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1.
研究了原子吸收限附近非对称布拉格条件下完整平板晶体的X射线异常透射.当衍射主要由原子散射因子的虚部引起时,在严格的布拉格角处,晶体内部驻波的波节位于衍射原子面上,从而导致异常透射的发生.透射波主要来源于晶体内部坡印廷矢量指向晶体下表面(入射面为上表面)的波场.该波场的有效吸收系数随非对称因子a的增大而减小,所以整个晶体的透射系数随a的增大而增大.当原子散射因子的实虚部对衍射的贡献之比一定时,晶体内坡印廷矢量偏离色散面实部法向的程度随反射的非对称程度的增大而增大. 关键词:  相似文献   

2.
麦振洪 《物理》2012,41(11):721-726
1912年4月,弗里德里希、克里平和劳厄成功地观察到X射线透过硫酸铜晶体后的衍射斑点!随后劳厄推导出描述晶体衍射的著名劳厄方程.由于晶体X射线衍射的发现,劳厄于1914年荣获诺贝尔物理学奖.1912年10月,W.L.布拉格通过X射线透射ZnS晶体实验,推导出了著名的布拉格方程.1915年布拉格父子荣获诺贝尔物理学奖.晶体X射线衍射的发现对自然科学的影响是深远的.2012年是劳厄发现晶体X射线衍射100年,文章回忆了这段光辉的历史及其对科学技术所产生的深远影响,以怀念科学先驱们对科学技术的贡献,弘扬他们对科学研究的认真严谨的科学态度、勇于创新的科学精神和谦逊无私的品德.  相似文献   

3.
利用同步辐射光源,在Ga和As的K吸收限之间调节入射X射线的能量时,在对称劳厄情况下,GaAs的(200)衍射峰附近可观测到从GaAs的入射面出射的Ga的K系荧光X射线.当入射X射线的能量改变时,荧光曲线的非对称性会发生变化,变化趋势与相应的对称布喇格情况相类似.但是,劳厄情况下的变化不能解释为晶体内部X射线驻波的波节面相对于GaAs(200)格子面的移动.在劳厄情况下,X射线驻波的振幅随入射角的变化与结构因子的相位密切相关,因此结构因子的相位变化也会导致荧光曲线的非对称性变化.在假设原子的荧光溢出与该原 关键词:  相似文献   

4.
本文对大学普通物理课程中不介绍劳厄方程的情况下如何阐明布拉格反射所包含的晶体衍射图象作了讨论.强调所有原子都参与衍射过程,从而避免低年级学生中极易产生的将布拉格反射混同于入射束在晶体表面作几何光学式的反射的错觉.而在介绍戴维森-盖末电子衍射实验时,又应注意阐明低能电子衍射与X射线衍射的异同,以便对二维与三维衍射加以区别,而不致引起概念上的混乱.  相似文献   

5.
X射线衍射的发现   总被引:1,自引:0,他引:1  
郭可信 《物理》2003,32(7):427-433
简单介绍了埃瓦尔德(Ewald P P)、劳厄(von Laue M)和布拉格父子(Bragg W H及Bragg W L)在1912年发现X射线衍射方面的贡献.1911年埃瓦尔德在索末菲的指导下在慕尼黑大学从事博士论文研究,劳厄在与他的讨论中了解到晶格的平移周期与X射线的波长属于同一量级,因此想到在二维光栅的两个衍射方程组中再加一个类似的方程,就可以描述X射线在三维晶体中的衍射.在此假设的指导下,Friedrieh W和Knipping P在1912年4月开始用CuSO4后来用闪锌矿(立方ZnS)进行实验,很快就得到X射线衍射的证据.这不但证明了X射线的波动性,还确定了晶体的三维周期性.老布拉格在1912年夏得知这个消息,与他儿子小布拉格一道尝试用X射线的粒子性解释它,并由小布拉格在剑桥大学重复这个实验.根据衍射斑点的椭圆形状和从Pope与Below那里学到的晶格理论(由此得知ZnS具有面心立方晶格),小布拉格将X射线在晶体中的衍射看作是X射线从一些晶格平面的反射,从而推导出著名的布拉格方程.布拉格父子开拓了X射线晶体结构分析这门新兴学科,从简单的无机化合物和矿物,逐渐发展到有机化合物和生物大分子.劳厄和布拉格父子分别强调慕尼黑和剑桥的优良科学环境对发现X射线衍射的重要性.鉴于埃瓦尔德在发现X射线衍射的作用及他后来在倒易格子及动力学衍射理论方面的贡献,不少晶体学家认为他也应获得诺贝尔物理奖.  相似文献   

