[Ifeffit] Brain teaser

[Matt Newville]

I'm not sure why the intensity would go up unless the ion chamber was
poorly set up.   But, as others have pointed out, the mirror reflectivity
for a Pt mirror should not change significantly over this energy range -
the energy range is not that close to the Pt L3 or L2 edges.    Depending
on where it was located, fluorescence from the Pt mirror might pollute the
signal in the I0 ion chamber, but that would also likely be a fairly
constant background.

But, why would you fill the I0 ion chamber with Argon?  A 10-cm ion chamber
filled with Ar would absorb about 50% of the beam at 12 keV.   Even at 24
keV, that would absorb 8% of the beam - not necessarily a problem but also
probably generating at least a micro-Amp, so way more signal than you would
need.

For mirror reflectivity curves, allow me to humbly remind everyone of

https://xraydb.xrayabsorption.org/reflectivity/Pt/21.45/2.5/10/s/1000/51000/50/platinum/linear

which is both interactive and works with X-ray energies above 30 keV.


On Wed, Jun 14, 2023 at 7:28 PM Anatoly Frenkel <
anatoly.frenkel at 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: image.png]
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-- 
--Matt Newville <newville at cars.uchicago.edu> 630-327-7411
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