25MeV/u 40Ar+93Nb反应中热核的激发能和核温度

利用半导体望远镜探测器和PPAC对25MeV/u ⁴⁰Ar+⁹³Nb反应中的带电粒子和余核进行了关联测量,对所得α粒子能谱用三源模型进行了拟合,并由余核飞行时间和粒子多重性得到热核激发能.通过对温度的修正,发现在本实验中有激发能E^*/A为4.3MeV,温度T_init为6.9MeV的热核形成.通过与其它实验结果的对比可以看出核物质在轻系统和重系统中行为的差异.     

25MeV/u 40Ar+93Nb反应中热核巨共振研究

对25MeV/u ⁴⁰Ar+⁹³Nb反应形成的热核发射的γ射线、轻带电粒子和蒸发余核进行了符合测量,从余核的飞行时间和轻带电粒子能谱得出非完全熔合反应形成的热核的初始激发能.GDR γ衰变的产额在研究的激发能范围内保持不变.用统计模型CASCADE程序对实验结果进行分析. 讨论了引起GDRγ衰变产额饱和的原因.当假定热核激发能大于250MeV时无GDR γ发射,则可以用CASCADE程序很好地拟合E_γ大于12MeV的实验谱.     

N,N-二甲基硫代乙酰胺S3(ππ*)态的衰变动力学 (cited: 1)

采用共振拉曼光谱和完全活化空间自洽场方法研究了N,N-二甲基硫代乙酰胺在被激发至S₃(ππ^*)态后的衰减动力学. 指认了紫外吸收光谱和振动光谱. 获得了乙腈、甲醇和水溶剂中不同激发波长下的A带共振拉曼光谱,以探测Franck-Condon区域的结构动力学. 开展了CASSCF计算以确定低能单重激发态和锥形交叉点的电子激发能和优化几何结构. 通过共振拉曼强度分析和CASSCF计算获得了结构参数、A带结构动力学和S₃(ππ^*)态衰减机制. 提出了主要衰减通道为_3,FC(ππ^*)→S₃(ππ^*)/S₁(nπ^*)→_1(nπ^*).     

中等质量热核三重碎裂

在25MeV/u ⁴⁰Ar+¹¹⁵In、¹⁰³Rh、⁹³Nb反应中对三重碎裂事件做了测量.用10块25cm×20cm位置灵敏平行板雪崩计数器(PPAC)组成的探测系统对中等质量热核其出射角大于32°的三重碎片,做了关联测量.裂片总动能(TKE),三体与二体的产额比(P₃₂),裂片质量、速度、关联角分布等量均由实验测得.从裂片质量比可粗略得到一个简单的经验表达式.利用一个简单的时—空模型对角关联函数进行模拟提取出了三体事件中两断点的时间差.在热核中P₃₂相对于Z²/A表现出较好的系统性.     

J/ψ辐射衰变中θ(1720)宽共振峰的矩分析

本文用矩分析法对J/ψ辐射衰变产生的θ(1720)宽共振峰的结构进行了研究.由于f'₂(1525)和θ(1720)二共振峰有重迭,为此我们讨论了2⁺⁺(f'₂(1525))+0⁺⁺+0⁺⁺和2⁺⁺(f'₂(1525))+0⁺⁺+2⁺⁺二种三态耦合结构模式,这对于弄清θ(1720)这个宽共振峰的结构,确定可能包含在其中的二个共振态,例如G(1590)和f₂(1720)的质量、宽度、自旋以及其它重要性质,进一步认识这二个令人关注的共振态是有帮助的.     

Xe原子偶宇称5p5(2P1/2)nl' [K']J (l'=1, 3)自电离态共振增强激发光谱线形研究

利用脉冲直流放电技术制备的Xe原子亚稳态5p⁵6s[3/2]₂和5p⁵6s'[1/2]₀, 在单光子为28000～42000 cm^-1能量范围内, 结合飞行时间质谱技术获得Xe原子5p⁵np'[3/2]₁,[1/2]₁和5p⁵nf'[5/2]₃自电离Rydberg态的共振增强激发光谱. 根据Fano线形公式对呈现明显不对称线形的激发谱进行系统地分析,获得系统的能级位置、量子亏损、线性因子、共振宽度、共振态寿命和衰减宽度等数据,其中线形因子和共振宽度相对有效量子数呈线性关系. 另外分析了5p⁵np'序列的能级间距.     

