Dear All,
The resolution of a diffractometer is often quoted in terms of "delta d / d"
or as full-width-at-half-height (FWHM, on the two-theta scale). The concept
of FWHM is fairly easy to understand and visualise - but I'm having trouble
grasping the concept of what "delta d / d" means in physical terms. What I
would like to know is:
1. How is "delta d / d" formally defined (an equation would help here!) - I
guess it arsies somehow from differentiating Braggs Law?
2. When a value of "delta d / d" is quoted in the literature, is this
conventionally taken to be the best achievable resolution for a given
diffractometer set-up?
3. Is there an "accepted" way of measuring resolution? I guess the answer
here is to use a suitable "standard" specimen with a known or "zero"
reflection broadening component arising from crystallite stress / strain
etc.
Finally, am I right in thinking that talking about resolution in terms of
"delta d / d" rather than FWHM is advantageous since it allows a relative
comparison of the resolution afforded by different techniques, e.g.
time-of-flight neutron vs. constant wavelength X-ray?
I'd be really grateful to hear from anyone with thoughts on this issue.
All the best,
Neil Hyatt.
