GDR STUDIES IN 28 Si + 124 Sn AT E * ~ 71 MeV

Giant Dipole Resonance (GDR) is a powerful tool for studying the average nuclear shape at high temperature (T) and angular momentum (J) [1]. In particular the variation of the GDR width (D) as a function of T and J, still remains a challenge. Although the Thermal Shape Fluctuation Model (TSFM), based on inhomogeneous damping is successfully able to describe the variation of GDR width with T and J in medium mass region, some discrepancies have been observed in A ~ 150 mass region [2]. It has been reported in ref. [3] that in addition to inhomogeneous damping, the contributions from intrinsic damping needs to be included to describe the observed Tand J-dependence of the GDR width in Si +Sn system at 149 MeV and 185 MeV. The intrinsic damping process is expected to have a steep T dependence. Therefore, study of the GDR in the same compound nucleus Gd at lower excitation energy will provide insight into the Tdependence of the GDR damping mechanism. With this motivation, the experiment was carried out using 135 MeV pulsed Si beam from PLF at Mumbai, bombarding an enriched 2.0 mg/cm thick Sn target producing Gd at E* ~ 71 MeV and ~ 26ħ. High energy rays were detected with an array of seven close-packed hexagonal BaF2 detectors, surrounded by cylindrical plastic detector for cosmic veto [3]. The angular momentum information is extracted using the multiplicity detector array consisting of 38 hexagonal BGO detectors configured in two equal closepacked groups placed above and below the target chamber. The n- discrimination was done using time of flight. Data were recorded for 0.1 pmC of incident beam particles using CAMAC based acquisition system LAMPS [4]. The background contributions were carefully monitored with blank target. In addition, high energy -ray spectra from 20 g/cm thick C target was recorded separately to assess the contribution coming from the Carbon impurity in Sn target. The extraction of GDR parameters using statistical model analysis is in progress and results will be presented.