abstract

Molecular dynamics calculations which are employed to model light particle emission in nuclear collisions at intermediate energies suggest that coalescence model analyses may be used to probe the time evolution of these systems and to provide information on the degree of thermal, chemical and isospin equilibrium achieved at particular stages of this evolution. This talk discusses the application of coalescence model analyses to explore light particle emission in reactions between 47A MeV projectiles and medium mass targets. The results provide evidence for increasing expansion of the hot composite nuclei as the projectile mass increases. Densities and temperatures of the freeze-out configurations in multi-fragmenting systems are derived.

abstract

The unexpectedly large cross-section reported for the reaction \(^{86}\)Kr + \(^{208}\)Pb = \(^{293}118 + n\) may be due to the lowering of the Coulomb barrier (measured with reference to the energy of the compound nucleus). Some consequences of this “unshielding” phenomenon are discussed.

abstract

The properties of the multifragmentation of “hot sources” produced in the \(^{40}\)Ca \(\!+\!^{40}\)Ca reaction have been studied at a beam energy 35 MeV/nucleon. Two signatures of prompt multifragmentation, which make use of special features of particle emission from the “freeze out volume”, together with an analysis of the reduced relative velocity between pairs of intermediate mass fragments, indicate the presence of a transition from sequential decay to prompt multifragmentation at an excitation energy of about 3 MeV/nucleon.

abstract

The construction of the multidetector CHIMERA designed to detect and identify charged particles and fragments emitted in heavy ion reactions at intermediate energy is in progress and is coming to an end. The construction of this multidetector is presented in this paper as well as the status of the project.

abstract

Fluctuations of the fragment-size distribution have been studied in the framework of a bond percolation model using the method of scaled factorial moments (SFM). The independence of SFM from fragment-size resolution but not power-law behavior (intermittency) characterizes the fluctuations at the percolation transition. The SFM determined for various individual fragment-size intervals converge to a value of \(\sim 1\) near the critical point. The convergence occurs even in very small systems, and events may be sorted according to measurable quantities. This may serve as a new possible signature of critical behavior in nuclear multifragmentation.

abstract

Description of a realistic dynamic model of nucleus–nucleus collisions and fusion reactions, combined with stochastic effects (fluctuations) is given. We solve Langevin equations of motion in which stochastic white noise term is added to deterministic conservative and dissipative forces. The equations of motion are solved in 4-dimensional configuration space including three geometrical variables defining shape of the system and one variable defining charge asymmetry. Dissipative forces are calculated assuming one-body dissipation mechanism. Two sources of fluctuations are considered: thermal fluctuations determined by the fluctuation–dissipation theorem (Einstein relation) and fluctuations associated with exchange of nucleons. The width of the thermal fluctuations turns out to dominate stochastic effects in fusion reactions. It is shown that in near-threshold fusion reactions, the fluctuations remove flux from reseparation processes and direct it to fusion (and vice versa). Consequently, fluctuations enhance sub-barrier fusion reactions and lower the effective fusion threshold.

abstract

The \(n/p\) asymmetry of the material found in the mid-velocity or “neck” region of an intermediate energy heavy-ion reaction is determined. In order to accomplish this task data from two different experiments are utilized. While the \(n/p\) asymmetry of the light particles is enriched in neutrons relative to the bulk matter, the total material found at mid-rapidity has an asymmetry very little different from that of the bulk system. This implies that, for the reaction studied, isospin equilibration plays a minor role in determining the isospin of the material found in the intermediate velocity region.

abstract

The development of Extensive Air Showers (EAS) is driven by the hadronic interactions of the primary and secondary particles with the atmospheric nuclei. Hence a careful analysis of the EAS appearance, in particular of the hadronic component, provides valuable information on features of the hadronic interaction. Especially, in ultrahigh energy regions extending the energy limits of man-made accelerators and the experimental knowledge from collider experiments, the hadronic interaction is subject of uncertainties and debates. Since the EAS development is dominantly governed by soft processes, which are not accessible to a perturbative QCD treatment, one has to rely on QCD inspired phenomenological interaction models, in particular on string models based on the Gribov–Regge theory, like VENUS, QGSJET and SIBYLL. Recent results of EAS experiments are scrutinised in terms of such models, used as generators in the Monte Carlo EAS simulation code CORSIKA.

abstract

Results of a complex analysis of \(^{40}\)Ar + \(^{159}\)Tb collision data obtained from inclusive and coincidence measurements are presented. The experimental results support the binary nature of projectile like fragments close in \(Z\) to the projectile. Indirect evidences for primary projectile and projectile like fragment breakup following transfer reaction and/or inelastic scattering were found.