Employing ternary fission of $^{242}$Pu as a probe of very neutron rich matter

Detailed assessments of the ability of recent theoretical approaches to modeling existing experimental data for ternary fission confirm earlier indications that the dominant mode of cluster formation in ternary fission is clusterization in very neutron rich, very low density, essentially chemically equilibrated, nucleonic matter. An extended study and comparison of these approaches applied to ternary fission yields in the thermal neutron induced reaction $^{241}$Pu($n_{\rm th}$,f) has been undertaken to refine the characterization of the source matter. The resonance gas approximation has been improved taking in-medium effects on the binding energies into account. A temperature of 1.29 MeV, density of $6.7 \times 10^{-5}$ nucleons/fm$^3$ and proton fraction $Y_p$ = 0.035 are found to provide a good representation of yields of the ternary emitted light particles and clusters. In particular, results for $Z= 1$ and 2 isotopes are presented. Isotopes with larger $Z$ are discussed, and the roles of medium and continuum effects, even at very low density are illustrated.