Isotopic dependence of the fragments' internal temperatures observed in multifragment emission

TL;DR

This study investigates how the internal temperatures of nuclear fragments depend on their isotopic composition, revealing that proton-rich isotopes are hotter and that this dependence varies with source properties, challenging previous interpretations of emission processes.

Contribution

It introduces a microcanonical statistical model to analyze isotope-dependent temperatures of nuclear fragments at breakup, providing new insights into their isospin sensitivity and emission mechanisms.

Findings

Proton-rich isotopes are hotter than neutron-rich ones.

Temperature dependence on isotopic composition varies with source isospin.

Sensitivity decreases as the excitation energy of the source increases.

Abstract

The internal temperatures of fragments produced by an excited nuclear source are investigated using the microcanonical version of the Statistical Multifragmentation Model, with discrete energy. We focus on the fragments' properties at the breakup stage, before they have time to deexcite by particle emission. Since the adopted model provides the excitation energy distribution of these primordial fragments, it allows one to calculate the temperatures of different isotope families and infer on the sensitivity to their isospin composition. It is found that, due to the functional form of the nuclear density of states and the excitation energy distribution of the fragments, proton rich isotopes are hotter than neutron rich ones. This property has been taken to be an indication of earlier emission of the former from a source that cools down as it expands and emits fragments. Although this scenario is incompatible with the prompt breakup of a thermally equilibrated source, our results reveal that the latter framework also provides the same qualitative features just mentioned. Therefore they suggest that this property cannot be taken as evidence for non-equilibrium emission. We also found that this sensitivity to the isotopic composition of the fragments depends on the isospin composition of the source, and that it is weakened as the excitation energy of the source increases.