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A Fission Chain Reaction

  • Teacher Resource
  • Posted 08.09.12
  • NOVA

In this video excerpt from NOVA's "Hunting the Elements," New York Times technology columnist David Pogue investigates the radioactive elements located at the bottom of the periodic table. Discover how scientists once thought that uranium was the end of the periodic table and find out how the table has grown since atomic scientists created synthetic elements. Visit the Nuclear Museum in New Mexico to learn about the process of nuclear fission and to see a demonstration of what happens inside a nuclear reactor.

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NOVA A Fission Chain Reaction
  • Media Type: Video
  • Running Time: 2m 45s
  • Size: 10.0 MB
  • Level: Grades 6-12

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Source: NOVA: "Hunting the Elements"

This media asset was excerpted from NOVA: "Hunting the Elements."

Teaching Tips

Here are some of the main ideas students should take away from this video:

  • All elements beyond bismuth in the periodic table are radioactive.
  • Bombarding an atom with neutrons can alter its nuclear and atomic structure.
  • Scientists began experimenting with neutron bombardment and synthesizing new elements in the first half of the 20th century.
  • In the process of nuclear fission, an unstable nucleus splits into two smaller atoms in a reaction that releases energy.
  • A nuclear chain reaction occurs when one reaction causes additional reactions. For example, a neutron can cause a uranium atom to undergo fission, which releases energy and several more neutrons, which then split more uranium atoms and release more energy and neutrons. The process continues until all the uranium is spent.

Questions for Discussion

    • What is nuclear fission?
    • In the demonstration seen in the video, what do the mousetraps and ping-pong balls represent?
    • Describe how a fission chain reaction can be self-sustaining.


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.

Resource Produced by:

WGBH Educational Foundation

Collection Developed by:

WGBH Educational Foundation

Collection Credits

Collection Funded by:

U.S. Department of Energy

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