Collective Flow: nuclear equation of state.

The determination of the equation of state (EOS), the relationship between pressure and volume for nuclear matter, is an important objective of nuclear physics. Information about the equation of state can be extracted from the collective flow of nuclear matter deflected sidewards from the hot and dense region formed by the overlap of projectile and target nuclei. The schematic diagram at the right illustrates the nuclear matter distributions for the projectile and target nuclei before the collision (on the left) and and a sidewards deflection of the nuclear matter after the collision (on the right) which is frequently termed "sidewards collective flow". This flow reflects the interplay of collective and random motions. For a thermalized system, the random motions of emitted fragments are dictated by the thermal energy, which is independent of mass. Contributions to the fragment energy due to collective motion, on the other hand, increase linearly with mass, making the flow more easily observed for heavier fragments

The figure to the right illustrates how the sidewards flow increases with fragment mass (A). Model calculations denoted by the curves in the figure imply that the fragment flow provides an excellent indication of the underlying flow of nuclear matter and pressure that drives this flow. Comparisons between the flow for different projectile and target nuclei and different incident energies now permit determinations of the incompressibility of nuclear matter.


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William G. Lynch, 1997