Systematic study of ${}^{16}\mathrm{O}$-induced fusion with the improved quantum molecular dynamics model

The heavy-ion fusion reactions with ${}^{16}\mathrm{O}$ bombarding on ${}^{62}\mathrm{Ni},{}^{65}\mathrm{Cu},{}^{74}\mathrm{Ge},{}^{148}\mathrm{Nd},{}^{180}\mathrm{Hf},{}^{186}\mathrm{W},{}^{208}\mathrm{Pb},{}^{238}\mathrm{U}$ are systematically investigated with the improved quantum molecular dynamics model. The fusion cross sections at energies near and above the Coulomb barriers can be reasonably well reproduced by using this semiclassical microscopic transport model with the parameter sets SkP* and IQ3a. The dynamical nucleus-nucleus potentials and the influence of Fermi constraint on the fusion process are also studied simultaneously. In addition to the mean field, the Fermi constraint also plays a key role for the reliable description of the fusion process and for improving the stability of fragments in heavy-ion collisions.

Figure 1

Fusion excitation functions of ${}^{16}\mathrm{O}+{}^{62}\mathrm{Ni},{}^{65}\mathrm{Cu},{}^{74}\mathrm{Ge}$, and ${}^{148}\mathrm{Nd}$. The solid circles denote the experimental data taken from Refs. [18, 19, 20, 21], respectively. The blue curves denote the results with an empirical barrier distribution in which the fusion barrier is obtained by using the Skyrme energy-density functional together with the extended Thomas-Fermi (ETF2) approximation [3, 4]. The solid squares and open circles denote the results of ImQMD with the parameter set SkP* and IQ3a, respectively. The statistical errors in the ImQMD calculations are given by the error bars.

Figure 2

The same as Fig. 1, but for reactions ${}^{16}\mathrm{O}+{}^{180}\mathrm{Hf},{}^{186}\mathrm{W},{}^{208}\mathrm{Pb}$, and ${}^{238}\mathrm{U}$. The experimental data are taken from Refs. [22, 23, 24, 25, 26]. Here the initial distance between the reaction partners in the $z$ direction (beam direction) is taken to be $d_0=40$ fm.

Figure 3

(a),(c) Nucleus-nucleus potential for ${}^{16}\mathrm{O}+{}^{74}\mathrm{Ge}$ and ${}^{16}\mathrm{O}+{}^{148}\mathrm{Nd}$. The circles and solid curves denote the results of the ImQMD simulations and the entrance-channel potential with the Skyrme energy-density functional plus the ETF2 approach, respectively. The squares denote the extracted most probable barrier height from the measured fusion excitation function. (b),(d) Empirical barrier distribution function proposed in Ref. [3].

Figure 4

The same as Fig. 3, but for ${}^{16}\mathrm{O}+{}^{186}\mathrm{W}$ and ${}^{16}\mathrm{O}+{}^{208}\mathrm{Pb}$.

Figure 5

Density distribution of ${}^{16}\mathrm{O}+{}^{186}\mathrm{W}$ at $E_{\mathrm{c}.\mathrm{m}.}=66$ MeV and $t=500$ fm/$c$.

Figure 6

Charge distribution of fragments in fusion reaction ${}^{16}\mathrm{O}+{}^{92}\mathrm{Zr}$ at an incident energy of $E_{\mathrm{c}.\mathrm{m}.}=45$ MeV and $t=700$ fm/$c$. The solid red bars and the black open bars denote the results with and without the Fermi constraint being taken into account, respectively. The inset in (a) shows fusion probability as a function of impact parameter for this reaction.

Figure 7

(a) Momentum distribution of nucleons along the $p_y$ axis in ${}^{16}\mathrm{O}+{}^{92}\mathrm{Zr}$ at $E_{\mathrm{c}.\mathrm{m}.}=45$ MeV and $t=700$ fm/$c$. (b) Corresponding density distribution of the system along the $z$ axis.