基于动力学形变的双核模型对超重核合成机制的研究
发布时间：2018-09-05 12:53
【摘要】：实验核物理学家们开展了一系列关于超重核合成的研究并获得了巨大的成功,GSI、RIKEN以及JINR等实验室成功合成了Z119的所有超重元素。与此同时,包括双核模型在内的许多描述超重核合成机制的理论模型也陆续被建立和发展起来。虽然理论计算的超重核产生截面与已知实验数据符合得很好,但是在预言未知超重核时,不同理论模型的结果之间存在较大的分歧。本论文从动力学形变效应的角度对现有的双核模型进行了改进。早先的双核模型理论研究假设,在超重核的形成过程中,相互作用的类弹和类靶碎片总是保持基态形变不变。但是我们认为,在描述超重核的形成过程时,除了需要考虑类弹和类靶碎片的质子数、中子数、两碎片核心间距等多个物理量外,还应考虑两碎片的动力学形变效应以及动力学形变效应与其他物理量间的耦合。在重离子熔合反应中,强库仑作用和核相互作用使得类弹、类靶碎片的形变总是随着时间发生改变,需要对其进行动力学处理。由于在重离子的熔合过程中发生了较大的能量弛豫耗散过程,处于高激发态的两碎片中的核子重新布居到不同的能级上,进而引起较大的且不可逆的形变。另一方面,考虑到两碎片的形变参量的改变使得它们的质量、碎片间的相互作用以及系统的驱动势随之发生改变,这些改变影响了其他物理量(如能量、角动量)的弛豫耗散过程、核子的转移过程以及系统的内部激发能,从而继续使得两碎片的形变发生改变。对包含了类弹和类靶碎片的质子数、中子数、两碎片核心间距以及两碎片的动力学形变的主方程的数值求解非常复杂,因此本文暂时将动力学形变自由度与其他自由度退耦合,并将类弹和类靶碎片的动力学形变的演化看成是弛豫耗散过程,通过求解含有两碎片动力学形变参量的Fokker-Planck方程,得到了两碎片的动力学形变的演化规律。把包含了类弹和类靶碎片的质子数、中子数的主方程与两碎片的动力学形变演化规律相结合,发展了与动力学形变效应相关的双核模型。研究结果表明:(1)类弹和类靶碎片的动力学形变的演化主要由两碎片的本征结构和两碎片间的相互作用所决定;(2)两碎片的动力学形变的演化存在关联,二者相互制约从而使得反应系统的驱动势向更低的位置移动;(3)类弹和类靶碎片的动力学形变的弛豫耗散的快慢还受到反应过程中的激发能、扩散系数以及反应系统的同位旋的影响;(4)动力学形变效应影响了系统的内部熔合位垒,从而改变复合核的熔合几率以及蒸发余核的产生截面。
[Abstract]:Experimental nuclear physicists have carried out a series of studies on the synthesis of overweight nuclei and have achieved great success in the synthesis of all the overweight elements of Z119 in the laboratories such as GSI RIKEN and JINR. At the same time, many theoretical models, including binuclear models, have been established and developed to describe the mechanism of overweight nuclear synthesis. Although the calculated cross sections are in good agreement with the known experimental data, there are large differences between the results of different theoretical models in predicting unknown overweight nuclei. In this paper, the existing binuclear model is improved from the point of view of dynamic deformation effect. The previous binuclear model theory hypothesized that the interacting projectile and target fragments always keep the ground state deformation unchanged during the formation of overweight nuclei. However, we think that in describing the formation of overweight nuclei, we need to consider not only the number of protons, the number of neutrons, the distance between two fragments, and so on, but also the number of projectile and target like fragments. The dynamic deformation effect of the two fragments and the coupling between the dynamic deformation effect and other physical quantities should also be considered. In the heavy ion fusion reaction, the deformation of projectile-like and target-like fragments always changes with time due to the strong Coulomb interaction and nuclear interaction. Due to the large energy relaxation and dissipation process in the fusion of heavy ions, the nucleons in the two fragments in the highly excited state are repopulated to different energy levels, thus causing a large and irreversible deformation. On the other hand, considering that the changes in the deformation parameters of the two fragments result in changes in their mass, the interaction between the fragments, and the driving potential of the system, these changes affect other physical quantities, such as energy, The relaxation and dissipation process of angular momentum, the transfer process of nucleon and the internal excitation energy of the system continue to change the deformation of the two fragments. The numerical solution of the main equations including the number of projectiles and target fragments, the number of neutrons, the distance between the two fragments and the dynamic deformation of the two fragments is very complicated, so the dynamic deforming degree of freedom is temporarily decoupled from the other degrees of freedom. The evolution of dynamic deformation of projectile and target like debris is regarded as a relaxation dissipation process. The evolution law of dynamic deformation of two fragments is obtained by solving the Fokker-Planck equation with dynamic deformation parameters of two fragments. A binuclear model related to the dynamic deformation effect is developed by combining the main equations including the number of protons and neutron numbers of projectile-like and target like fragments with the dynamic deformation evolution law of the two fragments. The results show that: (1) the evolution of dynamic deformation of projectile and target like debris is mainly determined by the intrinsic structure of two fragments and the interaction between two fragments, and (2) the evolution of dynamic deformation of two fragments is related. The two restrict each other to move the driving potential of the reaction system to a lower position; (3) the relaxation dissipation rate of the dynamic deformation of projectile and target like debris is also affected by the excitation energy during the reaction. The diffusion coefficient and the isospin effect of the reaction system; (4) the dynamic deformation effect affects the internal fusion barrier of the system, thus changing the fusion probability of the complex nucleus and the generation cross section of the evaporative residual nucleus.
