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 $50\text{MeV}∕\mathrm{nucleon}$ and $\text{Ni}+\text{Ni}$ at $82\text{MeV}∕\mathrm{nucleon}$.

Figure 1

Evolution of the nuclear potential $V_{A_T{A}_P}$ as a function of the relative distance for the ${}^{129}\mathrm{Xe}+{}^{120}\mathrm{Sn}$ system for ${\alpha }_a=0$, 0.1, and 0.2.

Figure 2

Example of nuclear dynamics obtained for the reaction ${}^{129}\mathrm{Xe+}{}^{120}\mathrm{Sn}$ at $E=50\text{MeV}∕\text{nucleon}$. From top to bottom, the initial impact parameters $b=9\text{fm}$, $b=6\text{fm}$, and $b=2\text{fm}$ are presented. In each case, from left to right figures correspond to the initial cluster configuration $\left(t=0\text{fm}∕c\right)$, the configuration before and after the reaggregation $\left(t=50\text{fm}∕c\right)$, and during the deexcitation $(t=300\text{fm}∕c)$.

Figure 3

Values of the different parameters of the model as a function of the beam energy for the reaction ${}^{129}\mathrm{Xe}+{}^{120}\mathrm{Sn}$ (filled circles) and ${}^{58}\mathrm{Ni}+{}^{58}\mathrm{Ni}$ (squares). From top to bottom, we present, respectively, the evolution of the parameter associated with the potential hardness ${\alpha }_a$, the rate of exchange of particles between the target and projectile, $x_{\mathrm{tr}}$ (in percent), and the percentage of nucleon-nucleon collisions in the overlap region, $x_{\mathrm{coll}}$ (in percent).

Figure 4

Bidimensional $Z\text{−}{v}_{∕∕}∕v_{\mathrm{proj}}$ for the reaction ${}^{129}\mathrm{Xe}+{}^{120}\mathrm{Sn}$ at $50\text{MeV}∕\text{nucleon}$ as given by the HIPSE event generator. Each panel is associated with a reduced impact parameter range indicated on top of the panel. For the sake of clarity, only $Z⩾3$ have been considered.

Figure 5

Same as Fig. 4 for fragments created after the reaggregation phase and before the deexcitation.

Figure 6

Same as Fig. 4 but for the atomic number distribution. In light gray, we present the initial charge distribution while dark gray corresponds to the distribution after deexcitation.

Figure 7

Mean total initial excitation energy [given by Eq. (3)] vs reduced impact parameter $b_{\mathrm{red}}$ for $\mathrm{Xe}+\mathrm{Sn}$ at 25, 50, and $80\text{MeV}∕\mathrm{nucleon}$.

Figure 8

Distributions of experimental (full circles) and calculated (histogram) ${\theta }_{\mathrm{flow}}$ for ${}^{129}\mathrm{Xe}+{}^{120}\mathrm{Sn}$ reactions at $25\text{MeV}∕\mathrm{nucleon}$ (top), $50\text{MeV}∕\mathrm{nucleon}$ (middle), and $\text{Ni}+\text{Ni}$ at $82\text{MeV}∕\mathrm{nucleon}$ (bottom). Data have been selected with help of criterium $\left(\mathrm{b}\right)$ (see text).

Figure 9

Impact parameter distributions for the reaction ${}^{129}\mathrm{Xe}+{}^{120}\mathrm{Sn}$ at $50\text{MeV}∕\text{nucleon}$ as given by the model. Unfilled histogram: all simulated events. Other histograms are labeled according to the selection discussed in the text. Note that, in cases (b) and (c) the distributions have been multiplied by a factor 4.

Figure 10

Three-dimensional plots (in log scale) $v_{∕∕}∕v_{\mathrm{proj}}\text{−}Z$. Top panels are for experimental data while bottom panels are for simulated data. Event selection corresponds to case (a) (see text). Only fragments with atomic numbers larger than or equal to three are included in the figure.

Figure 11

Experimental (black points) and calculated (filled histograms) atomic number multiplicity per event for the reactions indicated on top of each panel. Top, event selection (a); middle, event selection (b); bottom; event selection (c).

Figure 12

Mean kinetic energy in the center-of-mass as a function of the charge $Z$: experimental data (black points), simulated data (filled histograms). Reactions are indicated on top of each panel. Selections are (a), (b), and (c), respectively, from top to bottom.

Figure 13

Mean kinetic energy in the center of mass as a function of the center of mass emission angle. Black points are experimental data while filled histograms are for calculated data. The considered particles and the system under study are indicated in each panel. Events have been selected with the criterium (b). For $E∕A=50$ and $82\text{MeV}$, we also present in light gray the proton and $\alpha$ particle distributions obtained when nucleon-nucleon collisions are omitted $\left(x_{\mathrm{coll}}=0\%\right)$.

Figure 14

Experimental (black points) and calculated (filled histograms) $v_{∕∕}$ distributions calculated in the center of mass for different kinds of nuclear species for the three reactions indicated on top of each panel. Event selection: case (b)