Isotopic equilibrium constants for very low-density and low-temperature nuclear matter

TL;DR

This paper investigates isotopic equilibrium constants in low-density, low-temperature nuclear matter through ternary fission yields, comparing experimental data with relativistic mean-field model calculations to understand medium effects and equilibrium achievement.

Contribution

It introduces a method to determine equilibrium constants from ternary fission yields and compares them with theoretical models to explore medium modifications and equilibrium conditions in nuclear matter.

Findings

Equilibrium achieved for lighter isotopes.

Heavier isotopes show reaction quotients below equilibrium constants.

Medium effects influence yield reductions and neutron-rich isotope enhancements.

Abstract

Yields of equatorially emitted light isotopes, $1\le Z\le 14$, observed in ternary fission in the reaction $^{241}$Pu($n_{\rm th}$,f) are employed to determine apparent chemical equilibrium constants for low-temperature and low-density nuclear matter. The degree of liberation and role of medium modifications are probed through a comparison of experimentally derived reaction quotients with equilibrium constants calculated using a relativistic mean-field model employing a universal medium modification correction for the attractive $\sigma$ meson coupling. The results of these comparisons indicate that equilibrium is achieved for the lighter ternary fission isotopes. For the heavier isotopes experimental reaction quotients are well below calculated equilibrium constants. This is attributed to a dynamical limitation reflecting insufficient time for full equilibrium to develop. The role of medium effects leading to yield reductions is discussed as is the apparent enhancement of yields for $^8$He and other very neutron rich exotic nuclei.