HARDWARE FOR CHALLENGING SAMPLES

Cornell University, Ithaca NY

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. A new form of data collection has been developed that exploits the high precision and reproducibility of the MD2's x,y,z sample centering stages to make better use of crystals larger than the beam size, and to distribute x-ray damage over the entire volume of large crystals. This is accomplished by defining a 3-space scanning vector that spans the sample and scanning along this vector as part of the data collection process. Complete or partial data sets may be acquired at a number of discrete points along the scanning vector (discrete vector scanning) or continuously along the scanning vector, with small steps along the scanning vector asserted after acquisition of each frame in a data set (continuous vector scanning). We show that for both discrete and continuous vector scanning data collection, radiation damage effects on data quality are largely mitigated by equipartitioning damage across the volume of samples larger than the beam. Modifications of vector scanning methods are used to locate optimally diffracting regions of a heterogeneous crystal or to align samples embedded in opaque frozen, cryosolution.