ANL, Argonne, Illinois, USA
The GM/CA developed, quad-mini-beam collimator[*,**], advanced rastering and vector data-collection software tools[***], have enabled successful data collection on some of the most challenging problems in structural biology. There are two main sources of X-ray scattering (besides the sample) that reach the detector, contribute to back-ground and limit data resolution. These are scattering within the collimator that escapes the exit aperture and air-scattering of the direct beam before it terminates in the beamstop. Scattering from the collimator can be reduced by decreasing the exit aperture size. A quad mini-beam collimator was built consisting of 5/50, 10/70, 20/100 and 150/300 µm beam defining/exit aperture combination, respectively. Previous collimators were positioned in the X-ray beam by two motorized translational motions and two manual angular adjustments via a kinematic mount. Due to reduced tolerance in the new design, aligning each of the pin-hole combinations to high-precision required motorizing both translational and angular motions. Design and con-struction of the improved mini-beam collimator and the extent of background reduction will be discussed.
* Fischetti, et al.,JSR 16, 217-225 PMCID 2725011
** S. Xu, et al, AIP 1234, 897 - 900 (2010)
*** Hilgart, et al, J Synchr. Radiat. 2011:717-22. doi: 10.1107/S0909049511029918. Epub 2011 Jul 29
