I would have guessed that the increase in I0 is primarily due to Pt fluorescence. The yield does increase as the energy rises.
Carlo On Thu, Jun 15, 2023 at 9:45 AM Matt Newville <newvi...@cars.uchicago.edu> wrote: > 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.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: image.png] >> _______________________________________________ >> 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 >> > > > -- > --Matt Newville <newville at cars.uchicago.edu> 630-327-7411 > _______________________________________________ > 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 > -- Carlo U. Segre (he/him) -- Duchossois Leadership Professor of Physics Professor of Materials Science & Engineering Director, Center for Synchrotron Radiation Research and Instrumentation Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 se...@iit.edu http://phys.iit.edu/~segre se...@debian.org
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