Science 10
Name: ______________________
Date: _______________________
Period: ______________________
M&M Radioactive Decay Lab
Purpose: The purpose of this activity is to simulate the process of radioactive decay
and to illustrate the concept of half-life.
Prelab:
1. On the periodic table, the number of carbon is ___, and the atomic mass is
______. What do each of these numbers tell us?
2. Give the term for an element that has the same atomic number, but different
atomic mass: ____________
3. What particle in the nucleus is responsible for this difference in mass?
4. What is given off by unstable isotopes?
5. During radioactive decay, the ______ isotope decays into a ________ isotope
that has a different ___________ number.
Materials:


M&M candy pieces in a tube
Graph paper
Procedures:
1. Before you begin, wash your hands and then spread out a sheet of paper towel
on your lab table.
2. Obtain a tube of M&M and count the total number of M&M’s in the tube.
Record this number on your data table. Do not eat any of the M&M’s until
you’ve completed the experiment!
3. For the rest of the experiment, we’re making the following assumptions:
 The M&M candies are not atoms of radioactive element called “M&Mium.”
 When the “M” is facing upward, the atom has not yet decayed.
 When the “M” is facing downward, the atom has decayed.
4. Pour the M&Ms back into the tube and cap the tube. Gently shake for 10
seconds. Then gently pour the M&Ms onto the paper towel on your lab table. Be
careful not to spill the M&Ms or allow them to touch the lab table. Keep your
candy on the paper towel at all times.
5. Remove the M&Ms that have “decayed” (the M&Ms with the “M” faced down)
and set them aside. Count how many undecayed (radioactive) atoms remain and
record this number in your data table.
6. Place the remaining undecayed M&Ms back into the tube. Repeat step 4 and 5
until you’ve completed your data table and until all atoms have decayed.
1
Science 10
Name: ______________________
Date: _______________________
Period: ______________________
7. Following your teacher’s instructions, pool your data with the rest of the class
and record the totals in your data table.
8. Graph the number of undecayed atoms vs. time.
Observations:
Data Table for the Radioactive Decay of M&Mium
Trial
Number of Atoms
Decayed
Number of
undecayed atoms
remaining
Class Total
Class Average
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Questions & Conclusions (please answer on separate paper):
1. Construct a graph for your group’s data. Plot the number of half-lives on the
x-axis and the number of undecayed atoms on the y-axis. Choose an
appropriate scale that fills the page. Include a title and label your axes.
2. On the same graph, plot the class data. Use a different coloured pen or pencil
and create a key to differentiate between the two lines.
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Science 10
Name: ______________________
Date: _______________________
Period: ______________________
3. Describe the appearance of the two lines on your graph. Are they straight or
curved? What does this tell you about the relationship between the number of
half-lives and the number of undecayed atoms?
4. Which set of data provides a more convincing demonstration of half-life: you
group’s data or the class data? Why?
5. Suppose you had 600 atoms of M&Mium. How many decayed atoms would remain
after three half-lives? Show work.
6. Suppose you start with 3000 atoms of M&Mium and only 190 remain. How many
half-lives must have passed? Show work.
7. Describe one similarity and one difference between this (M&Ms) and actual
radioactive decay.
8. In this simulation, can you predict when a specific M&M will decay? Why or why
not?
9. What other household items could we use in this experiment to model
radioactive decay?
3