Finite-size effects on fragmentation in heavy-ion collisions

To investigate the influence of nuclear finite-size effects on the fragmentation in heavy-ion collisions, the fragment charge distributions of ${}^{40}$Ca+${}^{40}$Ca, ${}^{197}$Au+${}^{197}$Au, ${}^{120}$Xe+${}^{129}$Sn, and ${}^{58}$Ni+${}^{48}$Ca at intermediate incident energies are studied by using the improved quantum molecular dynamics model. Both the width of the wave packet at the coordinate space and the surface energy term strongly affect the formation and stability of fragments at intermediate-low energies. The wave-packet width influences the stability and the central densities of the initial nuclei. With increase of incident energies, the influence of the detail in description of individual nucleons and of their interaction via mean field on the fragment distributions weakens gradually.

Figure 1

Fragment charge distributions for central collisions of ${}^{40}$Ca+${}^{40}$Ca at incident energy of 35A MeV, ${}^{120}$Xe+${}^{129}$Sn at 39A MeV and ${}^{197}$Au+${}^{197}$Au at 35, 60A MeV. The solid squares and open circles denote the results of the ImQMD model and the experimental data, respectively.

Figure 2

Upper panels: Average number of emitted nucleons from the ground-state nuclei of ${}^{40}$Ca and ${}^{197}$Au at $t=3000$ fm/c with different wave-packet width. Lower panels: Central density of the ground-state nuclei of ${}^{40}$Ca and ${}^{197}$Au at $t=500$ fm/c.

Figure 3

Charge distributions of fragments of ${}^{40}$Ca+${}^{40}$Ca and ${}^{197}$Au+${}^{197}$Au at low and intermediate energies with different wave-packet width.

Figure 4

Time evolution of a typical event for the ground state ${}^{197}$Au and ${}^{90}$Zr by setting the surface energy coefficient $g_0=0$.

Figure 5

Charge distributions of fragments for ${}^{40}$Ca+${}^{40}$Ca and ${}^{197}$Au+${}^{197}$Au with different surface energy coefficients. The open and solid circles denote the results with the surface energy coefficient $g_0=7$ and 18 MeV$$fm${}^2$, respectively.

Figure 6

Calculated fragment charge distributions for (a) central collisions of ${}^{58}$Ni+${}^{48}$Ca at incident energies of 25 and 35A MeV and (b) peripheral collisions of ${}^{197}$Au+${}^{197}$Au at $E=35A$ MeV, with the ImQMD model by using the parameter set IQ3. The experimental data for the mean elemental event multiplicity [30] and the corresponding results of the statistical multifragmentation model (SMM) [30] are also presented for comparison in (b).

Figure 7

Isotope distributions for central collisions of ${}^{58}$Ni+${}^{48}$Ca at incident energies of 35A MeV with IQ3. $N$ and $Z$ denote the neutron and proton number of fragments, respectively.