Experimental signals of a nuclear liquid-gas phase transition

Abstract

Zn at beam energy of 35 MeV/nucleon. Yields of fragments arising from fragmenting quasi-projectiles (QPs) with different neutron-proton asymmetries were analyzed within the framework of the Landau free energy approach. Fits to the free energy of fragments as a function of fragment asymmetry showed three minima, indicating the system to be in a regime of a first-order phase transition. The QP temperature estimates were extracted from the analysis of N=Z fragment data. Additionally, we make use of a recent method based on quantum fluctuations of fermions to derive temperatures and densities of selected QPs. Critical scaling of these observables is found for systems which differ in neutron to proton asymmetry. The derived critical exponent β = 0.35 ± 0.01, belongs to the liquid-gas universality class.

Coulomb corrections to experimental temperatures and densities in Fermi-energy heavy-ion collisions

“…These experimental quantities and the corresponding critical values have shown a dependence on the system neutron-proton asymmetry. This paper extends our previous analysis [32][33][34] using protons as probe particles. We now provide additional results from the same experimental data set by Coulomb correcting temperature and density values.…”

“…In our recent works [32][33][34], we have reported on the experimental temperatures and densities of fragmenting systems produced in near Fermi-energy heavy-ion collisions by means of a quantum fluctuation method for protons. Since the protons represent the vapor phase, the derived densities and temperatures were shown to sample the vapor branch of the liquid-gas coexistence curve.…”

Novel technique to extract experimental symmetry free energy information for nuclear matter

“…Several studies [24][25][26] have shown this energy domain to be the region of the nuclear liquid-gas phase transition. In our recent works [27][28][29][30][31][32], we have analyzed fragment yield data to investigate the nuclear phase transition using the Landau free-energy approach [33,34]. In such an approach, the key assumption is that in the vicinity of the critical point, the fragment free energy per nucleon (F ) relative to the system temperature (T ) can be expanded in a power series in the fragment's neutronproton asymmetry m as given by the relation…”

“…Previously [31,32,50] the data were sorted into four different QP asymmetry bins of width 0.05, ranging from 0.04 to 0.24. In a subsequent paper [51], it was shown that values of T and ρ that correspond to an asymmetry bin width close to zero (as it should be for fixed A and Z) could be obtained by averaging values for all four asymmetry bins.…”

“…In this way, estimated errors on extracted F sym values were significantly minimized. The appearance of the three minima is a signature of a first-order phase transition of the system [27][28][29][30][31][32].…”