Phase Determination of Bragg Reflections by Wavelength-Modulated Diffraction

通过波长调制衍射确定布拉格反射的相位

基本信息

批准号：
12650664
负责人：
IWASAKI Hiroshi
金额：
$ 2.3万
依托单位：
Ritsumeikan University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12650664/
关键词：
crystal structure analysis phase of Bragg reflections synchrotron radiation X-ray diffraction anomalous scattering 結晶構造解析

项目摘要

X-ray diffraction method has long been used as a method of structure determination, but there exists a serious problem called "phase problem". That is, although it is possible to know the amplitude of Bragg reflections from measured intensity, it is not possible to get information on the phase of Bragg reflections. Taking advantage of high brightness and wavelength tunability of synchrotron radiation, this research was performed to develop a new method of phase determination by wavelength modulated diffraction. System most suitable to this purpose was constructed at the beamline BL-1 in the SR Center at Ritsumeikan University and software to handle measured data was developed. In the system, the double-crystal monochromator is repeatedly rotated so that the wavelength of incident radiation is continuously changed over the range in the vicinity of the absorption edge of an atom contained in a crystal, while the sample crystal is rotated synchronously to reflect the radiation of varying wavelength. Diffraction pattern is recorded on an imaging plate, in which Bragg reflections are seen as elongated spots with an intensity profile showing positive or negative gradients at the absorption edge. By solving simultaneous linear equations with measured intensity gradients as constant terms, the phase can be derived. Feasibility experiments using a ferrocene derivative crystal with the iron atoms as anomalous scatters was carried out with successful results.

X射线衍射方法长期以来一直用作结构确定方法，但是存在一个称为“相位问题”的严重问题。也就是说，尽管可以从测得的强度中知道布拉格反射的幅度，但不可能获得有关布拉格反射阶段的信息。利用同步加速器辐射的高亮度和波长可调性，进行了这项研究，以开发一种新的相位测定方法，通过波长调制衍射。最适合此目的的系统是在Ritsumeikan University SR中心的Beamline BL-1上构建的，并开发了用于处理测量数据的软件。在系统中，双晶单色仪反复旋转，以使入射辐射的波长在晶体中包含原子的吸收边缘的附近的范围内不断变化变化波长的辐射。衍射模式记录在成像板上，其中bragg反射被视为伸长斑的伸长斑，强度曲线在吸收边缘处显示正梯度或负梯度。通过将测量强度梯度作为恒定项求解同时线性方程，可以得出该相。使用铁原子用铁原子作为异常散射的可行性实验进行了成功的结果。