大爆炸动力学方程的研究与计算

发布时间：2018-01-29 01:02

本文关键词： 原初核合成大爆炸模型宇宙微波背景网络方程反应率　出处：《北京化工大学》2010年硕士论文　论文类型：学位论文

【摘要】： 大爆炸核合成是宇宙模型中非常重要的一环,它不仅是我们了解宇宙早期奥秘的窗口,同时也是探测基本物理最有力的工具,而且这一作用在今天显得更加重要。本文主要对标准的大爆炸模型下控制大爆炸核合成的动力学方程进行研究,并对其进行计算所需的初始量予以详细介绍,其中包括宇宙热力学量,各核素初始丰度,反应率等等。在核合成计算过程中,选取有效的数值方法来求解核反应网络方程是关键。由于天体环境的特殊性,核反应网络方程的刚性非常强,刚性系数大于1015司空见惯,这在计算时给我们带来了巨大的困难,为此我们介绍了相应的数值解法。同时我们更新核反应率数据库,利用新的反应率建立核反应网络方程并进行计算。其次,利用我国原子能科学研究院核天体实验小组测得的8Li(n,γ)9Li反应率,我们进行核合成模拟重点研究反应链8Li(n,γ)9Li(α,n)12B(β)12C对CNO的合成所起的作用。我们分别进行了两次核合成模拟计算,一次包括8Li(n,γ)9Li(α,n)12B(β)12C链,一次不包括此链,计算结果显示在添加了前人研究中忽略的8Li(n,γ)9Li(α,n)12B(β)12C链后12C的丰度增加了一个量级。为了弄清该反应链对碳氮氧元素合成的具体作用,我还进行了反应流量计算,通过分析碳氮氧的合成,此链在标准的大爆炸模型下开启了一条从轻元素到碳氮氧合成的重要通道,尽管绝对产额依然很小,但是由于宇宙早期第一代结构塌缩形成的星系的物理机制在很大程度上取决于当时气体云的成份,所以这一发现是十分重要的。
[Abstract]:The Big Bang nuclear synthesis is a very important part of the universe model. It is not only a window to understand the early mysteries of the universe, but also the most powerful tool to detect basic physics. And this role is more important today. In this paper, the dynamic equation of controlling the synthesis of the big bang nucleus under the standard big bang model is studied, and the initial amount needed for its calculation is introduced in detail. These include cosmic thermodynamic quantities, initial abundance of nuclides, reaction rates and so on. In the process of nuclear synthesis calculation, it is crucial to select effective numerical methods to solve the equations of nuclear reaction network, because of the particularity of celestial environment. The rigidity of the nuclear reaction network equation is very strong, and the rigidity coefficient is more than 1015, which brings us great difficulties in calculation. For this reason, we introduce the corresponding numerical solution. At the same time, we update the database of nuclear reaction rate, use the new reaction rate to set up the equation of nuclear reaction network and calculate it. Secondly. Using the reaction rate of 8Lin, 纬 ~ (9Li) determined by the experimental group of nuclear celestial bodies of the Institute of Atomic Energy Sciences of China, we have carried out the nuclear synthesis simulation to study the reaction chain 8Lin, 纬 ~ (9) Li (伪). The effect of Nb12B (尾 ~ (12) C) on the synthesis of CNO. We have simulated the nuclear synthesis twice, one time including 8Lin, 纬 ~ (9) Li (伪). The calculated results show that the addition of 8Lin, 纬 ~ (9) Li (伪), which is neglected in previous studies, has been carried out in the Nb12B (尾 ~ (12) C) chain, which is not included in this chain at one time. The abundance of 12C was increased by one order of magnitude. In order to find out the specific effect of the reaction chain on the synthesis of carbon, nitrogen and oxygen, I also calculated the reaction flow rate. By analyzing the synthesis of carbon-nitrogen-oxygen, the chain opens an important pathway from light elements to carbon-nitrogen-oxygen synthesis under the standard Big Bang model, although the absolute yield is still very small. But the discovery is important because the physical mechanism of galaxies formed by the collapse of the first generation of structures in the early universe depends to a large extent on the composition of the gas cloud at that time.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2010
【分类号】：P159

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