Abstract
A study of hot Giant Dipole Resonance (GDR) in nuclei of mass A=120130 in an excitation energy range from 150 to 330 MeV, where the GDR quenching is expected to arise, has been undertaken using the MEDEA multi-detector system. Hot nuclei were populated using complete and incomplete fusion reactions. The characterization of hot system was performed through the study of residue time of flight combined with the analysis of light charged energy spectra detected in coincidence. Gamma-ray energy spectra show an evolution of the GDR main features both in terms of width and multiplicity. Evidences of a saturation of gamma multiplicity appear at high excitation energy at variance with predictions of statistical model calculations. Gamma- ray energy spectra can been reproduced in a phenomenological way introducing in the statistical model a sharp suppression of the gamma-ray emission above E* = 240 MeV. A comparison of experimental data to models describing the GDR disappearance will be presented.
Highlights
IntroductionGiant Dipole Resonance (GDR) gamma emission was observed [1]
Because the Giant Dipole Resonance (GDR) gamma-rays can be emitted at all steps during the de-excitation process, the extraction of its parameters relies on a comparison of the experimental spectrum to a statistical model calculation performed with code DCASCADE taking into account the whole decay sequence
Excitation energies and masses of the compound systems were determined combining time of flight (ToF) information with the analysis of light charged particle spectra to determine the amount of pre-equilibrium emission
Summary
GDR gamma emission was observed [1]. This is at variance with the statistical model predictions which show a progressive increase of gamma-ray multiplicity with excitation energy, due to the higher number of steps available for the gamma-rays to compete with particle emission. Different theoretical interpretations have been suggested to reproduce the experimental behavior, but no precise understanding has been achieved, possibly due to the lack of data in the excitation energy region where the decrease of GDR emission sets in. In order to fill this gap, a study of emission from hot nuclei of mass A ~ 120 - 130 with excitation energies between 150 and 335 MeV was undertaken at the LNS Catania, using the MEDEA + SOLE + MACISTE setup [2]
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