# Videos

This page contains the list of (Youtube) videos I have made over time explaining SAXS and some of its workings. They are mostly sorted in order of appearance (newest on top). While this page is not always up-to-date, the newest videos are always available here.

Some new 2D fitting work I am developing at the moment (more information):

A presentation discussing a small-angle scattering technicality, what is the visibility of particular sizes in polydisperse samples? (more information):

A promotional video for a NIMS workshop:

A demonstration of small-angle scattering from a hair. This is a demonstration in which beams of laserlight (two lasers with different wavelengths are used to demonstrate the effect of different wavelengths as well) is shone upon two human hair samples. A small-angle scaattering pattern is seen on a whiteboard and analysed to determine the diameter of the hairs.

…and the calculation of their diameters from the small-angle scattering pattern

A demonstration of what we would see when we scatter from some samples, using a live Fourier Transform image of a laptop camera:

An explanation of what I did from 2009 to 2011 with a concise SAXS explanation and some elaboration on analysis methods:

A short explanation of small-angle scattering:

1. Hey!great videos, thanks!but i think at the 3rd one, where you calculate the diameters, towards the end of the video (around 4:17) you say q is wavelength independent, do you mean r is independent since you calculate q taking into account wavelength?

2. Hi Celen,

Thank you for your question. The definition of the scattering angle q makes this scattering angle independent of wavelength (this is achieved by dividing by the wavelength). Anything we calculate using q, such as the radius r, will then automatically also be wavelength independent.
So, if I understand your question correctly, the numerical values for the angle q are already wavelength independent because of the way we calculate these q-values.

This is not the case in the diffraction world, where the angles are usually given in degrees. While degrees are more closely associated with the concept of angles, these degrees are only useful if the wavelength is also given for that particular measurement.

3. Good afternoon Brian,

I wish to incorporate your video, entitled: “Small-angle X-ray Scattering (no voice-over, no closed caption)” in my x-ray safety training for my students. May I have your permission to do so? I will acknowledge your authorship of this clip in my presentations.

Thanks for kind consideration.

Auggie

4. Hi Auggie,

Sure thing, I’ve sent you the links to the full-scale versions in an e-mail.

Cheers,

B.

5. hi nice vids,

I wish to use your hi-res video in one of my presentations,
thank you very much.

6. Your videos seem to imply that scattered intensity can pass through the beam stop. This doesn’t seem to make any sense.

7. Dear Marty, That was more due to a limitation in my raytracing skills rather than a lack of understanding. In the simulated data and model data the beamstop is not explicitly drawn. Once I learn something else (Blender or somesuch), I might be able to update some of the videos, but until then I’m afraid there’s not much I can do.

8. Hi Brian,
I’d like to use your video “Small-angle X-ray Scattering (no voice-over, no closed caption)” in the ppt presentation of my diploma thesis which is based on usage of SAXS in regards of conformation of biopolyelectrolytes. May I have your permission to do so? I will acknowledge your authorship of this clip in my ppt.

Thanks

9. Dear Raksha,

That’s a good question, there are some similarities and some differences. I think it may make a good topic for a video, but here are the highlights:
The similarities are that:
1. Both techniques measure the intensity as a function of angle, though the angles are typically smaller in SAXS than XRD.
2. Both techniques show peaks for periodic structures, the larger the periodicity length, the smaller the angle at which the peak shows itself.
3. for any structure (crystalline or non-crystalline), there is a [000]-reflection. This is the one whose peak broadening we are typically investigating in SAXS.
4. Like XRD, we have a phase problem. We cannot say whether we are scattering from electron-dense objects in a “light” matrix or the other way around

The differences are that:
1. SAXS does not require the material to be crystalline. Any structure will affect the scattering pattern.
2. We don’t consider the scattering to be from individual atoms, but rather from contiguous regions of similar electron density.
3. We typically don’t have as many angles to worry about as the diffractionists, so perhaps SAXS is easier :)

Hope that helps!

