Ichak rentgenografiyasi: natijani ko'rsatadigan tayyorgarlik

Recording the reflections

An X-ray diffraction pattern of a crystallized enzyme. The pattern of spots (aks ettirishlar) and the relative strength of each spot (intensivlik) can be used to determine the structure of the enzyme.
When a crystal is mounted and exposed to an intense beam of X-rays, it scatters the X-rays into a pattern of spots or aks ettirishlar that can be observed on a screen behind the crystal. A similar pattern may be seen by shining a lazer ko'rsatkichi a ixcham disk. The relative intensities of these spots provide the information to determine the arrangement of molecules within the crystal in atomic detail. The intensities of these reflections may be recorded with fotografik film, an area detector (such as a pixel detector ) yoki bilan zaryad bilan bog'langan qurilma (CCD) tasvir sensori. The peaks at small angles correspond to low-resolution data, whereas those at high angles represent high-resolution data; thus, an upper limit on the eventual resolution of the structure can be determined from the first few images. Some measures of diffraction quality can be determined at this point, such as the mozaika of the crystal and its overall disorder, as observed in the peak widths. Some pathologies of the crystal that would render it unfit for solving the structure can also be diagnosed quickly at this point.
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One image of spots is insufficient to reconstruct the whole crystal; it represents only a small slice of the full Fourier transform. To collect all the necessary information, the crystal must be rotated step-by-step through 180°, with an image recorded at every step; actually, slightly more than 180° is required to cover reciprocal space, due to the curvature of the Evald shar. However, if the crystal has a higher symmetry, a smaller angular range such as 90° or 45° may be recorded. The rotation axis should be changed at least once, to avoid developing a "blind spot" in reciprocal space close to the rotation axis. It is customary to rock the crystal slightly (by 0.5–2°) to catch a broader region of reciprocal space.
Multiple data sets may be necessary for certain phasing methods. For example, MAD phasing requires that the scattering be recorded at least three (and usually four, for redundancy) wavelengths of the incoming X-ray radiation. A single crystal may degrade too much during the collection of one data set, owing to radiation damage; in such cases, data sets on multiple crystals must be taken.^[124]