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Half Life Pennyium Activity
Name: _________________________ Date: ______________ Per: _____
Introduction: Atoms found in nature are either stable or unstable. The nucleus of a radioisotope is unstable
(radioactive). In an attempt to reach a more stable arrangement of its protons and neutrons, the nucleus will
spontaneously decompose to form a different nucleus. If only the number of neutrons changes in the process,
different isotopes are formed. If only the number of protons changes in the process, then a different element
is formed. This decomposition of the nucleus is referred to as radioactive decay. During radioactive
decay an unstable nucleus spontaneously decomposes to form a different nucleus, giving off radiation in the
form of atomic particles or high energy rays.
The length of time it takes for half of a sample of radioactive material to decay is called the half-life. This
decay occurs at a constant, predictable rate. Each radioactive isotope has a characteristic half-life, ranging
from less than a second to millions of years. In this activity, you will use pennies that can land “heads up”
(nuclei that have undergone radioactive decay) or “tails up” (nuclei that haven’t yet decayed) as a simplified
model of half-life.
Looking at the above equation, our radioactive tails penny decays into a more stable heads penny. Often,
when a radionuclide decays, the decay product (the new nuclide) is also radioactive and will continue to decay
until it is stable! In this case, after one decay, our unstable tails penny is now a stable heads-up penny.
Pre-Lab Questions
1) Why do atoms go through radioactive decay?
2) What is a half-life?
3) In our activity for today, what side of the penny represents the stable, non-radioactive atom? _______
Materials: 100 pennies, 1 cup, 1 ziploc bag
(Be careful with the pennies!!)
Procedure:
Your 100 pennies should be in a cup. We are going to assume they all have not decayed yet, and are thus all
tails-up. (If you would like to you can place all of them tails-up).
1) Put your hand over the cup and shake it for several seconds.
2) Pour the pennies out onto the lab table.
3) Remove all the pennies that are heads-up and place them in the Ziploc bag.
 Note: The heads-up pennies are still present, they do not “disappear”, rather they are just not
radioactive anymore. For that reason, we are going to take them out to fit our simulation.
4) Count the numbers of pennies that were tails (“pennies remaining”) and put them back in the cup.
Record Data (next page).
5) Repeat steps #1-4 until the cup is empty!
6) Perform one additional trial by repeating steps #1-5, but this time use only 50 pennies to start. Be
careful when calculating % on this trial.
Data
Trial #1 (100 pennies)
Trial #2 (50 pennies)
Shake (HalfLife)
Pennies Tails Up
% Pennies Remaining
Pennies Tails Up
% Pennies Remaining
0
100
100
50
100
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Shake (Half-Life)
% Pennies Remaining
1) Theoretically 50% of our pennies should decay
with each shake. Fill out the theoretical amount
in the table to the right. Get this checked by
your teacher before moving on.
0
100
2) How did your data compare to the theoretical amount?
3
1
2
4
5
6
7
8
3) Use the graph to plot the % pennies remaining versus the shakes (half-lives). Label the axes so the reader
understands what you plotted.
 Use three colors: trial #1, trial #2, theoretical amount. Fill in the legend/key.
 Draw a smooth line or curve through the points. Do not connect the dots with straight lines.
 Make sure to title your graph as well.
LEGEND
4) Examine your graph for your trials. Is the rate of the number of heads produced over time linear or non-linear?
Does the rate seem to be constant over time or does it vary over time?
5) A half-life is the time required for one-half of the atoms of a radioisotope to emit radiation and to decay to
products. For the process of flipping pennies, what do the “heads” pennies and “tails” pennies represent
respectively, and the shakes?
Analysis:
6) Looking at the penny nuclear equation given on the front, classify it: an alpha, beta or a gamma decay. Which
description would describe the decay better: a new isotope is formed or a new element is formed? Why?
7) The penny nuclear equation given above would be classified as: an alpha, beta or a gamma decay. Which
description would best describe the decay: a new isotope is formed or a new element is formed? Why?
8) Based on this equation, if you begin with 200 pennies, and 3 half-lives pass, how many pennies do you have and
how many balloons do you have?
9) In this equation, which is more unstable, the “tails” penny or the balloon?
10) The penny nuclear equation given above would be classified as: an alpha, beta or a gamma decay. Which
description would best describe the decay: a new isotope is formed or a new element is formed? Why?
11) Based on this equation, if you begin with 300 pennies, and 2 half-lives pass, how many pennies do you have an
how many basketballs do you have?
12) In this nuclear example, why do you think the “tails” penny decays into a basketball?