F in apatite on LDE1

[Dominik]

I searched for this, as this must have been discussed multiple times, but could not find something: I am trying to find the interference of F with P Ka or one of its S-lines on LDE1, but it looks like only the F peak is present (I tried with/without int/diff). What am I missing? Is it just too small on LDE1? (I mean, it would be nice, if for whatever reason P would not be there.)

[Mike Jercinovic]

Hi Dominik,
This is exactly right.  Those are third order P lines, and you don't see them on the multilayer 'crystals'.  True to their nature, these Ovonyx monochromators suppress high order lines.  If you look at the F Ka region on a large TAP, you will see these P lines plain as day, but I do not see them at all on PC1 (your LDE1 equivalent I believe).

[Dominik]

That's perfect, thanks Mike. And yes, I also tried TAPL and saw the third order lines perfectly (and could not fully suppress these there using diff mode).

[sem-geologist]

I had to re look my high intensity WDS wavescans, and yep 3rd order P is not visible on any of REE phosphate. Can anyone point the physics behind this, how this higher order line suppression is possible?

[Probeman]

I searched for this, as this must have been discussed multiple times, but could not find something: I am trying to find the interference of F with P Ka or one of its S-lines on LDE1, but it looks like only the F peak is present (I tried with/without int/diff). What am I missing? Is it just too small on LDE1? (I mean, it would be nice, if for whatever reason P would not be there.)

Here is something else to consider regarding these higher order interferences when using LDE diffractors:

https://probesoftware.com/smf/index.php?topic=375.msg1974#msg1974

Depending on the exact value of the refractive index utilized, the position of the third order P Ka reflection will vary from one side of the F Ka line or the other.  This is apparently because the manufacturers did not utilize the refractive index properly when calculating the 2d "spacing" of their LDE diffractors as described by Julien Allaz:

https://probesoftware.com/smf/index.php?topic=375.msg1975#msg1975

[Probeman]

I had to re look my high intensity WDS wavescans, and yep 3rd order P is not visible on any of REE phosphate. Can anyone point the physics behind this, how this higher order line suppression is possible?

The higher order reflections are higher energy x-rays and require smoother layer interfaces which for LDEs are difficult to manufacture.

[Dominik]

Nice & very convenient! Thanks for the clarification.