[Ifeffit] [Ext] Brain teaser

[Anatoly Frenkel]

Thank you, Robert, Matthew, Jeff, Kirill, Terry and Sirine for great suggestions. 

I initially thought that the explanation for the linearity or the transmission signal is a superposition of two opposite trends: 1) increase of flux with energy due to the mirror effect and 2) similar decrease with energy due to the photon removal by first effect in the I0 detector. But I did not look into the main reason for the curving up of the I0 signal and I agree it is not a result of the reflectivity. I fill follow up on all suggestions, and, if something more definitive transpires, will report back. 

Thanks again for your time and advice!

Anatoly

> On Jun 15, 2023, at 2:10 AM, matthew marcus <mamarcus at lbl.gov> wrote:
> The mirror was set up for a run at the Pd K-edge, according to the problem statement.  Therefore, its nominal angle must be such as to put the critical energy >25keV.  An angle of 3mrad would do it. At that angle, the reflectivity (assuming  no roughness) goes up with energy in the relevant range, but only by a few percent.
> 
> We're not told what the ratio of gains of the current amps is, or whether the ion chambers have the same path length, so we can't tell whether the signals are comparable, as shown on the graph, or orders of magnitude different.
>    mam
> 
> On 6/14/2023 10:17 PM, Jeffrey Terry wrote:
>> Well, I’ll take a shot. Looks like the mirror angle is totally fubared, you are getting Bragg peaks from the coating or substrate that are giving you the peaks in Io. Since you have no idea what angle those are going through Io, they are unlikely to make it into either the sample or It. Since those photons are removed from the beam hitting the sample, they would show up as intensity dips in It. I’d bet that most (all?) of the reflected beam is not going into the sample. I’m kind of surprised It signal is as clean as it is, but then I don’t know the gains on either measurement amplifiers. I couldn’t find a flat mirror angle that would cause the cutoff at 12870? eV but since it is a collimating mirror who knows what range of angles were actually being hit.
>> Jeff Terry
>> Interim Chair, Department of Biology
>> Interim Chair, Department of Social Sciences
>> Professor of Physics
>> Professor of Mechanical, Materials, and Aerospace Engineering
>> Editor, Applied Surface Science
>> Illinois Institute of Technology
>> 3101 S. Dearborn St.
>> Chicago IL 60616
>> 630-252-9708
>>> On Jun 14, 2023, at 7:27 PM, Anatoly Frenkel <anatoly.frenkel at stonybrook.edu <mailto: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.png>
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