费米能区重离子碰撞中初始碎片的重构以及发射源性质的研究

发布时间：2018-03-01 04:41

  本文关键词： 中能重离子核反应 重构的初始碎片多重性 对称能系数 密度 温度　出处：《中国科学院研究生院(近代物理研究所)》2016年博士论文　论文类型：学位论文

【摘要】：核物质状态方程是目前国际核物理研究的热点之一。其中非对称核物质状态方程,特别是对称能的研究更是备受青睐。本论文首次从实验上对40MeV/nucleon的64Zn+112Sn反应中初始碎片的多重性进行了重构,并结合反对称分子动力学模型(AMD),利用重构的初始碎片多重性研究了反应中发射源的性质。同时提出了提取反应中发射源温度、密度和对称能系数的一新方法。实验上利用动力学聚焦原理来确定与探测到的次级中等质量碎片相关联的轻碎片多重性。利用这些数据,采用蒙特卡罗方法对反应中初始碎片的激发能和同位素多重性进行重构。重构的初始碎片激发能在1到4 MeV/nucleon之间时,对于给定的电荷数Z,激发能随碎片质量数A的增大有明显的下降趋势,并且与AMD以及统计多重碎裂模型(SMM)计算所得的激发能有较大不同。而重构的初始碎片的同位素多重性分布与AMD计算所得的初始碎片的同位素多重性分布符合很好。利用重构的初始碎片多重性,本论文研究了碎片质量的指数律分布以及反应中发射源的性质。重构的初始碎片质量数A≥15的同位素质量分布很好的满足指数律A-2.3分布,而较轻的碎片则明显低于该指数律分布。根据修正的Fisher模型,提取了反应中库仑能系数与温度的比值ac/T和对称能系数与温度的比值asym/T随碎片质量数A的变化关系。同时比较了所提取的asym/T的值和AMD采用不同密度相关对称能的Gogny相互作用计算所得的初始碎片中提取的asym/T的值。AMD计算中提取的asym/T的值与系统在碎片产生时的特定密度下对称能的值有明显的相关性。根据这一相关性,我们确定了反应中发射源的密度为ρ/ρ0=0.63±0.03。利用该密度,提取了反应中发射源的对称能系数和温度分别为asym=24.7±3.4 MeV和T=4.9±0.2 MeV。利用该自洽法我们研究了三个不同反应系统的发射源温度、密度,并且将发射源的密度与反应系统在演化中所达到的最大密度进行比较,得出在AMD中,中等质量碎片是产生于温度T~6 MeV、密度ρ/ρ0=0.67的统计平衡的冻结体积。这些研究对我们了解核物质状态方程有重要参考意义。
[Abstract]:The equation of state of nuclear matter is one of the hotspots in the international nuclear physics research at present. Especially, the study of symmetry energy is very popular. In this thesis, the multiplicity of initial fragments in the 40MeV / nucleon 64Zn112Sn reaction was reconstructed for the first time. Combining with the antisymmetric molecular dynamics model, the properties of the emission source in the reaction were studied by using the multiplicity of the reconstructed initial fragments, and the temperature of the emission source in the extraction reaction was proposed. A new method of density and symmetric energy coefficients-determination of the multiplicity of light debris associated with detected secondary intermediate-mass debris experimentally using the kinetic focusing principle. Monte-Carlo method is used to reconstruct the excitation energy and isotopic multiplicity of the initial fragments in the reaction. The reconstructed initial fragment excitation energy is between 1 MeV/nucleon and 4 MeV/nucleon. For a given charge number Z, the excitation energy tends to decrease with the increase of fragment mass number A. The calculated excitation energies of the reconstructed fragments are quite different from those calculated by AMD and the statistical multiple fragmentation model. The isotopic multiplicity distribution of the reconstructed initial fragments is in good agreement with the isotopic multiplicity distribution of the initial fragments calculated by AMD. Taking advantage of the multiplicity of initial fragments of reconstruction, In this paper, we study the exponential law distribution of debris mass and the properties of emission source in the reaction. The reconstructed isotopic mass distribution of the initial fragment mass number A 鈮，

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