On May 6, 2020, at 3:32 PM, Matt Newville
<newvi...@cars.uchicago.edu <mailto:newvi...@cars.uchicago.edu>>
wrote:
Hi Simon,
This is definitely a timely discussion for me, as I've been
spending part of the quartine working on collating data and
expanding datasets for an XAFS spectral database. I'm hoping to
have something ready for public comment and to start asking for
contributions of data in a few weeks, but I'll be happy to have
more discussion about that sooner too.
I generally believe that the monochromator I use at GSECARS is
both well-calibrated and reasonably accurate. That is, with 2
angular encoders with a resolution of >130,000 lines per degree
and an air-bearing, I believe the angular accuracy and
repeatability are very good. I believe there are equally good
moons in existence. As Matthew Marcus pointed to the Kraft
paper (which used an older source but 4-bounce mono to improve
resolution), we find that Fe foil is definitely better defined as
7110.75 and Cu foil is between 8980.0 and 8980.5 eV. That is,
we've measured multiple foils, found their first derivatives, and
refined the d-spacing and angular offset. We do this about once
per run, and the offsets tend to be very consistent. For sure,
there is some question about whether the Kraft numbers are
perfect. For sure, putting Fe foil at 7110.75 +/- 0.25 eV
appears to be "most right" to us.
I also believe that we should probably re-measure these metal
foils (and other compounds) with a single calibration set for
both Si(111) and Si(311). We will probably have time to do that
this summer in the time between "beamline staff can get back to
the beamline" and "open for outside users".
What I can tell you now is: I have some data on W metal, WO2,
and WO3 measured all at the same time on our bending magnet line,
with Si(111). An Athena project for this is attached (W.prj).
I cannot vouch for the absolute calibration.
I also attach a set of foils (V, Fe, Cu, Mo) measured with the
same calibration (and Si(111) on our ID line), after adjusting
d-space and offset to be close to the Kraft values
(CalibratedFoils2013.prj).
I also attach a set of foils (Fe, Cu, Au L3, Au L2, Au L1, Pb L3,
Pb L2, Pb L1 edges) measured in 2016 (again, using Si(111) on our
ID line), also with the same calibration values
(FeCu_Au_Pb.prj). I'm pretty certain these use the same
d-spacing as the 2013 Foils to at least 5 digits. For
completeness, all of the raw data files are also under
https://github.com/XraySpectroscopy/XASDataLibrary/tree/master/data
In my experience, the Pb L3 edge value has the biggest variation
in the literature, with values ranging from 13035 to 13055 eV
(possibly a typo somewhere along the line). Fortunately, the
Kraft-based calibration splits the difference and puts the value
at 13040 eV.
For W in particular, I will look if I have measured this recently
on our ID line. I can tell you that I use CdWO4 as a phosphor
and use that to focus our X-ray beam. I use this trick all the
time: any tail from the beam penetrating the phosphor is shortest
at the peak of the white-line and for CdWO4 that is always
between 10210 and 10215 eV.
I hope that helps. I am interested in trying to get all these
values as accurately as possible, so any comments or suggestions
would be most welcome.
--Matt
On Tue, May 5, 2020 at 5:14 PM Bare, Simon R
<srb...@slac.stanford.edu <mailto:srb...@slac.stanford.edu>> wrote:
All:____
__ __
We are wondering if others agree that the reported values for
the W L3 and W L2 edges are *incorrect*. We recently noticed
the following:____
__ __
The “Edge” – defined by the inflection point of the
absorption edge step____
__ __
When using the Ir L_3 edge (11215.0 eV) as a calibration, the
W L_3 - and L_2 -edges are *10203.4 eV* and *11542.4 eV*,
respectively. ____
__ __
When using the Pt L_3 edge (11564.0 eV) as a calibration, the
W L_3 - and L_2 -edges are *10203.3 eV* and *11542.4 eV*,
respectively.____
__ __
These observations are thus different than the reported
values of *10207.0 eV* and *11544.0 eV* for the L_3 and L_2
edges, respectively.____
__ __
Thanks in advance for the discussion and feedback.____
__ __
__ __
Simon R Bare____
/Distinguished Scientist____/
/SSRL, MS69____/
/SLAC National Accelerator Lab____/
/2575 Sand Hill Road____/
/Menlo Park CA 94025____/
__ __
simon.b...@slac.stanford.edu
<mailto:simon.b...@slac.stanford.edu>____
Ph: 650-926-2629____
__ __
<image001.png>
____
__ __
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--
--Matt Newville <newville at cars.uchicago.edu
<http://cars.uchicago.edu>> 630-252-0431
<W.prj>
<CalibratedFoils2013.prj>
<FeCu_AuPb.prj>
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