Isospin dynamics on neck fragmentation in isotopic nuclear reactions

TL;DR

This study uses an isospin dependent transport model to analyze neck fragmentation in isotopic nuclear reactions, revealing how neutron/proton ratios are sensitive to the nuclear symmetry energy, especially at sub-saturation densities.

Contribution

It introduces systematic analysis of isospin effects on neck fragmentation, highlighting the sensitivity of particle ratios to the symmetry energy's density dependence in nuclear reactions.

Findings

Neutron/proton ratios depend on symmetry energy stiffness.

Double ratio distributions show a flat tail spectrum.

IMF neutron/proton ratios are less sensitive to symmetry energy.

Abstract

The neck dynamics in Fermi-energy heavy-ion collisions, to probe the nuclear symmetry energy in the domain of sub-saturation densities, is investigated within an isospin dependent transport model. The single and double ratios of neutron/proton from free nucleons and light clusters (complex particles) in the isotopic reactions are analyzed systematically. Isospin effects of particles produced from the neck fragmentations are explored, which are constrained within the midrapidities ($|y/y_{proj}|<$0.3) and azimuthal angles (70$^{o}\sim$110$^{o}$, 250$^{o}\sim$290$^{o}$) in semiperipheral nuclear collisions. It is found that the ratios of the energetic isospin particles strongly depend on the stiffness of nuclear symmetry energy and the effects increase with softening the symmetry energy, which would be a nice probe for extracting the symmetry energy below the normal density in experimentally. A flat structure appears at the tail spectra from the double ratio distributions. The neutron to proton ratio of light intermediate mass fragments (IMFs) with charged number Z$\leq$8 is related to the density dependence of symmetry energy with less sensitivity in comparison to the isospin ratios of nucleons and light particles.