Fission of relativistic nuclei with fragment excitation and reorientation

TL;DR

This paper introduces a new approach to account for additional excitation of primary fragments in relativistic nuclear fission, improving agreement with experimental isotopic distributions by considering final state interactions.

Contribution

The novel method models the excitation of fragments due to final state interactions, addressing limitations of previous models in predicting fragment yields and distributions.

Findings

Enhanced excitation energy of primary fragments observed experimentally.

Final state interactions significantly alter isotopic distributions.

Large angular momentum transfers suggest need for advanced theoretical models.

Abstract

Experimental studies of fission induced in relativistic nuclear collisions show a systematic enhancement of the excitation energy of the primary fragments by a factor of ~ 2, before their decay by fission and other secondary fragments. Although it is widely accepted that by doubling the energies of the single-particle states may yield a better agreement with fission data, it does not prove fully successful, since it is not able to explain yields for light and intermediate mass fragments. State-of-the-art calculations are successful to describe the overall shape of the mass distribution of fragments, but fail within a factor of 2-10 for a large number of individual yields. Here, we present a novel approach that provides an account of the additional excitation of primary fragments due to final state interaction with the target. Our method is applied to the 238U + 208Pb reaction at 1 GeV/nucleon (and is applicable to other energies), an archetype case of fission studies with relativistic heavy ions, where we find that the large probability of energy absorption through final state excitation of giant resonances in the fragments can substantially modify the isotopic distribution of final fragments in a better agreement with data. Finally, we demonstrate that large angular momentum transfers to the projectile and to the primary fragments via the same mechanism imply the need of more elaborate theoretical methods than the presently existing ones.