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 de cay of the giant dipole resonance in these nuclei remains constant ove r the excitation energy range studied. This quenching of the gamma mul tiplicity cannot be explained by a continuous increase with temperatur e of the width of the resonance. Better agreement with the data is obt ained by assuming a cutoff of gamma emission from the resonance above an excitation energy of 250 MeV. The existing data do not show entranc e channel effects.