[Ifeffit] Re: Ifeffit Digest, Vol 22, Issue 1

Wed Dec 1 14:41:21 CST 2004

Hi, Bruce - Ge crystals certainly are a must. Shouldn't forget that people
use Si monochromator crystals at different temps also. Instead of making
a list of d spacings for each reflection, I would just keep values of the
lattice constants at a few reference temps and interpolate the lattice
constant a for the temp of interest, then any of the d spacings can be
calculated as d[hkl]=a/Sqrt[h^2+k^2+l^2] (if memory serves me correctly)
Same for Ge and Diamond since they are the same structure. That way it's
just a handful of numbers, no big deal.

Matt's point as to whether it really should be athena's job to read in all
file formats is a good one. Mostly you want to make it easy for a
new format to be added by the end user. A scripting language would
suffice although perl might be difficult for most people to deal with.
Perhaps the equation parser used in ifeffit could be deployed as end-user
configurable preprocessor for massaging beamline data into the right
form. If those were saveable as templates for different types of data it
would be convenient.

thanks -grant

On Wed, 1 Dec 2004 ifeffit-request at millenia.cars.aps.anl.gov wrote:

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> Today's Topics:
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>    1. common mono crystals (Bruce Ravel)
>    2. Re: common mono crystals (Matt Newville)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 1 Dec 2004 10:24:17 -0500
> From: Bruce Ravel <ravel at phys.washington.edu>
> Subject: [Ifeffit] common mono crystals
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Message-ID: <200412011024.17160.ravel at phys.washington.edu>
> Content-Type: text/plain;  charset="us-ascii"
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>
> Hi folks,
>
> One of my chores for today is to implement a utility in Athena for
> converting encoder readings in a raw data file into energy.  This will
> make some of the data in the Lytle database a bit easier to use.  One
> of the things that the user must specify is the d-spacing of the mono
> crystal.  I want to provide a menu of common crystals.
>
> The orange book is kind enough to provide an exhaustive list -- but
> it's kind of overkill.  Somehow I doubt if many people are using a
> sucrose 001 monochromator even though that d-spacing is given in the
> orange book ;-)  (Really!  It's on page 4-12!)
>
> I want to do an informal survey of what crystals the ifeffit crowd
> regularly uses.  I am certainly going to include Si111, Si311, and
> Si200 in the list, so I don't need to hear from people who use those
> crystals.  What others should go in the list?  Beryl?  Germanium?
> Graphite?  Let me know....
>
> Thanks,
> B
>
> --
>  Bruce Ravel  ----------------------------------- ravel at phys.washington.edu
>  Code 6134, Building 3, Room 405
>  Naval Research Laboratory                          phone: (1) 202 767 2268
>  Washington DC 20375, USA                             fax: (1) 202 767 4642
>
>  NRL Synchrotron Radiation Consortium (NRL-SRC)
>  Beamlines X11a, X11b, X23b
>  National Synchrotron Light Source
>  Brookhaven National Laboratory, Upton, NY 11973
>
>  My homepage:    http://feff.phys.washington.edu/~ravel
>  EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/
>
>
>
> ------------------------------
>
> Message: 2
> Date: Wed, 1 Dec 2004 09:58:12 -0600 (CST)
> From: Matt Newville <newville at cars.uchicago.edu>
> Subject: Re: [Ifeffit] common mono crystals
> To: ravel at phys.washington.edu,	XAFS Analysis using Ifeffit
> 	<ifeffit at millenia.cars.aps.anl.gov>
> Message-ID:
> 	<Pine.LNX.4.44.0412010940170.26700-100000 at millenia.cars.aps.anl.gov>
> Content-Type: TEXT/PLAIN; charset=US-ASCII
>
> Bruce,
>
> Diamond 111 is fairly common (I'd guess more common than anything
> but Si), and you probably meant Si(220) instead of (200).  InSb is
> probably the next most common for the 1 to 2 keV range.  I think
> the others are not so common for XAFS as the energy bandpass is
> too wide.  Also, Si at room temperature is slightly different than
> at LN2 temperature....
>
> But also needed for that calculation is the number of motor steps
> or encoder steps per angular unit.  OK, angular unit is probably
> most commonly in degrees, but I wouldn't assume that it's never in
> radians. For steps per angular unit, it's usually a many thousand
> steps per degree but it can be pretty much any number.
>
> So, it's complicated to convert 'steps' to eV.  Personally, I'm
> comfortable insisting that the beamline/facility provide energy in
> eV, keV, Angstroms. or at least angle in degrees with the
> monochromator lattice constant clearly given.
>
> That is, I don't think this should be athena's job.  I think it
> would be better to have more support for beamline-specific
> formats.  Then, if some particular beamline saves the "energy"
> in nanoJoules or milliradians that could be marked and
> auto-converted, but I don't think athena should worry about what
> kind of monochromator was used or steps-per-degree.
>
> The data in the Lytle archive is possibly a special case, because
> it's commonly available.  It's usually well marked for conversion
> to energy, but the data is poorly documented and spotty in quality
> and it's often hard to tell what exactly the columns are (e-yield
> v. fluorescence, for example).  That can make it hard to asses the
> quality of the data (is self-absorption a problem, etc).  I do use
> it sometimes, but the data is not all that reliable.
>
> Having a more complete and well-maintained database of data,
> including some of the data from the Lytle database would be nice.
> Any volunteers to work on that?
>
> --Matt
>
>
>
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> End of Ifeffit Digest, Vol 22, Issue 1
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