26 November 2014
I20-1 is now I20-scanning
I20-2 is now I20-EDE
Please reference the beamline and the branchlines with these new names in your publications.
The determination of the local structure around a photoabsorbing atomic site present at low concentration and/or in X-ray unfavourable heavy matrix is one of the particular strengths of I20-scanning when operating in the conventional scanning XAS mode. The high flux and high spectral purity are the key design parameters of this beamline. The beamline is equipped with an in-house designed four-bounce monochromator which consists of two pairs of counter-rotating crystals.The main advantages are: a) high stability and reproducibility, b) fixed exit by geometry, and c) angle and energy resolution of transmitted photons are not determined by the incident beam divergence.
|Energy range|| |
Si(111): 4 - 20 keV
Si (311)+: 7 - 34 keV
|Energy resolution|| |
Si (311)+: ΔE/E=2.8x10-5
|Flux at 10 keV (ph/s)||> 1012|
|Beam size at sample (µm)|| |
HxV = 400 x 300
+not available at current time
Status Update June 2018
The current incarnation of the four bounce monchromator has been in regular user use for the last two years. The Si(III) set of crystals work well with some minor issues. The monochromator takes some time to thermally equilabrate when changing edge thus the beamline is normally only used for one edge per experimental user session apart from adjacent edges. The monochromator is still vibration sensitive and hence the area around the I20 optics hutch is barriered off to prevent external stimuli to activate these modes.
The Si(311) set is not useable at this time. A major change to the first crystal design has been implemented and is undergoing final tests before probable installation in the beamline in November 2018. If this is succcessful it will show a path to getting high energy XAS (>19 keV) on the beamline. This is likely to be through a new monochromator design, and hence will not be a fast process.
The 64 element has had Xspress4 electronics fitted this year which has improved its performance radically making it simpler to collect data on samples with high scattter or other elements in high concentrations.
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