172Re的高自旋态研究

利用149Sm(27Al,4n)172Re反应产生并研究了双奇核172Re的高自旋态。实验中分别在130，135，140和150MeV束流能量下进行了激发函数测量，确立了最佳布居172Re核激发态的束流能量为130MeV。在130MeV能量下，进行了γ-γ符合测量。基于激发函数的测量结果和Kx-γ符合关系，指定了源于172Re的γ射线。通过分析γ射线之间的符合关系，建立了由6个转动带构成的172Re核的能级纲图。依据二准粒子Routhian的计算结果，以及B(M1)/B(E2)的实验提取值与理论值的比较，并结合相邻双奇核的带结构特征，给出了各转动带的准粒子组态。在推转壳模型框架下对转动带的顺排，动力学转动惯量进行了一些讨论

超铀区缺中子新核素~235 Am的合成与鉴别

本实验利用中国科学院高能物理研究所质子直线加速器提供的35MeV质子束流，轰击稀有放射性同位素靶238Pu，通过（p，4n）反应合成了超铀缺中子新核素235Am。反应产物是由氦喷嘴长毛细管传输系统传输和收集的，用快速化学分离方法分离出Am的同位素，使用两台高纯锗探测器对分离样品进行了X射线，γ射线和γ-γ（X）符合关系的测量，通过235Pu的衰变γ射线的生长——衰变趋势指定了235Am的生成，并通过Np的Kx射线的生长——衰变曲线确定了235Am的半衰期为（15±5）分钟。这是我国首次在超铀区合成缺中子新核素。

长白山红松阔叶混交林紫椴枝条的分解实验

研究了长白山北坡椴树 ( Tilia amurensis)枝条的分解进程。实验结果揭示 ,分解率是与各实验地的植被类型 ,海拔 ,生长季月平均大于 5℃的积温等密切相关。其枝条分解的保存率 ( Y)与分解年龄 ( x)的相关 ,可用指数模型 :Y=e- kx来拟合。在红松阔叶混交林 ,红松针叶混交林 ,岳桦云冷杉林及岳桦林中椴树枝条分解常数 K分别为 -0 .1 6 8与 -0 .1 2 7,-0 .1 0 2和 -0 .0 94。枝条原重量 5 0 %的分解年龄在上述 4个森林中分别是 4 ,5 ,6和 7a。实验还指出 ,在长白山红松阔叶混交林皆伐迹地的实验条件下适当的蔽荫和浇水对分解有正面影响 ,而且 ,枝条的分解率主要是以长白山不同海拔植被类型的温度条件而转移 ,特别是生长季的积温

Lattice Boltzmann study of hydrodynamic effects in lamellar ordering process of two-dimensional quenched block copolymers

By incorporating self-consistent field theory with lattice Boltzmann method, a model for polymer melts is proposed. Compared with models based on Ginzburg-Landau free energy, our model does not employ phenomenological free energies to describe systems and can consider the chain topological details of polymers. We use this model to study the effects of hydrodynamic interactions on the dynamics of microphase separation for block copolymers. In the early stage of phase separation, an exponential growth predicted by Cahn-Hilliard treatment is found. Simulation results also show that the effect of hydrodynamic interactions can be neglected in the early stage.

Studies on coarsening of microdomains in binary polymer mixtures by Lattice Boltzmann methods

An improved free energy approach Lattice Boltzmann model(LBM) is proposed by introducing a forcing term instead of the pressure tensor. This model can reach the proper thermodynamic equilibrium after enough simulation time. On the basis of this model, the phase separation in binary polymer mixtures is studied by applying a Flory-Huggins-type free energy. The numerical results show good agreement with the analytic coexistence curve. This model can also be used to study the coarsening of microdomains in binary polymer mixtures at the early and intermediate stages.

Composition effect on dewetting of ultrathin films of miscible polymer blend

Two kinds of dewetting and their transition induced by composition fluctuation due to different composition in blend [poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN)] films on SiOx substrate at 145 degrees C have been studied by in-situ atomic force microscopy (AFM). The results showed that morphology and pathway of dewetting depended crucially on the composition. Possible reason is the variation in intensity of composition fluctuation resulted from the change of components in polymer blend. Based on the discussion of this fluctuation due to the composition gradient, parameter of U-q0/E, which describes the initial amplitude of the surface undulation and original thickness of film respectively, has been employed to distinguish the morphologies of spontaneous dewetting including bicontinuous structures and holes.

Defect evolution and hydrodynamic effects in lamellar ordering process of two-dimensional quenched block copolymers

The effects of hydrodynamic interactions on the lamellar ordering process for two-dimensional quenched block copolymers in the presence of extended defects and the topological defect evolutions in lamellar ordering process are numerically investigated by means of a model based on lattice Boltzmann method and self-consistent field theory. By observing the evolution of the average size of domains, it is found that the domain growth is faster with stronger hydrodynamic effects. The morphological patterns formed also appear different. To study the defect evolution, a defect density is defined and is used to explore the defect evolutions in lamellar ordering process. Our simulation results show that the hydrodynamics effects can reduce the density of defects. With our model, the relations between the Flory-Huggins interaction parameter chi, the length of the polymer chains N, and the defect evolutions are studied.

STUDY OF COARSENING OF MICRODOMAINS IN BLOCK COPOLYMERS BY LATTICE BOLTZMANN METHODS

In order to understand the coarsening of microdomains in symmetric diblock copolymers at the late stage, a model for block copolymers is proposed. By incorporating the self consistent field theory with the free energy approach Lattice Boltzmann model, hydrodynamic interactions can be considered. Compared with models based on Ginzburg-Landau free energy, this model does not employ phenomenological free energies to describe systems. The model is verified by comparing the simulation results obtained using this method with those of a dynamical version of the self consistent mean field theory. After that,the growth exponents of the characteristic domain size for symmetric block copolymers at late stage are studied. It is found that the viscosity of the system affects the growth exponents greatly, although the growth exponents are all less than 1/3 Furthermore, the relations between the growth exponent, the interaction parameter and the chain length are studied.