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

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@millenia.cars.aps.anl.gov wrote:

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Today's Topics:

1. common mono crystals (Bruce Ravel) 2. Re: common mono crystals (Matt Newville)

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Message: 1 Date: Wed, 1 Dec 2004 10:24:17 -0500 From: Bruce Ravel Subject: [Ifeffit] common mono crystals To: XAFS Analysis using Ifeffit Message-ID: <200412011024.17160.ravel@phys.washington.edu> Content-Type: text/plain; charset="us-ascii"

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@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/

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Message: 2 Date: Wed, 1 Dec 2004 09:58:12 -0600 (CST) From: Matt Newville Subject: Re: [Ifeffit] common mono crystals To: ravel@phys.washington.edu, XAFS Analysis using Ifeffit Message-ID: 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 **************************************