[Ifeffit] Problem with Hephaestus at Ca L-edges (Matthew Marcus)

Matthew Marcus mamarcus at lbl.gov
Thu Sep 24 11:47:17 CDT 2015


What I was after was L3/L2, so I don't care about L1.  The attached plot doesn't show the jumps for both L2 and L3.

When you say that the edge jumps are 5.8,1.4 and 1.1, are you referring to mu(+)/mu(-)?  I was looking for (mu(+)-mu(-))_L3/(mu(+)-mu(-))_L2.

What about that seeming inconsistency between the values H. gives for the thickness needed for unit edge step and the cm^2/gm values reported? That seems to be a bug indpependent of
the tables used.
	mam

On 9/24/2015 9:15 AM, Matt Newville wrote:
> Hi Matthew, Jana,
>
> I think the Chantler values, especially in Hephaestus, are not particularly robust at the Ca L edges.
>
> To be clear, Elam gives L3, L2, and L1 energies as 346.2, 349.7,  and 438.4 eV, and the edge jumps as 5.8, 1.4, and 1.1.  I believe those edge jumps may have originated from Shaltout -- maybe Bruce can clarify that.
>
> The Chantler data from the NIST FFast web page (and in Hephaestus) are quite sparse.  This is a definitely a problem for using the anomalous scattering factors near edges. I've talked with Chris Chantler about this a few times over the years.  Not too long ago, he sent me data on a finer grid -- but he also told be recently that he hoped to have even better data he could send to me soon (all time-scales here on months-to-years here).
>
> I've included the finer data I have from Chantler into Larch. But the results for the Ca L edges are still not encouraging.   The attached figure and ASCII data file give the results for mu(E) (gr/cm^2) from Elam and from Chantler.  It's hard to see an L2 edge in either, and Chantler does not show an L1 edge.
>
> FWIW, the script to generate this is:
>
> ####################
> energies = linspace(300, 500, 101)
> muca_chantler = mu_chantler('Ca', energies)
> muca_elam = mu_elam('Ca', energies)
>
> newplot(energies, muca_chantler, ymax = 50000, label='Chantler')
> plot(energies, muca_elam, label='Elam')
>
> info_head = 'Ca edge Energy(eV)  Fyield   EdgeJump'
>
> info_l3 = ' L3       %.1f    %.5f    %.2f' % xray_edge('Ca', 'L3')
> info_l2 = ' L2       %.1f    %.5f    %.2f' % xray_edge('Ca', 'L2')
> info_l1 = ' L1       %.1f    %.5f    %.2f' % xray_edge('Ca', 'L1')
>
> write_ascii('CaMu.dat', energies, muca_elam, muca_chantler,
>               info_head, info_l3, info_l2, info_l1,
>               label='Energy  MuCa_Elam  MuCa_Chantler')
> ########################
>
>
> I'm not sure that gives a lot of insight except that not trusting Chantler's values for these values might be reasonable.
>
>
>
> On Thu, Sep 24, 2015 at 10:16 AM, Matthew Marcus <mamarcus at lbl.gov <mailto:mamarcus at lbl.gov>> wrote:
>
>     I'm not after absolute data, just the edge-jump ratio.  This would have to be extracted by peak+arctan fitting because any spectra will have peaks and a very limited
>     range between edges.  If the Chantler numbers are incorrect, then perhaps the edge-jump ratio is really 2.
>
>     Do you have a reference which can be cited?
>
>     I'll try the CXRO tool next, since CXRO specializes in soft X-rays.
>              mam
>
>
>     On 9/23/2015 11:49 PM, Jana Padeznik Gomilsek wrote:
>
>         It is very hard to measure or to calculate absolute absorption data, especially in the
>         vicinity of the absorption edges and especially in the soft x-ray region. Therefore there
>         are significant differences between the tables and I think nobody knows which
>         are better.
>         Chantler, for example, says the expected uncertainties of the tables in your region are
>         50 % to 100 % (http://physics.nist.gov/PhysRefData/FFast/Text2000/sec06.html#tab2).
>         I would doubt the Chantler's L3+.1 number, all other numbers look ok - this is what you
>         can get.
>
>         jana padeznik gomilsek
>
>             Message: 3
>             Date: Wed, 23 Sep 2015 18:02:08 -0700
>             From: Matthew Marcus<mamarcus at lbl.gov <mailto:mamarcus at lbl.gov>>
>             To: XAFS Analysis using Ifeffit<ifeffit at millenia.cars.aps.anl.gov <mailto:ifeffit at millenia.cars.aps.anl.gov>>
>             Subject: [Ifeffit] Problem with Hephaestus at Ca L-edges
>             Message-ID:<56034B90.70405 at lbl.gov <mailto:56034B90.70405 at lbl.gov>>
>             Content-Type: text/plain; charset=utf-8; format=flowed
>
>             I wanted to work out the edge-jump ratio between the L3 and L2 edges of Ca using Hephaestus.  I ran into two problems:
>
>             1.      The ratio implied by what it says for the unit-edge-step thickness does not agree with that derived by computing the absorption (cm^2/gm) above and below each edge and
>                      dividing the difference (L3+ - L3-)/(L2+ - L2-).
>
>             2.      The results differ wildly depending on which resource I use:
>
>                                   L3-.1       L3+.1     L2-.1       L2+.1    (L1+ - L1-)/(L2+ - L2-)
>             Elam               4759.796    27837.796 27478.018 38434.277   2.106375908
>             Chantler           4322.6       6547.121  32827.61 35436.543   0.852655473
>             Cromer-Leiberman   4288.524    33471.375 32786.294 47072.991   2.042659055
>
>             The Henke table doesn't yield an L2 edge jump at all, while the Shaltout yields the same results as Cromer-Leiberman. Which one should I trust and why?
>
>             This is old-style H. (V0.18), not Demeter.
>                      mam
>
>
>
>
>
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>
>
> --Matt
>
>
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