Nuclear matter symmetry energy at 0.03⩽ρ/ρ0⩽0.2

Measurements of the density dependence of the symmetry free energy in low-density clustered matter have been extended using the Neutron Ion Multidetector for Reaction Oriented Dynamics at Texas A&M University. Thermal coalescence models were employed to extract densities ρ and temperatures T for evolving systems formed in collisions of 47A MeV ⁴⁰Ar+¹¹²Sn,¹²⁴Sn and ⁶⁴Zn+¹¹²Sn, ¹²⁴Sn. Densities of 0.03⩽ρ/ρ₀⩽0.2 and temperatures in the range 5-10 MeV have been sampled. The symmetry free energy coefficients are found to be in good agreement with values calculated using a quantum statistical model. Values of the corresponding symmetry free energy coefficient are derived from the data using entropies derived from the model.