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/
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