Z. Phys. A - Atomic Nuclei 336, 387 390 (1990) Zeitschrift fiJr Physik A Atomic Nuclei 9 Springer-Verlag 1990 Interaction times in the 19F + 63Cu dissipative heavy ion reaction G. Cardella 1, M. Papa 1, G. Pappalardo 1, F. Rizzo 1, Q. Wang 1, ,, A. De Rosa 2, E. Fioretto z, G. lnglima 2, M. Romoli 2 M. Sandoli 2, R. Setola 2, L. Corradi 3, G. Montagnoli 3, D.R. Napoli 3, and A.M. Stefanini 3 1 Dipartimento di Fisica, Universitfi di Catania, Istituto Nazionale di Fisica Nucleare, Sezione di Catania, Italy 2 Dipartimento di Scienze Fisiche, Universit/t di Napoli Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Italy 3 Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Italy Received December 12, 1989 Coherence energies extracted from excitation functions and angular distributions for the fragments emitted in the a 9F _}_ 63Cu reaction, measured in the range 01ab = l0 ~ to 120~ at incident energies between 100 to 108 MeV (lab.), were compared to the Kun model of dissipative collisions. An overall agreement was found for the angu- lar distributions at forward angles. The general behavior of coherence energies was also properly described and interaction times were deduced. PACS: 24.60-k; 25.70-z. Introduction One of the most interesting features of dissipative heavy ion collisions is the possibility of determination of the interaction time. Several models have been proposed (see for instance', [1 4]) to allow the estimation of this funda- mental parameter from the analysis of the dependence of angular and Z distributions on the kinetic energy loss. Few years ago, fluctuations in the excitation func- tions for deep inelastic reactions were discovered [5-7] giving a new opportunity to extract characteristic times for these reactions. Different approaches [8, 9] have been proposed to interpret in the same framework both the angular distribution behavior and coherence energies ex- tracted from the cross section fluctuation analysis. In the present work we focused our attention to Kun model [9] which represents a natural development of the Stru- tinsky model [10, 11] of heavy ion collisions. In this model it is assumed that the rotational motion of the intermediate dinuclear system only weakly perturbs the radial motion of the colliding ions and provides an un- ified expression for both coherence energies and angular distributions. This approach has been recently checked by performing a study of 28Si+64Ni and 28Si+48Ti re- actions [12, 13]. In the present work we extensively in- * Institute of Modern Physics, Academia Sinica, Lanzhou, China vestigated its validity in the asymmetric system 19F + 63Cu for which previously measured excitation func- tions exist [14]. To complete the experimental informa- tion, we measured angular distributions in a large angu- lar range. Experimental results The angular distributions were measured using the 19F beam provided by the Tandem XTU accelerator of the Laboratori Nazionali di Legnaro, Padova (Italy). A self supporting 63Cu foil 300 gg/cm 2 thick was used as a target. The ejectiles were charge identified by means of A E-E technique using solid state detector telescopes at the forward angles and gas-solid state detector tele- scopes at backward ones. The incident energy was in- creased from 100 to 108 MeV in 2 MeV steps. An exam- Z 0 0 150 i00 50 I I I I 1 20 40 60 80 I00 E (MeV) Fig. 1. Energy spectrum of Z=7 fragments emitted in the 19F + 63Cu reaction at 108 MeV incident energy and 0~,b= 20 ~