Surface Boiling - a New Type of Instability of Highly Excited Atomic Nuclei

TL;DR

This paper introduces surface boiling as a new instability in highly excited atomic nuclei, explaining observed saturation patterns in nuclear caloric curves through a finite-system instability mechanism.

Contribution

It identifies surface boiling as a novel instability in finite nuclear systems, linking it to negative heat capacity and caloric curve behavior.

Findings

Finite and infinite systems become unstable at high excitation energies.

Surface boiling explains saturation-like patterns in nuclear caloric curves.

Negative heat capacity is associated with the instability.

Abstract

The evolution of the nuclear matter density distribution with excitation energy is studied within the framework of a finite-range interacting Fermi gas model and microcanonical thermodynamics in Thomas-Fermi approximation. It is found that with increasing excitation energy, both infinite and finite systems become unstable against infinitesimal matter density fluctuations, albeit in different ways. In modeling, this instability reveals itself via an apparent negative heat capacity of the system and is seen to result in the volume boiling in the case of infinite matter and surface boiling in the case of finite systems. The latter phenomenon of surface boiling is unique to small systems and it appears to provide a natural explanation for the observed saturation-like patterns in what is commonly termed caloric curves and what represents functional dependence of nuclear temperature on the excitation energy.