Talk:Resolution: Difference between revisions
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Each diffraction spot (i.e. reflection) in a diffraction pattern has a nominal resolution. The higher the diffraction angle (i.e. further from the center of the diffraction image where the incoming X-ray beam would hit), the higher the resolution. In a diffraction experiment, the goal is to collect as many reflections as possible. However, reflections of high resolution are more difficult to measure because the intensity of reflections drops off at higher diffraction angles (and with that, higher resolution). In a diffraction image, you will see high intensity spots near the center, and more and more faded spots as you move away from the center. The overall resolution of a diffraction data set refers to the resolution range of reflections measured. For example, "data were collected from 20.0 Angstroms to 2.3 Angstroms with an overall completeness of 96.5%" means that most reflections in this range were collected, and the data set would be described in brief as "2.3 A resolution" data set, referring to the high resolution limit of the data collection. | Each diffraction spot (i.e. reflection) in a diffraction pattern has a nominal resolution. The higher the diffraction angle (i.e. further from the center of the diffraction image where the incoming X-ray beam would hit), the higher the resolution. In a diffraction experiment, the goal is to collect as many reflections as possible. However, reflections of high resolution are more difficult to measure because the intensity of reflections drops off at higher diffraction angles (and with that, higher resolution). In a diffraction image, you will see high intensity spots near the center, and more and more faded spots as you move away from the center. The overall resolution of a diffraction data set refers to the resolution range of reflections measured. For example, "data were collected from 20.0 Angstroms to 2.3 Angstroms with an overall completeness of 96.5%" means that most reflections in this range were collected, and the data set would be described in brief as "2.3 A resolution" data set, referring to the high resolution limit of the data collection. | ||
==Resolution and | ==Resolution and crystal quality == | ||
The resolution of a diffraction pattern depends on how ordered the crystal is. If it is highly ordered (atoms are in defined positions throughout the crystal and over time), the crystal will diffract to high resolution. The more disorder there is (atoms moving over time, or the content of one unit cell different from the next), the lower the resolution of the diffraction image because the intensity of spots drops with increasing disorder. In order to still be able to measure these weak reflections, it is sometimes possible to increase the intensity of the X-rays used in the experiment, increase the exposure time or sensitivity of the detector or increase the size of the crystals. | The resolution of a diffraction pattern depends on how ordered the crystal is. If it is highly ordered (atoms are in defined positions throughout the crystal and over time), the crystal will diffract to high resolution. The more disorder there is (atoms moving over time, or the content of one unit cell different from the next), the lower the resolution of the diffraction image because the intensity of spots drops with increasing disorder. In order to still be able to measure these weak reflections, it is sometimes possible to increase the intensity of the X-rays used in the experiment, increase the exposure time or sensitivity of the detector or increase the size of the crystals. | ||
==Resolution and diffraction data quality== | ==Resolution and diffraction data quality== | ||
