中能重离子碰撞中集体流的同位旋效应

在同位旋相关的量子分子动力学模型的基础上,利用Skyrme–Hartree–Fock计算所得的中子、质子密度,同时利用费米气体模型得到相应的中子、质子费米面,抽样出稳定的⁵⁸Fe和⁵⁸Ni初始核.仔细研究了55MeV/u ⁵⁸Fe+⁵⁸Fe和55MeV/u⁵⁸Ni+⁵⁸Ni两个反应中集体流的同位旋效应.在不同碰撞参数下对不同类型的碎块,观察到丰中子反应系统⁵⁸Fe+⁵⁸Fe比⁵⁸Ni+⁵⁸Ni有更强的集体流,并能与实验结果定性符合.同时,研究了同位旋相关的对称能与核子–核子碰撞截面对集体流的影响.     

转动集体流的同位旋效应

在同位旋相关的量子分子动力学模型框架下,通过分析中间快度的方位角分布研究了40MeV/u ⁵⁸Fe+⁵⁸Fe和⁵⁸Ni+⁵⁸Ni反应体系在不同碰撞参数下的转动集体流,并且半经典地计算了转动观测量.发现丰中子体系(⁵⁸Fe+⁵⁸Fe)具有较强的转动集体流,这种现象在半周边碰撞中更加明显.转动集体流的同位旋相关性主要来自于核子–核子碰撞截面的同位旋相关性和对称能的影响.     

40Ca+58Fe,58Ni反应中的径向膨胀流研究

利用同位旋相关的Boltzmann-Langevin方程研究了⁴⁰Ca+⁵⁸Fe和⁴⁰Ca+⁵⁸Ni两个反应系统在53,100,150和200MeV/u入射能量下对心碰撞的径向膨胀流.发现对于丰中子系统⁴⁰Ca+⁵⁸Fe的径向膨胀流系统性地小于稳定系统⁴⁰Ca+⁵⁸Ni的径向膨胀流.在假定轰击能量与反应体系的压缩密度呈抛物线关系时,能够解释入射能量和径向膨胀流之间呈现的直线关系.提取了出现径向膨胀流的轰击能量阈值,发现对丰中子系统⁴⁰Ca+⁵⁸Fe得到的能量阈值小于稳定系统⁴⁰Ca+⁵⁸Ni所得到的能量阈值.     

中能重离子碰撞中的碰撞参数研究

在入射能量E为40和100MeV/u时,对¹¹²Sn+¹¹²Sn和¹²⁴Sn+¹²⁴Sn两个反应系统在不同碰撞参数下进行了同位旋相关的量子分子动力学模型计算,系统研究了阻塞率、线性动量转移、荷电粒子多重性、轻荷电粒子多重性、中子多重性以及束缚核总电荷Z_bound随碰撞参数的变化规律,结果表明,中子多重性对碰撞参数的依赖在两个能量下都存在着明显的同位旋效应,Z_bound在E为40MeV/u时存在着同位旋效应.同时讨论了在较低和较高能量时如何更合理地确定反应事件的碰撞参数.     

挤出流的同位旋效应

在同位旋相关的量子分子动力学模型框架下,研究了碰撞系统¹²⁴Sn¹²⁴+Sn和¹²⁴Ba+¹²⁴Ba的挤出流及其同位旋效应.发现丰中子系统¹²⁴Sn+¹²⁴Sn表现出较小的挤出流,挤出流的这种同位旋相关性主要是由核子–核子碰撞截面的同位旋相关性所决定的,只与对称能微弱相关.     

中能重离子碰撞中带电粒子多重性的同位旋效应

利用兰州4π带电粒子探测器阵列测量带电粒子多重性,研究了55MeV/u ⁴⁰Ar+^58,64Ni核反应中He和中等质量碎片的产额与反应系统同位旋的关系,以及这种同位旋效应与反应系统的碰撞参数(即碰撞的激烈程度)、系统的激发能的变化关系,对两个反应系统,观察到带电粒子多重性中He的比分随带电粒子多重性的增加而增大,带电粒子多重性中IMF的比分随带电粒子多重性的增加而先增大,后减小的规律.两个反应系统虽然具有相同的核电荷数,但轻粒子He和中等质量碎片在多重性中的比分有明显的同位旋相关性。     

30MeV/u 40Ar+58,64Ni和115In反应中中等质量碎片的角分布

在5°—140°范围内测量了30MeV/u ⁴⁰Ar束流轰击不同靶核(⁵⁸Ni、⁶⁴Ni、¹¹⁵In)后出射的中等质量碎片(IMF,Z=3—19)的角分布.用指数分布函数dσ/dΩ=N·exp(–θ/α)对出射碎片角分布分角区做了拟合.对3个反应系统分别提取出与相互作用时间有关的衰减因子α和与发射源强度有关的物理量N,讨论了α与N在不同角区与反应系统和出射IMF电荷数的关系.考察了角分布与同位旋自由度和反应系统对称性的关系.     

