TOWARDS LIMITING TEMPERATURES IN NUCLEI - THE BEHAVIOR OF COLLECTIVE MOTION

Gamma rays emitted from hot nuclei with mass around 115 and excitation energies between 350 and 550 MeV, formed in the Ar-36+Zr-90 reaction at 27 MeV/nucleon, have been measured. The gamma-ray yield from the decay of the giant dipole resonance in these nuclei remains constant over the excitation energy range studied. This quenching of the gamma multiplicity cannot be explained by a continuous increase with temperature of the width of the resonance. Better agreement with the data is obtained by assuming a cutoff of gamma emission from the resonance above an excitation energy of 250 MeV. The existing data do not show entrance channel effects.