DAVID POGUE (Technology Guru): At the bottom of the periodic table, beginning with number 84, polonium, all of the elements and their isotopes are radioactive, including the element that stands for both the promise and the peril of radioactivity: uranium: 92 protons, 92 electrons and 146 neutrons.

Before the nuclear age, uranium was thought to be the end of the periodic table, but in the last 70 years, scientists have left nature behind and created 26 new elements.

The age of manmade atoms began in the first half of the 20th century, when researchers began bombarding elements with neutrons.

Sometimes the neutron is simply absorbed, creating a new isotope, but sometimes the nucleus can't take the punishment. It becomes unstable and splits into two smaller atoms, in a powerful reaction, called fission, that releases large amounts of energy.

To learn more, I've come to the Nuclear Museum, in Albuquerque, New Mexico,…

MATTHEW DENNIS (Nuclear Engineer, American Nuclear Society, Trinity Section): Yeah, this is a mad science project.

DAVID POGUE: …where atomic scientist Matt Dennis has offered to demonstrate how a nuclear reactor works.

D'oh! You guys make a lot of jokes about "Gone fission?"

MATTHEW DENNIS: I actually have an atomic shirt that says something to that effect, so, yes, yes.

DAVID POGUE: I knew that! I knew that!

Okay, now, to the naked eye, this looks exactly like a nuclear reactor.

MATTHEW DENNIS: The similarities are the mousetraps are uranium atoms and the white ping pong balls are neutrons, which…you use one to start a chain reaction.

DAVID POGUE: In a reactor, one neutron splits a uranium atom, which releases energy and two or three more neutrons, which, in turn, split more atoms, releasing more neutrons and so on, causing a chain reaction.

MATTHEW DENNIS: So you get more and more neutrons, and thus, the chain reaction keeps going.

DAVID POGUE: All right, ladies and jelly spoons, here goes the orange ping pong ball. This evening's role, you'll be portraying the neutron. All right, I just drop it in here? Any old place?

MATTHEW DENNIS: Just drop it in right there. We'll start the chain reaction.

DAVID POGUE: Incoming neutron!

I'm sorry, Matt. The camera wasn't rolling. Can you set that up again?

From a single neutron, an escalating response. Our mousetrap reactor doesn't have many atoms, so the reaction dies quickly, but pack enough fissionable uranium atoms closely enough together and the whole thing can get out of hand pretty fast.

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