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 <mamar...@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.fren...@stonybrook.edu <mailto:anatoly.fren...@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> >>> _______________________________________________ >>> Ifeffit mailing list >>> Ifeffit@millenia.cars.aps.anl.gov <mailto:Ifeffit@millenia.cars.aps.anl.gov> >>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >>> Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit >> _______________________________________________ >> Ifeffit mailing list >> Ifeffit@millenia.cars.aps.anl.gov >> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >> Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit
