Excitation and photon decay of giant multipole resonances — the role and future of medium-energy heavy ions

Abstract

Inelastic scattering of mrdium 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 "0 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 che isoscalar giant quadrupole and isovector giant dipols resonances, are presented and compared with calculations. Decays to low-lying excited states are also discussed. Preliminary results from an experiment to isolate the J0fi Pb isovector quadrupole resonance using its gamma decay are presented.

Study of the continuum in heavy ion inelastic spectra by light particle coincidence measurements

“…At excitation energies above those of the known giant resonances, low cross-section structures superimposed on a large background have been observed [5,6], which have been attributed to multlphonon excitations built with the giant quadrupole resonance [ 7 ]. Heavy ions are also intensively used in the search for other high lying resonances [8]. It is consequently of paramount Importance to obtain precise knowledge of the different reaction mechanisms contributing to the continuum in heavy ion inelastic spectra.…”