| Giant dipole resonances have long been studied to probe the dynamics of fusion reactions. Until now, the GDR from such a heavy fusion reaction has not been measured in coincidence with the evaporation residue. Using the reaction 48Ca on 176Yb we measured the GDR in highly excited 224Th. Such ER coincidence measurements make possible the use of the GDR to better probe such highly fissile systems.; Previous evidence by Brinkman et. al. had indicated an excess cross section at high excitation energies from 16O + 208Pb. Our ability to study the cross section, angular momentum distribution and GDR from 48Ca on 176Yb provided an excellent opportunity to probe this effect further. The observed cross section did not exhibit the excess previously observed, supporting Berriman's et. al. assertion that the excess cross section is from incomplete fusion. However, the angular momentum distribution did indicate possible fission hindrance.; The experiment was performed at Argonne National Laboratory with a beam of 206 MeV, 219 MeV and 259 MeV 48Ca. A 150 crystal BaF 2 array was used for high energy γ-ray detection. A 48 crystal BGO array was used for multiplicity measurements and the Fragment Mass Analyzer provided particle identification. |
