Thanks for all helpful replies, below a summary of different moving
crystal scenarios.
For our particular case, I am quite convinced it was the glue
continuing to set/react after mounting. We had to glue some pins at
the last moment, without having time to leave them to set a few hours
as we do normally, and these were all litholoops if I remember
correctly.
After the moving, extending, away from the goniometer head, the
crystals stayed stable. This rules out ice between the head and base,
or loosening of the pin in the base. Other crystals were also stable,
ruling out something wrong with the goniometer setup, etc.
Summary of other possible moving events pointed out:
- ice crystals at the bottom of the base which slowly thaw
- loose pins in the base
- too weak magnets (too heavy base)
- too strong magnet, leading to whiplash effect, catapulting crystals
(this presumably only occurs when directly freezing crystals on the
beamline, not when mounting prefrozen crystals)
- incorrectly fastened goniometer, magnet etc.
PS new email address (forwarding will only work for a limited time):
[EMAIL PROTECTED]
Mark J. van Raaij
Dpto de Bioquímica, Facultad de Farmacia
Universidad de Santiago
15782 Santiago de Compostela
Spain
http://web.usc.es/~vanraaij/
