Representation of the constraints on the density dependence of symmetry energy (inset) and pressure as a function of the symmetry energy at saturation density in neutron matter. The hatched areas are extracted from recent analyses of nuclear collisions of Sn nuclei. Open rectangles and the symbol in the inset were obtained from the properties of individual nucleus.
EOS physics at FRIB
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The nuclear equation of state is a thermodynamic description of the average behavior of a large volume of nuclear matter in exact analogy to the equation of state of a gas or any other phase of matter. The nuclear symmetry energy is a component of the nuclear equation of state that describes the variation of the nuclear binding energy as a function of proton (Z) and neutron (N) numbers. While the range of neutron-to-proton number is relatively small in nuclei, neutron stars are thought to be close to pure neutron matter. In this case the nature and stability of phases within the star, the composition and the thickness of its inner crust, the frequencies of vibrations of the crust and its radius, among other properties, depend strongly on the symmetry energy and its density dependence.
Determination of the nuclear equation of state of asymmetric matter and understanding the nature of dense neutron-rich matter in neutron stars were identified in the Rare Isotope Science Assessment Committee report as a key issue driving the proposed construction of the Facility for Rare Isotope Beams at Michigan State University.
Preliminary constraints have been obtained recently at the sub-saturation density region. The goal of Symmetry Energy Project is to determine the density dependence of the symmetry energy beyond the normal nuclear matter density and to improve the constraints obtained in the subnormal nuclear matter density regions.