fragment plays a crucial role in determining the physical process behind its formation. In Fig. \[fig:1\], we display the average density $\left<\rho/\rho_0\right>$ reached in a typical reaction as a function of time at different incident energies for $^{132}$Sn + $^{132}$Sn by using the soft symmetry energy $\gamma_i~=~0.5$. The average nucleon density is calculated as [@Aich91] $$\begin{aligned}
\langle \rho \rangle ~=~\langle\frac{1}{A_T+A_P}&
&\sum_{i=1}^{A_T+A_P}\sum_{j=1}^{A_T+A_P}
\frac{1}{(2\pi L)^{3/2}}\nonumber\\
& &\cdot exp[-(\vec{r_i}-\vec{r_j})^{2}/2L]\rangle,\end{aligned}$$ with $\vec{r}_i$ and $\vec{r}_j$ being the position coordinates of the $i^{th}$ and $j^{th}$ nucleons, respectively.

As we have expected, with increasing of incident energy, the density is found to increase in the compression zone. Interestingly, at lower beam energies, the maximum density reached is lower and the reaction time is longer. With increasing incident energy, the life-time of the high-density nuclear matter gets shorter due to instability. For example, at b = 2 fm the average density reaches a maximum and is close to normal nuclear matter density at $t$= 18 and 33 fm/c, respectively, for E = 50 MeV/nucleon; but for the case of E = 600 MeV/nucleon, the respective times are 10 and 20 fm/c. This means that the difference between the two times is almost 15 fm/c at E = 50 