重离子全熔合反应中的Langevin统计涨落

在重离子反应中，尽管统计涨落是很明显的，但是在以前的关于重离子全熔合反应的理论模型中未加考虑．本工作在经典轨道模型框架内，在运动方程中包括了Ｌａｎｇｅｖｉｎ无规力，采用Ｍｏｎｔｅ－Ｃａｒｌｏ轨道抽样方法计算了１００Ｍｏ＋１００Ｍｏ和８６Ｋｒ＋１２３Ｓｂ全熔合反应的几率，并且与实验值进行了比较.It is not considered in the previous theoretical models on the complete fusion reactions, though the statistical fluctuation is very obvious. In the present work in framework of the classical trajetory model the Langevin random force is included in the motion equations. The fusion probabilities for the 100 Mo+ 100 Mo和 86 Kr+ 123 Sb reactions are calculated by Monte Carlo sampling of trajectories. The calculated fusion probabilities are also compared with the...     

重离子熔合反应系统中的准裂变(英文)

在重离子熔合反应中,准裂变与熔合过程之间相互竞争。在双核模型中,常常在主方程中加入Kramers公式来描述准裂变。但只有当准裂变位垒足够高时,该公式才能成立。在本工作中,把弹靶核的间距作为独立的动力学变量,通过求解主方程来自洽地同时描述双核模型向全熔合和准裂变过程的演化,因此检验了Kramers 公式的适用条件。此外,在重离子熔合反应过程中,把动力学形变的演化和核子的转移过程都看成是耗散过程,在系统的势能面的约束下,同时求解含有动力学形变参量和质量不对称度参量的一系列主方程。研究显示了动力学形变对准裂变质量分布的直接影响,得到了与实验观测值符合得很好的计算结果。In heavy ion fusion reactions, the quasifission(QF) is competing with fusion, and which is often described by incorporating the Kramers formula(KRA-F) into the master equation(ME) within the Di-Nuclear System(DNS) model. However the KRA-F works well only if the QF barrier is high enough. Presently by takingthe relative distance of nuclei as an independent dynamical variable, the evolution of the DNS towards fusion and QF are both treated as a diffusion process in a consistent way by solving MEs. The validity of the KRA-F is thuschecked. Furthermore, the dynamical deformation and the nucleon transfer in heavy ion fusion reaction process are viewed simultaneously as a diffusion process, and are treated by solving a set of MEs with the variables of thequadrupole deformation of each nucleus and the mass asymmetry variable in the potential energy surface(PES) of the system. The distinct influence of the dynamical deformation on the QF mass yield distribution is discussed,and the experimental observations can be well reproduced by the calculation.     

重离子裂变反应动力学研究

从实验角度评述了重离子裂变反应动力学研究现状．内容包括动力学裂变宽度、裂变时标、核粘滞性的温度和形变相关性以及从裂变实验上研究核粘滞性的方法等． The present status of the dynamics study for heavy ion induced fission reaction includesing the dynamical fission width,the fission time scale,the temperature and deformation dependence of the nuclear viscosity and the methods of the extracting viscosity from fission experiments induced by heavy ion reactions is reviewed.      

重离子熔合反应与双核模型

简单介绍了兰州-北京-吉森合作组对合成超重核的重离子反应进行的初步研究。研究的重点是熔合阶段的反应机制。在原有双核模型的基础上做了一些改进,把耗散相对运动过程与核子转移过程耦合起来,从更微观的角度来描写双核系统向全熔合复合核的演化。在双核过程中的每一步求解主方程,不对驱动势做谐振子近似。同时,还探讨了原子核形变与相对取向对驱动势的影响,存活几率与复合核蒸发中子的奇偶效应,以及入射道中原子核非弹性激发对俘获截面的影响等。In recent years, the Lanzou-Beijing-Giessen collaboration has studied the heavy ion reactions which are lead to the formation of super-heavy nuclei. The study emphases the mechanism of the fusion stage of the reactions. Based on the so called Di-nuclear System Model, some improvements have been made. The main points are the coupling of the dissipation of relative motion energy, angular momentum with nucleon transfer, and solving the Master equation in every step of the nucleon transfer with exact driving potentials, in order to describe the evolution of the system more microscopically. At the same time, we also discussed the effects of nuclear deformation and their relative orientation on the driving potentials, and studied the survive probability of the compound nuclei and its old-even effects, as well as the influence of inelastic excitations of nuclei in entrance channels to the capture cross sections.     

