利用同位旋相关的量子分子动力学(IQMD)模型，在三种不同对称势下，研究了反应体系48^Ca+48^Ca和40^Ca+40^Ca，以及124^Sn+124^Sn和124^Ba+124^Ba的径向流阈能，发现径向流阈能表现出同位旋相关性，丰中子体系的径向流阈能较小。这一结果和零温时饱和点处的不可压缩系数，随着相对中子过剩的增加而减小，所满足的抛物线规律一致。径向流阈能的同位旋效应对不同对称势的依赖，使得人们可以通过提取径向流阈能的同位旋相关性来确定核物质状态方程中的对称势，为实验确定对称能提供了一种新的方法。利用同位旋相关的Boltzmann-Langevin方程(IBLE)计算了入射能量为600MeV/nucleon时的Ne+ C, Al, Cu, Sn, Ta,Pb反应的碎裂截面。除了C靶，目前的理论计算和实验结果符合较好。只有Ta靶反应描述了实验数据中的奇偶效应。但理论结果很好地描述实验中发现的F碎片产额降低的现象。并根据同位素分布分析了F碎片产额减少的原因。研究了C与H，C，O 和N的反应在50，80和100MeV/nucleon能量下的碎裂反应。计算结果表明，碎片种类随着靶核质量的增加近似增加。对于C与C，O和N反应，能量从50到80MeV/nucleon时，碎片种类和一些碎片生成截面有一个明显的变化，而能量从80到100MeV/nucleon时，碎片生成截面没有发生明显的变化。利用改进的同位旋相关的量子分子动力学(ImIQMD)模型开展了如下几个方面的工作：系统研究了不同弹靶组合生成相同复合核62^Zn，76^Kr 和202^Pb的熔合反应。通过形变双中心壳模型计算得到的壳修正能量证明了熔合反应的入射道效应；理论计算所得熔合截面与实验符合较好；研究了几个反应体系的静态位垒，发现随着质量不对称度的增大，熔合位垒降低，不对称度大的体系熔合截面较大。由此，可以认为质量不对称度影响熔合过程，质量不对称度大的体系有利于复合核的形成。研究了反应32^S + 208^Pb, 34^S + 206^Pb, 36^S +204^Pb, 38^S + 208^Pb熔合位垒，计算结果与实验结果符合较好，表现出关于Z_{1}Z_{2}/(A_{1}^{1/3}+A_{2}^{1/3})的相关性。系统研究了八个丰中子和非丰中子熔合反应，发现丰中子熔合体系截面增强现象的原因之一是丰中子熔合体系的静态位垒小于非丰中子熔合体系的静态位垒；通过分析动力学熔合位垒，发现动力学位垒与入射能量有关：动力学位垒总是低于静态位垒，在入射能量比较高时，动力学位垒接近静态位垒；随着入射能量的降低，动力学位垒将会下降。研究了熔合过程中颈部N/Z、颈部核子转移等颈部动力学行为，发现丰中子系统在颈部形成过程中有明显的中子转移，这将会降低动力学位垒，提高熔合截面。通过研究产生复合核$_{90}^{216}$Th和$_{90}^{220}$Th的不同反应体系，发现原子核幻数的存在影响壳修正能量；计算得到的熔合概率与实验符合较好，反应82^Se + 134^Ba 和 82^Se +138^Ba熔合概率与其他反应比较发现，中子壳封闭82^Se +138^Ba反应的熔合概率较大。结果暗示重体系熔合反应依赖于碰撞核的壳结构，中子壳封闭N=82促进熔合反应进行。

In this dissertation, isospin effects in heavy-ioncollisions and the mechanism of synthesis of the superheavy nucleiare investigated based on the heavy-ion transport theories.The threshold energies of radial flow in reactions of48^Ca+48^Ca and 40^Ca+40^Ca, 124^Sn+124^Sn and 124^Ba+124^Ba in central collisions are investigated within an isospin dependent quantum moleculardynamics(IQMD) model by using three different forms of symmetryenergy. It is found that the neutron-rich system had smallerthreshold energy of radial flow and this quantity depends on the form of symmetry energy. It indicates that the threshold energy ofradial flow a new method to determine the symmetry energy of nuclear matter.The fragment cross sections are calculated for reactions of Necollisions with C, Al, Cu, Sn, Ta, and Pb targets at 600 Mev/nucleon using the the isospin-dependent Boltzmann-Langevin equation(IBLE).We found that the production cross sections for fragments Z=2 to 9 are qualitatively reproduced by the present calculations except forC target. The enhancement of even-Z fragments(C,O) cross sections shown in the experimental data is not well reproduced except for Ta target, however the observed suppression of the F fragment crosssections is described very well. The suppression of F production is discussed in terms of isotopic distribution of fragments. In order to understand the effects of heavy ion interaction with biomolecules well, we further predict the fragmentation cross sections ofreactions 12^C + 2^H, 12^C, 14^N, 16^O at beamenergies from 50 to 100 MeV/nucleon. It is found that fragment species increase approximately with increasing target mass. The obvious variation at the beam energies from 50 to 80 MeV/nucleon are showed for heavier targets.By using an improved isospin dependent quantum molecular dynamics(ImIQMD) model, the following contents are investigated emphatically based on the requirements from experimental research:The fusion cross sections in asymmetric and nearly symmetric reaction systems leading to the same compound nuclei 62^Zn,76^Kr and 202^Pb are studied. The calculated fusion cross sections agree quantitatively with the experimental data. Theentrance channel mass asymmetry dependence of compound nucleus formation is found by analyzing the shell correction energies,Coulomb barriers and fusion cross sections. The Coulomb barrier islower with larger mass asymmetry than that with smaller mass asymmetry. Compound nucleus formation is more favorable for systems with larger mass asymmetries.For reactions 32^S + 208^Pb, 34^S + 206^Pb, 36^S +204^Pb, 38^S + 208^Pb, the calculated fusion barriers agree with the experimental data. It indicates the dependence of Z_{1}Z_{2}/(A_{1}^{1/3}+A_{2}^{1/3}). Enhanced fusion sectionshave been investigated systematically for the neutron-rich projectiles, where the experimental data of the fusion cross sections are regenerated well. The reason is that static and dynamical Coulomb barriers for neutron-rich system are lower than the ones for non-neutron-rich case. By studying the dynamical effects on fusion reactions, we find that the dynamical barrier in fusion reaction is closely related to the incident energy and N/Zratio. We have further studied the dynamical behavior of the neck in fusion reactions, and find that, for neutron-rich system, themaximum value of the N/Z ratio at the neck region is larger than that for non-neutron-rich system, which causes the dynamical barrier lowering and thus enhance the fusion cross sections for neutron-richsystems.The fusion reactions leading to the same compound nuclei$_{90}^{216}$Th and $_{90}^{220}$Th are studied. It is found that the nuclear shell structure affects the shell correction energy. Thefusion probabilities in central collisions agree with experimental data well. Compared with other reactions leading to the same compound nuclei, the fusion probability for 82^Se +138^Bais larger than that for 82^Se + 134^Ba because 138^Ba has the closed neutron shell N=82. Consequently it suggests that neutron shell closure N=82 promotes fusion.