Class Copy

# Simulation of Radioactive Decay

Radioactive materials are harmful to living tissues. Their half-lives are difficult to measure without taking safety precautions. To eliminate these problems, you will simulate the decay of unstable nuclei by using harmless materials that are easy to observe. In this experiment, you will use pennies to represent nuclei. Each observation you make will represent one half-life for the "radioactive" atoms.

## Procedure

1. Copy the data table onto a separate sheet of paper or your journal.
2. Count out 100 atoms and place them in the cup.
3. Record the amount of radioactive atoms. With the first observation, you will have 100 radioactive atoms.
4. Carefully dump the atoms from the cup on to your desk top and arrange them into a single layer.
5. Remove all the atoms that have landed as heads and count them. These atoms represent decayed nuclei. They are now stable atoms. Set them aside on your desk.
6. Record the number of decayed atoms (stable) in the data table.
7. Record the number of remaining radioactive atoms in the data table.
8. Scoop up the radioactive atoms and put them in the cup.
9. Calculate the percent of the original material that decayed according to the following formula:

% decayed = 100 [ ( # of atoms decayed)   ÷   (# of radioactive atoms you started with on this step) ]

EXAMPLE Data Table
Observation Number of radioactive atoms (tails) Number of atoms decayed (heads) % decayed
1 100 (starting number) 52 100 (52/100) = 52%
2 48 22 100 (22/48) = 46%
3 26 12 100 (12/26) = 46%
4 14 10 100 (10/14) = 71%
5 4 1 100 (1/4) = 25%
6 3 1 100 (1/3) = 33%
7 2 2 100 (2/2) = 100%
Average % decay (52 + 46 + 46 + 71 + 25 + 33 + 100) / 7 = 53%

10. Repeat steps 3-9 until all of the atoms have decayed (you will have between 5-10 observations).
11. Average the percentage (%) decayed calculations and record.
12. Use graph paper to make a line graph of your results, with the number of radioactive atoms (tails) on the y-axis and the observation numbers (half-lives) on the x-axis.

Name:

## Simulation of Radioactive Decay

1. Certain elements are made up of _______________________ whose _____________________ are naturally _____________________.
2. The atoms of these elements are said to be _______________________ .
3. The nucleus of a _______________________ atom will decay into the nucleus of another _______________________ by _______________________   _______________________ and _______________________ .
4. It is _______________________ to predict when the nucleus of an individual radioactive atom will _______________________ .
5. If a large number of nuclei are present in a sample, it is possible to determine the _______________________   _______________________ in which _______________________ the nuclei in the sample will _____________________.
6. This time period is called the _______________________ of the element.

Student Data Table
Observation Number of radioactive atoms (tails) Number of atoms decayed (heads) % decayed
1 100 (starting number)

2

3

4

5

6

7

8

9

10

Average % decay

## Questions

1. The ideal average % decay is 50%. How does your average % decay compare to the ideal?

2. Record the calculations of the class average for the average radioactive decay rate.

3. Compare your average decay % data with class's average decay %.

4. Often the class average decay % is closer to the ideal 50% than an individual group's data.

5. Typically, each of your observations takes between 5 to 2 minutes. If each observation always took 1000 years, how many years would it have taken you to finish gathering the data?

6. Imagine each observation did take 1000 years. If you found an Altoids tin with the same number radioactive atoms in it (tails) as you had in observation 3, how old would that Altoid tin be?

7. Use what you learned from this activity to explain how scientists can use radioactivity to determine the age of a rock or fossil.