Studies On The Neutron Skin Thickness For Light Neutron-rich Nuclei

The sizes and the distribution of proton and neutron in nuclei are the basic physical quantities characterising the nuclear matter properties. Before RIB, the sizes of proton and neutron are mainly studied with the experiments of electron scattering and proton scattering, and many studies are limited to stable nuclei.Then, the accelerator upgrade and the the experimental method improvements make it possible the studies been extended to unstable nuclei approaching to the neutron or proton drip lines.I. Tanihata et al ?rst proposed the concept of “neutron skin” or “neutron halo” to explain some abnormal phenomenons of interaction cross section in light nuclei. As for the neutron rich nuclei, we know that the neutron halfdensity radius is larger than proton’s, which is called neutron skin. There is an equation that quantitatively describes the neutron skin thickness,which is neutron-proton rms radius di?erence,namely, δ_np= Rn- Rp. Moreover, the researches about the neutron skin have an important e?ect on nuclear symmetry energy and the structure of neutron stars. According to the de?nition of the neutron skin thickness, we need to measure the neutron and proton rms radii in order to get the neutron skin thickness. On one hand, neutron and proton density distributions were extracted through charge-changing cross section and interaction cross section in theory. On the other hand, we measure the chargechanging cross section for Al isotopes for the ?rst time in the lab.Theoretically, the Statistical abrasion-ablation（SAA） model combined with interaction cross section and charge radii has been used to extract the neutron rms radii for Na isotopes. Then, the neutron skin thickness of these isotopes can be obtained. It can be seen that the result is consistent with the systematical trend of theoretical calculations. It indicates the method of extracting proton and neutron radii is feasible. Then, the proton and neutron radii constants are introduced into the SAA-model. Using the improved model combined with the data of interaction cross section and charge-changing cross section, we extractthe neutron and proton rms radii.Experimentally, we analyze and deal with the data which are from the radioactive beam line RIBLL of heavy ion research facility in Lanzhou in 2012.The charge-changing cross section for28-32 Al isotopes at the energy of 50MeV/A are measured in the lab for the ?rst time. The data combined with interaction cross section can be used to deduced the the proton and neutron rms radii and to obtain the neutron skin thickness for Al isotopes.