[ccp4bb]: Problems with low mosaicity crystals

["Patrick J. Loll" <pat.loll@drexel.edu>]

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	Jim has an excellent point; low mosaicity xtals are expected to be
more sensitive to little hardware errors, since the reflxns spend less time
traversing Ewald's sphere.  We encountered similar results back in the dark
ages, when low mosaicity xtals revealed that the gear driving the omega
motor in our Nicolet diffractometer was actually out of round...the effect
was completely masked with "normal" crystals...[J Appl Cryst 23: 212 (1990)]

	At the same time, it's hard for me to stomach the notion that this
phenomenon is due to the loop vibrating in the cold stream...surely that
would give rise to the symptoms Peter Burkhard described, with a high
apparent mosaicity?  It seems that you'd need a low frequency (i.e., slow
relative to the spindle motion) or intermittent vibration to cause this
kind of error.  Do you know that the spindle rotation was 100% reliable
(see above paragraph)?

Pat

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Patrick J. Loll, Ph. D.                             (215) 762-7706
Associate Professor	                       FAX: (215) 762-4452
Department of Biochemistry
MCP-Hahnemann University
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Philadelphia, PA  19102-1192  USA

pat.loll@drexel.edu