Dear all,
in a recent synchrotron trip we had a problem with our crystals moving
after mounting them onto the goniometer, in some cases they moved out
of the beam and even out of the zoomed camera picture - it seemed the
pins, upon equilibrating to room temperature, extended. It happened
with pre-mounted litho-loops only, not with pre-mounted mitegen loops
on the same trip, so one possible cause is different metal allows used
in the pins, somehow the mitegen ones being more suitable.
We used two-component glue to stick the pins into the metal bases
(Spine), so that might be another possible culprit. Perhaps we did not
allow sufficient time for the glue to react before freezing into
liquid N2 and it continued its reaction upon thawing, somehow pushing
the pin a bit out of the base. In this case the difference between
litholoops and mitegen loops may have been the thickness of the pins,
the latter somehow allowing expansion of the glue along the sides, the
former not.
In any case, I am wondering if any of you has seen this before, so we
know how to avoid it in the future.
In some cases, it took 10-20 min. for the crystal to stop moving,
which, with the current data collection speed and robotic mounting, is
significant. Fortunately, it did not affect our trip too much, as we
has sufficient time in the end.
Greetings,
Mark
Mark J. van Raaij
Dpto de Bioquímica, Facultad de Farmacia
Universidad de Santiago
15782 Santiago de Compostela
Spain
http://web.usc.es/~vanraaij/
