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The FDA recently chose not to impose new regulations on...

Tue, 15 May 2012 10:19:50 -0400

The FDA recently chose not to impose new regulations on bisphenol-A, which has sometimes been used in food packaging. Let’s look at what bisphenol-A is, how it’s used to make materials, and why it can be harmful if people ingest it. Bisphenol-A is shown above. Like many chemicals, its name can tell you how it looks:

Bis (two)
phenol (the red circle on the left: a benzene ring attached to an OH)
A (acetone, where the 3 carbons in the middle come from)

So bisphenol-A is made by reacting 2 parts phenol with one part acetone. These are all common chemicals that don’t cost a lot, so bisphenol-A isn’t too expensive to make.

What makes it useful is the OH on each side. This makes it like a building block that can attach to something on each side. In other words, it can do something in two places or is bi-functional.

Building blocks that can attach on both sides can be used to make long chains. And polycarbonate (sometimes called Lexan) is a long molecular chain mostly made of bisphenol-A. Many things, like jet canopies, are made of polycarbonate. Unfortunately it’s also been used in food containers. We’ll talk about that next.

alchymista: A diffraction image of a protein crystal, which is...

Wed, 25 Apr 2012 10:03:10 -0400

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.

A synchrotron light source is a giant scientific facility made...

Tue, 24 Apr 2012 11:01:21 -0400

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...

Thu, 19 Apr 2012 12:27:59 -0400

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.

We said that you use a synchrotron light source to generate...

Tue, 17 Apr 2012 09:51:19 -0400

We said that you use a synchrotron light source to generate photons. Photons are light, so that’s why it’s called a light source. Often the photons you want are X-rays, which are photons with a short wavelength: 0.01 nanometers to 10 nanometers. The light we can see with our eyes has wavelengths of hundreds of nanometers.

Electrons traveling at close to the speed of light lose energy and give off the X-ray photons, which are drawn off in tangents while the electrons continue in a circle. You then make those X-rays hit a sample that you are doing some science on.

X-rays are often used by doctors to take photographs through the skin. So that’s one use of them. Can you think of another reason people would want to use extremely bright X-rays to study samples of material using a synchrotron?

What we mean by “synchrotron” is actually a...

Tue, 10 Apr 2012 09:53:48 -0400

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...

Tue, 03 Apr 2012 09:54:03 -0400

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)

We mentioned storing electricity in a battery. A battery stores...

Mon, 20 Jun 2011 11:50:00 -0400

We mentioned storing electricity in a battery. A battery stores energy electrochemically, meaning that electrons are “stored” in a chemical with high energy. Any chemistry that involves electrons as reactants and products is electrochemistry. A fuel cell is similar to a battery: both have two electrodes (anode and cathode) and an electrolyte.

There is more than one way to distinguish a battery and a fuel cell:

Batteries store their chemicals inside the battery, while fuel cells are fed from outside.
Fuel cells often involve catalysis, while batteries may not.
Fuel cells operate continuously. Batteries operate in a batch manner, i.e. charge/discharge.

There’s a dinner party tonight so the Clear Science staff...

Fri, 10 Jun 2011 13:00:06 -0400

There’s a dinner party tonight so the Clear Science staff is testing the kitchen equipment. Have a good weekend, Clear Scientists!

A current (simplified) view of the electrical grid shows that...

Thu, 09 Jun 2011 11:46:05 -0400

A current (simplified) view of the electrical grid shows that the demand for electricity and the amount of electricity generated must essentially match. This is done by ramping power plants up and down as people change how much electricity they want.

Solar power and wind power are not easy to regulate. But we want to be able to make them a large part of the grid, since they’re green. One way to do this is add electrical storage to the grid, which is like being able to put electricity in a box and save it for later. During periods of low demand you fill up the storage and then use it during high demand. A charged battery is an example of “stored” electricity.

Humanity uses about 15 TW of power. (That’s...

Thu, 26 May 2011 10:04:45 -0400

Humanity uses about 15 TW of power. (That’s 15,000,000,000,000 watts. TW means terawatt, which is a trillion watts.) By comparison 120,000 TW of sunlight falls on the Earth. Ideally, this means one hour of sunlight could power us for one year. Practically, the top end of what we could collect would be around 600 TW, which is still a huge number. In other words, solar power could solve a lot of problems.

Solar cells like those you have probably seen work by using sunlight to make electrons move in a circuit, which is electricity. The most common design is made of layers of n- and p-type semiconductors. Light separates an electron and a hole, and the semiconductor layers make them go different directions to recombine. You cleverly make the electron go through a circuit and you get electricity.

The challenges to widespread use of solar cells are cost and intermittency. This is a good problem for scientists and engineers.

We’re going to address the question of why making energy...

Fri, 20 May 2011 11:31:00 -0400

We’re going to address the question of why making energy generation more environmentally sustainable is an important but difficult problem. Take solar power. One very big problem with solar power one may not realize is that it is intermittent and unpredictable.

Of course you know the sun shines in the daytime and goes down at night. If you plot power generated versus time of day, this will produce a smooth parabola (arc or rainbow shape). When clouds go over, however, it causes sudden dips. Your solar array might even shut off.

