vorob’evy gory, Moscow, 119899 Russia Abstract—A simple semimicroscopic model providing the possibility of taking into account the influence of deformation, configuration, and isospin effects on the structure of giant dipole resonance is formulated. This model is applied for the description of global specific features of photoabsorption cross sections for spherical, deformed, and transition nuclei in the mass region 10 A 240. PACS numbers: 24.30.Cz, 25.20.Dc DOI: 10.1134/S1063779607020049 63Cu
1. INTRODUCTION During the last 50–55 years, properties of giant resonances (GRs) occurring in cross sections of many nuclear reactions as a collective “response” of the nucleonic system on external vibrational fields of various multipole orders have been studied extensively in nuclear physics. These studies have provided the possibility of understanding the nature of collective nuclear excitations, and have determined more precisely the characteristics of the effective interaction of nucleons in the nucleus. Information concerning the compressibility of nuclear matter important for astrophysics was obtained during investigation of isoscalar monopole resonance. Investigation of charge-exchange giant resonances contributed to understanding of reasons for the inadequacy of the theoretical estimates of the β decay rate. Significant work on systematization of the global characteristics of GRs—their energies, widths, degree of exhaustion of corresponding sum rules—was performed providing the possibility of tracing the influence of the structure of lower nuclear states on the properties of GRs. The proof of the existence of two-photon giant resonances [1, 2], and the possibility of excitation of multipole giant resonances in strongly heated nuclei [3, 4] can be mentioned among the latest achievements of the physics of GRs. Characterizing the present status of GR research, it can be said that conceptually this problem has been worked over rather well both experimentally and theoretically (see, e.g., overviews [5–12]). However, a microscopic approach that would provide the possibility of detailed description of GR properties for an arbitrary nucleus has not been developed, in spite of multiple attempts. This is clearly illustrated by the history of studies of giant electric dipole resonance. The possible existence of photoabsorption resonance was first pointed out in 1937 in [13], where a large photoneutron yield from
for the energy E = 17 MeV was registered, with the reaction Li(p, γ) used as the source of γ quanta. In 1945, the phenomenon of the giant dipole resonance (GDR) was actually predicted in [14], where it was shown that the average energy of electric dipole transitions can be calculated from the nucleus polarizability directly related to the symmetry energy in the semiempirical mass formula. The first experiments that proved the existence of the GDR were measurements
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