N NUCLEAR PHYSICS A ELSEVIER Nuclear Physics A599 (1996) 11le-116c Giant Dipole Resonance studied with GASP M. Cinausero% D. Bazzaccob, P.F. Bortignon% G. De Angelis% D. Fabris b, E. M. Fiore d, L. Fiore d, E. Fioretto% B. Fornal% N. Gellil, M. Lops b, F. Lucarellil, S. Lunardi b, G. Nebbia b, V. Paticchio d, G. Prete% C. Rossi-Alvarez b, G. Viesti b ~I.N.F.N.- Laboratori Nazionali di Legnaro, 1-35020 Legnaro (Pd), Italy bDipartimento di Fisica and I.N.F.N., Sezione di Padova, 1-35131, Padova, Italy CDipartimento di Fisica and I.N.F.N., Sezione di Milano, 1-20133, Milano, Italy dDipartimento di Fisica and I.N.F.N., Sezione di Bari, 1-70126, Bari, Italy eInstitute of Nuclear Physics, PL-31342, Cracow, Poland fDipartimento di Fisica and I.N.F.N., Sezione di Firenze, 1-50125, Firenze, Italy The giant dipole resonance (GDR) from the decay of excited 1SSEr nuclei populated in the reaction 64Ni + 9:Zr at 241 MeV has been studied by using the GASP spectrometer. High-energy ")'-rays spectra have been obtained in coincidence with the 80 elements of the GASP inner ball and with discrete transitions in the residual nuclei 155'lS4Er. GDR parameters extracted from the high-energy 7-rays spectra in coincidence with low-energy 7-ray fold k>10 are in good agreement with systematics as well as with predictions from adiabatic calculations. No signature for entrance channel effects in the decay of 156Er was therefore observed from this lineshape analysis of the high-energy "),-rays spectra in contrast with the case of the a64yb nucleus. 1. INTRODUCTION In recent years, a number of experiments have searched for entrance channel effects in the decay of compound systems formed by fusion of different (symmetric and asymmetric) projectile - target combinations [1]. High-energy 7-rays emitted in the decay of the giant dipole resonance (GDR) built on compound nucleus excited states have been proposed as a tool to search for these entrance channel effects [2,3]. In fact, GDR photons are supposed to be emitted prevalently in the early stages of the compound nucleus decay, where they are more effective in competing with particle emission. Furthermore the GDR lineshape is known to be very sensitive to the nuclear deformation. Sizeable differences have been evidenced, indeed, in high-energy 7-rays spectra mea- sured using different entrance channels for 164yb and lS°Er [2,3] compound nuclei. On the other hand, an earlier low statistics measurement of high-energy ")'-rays emitted from the decay of 156Er at 47 MeV of excitation energy [4] showed no difference between spectra measured in the 64Ni + 9~Zr and in the 12C + 144Sm systems. 0375-9474/96/$15.00 © 1996ElsevierScienceB.V. All rights reserved. PII: S0375-9474(96)00052- 8