Apparently, GI originally stood for "Galvanized Iron" and was then later extended, based on the misunderstnading that it stood for "Government Issue." See the
the current version of the wikipedia page and references therein.
I'm not a protein crystallographer, but I do work at a synchrotron and do lots of x-ray absorption and diffraction experiments. I've never had a problem with x-ray damage to my samples (mostly inorganic solids).
Susceptibility to radiation damage varies from material to material. From my understanding, protein crystals are particularly bad, presumably because they not respond well (in a chemical sense) to the large numbers of electrons generated after an x-ray absorption event. This basically causes impurities in the crystal (local changes in the structure factor) that degrade the diffraction measurement. Also, in your typical protein diffraction experiment, you irradiate a particular spot on the crystal for a very long time.
I would guess that this is not so much an issue in this case, because (1) no one is really interested in the chemical structure of the parchment itself, and (2) a particular spot on the sample is exposed only for a very short time.
Incidentally, there's a better write-up of this at Stanford:
http://news-service.stanford.edu/news/2005/may25/a rchimedes-052505.html
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Apparently, GI originally stood for "Galvanized Iron" and was then later extended, based on the misunderstnading that it stood for "Government Issue." See the the current version of the wikipedia page and references therein.
I'm not a protein crystallographer, but I do work at a synchrotron and do lots of x-ray absorption and diffraction experiments. I've never had a problem with x-ray damage to my samples (mostly inorganic solids). Susceptibility to radiation damage varies from material to material. From my understanding, protein crystals are particularly bad, presumably because they not respond well (in a chemical sense) to the large numbers of electrons generated after an x-ray absorption event. This basically causes impurities in the crystal (local changes in the structure factor) that degrade the diffraction measurement. Also, in your typical protein diffraction experiment, you irradiate a particular spot on the crystal for a very long time. I would guess that this is not so much an issue in this case, because (1) no one is really interested in the chemical structure of the parchment itself, and (2) a particular spot on the sample is exposed only for a very short time. Incidentally, there's a better write-up of this at Stanford: http://news-service.stanford.edu/news/2005/may25/a rchimedes-052505.html