Folks, As expected, discussion about to bathe or not to bathe are starting to expand into other aspects of data collection and processing. Along the way I saw reference to how we use our small beams on GM/CA beamlines in sector 23 of APS. Without going into discussions of advantages and disadvantages of various beam sizes, I'd like to clarify our usage of small beams. Our mini-beams (5-10 micron) are not a primary tool and are being used when larger (100x25 um) beams have had problems. These problems include Small crystals (less than 20-30 um) Streaky spots (from any size crystal) Very high mosaicity Inconsistent quality (order) throughout the crystal
When larger crystal is more or less homogeneous in its quality, larger beams are superior to be used and allow larger diffracting volume to work for you. This is especially true for avoiding the radiation damage as larger volumes allow equally lower flux to be used. We collect data from larger crystals and 5-10 um beams only when one or more of the above problems need to be resolved. For those who prefer bathing, the recommendation still is to keep the beam size closer to that of the sample. Air scatter, produced by the (part of the) beam which is not contributing to the Bragg spots, is still noticeable at most typical energies. Cheers, N. Ruslan Sanishvili (Nukri), Ph.D. GM/CA-CAT, Bld. 436, D007 Biosciences Division, ANL 9700 S. Cass Ave. Argonne, IL 60439 Tel: (630)252-0665 Fax: (630)252-0667 [EMAIL PROTECTED]
