1Y13: Difference between revisions

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Revision as of 15:22, 11 July 2011

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Kay

Bureaucrats

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 thus proving that both datasets were interrupted for 20 minutes around frame 370.
-The really weird thing here is that both datasets appear to be collected at the same time, but at different wavelengths (E1 at 0.9794 Å, E2 at 0.9184 Å), and yet the individual parts merge as follows: using the following [[XSCALE.INP]]:
+Interestingly, both datasets appear to be collected at the same time, but at different wavelengths (E1 at 0.9794 Å, E2 at 0.9184 Å), and yet the individual parts merge as follows: using the following [[XSCALE.INP]]:
   UNIT_CELL_CONSTANTS=103.316   103.316   131.456  90.000  90.000  90.000
   SPACE_GROUP_NUMBER=96
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 proving that the second parts of datasets E1 and E2 should be treated separately from the first parts.
-Upon inspection of the cell parameters, we find that the cell axes of the second "halfs" are shorter by a factor of 0.9908 when compared with the first parts. This suggests that they were collected at a longer wavelength! But then the wavelength values in the headers are most likely completely wrong: we can speculate that the two first parts were collected at the SeMet peak wavelength, and the two second parts at the inflection wavelength.
+Upon inspection of the cell parameters, we find that the cell axes of the second "halfs" are shorter by a factor of 0.9908 when compared with the first parts. This suggests that they were collected at a longer wavelength, or that radiation damage changed the cell parameters during the 20-minute break - usually it makes them longer (Ravelli ''et al.'' (2002), J. Synchrotron Rad. 9, 355-360), but this may be the exception to the rule! Maybe the crystal even was exposed to the beam during that time, in an attempt to try radiation-damage induced phasing (see e.g. Ravelli ''et al'' Structure 11 (2003), 217-220).
-The almost-simultaneous DATEs in the headers may be explained by an inverse-beam measuring strategy which alternatingly collects 4 frames in one orientation as E1, then rotates the spindle by 180° and collects 4 frames into E2. For some reason, the beamline software did not write the correct wavelength into the headers.
+The almost-simultaneous DATEs in the headers may be explained by a wavelength-switching measuring strategy which alternatingly collects 4 frames at one wavelength as E1, then changes the wavelength and collects 4 frames into E2.
-Alternatively it may be the case that the crystal just changed its cell due to radiation damage during the 20-minute break - or that it even was exposed to the beam during that time, in an attempt of radiation-induced (papers by Ravelli ''et al'').
 So this little detective work appears to give us useful information about what happened in the morning of Sunday June 27, 2004 at ALS beamline 821 - but some questions remain.