Excitation and fission decay of new isoscalar giant resonances

Abstract

The excitation of high lying giant resonances and their fission decay properties are discussed. (A) A survey is given on recent hadron scattering experiments in which evidence for new high lying giant resonances in heavy nuclei is obtained. In all experiments the high lying giant octupole resonance is found. In addition our Julich results indicate the existence of an isoscalar dipole resonance which represents a compressional mode of excitation. Results of 200 MeV proton scattering confirm our results. In small angle scattering experiments different multipole components can be separated, a good example is the giant octupole resonance which is dominating the higher energy spectrum at 4–5°. By comparing giant resonances in 208Pb and actinide nuclei deformation effects are discussed. (B) The 238U(α,α′f) reaction has been studied at Eα = 172 MeV. The coincidence spectra indicate strong fission threshold peaks at excitation energies above Bf, Bnf and B2nf. At EX ≈ 21 MeV a pronounced structure is observed which is interpreted as decay of the new giant resonances (L = 1 and 3). Very different from this the fission decay of the giant quadrupole resonance is small.