Archive for October, 2008

Neutrons on the case

October 28th, 2008 by Gene

The TV show CSI and its spinoffs have turned forensic scientists into pop heroes. We’ll look at how engineers turned science into a tool forensic scientists use to catch the bad guys – today on Engineering Works!

CSI fans know that forensic scientists can find out a lot from tiny bits of stuff at crime scenes – who that hair belonged to; what kind of paint is on that car bumper; where that bit of dirt came from – the little things that trip up the bad guys.

When Gil Grissom confronts the murderer with the bit of hair that belongs to her, he knows what he’s talking about because of a nifty analytical tool called neutron activation analysis.

Neutron activation analysis uses neutrons from a nuclear reactor to show researchers exactly what stuff is made of. Hair, for instance – the stuff of TV and real-life murder mysteries.

Hair is mostly protein, but it also has tiny amounts of trace elements, as many as 14 of them. The elements in your hair will be different from those in our hair. When neutrons hit these elements, the combination in your hair gives off a pattern of radiation that’ll be different from mine. So Grissom knows it was you and not me that done it.

Neutron activation analysis is used in a lot of other things, from archaeology to semiconductor manufacturing, to identify traces of different substances.

We’ve identified that our time is up for now. See you next time.

Cosmic rays to the rescue

October 21st, 2008 by Gene

It’s cosmic rays to the rescue – seriously. We’ll find out how. Today, on Engineering Works!

Here’s a question for you. How would you find a nuclear bomb in the millions of trucks and cargo containers that come into the United States every year? The answer worries anti-terrorism experts a lot. Nobody knows.

Cosmic rays may help. Engineers and scientists at the Los Alamos National Laboratory are building a new sensor that uses cosmic rays to detect uranium or lead used to shield it. In case you’ve forgotten, cosmic rays are streams of particles that bombard the earth all the time from space.

These particles – physicists call them muons – zip right through most things, including you and me. Steel plates hardly slow them down. Ditto for aluminum. They cruise right along until they hit something really dense. Like lead or uranium. Then they bounce, or scatter.

The useful thing about all this is that the particles scatter differently depending on what they hit. Steel scatters differently from lead. Lead scatters differently from uranium. And you can program a computer to tell the difference. You don’t even need a person to interpret an x-ray image. The new sensor should be safer and more sensitive than x-rays, big enough to handle big trucks and cargo containers and fast enough that it won’t cause traffic jams at ports and border crossings.

Our cosmic rays are pretty scattered right now, so we’ll see you later.

EngineeringWorks! is made possible by Texas A&M Engineering and produced by KAMU FM in College Station. Learn more about engineering. Visit us on the World Wide Web.

Atomic clocks

October 14th, 2008 by Gene

We’re going to do this one on time. Come along with us as we figure out how. Atomic clocks, today on Engineering Works!

Time never stops. We’ve been keeping track of it for a long time, and we’ve done it a lot of different ways – sundials, dripping water, candles with marks on them, springs and gears and pendulums, quartz crystals and electricity.

All of these timekeepers have one thing in common. They keep track of the interval between one tick and the next. And they all have a problem — the same problem. The intervals they measure aren’t always the same. They’re probably not that different, but they vary — a little or a lot. If you need to measure time exactly — to navigate a space probe or use a global positioning system – they’re not good enough.

This is where special clocks called atomic clocks come in. Instead of pendulums and gears or even quartz crystals, atomic clocks use the vibration between the nucleus and electrons of atoms — usually cesium atoms — to set the interval we use to measure time passing. Even this interval varies a little. But not much. The atomic clock at the Naval Observatory near Washington, D.C., is accurate to within about one second in 20 million years.

If you think this is accurate, clocks based on hydrogen atoms do even better over the short term. But over longer periods of time, cesium is better.

Time’s up. We’ve got to go now.

EngineeringWorks! is made possible by Texas A&M Engineering and produced by KAMU FM in College Station. Learn more about engineering. Visit us on the World Wide Web.

Bullet proof

October 7th, 2008 by Gene

We’re going to take a shot at understanding how bulletproof vests save lives. Today on Engineering Works!

Everybody knows about armor. You know, the metal suits knights used to thrash around in. You’d expect that kind of armor to stop bullets. Using armor made of cloth to protect yourself from gunshots sounds a little odd. But it works, if it’s the right cloth.

The cloth bulletproof vests are made from is special. It’s woven from plastic fibers called aramids. The best-known is probably Kevlar, made by DuPont. Aramid fibers are hard to break because of the way the molecules they’re made from fit together. And they hardly stretch at all. This is important, because it means that the cloth in bulletproof vests can absorb almost all the energy from that speeding bullet.

Bullets hurt you by transferring the energy they carry to your tissues when they hit. If a bulletproof vest absorbs most of the energy before it gets to you, you don’t get hurt – at least not as badly.
Bulletproof vests work best against pistol-sized bullets. Some vests get help against rifle bullets from ceramic or metal plates. The faster, heavier bullets from rifles break into smaller lighter pieces that the cloth armor can handle.

Engineers also use aramid fibers like Kevlar to design and build other things that have nothing to do with bullets — boat hulls, tires, spacecraft parts, tennis racquets.
Bullets or just a hard serve, aramid fibers are good to have around.

EngineeringWorks! is made possible by Texas A&M Engineering and produced by KAMU FM in College Station. Learn more about engineering. Visit us on the World Wide Web.