关于π-π共振态

本文从解析性和么正性出发,对具有共振行为的π-π散射分波振幅的形式作了普遍的讨论。理论中包含了一个标志与Breit-Wigner共振形式偏离的函数F_(l)^I)(v),当F_(l)^I)(v)=1时,振幅恰好具有Breit-Wigner共振形式。具体计算表明,这个函数与1有一定的偏离。利用ND^-1方法、交叉对称性、ρ与f⁰的Bootstrap近似,将所得到的振幅与-90的共振解。计算中考虑了非弹性过程和负半轴色散积分的贡献。计算结果得到,对于J=1,I=1态,v_R=6.4,Г₁=0.12;对于J=2,I=0态,v_(R2)=20,Г₂=0.016。这相当于m_ρ=762MeV,m_f⁰=1283MeV,ρ的半宽度约为45MeV。它们与目前的实验数据是很好符合的。     

弹性共振散射反应的厚靶实验设计

为了开展次级束引起的弹性共振散射反应的厚靶实验, 在北京HI-13串列加速器的次级放射性核束装置上建立了一套包含飞行时间和大面积双面硅微条探测器的探测系统, 并用57.0MeV ¹⁷F次级束轰击7.66mg/cm²的(CH₂)_n靶对¹⁷F+p弹性共振散射反应进行了试测量.     

ι-E疑难和推广的矩分析

本文引进过程e⁺e^－→J/ψ→γB,B→P₁P₂P₃的矩的光子角分布来讨论ι-E疑难,得到了判断J/ψ→γKKπ过程中产生的共振峰是否包含E(1⁺⁺)分量的一个有效判据.     

低能K-π散射

本文用L.A.P.Balázs处理低能π-π散射问题的方法,计算了低能K-π散射问题。得到了K-π散射I=1/2的P波共振位置(S_R)^1/2=854MeV,半宽度[Г₁^1/2]/2=126MeV和过程π+π→K+K的振幅的唯象常数ξ=0.3μ^-2,共振位置与目前的实验符合较好。     

Damping of giant monopole resonances within a linearized Landau-Vlasov dynamics

Isoscalar monopole vibrations in spherical nuclei are studied within the Landau-Vlasov dynamics. Energy and strength of the giant monopole resonance (GMR) are well reproduced. The Landau damping of the monopole vibrations is analyzed. It is found that the local Fermi surface corresponding to the GMR is deformed. The collision integral is included within the relaxation time approximation. The found total width is too small to explain the observed one in heavy nuclei. Because the Landau damping is sensitive to the effective nuclear force the missing part of the width can be connected to certain properties of the latter.     

热核上的isovector巨多极共振

将有限温度自洽半经典sumrule方法应用于研究热核上的isovector巨多极共振。用扩展Skyrme力计算了isovector巨单极共振(GMR),巨偶极共振(GDR)和巨四极共振(GQR)的平均激发能量的温度效应。 关键词：     

Finite Temperature Self-Consistent Semiclassical Approach to the Incompressibility of Hot Nuclei

The self-consistent semiclassical approach is extended from zero temperature to finite temperatures. The nucleon densities of a hot nucleus at thermal equilibrium are determined. The centroids of isoscalar giant monopole resonances(GMR) are evaluated by making use of these densities with sum rules. The incompressibility of hot nuclei is studied with these centroids. It is found that the incompressibility decrepes as the temperature increases. A non-self-consistent finite temperature semiclassical approach with a Woods-Saxon mean field is also presented and compared with the self-consistent result.     

Giant Multipole Resonances in an excited core model

The Giant Multipole Resonances (GMR) of (sd)-shell nuclei have been calculated in an excited core model where the low lying excited states of the valence nucleons are coupled to the GMR of the ¹⁶O-core by means of a separable two-body residual nucleon-nucleon interaction. The results of such a calculation of the GMR of ²⁰Ne and ²²Ne are compared with the available experimental data; the characteristic details of the strength distribution can be reproduced rather satisfactorily.     

