MICRODIFFRACTION DEVELOPMENT

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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. During this cycle we have performed the following developments related to the BioCAT micro diffraction program. We made a new version of the sample alignment system. The prism was replaced by a smaller one and the assembly was moved upstream the sample position next to the aperture side. This allows moving the sample holder near the front window of the He chamber and therefore reduces the air gap between sample and chamber. We observed a significant reduction of air scattering with this new arrangement. We also incorporated a set of slits and a long snout that can be evacuated. The arrangement is located immediately downstream the KB mirrors to provide a clean and well-defined beam with very low parasitic scattering. This combination of slits and aperture yielded very clean backgrounds, which is essential when dealing with weak and diffuse scattering/diffraction signals.The CCD detector mount was also modified by incorporating rails that allows moving it along the beam direction. These rails help reduce the time needed to relocate the detector when changing the camera length. New flight tubes were also incorporated to the system. These are standard stainless steel tubes that allow selecting chamber distances from 100 mm to 300 mm very easily. The ability to maintain samples at cryogenic temperature in the instrument have been also improved.