35MeV/u36Ar+124Sn反应中类弹产物的同位素分布特性

测量了35MeV/u³⁶Ar+¹²⁴Sn反应中5.3°处类弹产物的同位素分布,观察到随着出射动能的增加,产物的平均中质比逐渐减小而接近弹核的平均中质比.同位旋相关的量子分子动力学计算表明,随着反应时间的增加,类弹产物的平均出射动能逐渐减小而平均N/Z值则逐渐增大.另外,碰撞参数也影响类弹产物的同位素组成:随着碰撞参数的减小,类弹产物的平均N/Z值减小.     

径向膨胀流的同位旋效应

利用同位旋相关的量子分子动力学模型,研究了¹²⁴Ba+¹²⁴Ba和¹²⁴Sn+¹²⁴Sn两个系统在不同入射能量下对心碰撞的径向膨胀流.发现丰中子系统¹²⁴Sn+¹²⁴Sn的径向膨胀流系统性地小于系统¹²⁴Ba+¹²⁴Ba的径向膨胀流.同时发现这种差别主要来自于核子–核子碰撞截面的同位旋相关性而几乎与对称能无关.     

35MeV/u 36Ar+112,124Sn反应中中等质量碎片关联函数的入射道依赖

³⁶Ar+^112,124Sn反应中小角关联出射的中等质量碎片(IMF)约化速度关联函数. 结果表明³⁶Ar+¹²⁴Sn反应系统中的约化速度关联函数在小约化速度处的反关联程度比³⁶Ar+¹¹²Sn反应系统中的强, 表现出明显的入射道依赖性. 考察出射粒子对的单核子总动量时, 发现这种差异主要来自于高动量粒子对的贡献. 用三体弹道理论模型MENEKA分别计算了两个系统的IMF发射时标, 在³⁶Ar+¹¹²Sn反应系统中约为150fm/c, 而在³⁶Ar+¹²⁴Sn反应系统中, 约为120fm/c. 同位旋相关的量子分子动力学计算表明, ³⁶Ar+¹²⁴Sn系统中IMF的发射时间谱比³⁶Ar+¹¹²Sn系统略有前移, 相应地, 其中心密度从最高点随时间的下降亦比³⁶Ar+¹¹²Sn系统略快.     

Learning about the nuclear equation of state using flow

We present results for transverse flow, the balance energy, and elliptic flow for Ar+Sc, ⁵⁸Fe+⁵⁸Fe, ⁵⁸Ni+⁵⁸Ni, Kr+Nb, and Au+Au. We find that a soft equation of state is required to explain these results. We find that a momentum dependent formulation of the nuclear mean field is required. A 30% density dependent reduction of the in-medium nucleon-nucleon cross sections in BUU is required to reproduce the observed balance energies for light systems.     

Probing Balance Energy Using Momentum- and Isospin-Dependent Potential

Using the momentum- and isospin-dependent Boltmann-Uehling-Uhlenbeck （BUU） model, we investigate the transverse flow and balance energy in two isotopic colliding systems ^48Ca＋^58Fe and ^48Cr＋^58Ni by adopting different symmetry potentials. By comparing the results between the two colliding systems, we find that the difference between the balance energies of two isotopic systems can be considered as a sensitive probe to the density dependence of symmetry energy.     

Isospin effects of projectile fragmentation in a Boltzmann-Langevin approach

The iso spin effects of projectile fragmentation at intermediate energies are investigated using an iso spindependent Boltzmann-Langevin model.The collisions of mass-symmetric reactions including ~(58)Fe,~(58)Ni+~(58)Fe,and~(58)Ni at intermediate energies,in the 30 to 100 MeV/A range,are studied for different symmetry energies.Yield ratios of the isotopic,isobaric,and isotonic pairs of fragments from the intermediate-mass region using three symmetry energies are extracted as functions of the N/Z ratio of the composite systems in the entrance channel and the incident energies.It is found that the yield ratios are sensitive to symmetry energies,especially for neutron-rich systems,and the calculations using soft symmetry energy are closer to the experimental data.The iso spin effect is stronger for the soft symmetry energy,owing to the competition of the repulsive Coulomb force and the symmetry energy attractive force on the proton.For the first time,the splits are presented,revealing a transition from the iso spin equilibrium at lower energies to translucency at intermediate energies.The results show a degree of transparency in that intermediate mass fragments undergo a transition from dependence on the composite systems in the entrance channel to reliance on the projectile and target nuclei.     