Model for the evolution of hot and compressed spherical nuclei

A hydrodynamical approach and the Thomas Fermi approximation have been used to study the evolution of hot and compressed nuclei. Spherical symmetry was assumed in the calculation. The dynamical equations have been transformed into “Schrödinger like” equations (using the Madelung transformation) and were solved numerically. Dissipation was simulated in the same way as in the Navier-Stokes equation by introducing shear and bulk viscosities. Global as well as local thermal equilibrium have been studied. The model has been applied to small amplitude oscillations (the breathing mode) and to the stability of hot and compressed nuclei. It was found that compression is more efficient to break nuclei than thermal excitation. The relaxation time for global equilibrium was estimated to be of the order of 10^?22 s. It was found that the results obtained in the case of global and local thermal equilibrium are very similar.     

Collective excitations in neutron-rich nuclei within the model of a Fermi liquid drop

We discuss a new mechanism of splitting of giant multipole resonances (GMR) in spherical neutron-rich nuclei. This mechanism is associated with the basic properties of an asymmetric drop of nuclear Fermi liquid. In addition to well-known isospin shell-model predictions, our approach can be used to describe the GMR splitting phenomenon in the wide nuclear-mass region A ～ 40–240. For the dipole isovector modes, the splitting energy, the relative strength of resonance peaks, and the contribution to the energy-weighted sum rules are in agreement with experimental data for the integrated cross sections for photonuclear (γ, n) and (γ, p) reactions.     

Statistical properties and stability of hot nuclei

Results of temperature-dependent Hartree-Fock calculations for equilibrated hot nuclei are presented, extending to the highest temperatures at which the nuclei remain stable. A subtraction procedure developed earlier for isolating the properties of the nucleus from the nucleus + vapor system is applied. The temperature dependence of various quantities characterizing hot nuclei is investigated. The influence of different effective interactions in the Hartree-Fock equations is examined. Special attention is devoted to the study of the high-temperature stability limit of hot nuclei. This limit in nuclei with the Coulomb interaction artificially switched off (i.e. uncharged nuclei) is shown to correspond to the critical temperature of the liquid-gas phase transition expected on the basis of hot nuclear matter calculations. In realistic charged nuclei the Coulomb repulsion causes a nucleus to become electrostatically unstable and to fall apart at much lower temperatures than its uncharged partner. The approach to and the temperature of this Coulomb instability are very sensitive to the choice of the nuclear interaction. Studying this instability in compound nuclei with different charge-to-mass ratio provides a sensitive measure of the temperature dependence of the nuclear surface properties as well as of certain features of the nuclear equation of state.     

Dynamical aspects of intermediate-energy nucleus-nucleus collisions

The Uehling-Uhlenbeck collision term is derived from coupled equations of motion for the one-body density matrix and the two-body correlation function as obtained from the density-matrix hierarchy. The respective approximations introduced are related with energy and momentum conservation in single nucleon-nucleon collisions and found numerically to be approximately valid for energetic nucleon-nucleon collisions in case of intermediate energy heavy-ion reactions. Primary collision times of nucleons in the dinuclear reaction zone are calculated for various laboratory energies and the approach to local equilibrium is followed in time. Average relaxation times for highly excited finite nuclear systems are found to be considerably shorter than for related infinite nuclear matter problems, however, still too large as to allow for the formation of hot spots in nuclei.     

IrMn基反铁磁自旋阀的巨磁电阻效应

用第一性原理方法研究了在微观尺度具有三重对称磁结构的IrMn合金的反铁磁自旋阀(AFSV)的电子输运.研究表明:基于有序L1₂相IrMn合金的Co/Cu/IrMn自旋阀的巨磁电阻(GMR)效应具有三重对称性,可以利用这一特性区分反铁磁材料的GMR与传统铁磁材料的GMR.基于无序γ相IrMn合金的IrMn(0.84 nm)/Cu(0.42 nm)/IrMn(0.42 nm)/Cu(0.42 nm)(111) AFSV的电流平行平面构型的GMR约为7.7％,大约是电流垂直平面构型的GMR(3.4％)的两倍,明显大于实验中观测到的基于共线磁结构的FeMn基AFSV的GMR. 关键词： 反铁磁自旋阀 巨磁电阻效应 非共线磁结构 电流平行平面结构