armandb
Hi everyone,
I am not sure of the LP correction in my case. The Bruker diffractometer with the Goebel mirror has been use for the measurement. As I good remember the Bruker Goebel mirror in general has a very small Bragg angle, hence radiation is almost not polarized.
In the Topas tutorial is:
"Check LP factor and set the monochromator angle to 90deg 2th, as neutron data are unpolarized."
If I good understand, I should in this case the set the diffraction angle to 90deg 2th and refine it? Is it true? Thanks for yours help.
PS. I didn't used secondary beam monochromator.
Cheers,
Armand
alan-coelho
Hi Armand
>If I good understand, I should in this case the set the diffraction
>angle to 90deg 2th and refine it? Is it true?
I wouldnt refine on LP_Factor unless againts a standard and you would need a large 2Th range. Typically there are strong correlations with beq parameters below 120 degrees 2Th. Note, beq applies a scaling that Gaussion with 2Th; the scaling for LP_Factor is a U shape across 2Th.
>PS. I didn't used secondary beam monochromator.
If using a point detector in the secondary beam (ie. the beam from sample to detector) then a monochromator is usually placed after the receiving slit to allow the passage of CuKalpha radiation only. Without the secondary monochromator Kbeta peaks are visible.
For a Goebel mirror I'm pretty sure that the geometry is such that setting the angle for LP_Factor to the that of the Goebel mirror is the correct procedure; similar to the secondary monochromator.
A way of accurately determing the value for LP_Factor is to scan with the mirror and without. Often not done and probably Ok not to do so unless accurate beqs are sought.
Cheers
Alan