Back to Toolbox

Data Collection: Practical Considerations


Assuming you have managed to get a crystal frozen in a loop and mounted on the goniometer, the first thing you need to do is center the crystal. This can be done manually, or using the software at the synchrotron. The key is to make sure you center on a relatively thick part of the crystal, and that the beam (which usually coincides with the center of rotation) stays on the crystal for the majority of 360 degrees. If there is any ice the crystal try not to hit this, or if possible use a different crystal. Similarly be aware of any cracks or warping of the crystal as this can lead to problems in the data processing.

Once back in the control room it is best to take a test image. I normally go for a 0.5 degree oscillation and about three, 3 second passes at the synchrotron, or 15 minutes at home. You want to check:

  1. That you have crystal diffraction.
  2. That the spots are relatively well formed (not smeared, streaked or overloaded).
  3. That the image goes out to a reasonable resolution (depends on your desperation for data!).
  4. That you exposure time is long enough to get high resolution spots without overloads in the middle of the image.

Even if this is not the case, you want to next take an image 90 degrees away from the first and check this one as well. You may find that you have to try a number of different degrees to find the best part of the crystal, and perhaps play around a bit with the exposure time.

good image

This is an example of a reasonably good image with clearly defined spots, although there are some clear overloads in the center.


Once you have two good images you need to calculate a data collection strategy...


Back to Toolbox