We do some pretty cool stuff around the synchrotron, but I often forget that a lot of it is cutting edge. Nevertheless, there are still times when something catches me off guard, and I have to stop and say, “Whoa…”
I had one of those moments this morning in a seminar (see #3 below), and it got me thinking – what are some other examples? And that was the origin of today’s “Five for Friday”.
1) The earth’s curvature matters.
Ok – first let me give some background. At my beamline, we’re looking at small things (usually protein crystals) with an even smaller X-ray beam. The crystals are about 50 microns in size. That’s about the thickness of a piece of paper. And sometimes, the X-ray beams are as small as 1 micron. In other words, when you build these beamlines, microns matter. Which brings us back to the earth’s curvature…
The earth, of course, is round. But we hardly ever need to treat it that way. Day-to-day, it’s fine to think of it as flat. But what if you’re constructing a 75 meter beamline? Well, the earth has a radius of roughly 6400 kilometers. Now think of a triangle. Two of its legs are 6400 km long, and the third is a very tiny 75 m long:
Out of the full 360 degrees of the earth’s circumference, the 75 m beamline only accounts for a minuscule 0.00067° (roughly 12 microradians, if you prefer). However, over that distance and with that angle, the earth drops off by nearly one millimeter. That is huge, when you’re trying to keep track of a one micron beam. Even before we focus the beam, if we miss by 1 mm, we cut the beam in half.
What does this mean? Well – those of you who have a little construction experience are familiar with the plumb-bob. It uses the earth’s gravity to help you make sure that the walls of your house are straight. But don’t use it on a beamline. It won’t work. Neither will a bubble level. You have to use a laser level.
2) Temperature matters.
We’ll make this quick. I already talked about the one micron beams and the 75 m beamline. What happens if one end of the beamline changes temperature by one degree, relative to the other end of the beamline?
Let’s assume that you construct things out of steel, and that your components sit about one meter off the ground. Steel expands or contracts by 12 microns per meter for a one degree temperature change. If your components move by 12 microns, you’ve just lost your 1 micron beam.
(For those of you who wish to get picky – yes, I’m simplifying things. It doesn’t really matter. You get the same result.)
3) The earth’s magnetic field matters.
This was from this morning’s seminar, where I was hearing about the next generation of light sources. I work at a source which is frequently described as the “third generation” within the community. Out in California, they’ve built the fourth generation – a free electron laser.
The “pink lemonade”* description of the machine is that you create incredibly intense X-rays by sending fast moving electrons through an oscillating magnetic field. Well – if you don’t account for changes in the earth’s magnetic field (or if you don’t shield your device from those changes), your free electron laser doesn’t work.
* I once used a raspberry lemonade and a salt shaker at The Olive Garden to try to explain my job to my mother. Enough said.
4) Earthquakes matter.
On March 28, 2005, there was a major earthquake of the coast of Sumatra. This is what we saw at our beamline – half an hour later and half a world away.
5) Science that matters.
The scientists who visit and work at my beamlines are trying to determine biological structures using crystallography. Once you know structure, you can understand function, gain insight into disease, develop drugs, and so on. The 2009 Nobel prize in chemistry was awarded to some scientists who determined the structure of a very large molecule: the ribosome.
This past week, scientists from The Scripps Research Institute announced the largest structure ever solved: the adenovirus. (This is the things that is responsible for 10% of colds.) And the data were collected at my beamline.