Technical Information SAXS/WAXS
This page details the technical specifications of the SAXS beamline. For information about beamline supported sample environments please refer to the SAXS/WAXS Sample Environments page. 
Commissioning of the beamline optics was completed in 2009 and the full range of energies and camera lengths is available with the beamline running a full operations program since mid-2009. Development of the endstation has provided rapid & reliable methods for video camera based sample alignment and a flexible sample stage allows straightforward sample mounting. Sample mounting is continuing to be developed on the beamline with a focus on improved efficiency and higher sample throughput.
The core detector on SAXS/WAXS is a Pilatus3 2M. with excellent dynamic range, low noise and short exposures with up to 25 frames per second. Changing camera lengths is very easy and takes about 5 to 10 minutes (depending on distance change and extent of automated alignment required). We recommend taking blocks of data in a SAXS or WAXS configuration (for example at least an hour each) between changes. Please don't plan to change camera length more frequently (eg, not between individual samples, points in time/temperature series or other short runs).
Schematic Diagram of the SAXS/WAXS Beamline
Technical Specifications
Source | In-vacuum undulator, 22 mm period, 3 m length, Kmax 1.56 |
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Energy range | ~5 - 20 keV |
Energy resolution | ~2 eV |
Beam size (at sample position) | [Standard] H: 250 µm × V: 25 µm (FWHM) [Microfocus] H: 35 µm × V: 4 µm (FWHM) (at 12.4 keV ONLY) [Defocused] H: 250 µm × V: 450 µm (FWHM, vertical defocused) |
Maximum flux | 2 x 1013 photons per second at 8 keV. 8 x 1012 photons per second at 11.5 keV. |
q-range | [In-Air Environments] 0.0015 - 3.0 Å-1 (using 2+ camera lengths between ~700 and 7000 mm) [In-Vacuum Environments] 0.0015 - 5.0 Å-1 (using 2+ camera lengths between ~700 and 7000 mm) The Pilatus3 2M detector is fully motorized for automated camera length changes |
Beam divergence at sample position | 140-260 µrad horizontal 30 - 60 µrad vertical depending on focal position. |
Instrument background (assuming 1mm sample pathlength) | In-air samples: background < 0.02 cm-1 @ q=0.01 Å-1 In-vacuum samples: background < 0.00001 cm-1 @ q=0.01 Å-1 |
Q-range & SAXS Camera Lengths
Quick reference table (below) of Q-ranges are calculated for an 8.2 keV (1.51201 Å wavelength), 12.4 keV (0.999877 Å wavelength), and 20.0 keV (0.619924 Å wavelength) beam. These scattering angle ranges may be further adjusted by selecting different beam energies* (5.2 - 21 keV) or by slightly modifying the camera length. Please use the q-calculator to determine your preferred SAXS camera setup(s). The Q-range, beam energy, and camera length required for an experiment must be included in applications for beam time. If you need additional help in choosing your setup, please contact beamline staff.
Camera length (mm) | Approximate Q-range (Å-1) at 8.2 keV | Approximate Q-range (Å-1) at 12.4 keV | Approximate Q-range (Å-1) at 20.0 keV |
|---|---|---|---|
700** | 0.015 - 1.64 | 0.023 – 2.40 | 0.037 - 4.00 |
1000 | 0.011 - 1.17 | 0.016 – 1.76 | 0.026 - 2.84 |
2000 | 0.005 - 0.59 | 0.008 - 0.89 | 0.013 - 1.44 |
3000 | 0.0036 - 0.39 | 0.005 – 0.60 | 0.009 - 0.96 |
4000 | 0.0027 - 0.29 | 0.004 – 0.45 | 0.007 - 0.72 |
5000 | 0.0021 - 0.23 | 0.003 – 0.36 | 0.005 - 0.58 |
6000 | 0.0018 - 0.20 | 0.003 - 0.30 | 0.004 - 0.48 |
7000 | 0.0015 - 0.17 | 0.002 - 0.26 | 0.004 - 0.41 |
*Choose higher energies to preference high q-values and lower energies to preference low q-values. (See figure below)
** Maximum achievable q-values at short camera lengths can be influenced by shadowing from gate valves/nosecones etc.
Scattering from SBA-15 comparing camera length and energy changes. Scattering intensity is arbitrary and has been offset for clarity.
Instrument Background
The beamline is well suited to analysing weakly scattering samples due to high flux and low parasitic scattering. An in-vacuum sample chamber is available for particularly weak scattering samples, either in transmission or grazing incidence geometries.
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 1.0 mm sample thickness), for samples either measured in air or in vacuum.
For measurement in air, the instrument background is controlled by air scattering above approximately 0.01Å-1 . Below approximately 0.01 Å-1, the instrument background is controlled mostly by the instrument itself, primarily by weak scattering from the silicon nitride vacuum windows either side of the sample. . There is a good chance of getting usable data if the net scattering (sample minus background) is a few percent above the instrument background.
For in-vacuum measurement, all sources of background have been controlled and there is almost no background intensity above ~ 0.005 Å-1, especially for camera lengths under 3 m. Below ~ 0.005 Å-1 the instrument background currently rises due to parasitic scattering from the beamline optics, ultimately because of figure errors on the HFM which can only be partially removed by the beamline’s slit system. The instrument background between 0.0015 - 0.004 Å-1 would only affect the weakest of scattering solid samples run in vacuum, whose mount or containment itself does not cause any scattering. In the case of proteins, scattering from the capillary and the solvent typically dominate the measurement, not the instrument background.
For weakly scattering samples, it may be worth doing some planning calculations to check whether the scattering is likely to be observable. The main thing to know is how much background will come from your sample mounting system, as this usually dominates over the instrument background. A signal:noise of ~1.02 (i.e. only 2% signal) is usually measurable given the accuracy of normalisation is well below 0.1% (depending on transmitted flux). Some general suggestions are:
samples run in capillaries, or between tapes like Kapton: the background will be controlled by your sample cell, mount or solvent, not the optics
For water based solutions (e.g. proteins) the background will be controlled mostly by the cell below ~0.02 cm-1, and at higher q by the solvent (note: water scattering intensity is = 0.0163 cm-1).
the vacuum in the sample chamber is below 1 x 10-5 mbar. Your samples will need to be compatible with low vacuum.
for in-vacuum grazing incidence WAXS, the instrument background is so low that sub-monolayer GIWAXS has been done on crystalline polymer films.
Beamline Flux
The beamline is capable of utilising x-rays in the range of 5.5 - 21 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.
Detector Specifications
The SAXS beamline uses a Pilatus3 2M detector (254 mm x 289 mm) for data collection. The detector is in-vacuum and fully motorised, for fast, automated changes of configuration (e.g. SAXS camera length).
The large area detector provides excellent for 2D SAXS and WAXS data collection, dependent of cameral length and beam energy chosen (choose shorter camera lengths for WAXS and longer camera lengths for SAXS). Time-resolved data collection is also well supported as the Pilatus detector is capable of collection at 25 Hz (Pilatus3 2M).
Detector | Specifications |
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Dectris - Pilatus3-2M |
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