[Solved]How to create synchrotron instrumental convolutions using TOPAS?

iangie

Dear TOPAS users,

I have run a NIST SRM 660b pattern in a synchrotron beam line, where instrumental fundamental parameters are not available, but I have the approximate beam wavelenght.
Could you please give me some tips about how to parameterize the instrumental profile?
Say, should I determine the accurate wavelength first or determine the instrumental convolutions by "empirical parameterization" first, or I can refine them together.

Thank you very much!

P.S. I know TOPAS is good at analyzing synchrotron data as well. But there is no single paragraph in User Manual/ Technical reference/ Tutorial dedicate to synchrotron data analysis.
I think we need change some default value like yminymax, x_calculation_step, la, lo, lh, etc, right?
And I find if both lh and lg are not used, the program will give error message "floating point division by zero" then freeze.

ahhill

Dear iangie

For ID31 I use the following as a starting approximation to describe the peak shape and instrument details.

x_calculation_step = Yobs_dx_at(Xo); convolution_step 4
bkg @ 0 0 0 0

start_X 1.9 ' choose whatever is appropriate
finish_X 30 ' choose whatever is appropriate
extra_X_right 0.05

lam ymin_on_ymax 0.0001 la 1.0 lo 0.354134 lh 0.1
LP_Factor( 90)

prm pr1 0.007
prm pr2 0.007
prm pr3 0.007
prm pr4 0.007

Zero_Error(zero, 0.002)
Simple_Axial_Model(axial, 1.07693`_0.04475)

str

...
...

lor_fwhm = pr1 Tan(Th) + pr2/Cos(Th) ;
gauss_fwhm = pr3 Tan(Th) + pr4/Cos(Th) ;

That should start you off, but it depends a lot on what the beamline was of course.

ahhill

Sorry, I hadn't read correctly that you only have the approximate wavelength.

I would suggest you go and ask the instrument scientist what the true wavelength was.

iangie

Thank you ahhill,

Although I am not using ID31 beam line, this template is extremely helpful to me. Thank you very much.

BTW, I think these two lines should be placed out of Str, since we use them to descibe instrument broadening, not sample related broadening, am I right?

lor_fwhm = pr1 Tan(Th) + pr2/Cos(Th) ;
gauss_fwhm = pr3 Tan(Th) + pr4/Cos(Th) ;

iangie

Hi ahhill,
The "approximate wavelength" is from beamline scientist. I just don't trust the last two decimal before I get it from refinement of my own NIST SRM 660b pattern.
Theoretically, we should be able to tell the wavelength from SRM pattern.

ahhill

iangie:1304170756 wrote BTW, I think these two lines should be placed out of Str, since we use them to descibe instrument broadening, not sample related broadening, am I right?
lor_fwhm = pr1 Tan(Th) + pr2/Cos(Th) ;
gauss_fwhm = pr3 Tan(Th) + pr4/Cos(Th) ;

In our case on ID31 the instrumental broadening is absolutely tiny, and the majority of the peak broadening comes from the sample. So I keep those in the str part.

iangie

Hi Adrian,
I got it.
Thank you for your help :)

yamasaki3

Thank you ^^

prid

Fantastic, thanks!

oppomix13

Thanks for guiding

zeun4749

x_calculation_step = Yobs_dx_at(Xo); convolution_step 4
bkg @ 0 0 0 0

THanks!

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