80.6MeV ~(16)O轰击~(27)Al反应的弛豫过程的研究

从80.6MeV~(16)O ~(274)Al出射类弹碎片的测量实验结果导出了角分布衰减系数、电荷分布及电荷分布的一次矩和二次矩随TKEL的变化,对该反应中的弛豫过程进行了分析。并讨论了势能面对电荷分布的一次矩和二次矩的影响。     

80.6MeV~(16)O轰击~(27)Al出射类弹碎片的测量

用大面积位置灵敏电离室测量了80.6MeV~(16)O轰击~(27)Al时产生的出射类弹碎片,得到了从Li到Na的能谱、角分布、E-θ平面上的d~2σ/dQ dE等高线图及Z分布;导出了准弹和深部非弹的截面;并对实验结果进行了讨论.     

16O轰击27Al α粒子发射的研究

用ΔE-E半导体望远镜测量了84.5MeV及62.0MeV ¹⁶O轰击²⁷Al产生的α粒子, 得到了α粒子的发射能谱、角分布、E-θ平面上d²σ/dE﹒dΩ等高图及核温度随发射角的变化. 对产生α粒子的直接机制作了讨论.     

~(12)C轰击~(12)C,~(27)Al,~(nat)Ca反应中发射α粒子的测量与分析

我们测量了69.5MeV~(12)C轰击~(12)C,~(27)Al,~(nat)Ca反应中出射的α粒子的能谱和角分布.用快粒子激子模型理论计算了包含平衡和前平衡出射的α粒子成份.在这三个反应中它们构成α产额的绝大部分,其中前平衡发射的α粒子估计分别占11％、14％、16％.尚有一部分来自其它反应机制的贡献.     

Collective Flows of ~(16)O+~(16)O Collisions with α-Clustering Configurations

The main purpose of the present work is to discuss whether or not the collective flows in heavy-ion collision at the Fermi energy can be taken as a tool to investigate the cluster configuration in light nuclei. In practice, within an extended quantum molecular dynamics model, four α-clustering(linear chain, kite, square and tetrahedron)configurations of 160 are employed in the initialization, ~(16)O+~(16)O around the Fermi energy(40-60 MeV/nucleon)with impact parameter 1-3 fm are simulated, and the directed and elliptic flows are analyzed. It is found that collective flows are influenced by the different α-clustering configurations, and the directed flow of free protons is more sensitive to the initial cluster configuration than the elliptic flow. Nuclear reaction at the Fermi energy can be taken as a useful way to study cluster configuration in light nuclei.     

80.9MeV~(16)O+~(27)Al能量耗散和核子交换的关系

用带△E-E望远镜系统的飞行时间系统测量了80.9MeV~(16)O+~(27)Al反应出射产物的三重微分截面d~3σ/dA·dZ·DE.对该反应中所出现的能量耗散和核子交换的关系进行了讨论.     

97MeV~(16)O轰击~(51)V靶出射α粒子的测量与理论分析

用不同种类的粒子望远镜测量了97MeV~(16)O+~(51)V反应中出射的α粒子.得到了单举α粒子能谱、角分布、E-θ平面内的d~2θ/dEDΩ截面等高图及速度平面内的d~2θ/PCdEdΩ截面等高图.区分了复合核蒸发的α粒子与直接机制发射的α粒子.用激子模型对预平衡发射的α粒子贡献进行估计,得到的预平衡发射和复合核蒸发分别在α粒子总产额中所占的比份.     

720MeV~(12)C轰击~(232)Th裂变反应发射的质子和α粒子

本文介绍了720MeV ~(12)C轰击~(232)Th裂变反应发射的质子和α粒子的三重微分截面.实验结果证实p和α的发射先于裂变过程,p和α能谱的低能成分来源于类靶余核的准热蒸发.本文用运动源模型拟合了p和α能谱.用聚合模型很好地重现了α能谱。     

~(12)C(~7Li,t)~(16)O和~(20)Ne(d,~6Li)~(16)O反应的研究

本文把用于处理重离子引起的单粒子转移反应的Goldfarb-Buttle方法推广到多粒子转移反应。计算了~(12)C(~7Li,t)~(16)O和~(20)Ne(d,~6Li)~(16)O反应,用了~(16)O的全相干波函数,考虑了某些反冲因素,并将结果与实验作了比较。     

