A crystal sitting in a crystalline powder floods the first pass with spots that are not its
own. Two in-house crystals gave 2112 spots a frame against the 80 a clean crystal on the same
beamline gives, and no scheme indexed a single validation frame; the FFT took a 10-30 A cell
out of the shells. A third dataset, with no powder at all, failed for the neighbouring reason:
its file beam centre is 170 px out, and the measured centre was tested with the full spot list,
indexed nothing there either, and was thrown away.
Powder rings are now MEASURED from each run's own pre-scan spots rather than read off the fixed
hexagonal-ice list, and reported on every run (POWDER_*) whether or not anything acted on them -
hexagonal ice is the only phase that can be named in advance, and 16 of the 24 rings on one of
these crystals are ice while the rest are not.
A first pass that ends with no usable lattice then retries over how much of each frame it reads:
the strongest 30, 80, 200 or all spots an image, each at the file's resolution and at the
resolutions a quarter and a half of this sample's own spots lie coarser than, with the measured
rings set aside where there are any. Decided late on the validation-frame count, the way the
rotation-axis sign already is, and adopted only on a win of a sixth of the frames. The same
ladder is asked inside the beam-centre check, where a centre that is wrong and a spot list that
is too deep otherwise hide each other.
Measured over 146 datasets: unchanged on all of them - the open arm scores 91/99 either way and
the 46 SLS datasets are identical on every scientific field - while the three that failed now
index. The deposited cell is recovered to 0.1% on the beam-centre case, at 100% of frames and
0.597 A.
leonarski_f
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