>I converted the data to 2th, using a popular synchrotron
>wavelength (0.7 A) for everybody's convenience. You can see by yourself
>that the 200 peak has about 0.013 degrees FWHM. Clearly, the FWHM depends
>on the wavelength you choose, so I guess I could have gotten to 0.006 using
>a shorter wavelength. As I already said, what matters is the deltad/d
>resolution, in this case 7x10-4.
Of course, it matters also for poor conventional X-ray powder
diffractionists which have generally only one wavelength at their
disposal (1.54A). But due to this fact, they (at least me) have this
reference in mind : FWHM= 0.04� (2th) at 1.54A. So that, when
synchrotron data claim FWHM = 0.02� at 0.77A, we (at least I)
just think that, well, this is the same that we can do at home ;-).
We can also transform our 1.54A data into 0.77A data and divide
the FWHM by almost a factor 2. But this is not the game we want
to play here.
This was the subject of poster P07.01.001 at IUCr XVIII, Glasgow .
The whole poster may be seen at :
http://sdpd.univ-lemans.fr/glasgow/poster/glasgowposter.html
As a conclusion, in "equivalent conventional X-ray at 1.54A", your
MgO pattern presents FWHM ~0.03�, when I was expecting 0.006�.
But it is really fine, for neutron data, and it is better than we can
do (unless enlarging our diffraction radius, like on synchrotron
instruments, but with large intensity lost).
Best,
Armel