Don’t worry, atomgoren! The Clear Science staff are all...

Fri, 20 May 2011 11:07:32 -0400

Don’t worry, atomgoren! The Clear Science staff are all fine. Things have just been busy. We’re going to resume on a schedule a little slower. By the way, Clear Science is over a year old now.

Thanks whimsicalday! The Clear Science staff has been very busy...

Thu, 19 May 2011 09:48:53 -0400

Thanks whimsicalday! The Clear Science staff has been very busy with science. We’ll be posting again shortly.

You may wonder, even though the Fukushima reactors were...

Wed, 16 Mar 2011 11:00:00 -0400

You may wonder, even though the Fukushima reactors were immediately shut down during the Sendai earthquake, why are they having a possible meltdown several days later? The figure shown above is from the website AllThingsNuclear. This plot shows the gallons per minute of cooling water boiled by a reactor of the Fukushimi type as a function of time since shutdown.

Even after control rods are inserted and a reactor is shut down, neutrons will still be produced for some time in the fuel rods. Over time the reaction will slow down and stop, but it is not instant on/off. Engineers use fairly complicated mathematics called control systems to regulate things like this that have time lags between a control input (“turn off”) and a system response (it actually turning off).

Even a week after shutdown, the reactor needs to boil off 60 gallons of cooling water per minute to stay at a steady temperature. This is all planned for. The problem in Japan is that the fossil fuel generators meant to keep cooling water flowing in an emergency failed.

Let’s consider a nuclear reaction with uranium-235 as the...

Wed, 16 Mar 2011 10:30:07 -0400

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.

Clear Science sources for technical info on nuclear plants

Tue, 15 Mar 2011 15:50:02 -0400

The Clear Science staff thought our readers might want to check out our favorite sources concerning the nuclear plant accidents in Japan. We made use of these writing today’s post.

The Union of Concerned Scientists Tumblr site: All Things Nuclear
The informative posts on BraveNewClimate
And of course Wikipedia, which we believe is the greatest scientific resource ever created in human history

In light of the emergencies at the Fukushima I and II power...

Tue, 15 Mar 2011 10:00:08 -0400

In light of the emergencies at the Fukushima I and II power plants in Japan, we’re going to talk about nuclear power plants for a while. Nuclear power is not super-complicated: there is nuclear fuel, for example either UOX or MOX pellets (uranium oxide or mixed uranium and plutonium oxides in this case), which are packed into zircaloy ceramic rods. The job of the rods is to get hot. This is just like in a fossil fuel power plant, when it’s the coal or oil’s job to get hot.

The fuel rods are surrounded by water, which gets hot, boils, and carries the heat away. In the picture above, the red line is the heat generation profile in the rods: they generate the most heat at their center. Think of the heat as a thing that is generated there, diffuses through the solid rod to the outside, transfers to the cooling water, and exits with the water as it boils and becomes steam.

If there is an interruption in this heat transfer path, then heat will begin to build up. Think of it as a heat traffic jam. If the heat begins to collect in one spot, the temperature there will rise. The zircaloy and nuclear fuel pellets are ceramics and have extremely high melting points. However, if you get a big enough heat traffic jam, they will eventually melt. That’s called a meltdown.

The reason small changes in a logarithm (like MMS scale) mean...

Mon, 14 Mar 2011 13:30:08 -0400

The reason small changes in a logarithm (like MMS scale) mean big changes in what the logarithm is applied to (like actual earthquake magnitude), is because logarithms count what are called orders of magnitude. A plain-English way to say this is that logarithms tell you how many zeros a number has.

Things in the hundreds have 2 zeros. Things in the millions have 6 zeros. You see how it goes. For this reason, a logarithmic scale can be used to talk about huge ranges, such as the size of the solar system compared to the size of an atom (which is about 23 orders of magnitude in difference).

Logarithms also have properties that we humans often perceive as beauty.

Last week on March 11, 2011 a powerful earthquake occurred with...

Mon, 14 Mar 2011 11:00:08 -0400

Last week on March 11, 2011 a powerful earthquake occurred with an epicenter 80 miles off the coast of Japan near the city of Sendai, which has a population of about one million people. The Clear Science staff has heard the magnitude of the Sendai earthquake reported from 8.8 - 9.0 on the moment magnitude scale (MMS). The MMS is similar to the Richter scale, a name which is still sometimes used colloquially. (And why not? People know what it means!)

The MMS is a logarithmic scale, meaning that each number higher is actually ten times more powerful in magnitude. That’s why a big truck going by your house might be a 3-4 on the scale, but a huge earthquake that results in massive loss of life will be an 8 or 9. The largest earthquake ever recorded on Earth was the 1960 Valdivia earthquake in Chile, which was a 9.5. If you run through the logarithm math, this is 3.2 times larger than the Sendai earthquake that just happened.

The measurement scale for sound pressure, decibels, is also a logarithmic scale, in which small changes in number signal huge changes in loudness. (Decibels or dB are actually a logarithm multiplied times 20, so every 20 is 10x higher.)