marchrhys
Hi
I am in the process of looking at some ceria data collected on Polaris, ISIS. I have been using the Polaris instrument setup from the topas wiki.
I've been trying to include strain and crystallite size (as this will be useful for some further projects) but have been coming up with some problems. When including the Strain_L or Strain_G keywords I keep on getting an error stating "Negative FWHM encountered". When including the TOF_CS_L or TOF_CS_G keywords I keep on getting an error stating "Equation error for Constant in get_d".
I was wondering if anyone can help with pointing me in the right direction? I've noticed that the setup for the peak shape is different to the example given in ceria size/strain example. I've attached the .inp file in case this helps.
Thanks
Rhys
rowlesmr
Hi Rhys
'TOF_CS_G(CSG, 300, t1)
'TOF_CS_L(CSL, 300, t1)
'Strain_L(!stL, .05)
'Strain_G(stG, .05)
t1 is a value that you need to put in. From the technical reference: "t1 is the calibration constant appearing in the argument of the macro TOF_x_axis_calibration." It appears that t1 == difc_b5, in your case.
The negative FWHM probably comes about because the strain macros you've put in are for constant wavelength.
I don't know how the TOF equations were derived, so I don't know how to convert the strain equations.
johnsoevans
The Polaris example input files use what's currently "the best" descriptor for peak shapes etc and supercede the older CeO2 example.
In addition to Matthew's comments note that it doesn't really make sense to refine size/strain on CeO2 as it's the standard used to define the instrument resolution function.