Trouble in Paradise? Internal diffraction in PILATUS-like detectors

Internal detection surface diffraction effects leading to a reduction of detected counts (black lines on the real image, over which about 10% fewer counts were detected than the surrounding pixels). Image on the right shows the calculated pattern for the chosen energy. Energy used: 8285 eV, Reflection indices detected: (117). Image courtesy of Christian Gollwitzer at PTB.

A great many of the data correction issues in small-angle scattering can be resolved by trading a kidney for a PILATUS detector [1] (or similar [2]). These are detectors using a single crystal sensor as detection surface, and have extremely low noise, low distortion, high dynamic range and single photon sensing capabilities. However, as investigated by Gollwitzer and Krumrey (arXiv version here), this type of detector we so adore for its good detection characteristics may need a bit more data adjustment than expected. Read more »

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New Live Fourier Transform code

A screenshot from the Live Fourier Transform program

More about this next week, but Ingo has kindly provided a Windows executable version of one of the latest development builds of the Monte Carlo code (with GUI). While I have not yet had the chance to test it (being on a mac myself), please go ahead and get it from here!

Some of you may have seen the Live Fourier Transform video that was made a while ago. I am happy to tell you that there is now a new, better version out of that program (still rather small and straightforward, though). Read more »

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Tweaking the Ultra-SAXS machine

A sample (blue) and background (green) measured on the slightly optimised Bonse Hart system. Scale is "symlog", meaning it is linear between 10e-3 and -10e-3 (hence the strange bump).

It has been a very quiet four months (since this post) on the Bonse Hart front, as the generator was out of order (yes, again, and again). However, on one of the last days of 2013, something stirred in the lab, unsettled some dust and replaced the broken part. While I am not quite sure if the cause has been fixed or just the symptoms, the end result is that I can run the generator again at (at least) 10% power without things blowing up at me. Read more »

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Once more: writing data correction software

data correction feature image

With the Bonse Hart instrument out of commission still (yet another failure in the X-ray generator target assembly), I decided it may be time to have another look at the data correction procedures. Some of you may remember that I wrote a comprehensive review of all conceivable corrections in a recent open-access review paper, and while I implemented some of the corrections mentioned therein, it might be time to implement most of them. Read more »

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How to fit a scattering pattern part 2: Some simple fits

Previous fit, but instead of spheres, we are fitting using long cylinders.

Note: Part one of this three- or four-part series can be found here. Additionally, my topical review paper on SAXS data collection and correction which also lightly discusses data fitting is available open access here.

After the initial “scoping out” of a collected scattering pattern, it is time to try to see what can be done in terms of fitting in step 2. Here, we are trying to see if parts of the scattering pattern might be described by some basic scattering functions.  Read more »

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Monte Carlo; now getting a GUI!

McSAS_gui

There have been many developments on the Monte Carlo program that I have been rather silent about. For those that forgot: this is the method that allows the determination of a particle size distribution (or rather a scatterer size distribution) from a small-angle scattering pattern if you select a shape. It is described in detail here, but the supplementary information shows the real strength of the method: it can retrieve a wide variety of realistic size distributions. Read more »

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