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| SAXS Technical Specifications |
SAXS Beamline Technical Specifications
Endstation of the SAXS / WAXS beamline. Commissioning of the beamline optics is complete and the full range of energies and camera lengths is available. Development of the endstation has provided rapid & reliable methods for video camera based sample alignment and a flexible sample stage allows straightforward sample mounting. SAXS, WAXS, GISAXS and anomalous scattering experiments are all possible with a fully functional endstation. Two Pilatus detectors are in operation for SAXS (1M detector) and WAXS (200k detector) and may be run concurrently with excellent dynamic range, low noise and short exposures with up to 30 and 150 frames per second. A MAR-165 CCD (165 mm diameter) is also available for SAXS data collection.
Schematic Diagram of the SAXS /WAXS Beamline Index to sections below
Technical Specifications
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Q-range & SAXS Camera LengthsQ-ranges are calculated for a 12 KeV beam (1.0322 Å wavelength). These scattering angle ranges may be further adjusted by selecting different beam energies (5.2 - 20 KeV) or by slightly modifying the camera length by attaching longer or shorter nosecones. The Q-range required for an experiment must be included in applications for beamtime; if additional information is required please contact beamline staff.
Diagram of the different camera lengths available on the SAXS / WAXS beamline.
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Instrument BackgroundThe beamline is well suited to analysing weakly scattering samples due to high flux and low parastic scattering. How weak a scatterer can be analysed? Below is the measured background intensity at two main camera lengths calibrated into absolute intensity units (assuming a 1.5mm sample thickness). Above approx 0.01 Å-1 the background is controlled by air scattering, or for solutions by water scattering (note water = 0.016cm -1). Below ~ 0.01 Å-1 the background is controlled mostly by the instrument itself - assuming the sample mount (capillaries, substrates, etc...) produce no scattering. There is a good chance of getting usable data if the net scattering (sample minus background) is a few percent above the instrument background. If you have a reasonable idea of your sample structure, concentrations, etc., it is worth doing some planning calculations to check whether the scattering is likely to be observable.
Calibrated for a 1.5mm water path length. The 1.6m data were collected with a 10mm longer air path with air scattering, although low, dominating the background above 0.01 Å-1. Back to Index
Beamline FluxThe beamline is capable of utilising x-rays in the range of 5.2 - 20 KeV with the optics optimised for the 8 - 12 KeV range. The flux delivered at the sample position is dependent upon the undulator harmonic selected as shown below for the 5th and 7th harmonics. The 3rd, 5th, 7th, 9th and 11th harmonics may be selected to cover the full energy range with somewhat lower flux delivered for higher harmonics and higher energies.
Flux at the sample position for 5th and 7th undulator harmonics. Back to Index.
Detector SpecificationsThe SAXS beamline primarily uses two Pilatus detectors for SAXS (1M, 170 mm x 170 mm) and WAXS (200k, 33 mm x 170 mm) data collection although a MAR-165 CCD (165 mm diameter) is also available. The Pilatus detectors provide excellent 2D data collection for SAXS and some limited 2D WAXS collection allowing better particle statistics and sensitivity. However, the beamline is not optimised for full 2D WAXS data collection. Time-resolved data collection is also well supported as the Pilatus detectors are capable of collection at 30 Hz (1M) and 150 Hz (200K). For greater detail on the detectors please refer to the SAXS / WAXS Detectors page (under construction).
In the majority of experiments the Pilatus 1M detector is used for SAXS data collection because the detector offers very low noise, a large dynamic range and rapid data collection over a large active area. Dead space due to intermodule gaps is overcome by radial integration with the detector slightly offset. The dynamic range and single photon resolution of the Pilatus 1M detector allow a full range of scattering information to be collected in a single exposure, as shown below, by resolving data that would otherwise be lost due to the background. However, at the cost of higher background and slower data collection the MAR-165 detector provides superior data resolution due to a smaller pixel size. If the MAR-165 detector is likely to be required for your experiment please contact beamline staff and include this in the experimental section of your applications for beamtime.
R. Haverkamp, et. al., July 2009. SAXS data collected using the Pilatus 1M detector. Back to Index.
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