Production cross sections for intermediate mass fragments from dynamical and statistical decay of projectile-like fragments in ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ and ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ collisions at $35A$ MeV

Background: In heavy-ion collisions at intermediate energies the production of light charged particles and intermediate mass fragments (IMFs) is due to different reaction mechanisms and different time scales, ranging from fast dynamical processes to statistical emission from the equilibrated system.

Purpose: We compare the IMF statistical and dynamical emission probabilities in collisions of a neutron-rich ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ system and a neutron-poor ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ system at the laboratory energy of 35 $A$ MeV.

Method: The IMFs production mechanism in semiperipheral reactions has been investigated in our previous works. In this paper, the analysis is expanded for the same set of data and production cross sections have been evaluated for dynamical and statistical emission in a coherent way for light and heavy fragments.

Results: The data analysis has evidenced a strong competition between dynamical and statistical emission mechanisms. Probability of the dynamical emission of IMFs is strongly influenced by the ($N/Z$) ratio of the colliding system.

Conclusions: It is demonstrated that the statistical emission is equally probable for the two systems, while the dynamical emission is enhanced for the neutron-rich system, especially for heavy fragments ($Z\ge 6$). The observed effect points at a high sensitivity of the prompt-dynamical emission to the ($N/Z$) ratio of a given system.

Figure 1

Panels (a) and (c): Atomic number $Z$ vs parallel-to-the-beam velocity $V_{\mathrm{par}}$ plots for PLF residues in the ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ and ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ systems, respectively. Panels (b) and (d): $Z$ vs $V_{\mathrm{par}}$ plots for IMFs and TLFs in coincidence with PLF residues for the same systems.

Figure 2

(a) Probabilities of different IMF multiplicities (in coincidence with PLF residues) normalized to the number of selected events for the ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ (full circles) and ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ (empty triangles) systems. (b) Cross sections corresponding to different IMF multiplicities for the same systems. (c) Ratios of probabilities displayed in panel (a) for the ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ and ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ reactions, plotted as a function of the IMF multiplicity. All the plots are corrected for detection efficiency.

Figure 3

Plots for the ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ system: (a) Relative velocity between PLF and IMF for IMFs of $Z=10$, normalized to the velocity given by the Viola systematics (black line). Dashed area represents events satisfying condition of Eq. (1). (b) Distribution of the velocity component $V_{\mathrm{par}}$ (parallel to the beam axis) in the laboratory reference frame for IMFs of $Z=10$ (black line). Dashed area represents events satisfying condition of Eq. (1). (c) Invariant cross-section plot ($V_{\mathrm{par}}$ vs $V_{\mathrm{per}}$, where $V_{\mathrm{per}}$ is the perpendicular component) for PLF residues. (d) Invariant cross-section plot for IMFs of $Z=10$. (e) Angular distribution of IMFs of $Z=10$ originated from PLF* splitting (full black line). (f) Invariant cross-section plot for IMFs of $Z=10$ and $\text{cos}\left({\theta }_{\mathrm{prox}}\right)<0$.

Figure 4

(a) Dynamical IMF emission cross sections (in mbarn) for the ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ (full circles) and ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ (empty circles) systems. (b) Statistical IMF emission cross sections (in mbarn) for the ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ (full triangles) and ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ (empty triangles) systems. (c) Ratios of the cross sections for the two Sn + Ni systems, neutron rich over neutron poor, for the dynamical (circles) and statistical emission (triangles). The cross sections in panels (a) and (b) and the ratios in panel (c) are plotted as a function of $Z$ of the IMF.

Figure 5

(a) Ratio of the dynamical component of the cross section to its combined (dynamical + statistical) value plotted as a function of the IMF atomic number $Z$, for the ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ (full circles) and ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ (empty circles) systems. (b) Ratios of the dynamical-to-statistical cross sections plotted as a function of the IMF atomic number $Z$ for both Sn + Ni systems.