6.
劳厄对晶体衍射的发现   总被引:1,自引:0,他引:1  
介绍了劳厄提出晶体衍射思想的科学背景及当时的实验过程,并探讨在劳厄发现晶体衍射的过程中其科学思想的形成及X射线晶体衍射的发现带给我们的启示及影响.  相似文献   

7.
本文基于X射线衍射动力学分析了劳厄晶体的分束特性,模拟了晶体吸收和入射光角发散对于透射光和衍射光摇摆曲线的影响,定量给出晶体衍射面内角调节范围和晶体加工厚度对于劳厄衍射分束比的调制.在实验中,采用分析晶体和分束晶体的消色散配置限制入射光角发散的影响,实现300μm厚Si(220)晶体面内角调节劳厄衍射分束的精确测量,并得到300μm, 400μm和500μm厚度Si晶体分束比的调节范围,实现了透射光和衍射光强度的定量调制.  相似文献   

8.
冯端  冯少彤 《物理》2003,32(7):434-440
文章概述了晶体X射线衍射理论的发展过程,介绍了不同形式的衍射几何理论、劳厄方程、布拉格方程与埃瓦尔德作图法,讨论了它们之间的异同之处.文章还介绍了运动学衍射理论和不同形式的动力学衍射理论,后者包括达尔文的简化处理、埃瓦尔德的表述和劳厄的表述,并对其物理后果进行了讨论,强调了动力学理论所预言的电磁波在周期结构中传播所引起的能隙.  相似文献   

9.
一维光子晶体非线性色散特性的分析   总被引:10,自引:8,他引:2  
黄晓琴  崔一平 《光子学报》2005,34(3):473-476
从无限周期一维光子晶体的色散关系和有限周期光子晶体的透射系数两个方面,对有限和无限周期光子晶体有效折射率的实部和虚部特性曲线分别进行了计算和分析.结果表明一维光子晶体的色散曲线与弹性电偶极子的经典色散曲线类似,在光子晶体的导带为正常色散,而在禁带呈现反常色散.并且用简约布里渊和扩展布里渊区色散曲线对文献报道中存在的两种矛盾的计算结果进行了理论的探讨.解释了导致对一维光子晶体有效折射率计算存在两种不同结果的原因.  相似文献   

10.
张涛 《物理》2012,41(11)
100年前,德国人劳厄发现X射线通过晶体时可以发生衍射效应.随后,英国的布拉格父子等人发展出一系列实验和分析方法,利用X射线晶体衍射解析出具有原子分辨率的分子结构.在过去的100年中,X射线衍射分析对世界的科学发展乃至人们的生活都产生了至关重要的影响,并且在这100年间,X射线衍射实验方法和分析方法也有了长足进步.硬X射线自由电子激光的出现为X射线衍射分析进一步发展提供了更广阔的空间,可以预期,基于自由电子激光的X射线衍射分析会进一步在物理、化学、生物等学科中发挥更为重要的影响.  相似文献   

11.
A solution of the problem of dynamical diffraction for X‐ray pulses with arbitrary dimensions in the Bragg and Laue cases in a crystal of any thickness and asymmetry coefficient of reflection is presented. Analysis of pulse form and duration transformation in the process of diffraction and propagation in a vacuum is conducted. It is shown that only the symmetrical Bragg case can be used to avoid smearing of reflected pulses.  相似文献   

