超重元素的合成是核物理研究的前沿课题之一。本研究工作在双核系统（DNS）模型的基础上围绕着超重元素 Z=119、120、121和 126 的合成机制开展研究，计算了合成超重元素 Z=119、120、121 和 126的产生截面。在考虑实验可行性的基础上，预言合成超重核的最佳弹靶体系、最大蒸发剩余截面（ERCS）并给出反应所需的最佳入射能量。分析了弹靶碰撞方向、弹核同位旋、质量不对称度和靶核同位旋对蒸发剩余截面的影响。主要研究内容如下：

       1、为合成超重元素Z=119，计算了 ⁴²Ca+²⁵²Es、⁴⁴Ca+²⁵²Es、⁴⁴Ca+²⁵⁴Es、⁴⁸Ca+²⁵²Es、⁴⁸Ca+²⁵⁴Es、⁵⁴Cr+²⁴³Am、⁵⁰Ti+²⁴⁷Bk和 ⁵⁰Ti+²⁴⁹Bk的蒸发剩余截面。预言合成超重元素Z=119 的最佳反应是 ⁴⁸Ca+²⁵⁴Es→3n+²⁹⁹119，对应的最佳入射能量和最大蒸发剩余截面分别为 E_c.m.=210.9 MeV 和σ_ER^max = 4237 fb。通过对比反

应 ⁴⁴Ca+²⁵⁴Es 和 ⁴⁸Ca+²⁵⁴Es，分析了弹核同位旋对蒸发剩余截面的影响。

       2、为合成超重元素Z=120，计算了 ⁴⁶Ca+²⁵⁷Fm、⁴⁸Ca+²⁵⁷Fm、⁴⁶Ti+²⁵¹Cf、⁵⁰Ti+²⁵¹Cf、⁵⁰Ti+²⁵²Cf、⁵⁴Cr+²⁴⁸Cm、⁵⁵Mn+²⁴³Am 和 ⁶⁴Ni+²³⁸U的蒸发剩余截面。预言合成超重元素 Z=120 的最佳反应是 ⁴⁶Ti+²⁵¹Cf→2n+²⁹⁵120，对应的最佳入射能量和最大蒸发剩余截面分别为 E_c.m.=212.6 MeV 和σ_ER^max = 4229 fb。通过比较反应 ⁵⁰Ti+²⁵²Cf 和 ⁵⁴Cr+²⁴⁸Cm，分析了质量不对称度对内部熔合位垒以及蒸发剩余截面的影响。

       3、为合成超重元素 Z=121，考虑靶核半衰期的前提下，选取 25 个反应体系，计算了合成超重元素 Z=121 的蒸发剩余截面。在考虑实验可操作性的基础上，预言反应 ²⁵²Es (⁴⁶Ti, 1n) 最有可能在实验上合成 Z=121 号未知新核素，对应的最佳入射能量和最大蒸发剩余截面分别为 E_c.m.=209.4 MeV 和 σ_ER^max = 1068 fb；分析了上述反应的最大蒸发剩余截面出现在 1n 蒸发道的具体原因；通过对比反应 ⁴⁶Ti+^{252,253,254,255}Es 的俘获截面、熔合几率、存活几率和蒸发剩余截面，分析了靶核同位旋对蒸发剩余截面的影响。

       4、 为合成超重元素Z=126， 选取23个弹靶体系 ， 计算合成超重元素Z=126的蒸发剩余截 面 。 预言合成超重元素 Z=126的最佳反应是²⁴⁸Cm (⁶⁶Zn, 2n)，对应的最佳入射能量和最大蒸发剩余截面分别为 Ec.m.=300.9 MeV和 σ_ER^max = 0.813 fb。分析了准裂变位垒与质量不对称度、库仑因子的关系。本研究工作的创新点如下：（1）计算了超重元素 Z=119的产生截面，预言合成 Z=119 的最佳反应体系为 48Ca+254Es，最大蒸发剩余截面 σ_ER^max = 4237fb；（2）计算了超重元素 Z=120的产生截面，预言合成 Z=120 的最佳反应体系为 ⁴⁶Ti+²⁵¹Cf，最大蒸发剩余截面 σ_ER^max  = 4229 fb；（3）为合成超重元素 Z=121，在考虑弹靶可利用性的前提下，计算了 25 个反应体系的产生截面，考虑实验操作性的基础上，预言反应 ⁴⁶Ti+²⁵²Es 为产生超重元素 Z=121的最佳反应体系，最大蒸发剩余截面 σ_ER^max  = 1068 fb；（4）预言 ²⁴⁸Cm (⁶⁶Zn, 2n) 是合成超重元素 Z=126 的最佳反应体系，但最大蒸发剩余截面 σ_ER^max  = 0.813 fb 非常低，目前低于实验可测量极限。

