I've seen haunted crystals before - the culprit was indeed with the
mounting of the pins in their bases (I was re-using some pins and
apparently the adhesive had cracked or otherwise failed). Fortunately I
never leave home without a tube of Duco cement and was able to correct
the problem in situ.
kmj
Mark J. van Raaij wrote:
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/
