Thor’s Nuclear Hammer

Use of thorium instead of uranium may be breakthrough in energy production. Recently, India has announced their intent to produce nuclear power using thorium. The thorium reactor under development would be the first of its kind.
   The development of workable, industrial-scale thorium reactors has for decades been a dream for nuclear engineers and environmentalists alike with the hope that it becomes a major alternative to fossil fuels. Thorium has considerable advantages over uranium. Thorium is more abundant and using it does not involve releasing large quantities of carbon dioxide, making it less harmful to the climate than fossil fuels.
   The Bhabha Atomic Research Center (BARC) in Mumbai is finalizing the site for construction of a new large-scale experimental reactor. If all goes according to plan, the reactor could be operational by the end of the decade. The reactor is designed to produce 300 megawatts of electricity—about one fourth of the output of a typical nuclear plant.

   Producing a workable thorium reactor would be a huge breakthrough in energy production. Using thorium—a moderately radioactive element named after Thor, the Norse god of thunder—as a source for nuclear power is not new technology. Early research carried out in the U.S. during the 1950s and 60s was promising, but abandoned in favor of using uranium. Some believe this is at least partly because nuclear power programs in developed countries produce plutonium as a byproduct which can be used to create nuclear weapons. Unlike uranium, thorium reactors do not produce plutonium. Also, the waste from thorium reactors is less dangerous and remains radioactive for hundreds rather than thousands of years. For governments worried about nuclear waste and the possibility of terrorists getting their hands on plutonium, this is a distinct advantage. 
   Another reason for the attention on thorium is that the world’s supply of uranium is being rapidly depleted. Thorium is more than three times as abundant and contains 200 times as much energy density compared to uranium. India has the largest thorium deposits in the world, nearly 40% of the world’s supply, giving them additional incentive to develop the technology for export.
   One potential problem is that thorium reactors need a trigger fuel to initiate operation. Usually plutonium is used as a trigger fuel, but that could pose a problem for import and export. New reactors will eventually be developed to use low-enriched uranium as a trigger fuel which will make it much easier to market the technology abroad.
   Kirk Sorensen, a spokesperson for Teledyne Brown Engineering and former NASA aerospace engineer, sums up thorium’s potential “Conflicts that we see today based around energy could go away. Thorium energy sources don’t emit carbon dioxide or greenhouse gasses, and don’t produce dangerous waste. It could enable us to have cleaner water, cleaner air, and less intrusion on our environment.”

A Better Battery

Schematic of a magnesium (Mg)/antimony (Sb) battery
made of three liquid layers and running at 700 °C.

One of the cutting-edge areas of study in chemistry today is materials chemistry for battery development. Researchers at Massachusetts Institute of Technology have developed a new type of battery that could provide affordable, large-scale energy storage. Current batteries are unable to meet the low-cost, long-lifespan demands for supplementing our electrical power grid. This new type of battery would make it economical for utility companies to integrate wind and solar power with more traditional sources because they could store the electricity from these intermittent sources.
   Led by Materials Chemistry Professor Dr. Donald Sadoway, the MIT team has developed a liquid-metal based battery made from antimony, magnesium, and a mixture of magnesium-, potassium-, and sodium-chloride salt. Heated to more than 700 °C, these materials melt; and because they have variable densities, they settle into three distinct layers. The top (negative) magnesium layer and the bottom (positive) antimony layer form the electrodes of the battery, and the middle molten salt layer is the electrolyte. An electrolyte is a medium through which charged particles flow as the battery is charged or discharged.
   As the battery discharges, the magnesium atoms ionize, losing two electrons to the external circuit, and travel through the electrolyte to the positive electrode where they pick up two electrons and change back to ordinary magnesium, forming an alloy with antimony. Charging the battery runs the process in reverse, driving magnesium out of the alloy and back across the electrolyte to the negative electrode.
   While most batteries do not work well at high temperatures, this system needs high temperatures to run. Dr. Sadoway’s was inspired by his earlier work on the electrochemistry of industrial aluminum smelting. Sadoway says his new battery process is like running a smelter in reverse.
   Why magnesium and antimony? There are a couple good reasons, first of which are their different densities which allows for stratification. Also, both elements display good electrochemical properties. But most import, both are relatively abundant and inexpensive elements compared to other elements that have been tried. That keeps the cost of the batteries low. They have achieved up 69% energy efficiency with this setup.
   The team isn’t the first to research liquid-battery systems, but Dr. Sadoway says he and his team are the first to produce a working storage system in this way. Over the past few years, they have scaled up their experiment from about 4 cm in diameter to a 15 cm prototype with 200 times more storage capacity than their original version. Currently, they are focusing their efforts on improving the insulation and heating of the containers that hold the molten materials to reduce the operating temperature and cut energy costs. According to Sadoway, if they can commercialize the technology, “…it could be a game-changer”.

Cretaceous Park

A comparison of deinonychus (above)
and velociraptor (below). 