     The synthesis of superheavy elements has been one of the frontier issues in nuclear physics. This paper mainly carries out a detailed study for the synthesis of superheavy

elements Z=119, 120, 121 and 126 within the frame work of dinuclear system model. Theoretical production cross sections have been calculated for the superheavy elements Z=119, 120, 121 and 126. By considering the experimental feasibility, the most favorable projectile-target combination, evaporation residue cross sections and the incident energy for synthesis the superheavy elements have been given. The influence of orientation effect, projectile isospin, mass asymmetry and target isospin on the evaporation residue cross sections has been analyzed meticulously. The specific contents are summarized as follows：

     Firstly, for the synthesis of superheavy element Z=119, within the framework of dinuclear system model, the evaporation residue excitation functions of  ⁴²Ca+²⁵²Es、⁴⁴Ca+²⁵²Es、⁴⁴Ca+²⁵⁴Es、⁴⁸Ca+²⁵²Es、⁴⁸Ca+²⁵⁴Es、⁵⁴Cr+²⁴³Am、⁵⁰Ti+²⁴⁷Bk and ⁵⁰Ti+²⁴⁹Bk have been calculated. The system ⁴⁸Ca+²⁵⁴Es→ 3n+²⁹⁹119 is the promising one with the maximal evaporation residue cross section σ_ER^max = 4237 fb and the incident energy E_c.m.=220.1 MeV. The influence of projectile isospin on evaporation residue cross section have been investigated by comparing ⁴⁴Ca+²⁵⁴Es and ⁴⁸Ca+²⁵⁴Es.

    Secondly, for the synthesis of superheavy element Z=120, the evaporation residue excitation functions of ⁴⁶Ca+²⁵⁷Fm、⁴⁸Ca+²⁵⁷Fm、⁴⁶Ti+²⁵¹Cf、⁵⁰Ti+²⁵¹Cf、⁵⁰Ti+²⁵²Cf、⁵⁴Cr+²⁴⁸Cm、⁵⁵Mn+²⁴³Am and ⁶⁴Ni+²³⁸U have been calculated. ⁴⁶Ti+²⁵¹Cf→ 2n+²⁹⁵120 is the optimal one, corresponding to the maximal evaporation residue cross section σ_ER^max = 4229 fb and the incident energy E_c.m.=212.6 MeV. In addition, effect of mass asymmetry on evaporation residue cross section has been studied by comparing ⁵⁰Ti+²⁵²Cf and ⁵⁴Cr+²⁴⁸Cm.

    Thirdly, for the synthesis of superheavy element Z=121, The evaporation residue excitation functions of 25 reaction systems have been calculated after considering the half-lives of projectile nuclei. On the basis of considering experimental operability, ²⁵²Es(⁴⁶Ti, 1n) is the optimal projectile-target combination for the synthesis of superheavy element Z=121 with the maximal evaporation residue cross section (incident energy) σ_ER^max = 1068 fb (E_c.m.=209.4 MeV). The specific reasons why the maximal evaporation residue cross section of the above reaction system appeared at 1n evaporation channel are analyzed. By comparing the capture cross section, fusion probability, survival probability and evaporation residue excitation functions of ⁴⁶Ti+ ^{252,253,254,255}Es, the influence of projectile isospin on evaporation residue cross sections has been analyzed. 

      Lastly, the evaporation residue excitation functions of 23 stable reaction systems have been calculated for the synthesis of superheavy elements Z=126. ²⁴⁸Cm(⁶⁶Zn, 2n) is found to be the the best choice and the maximal evaporation residue cross section (incident energy) is σ_ER^max = 0.813 fb (E_c.m.=300.9 MeV). Dependence of quasi-fission barrier on mass asymmetry and Coulomb factor has been studied. 

      The innovations of this paper are as follows: 1. The production cross sections of the superheavy element Z=119 have been calculated, ⁴⁸Ca+²⁵⁴Es is found to be the optimum system for the synthesis of Z=119 with the maximal evaporation residue cross section σ_ER^max = 4237 fb. 2. The evaporation residue excitation functions have been calculated for the synthesis of superheavy element Z=120, ⁴⁶Ti+²⁵¹Cf is the probable choice with σ_ER^max = 4229 fb. 3. The evaporation residue excitation functions of 25 reaction systems have been calculated for the synthesis of Z=121 after considering the availability of projectile and target, ⁴⁶Ti+²⁵²Es is the best projectile-target combination with σ_ER^max = 1068fb. 4. This paper predicts that the reaction ²⁴⁸Cm (⁶⁶Zn, 2n) is the promising one for the synthesis of superheavy element Z=126 with the maximal evaporation residue cross section σ_ER^max = 0.813 fb which is too low to be detected in experiment currently.