生成超重核的熔合反应中的动力学形变效应

利用包含动力学势能面的双核模型对超重核的生成机制中的一些问题进行了研究。对双核系统的粒子交换势能面进行的计算结果表明,反应过程中原子核动力学形变对于粒子交换势能面的结构有显著的影响。进一步计算了生成超重核的熔合几率,结果显示,原子核的动力学形变导致内熔合位垒升高,进而明显降低了生成超重核的熔合几率。Some aspects in the fusion mechanism for the production of superheavy nuclei are investigated with the dinuclear system model with dynamical potential energy surface. The calculation results about the potential energy surface indicate that the inclusion of nuclear dynamical deformation affects the structure of potential energy surface significantly.The investigation on the fusion probability to synthesize superheavy nuclei indicates that the fusion probability decreases significantly due to the increase of the inner fusion barrier for the inclusion of the nuclear dynamical deformation.     

重离子熔合势垒的动力学模型研究

在改进的量子分子动力学模型基础上系统地研究了超重核合成中的入射道静态势和动力学势.从入射道静态势给出了质量不对称度与静态势垒高度以及质量不对称度与接触点驱动势的关系.动力学势垒高度是能量依赖的,随着入射能量的增加而增加,最终趋近于密度冻结势垒高度;动力学势垒高度随着入射能量的降低而降低,它的最低值接近于绝热势垒高度.在冷熔合反应中,动力学势垒的最低值所对应的入射能量可能是合成超重元素最佳入射能的选择     

重离子熔合反应形成超重核的截面研究

在双核系统框架下,通过数值法解主方程计算了双核间的核子跃迁全熔合几率.两碰撞核内部激发能由相对运动能损提供,因此能够将核子转移过程与相对运动耦合起来.对一些以Pb为靶的形成超重核的冷熔合反应,计算了最佳激发能、形成双核系统的俘获截面、复合核形成几率及存活几率等,所得到的形成超重核蒸发剩余截面与已知实验值符合较好. In the concept of Dinuclear system (DNS) the complete fusion probability of two touch nuclei via nucleon transfer is described by numerically solving the Master equation. The excitation energy of two colliding nuclei is supplied by the energy dissipation of their relative motion, thus the nucleon transfer process and the relative motion are coupled. For Pb based cold fusion reactions to form super heavy nuclei, the optimal excitation energy, the capture cross section to form a DNS ...     

熔合反应中动力学势垒的研究

用改进的量子分子动力学模型研究了与入射能量相关的重离子熔合势垒. 随着 入射能的降低可以观察到动力学势垒的最低值, 这个最低动力学势垒与绝热势垒 非常接近；动力学势垒随着入射能的增加而升高, 最终接近于静态势垒(非绝热势垒). 基于动力学势垒的研究, 对于重离子熔合反应的额外推动(extra-push)给出了微观理解,对势垒贯穿给出了一种新的解释. 为进一步理解动力学势垒, 还研究了颈部的形成和体系的动力学形变, 分析了动力学势垒降低的原因.     

用He离子诱导的裂变激发函数探测核摩擦强度(英文)

随机模型被用于分析3He+197Au,3He+208Pb和3He 186W反应测量的裂变激发函数。提取的鞍点前摩擦强度约为4×1021s-1。揭示了能级密度参数的大小在约束核摩擦强度中的作用。计算表明,高激发条件能能显著增强裂变截面对核耗散的敏感性。     

裂变过程的动力学和统计自洽描述及不同方法之间的分析与比较

简要介绍了裂变过程动力学和统计自洽描述的研究概况、意义及应用前景.重点描述了考虑扩散动力学过程的裂变道理论以及P.Frobrich等人依据Strutinsky方法给出的Kramers-modified Bohr-Wheeler公式,并以n+²³⁸U,激发能至80MeV为例对上述两种模型进行了较详细的分析与比较.     

重离子熔合反应的相互作用势

运用Skyrme势及快过程近似与绝热过程近似两种极限,计算了几组重离子之间的相互作用势,应用此相互作用势计算了熔合反应截面,与实验结果进行了比较.     

快重离子引起的辐照效应

用PAT、CEMS、SEM和TEM分析观测了HIRFL提供的能量为几十MeV到几百MeV的碳离子在Ni、马氏体时效不锈钢、HT—9铁素体钢和316L不锈钢中引起的辐照效应,包括辐照引起的偏析、脱溶、相变和肿胀,以及辐照肿胀随辐照温度的变化关系,研究了510MeV的碳离子在高纯Ni中的损伤分布,并给出了95MeV的Ar离子模拟宇宙射线在宇宙飞行器中引起数字半导体器件“软故障”的最近结果。 The radiation effects were studied by means of PAT, CEMS, SEM and TEM in nickel,martensitic ageing stainless steel, ferrite steel HT-9 and stainless steel 316L induced by carbon ionswith energy of tens of MeV to hundreds of MeV delivered by HIRFL. It includes segregate,preciptale, phase change and void swelling, as well as temperature-relativity of the irradiationswelling. The damage distribution was also studied in nickel irradiated by 510MeV C~(6+). And the recentresults of Ar ions ...     

