Fitting individual peaks to TOF data

helenmc

Dear all,

I have a nice set of data from J-PARC (PLANET beamline) and I'm just starting to use TOPAS for refinement of TOF data. I've hit a little bit of a wall when trying to fit individual peaks (I'd like this for two reasons, one to model the broad bump of an amorphous component to my samples and the other to fit new peaks so that I can index them)

I've not had any problem implementing the TOF peak shape into the str and hkl_is parts of the file - but I can seem to fathom how to do this for an individual peak. (I've tried using the more conventional PV type to do this but it is very unstable).

I'm assuming I need to indicate a sort of 'TOF_PV' at the peak_type stage?

Best wishes,
Helen

johnsoevans

Helen,

Have you looked at: http://topas.dur.ac.uk/topaswiki/doku.php?id=time_of_flight_tof_peak_fitting

Does it solve your problems?

John

alancoelho

Hi Helen

To add a pseudo-Voigt then the following should work:

xo_Is
peak_type pv
pv_lor @ 0.5
pv_fwhm @ #1 min #2 max #3
xo #4 min #5 max #6 I # 7

where #n are numbers dependent upon the x-axis. You could also use d_Is.

If you get stuck then send me the INP and data file and I will have a look.

cheers
alan

helenmc

Thanks very much for getting back to me John and Alan, I'll work on these and see how I go.

Best,
H

helenmc

I've managed it! The key thing was moving the TOF convolutions into the str section.

Having said that I will have a crack at John's method using the hkl_Is phase - the only thing is, can I fit more than one peak at a time within one hkl_Is - or would I have to define a separate one for each peak (like the d_Is and xo_Is)?

Many thanks,
Helen

johnsoevans

I think it's written for one peak at a time currently.