Ultimate Source Of Nuclear Energy

We have been asked during our energy program how nuclear energy fits into the mix when all of our other forms of energy derive ultimately from the sun.

The tie-in is actually pretty interesting. Most of the energy we use comes directly or indirectly from the sun, which is “burning” hydrogen created during the Big bang. Stars fuse hydrogen atoms into heavier elements only up to iron. The planets, and all the elements heavier than iron (further down the periodic table) are composed of stuff created in supernovae, dying exploding stars, that preceded the sun. Only a supernova is energetic enough to create the exotic and unstable elements up to uranium. So nuclear reactors, which run primarily on uranium, ultimately derive their energy also from stars, although not our sun.

Thorium Nuclear Power questions

We were pleased to get this question because we had just read an article about it. One of the challenges with thorium for reactor fuel is that it has been historically very expensive, monetarily and environmentally, to process. There is a project at LANL that has taken on thorium chemistry. It is called Th-ING, Thorium Is Now Green. This team has developed a much cleaner and much cheaper way to process thorium that avoids exotic chemistry, high temperatures, etc. It sounds very promising. There is a technical article about Th-ING at: http://www.lanl.gov/science/NSS/issue2_2011/story6full.shtml .

By the way, another development happening here is a program experimenting with sandwiches of materials with atom-thick layers of, for example, copper and niobium, that results in a sheet with not only extraordinary strength, but an ability to repair itself, or heal, from radiation damage. These materials may one day serve to shield or replace materials used in nuclear reactors today that become brittle with continued exposure to radiation.

Van de Graaff generator questions

Where did you get the big globe? What is it called?

          The machine is a Van de Graaff generator, named for its inventor, Robert Van de Graaff. We bought ours (we have four of them) from a scientific supply company. They are very cool machines. Do you agree?

Why did the big rubber band break? Did electricity cause the break?

          There are two things that make the belts break. One is friction. The belts run for a long time quite fast over the rollers and this makes them wear out, and has nothing to do with the electricity.

          The other thing is a direct result of the electricity. There are tiny sparks inside the machine all the time. These sparks form a chemical from the oxygen in the air called ozone. Ozone is a strong chemical, and it attacks rubber, breaking it down and weakening it. This happens to all our rubber belts sooner or later and we have to replace them. The used, broken belts are usually pretty crumbly when we take them out of the Van de Graaff generator.

Why did you turn the machine on and off with the stick?

          This is an EXCELLENT question! The stick we used is made of plastic, which doesn't conduct electricity. The switch is on the base of the machine, which is separated from the ball by a plastic column. The plastic column is also an insulator and doesn't conduct electricity. When the generator is running, electrons are pulled from the base and added to the ball. This gives the base and the ball opposite charges, and it can be a lot of electricity.

          Working with and around the generator builds up a charge on the operator, and touching the base often gives us shocks. Using the insulated stick helps prevent some of those shocks because it doesn't conduct electricity. We aren't really touching the switch. It is a matter of avoiding getting another shock. We get enough doing this demonstration as it is.

Wilberforce Pendulum questions

Why did the Wilberforce pendulum swing?

I beg your pardon, but my pendulum doesn't swing! (See the real answer below.)

5.) Why does the pendulum stop, turn, and then bounce up and down?

If you have a slinky handy, try this: hold the two ends of the slinky, one in each hand. Leave five or six coils between your fingers and pull the slinky slightly open. Can you feel it twisting? The coils of a slinky, as they bounce in and out do two things. One is they bounce, the other is they twist. When they are bouncing, they are producing a strong twisting force, and when they twist they produce a bouncing force. The result is that they go back and forth between just bouncing and just twisting.

I am really glad you didn't ask me how the slinky remembers what it was doing last when it is exactly in between bouncing and twisting. I don't know the answer to that. Maybe it has to do with the way the slinky spirals and the direction the weight is turning. I'll have to watch more carefully next time!

6.) What is the pendulum used for?

The Wilberforce Pendulum is useful for teaching students about physics and not much else. On the other hand, a scientist here at the lab told me that NASA once launched a satellite that had springy antennas (so they could fold up for launch) and when it got into orbit it acted in a very confusing way, and wouldn't stay aimed straight. They figured out that the antennas were bouncing around like the Wilberforce pendulum and upsetting the satellite.