弱束缚弹核引起的熔合反应

⁶Li, ⁹Be为弱束缚核. 通过弱束缚弹核⁶Li, ⁹Be轰击靶²⁰⁸Pb,²⁰⁸Be的实验熔合激发函数与理论预言的比较, 讨论了弱束缚弹核破裂对熔合过程 的影响. 比较结果显示, 弱束缚弹核与重靶核的完全熔合截面在垒上能区 明显压低. 由部分熔合截面与完全熔合截面之和得到总熔合截面. 研究结果 表明, 破裂对总熔合截面几乎没有影响. 由此可见, 弱束缚核的部分熔合 可能发生在强吸收区域附近. 最后还给出了全熔合截面与部分熔合截面 之间的关系.     

非全熔合反应裂变角分布

采用核固体径迹探测器测量了¹⁶O+¹⁵⁹Tb、¹⁶O+¹⁹⁷)Au和¹⁶O+²⁰⁹Bi反应碎片角分布,扣除中等质量碎片(IMF)的贡献,用过渡态统计模型(TSM)和单个自旋标准理论拟合实验的裂变角分布,提取裂变核的自旋. 讨论了它随质心系入射能量的变化.     

重离子周边碰撞和中心碰撞引起的不同裂变行为

本实验同时研究了4 0Ar+209Bi反应中周边碰撞和中心碰撞两者产生的关联裂变碎片,以及其与α粒子的再关联.对裂变碎片质量分布和能量分布随热裂变核初始温度演化的系统分析,发现中心碰撞和周边碰撞所形成的热核存在着不同的裂变行为. Correlated fission fragments from the 40Ar+209Bi reaction and their further correlation with α particles have been studied for peripheral and central collisions simultaneously. The existence of different fission behavior of hot nuclei formed in central and peripheral collisions was found from the systematic analysis of the mass and energy distributions of fission fragments as a function of the initial temperature of hot fissioning nuclei.     

Role of Barrier Modification and Nuclear Structure Effects in Sub-Barrier Fusion Dynamics of Various Heavy Ion Fusion Reactions

The role of barrier modifications and the relevant nuclear structure effects in the fusion of the \( {}_8{}^{16}O+{}_{62}{}^{144,148,150,152,154}Sm \) and \( {}_3{}^{6,7}Li+{}_{62}{}^{152}Sm \) systems is analyzed within the context of the energy-dependent Woods-Saxon potential model (EDWSP model) and the coupled channel model. For the \( {}_8{}^{16}O+{}_{62}{}^{144,148,150,152,154}Sm \) reactions, where the colliding pairs are stable against breakup, the collective excitations and/or static deformations are sufficient to account for the observed fusion enhancement. In contrast, the model calculations overpredict the complete fusion data at above - barrier energies for the \( {}_3{}^{6,7}Li+{}_{62}{}^{152}Sm \) systems, where the importance of projectile breakup effects has been pointed out. Due to the low threshold of the alpha-breakup channel, the weakly bound projectiles \( \left({}_3{}^{6,7}Li\right) \) break up into charged fragments before reaching the fusion barrier and consequently the complete fusion cross section is suppressed by 28% (25%) in the \( {}_3{}^6Li+{}_{62}{}^{152}Sm\;\left({}_3{}^7Li+{}_{62}{}^{152}Sm\right) \) reaction with respect to predictions of coupled channel calculations. However, the EDWSP model based calculations can minimize the suppression factor by as much as of 13% (8%) in the \( {}_3{}^6Li+{}_{62}{}^{152}Sm\;\left({}_3{}^7Li+{}_{62}{}^{152}Sm\right) \) reaction with reference to the predictions made by the coupled channel calculations. Therefore, the complete fusion data of the \( {}_3{}^6Li+{}_{62}{}^{152}Sm\;\left({}_3{}^7Li+{}_{62}{}^{152}Sm\right) \) reaction at above - barrier energies is reduced by 15% (17%) with respect to the expectations of the EDWSP model. The extracted suppression factors for the studied reactions are due to the modifications of the barrier profile as a consequence of the energy - dependence in nucleus-nucleus potential, and thus greater barrier modifications occur for more weakly bound system, which in turn, confirms the breakup of projectile in the incoming channel.     

重离子惯性聚变的研究

本文描述了重离子惯性聚变的研究现状和用于重离子惯性聚变的重离子加速器． The present researching status and the heavy ion accelerators used for inertial fusion of heavy ions are decribed in the paper.