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published by the PhET
supported by the National Science Foundation
This resource simulates a nuclear chain reaction, as users fire a neutron gun to induce fission in a radioactive isotope. It initiates with a single Uranium-235 nucleus alongside a graph displaying potential energy. Fire away and watch the nucleus split into two daughter nuclei. Next, start a chain reaction by using multiple U-235 nuclei, or prevent one by introducing non-radioactive isotopes. Switch the tab to "Nuclear Reactor" and adjust control rods to manage the reaction.

Editor's Note: For secondary learners, we recommend using this simulation after completing the PhET Simulation "Isotopes and Atomic Mass". Students will have a clearer understanding of the atomic symbols and factors that affect stability of an atomic nucleus. See Related Materials for a link to a printable student guide appropriate for grades 8-12.

This item is part of a larger collection of simulations developed by the Physics Education Technology project (PhET).

Please note that this resource requires Java Applet Plug-in.
Subjects Levels Resource Types
Education Practices
- Active Learning
= Modeling
Modern Physics
- Nuclear Physics
= Models of the Nucleus
= Nuclear Reactions
= Radioactivity
- High School
- Middle School
- Lower Undergraduate
- Instructional Material
= Activity
= Interactive Simulation
= Model
Intended Users Formats Ratings
- Learners
- Educators
- General Publics
- application/java
- text/html
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Access Rights:
Free access
© 2009 University of Colorado at Boulder
Additional information is available.
U-235, fission, fission simulation, isotopes, nuclear energy, nuclear fission, nuclear power, nuclear properties, nuclear reactor, radioactive isotopes, radioactivity, radioactivity simulation, unstable atom, unstable atom, uranium isotopes
Record Cloner:
Metadata instance created July 19, 2011 by Caroline Hall
Record Updated:
August 18, 2016 by Lyle Barbato
Last Update
when Cataloged:
June 15, 2010
Other Collections:

AAAS Benchmark Alignments (2008 Version)

3. The Nature of Technology

3C. Issues in Technology
  • 6-8: 3C/M5. New technologies increase some risks and decrease others. Some of the same technologies that have improved the length and quality of life for many people have also brought new risks.
  • 9-12: 3C/H3. In deciding on proposals to introduce new technologies or curtail existing ones, some key questions arise concerning possible alternatives, who benefits and who suffers, financial and social costs, possible risks, resources used (human, material, or energy), and waste disposal.
  • 9-12: 3C/H5. Human inventiveness has brought new risks as well as improvements to human existence.

4. The Physical Setting

4D. The Structure of Matter
  • 6-8: 4D/M1a. All matter is made up of atoms, which are far too small to see directly through a microscope.
  • 9-12: 4D/H1. Atoms are made of a positively charged nucleus surrounded by negatively charged electrons. The nucleus is a tiny fraction of the volume of an atom but makes up almost all of its mass. The nucleus is composed of protons and neutrons which have roughly the same mass but differ in that protons are positively charged while neutrons have no electric charge.
  • 9-12: 4D/H2. The number of protons in the nucleus determines what an atom's electron configuration can be and so defines the element. An atom's electron configuration, particularly the outermost electrons, determines how the atom can interact with other atoms. Atoms form bonds to other atoms by transferring or sharing electrons.
  • 9-12: 4D/H3. Although neutrons have little effect on how an atom interacts with other atoms, the number of neutrons does affect the mass and stability of the nucleus. Isotopes of the same element have the same number of protons (and therefore of electrons) but differ in the number of neutrons.
  • 9-12: 4D/H4. The nucleus of radioactive isotopes is unstable and spontaneously decays, emitting particles and/or wavelike radiation. It cannot be predicted exactly when, if ever, an unstable nucleus will decay, but a large group of identical nuclei decay at a predictable rate. This predictability of decay rate allows radioactivity to be used for estimating the age of materials that contain radioactive substances.

11. Common Themes

11B. Models
  • 6-8: 11B/M1. Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe directly. They are also used for processes that are too vast, too complex, or too dangerous to study.
  • 6-8: 11B/M4. Simulations are often useful in modeling events and processes.
11D. Scale
  • 6-8: 11D/M3. Natural phenomena often involve sizes, durations, and speeds that are extremely small or extremely large. These phenomena may be difficult to appreciate because they involve magnitudes far outside human experience.
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Record Link
AIP Format
(PhET, Boulder, 2009), WWW Document, (
PhET Simulation: Nuclear Fission (PhET, Boulder, 2009), <>.
APA Format
PhET Simulation: Nuclear Fission. (2010, June 15). Retrieved June 7, 2023, from PhET:
Chicago Format
National Science Foundation. PhET Simulation: Nuclear Fission. Boulder: PhET, June 15, 2010. (accessed 7 June 2023).
MLA Format
PhET Simulation: Nuclear Fission. Boulder: PhET, 2009. 15 June 2010. National Science Foundation. 7 June 2023 <>.
BibTeX Export Format
@misc{ Title = {PhET Simulation: Nuclear Fission}, Publisher = {PhET}, Volume = {2023}, Number = {7 June 2023}, Month = {June 15, 2010}, Year = {2009} }
Refer Export Format

%T PhET Simulation: Nuclear Fission %D June 15, 2010 %I PhET %C Boulder %U %O application/java

EndNote Export Format

%0 Electronic Source %D June 15, 2010 %T PhET Simulation: Nuclear Fission %I PhET %V 2023 %N 7 June 2023 %8 June 15, 2010 %9 application/java %U

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PhET Simulation: Nuclear Fission:

Is By The Same Author and Covers a Similar Topic As PhET Simulation: Isotopes and Atomic Mass-Java Version

A link to the PhET Simulation "Isotopes and Atomic Mass", which would be beneficial as a companion resource to "Nuclear Fission".

relation by Caroline Hall

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