- X-ray tubes. Work by accelerating electrons from a source (air or a metal) along a tube and into a dense metal. When the electrons strike the metal, they lose kinetic energy as heat or as high frequency photons (x-rays). With this method, there is a definite maximum frequency (the fastest electrons) but there is a spectrum below it because of the random nature of the final collision.
- Cyclotrons. Work by accelerating electrons in a spiral with an alternating electric field pointing along the plane of the spiral and a magnetic field pointing perpendicular to the spiral (this is what makes the electrons spiral...:) ). Apparently x-rays are often produced in the same way as in x-ray tubes, by firing electrons at a piece of metal, but also from accelerating a charge in a magnetic field. The radiation frequency is dependent on the frequency of oscillation, and you also get higher harmonics of this radiation, but there is some spread due to non-uniformity of the magnetic field.
- Synchrotrons. What could be better than a cyclotron than a relativistic cyclotron! Basically, when you solve all the equations and include relativistic considerations, you get two regimes of x-ray production: monochrome and broadband. Synchrotrons produce the radiation via emissions from the electrons. So synchrotrons are the best source, but one of the most expensive!
Saturday, March 24, 2012
X-Ray Sources
X-ray sources are obviously an important part of x-ray crystallography. In the modern age there are now several sources of x-rays that are used for crystallography. It seems that the most important features of the source are to produce definite x-ray frequencies, monochromatic x-rays and a spectrum of different wavelength x-rays.
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Nice post (as always Josh ^_^) about x-ray sources.
ReplyDeleteI just finished reading this article:
http://en.wikipedia.org/wiki/Goiania_accident
which really highlights the need for tight regulation of radioactive sources, as well as other potentially harmful equipment.
On Dave's link, just reading down to the Events/The source is sold and dismanted:
ReplyDeleteOn September 18, Roberto dos Santos Alves sold the items to a nearby scrapyard. A scrapyard employee came to the house, loaded the contents into a wheelbarrow, and transported them to yard, and unloaded them. That night the owner, Devair Alves Ferreira, who lived next door to the yard, went in the yard's garage and noticed the blue glow from the punctured capsule. Thinking the capsule's contents were either valuable or even supernatural, he immediately brought it into his house. Over the next three days, he invited friends and family to view the strange glowing substance, and offered a reward to anyone who could free it from the capsule-- he mentioned that he intended to make a ring out of it for his wife, Gabriela Maria Ferreira. On September 21 at this scrapyard, a friend of Devair Alves Ferreira's (given as EF1 in the IAEA report) succeeded in freeing several rice-sized grains of the glowing material from the capsule using a screwdriver. He shared some of these with his brother, claimed some for himself, and the rest remained in the hands of Devair Alves Ferreira who readily began to share it with various friends and family. That same day, his wife, 37-year-old Gabriela Maria Ferreira, began to fall ill. On 25 September 1987, Devair Alves Ferreira would sell the scrap metal to another scrapyard.
Trajedy with what happened to the family, again with Dave's pt of regulating radioactive sources.
Also, not that I don't believe every cartoon, but why would the material be glowing blue?
All this sort of reminds me of using x-rays to fit shoes. Perhaps okay for the customer, but the sales assistant...
Having good detector is also important in x-ray crystallography and other areas of research. The simplest choice would be to use a photographic film. A better option would be to use a charge-coupled device (CCD). The Nobel Prize in physics in 2009 was given to Willard S. Boyle and George E. Smith for this invention.
ReplyDeleteI imagine it would be pretty difficult to overstate the importance of the CCD. Digitisation for the win! This got me thinking: how many analogue devices are currently state of the art? Are there applications that will always require analogue measurement or will always be most accurately measured by analogue methods?
ReplyDeleteThis reminds me of a method of integration Timo told me about known as "Chemist's integration". It involves integrating a data set by taking the print out, cutting out the area and weighing it. This is best done somewhere with a very accurate balance (e.g. a chem lab). This kind of ingenuity is pretty cool, although not restricted to analogue examples.
Great method of integration...
ReplyDeleteOn analogue computing, I recall from 3rd year fields that analogue computers had some interesting and quite exclusive features that made them useful for some applications even today (besides the fact that they are usually cheaper than photonic waveguides... :)). Perhaps another trip to Timo-land is required? I think that you'd also need pretty accurate scissors for Chemist's Integration.... Perhaps if you used heavy-metal ink, you could measure the printout directly using x-ray diffraction and then not have to deal with cutting anything out? But then you would have to deal with the damage to the paper... :(. It's a hard life being a print-out!
ReplyDeleteTimo-land...
DeleteThe blue glow is from Cherenkov Radiation, I would guess.(spelling of Russian names is ambiguous, especially when I can't quite remember it. Seriously though, Russian name spelling isn't very standardised in Roman characters like ours). It is the radiation emitted when a charged particle (e.g. electron!) passes through a medium for which the phase velocity is less than the speed of light. Molecules in the medium get momentarily excited/polarised and then release blue light (perhaps because they are sad?) as they relax. Perhaps the metal had condensation on it or a water barrier to try to shield us from its ultimate power? Perhaps it had a phosphorous coating to alert people to its radioactivity? Like the process used in the glowy radium paint used on watch hands. I must say, though, I'm a bit disturbed at the alleged desire for glowy blue stuff... but magical rings are otherwise hard to come by. Radioactive gold sourced from the old Radon laboratories next to Parnell doesn't glow after all.
ReplyDeleteThe radiation story is also similar to one I've heard. I think the problem is particularly prevalent in South America (gold has similar problems, but the injury to the family is then more from guns rather than alpha radiation from radioactive dust), where the authorities can spend months or sometimes years tracking down walk-about radioactive stuff (including clothes, which need to be disposed of at the facility). The story I read in National Geographic (I think) was about one guy who took home a piece of his day's work. His wife developed cancer (which he didn't think was related to the hunk of radioactive stuff sitting on his mantlepiece!) and the chunk of metal was only found when a workmate accidentally brought his radiation sensor over to the guy's house! I think that the protocols here are pretty good, don't eat anything radioactive (bad juju, just like being shot with uranium-tipped bullets!), or inhale it, dispose of clothing etc. at the facility and always wear a radiation sensor (even at home). Oh, and don't keep radium in your desk's top drawer (poor Marie Curie).
An interesting quantum idea: if one could influence the energy levels of a radioactive nucleus, potentially you could stabilise the element with an external field. I've been wondering if there was a remotely plausible way to do this considering the multitude of examples in the comic-book and action-scifi-movie literature.
Another interesting radiation fact is the large amounts of radiation we get from simply living above Australia (in Mt Isa, they eat thorium for lunch, don't the Andy? :) At least lead, they've too many plumbers (pun) :) ), and also how much elevation changes your exposure. It is not so interesting how x-ray diagnosis increases your exposure, however.
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ReplyDeleteThanks Josh. Let's be nice to Andy.
ReplyDeleteOn the methods of integration, there's
Tai's method ...published in 1994.
(It's an interesting read)