Absorption_With_Sample_Thickness_mm_Shape_Intensity

jlipp20

According to the book "Rietveld Refinement: Practical Powder Diffraction Pattern Analysis Using Topas" by Dinnebier, Leineweber, and Evans (2019), the factor to scale peaks due to absorption should be:

'A = 1 - exp(-ueff*ts*2/sin(theta)"

and can be implemented by the following Topas code:

"scale_peaks = 1-exp(-uT 2 / Sin(Th));" (page 45)

I have noticed that the Topas code in the "Absorption_With_Sample_Thickness_mm_Shape_Intensity" and Absorption_With_Sample_Thickness_mm_Intensity" macros (at least in Topas version 6) uses the value 0.2 instead of 2:

scale_pks = (1 - Exp(-.2 CeV(u, uv) CeV(d, dv) / Sin(Th)));

Is this an error in the macro?

- Jeremiah

jlipp20

My apologies, I just realized that the reason for this comes from the units. The absorption coefficient is in cm^-1, but the thickness is input in mm. Therefore the macro uses 0.2 instead of 2.
I do not seem to have the option to delete this thread, otherwise I would. Again, I apologize for taking up your time.

- Jeremiah

Ramon13

jlipp20
Hi Jeremiah (and anyone else reading this),

I noticed from the manual that there's the Absorption_With_Sample_Thickness_mm_Shape and Absorption_With_Sample_Thickness_mm_Intensity functions. Usually, I just use the common Absorption function (usually towards the very end of my refinement) but I'm curious now as to whether the other 2 functions are better to use for accuracy as the user has the ability to input the thickness [mm] and LAC quantities which they can get from direct measurement of the sample and the Mixture_LAC_1_on_cm function in JEdit. What do you think? Maybe a combination of the shape and intensity functions is the way to go? I'm unsure now.

I've also heard that some people weigh their packed samples before scanning (presumably to put the sample mass [g] into some sort of function to better estimate the packing density and (presumably) link that with the absorption too.

I'd love to hear everyone's thoughts here as it's not difficult to weigh my samples, and if it makes a considerable difference to accuracy then I think it's definitely worth doing!