Xingliangzhang These are Kikuchi lines that usually are observed in the electron diffraction from thick specimen. For X-ray they are called Kossel lines. Well, if you are so called high throughput structural biologist, you can forget about that, It is hard core diffraction physics. But if you think you have to know what it is - explore more the web.
Copied from: Kikuchi lines pair up to form bands in electron diffraction from single crystal specimens, there to serve as "roads in orientation-space" for microscopists not sure what they are looking at. Intransmission electron microscopes, they are easily seen in diffraction from regions of the specimen thick enough for multiple scattering[1]. Unlike diffraction spots, which blink on and off as one tilts the crystal, Kikuchi bands mark orientation space with well-defined intersections (called zones or poles) as well as paths connecting one intersection to the next. Experimental and theoretical maps of Kikuchi band geometry, as well as their direct-space analogs e.g. bend contours, electron channeling patterns, and fringe visibility maps are increasingly useful tools in electron microscopy of crystalline and nanocrystalline materials[2]. Because each Kikuchi line is associated with Bragg diffraction from one side of a single set of lattice planes, these lines can be labeled with the same Miller or reciprocal-lattice indices that are used to identify individual diffraction spots. Kikuchi band intersections, or zones, on the other hand are indexed with direct-lattice indices i.e. indices which represent integer multiples of the lattice basis vectors a, b and c. Kikuchi lines are formed in diffraction patterns by diffusely scattered electrons, e.g. as a result of thermal atom vibrations[3]. The main features of their geometry can be deduced from a simple elastic mechanism proposed in 1928 by Kikuchi[4], although the dynamical theory of diffuse inelastic scattering is needed to understand them quantitatively[5]. In X-ray scattering these lines are referred to as Kossel lines [6]. See also in a dissertation by Eric Sutter "The Theory of Kossel Lines" http://adsabs.harvard.edu/abs/2000PhDT.......109S Or in http://scripts.iucr.org/cgi-bin/paper?S0021889805024660 Dr Felix Frolow Professor of Structural Biology and Biotechnology Department of Molecular Microbiology and Biotechnology Tel Aviv University 69978, Israel Acta Crystallographica F, co-editor e-mail: [email protected] Tel: ++972-3640-8723 Fax: ++972-3640-9407 Cellular: 0547 459 608 On Sep 14, 2010, at 08:59 , Mark J van Raaij wrote: > Interesting! it appears to be some kind of "secondary order"...I hope someone > wise/experienced can shed more light on this. > the diffraction spots appear to fall consistently in the middle of the > hexagonal(ish) grid lines, so it must be some partial order effect related to > the unit cell. > do you also see this with data collected from an unfrozen crystal? if so, it > is a crystal property. > you also appear to have quite strong solvent/ice rings, in any case I would > optimise the cryo-protection/freezing procedure. > Mark > > Quoting xingliang zhang <[email protected]>: > >> Dear everyone, >> >> Recently,we collected data of a native protein crystal on synchrotron in >> Shanghai. When we did with the original data with HKL2000, we found an >> unconversant phenomenon ,just as the picture in the enclosure, there were >> some grid indicated by arrows appearing on the low resolution areas.The >> crytal grew in 20%PEG3000,100mMTris-Cl,200mM Ca(OAc)2 ,and the >> cryo-protectant is 20% sucrose mixed with well buffer?Who can tell me the >> reasons it appear the grid ?because of the sucrose? I'll appreciated for any >> explains and suggestion. >> >> >> >> Best wishes >> >> >> >> xingliangzhang >> >> >> -- >> >> Best wishes! >> xingliangcheung,PhD,candidate >> >> Protein crystallography Lab ,College of biological sciences ,China >> agricultural university. >> >> No. 2 yuanmingyuan west road HaidianDistrict, Beijing, 100193 >> >> Tel:01062814122, >> >> E-mail:[email protected] <e-mail%[email protected]> >>
