Enhancement of kinetic energy fluctuations due to expansion

Global equilibrium fragmentation inside a freeze-out constraining volume is a working hypothesis widely used in nuclear fragmentation statistical models. In the framework of classical Lennard-Jones molecular dynamics, we study how the relaxation of the fixed volume constraint affects the posterior evolution of microscopic correlations, and how a nonconfined fragmentation scenario is established. A study of the dynamical evolution of the relative kinetic energy fluctuations was also performed. We found that asymptotic measurements of such an observable can be related to the number of decaying channels available to the system at fragmentation time.

Figure 1

Upper panel: energy $E_{\mathit{crit}}$ at which transition signals are detected in a confined, finite size fragmenting system, as a function of the system density. Lower panel: same transition line in the temperature-density plane (see text for details). The arrows indicate the density values considered for the present calculations.

Figure 2

(Color online) Confined ECRA vs asymptotic MST mass spectra calculated for three different initial densities: $\rho =0.026{\sigma }^{-3},0.1{\sigma }^{-3}$, and $0.6{\sigma }^{-3}$ shown in first, second, and third columns, respectively.

Figure 3

(Color online) Upper panels (a,b,c): MST fragment spectra calculated at $t=20,30,40$, and $300t_0$ for a $\rho =0.6{\sigma }^{-3}$ system at three different energies. Middle panels (d,e,f): $A_K\left(t\right)$ (red circles) and MST-biggest cluster mass (dashed lines) as a function of time. Lower panels (g, h,i): Total kinetic energy (solid line) and Kinetic energy fluctuations (red circles) as a function of time.

Figure 4

Top: relative kinetic energy fluctuations as a function of the total energy for densities ${\rho }_1$ (circles), ${\rho }_2$ (squares), and ${\rho }_3$ (diamonds). Middle: same as top, but evaluated at the time of ${\sigma }_K$ stabilization [$t\left({\rho }_1\right)\sim 5t_0$, $t\left({\rho }_2\right)\sim 30t_0$, $t\left({\rho }_3\right)\sim 40t_0$]. Bottom: same as top, but evaluated for asymptotic configurations. See text for details.