Angular momentum dependence of the GDR width in Sn nuclei at fixed excitation energy

High-energy γ-rays from the decay of the giant-dipole resonance (GDR) in the hot 106Sn compound nucleus and its daughters were measured in coincidence with heavy recoiling evaporation residues. The compound nucleus was formed at excitation energy E* = 80 MeV using the reaction 56Ni+48Ti at a bombarding energy of 260 MeV. The analysis yields the GDR width for two different intervals of angular momentum left angle J right angle =24 and 36 ℎ. The present data, combined with previous data at higher angular momentum permit a study of the angular momentum dependence of the GDR width for 10≤J ≤60ℎ at approximately fixed temperature. The width of the GDR is found to be roughly constant for J < 35ℎ, increasing rapidly for higher angular momenta. The data are found to be in good agreement with theoretical calculations within an adiabatic model describing thermal fluctuations of the nuclear shape. The model also reproduces the much weaker angular momentum dependence of the GDR width in the heavier nucleus 176W. (orig.)