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

[Matt Newville]

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> 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>
>>> To: XAFS Analysis using Ifeffit<ifeffit at millenia.cars.aps.anl.gov>
>>> Subject: [Ifeffit] Problem with Hephaestus at Ca L-edges
>>> Message-ID:<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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