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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 its daughter element. Each radioactive element has its 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

  1. Collect 100 pennies and place in a jar.
  2. Shake jar of pennies for 10 seconds. This will represent one half-life for the "radioactive pennies"
  3. 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.
  4. Assume all the pennies that are tails have "decayed" and are no longer radioactive. Remove these decayed pennies and set aside.
  5. Return all remaining "radioactive heads" to the jar and repeat steps 2-4.
  6. 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.

   

3

     

4

     

5

     

6

     

7

     

8

     

9

     

10

     

 

Graph

1. On a piece of graph paper, create a graph that will plot:

# of radioactive atoms remaining (heads) vs. time (in seconds)

  1. Label each axis of the graph and make sure that both time and # of heads are laid out in equal intervals.
  2. Plot a point for each half-life using the data from your table.
  3. Draw a best curve line through the plotted data points.
  4. Give your graph a descriptive title.

 

Analysis

  1. Describe shape of graph and trend (increasing, decreasing, linear, curving, etc.)

     

  2. a. How much time (in seconds) did it take to reduce the number of radioactive pennies to about 1/2?

_______

  1. How many half-lives in this? ______

   3.  a. After 2 half-lives, how many radioactive pennies (heads) were left? ______

 

  1. 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

  1. The two bombs dropped at the end of WWII on Hiroshima and Nagasaki, were fueled by Uranium-235 and Plutonium-239, respectively.
  1. Explain why people still feel the affects of the atomic bomb in Japan today (almost 60 years later)

     

  2. How much time would it take for Plutonium-239 to decay to 12% its 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.

 


 

contact: school@communityschoolhouse.org