Study of neutron activation yields in spallation reaction of 400 MeV/u carbon on a thick lead target

The spallation-neutron yield was studied experimentally by bombarding a thick lead target with 400 MeV/u carbon beam. The data were obtained with the activation analysis method using foils of Au, Mn, Al, Fe and In. The yields of produced isotopes were deduced by analyzing the measured γ spectra of the irradiated foils. According to the isotopes yields, the spatial and energy distributions of the neutron field were discussed. The experimental results were compared with Monte Carlo simulations performed by the GEANT4+FLUKA code.     

创生激活:让数学课堂教学真正发生

<正>1问题的提出“激活”一词,其本意一般是指刺激机体内某种物质,使其活跃地发挥作用.创生激活就是指创立、生长出激活课堂教学的方法与策略,使教与学真正发生,并使其活跃起来.就数学课堂教学而言,从环节来看,研究对象的获得、探究、应用等是构成数学课堂“机体”的三种“物质”.但是,通过观课,我们发现,大量的数学课堂教学中普遍存在着忽视问题情境创设的原则,忽视探究过程深化的要义,忽视例题变式延伸的路径等现象,使之课堂教学的三个环节并没有活跃地发挥作用,     

Study of neutron spectra in a water bath from a Pb target irradiated by 250 MeV protons

Spallation neutrons were produced by the irradiation of Pb with 250 MeV protons. The Pb target was surrounded by water which was used to slow down the emitted neutrons. The moderated neutrons in the water bath were measured by using the resonance detectors of Au, Mn and In with a cadmium (Cd) cover. According to the measured activities of the foils, the neutron flux at different resonance energies were deduced and the epithermal neutron spectra were proposed. Corresponding results calculated with the Monte Carlo code MCNPX were compared with the experimental data to check the validity of the code. The comparison showed that the simulation could give a good prediction for the neutron spectra above 50 eV, while the finite thickness of the foils greatly effected the experimental data in low energy. It was also found that the resonance detectors themselves had great impact on the simulated energy spectra.     

从一道高考模拟题谈错位数的递推计算

1 问题提出 今年我市高三模拟考试中出现这样一个题目:A、B、C、D四人玩一项游戏,有1号、2号、3号、4号四个座位.已知A不坐1号位,B不坐2号位,C不坐3号位,D不坐4号位,则不同的坐法结果有______种.     

环流形上的极值度量——存在性和K-稳定性

本文主要研究环流形上的极值度量的存在性和K-稳定性.本文将Donaldson关于环流形上有关常数量曲率度量的稳定性概念的约化推广到一般的极值度量的情形.通过这个约化,本文证明环流形上极值度量的存在性可以推出流形对于环形变的相对K-稳定性.在不知道是否存在极值度量的情形下,本文还给出环流形相对K-稳定的一个充分性条件.对环曲面的情形,基于Arrezo-Pacard-Singer的工作,本文证明任意一个环曲面上存在含有极值度量的Ka¨hler类,并给出一些环曲面上有不存在极值度量的K¨ahler类的例子.关于一般的环流形上的极值度量的存在性,本文用变分方法研究其弱解,证明在能量泛函逆紧性假设下,存在弱极小化子.     

碳气凝胶薄片的制备及表面密度致密层去除工艺

 研究了不同密度和厚度的碳气凝胶薄片的制备及其表面致密层去除工艺。在以间苯二酚、甲醛为原料制备有机及碳气凝胶块体材料的基础上,结合自制活动式微模具成型工艺,制备了厚度在80~350 μm,密度在50~600 mg·cm^-3范围内变化的碳气凝胶薄片。采用场发射扫描电镜、X射线相衬成像和表面轮廓仪-台阶仪等手段对其表面和内部微观结构进行了表征。测试结果表明,碳气凝胶薄片与块体的内部结构相同,但薄片表面存在一层和内部结构截然不同的致密层。采用不同粗糙程度的材料对薄片进行了表面微处理,成功去除该致密“皮”层。     

erent Phase Control in e-Ar Scattering in a Bichromatic Laser Field in the Second Born Approximation

We study the elastic scattering of atomic argon by an electron in the presence of a bichromatic laser field in the second Born approximation. The target atom is approximated by a simple screening potential. We explore the dependences of the differential cross sections on the relative phase φ between the two components of the radiation field and discuss the influence of the number of photons exchanged on the phase-dependence effect. Moreover, for different scattering angles and incident electron energies, the differential cross sections are notably different.     

分划板失调时猫眼系统的反射特性

为降低光电装备猫眼效应,减小光学窗口被激光主动侦察系统探测到的概率,对分划板失调情况下猫眼系统的反射特性进行了研究。基于几何光学与2维平面波角谱衍射理论,推导并仿真了平面波通过分划板失调猫眼系统在出射面上的衍射光场分布特性,实验验证了猫眼目标的反射特性。研究结果表明:分划板失调会导致猫眼系统出射面的回波光斑发生椭圆形变,而斜入射探测激光会使这一现象更加明显。利用这一特性对猫眼系统进行改进,会大大增加激光主动侦察系统区分形变猫眼目标和漫反射背景干扰的难度。