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RADIOACTIVE PENNIES
A Radioactive Half-Life Lab Activity
Introduction
Radioactive half-life is the time it takes for one-half of the atoms of a
radioactive substance to decay into it’s daughter element. Each radioactive
element has it’s own half-life, ranging from fractions of a second (as with the
heavier synthetic elements) to billions of years, as with Uranium-238. In this
lab activity, you will simulate radioactive decay using pennies.
Materials
100 pennies per pair, jar, and tray
Graph paper, ruler, etc.
Procedure
- Collect 100 pennies and place in a jar.
- Shake jar of pennies for 10 seconds. This will represent one half-life for
the "radioactive pennies"
- After 10 seconds, pour all the pennies onto a tray. Record the number of
heads and tails on the data table on the back of this lab sheet.
- Assume all the pennies that are tails have "decayed" and are no
longer radioactive. Remove these decayed pennies and set aside.
- Return all remaining "radioactive heads" to the jar and repeat steps 2-4.
- Continue to repeat the process until one penny is left in the jar.
Data Table
|
# of
half-lives |
Time
(in seconds) |
# of radioactive atoms remaining (heads) |
# of atoms decayed to daughter atom (tails) |
|
0 |
0 |
100 |
0 |
|
1 |
10 sec. |
|
|
|
2 |
20 sec. |
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3 |
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4 |
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5 |
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6 |
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7 |
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8 |
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|
9 |
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10 |
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Graph
1. On a piece of graph paper, create a graph that will plot:
# of radioactive
atoms remaining
(heads) vs. time (in
seconds)
- Label each axis of the graph and make sure that both time and # of heads
are laid out in equal intervals.
- Plot a point for each half-life using the data from your table.
- Draw a best curve line through the plotted data points.
- Give your graph a descriptive title.
Analysis
Describe shape of graph and trend (increasing, decreasing, linear,
curving, etc.)
a. How much time (in seconds) did it take to reduce the number of
radioactive pennies to about 1/2?
_______
- How many half-lives in this? ______
3. a. After 2 half-lives, how many radioactive pennies
(heads) were left? ______
- About what percentage does this represent? _______
4. How many radioactive half-lives will it take to reduce the
radioactivity to about 12% of the original amount?
______
5. Can you predict which penny in your jar will decay? Explain why or
why not.
6. How does this graph model radioactive decay of any radioactive element?
Application
Use the chart below, answer the following questions.
|
Radioactive Element |
Half-life |
|
Uranium-235 |
700 million years |
|
Plutonium-239 |
24,100 years |
|
Iodine-131 |
8 days |
|
Carbon-14 |
5,760 years |
- The two bombs dropped at the end of WWII on Hiroshima and Nagasaki, were
fueled by Uranium-235 and Plutonium-239, respectively.
- Explain why people still feel the affects of the atomic bomb in Japan
today (almost 60 years later)
- How much time would it take for Plutonium-239 to decay to 12% it’s
original radioactivity level?
2. Nuclear waste dumped at Hanford Nuclear Depository in Eastern
Washington is mostly Plutonium-239. If government regulations state that 10
half-lives must pass before the waste is safe for exposure to humans, how
many years must pass before the waste can be released safely?
3. Why does Iodine-131 make a good radioactive element to use as tracer
in medical tests?
4. Dating fossils is found by determining the percentage of radioactive
Carbon-14 atoms that remain in the bones. If the percentage of the Carbon-14
atoms is 25% of normal, roughly, how old might the fossils be (in years)?
5. Do radioactive elements remain radioactive forever? Explain.
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