B.

10. Hi Brian,
That was very good information,thanks for sharing.
I am currently working on XRD . Can we perform SAXS analysis of a tablet, a whole tablet i.e without crushing?
Can this technique be used for quatification analysis?

Regards,
Raksha

11. Dear Raksha,

SAXS on a tablet (in transmission mode) should be possible, but beware of nanostructure created in the tablet pressing procedure. In other words, if tiny pockets of empty space, voids or cracks are generated when you press a tablet, those will show up in the SAXS signal.

Best way is to try it and see what you get. Also, a good way to test is to try and look at the tablet structure under an electron microscope to get an idea of what you will see in the SAXS signal. If you want to see a diffraction peak of a very large lattice parameter, you’re probably fine. Check out what thickness you need to get the X-ray beam through your tablet using the site here:
http://11bm.xray.aps.anl.gov/absorb/absorb.php

SAXS can be used quantitatively if you have a good idea what the phases in your system are. For this, you will need an absolute intensity calibration standard.

Cheers,

Brian.

12. Hi Brian!
I would like to ask you how does the SAXS help to identify the pore shape (the network system) of the porous materials ?

13. Hello Youssef,

Thanks for asking. If you are talking about ordered pore structures (like from etched block copolymer systems), the resulting diffraction peaks at small angles can tell you something about the structure. I have very little experience with these, so I’ll point you to Martin’s review for those: http://pubs.rsc.org/en/content/articlelanding/2013/cp/c3cp50293g

As for non-ordered porous systems, there are two options: either your sample has an aligned porous structure (giving you an anisotropic scattering pattern) or it has a non-aligned porous structure. In the first case, *some* information can be gleaned from the scattering pattern on the pore shapes.

In the second case (isotropic scattering from a porous structure), it is usually not possible to separate the pore shape from the polydispersity. The scattering pattern itself can be fit using a multitude of models, each using different pore shapes and polydispersities. In other words, if you change the assumptions on the elementary shape of the pores (e.g. from spherical to cylindrical), you can still find a polydispersity that will allow you to fit your data. More information on that in the introduction of my open-access review paper: http://dx.doi.org/10.1088/0953-8984/25/38/383201

Good luck!

B.

14. Hello,
Yes it’s about ordered mesoporous materials (with block copolymer as a surfactant), where SAXS ‘s been usually used to identify the structure or to confirm images got by the SEM (Scanning Electron Microscope) or TEM (Transmission Electron Microscope).
Thanks a lot.

15. Hi Brian!
First of all thank you for your nice videos.
Can you do any video for SANS and SAXS date analysis?

16. Dear Brain,

I’d like to ask your permission to use your video “Small-angle X-ray Scattering (no voice-over, no closed caption)” in my presentation about SAXS for student in Thailand. I’ll acknowledge your authorship in my ppt presentation.

Thank you very much

Siriwat

17. Hi Siriwat,

Cheers,

Brian.

18. Dear Sir
I am a beginner and I want to learn about SAXS .Can you suggest me any videos or papers which can be helpful ? I want to learn to calculate pore structure (diameter,wall thickness),mesoporous order and space group of mesoporous material

19. Hello Aman,

What you need for that is a mix of crystallographic knowledge (for calculating order and space groups) and scattering knowledge (for calculating diameter and wall thickness). That mix will take you a few years to learn and a while longer to apply. I do not have any videos on that particular topic, but the introduction to fourier transforms is probably a good place to start. Are you in this for a Ph.D. project?

Cheers,

Brian.

