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.
SEP researchers and their colleagues at the National Superconducting Cyclotron Laboratory (NSCL) on the campus of Michigan State University have recently developed a consistent theoretical interpretation of a range of nucleus-nucleus collision data previously measured at the NSCL. The crosshatched region of the graph shows the allowed values for the symmetry energy and its contribution to pressure in pure neutron matter at saturation density.