D. Doré

Energy-light relation for CsI(T1) scintillators in heavy ion experiments at intermediate energies

Abstract In this paper an original energy relation for light scintillation in a CsI(T1) detector is established. It is dependent on the charge and mass of the particle (fragment) and is a direct light-to-energy function suitable for the calibration of CsI(T1) detectors used in heavy-ion studies at intermediate energies. Resulting calibration with this function and energy spectra for light ions, obtained from a heavy ion experiment, are presented.

Projectile excitation energy evolution in peripheral collisions for 16O + 197Au at 32.5, 50 and 70 MeV/N

Abstract A comparison of the multiple breakup of 16 O projectiles scattered by a Au target at three different energies (32.5, 50 and 70 MeV/N) is presented. The excitation energy spectra of the primary projectile-like nuclei decaying into specific output channels were reconstructed. The excitation energy of the target is found to increase faster with beam energy than the one for the quasi-projectile.

Dissipative binary mechanisms in 24Mg + 12C collisions at 25A and 35A MeV☆

Abstract A study of the most violent collisions in the 24Mg+12C reactions at 25A and 35A MeV has been carried out. Experimental data, for those events in which the total charge of the system has been detected, are compared to simulations based on statistical fragmentation codes. For violent events, a binary mechanism appears to be competing successfully with compound nucleus formation.

On the breakup of excited 16O projectiles into four alphas at intermediate energies

Abstract Mechanisms of the breakup into four alpha particles of 16 O projectiles excited from peripheral collisions with 197 Au target nuclei have been investigated at 50 and 70 MeV/N. The experimental distributions of relative angles between alpha particles in the rest frame of the primary oxygen nucleus are compared to theoretical predictions based on prompt fragmentation and binary sequential decay. The results are compared to similar studies for that channel at loweer energy, 32.5 MeV/N, where the breakup of 16 O was shown to be consistent with sequential emission of alpha particles.

Excitation energy evolution and multi-particle correlations in heavy ion peripheral collisions at intermediate energies

Abstract Quasi-elastic and transfer reaction cross section systematics, excitation energy partition and multi-particle correlations are presented for projectile fragmentation following the reaction of 16 O projectiles at 50–70 A MeV on 197 Au target. Results are compared to breakup mechanism predictions from sequential and multifragmentation models.

Excitation energy in quasi-elastic and transfer reactions in 16O + 197Au at intermediate energies☆

Abstract Several breakup channels of an excited projectile were studied from measurements of charged fragments produced in peripheral collisions of 16 O on 197 Au at 50 A and 70 A MeV. Absolute fragmentation cross sections and projectile and target excitation energies were measured. An important result is that, with increasing incident energy, target excitation energy rises faster than projectile excitation. Transfer reactions were also examined and fragmentation cross sections in transfer reactions for many channels were estimated. Transfer reactions appear to have a fairly large cross section even at 70 A MeV. These experimental results are compared to data at 32.5 A MeV and systematic study of various parameters are presented for a wide range of the intermediate-energy domain.

Statistical and sequential breakup of 24Mg in peripheral reactions at intermediate energies

Abstract The fragmentation of the projectile 24 Mg, excited in peripheral collisions on 197 Au and 12 C targets, has been investigated at 25A MeV and 35A MeV with a large scintillator detector array. Projectile breakup events were selected in the off-line analysis, by requiring that the total detected charge in one event be equal to that of the projectile. The projectile-like nucleus (PLN) excitation energies have been reconstructed and compared to results at 50A MeV and 70A MeV. The branching ratios of 2-, 4-, 5-, and 6-fold decays show a linear dependence, characteristic of statistical decay. Global variable analysis in terms of relative angles was applied to the six-alpha exit channel and the corresponding data have been compared to theoretical calculations based on simultaneous and sequential binary decay. The latter have been divided into sequential fission and sequential evaporation decays. The data has been found to be consistent with a sequential evaporation decay mechanism for a wide range of the intermediate-energy domain.

Statistical signatures of the quasi-projectile breakup at 70A MeV

Abstract Exit channel cross sections in quasi-elastic and transfer reactions have been measured in the 24 Mg+ 197 Au reaction at 70 A MeV. The Q -value dependence of the cross section, and the linear relation between the logarithm of P n / P 2 an d E − 1 2 , show that even at 70 A MeV, deexcitation is statistical. The absence of entrance channel effects indicates the thermalization of the quasi-projectile formed via transfer reactions.

Time scale in 24Mg projectile breakup at 25A and 35A MeV

Abstract The time scale involved in the breakup of 24 Mg projectiles into the 6α and the 5αpH channels has been investigated by examining distortions and shifts in the fragment velocity distributions due to the Coulomb field of the target. Assuming a fixed angular momentum range of 4 to 8 ħ strok; for both channels, we deduce time scales of (5.1 – 6.8) × 10 −22 s for the six-alpha channel at 3.4 MeV of excitation per nucleon and (3.0–5.9) × 10 −22 s for the 5αpH channel at 4.5A MeV of excitation.

Quasi-Projectile Formation and Decay Comparisons Between 58Ni+C and 58Ni+Au Reactions at 34.5A MeV

It is now well known that collisions between heavy ions in the Fermi energy domain produce mainly binary type events[1]-[5]. It seems that this binary character dominates even for the most violent reactions[1, 3, 4]. However, what is still not well understood is the deexcitation stage of the two principal emitters and the effects produced by the entrance channel dynamics. An important factor in this energy range is that many processes are possibly in competition and it is experimentaly difficult to isolate each of them. Processes such as the progressively vanishing fusion, binary deep inelastic collisions and the appearance of nucleon-nucleon scattering are all present in the Fermi energy range. Furthermore, detected particles could have been emitted on a large time scale from very different stages of the decay, ranging from pre-equilibrium process to evaporation. Within the statistical break-up hypothesis, where the two principal emitters are considered as thermalized nuclei, we expect only the excitation energy of each emitter, and not the way it is reached, to be a determinant quantity for the disintegration exit channels. On the other hand, typical violence of these collisions can also lead to important deformations of the two main products of the reaction. Such deformations were observed recently by the rupture of neck-like structures linking the reaction partners[6]-[9]. In an asymmetric collision, we could expect the biggest nucleus to sustain the largest deformation. By its subsequent disintegration toward a more stable state, it could be possible to observe the effects of such a deformation on the deexcitation mode of the nucleus.