Peeling away surface neutrons from 209Bi in asymmetric collisions

The emission of spectator neutrons and protons in ultracentral collisions of Bi with the same (Bi) or lighter (W, Cu) target nuclei has been simulated using the Abrasion-Ablation Monte Carlo for Colliders model with MST clustering (AAMCC-MST). It was shown that the detection of forward neutrons and protons in such collisions allows the analysis of the [Formula: see text] ratio at the nuclear periphery. The cross-sections to produce a given number of spectator neutrons [Formula: see text], the average number of spectator neutrons [Formula: see text] and protons [Formula: see text] in ultracentral collisions were calculated with and without consideration of the neutron skin in Bi. The ratio [Formula: see text] was found to be particularly sensitive to the presence of neutron skin in Bi–W collisions, providing a potential probe of the enrichment of the nuclear surface by neutrons. However, this sensitivity disappears in Bi–Cu collisions due to the involvement of inner nuclear layers to the spectator emission.