| Theoretical calculations within the adiabatic thermal shape fluctuation model predict differences in the behavior of the Giant Dipole Resonance (GDR) width between nuclei with and without shell effects. At low temperatures, in nuclei with strong shell effects, the width is predicted to be suppressed relative to nuclei where shell effects are weak.; Studies have been performed on the GDR properties of nuclei with strong shell effects (208Pb), and weak shell effects (Sn and Cu). The data for nuclei where shell effects are weak show a deviation from predictions at low temperatures. To investigate this discrepancy, an experiment was performed to measure the GDR width in 120Sn at lower temperatures than have previously been measured.; The width of the GDR built on excited states in 120Sn was studied by means of inelastically scattered 17O particles. This technique allowed for the first measurement of the GDR width at a temperature as low as 1 MeV in Sn. A GDR width of 4 ± 1 MeV consistent with the GDR width of the ground state was extracted. This result does not confirm the adiabatic coupling calculations of the evolution of the width as a function of temperature, and indicates an overestimation of the influence of thermal fluctuations. |
