About Peak Shape Parameter Refinement

john201004

When we analyse thermal cycled data we need to first obtain instrumental function (or peak shape function) from standard samples such as silicon. Then, we can use these profile parameters form standard sample to carry out our fitting procedures on actual data in question. For multiphase fitting we can simply use one fixed profile function to all phases. However, in tutorial below

http://www.dur.ac.uk/john.evans/topas_workshop/tutorial_multiphaseriet.htm

it suggested that we can get better results after refining the peak shapes separately for each different phases. I know we definitely can get better results since we have more refinable parameters in our fit. But why we refine them? aren't they suppose to have same value? In what circumstance we are allowed to refine peak shape parameters separately?

Sincerely

johnsoevans

Peak shapes will usually have both an instrumental contribution (which may remain fixed throughout a VT experiment or may not depending on set up) and a sample contribution. The sample contribution will in principle be different for each phase.

john201004

Thank you for your answer and time!

Is that means we have to refine peak shape for each phases individually for one data sets (for one temperature) and then keep them as fixed during rest of the temperature data refinements? or we have to refine them for each temperatures?

johnsoevans

You have to look at the data. If the peak shapes change then you need to refine. It's often useful to refine peak shape values in an initial round of data analysis. Then plot them to see if they change significantly with T. If changes are minor and have no significant impact on wRp then you would fix in a subsequent round.

john201004

Thank you!