SLAC National Accelerator Laboratory
BL4-2 Biological Small Angle Scattering/Diffraction

Creating Mask Files with OTOKO

Two mask files (Q01000.msk and Q02000.msk in this example) should be created in order to avoid the use of inactive detector areas in data processing. Q01000.msk will have the value of 1.0 over the entire active detector range and Q02000.msk will in addition mask the channels covered by the beamstop.

The boundaries of the active/inactive detector areas can be determined by running OTOKO and using the ".cur" command (plots a data file with a cursor).  The outside boundaries of the detector can be determined by examining a detector response file and the beamstop boundaries by examining a protein or buffer data file.  Avoid using the outer edges of the detector (peaks in response pattern).  A typical active range of the detector area would cover channels ~140 through ~940 with channels ~400 through ~500 being behind the beamstop.

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Click left button to get reading and right button to exit

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It is not neccessary to give an output name, only to make a note of the coordinates chosen in the graph for ".xax."

Use ".xax" in OTOKO (select the block option) to generate the two mask files which will have the value of 1.0 in the active ranges and 0.0 elsewhere. This output name will be the *.msk file.

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Mask files are also available from B-SAXS staff upon request.