Towards limiting temperatures in nuclei: The behavior of collective motion

Abstract

Gamma rays emitted from hot nuclei with mass around 115 and excitation energies between 350 and 500 MeV, formed in the $^{36}\mathrm{Ar}$ + $^{90}\mathrm{Zr}$ reaction at 27 MeV/nucleon have been measured. The \ensuremath{\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 \ensuremath{\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 \ensuremath{\gamma} emission from the resonance above an excitation energy of 250 MeV. The existing data do not show entrance channel effects.