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, $\rho$, and temperatures, $T$, for evolving systems formed in collisions of 47 $A$ MeV ${}^{40}$Ar + ${}^{112}$Sn,${}^{124}$Sn and ${}^{64}$Zn + ${}^{112}$Sn, ${}^{124}$Sn. The yields of $d$, $t$, ${}^3$He, and ${}^4$He have been determined at $\rho$ = 0.002 to 0.032 nucleons/fm${}^3$ and $T$= 5 to 10 MeV. The experimentally derived equilibrium constants for $\alpha$ 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.