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published by the PhET
written by Drew Isola
This student hand-out was created specifically to accompany the PhET simulation "Alpha Decay". Appropriate for grades 8-12, it provides guided directions to help students understand the random nature of decay of a radioactive substance (Polonium-211). As they watch the alpha particle eject from the nucleus, they can see the "parent" decay into an atom with a mass number of 4 less than the original. Reset the nucleus to see the randomness. Next, the ante is upped, as students switch the view to "Multiple Atoms". They can empty a "Bucket" of 100 Polonium-211 atoms and watch a pattern of decay simulated among multiple particles. Even though the decay rate of an individual atom is not predictable, the simulation clearly depicts the trend that half the atoms will decay by the designated half-life.

The alpha decay simulation, which must be open and displayed to perform this activity, is available from PhET at: Alpha Decay.

This lesson is part of PhET (Physics Education Technology Project), a large collection of free interactive simulations for science education.
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
= Problem/Problem Set
= Student Guide
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© 2010 University of Colorado at Boulder
Additional information is available.
alpha decay, alpha particle, atom, chain reaction, fission, isotope, nuclear properties, radioactive isotope, radioactivity, radioactivity lesson
Record Cloner:
Metadata instance created July 21, 2011 by Caroline Hall
Record Updated:
August 18, 2016 by Lyle Barbato
Last Update
when Cataloged:
June 26, 2010
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AAAS Benchmark Alignments (2008 Version)

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.

Common Core State Standards for Mathematics Alignments

Standards for Mathematical Practice (K-12)

MP.4 Model with mathematics.

High School — Functions (9-12)

Interpreting Functions (9-12)
  • F-IF.6 Calculate and interpret the average rate of change of a function (presented symbolically or as a table) over a specified interval. Estimate the rate of change from a graph.
Linear, Quadratic, and Exponential Models? (9-12)
  • F-LE.1.c Recognize situations in which a quantity grows or decays by a constant percent rate per unit interval relative to another.
  • F-LE.5 Interpret the parameters in a linear or exponential function in terms of a context.
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D. Isola, (PhET, Boulder, 2010), WWW Document, (
D. Isola, PhET Teacher Activities: Alpha Decay Simulation Lab, (PhET, Boulder, 2010), <>.
APA Format
Isola, D. (2010, June 26). PhET Teacher Activities: Alpha Decay Simulation Lab. Retrieved April 20, 2021, from PhET:
Chicago Format
Isola, Drew. PhET Teacher Activities: Alpha Decay Simulation Lab. Boulder: PhET, June 26, 2010. (accessed 20 April 2021).
MLA Format
Isola, Drew. PhET Teacher Activities: Alpha Decay Simulation Lab. Boulder: PhET, 2010. 26 June 2010. 20 Apr. 2021 <>.
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@misc{ Author = "Drew Isola", Title = {PhET Teacher Activities: Alpha Decay Simulation Lab}, Publisher = {PhET}, Volume = {2021}, Number = {20 April 2021}, Month = {June 26, 2010}, Year = {2010} }
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%A Drew Isola
%T PhET Teacher Activities: Alpha Decay Simulation Lab
%D June 26, 2010
%C Boulder
%O application/ms-word

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%0 Electronic Source
%A Isola, Drew
%D June 26, 2010
%T PhET Teacher Activities: Alpha Decay Simulation Lab
%V 2021
%N 20 April 2021
%8 June 26, 2010
%9 application/ms-word

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PhET Teacher Activities: Alpha Decay Simulation Lab:

Accompanies PhET Simulation: Alpha Decay

This is a link to the PhET simulation "Alpha Decay", which this student guide was specifically created to accompany.

relation by Caroline Hall
Covers the Same Topic (Different Course Level) As PhET Teacher Activities: Alpha Decay Investigations

In this more-advanced lesson for algebra-based and AP high school physics, students analyze the math behind radioactive decay and relate their predictions to the simulation.

relation by Caroline Hall

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