A. Demeyer

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.

The third particle in deep inelastic collisions

Angular correlations between charged reaction products have been measured for the reaction14N+27A1 at 70 and 100 MeV. Light particle evaporation from the heavy recoil is shown to be the dominant process. In addition, however fast alphas are observed for all reaction channels. From the three-body kinematics we conclude that these alphas are emitted from the contact zone between the two heavy ions. A comparison of the results forELab=70 and 100 MeV excludes an explanation of this process by the recently suggested “Piston” or “hot-spot” models.

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.

Investigation of the Kr + Au system at 22 MeV/u

We have measured the mass, the atomic number and the kinetic energy of the fragments emitted between 6° and 21° in the 22 MeV/u84Kr +197Au reaction. As in the case of a similar experiment at 35 MeV/u we found products with a velocity substantially smaller than the one of the projectile.

Preequilibrium emission in heavy ion collisions: A dynamical approach

A coupled treatment of both dynamics and G.D.H. Model is proposed to treat “prior equilibration” phase in heavy ion collisions. Assumptions and coupling effects are discussed in details, and a numerical procedure is developped. Comparison with27A1(14N,X) at energies standing from 7–30 MeV/nucleon is presented. Proton and helium 4 productions, angle integrated spectra and angular distributions are compared. Incomplete fusion to fusion ratio is correctly reproduced in the intermediate incident energy region. A part of the linear momentum lost can be explained and a non negligeable transverse momentum is predicted for the fusion events. Differents types of experimental data are needed to test the validity of this approach and further developments are discussed.

Energy dissipation in light heavy ion reactions

Analysis of the energy dissipation for light heavy ions (12C,14N,16O,22Ne) reactions has been attempted. Classical models with or without a friction term and the diffusion model have been compared to the data. Fragmentation and prompt collective excitation have been considered also.

Local equilibration and diffusive phenomena in40Ar+27Al and14N+27Al heavy ion reactions

Extensive analysis of the energy dissipation and nucleon exchange has been done with heavier systems. Here we choose the two light systems40Ar+27Al (Elab=340 MeV) and14N+27Al (Elab=100 MeV) in order to study the correlation of the energy dissipation with the variance of the charge distributions as a function of total kinetic energy loss bins. Considerable energy damping is found to occur in the approach phase which cannot be explained by a simple Fokker-Planck diffusion model. Indeed a model which interprets the collision as a local equilibration followed by diffusive phenomena is more appropriate to fit the data.