Final excitation energy of fission fragments

TL;DR

This paper investigates how excitation energy is distributed between fission fragments, emphasizing the role of intrinsic energy before scission and challenging the assumption of equal temperature sharing in models.

Contribution

It introduces a level density-based approach to intrinsic excitation-energy partition, revealing excitation-energy sorting at high energies.

Findings

Intrinsic excitation energy exchange occurs only before scission.

Models assuming equal temperature sharing may be inaccurate.

Excitation-energy sorting occurs at energies above the transition point.

Abstract

We study how the excitation energy of the fully accelerated fission fragments is built up. It is stressed that only the intrinsic excitation energy available before scission can be exchanged between the fission fragments to achieve thermal equilibrium. This is in contradiction with most models used to calculate prompt neutron emission where it is assumed that the total excitation energy of the final fragments is shared between the fragments by the condition of equal temperatures. We also study the intrinsic excitation-energy partition according to a level density description with a transition from a constant-temperature regime to a Fermi-gas regime. Complete or partial excitation-energy sorting is found at energies well above the transition energy.