Laboratory Tests of Low Density Astrophysical Equations of State

Clustering in low density nuclear matter has been investigated using the NIMROD multi-detector at Texas A&M University. Thermal coalescence modes were employed to extract densities, ρ, and temperatures, T, for evolving systems formed in collisions of 47 A MeV ⁴⁰Ar + ¹¹²Sn,¹²⁴Sn and ⁶⁴Zn + ¹¹²Sn, ¹²⁴Sn. The yields of d, t, ³He, and ⁴He have been determined at ρ = 0.002 to 0.032 nucleons/fm³ and T= 5 to 10 MeV. The experimentally derived equilibrium constants for α particle production are compared with those predicted by a number of astrophysical equations of state. The data provide important new constraints on the model calculations.