common mono crystals
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/
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
participants (2)
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Bruce Ravel -
Matt Newville