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Suppression of multiplicity fluctuations has been observed for three light fermions (protons, tritons and 3He) in the multifragmentation of reconstructed hot quasi-projectiles produced in collisions of 32S (45 MeV/nucleon) with 112Sn. This suppression, predicted by recent calculations, is attributed to Pauli blocking and has also been observed in experiments with trapped Fermi gases. Experimental results on nuclear temperature and density employing a quantal approach based on momentum and multiplicity fluctuations are also presented. The extracted temperatures show a noticeable reduction when compared to a similarly derived classical method. This reduction in temperature is in agreement with previous predictions indicating that classically derived methods overpredict nuclear temperature as they do not take into account the Fermi motion of the nucleons. The present results underline the role of quantum statistics in nuclear disassembly and suggest the need for proper quantum treatment when dealing with the thermodynamic properties of fragmenting heavy ions. [ABSTRACT FROM AUTHOR]

Fragment yield data, selected with different values of the isospin asymmetry of the quasiprojectile from 78, 86Kr+58, 64Ni reactions at Elab = 35 MeV/nucleon, have been analyzed within the framework of Landau free energy approach. Fits to the free energy data indicated the system to be in the regime of a first-order phase transition. The plot of free energy versus isospin asymmetry of the fragments showed a systematic change with increasing isospin asymmetry of the fragmenting source. This observation demonstrated the role of quasiprojectile isospin asymmetry as an external field which governed the minima positions in the free energy plot. The position of the central minimum was found to be in close agreement with the average isospin asymmetry of the fragments calculated excluding neutrons and protons. Significant deviations from the free energy plot were observed for N = Z fragments, particularly for the lighter ones, which could be corrected after inclusion of odd-even effects in the analysis. Analysis of yield data of N = Z nuclei gave a reasonable estimate of temperature. Analysis of free energy data gated with excitation energy of the fragmenting source showed a dependence of fit parameters of Landau free energy equation on the excitation energy as well as isospin asymmetry of the source. [ABSTRACT FROM AUTHOR]

In this report, we review the isospin dependence of various forms of the collective flow in heavy-ion reactions from Fermi to relativistic energies. The emphasis will be on suggested possible applications in directly exploring the underlying isovector potential and thus the Equation of State (EoS) of asymmetric nuclear matter, in particular in density regions far away from normal conditions. We also discuss forthcoming challenges and opportunities provided by high-energy radioactive beams. [ABSTRACT FROM AUTHOR]

The quantum-fluctuation method using Coulomb corrections is explored to extract temperatures and densities of hot nuclear systems produced in Fermi-energy heavy-ion collisions. The role of the neutron-proton asymmetry of the system was investigated. Temperature values were observed to not depend on the system neutron-proton asymmetry while a clear dependence is seen for density values. Coulomb corrections have been shown to lower temperature values by almost 2 MeV. On the other hand, density results exhibit a small variation. [ABSTRACT FROM AUTHOR]

Correlations of midrapidity light charged particles (LCPs) and intermediate mass fragments (IMFs) with projectile-like fragments (PLFs) have been examined from the 35 MeV/u 70Zn + 70Zn, 64Zn + 64Zn, and 64Ni + 64Ni reaction systems. A new method was developed to examine the flow of the particles with respect to the PLF. The invariant PLF-scaled flow allowed for the dynamics of the midrapidity Z = 1-4 particles to be studied. Strong differences in the PLF-scaled flow were observed between the different isotopes. In particular, the most n-rich LCPs exhibited a negative PLF-scaled flow in comparison to the other LCPs. A classical molecular dynamics model and a three-body Coulomb trajectory simulation were both used to show that the PLF-scaled flow observable could be connected to the average order of emission of the LCPs. The experimental results suggest that the midrapidity region is preferentially populated with neutron-rich LCPs and Z = 3-4 IMFs at a relatively early stage in the collision. The deuteron and ³He particles are emitted later followed, lastly, by protons and alphas. The average order of emission of the midrapidity LCPs was extracted from the constrained molecular dynamics simulations and showed good agreement with the emission order suggested by the experimental PLF-scaled flow results. [ABSTRACT FROM AUTHOR]

The symmetry energy contribution to the nuclear equation of state impacts various phenomena in nuclear astrophysics, nuclear structure, and nuclear reactions. Its determination is a key objective of contemporary nuclear physics, with consequences for the understanding of dense matter within neutron stars. We examine the results of laboratory experiments that have provided initial constraints on the nuclear symmetry energy and on its density dependence at and somewhat below normal nuclear matter density. Even though some of these constraints have been derived from properties of nuclei while others have been derived from the nuclear response to electroweak and hadronic probes, within experimental uncertainties-they are consistent with each other. We also examine the most frequently used theoretical models that predict the symmetry energy and its slope parameter. By comparing existing constraints on the symmetry pressure to theories, we demonstrate how contributions of three-body forces, which are essential ingredients in neutron matter models, can be determined. [ABSTRACT FROM AUTHOR]

The NIMROD-ISiS array was used to study the transverse flow of intermediate mass fragments in 35 MeV/nucleon 70Zn + 70Zn, 64Zn + 64Zn, and 64Ni + 64Ni reactions. The intermediate mass fragment flow was previously shown to be sensitive to the density dependence of the symmetry energy. To explore the model dependence of the results, the antisymmetrized molecular dynamics, constrained molecular dynamics, and stochastic mean-field models were each compared to the experimental results to extract information on the form of the symmetry energy. The results demonstrate that sensitivity of the models to the nuclear equation of state can vary significantly based on the treatment of the nuclear dynamics. Despite the differences in the sensitivity, improved agreement with the experimental data is observed for each model with a stiff density dependence of the symmetry energy. [ABSTRACT FROM AUTHOR]

Previous work has quantified the degree of neutron-proton equilibration in heavy-ion nuclear collisions by observing the convergence of isospin observables (such as the isoscaling parameter a) to an expected value based on similar symmetric reaction systems. We present a new signature of equilibration: the convergence of the isospin asymmetry (as quantified by three isoscaling metrics) of two mirror asymmetric reaction systems toward each other rather than a predefined point. For the reactions of 35 MeV/u 64,70Zn+64,70Zn and 64Zn,64Ni+64Zn,64Ni the neutron-proton equilibration was found to be approximately 80%, and this result is compared directly to previous work. [ABSTRACT FROM AUTHOR]

We study neutron-proton equilibration in dynamically deformed atomic nuclei created in nuclear collisions. The two ends of the elongated nucleus are initially dissimilar in composition and equilibrate on a subzeptosecond time scale following first-order kinetics. We use angular momentum to relate the breakup orientation to the time scale of the breakup. The extracted rate constant is 3zs-1, which corresponds to a mean equilibration time of 0.3 zs. This technique enables new insight into the nuclear equation of state that governs many nuclear and astrophysical phenomena leading to the origin of the chemical elements. [ABSTRACT FROM AUTHOR]