Nuclear Physics A568 (1994) 121-140 North-Holland zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA NUCLEAR PHYSICS A Production of heavy residues in nuclear collisions leading to 2, + 2, > 75 at bombarding energies of E/A = (11.4-15.3) MeV/u F.P. Hessberger, V. Ninov zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG Geseilschaft fiir Schwerionenforschung mbH, GSI, Darmstadt, Germany D. Ackermann ’ Technische ~~hschuie Darmstadt, Darmstadt, Germany A. Liittgen t Rheinische-Friedrich-W helms-Universitiit Bonn, Bonn, Germany Received 1 June 1992 (Revised 7 July 1993) Abstract Heavy residues, produced in aAr, 84Kr and 86Kr induced reactions at E/A = 14.5 MeV/u, E/A= 11.6 MeV/u and E/A = 11.4 MeV/u, respectively, have been separated from the projectile beam by the velocity filter SHIP and identified by means of a-spectroscopy. The observed reaction products were assigned to evaporation residues from compound or ~m~und-like nuclei up to 2 = 96 rather than from products from deep-inelastic processes. This interpretation is based on the velocity distributions, which peak close to rcN, the indepen- dence of the residue mass distributions from the entrance channel, and from comparisons of the observed mass distributions with results from statistical model calculations. The observed residue cross sections were found to be in the same order as or even higher than the values obtained at bombarding energies close to the fusion barrier. This we regard as a confirmation that fission is a process of low probability at high excitation energies. An analysis of the velocity distributions of the evaporation residues showed that particle emission from a thermally equilibrated compound nucleus dominates; contributions from pre- equilibrium emission are small. Key words: NUCLEAR REACTIONS: 139La, 14’Ce, 141Pr, 142Nd, 144*148~150~1s4Sm, 158*160Gd, 159n 165~~ *76Hf, 18’Ta, 184W,Pt, “‘Bi, (84Kr:X) E’= 975 MeV; 238U(40Ar, X) E = 580-610 MeV; iooRu, ro2Pd, “‘Ag 107,109 Ag cs6Kr, X) E = 980 MeV; measured evaporation residues, velocity distributions; deduced linear-momentum transfer, evaporation residue (r, mass distribu- tions. Enriched targets, velocity filter, ion-implanted silicon detectors, identification by a-spec- troscopy. ’ Present Address: Instituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, 35020 Legnaro, Padua, Italy. t Deceased on January, 6th, 1993. 03759474/94/$07.00 0 1994 - El sevier Science B.V. All rights reserved SSDI 0375-9474(93)E0456-I