Effects Of Symmetry Energy On The Emission Of Light Charged Particles In Fission Reaction

The equation of state for the asymmetry nuclear matter is one of the most important topic in nuclear field, and it’s an essential relevance in solving the evolution of the neutron star, the structure and reactions involving the neutron rich nuclei. Although progresses have been made on constraining the symmetry energy(Esym(ρ)) around the saturation density(ρ = ρ0), the uncertainty is not yet convincing, especially for the high density region, where the trend of Esym(ρ) is not clear. Based on the improved quantum molecular dynamics(ImQMD) model and the experimental data of 35MeV/u40 Ar +197Au, the characteristics of the dynamics fission and the isospin e?ects of light charged particles(LCP)emission hierarchy, has been investigated in this thesis, demonstrating that dynamic fission is a preferable tool to study the Esym(ρ) around ρ0.This thesis reconstructs the fission events using the velocity of fission fragments,measured by the PPACs. It confirms that the fragment mass variance increase with the violence of the collision, indicating the onset of dynamics fission. Comparing the ratio of the yield of p, d, t,3He,4He,6He,between the 158?and 80?, the neutron rich particles are more abundant at the forward angle. So model independently, it suggests that more neutron rich emission occurs in dynamic stage.For studying the isospin e?ect along the whole reaction process more quantitatively,we analyze the energy spectra of p, d, and t particles at these low angles, with moving source model, and decompose the emission contributions from three sources, intermediate velocity source(Int-Src), compound nucleus source(CN-Src) and fission fragment source(FF-Src), corresponding to the early dynamic stage, statistical emission stage and post-scission stage respectively. By a minimum χ2analysis, the yields of p, d and t, for these three sources are extracted. A hierarchy of emission from triton to deuton and proton is observed in the multiplicity ratio between the Int-Src and the CN-Src, a reverse one in the FF-Src and CN-Src. With respect to the statistical emission of CN, this ratio is sensitive to the dynamical emission at early stages of the reaction and to statistic emission lasting up to the scission point. Calculations with the ImQMD model qualitatively support the picture that more free and bound neutrons are emitted during the early stage, showing a clear dependence of < N/Z > on the parametrization of the symmetry energy. The time-dependent isospin composition of the emitted particles thus may be used to probe the Esym(ρ) at ρ < ρ0, and further calculation with ImQMD show that the angle-dependent isospin composition of the emitted particles also may be another probe.In order to achieve a quantitative constraining on the symmetry energy at subsaturation density, we has performed a new fission experiment 30MeV/u40 Ar +197Au on the RIBLL1 terminal at Heavy Ion Research Facility in Lanzhou(HIRFL). Based on Geant4 Shielding library, this thesis conducts a full simulation for the neutron shielding at RIBLL1 for primary beam experiments. It is shown both the simulations and the realtime monitory, the neutron radiation at the DAQ area is greatly suppressed by ～ 3 order of magnitude. At the end of this thesis, the performance of PPACs and semiconductor telescopes are studied, and some preliminary results of this experiment is introduced.