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Can someone explain X=Ray Diffraction to me in nice, small words I can understand?

Also, how did I forget that I think iced coffee is gross?

Also in case I didn't mention it, I am mostly sure I aced A&P in the end. Today I ordered my book for the psych class and here's the sick part. I can't wait to get it and look at it. I love school.



( 19 comments — Leave a comment )
May. 15th, 2008 09:05 pm (UTC)
yay school! why do you think i have three degrees? i would go back in a heartbeat. mama needs a ph.d.!
May. 15th, 2008 09:08 pm (UTC)
Despite my current plan of getting an associate's ASAP, I confess my long term plan involves a second BS and and MSN. From there, who knows. More letters, please.
May. 15th, 2008 09:11 pm (UTC)
bring on the letters! you'd look lovely in more letters, my dear ...
May. 15th, 2008 09:05 pm (UTC)
because I was reading about various psychoanaleptics, like you do, and reading about Haldol, and then about benzene, and how its structure was discovered, and then I stopped understanding my wikisurfing, and needed help.
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May. 15th, 2008 09:22 pm (UTC)
The profoundly annoying irony about my decision to major in Sociology is that I chose it because I loved the intro class - which I somehow got a freaking C in. Lovely.
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May. 15th, 2008 09:31 pm (UTC)
HA! That's so familiar.
May. 15th, 2008 11:02 pm (UTC)
X rays are just another kind of electro-magnetic waves... like black lights. They do something special when they hit crystals... think like how black light makes some materials fluorescence. Well x-rays will bounce off crystals and reveal specific patterns. Think about how light goes through a pretty crystal and breaks into the spectrum... well xrays will bounce off and can reveal special patterns. These patterns can help scientists figure out what a substance is actually made of. And it's because the x-rays get scattered by the actual atoms of the crystal it goes through. Similarly, cathode ray (another electromagnetic wave) diffractions helped scientists prove that atoms make up stuff... different patterns mean different kinds of atoms.
May. 15th, 2008 11:12 pm (UTC)
Physics was always my worst subject. Thanks for explaining.

Jack is now disputing with me about whether this is physics.
May. 16th, 2008 01:06 am (UTC)
Everything is physics. :)

May. 16th, 2008 03:28 am (UTC)
Yeah! See!
May. 16th, 2008 01:45 pm (UTC)
Dang girl, you good at this.
May. 16th, 2008 12:54 am (UTC)
Yay someone actually caring about my thesis work

[Measurement of electrostriction in piezoelectric crystals using four-circle x-ray diffraction, yo.]

May. 16th, 2008 03:28 am (UTC)
that's hot.
May. 16th, 2008 11:33 am (UTC)
If you ever want to see an XRD machine, we have one here in our department! We use it mostly for inorganic mineral crystals, but it can be used for other molecules as well.

The sample in question, usually of an unknown substance, is exposed to X-rays that are directed at the sample in straight parallel waves. As you know, all molecules have different structures, but that structure is uniform for each molecule of the same substance. Therefore the X-rays will move through and, in essence, "bounce off" (aka "diffract") various parts of the crystal or molecule. You can then use a detector to determine the intensity of the diffracted X-ray pattern. Those rays that were initially parallel will show up as a unique diffraction pattern for each type of crystal or molecule. The diffraction pattern provides info on the order, spacing, and angles of the crystal/molecule structure. There are established databases that have all the info on orders, spacings, and angles for a whole bunch of crystals/molecules. You can then compare your findings with that database and subsequently identify your unknown substance.

I have a couple books with info on this technique if you are really really interested and want to learn more. Just a bit of light recreational reading ...
May. 16th, 2008 01:38 pm (UTC)
Interesting. So... how did they figure out what things were before the established database? Like when Kathleen Lonsdale defined the structure of Benzene in early part of the last century?
May. 16th, 2008 04:27 pm (UTC)
They established the data base by analyzing substances whose composition they already knew. The methods they used to figure that out could be quite complicated depending on the substance. Now that the database is established, one simple XRD test can identify unknown substances. I'm admittedly not as familiar with the methods used for organic molecules in XRD. Most of my experience is with inorganic crystallography. I believe Lonsdale used crystallized benzene and compared it to known crystallographic structures until she found a close match. Benzene has a hexagonal structure which is actually a really common crystal structure in a lot of geologic minerals, like quartz. I think Lonsdale also combined the XRD with other techniques to confirm the hexagonal structure outline.
May. 16th, 2008 06:14 pm (UTC)
Yeah, I reached the X-Ray diffusion topic kind of backwards; I was looking at Haldol and some other neuro drugs and wikipedia was talking about benzene being in there so I looked up benzene and read the story of how they discovered it. It was neat to read about a female scientist so early in the century too!
May. 16th, 2008 01:55 pm (UTC)
yah, I was gonna say it but my workplace is as concise as I am
"XRD - X-ray diffraction. What is it?

XRD is an analytical tool that permits "definitive" identification of crystalline inorganic pigments, using very small samples.
How does it work?

X-rays are diffracted (bent) or reflected in a manner determined by a material's crystalline structure. The angles and intensity of the diffractions and reflections are recorded and interpreted by comparison with references."
May. 16th, 2008 06:14 pm (UTC)
thank you! i am so glad i have so many scientifically-bent people on my friends list.
( 19 comments — Leave a comment )


keep it dark

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