Neutron skin and its effects in heavy-ion collisions

Neutron skin is an exotic phenomenon that occurs in unstable nuclei.In this study,the various efects of the neutron skin on nuclear reactions and their relationship with the properties of nuclear structures are reviewed.Based on numerous studies using theoretical models,strong correlations have been found between the neutron skin thickness and the neutron removal cross section,neutron/proton yield ratio,t∕3He yield ratio,neutron-proton momentum diference,isoscaling parameter,photon production,reaction cross sections for neutron-induced reactions,charge-changing cross-sectional diferences of mirror nuclei,astrophysical S-factor,and other quantities in nuclear reactions induced by neutron-rich nuclei.Moreover,the relationships between the neutron skin thickness and certain properties of the nuclear structure,such asα-cluster formation,αdecay,nuclear surface,nuclear temperature,and proton radii diference of mirror nuclei,have also been investigated.Furthermore,it has also been shown that the neutron skin plays a crucial role in relativistic heavy-ion collisions.Experimentally,an unstable nucleus with a neutron skin can be generated by radioactive nuclear beam facilities,and the thickness of the neutron skin can be extracted by measuring the sensitive probes,which further helps impose stringent constraints on the equation of state of asymmetric nuclear matter and the properties of neutron stars.

Precise machine learning models for fragment production in projectile fragmentation reactions using Bayesian neural networks

Machine learning models are constructed to predict fragment production cross sections in projectile fragmentation(PF)reactions using Bayesian neural network(BNN)techniques.The massive learning for BNN models is based on 6393 fragments from 53 measured projectile fragmentation reactions.A direct BNN model and physical guiding BNN via FRACS parametrization(BNN+FRACS)model have been constructed to predict the fragment cross section in projectile fragmentation reactions.It is verified that the BNN and BNN+FRACS models can reproduce a wide range of fragment productions in PF reactions with incident energies from 40 MeV/u to 1 GeV/u,reaction systems with projectile nuclei from^40 Ar to^208 Pb,and various target nuclei.The high precision of the BNN and BNN+FRACS models makes them applicable for the low production rate of extremely rare isotopes in future PF reactions with large projectile nucleus asymmetry in the new generation of radioactive nuclear beam factories.

SECURITY UPDATE

Just when world leaders thought that they could breathe easily after the successful Iran nuclear deal,nuclear security issues have been catapulted to the top of their agendas following North Korea’s recent testing of its nuclear bombs’capabilities.