Uranium On a Diet

Author: Mark Roland
Edited by Rachel Hughes and Stephanie Nardei


1 Class Period

Preparation Time:

10 minutes

Materials: Handouts
Periodic Tables
Internet access and Averkey for class display of animation and applets

During this lesson, students will work on a thought exercise about how the Theory of Relativity can explain the energy of nuclear reactions. It can hardly count as a discovery lesson, but not too many people other than Einstein would have thought of this one on their own. The lesson is designed so students can see how nuclear reactions differ from other chemical reactions that they have studied. They will be adding up the atomic masses of both the product and reactant side of an example of uranium decomposition, demonstrating the mass loss involved.

Purpose –The purpose of this lesson is for students to explore the ideas of nuclear power by having them “discover” relativity.

Students will be able to:
1. Define the variables in the equation .
2. Demonstrate how the Theory of Relativity can be used to explain nuclear energy.
3. Define a nuclear chain reaction.

National Science Education Standard:
Content Standard B-Physical Science
• The nuclear forces that hold the nucleus of an atom together at nuclear distances are usually stronger than the electric forces that would make it fly apart. Nuclear reactions convert a fraction of the mass of interacting particles into energy, and they can release much greater amounts of energy than atomic interactions. Fission is the splitting of a large nucleus into smaller pieces. Fusion is the joining of two nuclei at extremely high temperature and pressure, and is the process responsible for the energy of the sun and other stars.

Related and Resource Websites
http://www.atomicarchive.com/Fission/Fission2.shtml (fission energy info)
http://www.npp.hu/mukodes/anim/Uuu13-e.htm (flash animation of fission)
http://lectureonline.cl.msu.edu/~mmp/applist/chain/chain.htm (nuclear chain reaction applet)


1. As students enter the classroom, have this equation posted on the board:

Ask them to consider these questions:
a. What type of reaction is this?
b. Why is it giving off energy?
c. What does the law of Conservation of Mass state?
Can you demonstrate it holding true with this equation?

2. Go over the answers to these questions with the class. Make sure that students understand the last one very well. By adding up the mass on either side of the equation, you can see that the mass of the products equals the mass of the reactants. In fact, you can see that the number of atoms does not change, so you don’t even have to look at the actual masses. This is important because of a common misconception with nuclear energy. Uranium does not “burn” and disappear in order to account for the mass loss of a nuclear reaction. Going over these questions will keep in mind that this is NOT what happens for combustion reactions. There is no mass loss involved.

3. Distribute the handout titled “Relativity.” (It says Uranium on a Diet on the top) Allow students about 10 minutes to complete it. They will need periodic tables.

4. Go over the handout and explain the results further as necessary. Answer any questions that students might have.

5. Have students look at the website labeled fission energy info, or distribute as a handout. This shows the energy released from just one atom of uranium being split. Explain to students that the gamma radiation can give you radiation sickness.

  • What do they know about radiation sickness?
  • Why does gamma radiation affect the body?
  • How do other forms of radiation affect the body?

6. The flash animation can be shown next, although if time is an issue, skip to the next step. This flash animation is a cool representation of the fission of an atom of uranium through the collision of a neutron. If you look closely, you can see the different products, such as three more neutrons, two smaller atoms, and three different types of radiation. Notice the large kinetic energy of the products right after collision.

7. The last website, titled nuclear chain reaction applet, is a demonstration of how fast a chain reaction can occur. This will help students understand how a nuclear reactor works, and how an accident can occur if these reactions are not controlled.


Have students fill out an “exit card” with an explanation of today’s lesson in their own words. This should include all the information from the objectives, including what the variables stand for in , and how this equation can be used to explain nuclear energy. They should also include a description of how a nuclear chain reaction progresses.

If more in-depth coverage of nuclear chemistry is desired, an exercise for balancing nuclear reactions could be assigned.

Embedded Assessment
Students can be assessed during class discussion, how well they complete the activity sheet and through the exit card.
























PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:

NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award


Supported by NIEHS grant # ES06694

1996-2007, The University of Arizona
Last update: November 10, 2009
  Page Content: Rachel Hughes
Web Master: Travis Biazo