USING COINS TO MODEL
RADIOACTIVE DECAY
GENERAL SCIENCE / HARD LEVEL
Introduction
Scientists can determine the age of very old objects based on the
known rates of decay of the radioactive isotopes of certain elements.
The amount of time necessary for one-half of the atoms in a
radioactive sample to decay is known as the half-life. In this activity,
you will model radioactive decay using coins.
Time Needed
45 minutes
What You Need
✎ 100 pennies
✎ container (e.g., cup or bowl) large enough to
✎
hold 100 pennies
large table
Safety Precautions
Please review and follow the safety guidelines at the
beginning of this volume.
What You Do
1. Place all of the pennies into the container.
2. Toss the pennies from the container onto the table.
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3. Identify all of the pennies that landed with the “tails” side up,
and place them on the left side of the table in 1 vertical column.
4. Take all of the remaining pennies and put them back into the
container.
5. Toss the pennies form the container onto the table, away from
your column.
6. Find all of the pennies that landed with the “tails” side up, and
place them in a another column to the right of your previous
column (Figure 1).
table
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Figure 1
7. Repeat steps 5 and 6 until all of the pennies have been placed
in columns. If no pennies land “tails” side up, leave an empty
column for that toss.
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Observations
1. About what fraction of the pennies come up tails each toss?
2. Are there more or fewer pennies that come up tails with each
toss?
3. How does this relate to radioactive decay and half-life?
4. What other object could you use to model the decay of
material with a longer half-life?
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JUNIOR SCIENCE EXPERIMENTS ON FILE,TM VOLUME 2
1.0 Safety Guidelines (page 1)
1.0 SAFETY GUIDELINES
GENERAL
get your teacher’s permission for experiments performed
• Always
at school, and your parent’s permission for experiments performed
•
•
•
•
•
•
•
•
at home, before attempting any experiment.
Read all instructions for an experiment several times before
starting the experiment, and follow the directions exactly as they
appear in this volume.
If an experiment requires adult supervision, do not perform the
experiment unless you have an adult supervising you the entire
time you are performing the experiment.
Wash your hands before the start of, and after, each experiment
you perform.
Keep your work area clean.
Never eat or drink while performing a lab experiment. Never taste a
substance used in an experiment unless you are told that it is safe
to do so.
Be aware of the location of equipment that you may need in an
emergency, such as running water, an eyewash if you are at school,
a fire extinguisher, etc.
If you are going outside, make sure you have teacher or parent
permission to go. Take a buddy with you and dress appropriately for
the weather. Make sure you or someone who accompanies you is
familiar with the area, and bring along a first-aid kit in case of an
emergency.
Never look directly into the Sun.
CHEMICAL SAFETY
wear goggles when working with chemicals, such as acids
• Always
and bases, and near heat sources like flames. If at all possible,
•
•
•
avoid wearing contact lenses when working with chemicals.
If any substance gets into your eyes, notify an adult (e.g., your
teacher or parent) immediately and flush your eyes with running
water for at least 15 or more minutes. Do not mix chemicals unless
you are told to do so by a teacher or parent.
Never touch, taste, or smell chemicals unless instructed to do so.
Keep chemicals in closed containers when they are not in use.
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1.0 Safety Guidelines (page 2)
JUNIOR SCIENCE EXPERIMENTS ON FILE,TM VOLUME 2
of all used chemicals properly. Do not pour any chemicals
• Dispose
or solids down the drain unless instructed to do so.
safety gloves and a plastic apron when handling chemicals. If
• Use
any chemicals spill on your skin, rinse it with running water for at
•
•
least 10 minutes, and notify your teacher or parent immediately.
Take precautions to avoid spilling chemicals. If a chemical spills on
any surface, notify your teacher or parent immediately to assist with
clean-up.
Exercise caution when using sharp instruments such as knives or
scissors. Always cut away from yourself, not toward yourself. If you
are cut, notify your teacher or parent immediately.
GLASSWARE
glassware when you are finished with the experiment.
• Clean
careful when using glassware. If a piece of glassware breaks,
• Be
have an adult assist you in clean-up to avoid injuries due to broken
glass. Never use broken or damaged glassware.
FIRE SAFETY
not heat glassware that is not completely dry. Do not pick up
• Do
hot glassware without heat-resistant gloves or tongs.
heating glassware, keep it away from yourself and from
• When
others.
not heat anything unless instructed to do so by a teacher or
• Do
parent.
not heat substances in a closed container.
• Do
an experiment, make sure that all heating sources are turned
• After
off and that all flames have been put out.
not reach across such heating sources as flames.
• Do
back long hair. Do not wear clothing with loose sleeves, scarves,
• Tie
bows, ties, or anything else that may hang into a fire. Do not wear
long earrings.
ELECTRICAL SAFETY
not touch electrical equipment if your hands are wet.
• Do
not plug many electrical devices into one outlet or use an
• Do
extension cord.
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