12.
X-ray asymmetrical Laue diffraction in a perfect crystal with plane front surface was considered taking into account the two-dimensional curvature of a wave incident on the crystal. Using an appropriate Green function the dependences of rocking curves on deviation angles from selected exact Bragg direction were examined in the diffraction plane and in the direction perpendicular to the diffraction plane in locally plane wave approximation. The dependence of rocking curves on the degree of asymmetry of diffraction geometry was investigated. Analytical expressions for half widths of rocking curves in the diffraction plane and in the direction perpendicular to the diffraction plane are obtained. Some requirements to spatial and temporal coherence are estimated.  相似文献   

13.
A theoretical framework is presented to treat both imaging and diffraction experiments performed with point-focus and line-focus X-ray sources, with particular emphasis on two-dimensional and planar X-ray waveguides. In particular, point-projection and line-projection microscopy has been approached within the Huygens-Fresnel formalism; point-projection and line-projection diffraction, such as spatially-resolved Bragg/Laue diffraction of crystalline samples in a regime of dynamical scattering, has been treated both by means of the Huygens-Fresnel formalism and of the Takagi-Taupin dynamical theory. Both in point- and line- projection geometry, simply rotating the investigated crystalline samples, it is possible to switch from Fresnel self-imaging to Bragg/Laue diffraction conditions. This means to image, within the same experiment, either morphological features, with a sub-micrometric resolution, out of the exact diffraction condition, or the structure order on an atomic scale if placing the sample in diffraction.  相似文献   

14.
Symmetrical Laue diffraction in a perfect crystal with a plane entance surface is considered. The two dimensional curvature of the wave front of the incident beam is taken into account. Using the corresponding Green function, a general expression for the amplitude of diffracted wave in the crystal is presented. Based on this expression, the concept of a locally plane wave is analyzed taking into account two-dimensional curvature of the wave front. This concept is used for obtaining the rocking curves depending on the angles of deviation from the chosen exact Bragg direction in both the diffraction plane and in perpendicular direction. The obtained result is compared with the result of the standard dynamical diffraction theory.  相似文献   

15.
The interbranch scattering of X-rays at dislocations is studied experimentally and with the aid of numerical simulations. Narrow beam of a small divergence is used for the study which is made both in the Laue and Bragg case of diffraction. The role of interbranch scattering in the formation of defect contrast in X-ray topography is discussed.  相似文献   

16.
Dynamical diffraction equations for X-ray beams are considered with retaining the second-order derivatives of amplitudes in the direction perpendicular to the diffraction plane. For the dynamical diffraction problem, the retarded Green function is determined in case of a perfect crystal. Amplitudes of transmitted and diffracted waves in the crystal are represented as convolution over the crystal surface with use of determined Green function. Such representation can be used for solving diffraction problems in Laue and Bragg geometries in perfect crystals with both plane and not plane entrance and exit surfaces.  相似文献   

17.
在Ga的K吸收限附近的强反常散射条件下,测定了GaAs(600)对称Bragg情况的衍射波和透射波的摇摆曲线,并将其和X射线衍射动力学理论的相应计算结果作了比较,指出了原子吸收限附近Bragg情况的透射波在研究反常散射中的应用价值 关键词:  相似文献   

18.
Based on the behavior of the elastic scattering data, we introduce an almost model-independent parameterization for the imaginary part of the scattering amplitude, with the energy and momentum transfer dependences inferred on an empirical basis and selected by rigorous theorems and bounds from axiomatic quantum field theory. The corresponding real part is analytically evaluated by means of dispersion relations, allowing connections between particle–particle and particle–antiparticle scattering. Simultaneous fits to proton–proton and antiproton–proton experimental data in the forward direction and also including data beyond the forward direction lead to a predictive formalism in both energy and momentum transfer. We compare our extrapolations with predictions from some popular models and discuss the applicability of the results in the normalization of elastic rates that can be extracted from present and future accelerator experiments (Tevatron, RHIC and LHC). PACS 13.85.Dz, 13.85.-t  相似文献   

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