Neutron TOF data indexing

leburv

Hello everyone.

Could you please suggest the key words I should use when indexing TOF data as opposed to when indexing XRD 2th?

For instance, is there a TOF equivalent of the following:

- index_lam xxx
- index_max_th2_error xxx
- load index_th2 index_I {xxx xxx} ?

Also, should I include "neutron_data" in the inp file?

Topas version is 7, if matters.

Thank you,
Dmitry

alancoelho

Hi Dmitry

Use index_d instead of index_th2. The program will then convert the d-values to 2Th.

Set dummy values for index_lam and then chose a index_max_th2_error value; ie.

index_lam 1
index_zero_error   
index_max_Nc_on_No 3
index_max_th2_error .02

load index_d {
   4.121799	
   ...
}

Let me know if you get stuck.

cheers
alan

leburv

Hello Alan,

Thank you very much, it works.
I had my TOF data in units of TOF, so the TOF->d conversion was another necessary step for the script to work.

The inp file now runs successfully, ndx is created, and I can compare the found peaks against the proposed peaks, but there a cosmetic thing that doesn't work for me: I would like to overlap the actual data (my xye file) over the simulated peaks (the inp with ndx) - and the two don't coincide for some reason because the x values are different. It's as if the choice of wavelength (the dummy value) was off. I then set it to the central wavelength of my neutron data (which happens to be much larger than lam 1) - and although the file still runs, the generated ndx file is empty. Can it be that I am beyond the allowed threshold of wavelengths?

If you know what I mean, is there a way to overlap the data file and the inp file in this case?

Thank you,
Dmitry

alancoelho

There are a few things to try. It might be best if you sent me your indexing INP file as well as the XYE file and I will see how best way to do display the data.

alancoelho

Hi Dmitry

The simplest is to convert the XYE data to 2Th data using Excel; ie.

Th2 = ArcSin(Lam/ (2 d)) 360 / Pi

d = TOF / 1.13149

The GUI is then familiar; the attached screen shot shows everything working. Note, the file th2.xy is the tof data converted to 2Th data for a Lam=1.

An indexing phase was created and and your INP file pasted into it using "Paste INP to node/Selections"

Then the NDX file is then pasted into the Indexing phase.

cheers
alan