Inverse Beam SAD

What is an Inverse Beam SAD data collection?

The circle on the figure below represents 360o sweep on the same crystal with the same energy. For example, GDA will first collect sweep 1 (0 to 45o), then sweep 2  at 180o apart (181 to 225o), followed by sweep 3 (46 to 90o) and so on...

The advantage using inverse beam SAD data collection compared to regular SAD data is that the Friedel pairs will be collected with equivalent dose. It will result in a better assesment of the anomalous signal less polluted by radiation damage.

How to set an inverse beam SAD data collection

In GDA, go to "Data Collection" then click on the tab "Data Collection Table Input"

Note: Click on the images to view full size

Enter the parameters required for your data collection. For example omega start 0 degree, 0.1o oscillation, 0.040s exposure, energy at 12658 eV and 1800 images for total oscillation of 180o. You need to be aware that after converting into inverse beam SAD mode the total oscillation will doubled and be effectively 360o in this case. 



Then convert entry into inverse beam SAD as shown below:

In this example we choose to do wedge of 25o (250 images with 0.1o oscillation). Note that for inverse beam SAD data collection we recommend to use 5o  wedge or lower.

The data collection has been broken up into 25o wedges and reorganized so that each wedge is collected 180o apart. The prefix name has also been updated to indicate which wedge is collected: A or B, with B meaning same wedge as A + 180o. To run it just click on the "Run All" button.

The results will appear as 2 distinct data sets: Lysozyme_A and Lysozyme_B. You will need to merge the data sets to process it later on.



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