Direct neutron decay of the isoscalar giant dipole resonance

Abstract

The direct and statistical neutron decay of the isoscalar giant dipole resonance has been studied in 90Zr, 116Sn, and 208Pb using the (α, α’ n) reaction at a bombarding energy of 200 MeV. The spectra of fast decay neutrons populating valence hole states of the Z, N − 1 nuclei were analyzed, and estimates for the branching ratios were determined. The observation of the nucleon-direct-decay channels helped to select giant-resonance strengths and suppress the underlying background and continuum, which led to an indication of the existence of a new mode with L = 2 character, presumably the overtone of the isoscalar giant quadrupole resonance.