张量力在~(16)O+~(16)O熔合动力学中的效应

利用时间相关Hartree-Fock理论和完整Skyrme有效相互作用研究了~(16)O+~(16)O碰撞在库仑位垒附近的熔合动力学。数值计算是在没有任何对称性约束的三维笛卡尔基下完成。将时间相关Hartree-Fock理论和冻结密度近似下的能量密度泛函方法给出的库仑位垒与实验结果进行了比较,发现同位旋标量的张量项能降低自旋饱和体系~(16)O+~(16)O的库仑位垒,而库仑位垒高度随着同位旋矢量的张量项的耦合常数减小而降低。并计算了包含和不包含张量力的~(16)O+~(16)O熔合截面,发现张量力对~(16)O+~(16)O碰撞在库仑位垒附近的熔合动力学影响较小。     

~(12)C ~(27)Al,~(40)Ca耗散碰撞的扩散模型分析

在扩散模型的框架内,用假定中间组合系统以一个统计的寿命衰变的方法分析了68MeV~(12)C ~(27)Al和68.6MeV~(12)C ~(40)Ca的耗散碰撞中产生的产物的三重微分截面d~3σ/dZdEdθ的一般趋向。导出了中间组合系统的半衰期及产生全阻尼深部非弹性产物的平均互作用半径。简单地对计算的角分布及Wilczynski图与实验测量结果进行了比较,讨论了产生二者之间的差异的可能原因。     

~(16)O ~(24)Mg和~(20)Ne (24)Mg弹性散射的机制

本文考虑了两碰撞核间核子结团的转移机制,解释了象~(16)O ~(24)Mg和~(20)Ne ~(24)Mg这样一些4N核间的弹性散射微分截面后角振荡上升的反常现象.在原子核分子轨道模型的理论框架下,将交换势的强度作为唯一的可调参数,数值计算较自然地拟合实验结果.     

Investigation of α-nucleus interaction in the 27Al (α,α)27Al scattering and 27Al (α, d )29Si reaction

Full finite-range macroscopic calculations in the distorted-wave Born approximation have been performed using the molecular and Michel α-nucleus potentials to analyze the angular distributions of cross-sections of the ²⁷Al(α, d)²⁹Si reaction, at 26.5 and 27.2 MeV incident energies, leading to seven transitions up to the excitation energy E _X = 4.08 MeV of the final nucleus. The parameters of the two types of the α-nucleus potentials are determined from the elastic-scattering data. Both the molecular and Michel potentials, without any adjustment to the parameters needed to fit the elastic-scattering data, are able in most cases to reproduce, simultaneously, the absolute cross-sections particularly at large angles, where the previous calculations failed to reproduce by orders of magnitude, and the gross pattern of angular distributions of the reaction. The deuteron-cluster spectroscopic factors for most of the seven transitions, deduced using the two α-²⁷Al potentials, differ from those obtained in earlier works. The spectroscopic factor for the ground-state transition, deduced in the present work for the 25.8 MeV data, agrees well with the shell model prediction. Received: 15 July 2002 / Accepted: 8 August 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: akbasak2001@Yahoo.com Communicated by G. Orlandini     

高能α粒子轰击Yb箔制备~(178)Hf~(m2)核素的初步研究

在CS30回旋加速器上利用27MeV的α粒子束轰击天然金属Yb箔.对辐照样品进行了分析,确定产生的178Hfm2核素约1.5×1011个,辨识出样品中主要的长寿命核素,并推断产生这些核素可能的核反应通道.基于对样品放射性剂量率跟踪监测结果,初步确定了样品的冷却时间.这些研究结果一方面验证了所选择的制备途径是可行的,另一方面也为进一步开展该核素制备技术研究提供了参考依据.     