20. Hi Brian,
Wanted to if you had used the IRENA macro for Igor from Argonne National Lab. If so, would it be possible to list major differences between IRENA and McSAS? The main reason for leaving this comment was I could not find the example data set in the repository to try McSAS. I read in the issues section of the repository that an example data set was added on 10/2015 but I was unable to find it. The downloaded zip file does not have it either. I tried using SAXS data I have (which I used with the IRENA macro) and it returned an “zero – size array to reduction operation maximum which has not identity [ValueError in._amax()]” error. Since I do not know a proper way to submit error messages I have listed it out here. The data I used was three columns separated by semicolon q, I, E. The third column is not exactly error. Does q have to be in a specific unit? Mine was in A^-1. Is there a python program to go from SAXS 2D corrected/smoothed scan image to McSAS ready data?
Thank you.

21. Hello Aashish,

As for loading your data, the important thing is that you have a three-column ascii file (i.e. already reduced to one dimension from the 2D scattering pattern), and should look like the structure of the example data. If you cannot find the example data with your version, you can find it online here: https://bitbucket.org/pkwasniew/mcsas/src/4c7a3b4db230a5257f4b5e7276f89c4f64507d8e/testdata/quickstartdemo1.csv?at=smearing

Your data should be in the units of reciprocal meters for the intensity (or arbitrary units if you don’t have it in absolute units), and reciprocal nanometers for Q. If you get this wrong, things will just be shifted a bit.

To my great shame, I never managed to get very far with Irena. However, the difference, roughly speaking, is in the approach to the data fitting. Ingo explained that nicely for the difference between SASfit and McSAS in one of his abstracts, where you can substitute SASfit for Irena. This abstract is in the second section here: http://www.lookingatnothing.com/index.php/archives/2174

Let me know if you have any other questions.

22. Hi Brian,

Thank you for uploading the example data. I think my data was three columns separated by semi-colon text ascii file. It was a 1D average spectrum of the 2D scattering data. I will run the example data and try to run my data and will let you know if I have any success.
Thank you once again.

23. Hello Brian,

I wish to incorporate part of your video (explanation of SAXS), entitled: “WhatIDo and Small-angle X-ray scattering explanation (no voice-over, no closed caption)” in my class project presentation about some SAXS applications. May I have your permission to do so? I will acknowledge your authorship of this clip in my presentations.

Thank you for kind consideration.

Yana

24. Dear Yana,

I sent you an e-mail with the approval. Thanks for your interest!

Cheers,

B.

25. Dear Brian,

I’ve send an email to you on 15 Feb 2017, regarding SAXS workshop in Thailand. I’m not sure whether you received my email or not.

Thank you

26. Dear Brian,
Your videos are being a great help to me in understanding about SAXS. However, I had a query that sometimes even on increasing the concentration of liquid samples, there is no scattering observed on the detector? What could be the probable reason for that? Moreover, why intensity is depicted in terms of arbitrary units ?

27. Dear Shweta,

scattering on the detector is dependent on two things: concentration and contrast. If you increase the concentration, but see nothing, it may be that the scattering length density contrast between the two phases is negligible (you can check with a scattering length density contrast calculator).

As for intensity in arbitrary units, 9 times out of 10, this is because people are lazy or unaware of how easy it is to scale to absolute units. There are a few methods available to scale to absolute units, the simplest is by using the glassy carbon sample from NIST. This does require, however, that you can measure your transmission factors!

Cheers,

Brian.

28. Dear Brian,
Thankyou very much for the response. However, I am trying to calculate the SLD for the liquid sample (Copper oxide nanoparticles in ethanol) however, my query is that how would I know about the desirable range whether the sample is giving the negligible value. Can you suggest where can I find information related to Calculation of SLD ?
Thanks
shweta

29. Dear Shweta,

Copper oxide in ethanol sounds like it should definitely give you a signal, probably at concentrations of several mg/L. However, there could be practical problems, such as the copper sinking to the bottom of your liquid cell. Also, check the X-ray absorption energies of copper, and compare it with the copper k-alpha photon energies you’re using. I’m not sure there would be issues, but it might cause some funny scattering or absorption behaviour if they’re very close.

If you want to calculate the SLD, I usually use this one:
https://www.ncnr.nist.gov/resources/activation/