Heavy Ion Phase Space Exploration Research Articles

Examination of cluster production in excited light systems at Fermi energies from new experimental data and comparison with transport model calculations

Four different reactions, $^{32}$S+$^{12}$C and $^{20}$Ne+$^{12}$C at 25 and 50 MeV/nucleon, have been measured with the FAZIA detector capable of full isotopic identification of most forward emitted reaction products. Fragment multiplicities, angular distributions and energy spectra have been measured and compared with Monte Carlo simulations, i.e. the antisymmetrized molecular dynamics (AMD) and the heavy-ion phase space exploration (HIPSE) models. These models are combined with two different afterburner codes (HF$l$ and SIMON) to describe the decay of the excited primary fragments. In the case of AMD, the effect of including the clustering and inter-clustering processes to form bound particles and fragments is discussed. A clear confirmation of the role of cluster aggregation in the reaction dynamics and particle production for these light systems, for which the importance of the clustering process increases with bombarding energy, is obtained.

Pre-equilibrium Effects of the Hot Nuclei De-excitation via GDR Emission --- Theoretical Approach

The hot rotating nuclei could be formed in the complete and incomplete fusion reaction of two heavy ions. At low bombarding energies the reaction goes via compound nucleus formation and subsequent evaporation of charged particles, neutrons and $\gamma$-rays. However, with increasing the energy of the projectile, the emission of particles during the equilibration process becomes more and more probable. This effect can be estimated by the Heavy-Ion Phase-Space Exploration (HIPSE) code which describes the production of clusters of various size from nucleons initially in the target or projectile. This dynamic evolution finalizes with the compound nuclei, quasi-fission or multi-fragmentation products. The hot rotating nuclei produced in fusion reaction can de-excitate by evaporation of particles and emission of $\gamma$-rays from the Giant Dipole Resonance, or by fission into two fragments. These processes, evaporation and fission, are described within statistical codes such as GEMINI++ or in dynamical approaches by solving the transport equations of Langevin type. In the present article we will concentrate on the possible effect of the pre-equilibrium emission on the strength function of the effective Giant Dipole Resonance, which can be described within Thermal Shape Fluctuation Model (TSFM) approach.

A model for projectile fragmentation

A model for projectile fragmentation is developed whose origin can be traced back to the Bevalac era. The model positions itself between the phenomenological EPAX parametrization and transport models like "Heavy Ion Phase Space Exploration" (HIPSE) model and antisymmetrised molecular dynamics (AMD) model. A very simple impact parameter dependence of input temperature is incorporated in the model which helps to analyze the more peripheral collisions. The model is applied to calculate the charge, isotopic distributions, average number of intermediate mass fragments and the average size of largest cluster at different Zbound of different projectile fragmentation reactions at different energies.

Projectile fragmentation reactions of40Ar at 57 MeV/nucleon

The projectile fragmentation reactions of ${}^{40}$Ar at 57 MeV/nucleon on ${}^{9}$Be and ${}^{181}$Ta targets have been studied by the Radioactive Ion Beam Line in Lanzhou (RIBLL) at the Heavy-Ion Research Facility in Lanzhou (HIRFL). The momentum distributions of fragments have been measured and the competition between different mechanisms are observed. The production cross sections have been obtained and compared with the empirical parametrization of fragmentation cross section (EPAX), abrasion-ablation (AA), and heavy-ion phase space exploration (HIPSE) models, and the target dependence of fragment cross sections has also been discussed.

Model for projectile fragmentation: Case study for Ni on Ta and Be, and Xe on Al

For projectile fragmentation, we work out details of a model whose origin can be traced back to the Bevalac era. The model positions itself between the phenomenological empirical parametrization of fragmentation cross sections (EPAX) and microscopic transport models like the heavy ion phase-space exploration (HIPSE) model and antisymmetrized molecular dynamics (AMD) model. We apply the model to some recent data of projectile fragmentation of Ni on Ta and Be at beam energy 140 MeV/nucleon and some older data of Xe on Al at beam energy 790 MeV/nucleon. Reasonable values of cross sections for various composites populated in the reactions are obtained.

Isoscaling in projectile fragmentation reaction induced by 40,48Ca and 58,64Ni

The reactions of 40,48Ca + 9Be and 58,64Ni+ 9Be at 140 A MeV were studied by using the heavy ion phase-space exploration(HIPSE) model. Isoscaling behavior was observed. By introducing different evaporation method for the hot (before evaporation) fragments, the effect of evaporation on the isoscaling behavior by HIPSE model has been discussed.

Isoscaling Behavior in 48,40Ca+9Be Collisions at Intermediate Energy Investigated by the HIPSE Model

The fragment production cross sections for 140 MeV/nucleon 48,40Ca+9Be reactions are calculated by the heavyion phase space exploration (HIPSE) model. Isoscaling behavior is observed. The isoscaling parameters α and β for both heavy and light fragments from the HIPSE model calculations are in good agreement with the experimental data. It is shown that the potential parameters in the HIPSE model have very little effect on the isoscaling parameters. The effect of the excitation energy and evaporation on the isoscaling behavior is also discussed.

Isoscaling behavior studied by HIPSE model

The isoscaling behavior in the reaction system of 58,64Ni + 9Be has been studied by using the heavy-ion phase-space exploration(HIPSE) model. The extracted isoscaling parameters α and β for both heavy and light fragments for HIPSE model calculations are in good agreement with recent experimental data. The investigation shows that the parameters in the HIPSE model have some effect on the isoscaling parameter. The isoscaling parameters for hot and cold fragments have been extracted.

Transport model simulations of projectile fragmentation reactions at 140 MeV/nucleon

The collisions in four different reaction systems using $^{40,48}\mathrm{Ca}$ and $^{58,64}\mathrm{Ni}$ isotope beams and a Be target have been simulated using the heavy ion phase space exploration and the antisymmetrized molecular dynamics models. The present study mainly focuses on the model predictions for the excitation energies of the hot fragments and the cross sections of the final fragments produced in these reactions. The effects of various factors influencing the final fragment cross sections, such as the choice of the statistical decay code and its parameters, have been explored. The predicted fragment cross sections are compared to the projectile fragmentation cross sections measured with the A1900 mass separator. At $E/A=140$ MeV, reaction dynamics can significantly modify the detection efficiencies for the fragments and make them different from the efficiencies applied to the measured data reported in the previous work. The effects of efficiency corrections on the validation of event generator codes are discussed in the context of the two models.

Event generator for nuclear collisions at intermediate energies

An event generator, HIPSE (heavy-ion phase-space exploration), dedicated to the description of nuclear collisions in the intermediate energy range is presented. Based on the sudden approximation and on geometrical hypothesis, it can conveniently simulate heavy-ion interactions at all impact parameters and thus can constitute a valuable tool for the understanding of processes such as neck emission or multifragmentation in peripheral or∕and central collisions. After a detailed description of the ingredients of the model, first comparisons with experimental data collected by the INDRA Collaboration are shown. Special emphasis is put on the kinematical characteristics of fragments and light particles observed at all impact parameters for $\text{Xe}+\text{Sn}$ reactions at 25 and $50\phantom{\rule{0.3em}{0ex}}\text{MeV}∕\mathrm{nucleon}$ and $\text{Ni}+\text{Ni}$ at $82\phantom{\rule{0.3em}{0ex}}\text{MeV}∕\mathrm{nucleon}$.