Study Of The Probes Sensitive To Neutron Skin Thickness

Nuclear radii and density distributions are among the most fundamental properties of nucleus. Before the production of radioactive ion beam, nucle-ar density distribution are mainly studied with electron scattering and proton scattering, and the studies are limited to stable nuclei. In1980s, with the de-velopment of RNB, the studies of nuclear density distribution are extended to unstable nuclei even up to the neutron and proton drip lines.For neutron rich nuclei far from the β-stability line, with neutron number (N) is much larger (Z), the neutron density distribution is much larger than that of the proton in the surface region, which is called neutron skin. The neu-tron skin thickness is defined as the difference between root mean square (RMS) radii of neutron and proton:δnp=<r2n>1/2-<r2>1/2. If the RMS radii of neutron and proton are measured experimentally, the neutron skin thickness will be obtained. The density distribution of proton can be measured accurately with electric magnetic interaction (eg. electron scattering), while that of neutron is very difficult to determined with the electric magnetic interaction due to its electric neutrality. Currently, the neutron density distribution is mainly studied with strong interaction probes. However, the results from different experimental method are very different, and it is also model dependent. Therefore, it is de-sirable to seek for new probes of neutron skin thickness, which is the start point of this thesis. From this point, we have studied the neutron skin thickness both theoretically and experimentally.In the theoretical study, we have simulated the collisions of50Ca+12C and68Ni+12C50MeV/A within the framework of isospin dependent molecular dynam-ics (IQMD) model. The two-parameter Fermi distribution from droplet model are used in the initialization. By changing the diffuseness parameter in this distri-bution, projectiles with different neutron skin thickness are obtained. The light fragments production with different neutron skin thickness are studied, from which a linear relationship between triton to3He ratio R(t/3He) is obtained. This linear dependence could be used to extract neutron skin thickness experi-mentally. It is also found that the ratio between R(t/3He) and neutron to protonratio R(n/p) almost keeps constant with increasing neutron skin thickness, whichindicates that we can obtain equally results in extracting neutron skin thicknesswith the two diferent approaches. However, the triton and3He are charged par-ticles, which can be easily measured experimentally, so to extract neutron skinthickness from R(t/3He) is more practical.Due to the conservation of mass and charge, and the production of light-s fragments being dependent on neutron skin thickness, the production of theheavy ones should also be sensitive to neutron skin thickness. The The prefrag-ments produced in IQMD are excited, which is not the camparable with the fnalproducts measured experimentally. Therefore the primary fragments from IQMDare de-excited with GEMINI code. From the study of the isotopic distribution forheavy residues after de-excitation, it is found that larger neutron skin thicknesswill suppress the production of isotopes of neutron rich side. It is also found thatthe component neutron to proton ratio (N/Z) of the heavy residues will decreaselinearly with increasing neuron skin thickness. The isoscaling behaviors of heavyresidues are also studied, which indicates that the isoscaling parameter α dis-plays a linear dependence on neutron skin thickness as well. With correlationsbetween neutron skin thickness and all the observables above, some informationabout neutron skin thickness could be obtained from the distribution of fragmentsproduction.Measurement of reaction cross section is traditionally used to study nucleardensity distribution. M. Takechi et al. have measured the total interaction crosssection σIof2032Ne isotopes. If the charge-changing cross sections of Ne isotopesare also measured, the neutron and proton density distribution will be deducedfrom combined analysis of σIand σcc, and then the neutron skin thickness willbe obtained from the density distributions. Based on this physical motivation,we have measure the charge-changing cross section of2127Ne isotopes on theradioactive beam line RIBLL1of heavy ion research facility in Lanzhou (HIRFL)in2012. With the existing data of interaction cross section σI, and the charge-changing cross section σccof present work, the density distribution of neutron and proton will be extracted with the help of statistical abration-ablation (SAA)model, the neutron skin thicknesses are deduced. The results indicate that theneutron skin thickness increase with increasing of the diference between singleneutron separation energy and that of proton. This result keeps good agreementwith the previous data.