GIANT-DIPOLE RESONANCE IN A-SIMILAR-TO-40 HOT NUCLEI FROM COINCIDENCEMEASUREMENTS

The emission of high-energy gamma-rays in the deexcitation of hot Ca-4 0 and K-39 nuclei formed in heavy-ion fusion reactions at excitation e nergy E(x) similar to 90 MeV has been studied. The high energy gamma-r ays were measured in coincidence with evaporation residues or light ch arged particles. The gamma spectrum from the self-conjugated compound nucleus Ca-40 shows an appreciable yield suppression in the Giant Dipo le Resonance (GDR) energy region with respect: to the K-39, due to iso spin selection rules in the dipole gamma-decay. The spectral line shap es of the gamma spectra are well reproduced by using a statistical cod e which treats explicitly the isospin quantum number in evaluating lev el densities and transmission coefficients. The GDR parameters determi ned from the present coincidence measurements are in good agreement wi th the systematic in the A similar to 40 mass region at lower bombardi ng energy based on the analysis of inclusive spectra.