40 Ca+58Fe，58Ni反应中的径向膨胀流研究

利用同位旋相关的Boltzmann-Langevin方程研究了^40Ca ^58Fe和^40cA ^58Ni两个反应系统在53,100,1506 200MeV／u入射能量下对心碰撞的径向膨胀流,发现对于丰中子系统^40Ca ^58Fe的径向膨胀流系统性地小于稳定系统^40Ca ^58Ni的径向膨胀,在假定轰击能量与反应体系的压缩密度呈抛物线关系时,能够解释入射能量和径向膨胀流之间呈现的直线关系,提取了出现径向膨胀流的轰击能量阈值,发现对丰中子系统^40Ca ^58Fe得到的能量阈值小于稳定系统^40Ca ^58Ni所得到的能量阈值。     

Radial Expansion Flow in Reactions of 40Ca+58Fe and 40Ca+58Ni

By means of using an isospin-dependent Boltzmann-Langevin equation which includes isospin-dependent symmetry energy, Coulomb energy, isospin-dependent nucleon-nucleon cross sections, Pauli blocking, and initialization, the radial expansion flow of reaction systems ⁴⁰Ca+⁵⁸Ni and ⁴⁰Ca+⁵⁸Fe at 53, 100, 150, and 200 MeV/u in the central collisions were studied. It has shown that the more neutron rich system exhibits smaller radial expansion flow. It was found that the neutron rich system had smaller threshold energy which may provide a new method to determine the isospin dependent nuclear equation of state from calculated result and linear fitting result.     

超重核合成的同位素依赖探讨

利用二参量Smoluchowski方程计算了54Fe+204Pb,56Fe+206Pb,58Fe+208Pb冷熔合和32,34,36S+238U热熔合的复合核形成截面和蒸发残余截面, 结果清楚地显示出超重核合成截面随同位素的变化。 由于较低的入射道库仑位垒、 较低的不对称裂变谷中的条件鞍点和较小的中子分离能, 一般地说, 丰中子同位素的超重核形成截面明显增强。 The cross sections of the compound nucleus formation and e vaporation residue for the 54Fe+204Pb, 56Fe+206Pb, 58Fe+208Pb cold fusion and 32,34, 36S+238U hot fusion have been calculated by using a two parameter Smoluchowski equation. Our results clearly show the isotope dependence of superheavy nucleus production. The formation cross sections of the neutron rich isotope are, generally speaking, obviously enhanced due to the lower Coloumb barrier , lower height of the conditional saddle point, and smaller neutron separation energy.     

Entrance Channel Mass Asymmetry Effects in Sub-Barrier Fusion Dynamics by Using Energy Dependent Woods–Saxon Potential

The present article highlights the inconsistency of static Woods Saxon potential and the applicability of energy dependent Woods Saxon potential to explore the fusion dynamics of ~(48)_(22)Ti+~(58,60,64)_(28)Ni,~(46)_(22)Ti+~(64)_(28)Ti+~(50)_(22)Ti+~(60)_(28)Ni,and~(19)_9F+~(93)_(41)Nb reactions leading to formation of different Sn-isotopes via different entrance channels.Theoretical calculations based upon one-dimensional Wong formula obtained by using static Woods Saxon potential unable to provide proper explanation for sub-barrier fusion enhancement of these projectile-target combinations.However,the predictions of onedimensional Wong formula based upon energy dependent Woods Saxon potential model(EDWSP model) accurately describe the observed fusion dynamics of these systems wherein the significantly larger value of diffuseness parameter ranging from a = 0.85 fm to a = 0.97 fm is required to address the experimental data in whole range of energy.Therefore,the energy dependence in nucleus-nucleus potential simulates the influence of the nuclear structure degrees of freedom of the colliding pairs.     

DETERMINATION OF THE AVERAGE NEUTRON ENERGY USING CROSS SECTION RATIO OF 58Ni(n,p)58m+gCo and 58Ni(n,2n)57Ni REACTIONS

The method of determination for average neutron energy from D-T reaction by using two silicon semiconductor detectors and the cross section ratios of ⁵⁸Ni(n,p)^58m+gCo and ⁵⁸Ni(n,2n)⁵⁷Ni reactions is described.The plot of the cross section ratio against the neutron energy has been obtained.The results have been compared with existing data.