在重核和超重原子核中量子混沌问题的研究

通过观察和分析重核和超重核中量子谱的统计性质 ,研究有限物理体系中量子混沌的一些问题 .介绍了原子核中量子谱显示的有序 -混沌现象随激发能变化的实验数据 ,研究了超重核体系中量子谱相邻能级间距分布的规则性随体系的依赖关系 ,并预言了稳定的超重体系 .给出了原子核有序混沌相变现象与原子核形变以及原子核转动的依赖关系 ,讨论了量子体系中的对效应对有序 -混沌相变的影响 .最后 ,用有序 -混沌相变的概念解释和理解了核物理中一些重要的实验现象. Some aspects of quantum chaos in a finite system had been studied based on the analysis of statistical behaviors of quantum spectra in heavy and superheavy nuclei. The dependence of the transition from order to chaos on nuclear deformation and nuclear rotatation had been described. The influence of pairing effect on the statistical properties of spectra is also discussed. Some important experiment phenomena in nuclear physics had been understood from the point of view of interplay...     

相对论重离子碰撞的趋平衡问题

从相对论ＢＵＵ理论出发,研究了１ＧｅＶ／ｕ能区重离子碰撞全局和局域平衡性质．研究结果表明,在该能区平均场对反应动力学过程仍有相当的作用;对有限核系统的反应动力学过程的时间演化的研究表明,有限核系统未能达到全局平衡,在中心区基本达到局域平衡．因而在该能区的重离子碰撞中引入完全热平衡概念时,需谨慎考虑．The equilibration in relativistic heavy ion collisions for systems 16 O+ 16 O, 40 Ca+ 40 La and 139 La+ 139 La is studied with RBUU theory. We have found that the mean field still plays a role in addition to the collision term in the equilibration process in relativistic heavy ion collisions at energy around 1 GeV/u. For finite systems, the systems do not reach complete equilibrium. But at the center zone, the local equilibrium is almost reached.     

碰撞参数的混杂效应及其对观测量的影响

基于改进型量子分子动力学（ImQMD）模型,讨论了中低能区重离子碰撞实验上利用多重数定义的中心碰撞和理论上利用固定碰撞参数定义的中心碰撞的差别及其影响。在束流能量为50 MeV/u时,发现两种方法得到的碎块电荷多重数分布、碎块的平均动能的结果的最大偏差约有50%。两种方法对于同位旋敏感观测量--并合不变的中子-质子产额比的影响在5%~15%之间。研究表明,利用中低能重离子碰撞精确获取核物质状态方程或者介质中核子-核子散射截面时,必须考虑碰撞参数混杂的效应。     

In-medium NN→NΔ cross section and its dependence on effective Lagrange parameters in isospin-asymmetric nuclear matter

The in-medium NN→N△ cross sections and its differential cross sections in isospin asymmetric nuclear medium are investigated in the framework of the one-boson exchange model by including isovector mesons, i.e., δand p mesons. Our results show that the in-medium NN→N△ cross sections are suppressed when the density increases, and the differential cross sections become isotropic with an increase in the density around the △ threshold energy. The isospin splitting on the medium correction factor, R =σ_(NN→N△)~*/σ_(NN→N△)~(free) is observed for different channels of NN→N△, especially around the threshold energy for all the effective Lagrangian parameters. By analyzing the selected effective Lagrangian parameters, our results show that the larger effective mass is, the weaker medium correction R is.     

The Δ mass dependence of the M matrix and its influence on the NΔ→NN cross-sections

TheΔmass dependence of the M matrix and its influence on the NΔ→NN cross-sections are investigated in the one-boson exchange model.Our calculations show that theΔmass dependence of the momentum of the outgoingΔand the M matrix affects the calculations ofσNΔ→NN,especially around the threshold energy.     

原子核的大质量转移反应和丰中子超重核的产生(英文)

迄今为止,人们合成的超重核都是缺中子的,无论是熔合-裂变反应还是碎化过程都无法使产物达到周期表的“东北区域”。而重核之间(如U核之间) 的近垒大质量转移反应则可能是目前生成丰中子超重核和达到未知丰中子重核区域的唯一途径。在改进的量子分子动力学(ImQMD) 模型结合统计模型框架内,研究了U+U等反应体系的大质量转移反应,计算了反应产生的初生态碎片的质量和电荷分布,并成功再现了产物的终态质量和电荷分布。通过比较3 个反应136Xe+248Cm,48Ca+248Cm和238U+248Cm 产生的106号元素的截面大小,揭示了U+U等重核大质量转移反应对产生丰中子超重核是非常有利的。For elements with Z > 100 only neutron deficient isotopes have been synthesized so far. The “northeast area” of the nuclear map can be reached neither in fusion-fission reactions nor in fragmentation processes.The large mass transfer reactions in near barrier collisions of heavy (U-like) ions seem to be the only reaction mechanism allowing us to produce neutron rich heavy nuclei including those located at the superheavy(SH) island of stability and unexplored area of heavy neutron-rich nuclides. This study is extremely important for nuclear astrophysical investigations and, in particular, for the understanding of the r process. In this paper within the Improved Quantum Molecular Dynamics (ImQMD) model combining with the statistical-evaporation model, the large mass transfer reactions, like 238U+238U have been studied. The charge and mass distributions of transiently formed primary fragments are investigated within the ImQMD model and de-excitation processes of those primary fragments are described by the statistical decay model. The mass distribution of the final products in 238U+238U collisions is obtained and compared with the recent experimental data. Through compared the formation cross sections of transfermium element 106 by three reactions of 136Xe+248Cm, 48Ca+248Cm and 238U+248Cm, it is explored that the large mass transfer reactions, like U+U are very benefit for the production of SH nuclei.     

Understanding of the dissipation mechanism in ternary fission for the system 197Au+197Au

The mass number distributions of three fragments from the ternary fission of the system ¹⁹⁷Au+¹⁹⁷Au are reproduced rather well by using the improved quantum molecular dynamics (ImQMD) model without any adjusting parameter. It is found that the probability of ternary fission evidently depends on the incident energy and the impact parameter, and the two-body dissipation is the main mechanism responsible for the formation of the third fragment with comparable mass.     

Study on the formation of the composite system of 238U+238U

Strongly damped reactions of ²³⁸U+²³⁸U, at E_cm= 680—1880 MeV have been studied based on the improved quantum molecular dynamics model. We find that at a certain energy region the entrance channel potential is weakly repulsive and the dissipation is very strong after touching configuration, these two effects make the time delay of re-separation for colliding system. The single particle potential well of the transiently formed composite system has Coulomb barrier about 15—20 MeV high at the surface, which makes the excited unbound protons being still embedded in the potential well and moving in a common mono-single particle potential for a period of time and thus restrains from quick decay of the composite system.     

中能重离子碰撞中的同位旋效应

利用改进的量子分子动力学模型,研究了中心和擦边重离子反应中的同位旋效应.研究结果表明,在丰中子体系的中心和擦边反应中出射核子的N/Z都对对称势敏感,但对称势的密度依赖对中心和擦边反应的影响显示不同的特征.     

量子效应和单体摩擦

本文在考虑Pauli原理的情况下,用Monte-Carlo方法较真实地模拟了一体耗散的影响,观察了在耗散过程中,随着体系集体振动振幅或频率的增加量子效应由明显到消失的过程,最后推导了包括部分量子效应的墙公式.