Even though the movie Jurassic Park was ground breaking for its time, it got a lot of its facts wrong, especially with velociraptor. Velociraptors were not as large as what was shown in the movie. They were actually only about 1 meter tall and 2 meters long, most of which was tail. Adults weighed about 9-14 kilograms, looking somewhat like a turkey with a long tail. Velociraptors were similar to birds in many ways. They had feathers, hollow bones, and a wishbone. They also built nests. The more that we learn about these animals the more we see them as prehistoric birds.
   Fossil evidence suggests that velociraptors were solitary creatures and did not hunt in packs, as portrayed in the film. There is a famous fossil specimen of velociraptor locked in combat with protoceratops, a small horned dinosaur about the size of a sheep, but no pack of velociraptors engaging in this or any other hunt has ever been found. Velociraptors were also not found in Montana or even the United States, as the movie suggests. They have only been found in Mongolia.
   Another myth that I would like to dispel is that velociraptors were intelligent. Certainly not smarter than dolphins or primates, as suggested in the movie. The velociraptors in Jurassic Park were actually modeled after deinonychus, a larger cousin to velociraptor which also was feathered. Deinonychus did occasionally hunt in packs and was probably a bit more intelligent, but that is a relative term when talking about dinosaurs!
   Velociraptors had bird-like claws. Its middle claw was retractable and could extend out to about 8 cm for slashing and stabbing its prey. This was velociraptor’s main weapon, similar to the spurs on a rooster. Because velociraptor hunted, it was probably warm blooded. Cold blooded animals don’t usually hunt, instead preferring to wait for their prey to come to them.
   But the largest myth perpetrated by the movie is contained in its title. Velociraptor lived during the late Cretaceous, about 70 million years AFTER the end of the Jurassic period. Maybe Cretaceous Park just didn’t have the same ring to it.

What Apollo 11 Left Behind

The Apollo 11 Lunar Laser Ranging Experiment.

Neil Armstrong and Buzz Aldrin left behind more than just their footprints on the Sea of Tranquility when Apollo 11 returned home. They left behind an experiment that is still running today. Circled by footprints in the Moon dust is an array of 100 mirrors pointing towards Earth, known as the Lunar Laser Ranging Experiment (LLRE). The Apollo 11 astronauts left it there during their final Moon walk. Today, over forty years later, the device still works.
   Using these mirrors, we can bounce laser pulses off the Moon’s surface to measure the Moon’s distance very precisely. This allows us to track the moon’s orbit over time and test theories of gravity.
   Directed by telescope, a laser sends a pulse of photons which hit the array and bounce straight back to where they came from. About 2.5 seconds later, a detector on Earth catches one of the returning photons. This allows us to pinpoint the Moon’s distance with incredible precision, to within a few millimeters. 

A graph showing photons returned from the LLRE. Credit: APOLLO Collaboration.

   It is extremely difficult to catch these reflected photons, which scientists have described as like hitting a moving dime with a rifle bullet from three kilometers away. Yet astronomers at the Apache Point Observatory in New Mexico have been doing just that with their laser ranging system and 3.5 m telescope. 
   By carefully tracing the Moon’s orbit, we have learned that it is moving away from Earth at a rate of 3.8 cm per year (due to our oceanic tides). We have also verified that the universal force of gravity is very stable. Newton’s gravitational constant has changed less than one part in 100 billion since the experiment began. Physicists use the laser results to check general relativity, Einstein’s theory of gravity. Einstein’s equations predict the shape of the Moon’s orbit perfectly.
   The LLRE requires no power source and it hasn’t been covered with dust or destroyed by meteoroids, as feared by Apollo 11 planners. So lunar ranging should continue for decades or even centuries, further increasing our understanding of gravity.

Newton’s Most Famous Equation

Diagram of the torsion balance experiment
performed by Henry Cavendish in 1798.

According to Newton’s law of gravity, every object in the universe attracts every other object, with a gravitational force proportional to the product of their masses and inversely proportional to the square of the distance between them. 


