Highly selective studies of GDR in164Er

Abstract Exclusive measurements of high energy γ-rays in the decay of 164 Er, formed in the reaction 40 Ar+ 124 Sn, have been performed to study angular momentum dependence of the giant dipole resonance (GDR) strength function. The γ-ray spectra were measured in coincidence with A=160 evaporation residues (4n channel at E beam = 163 MeV and 187 MeV. A statistical model analysis, incorporating a two-component GDR strength function, shows increase in the GDR width as the average spin of the compound nucleus increases from 26ħ, (at 163 MeV to 54ħ (at 187 MeV). This is consistent with the predictions of a thermal shape fluctuation model.