【学位授予单位】：中国科学院研究生院(近代物理研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O571.6
本文编号：2224333
[Abstract]:Experimental nuclear physicists have carried out a series of studies on the synthesis of overweight nuclei and have achieved great success in the synthesis of all the overweight elements of Z119 in the laboratories such as GSI RIKEN and JINR. At the same time, many theoretical models, including binuclear models, have been established and developed to describe the mechanism of overweight nuclear synthesis. Although the calculated cross sections are in good agreement with the known experimental data, there are large differences between the results of different theoretical models in predicting unknown overweight nuclei. In this paper, the existing binuclear model is improved from the point of view of dynamic deformation effect. The previous binuclear model theory hypothesized that the interacting projectile and target fragments always keep the ground state deformation unchanged during the formation of overweight nuclei. However, we think that in describing the formation of overweight nuclei, we need to consider not only the number of protons, the number of neutrons, the distance between two fragments, and so on, but also the number of projectile and target like fragments. The dynamic deformation effect of the two fragments and the coupling between the dynamic deformation effect and other physical quantities should also be considered. In the heavy ion fusion reaction, the deformation of projectile-like and target-like fragments always changes with time due to the strong Coulomb interaction and nuclear interaction. Due to the large energy relaxation and dissipation process in the fusion of heavy ions, the nucleons in the two fragments in the highly excited state are repopulated to different energy levels, thus causing a large and irreversible deformation. On the other hand, considering that the changes in the deformation parameters of the two fragments result in changes in their mass, the interaction between the fragments, and the driving potential of the system, these changes affect other physical quantities, such as energy, The relaxation and dissipation process of angular momentum, the transfer process of nucleon and the internal excitation energy of the system continue to change the deformation of the two fragments. The numerical solution of the main equations including the number of projectiles and target fragments, the number of neutrons, the distance between the two fragments and the dynamic deformation of the two fragments is very complicated, so the dynamic deforming degree of freedom is temporarily decoupled from the other degrees of freedom. The evolution of dynamic deformation of projectile and target like debris is regarded as a relaxation dissipation process. The evolution law of dynamic deformation of two fragments is obtained by solving the Fokker-Planck equation with dynamic deformation parameters of two fragments. A binuclear model related to the dynamic deformation effect is developed by combining the main equations including the number of protons and neutron numbers of projectile-like and target like fragments with the dynamic deformation evolution law of the two fragments. The results show that: (1) the evolution of dynamic deformation of projectile and target like debris is mainly determined by the intrinsic structure of two fragments and the interaction between two fragments, and (2) the evolution of dynamic deformation of two fragments is related. The two restrict each other to move the driving potential of the reaction system to a lower position; (3) the relaxation dissipation rate of the dynamic deformation of projectile and target like debris is also affected by the excitation energy during the reaction. The diffusion coefficient and the isospin effect of the reaction system; (4) the dynamic deformation effect affects the internal fusion barrier of the system, thus changing the fusion probability of the complex nucleus and the generation cross section of the evaporative residual nucleus.
【学位授予单位】：中国科学院研究生院(近代物理研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O571.6
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