16O+232Th垒下全熔合裂变

利用裂变碎片的折叠角分布,从实验上实现了全熔合裂变和转移跟随裂变两种成份的区分.在此基础上测量了质心系能量72.61至80.11MeV ¹⁶O+²³²Th全熔合裂变截面和碎片角分布.包含靶核静态形变效应的耦合道模型计算与实验激发曲线一致.然而,裂变统计理论无法解释实验上观察到的全熔合裂变碎片角分布.而鞍点模型与断点模型的理论预言有较明显的差别.     

钕玻璃发光量子效率的光声测量

建立了一种新的测量钕玻璃中激活离子发光量子效率的光声方法,其原理为通过测量的钕玻璃中Nd~(3+)的两个吸收峰的吸收幅值及光声信号的幅值计算出发光量子效率.所得结果与以前用其它方法估算和测得的结果相符.     

良导体热导率不同测量法的比较

维德曼-弗兰兹定律指出金属的热导率和电导率的比值是常数,本文先测量了一定温度下的材料的电阻率,再由电阻率计算出材料的热导率,并与利用热波法得到的热导率进行比较,其结果相近.     

X射线吸收谱对Ga0.946Mn0.054As薄膜中缺陷的研究

采用低温分子束外延法(LT-MBE)制备出Ga_0.946Mn_0.054As稀磁半导体(DMS)薄膜.通过X射线吸收谱(XAS)研究影响Ga_0.946Mn_0.054As薄膜性质的主要缺陷Mn间隙原子(Mn_I)和As反位原子(As_Ga).实验结果表明,在较低生长温度(T_S=200℃)下Ga_0.946Mn_{0.054 关键词： 0.946}Mn_0.054As稀磁半导体')" href="#">Ga_0.946Mn_0.054As稀磁半导体 X射线吸收谱 As反位缺陷 Mn间隙原子     

地基人工VLF 电波对辐射带电子的调制

辐射带电子的加速与沉降机理是空间物理研究的重要课题.法国DEMETER电磁卫星观测到了美国NPM发射站VLF信号及与之相关的高能电子沉降事例.本研究工作将根据基于回旋共振相互作用的准线性扩散理论,通过对局域投掷角扩散系数的计算,来说明受VLF影响的高能电子的投掷角分布与电子的能量及所处位置的关系.理论计算较好地解释了DEMETER卫星在NPM实验期间所观测到的电子沉降事例.在此基础上进一步讨论了通过人工方式对辐射带高能电子施加影响的效率问题. 关键词： 回旋共振 投掷角散射 电子沉降     

基于改进ICP算法的曲面特征配准研究

随着3D激光扫描技术的发展,点云数据的应用越来越广泛.然而点云配准一直是点云数据预处理过程中的一个关键问题.目前ICP算法是实现点云配准的主流算法.然而面对数据量大、噪声大的点云数据时,ICP算法在执行的配准效率和执行效果上不够理想.本文通过PCA算法,提取了点云数据集的方向向量,根据源数据与目标数据的方向向量,初步设定了旋转矩阵R的值.此外,定义了源数据与目标数据的曲面距离,在此基础上改进了传统的ICP算法.将改进后的ICP算法成功的应用到点云数据配准中来,提高了点云数据的配准效果,并压缩了算法的执行时间.     

Study of heat transfer characteristics in PCFG fabrication technology using heat method

The fiber gratings fabrication technology with the heating method in a photonic crystal fiber (PCF) based on structural change is examined. The principle of photonic crystal fiber gratings (PCFGs) is analyzed in theory. The heat transfer theory and finite element method are used to examine the thermal field distribution in the fiber and the influence of the air hole structure in the cladding, and the parameters of the laser beam in the process of grating fabrication are discussed. The results show that gratings can be formed by the periodic collapse of air holes in the cladding of PCFs. Under double-point heating condition, the energy is uniformly distributed in the radial direction and is approximate to Gaussian distribution in the axial direction. With the same size of the luminous spot, as the layers and radius of the air holes increase, the laser power needed to make the air holes collapse decreases. With the same laser power, as the luminous spot radius increases, the needed heating time increases. Moreover, the relationship between the laser power needed and the air filling rate is obtained as the number of layers of the air holes changes from 1 to 7. This kind of PCFG can overcome the long-term thermal instability of conventional gratings in substance and thus has great potential applications in the related field of optical fiber sensors.     

Influence of Gamma-Ray Irradiation on Absorption and Fluorescent Spectra of Nd：YAG and Yb：YAG Laser Crystals

We investigate the influence of gamma-ray irradiation on the absorption and fluorescent spectra of Nd^3＋：Y3A15 O12 （Nd： YAG） and Yb^3＋ ： Y3A15 O12 （Yb： YAG） crystals grown by the Czochralski method. Two additional absorption （AA） bands induced by gamma-ray irradiation appear at 255nm and 340nm. The former is contributed due to Fe^3＋ impurity, the latter is due to Fe^2＋ ions and F-type colour centres. The intensity of the excitation and emission spectra as well as the fluorescent lifetime of Nd：YAG crystal decrease after the irradiation of 100 Mrad gamma-ray. In contrast, the same dose irradiation does not impair the fluorescent properties of Yb：YAG crystal. These results indicate that Yb： YA G crystal possesses the advantage over Nd： YA G crystal that has better reliability for applications in harsh radiant environment.     

Effect of the Tensor Force on Charge-Exchange Spin-Dependent Multipole Excitations

The charge-exchange spin-dipole （SD） and spin-quadrupole （SQ） strength functions of 90Zr are calculated with and without the tensor terms of the Skyrme interaction in self-consistent HF＋RPA approach. It is found that, in SD and SQ transitions, the RPA correlations associated with the tensor terms shin dramatically the strengths of （Ylσ）λ = l？1 and （Ylσ）λ = 1 modes upward and downward, respectively, and also shift the strengths of （Ylσ）λ = l ＋ 1 modes upward. The coupling between （Yl = λ ？ 1σ）λ and （Yl = λ ＋ 1σ）λ modes arising from the tensor correlation is noticeable. The RPA tensor correlations produce strengths of SD and SQ modes, which are distributed in a much wider energy range, and the （Ylσ）λ = l ？ 1 modes dominate the high energy part of the strength functions. These energy shifts and coupling effects of different modes can be understood qualitatively by expressing a finite range tensor force in a separable form.     

纪念黄胜年先生逝世一周年

2010年1月8日是黄胜年先生逝世周年纪念日.我们特写此文来缅怀这位新中国培养的核物理学家、受人爱戴的同事.