F = G x m1 x m2 / r²


   This equation is one of the most famous in physics, almost as famous as Einstein’s equation relating energy and mass. F is the force between two masses, m1 and m2. The distance between the centers of the two masses is r, and G is Newton’s gravitational constant. Newton’s constant can’t be deduced purely from math. In order to calculate G, the gravitational force between two known masses at some known distance must be measured. Ironically, Newton never knew the value for his own constant. 
   Because gravity is so weak, G was too small to measure until the end of the 18th century. In 1798, the British scientist Henry Cavendish was able to work out the value of this constant in an experiment designed to determine the mass of the Earth. He used a torsion balance: two lead balls attached to the ends of a light, wooden rod suspended by a thin wire. He then brought two larger lead balls next to the smaller ones, so that they would exert a gravitational force and twist the rod a small amount. Cavendish’s experiment was remarkably sensitive for its time. The twisting force exerted in his experiment was roughly equivalent to the weight of a grain of sand. Cavendish was careful to prevent wind and temperature changes from interfering by placing the whole apparatus in wooden box enclosed in a shed. He used a telescope to observe the motion of the rod, which was only 4.1 mm. By using a vernier scale he was able to achieve an accuracy on the order of one hundredth of an inch. It would be nearly a century before someone would produce a more accurate result. 
   In metric units, G is the gravitational force between two one-kilogram masses separated by one meter, about 6.7 x 10^-11 newtons. That is a very small force, considering a newton is about one fifth of a pound. For example, consider how massive an object would have to be in order to exert one newton of force on a one hundred kilogram man at a distance of 10 meters. If you do the math, you will find that the mass, m1 = (F x r²) / (G x m2) = 6.7 billion kilograms, about the same as the mass of the Great Pyramid of Giza. So even if you had an 10-meter-radius sphere made of solid lead, it would not exert a full newton of gravitational force even if you lying on top of it (assuming you don’t weigh more than 100 kg).
   It should be noted, of course, that although Newton’s law of gravity is sufficiently accurate for most practical purposes, Einstein’s theory of general relativity must be employed when the objects being studied are moving at relativistic speeds or if their masses are large and close together. That is why there is a slight discrepancy in the orbit of Mercury when comparing its observed motion with its predicted motion using Newtonian calculations.

The Next Materials Revolution

A model showing graphene’s chicken wire structure.

What started with a few experiments with Scotch tape and a pencil could some day become the next materials revolution as important as the silicon chip or even plastic. 
   In 2004, Konstantin Novoselov was a post-doctorate researcher studying conductivity in the lab run by Andre Geim at the University of Manchester. Creating graphene started as one of their after-hours projects they were doing for fun. Geim and Novoselov were trying to creating a substance that was only one atom thick. They spent a while trying to make the thinnest possible slice of graphite, to see if it would work. Over the next few weeks they made several attempts. At about the same time the lab had received an electron microscope that they could use to see atomic structures. Geim and Novoselov wanted a good structures to look at, and graphite came up as an obvious choice. 
   They discovered that the best way to prepare a smooth surface on the graphite was to take a piece of Scotch tape and use it to peel away any dust or residue. They were throwing away the tape, but then at some point it was suggested that they should take a look at the residue on the tape and see if it would work as a transistor. On the first attempt they were nearly successful and over many months they improved the conductivity of the graphite by making it thinner and thinner. Eventually they were able to produce the two-dimensional material with its characteristic chicken-wire structure. The uniquely symmetrical arrangement of electrons enhanced conductivity and strength, and they announced graphene’s properties in 2004.
   Almost immediately there was a flood of talk of what this material could be used for, creating everything from super-strong aircraft to paper-thin, foldable touch screens. Graphene could replace glass since it is perfectly transparent. Graphene could also be layered with plastic, revolutionizing nanotechnology. Integrating graphene into existing technology will take years. Geim and Novoselov are trying to show how graphene can be used as a conductor instead of silicon as the main material in electronic circuitry, but it may take decades before the technology becomes commercially viable. Graphene will most certainly be used in the creation of lighter, stronger, more flexible materials that will find uses in prosthetics, aerospace design, and mobile phone technology. The possibilities are endless.

Graphene

Anyone want to reproduce a Nobel Prize-winning experiment? The materials list is quite extensive: a pencil and scotch tape. A pencil contains graphite, which consists of sheets of carbon in a hexagonal lattice. When you write on the sticky side of the tape, layers of graphite slide off the tip of the pencil and stick to the tape. 

The atomic structure of graphite. One sheet of graphite,
when isolated, is known as graphene.

   By folded the tape in half, you will cleave the flakes of graphite when you open it back up. If you repeat this procedure a few times you will create increasingly thin layers where some will be only a single atom thick. You have created graphene.
   Graphene is the thinnest material known to man. Not only that, it is the strongest. It conducts electricity as well as copper and it is also the best thermal conductor. 
   In 2004, Konstantin Novaselov and Andre Geim created graphene using this technique known as micromechanical cleavage. Their success was quite unexpected because it was thought a single layer of graphite would not be chemically stable. In 2010, Novaselov and Geim were awarded the Noble Prize in physics for their discovery. Apparently, creating a two-dimensional crystal is a big deal!
   Graphene conducts electrons faster than any other substance at room temperature, 100 times faster than silicon. This is because of the extraordinarily high quality of the graphene lattice where the atoms line up so regularly that there is not a single atom out of place. With no defects in the hexagonal lattice, the electrons do not scatter. They travel so fast that relativity must be used to fully understand how they move. The carbon atoms in the lattice create very strong yet flexible bonds, making graphene bendable and 200 times stronger than steel by weight.
   Welcome to nanotechnology, where very tiny devices are less than 100 nanometers in size. A nanometer is a billionth of a meter (1 nm = 1/1,000,000,000 m). That is roughly the size of 10 atoms. Scientists are exploring graphene’s unique material properties to create thin, mechanically tough, electrically conducting, transparent films. Such films are badly needed in a variety of electronics applications from touch screens to solar cells. We will finish up our discussion of graphene and other possible applications in next week’s column.