兰州大学机构库 >物理科学与技术学院
中能重离子碰撞与对称能的密度依赖性
Alternative TitleIntermidiate energy heavy ion collisions and density dependent symmetry energy
张芳
Thesis Advisor左维
2008-05-25
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword输运模型 核物质状态方程 单粒子势 对称能 中-质比 中-质微分流 椭圆流 pion 介子比
Abstract物理学的很多领域,从凝聚态、天体物理到格点QCD都会涉及到核物质状态方程。经过几十年的努力,对称核物质状态方程已基本限定,但是对非对称核物质状态方程,尤其是密度依赖的对称能仍然知之甚少。非对称核物质状态方程的探索有助于研究不稳定核结构和天体物理中的一些关键问题:如超新星爆发机制、中子星里的Kano 凝聚、超新星形成过程的核合成和¯稳定线附近的中子星里的质子分数和电子化学势等。基于多体理论我们知道非对称核物质状态方程与中子过剩±的二次方有关,然而不同的多体理论给出了的密度依赖的对称能行为有很大的不同,有的甚至在高密处给出了相反的行为。放射性核束引起的重离子碰撞为我们在实验室里研究密度依赖的对称能提供了唯一机遇。基于同位旋依赖的输运模型,确定了很多做为对称能探针的实验观测量,比如中子-质子比、双中-质比、同位旋扩散和中子 -质子关联函数等。本论文就是为寻找对对称能敏感的观测量而进行的理论工作。 在第一章我们给出了重离子碰撞的历史的回顾和当前的发展方向、基本特点核前景。包括重离子碰撞的按能量分类和反应机制以及放射核束性引起的反应,重离子碰撞在生物、医学及其它领域的用。 第二章简单介绍了描述中能重离子碰撞的两种输运模型:量子分子动力学(QCD)和BUU方程。这两种模型里都包含平均场核核子-核子碰撞。并对本论文所用的BUU单粒子势做了详细介绍,给出了由IBUU单粒子势得出的对称势和标量势的形式。 在第三章里我们基于同位旋和动量依赖的输运模型IBUU04,利用对对称能敏感的观测量研究了对称能的高密行为。主要包括:用Sn + Sn反应系统,首先研究了入射能量、碰撞参数以及同位旋依赖的中子-质子比,发现在入射能量为400/AMeV,中心碰撞时,丰中子系统中的中-质比对对称能比较敏感;由于双中-质比可以有效的减少系统误差和减弱库仑效应的影响,因此我们利用双中-质比研究了密度依 赖的对称能的同位旋效应。在四种入射能量时利用中-质微分流研究了密度依赖的对称能,发现中-质微分流在入射能量为每核子400MeV时对对称能最为敏感;同时研究了碰撞参数参数对中-质微分流的影响。然后利用径向流和椭圆流对对称能的密度依赖型进行了研究。我们还三种入射能量情况下研究了 比率对密度依赖的对称能的敏感性。 在论文的最后我们给出了整个工作的总结和对未来工作的展望。
Other AbstractFrom State of aggregation、astrophysics to latter QCD, many fieldsin physics related to the equation of state in nuclear matter. The equation of state in symmetric nuclear matter is well constrained after many effort on this question in the past decades. But for the equation of state in asymmetric nuclear matter, especially the density dependence of the symmetry energy is still very poorl-y known.. The EOS of asymmetric nuclear matter is important for understanding the structure of unstable nuclear matter and the problems in astrophysics. Such as: the mechanism of type II supernova explosions, Kaon condensation in neutron stars, synthesis of nuclei in neutron star mergers, the proton fraction and electron chemical potential of neutron stars at equilibrium. i.e. Calculations based on microscopic many-body theories have predicted that the equation of state of isospin-asymmetric nuclear matter depends quadratically on the neutron excess .But the symmetry energy,and especially its density dependence vary widely among theoretical predictions, in particular the symmetry energy at high densi-ties. Fortunately, heavy ion collisions induced by radioactive beams provide a powerful tool for extracting useful information about the symmetry energy in laboratory. Based on isospin-dependent transport model calculations, many experimental observableshave been proposed as promising probes to the density dependence of the symmetry energy, such as the free neutron to proton ratio, double neutron to proton ratio, isospin diffusion and the neutron –proton correlation function. This thesis is devoted to the theoretical study on probing the observables which sensitive to the density dependence of the symmetry energy. The history review、present development、basic feature and prospect gave in chapter I. Heavy ion collisions can be divided into: low energy collisions, intermediate energy collision, high energy and relativistic energy collisions. The reaction mechanism in different energies and the reaction induced by radioactive beams, the applied of heavy ion collision in biology, medicine and in other fields also included. In chapter II we present two transport models used in intermediate energy reactions: one is Quantum Molecule Dynamics(QCD), the other is Boltzmann-Uehling-Uhlenbeck(BUU) equation. These two models contain both the mean field and hard collisions. Then we give adetail description about isospin-dependence single particle potential used in our...
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Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/229009
Collection物理科学与技术学院
Recommended Citation
GB/T 7714
张芳. 中能重离子碰撞与对称能的密度依赖性[D]. 兰州. 兰州大学,2008.
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