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published by the PhET
supported by the National Science Foundation
This resource simulates the process of alpha decay, a type of radioactive decay in which an atomic nucleus emits an alpha particle. A number of different radioisotopes will undergo this type of decay; this web page simulates the Polonium-211 atom. Users can watch a single atom decay or work with a "Bucket O' Polonium" to view a pattern of decay.

Editor's Note: Radioactive decay happens when an atomic nucleus of an unstable atom loses energy by emitting ionizing radiation. If you take a sample of a particular radionuclide, the half-life is the time it takes for half the atoms to decay. The Bucket O' Polomium" activity could be invaluable to help students understand the concept of half-life. They can observe 100 virtual polonium-211 atoms in the process of decay. Pause the action every 1/2 second  to get a feel for the math associated with radioactive decay. Simple enough for grades 7-8, but can be adapted for AP Physics as well.

See Related Materials for a link to a student guide specifically developed by the PhET team for use with this simulation.

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
- application/java
- text/html
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Free access
© 2009 University of Colorado at Boulder
Additional information is available.
alpha decay, fission, fission simulation, half-life, isotopes, nuclear fission, nuclear properties, polonium-11, radioactive decay, radioactive isotopes, radioactivity, radioactivity simulation, unstable atom
Record Cloner:
Metadata instance created July 21, 2011 by Caroline Hall
Record Updated:
August 18, 2016 by Lyle Barbato
Last Update
when Cataloged:
June 15, 2011
Other Collections:

AAAS Benchmark Alignments (2008 Version)

3. The Nature of Technology

3C. Issues in Technology
  • 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/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: Alpha Decay, (PhET, Boulder, 2009), <>.
APA Format
PhET Simulation: Alpha Decay. (2011, June 15). Retrieved April 10, 2021, from PhET:
Chicago Format
National Science Foundation. PhET Simulation: Alpha Decay. Boulder: PhET, June 15, 2011. (accessed 10 April 2021).
MLA Format
PhET Simulation: Alpha Decay. Boulder: PhET, 2009. 15 June 2011. National Science Foundation. 10 Apr. 2021 <>.
BibTeX Export Format
@misc{ Title = {PhET Simulation: Alpha Decay}, Publisher = {PhET}, Volume = {2021}, Number = {10 April 2021}, Month = {June 15, 2011}, Year = {2009} }
Refer Export Format

%T PhET Simulation: Alpha Decay
%D June 15, 2011
%C Boulder
%O application/java

EndNote Export Format

%0 Electronic Source
%D June 15, 2011
%T PhET Simulation: Alpha Decay
%V 2021
%N 10 April 2021
%8 June 15, 2011
%9 application/java

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PhET Simulation: Alpha Decay:

Accompanies PhET Teacher Activities: Alpha Decay Simulation Lab

This student guide will help secondary students understand the random nature of radioactive decay, yet also figure out that it obeys patterns of predictability that can be measured in half-life. It was created by a PhET team member for use with "Alpha Decay".

relation by Caroline Hall
Supplements Marie Curie and the Science of Radioactivity

This online historical exhibit from the American Institute of Physics provides insight into the life and accomplishments of Marie Curie, whose pioneering work with radioactive materials led to two Nobel Prizes and the discovery of polonium and radium.

relation by Caroline Hall
Accompanies PhET Teacher Activities: Alpha Decay Investigations

An lesson plan for high school physics by a "Gold-Star" winning PhET team member, developed to accompany the simulation Alpha Decay. Requires a basic understanding of half-life and knowledge of the math underlying nuclear decay.

relation by Caroline Hall
Same topic as NASA: Radioisotope Power Systems

Excellent multimedia resource to show the practical application of alpha decay processes in space exploration. The current fuel source for missions to Mars and beyond is Plutonium 238, which undergoes alpha decay.

relation by Caroline Hall

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