[Ifeffit] EXAFS Divination Dataset

[Scott Calvin]

Hi all,

The EXAFS Divination Dataset is here: http://www.xafs.org/EXAFS_Divination_Set

You may well be asking, "What is the EXAFS Divination Dataset"?

It's a set of data collected on mixtures of iron compounds, mostly 
oxides of one sort or another. My research assistants have mixed 
random amounts of the compounds together--they know how much they 
used of each, but I don't, you don't, and (if you're a mentor to 
those learning XAFS), your students don't either.

Thus, if you wish, you can try your hand at analyzing the data, 
knowing that when you're done, you can find out what the 
honest-to-goodness right answer is (how refreshing!). Or you can make 
your students try it, either as practice or to assess their current skills.

My own motivation is to find out how accurate XAFS analysis really is 
for this kind of problem. Some researchers have attacked that 
question from the bottom up, evaluating the uncertainties inherent in 
each step of analysis. I'd like to complement that by looking at the 
issue from the top down, using these double-blind conditions to 
determine how much accuracy we can get in practice. So although 
you're free to use the dataset as you will (and there are a bunch of 
standards in there), if you'd like to know the correct phase 
identifications and answers, then I'd like to know the answers you 
got (including things like nearest-neighbor bond length if you got 
them), your level of expertise, an estimate of the time it took, and 
a brief (or not brief, if you prefer) description of the methods you 
used. (Note: If you do that, please don't respond to this email, as 
your findings will be posted to the entire list! Email to me directly 
at SCalvin.mailaps.org or SCalvin.slc.edu. Likewise, please don't use 
this list to discuss your attempts to fit samples in the dataset, as 
that will compromise my experiment.) If I end up publishing this 
study, I won't do so in a way that allows people to identify which 
analysis was done by whom. I will include you in the acknowledgments 
if you so choose.

Some details of the dataset:

The set consists of raw data files from X-11B at the NSLS. There are 
multiple scans for each sample and standard, and the data quality 
varies from moderate to good. Each sample and standard was measured 
at a different random temperature between 303 and 403 K; this reduces 
(but does not eliminate) the utility of methods like linear 
combinations of standards.

There are seven standards: iron metal, Fe2O3, Fe3O4, FeO, 
alpha-FeOOH, gamma-FeOOH, iron(II) oxalate hydrate. Matt--you can put 
these standards in your library if you'd like, although temperature 
information will necessarily be missing until my study is complete (I 
don't even know the temperatures they were measured at yet).

The first part of the dataset consists of mixtures where the 
constituents are known, but the fractions aren't. These problems are 
presumably pretty easy. In fact, if you or a student of yours wanted 
to take a very quick stab at these using linear combination methods, 
that's fine--just let me know that's what you did when you send the 
request for the answers. It will be interesting to see how far off 
linear combination methods are when the temperatures of the samples 
and standards are signficantly different.

The second part consists of 2-3 standards mixed together, but you 
don't know which ones or how much of each.

The third part consists of 1-2 standards that are specified, and one 
mystery compound that is not, except to say that it is a fairly 
simple organic compound (salt, probably) of iron. I don't yet know 
what it is; I had a colleague in the chemistry department pick 
something and order it for me, and then my students prepped it.

The fourth part is 1-2 standards and the mystery compound, none of 
which are specified.

Feel free to attack any parts of this you want, in any order, with 
any degree of seriousness. If you tell me that you eyeballed sample 
B5 and it looks like 60% iron metal and 40% Fe2O3, that's fine. :) I 
want a sense of how well various techniques work, not necessarily 
everyone's best effort. On the other hand, if you consider it a 
matter of personal pride to do as well as you can, then by all means...

--Scott Calvin
Sarah Lawrence College