Neutron skin and its effects in heavy-ion collisions

Neutron skin is an exotic phenomena in unstable nuclei. The various effects in nuclear reactions caused by the neutron skin and also its relation with the properties of nuclear structure are reviewed in this article. Based on numerous studies with theoretical models, strong correlations have been found between the neutron skin thickness and neutron removal cross section, neutron/proton yield ratio, t/\ch{^3He} yield ratio, neutron-proton momentum difference, isoscaling parameter, photon production, reaction cross sections for neutron induced reactions, charge-changing cross sections difference of mirror nuclei, astrophysical $S$-factor, and other quantities in nuclear reactions induced by neutron-rich nuclei. Moreover, the relationships between neutron skin thickness and some properties of nuclear structure, such as $\alpha$-cluster formation, $\alpha$ decay, nuclear surface, nuclear temperature, and proton radii difference of mirror nuclei, have also been investigated. It also has been shown that the neutron skin plays a crucial role in relativistic heavy-ion collisions. Experimentally, an unstable nucleus with neutron skin can be generated by radioactive nuclear beam facilities, and the thickness of neutron skin could be extracted by measuring the sensitive probes, which further helps giving stringent constraints on the equation of state of asymmetric nuclear matter and properties of neutron stars.