Hi Anatoly,

reflectivity of Pt over that energy range does not vary that much:

image.png

I guessed what angle you were set for, assuming Pd K-edge...
So something wrong with I0?

-R.


On Wed, Jun 14, 2023 at 5:28 PM Anatoly Frenkel <anatoly.frenkel@stonybrook.edu> wrote:
Hello, all. It is a low- to medium- level brain teaser.

Pt-coated collimating mirror was in place for Pd K-edge measurement, but Au L3-edge of Pd-Au alloy was measured (for testing purposes). I0 and It detectors were both Ar filled ionization chambers. Because of the energy dependence of reflectivity of the Pt mirror, I0 intensity was strongly nonlinear (blue curve). However, the transmission intensity in the It detector was almost linear (red curve). Why? 

Anatoly

image.png
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