Nuclear Physics

Materials:
Small plastic or cardboard box with lid
200 pennies
Computer with graphing software
50 thumbtacks (with flat, domed heads)
Materials for Exploring Further:
Kit of radioactive rocks
Geiger counter (radiation monitor)
Gas discharge tubes with power supply (H, He, Ne, Ar)
Handheld visual spectroscope
Periodic table

In this lab, you will investigate the meaning of half-life and learn how it is used to measure the decay of unstable atoms. 
Procedure 

Experiment 1: Radioactive Decay of Pennies 


In this experiment, pennies that are placed heads-up will represent unstable, radioactive atoms (atoms that have not yet decayed). Pennies that are placed tails-up will represent stable atoms (atoms that have already decayed).
Place 200 pennies heads-up in the bottom of the plastic box. Record the number of pennies in the box that are unstable (heads-up) and the number that are stable (tails-up) in data table 1, in the row for 0 half-lives passed.
Place the top on the box and shake the box vigorously for a few seconds. Remove the top. Count and remove all pennies that are now stable (tails-up). Record the number of unstable (heads-up) and stable (tails-up) pennies in data table 1, in the row for 1 half-life passed. Remove all stable (tails-up) pennies from the box and set them aside.
Repeat step 3 nine more times, counting and removing all pennies that become stable (tails-up) each time. Record your data in data table 1.
Use a computer to graph the data. Follow instructions in the graphing software package or from your teacher in order to make the graphs. Plot the number of half-lives on the x-axis and the number of unstable (heads-up) pennies on the y-axis.


Data Table 1: Radioactive Decay of Pennies


Half-lives passed
Unstable pennies
Stable pennies
0
200
0
1
105
95
2
51
149
3
28
172
4
13
187
5
7
193
6
4
196
7
3
197
8
1
199
9
0
200
10
0
200



Experiment 2: Radioactive Decay of Thumbtacks 


For this experiment, thumbtacks with their points sticking straight up will represent unstable atoms (atoms that have not yet decayed). Thumbtacks with points touching the table will represent stable atoms (atoms that have already decayed).
Place 50 thumbtacks with points sticking straight up in the bottom of the plastic or cardboard box. Record the number of thumbtacks in the box that are unstable (pointing up) and stable (pointing down) in data table 2, in the row for 0 shakes.
Place the top on the box and shake the box vigorously for a few seconds. SAFETY NOTE: Ensure the top is fastened securely before you begin shaking! Remove the top. Count and remove all thumbtacks that are now stable (pointing down). SAFETY NOTE: Handle thumbtacks with caution, and place "decayed" thumbtacks away from your working surface and away from the working space of any classmates. Record the number of thumbtacks that are unstable (pointing up) and stable (pointing down) in data table 2, in the row for 1 shake.
Repeat step 3 nine more times.
Use a computer to graph the data. Follow instructions in the graphing software package or from your teacher in order to make the graphs. Plot the number of shakes on the x-axis and the number of unstable (points-up) thumbtacks on the y-axis.


Data Table 2: Radioactive Decay of Thumbtacks


Shakes
Unstable thumbtacks
Stable thumbtacks
0
50
0
1
38
12
2
28
22
3
23
30
4
19
37
5
16
42
6
14
46
7
10
49
8
8
49
9
6
50
10
4
50




Analyze

1. What happens to the number of unstable pennies as the number of half-lives increases?