Mechanisms of Coulomb dissociation processes

TL;DR

This study investigates Coulomb dissociation of $^8$Li nuclei on Pb targets at intermediate energies, revealing it as a two-step process involving projectile excitation and decay, with detailed insights into the reaction mechanisms and nuclear deformations.

Contribution

It provides experimental evidence and detailed analysis of the two-step Coulomb dissociation process, including the role of projectile excitation and decay pathways, at intermediate energies.

Findings

Coulomb dissociation is a two-step process involving excitation and decay.

Projectile in the approaching phase is braked and undergoes forced oscillation.

Primary excited states decay promptly or with delay, contributing to different reaction channels.

Abstract

The Coulomb dissociation is studied of the $^8L$i nuclei on Pb target at energies 40.3 and 69.5 MeV/nucleon, in the experiment NSCL #03038. The $^{6,7}$Li, $^{4,6}$He, and $^2$H fragments were identified. The resonance decay and the direct breakup reactions were observed. The data give experimental evidence that the Coulomb dissociation is a two-step process. The projectile in the approaching phase is braked down and the valence neutron gets forced oscillation. The increasing Coulonb force holds the projectile and brings through the excited states up to the closest approach point. There released, the projectile is trapped into a primary, highly excited state in the continuum. The lifetime of the primary state depends on the multipolarity of the deformed projectile. At intermediate energy the collision is a sudden reaction, the valence neutron may stay --- during the impact --- in the forward or backward hemisphere of the nucleus, and the orbit of the valence neutron gets prolate or oblate, dipole or multipole deformation and the nucleus gets single-particle or collective excitation. The primary excited states, developing will decay prompt or delayed into the same reaction channel, resulting in the two decay mechanisms.