C. Ngô

Investigation of the 40Ar + 197Au, 238U systems at 44 MeV/u

Abstract We have measured the angular correlation between two fragments emitted in the reactions Ar + Au and Ar + U at 44 MeV/u at GANIL. The aim was to investigate the amount of initial linear momentum transferred from the projectile to a fissioning nucleus. It turned out that this amount is much smaller than can be extrapolated from previous experiments. Furthermore, the probability of forming a fissioning nucleus is very small.

Linear momentum transfer investigated in the 20Ne + 197Au and 209Bi systems at 30 MeV/u

Abstract We have measured at SARA the correlation of fission fragments produced in the reactions 20 Ne + 197 Au and 20 Ne + 209 Bi at 30 MeV/u. The results show that the most probable amount of linear momentum transferred from the projectile to the fissioning nucleus is about 80 %. This corresponds to about 3.7 GeV/ c . The fission cross section is still rather large at this bombarding energy: 1.6±0.3 b for the Au target and 2.2±0.5 b for the Bi one. We present the results of a Monte-Carlo simulation which allows us to reproduce most of the experimental data under certain conditions which are discussed.

Emission of prompt nucleons in heavy ion collisions

We describe a simple dynamical model for the production of prompt nucleons at the very beginning of a heavy ion collision. Approximations often used in previous calculations (neglect of Pauli blocking, of window velocity and of its extension) have been checked. We apply the model to the calculation of prompt emitted neutrons in incomplete fusion reactions observed on the20Ne+165Ho system at 220, 402 and 700 MeV. Results of the model are extensively discussed.

Investigation of linear momentum transfer on the 35 MeV/u Ar+U system

We have measured, at GANIL, the angular correlation between two fission fragments in the reaction Ar+U at 35 MeV/u. The results are discussed in terms of the maximum energy that a nucleus can carry.

Nuclear fragmentation processes in the 20Ne + 27Al system at 30 MeV/A

Abstract Inclusive energy spectra and angular distributions of Z ≦ 9 fragments from the Ne + AI reaction have been measured at 30 MeV/A. The spectra present three components. The high-energy component has a reduced momentum width σ0 of approximately 65 MeV/c, which is lower than the values observed in reactions induced by relativistic heavy ions. Conversely, for the low-energy component, the results are rather similar to high-energy heavy-ion data.

Investigation of the fusion process in the Ar-induced reaction on natAg at 19.6 MeV/nucleon

Abstract We have measured at SARA the correlation angle between fission fragments and the velocity spectra of evaporation residues produced in the reaction 40Ar + natAg at 19.6 MeV nucleon . The results show that, in both cases, the most probable linear momentum transferred from the projectile to the fused system is about 80%. The total fusion cross section is still large at this bombarding energy: 880 ± 200 mb. However, we point out the need for a simultaneous analysis of the transferred linear momentum and the associated residual mass; different alternative scenarios during the early stage of the reaction are presented here. A discussion of the results indicates the need for caution with such an intermediate-mass system, before setting any definitive conclusions.

Investigation of linear momentum transfer on the20NeJ197Au system at 30 MeV/A

We have deduced the linear momentum transferred from the projectile to the fissioning nucleus in the reaction20Ne+197Au at 30 MeV/A by measuring the folding angle between the two fission fragments. We found that the most probable linear momentum transfer represents 76% of the initial value.

Investigation of the 84Kr + 92, 98Mo, natAg and 197Au systems at 22 MeV/u

Abstract We have investigated the 84 Kr + 92 Mo, 98 Mo, nat Ag and 197 Au systems at 22 MeV u at GANIL. The reaction products have been detected between 6° and 12° in the laboratory. We found products with a kinetic energy, an atomic number and a mass substantially smaller than those of the projectile. We present extensively the results of the inclusive experimental study of these products. We propose a possible interpretation for their formation: they could be produced in a partial fusion of the participants with the projectile spectators followed by a break-up of the two initial pieces. So far, such an interpretation agrees with the inclusive measurements but the results of coincidence experiments are now needed to confirm these ideas.

Nucleon currents between highly excited nuclei: (II). Influence of the relative motion

Abstract A finite-temperature Thomas-Fermi method has been used to study the nucleon flux between two hot semi-infinite slabs of nuclear matter in arbitrary relative motion. As an application, we estimate the imaginary part of the optical potential associated with nucleon transfer at the strong absorption radius. Analytical fits to the exact results are given for head-on and tangential collisions at zero temperature.

Peripheral collisions in the 84Kr + 92,98Mo, natAg and 197Au reactions at 22 MeV/u

Abstract Peripheral reactions induced on 92 Mo, 98 Mo, nat Ag and 197 Au targets by 22 MeV per nucleon krypton beam were studied. Fragments observed with velocities close to the beam velocity can be interpreted as coming from a quasi-fragmentation of the projectile. The isotopic distributions measured for the fragments produced with the Kr projectile reflect some influence of the composite system. Thus it seems that projectile fragmentation is not the only mechanism involved in these reactions and that the mean field interaction still plays an important role at this energy.