Clear Science!

alchymista:

A diffraction image of a protein crystal, which is created by using a particle accelerator to irradiate the protein with X-rays. This technique enables scientists to see internal structures of complex protein molecules such as enzymes. (via)

Here’s a fine example of science using X-ray diffraction. This pattern is created by interference at certain angles of X-rays bouncing off the atoms in the protein. And from this, you can figure out the arrangement of the atoms.

The “particle accelerator” here is probably a synchrotron light source, where the scientists travelled to do the experiment.

(via fyeahchemistry)

A synchrotron light source is a giant scientific facility made to generate X-rays. We wondered what X-rays could be useful for. It turns out they have just the right wavelength to figure out the location of atoms in a solid material.

X-rays with their wavelengths lined up strike the sample material at some angle, and they get bounced off elastically by the electrons in the atoms. Then you detect the bounced off X-rays at the same angle.

At some special angles, X-rays bouncing off different atoms will overlap, but their wavelengths might not line up anymore. You Clear Scientists know that overlapping light waves interfere with each other. And from this interference, you can use geometry to figure out the atomic spacing (5 nm in this example).

mdt:

Handmade particle accelerator unveiled at Milan Design Week, Higgs-Boson a no-show http://engt.co/I523GW

It shouldn’t surprise any of you Clear Scientists if it’s possible to make a small, handmade particle accelerator. In fact the first cyclotron, built by Lawrence and Livingston in 1931, was just 4.5 inches in diameter. It applied a voltage of 1800 volts to accelerate particles to 80,000 electron-volts. (This was the trick: How do you keep from needing 80,000 volts?)

This first, small cyclotron was the predecessor to the big synchrotrons we’ve been talking about lately.

Any idea how this handmade particle accelerator would work? We’re not sure yet, just taking a glance.

What we mean by “synchrotron” is actually a synchrotron light source, but you hear people use both words for it. It’s a particle accelerator used to produce electromagnetic radiation (“light”) such as X-rays. This light is very bright, and is useful to do experiments.

The National Synchrotron Light Source (NSLS) is pictured, where electrons are accelerated to 2.8 GeV (giga electron volts, which is a high energy). The electrons lose energy and give off photons, and these photons are pulled off in beamlines, which go off at tangents from the ring.

The larger ring at NSLS has a circumference of 170 meters. The largest synchrotron light source in the USA is 1104 meters: the Advanced Photon Source (APS) at Argonne National Lab, near Chicago. 

The Clear Science staff has been busy with science lately. We just returned from Brookhaven National Lab in Upton, New York. There we were doing X-Ray experiments at the NSLS or National Synchrotron Light Source (marked as 10 above). Around Brookhaven you just call that the light source. So if you get on a shuttle bus, you tell the driver “light source, please.”

Photo from the Brookhaven National Laboratory Flickr page:

1. Relativistic Heavy Ion Collider (RHIC)
2. Alternating Gradient Synchrotron (AGS)
3. AGS Booster
4. Linear Accelerator (LINAC)
5. Tandem to Booster Line 
6. Radiation Therapy Facility
7. Medical Research Reactor (closed)
8. Scanning Transmission Electron Microscope (STEM)
9. Center for Functional Nanomaterials (CFN)
10. National Synchrotron Light Source (NSLS)
11. High Flux Beam Reactor (closed)
12. Tandem Van de Graaff and Cyclotron
13. Graphite Research Reactor (closed)

Let’s consider a nuclear reaction with uranium-235 as the fuel. Inside the fuel rods, a neutron with the appropriate energy collides with a uranium-235 atom and is incorporated into this atom’s nucleus. The uranium atom now has an extra neutron and becomes uranium-236. However, uranium-236 is unstable and immediately decays to two smaller atoms—the fission products. Many different fission products are made, such as cesium-133, iodine-135, etc. Wikipedia has a nice entry explaining the fission product yield for uranium-235.

Breaking atomic bonds also releases energy in the form of heat. The purpose of a nuclear power plant is to capture this heat and turn it into electricity. This is analogous to a fossil fuel power plant, where chemical bonds are broken to release heat.

When the uranium-236 decays, extra neutrons (and some other things) are also released. These are called prompt neutrons because they come directly from the fission reaction. (They’re produced promptly.) These neutrons collide with more uranium-235 and the reaction continues. Fission products can also sit around for a while and then decay to produce neutrons, and these are called delayed neutrons. If neutrons are being produced, the fission reaction will continue, and the rate of reaction will be a function of the number of neutrons being produced.

We talked about frets on a guitar and how when you push the string into the fret board it raises the pitch on the note by changing the length of the standing wave on the string. Another interesting thing you can do is this: after plucking the open string, just lightly touch the string with your finger at the 12th fret. A sound like a bell or flute will result, as you create the second harmonic of the original standing wave.

Here’s what happens: by touching the string lightly while it’s vibrating, you cause it to come to rest at that point you’re touching. This results in another node, as shown above with the second harmonic. Touching the string at the 7th or 5th fret can make the third and fourth harmonics, with higher numbers of nodes.

But if you touch the string someplace that does not result in equal segments between nodes, no harmonic is produced and the string stops. This is simply math. Guitar players can tell you all the spots where harmonics can be produced, even if they don’t care too much about the math and physics behind it. (Some of them care though!)

Since we were talking about guitars and how their pickups work, the Clear Science staff wanted to point out that all kinds of physics can be illustrated with a guitar. Take for example the vibration of the strings, which produces the notes. The strings are held stationary two places: at the nut, shown by the blue line, and at the bridge, shown by the grey line.

When you pluck a string, you set up a standing wave, with stationary nodes at the nut and bridge. When you fret the string (i.e. push it down with your finger), you change the distance between these nodes, and it changes the note.

The 12th fret is exactly halfway along the string, and when fretted there will produce a note one octave higher than the unfretted string. (For example, the top string is generally an E, and the note at the 12th fret is a higher E.) The 7th fret is 2/3 of the way along the string, and the 5th fret is 3/4. These special frets are usually marked with pearling or with some dots.