~(16)O巨偶极共振的精细结构

电巨偶极共振(GDR)的精细结构是原子核在高激发态下仍表现出有复杂结构的一个典型例子.例如~(16)O在GDR区的21,22,23,24,25(MeV)的五个共振峰在(γ,n)和(γ,p)反应中同时被确证.偶极强度的分布情况是22,24两个峰占有60%,其它每个峰都是占百分之几的比例.2p-1h(以p表粒子,h表空穴)壳模型组态混合的计算,在GDR区只能给出22和24 MeV的二个峰.因此强度函数的上述结构无疑表示GDR在向复合核态延展过程中,与该能区的其它多粒子激发有特殊的耦合。     

~(12)C ~(159)Tb、Ag和~(89)Y核反应中发射轻粒子的测量

本文报道了用71.5MeV的~(12)C重离子轰打~(159)Tb、Ag和~(89)Y靶,测出了发射α粒子的能谱和角分布,以及发射氘和质子的一些角分布。所测到的α颗子能谱为钟罩形连续谱,其最可几能量接近于库仑位垒。对于~(159)Tb靶和Ag靶,α粒子角分布在近于或小于擦边角处成峰;而对~(89)Y靶,从最小测量角(40°)开始,微分截面随角度增加单调下降。α粒子发射截面均远远大于统计级联蒸发截面值。发射质子与氘的角分布,均随角度增加呈指数下降趋势,它表现出前平衡发射的特征。为了解释α粒子角分布中的各向异性部分,提出了强阻尼粘合转动的概念,它是以不完全熔合反应模型作为基础的。     

轰击能在5.3MeV/A以下的(16)~O+(27)~Al反应的研究

对轰击能在5.3MeV/A以下的~(16)O+~(27)Al系统产生的准弹和深部非弹反应作了较细致的研究.给出了反应产物的能谱、角分布、电荷分布及E-θ平面上的(d~3σ/dEdΩdZ)等高图,并分析了它们随轰击能量的演交过程.讨论了作为轰击能量的函数,准弹和深部非弹是如何竞争的.也讨论了轻系统中能量和质量弛豫过程的特征及核结构效应的影响.     

~(16)O+~(12)C反应全熔合激发函数的测量

我们用位置灵敏的ΔE-E望远镜系统测量了入射能量为50—90MeV范围内的~(16)O+~(12)C反应全熔合截面,发现全熔合激发函数是不平滑的,存在着一些结构,其峰位约在26.0,31.0和36.4MeV。对实验结果进行了分析和讨论,并与前人的工作进行了比较。     

Thermonuclear ~(19)F(p,α_0)~(16)O reaction rate

The thermonuclear~(19)F(p,α_0)16O reaction rate in the temperature region 0.007–10 GK has been derived by re-evaluating the available experimental data, together with the low-energy theoretical R-matrix extrapolations.Our new rate deviates by up to about 30% compared to the previous results, although all rates are consistent within the uncertainties. At very low temperature(e.g. 0.01 GK) our reaction rate is about 20% lower than the most recently published rate, because of a difference in the low energy extrapolated S-factor and a more accurate estimate of the reduced mass used in the calculation of the reaction rate. At temperatures above ~1 GK, our rate is lower, for instance, by about 20% around 1.75 GK, because we have re-evaluated the previous data(Isoya et al., Nucl. Phys.7, 116(1958)) in a meticulous way. The present interpretation is supported by the direct experimental data. The uncertainties of the present evaluated rate are estimated to be about 20% in the temperature region below 0.2 GK,and are mainly caused by the lack of low-energy experimental data and the large uncertainties in the existing data.Asymptotic giant branch(AGB) stars evolve at temperatures below 0.2 GK, where the~(19)F(p,α)16O reaction may play a very important role. However, the current accuracy of the reaction rate is insufficient to help to describe, in a careful way, the fluorine over-abundances observed in AGB stars. Precise cross section(or S factor) data in the low energy region are therefore needed for astrophysical nucleosynthesis studies.     

Intermediate Energy Pion-~(20)Ne Elastic Scattering in the α+~(16)O Model of (20)~Ne

We present an analysis of π-20Ne elastic scattering at intermediate energy basing on the α+16O model of the20Ne nucleus and in the framework of Glauber multiple scattering theory. Satisfactory agreement with the general features of the experimental data of pion elastic scattering on the neighboring 4N-type nuclei is obtained without any free parameters. Compared with the experimental angular distributions of pion elastic scattering on12C,16O,24Mg,and28Si nuclei, the difractive patterns and the positions of the dips and peaks in the angular distributions of π-20Ne elastic scattering are reasonably predicted by the calculations.