This looks like stacking or shift disorder which can occur when perfect 3 dimensional order breaks down. For example one can have a situation where the lattice is preserved in 2 dimensions but the planes can slide with respect to one another destroying the order in the 3rd dimension, thereby giving rods in reciprocal space rather than spots. Preservation of order in 1 dimension but with the 1 D lattices shifted with respect to each other gives diffuse planes in reciprocal space. If displacements are non random, than the diffuse scatter might only occur for certain reflections.

As sharp spots are also present, it is likely that the 3D order is preserved over much of the sample. To analyse properly one would have to record diffraction over small angular increments (similar to 3D reciprocal space mapping) and perhaps identify the hkl value of reflections which exhibit strong, weak or absent effects of this type.

The reason for the behaviour can become clear when the structure is known and weak lattice interactions identified. However, if these effects are preventing you determining the structure then this statement is not particularly useful.

If really interested you can of course google for such types of disorders and find examples with similar types of streaking (e.g. in J. Appl. Cryst. (1971). 4, 329 http://journals.iucr.org/j/issues/1971/04/00/a08549/a08549.pdf ). Alternatively read "ancient" text books such as Hosemann and Bagchi.

From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Margriet Ovaere
Sent: 28 January 2009 13:52
To: [log in to unmask]
Subject: [ccp4bb] small lines in diffraction pattern

In the diffraction pattern of crystals of an RNA decamer, small lines appeared (see pictures attached). We've tried different crystals but they all showed the same small lines. Has anybody seen this phenomena before and has got an explanation for it please..?

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