【摘要】：實(shí)驗(yàn)核物理學(xué)家們開(kāi)展了一系列關(guān)于超重核合成的研究并獲得了巨大的成功,GSI、RIKEN以及JINR等實(shí)驗(yàn)室成功合成了Z119的所有超重元素。與此同時(shí),包括雙核模型在內(nèi)的許多描述超重核合成機(jī)制的理論模型也陸續(xù)被建立和發(fā)展起來(lái)。雖然理論計(jì)算的超重核產(chǎn)生截面與已知實(shí)驗(yàn)數(shù)據(jù)符合得很好,但是在預(yù)言未知超重核時(shí),不同理論模型的結(jié)果之間存在較大的分歧。本論文從動(dòng)力學(xué)形變效應(yīng)的角度對(duì)現(xiàn)有的雙核模型進(jìn)行了改進(jìn)。早先的雙核模型理論研究假設(shè),在超重核的形成過(guò)程中,相互作用的類彈和類靶碎片總是保持基態(tài)形變不變。但是我們認(rèn)為,在描述超重核的形成過(guò)程時(shí),除了需要考慮類彈和類靶碎片的質(zhì)子數(shù)、中子數(shù)、兩碎片核心間距等多個(gè)物理量外,還應(yīng)考慮兩碎片的動(dòng)力學(xué)形變效應(yīng)以及動(dòng)力學(xué)形變效應(yīng)與其他物理量間的耦合。在重離子熔合反應(yīng)中,強(qiáng)庫(kù)侖作用和核相互作用使得類彈、類靶碎片的形變總是隨著時(shí)間發(fā)生改變,需要對(duì)其進(jìn)行動(dòng)力學(xué)處理。由于在重離子的熔合過(guò)程中發(fā)生了較大的能量弛豫耗散過(guò)程,處于高激發(fā)態(tài)的兩碎片中的核子重新布居到不同的能級(jí)上,進(jìn)而引起較大的且不可逆的形變。另一方面,考慮到兩碎片的形變參量的改變使得它們的質(zhì)量、碎片間的相互作用以及系統(tǒng)的驅(qū)動(dòng)勢(shì)隨之發(fā)生改變,這些改變影響了其他物理量(如能量、角動(dòng)量)的弛豫耗散過(guò)程、核子的轉(zhuǎn)移過(guò)程以及系統(tǒng)的內(nèi)部激發(fā)能,從而繼續(xù)使得兩碎片的形變發(fā)生改變。對(duì)包含了類彈和類靶碎片的質(zhì)子數(shù)、中子數(shù)、兩碎片核心間距以及兩碎片的動(dòng)力學(xué)形變的主方程的數(shù)值求解非常復(fù)雜,因此本文暫時(shí)將動(dòng)力學(xué)形變自由度與其他自由度退耦合,并將類彈和類靶碎片的動(dòng)力學(xué)形變的演化看成是弛豫耗散過(guò)程,通過(guò)求解含有兩碎片動(dòng)力學(xué)形變參量的Fokker-Planck方程,得到了兩碎片的動(dòng)力學(xué)形變的演化規(guī)律。把包含了類彈和類靶碎片的質(zhì)子數(shù)、中子數(shù)的主方程與兩碎片的動(dòng)力學(xué)形變演化規(guī)律相結(jié)合,發(fā)展了與動(dòng)力學(xué)形變效應(yīng)相關(guān)的雙核模型。研究結(jié)果表明:(1)類彈和類靶碎片的動(dòng)力學(xué)形變的演化主要由兩碎片的本征結(jié)構(gòu)和兩碎片間的相互作用所決定;(2)兩碎片的動(dòng)力學(xué)形變的演化存在關(guān)聯(lián),二者相互制約從而使得反應(yīng)系統(tǒng)的驅(qū)動(dòng)勢(shì)向更低的位置移動(dòng);(3)類彈和類靶碎片的動(dòng)力學(xué)形變的弛豫耗散的快慢還受到反應(yīng)過(guò)程中的激發(fā)能、擴(kuò)散系數(shù)以及反應(yīng)系統(tǒng)的同位旋的影響;(4)動(dòng)力學(xué)形變效應(yīng)影響了系統(tǒng)的內(nèi)部熔合位壘,從而改變復(fù)合核的熔合幾率以及蒸發(fā)余核的產(chǎn)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.
【學(xué)位授予單位】：中國(guó)科學(xué)院研究生院(近代物理研究所)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：O571.6

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本文編號(hào)：2224333