Name ___________________
Date ____________
PS/ES Per. __________
Mr. Landsman
Modeling Radioactive Decay
…with candy, what else is there?
Background:
Geological processes often reveal relative time, for example: Superposition.
The analysis of layers cannot in itself indicate the actual or absolute age of rock.
Absolute time, expressed in years, is best determined by testing radioactive
isotopes in a rock and comparing the ratios between the original isotope and the
decay product. In this activity, you will create and operate a model of radioactive
decay in which candies (or pennies) represent radioactive isotopes.
Materials:
Plastic box
100 candies
Graph paper
Colored pencils
Napkins
Toothbrush
Procedure:
1. Place exactly 100 candies LETTER SIDE DOWN (tails) in the container.
2. Close the cover and carefully shake the box up and down giving all particles
an equal chance of flipping over.
3. Open the box and remove the flipped candies (heads).
4. Count and record the number of UNCHANGED candies remaining in the
box. Record this number in your table.
5. Repeat steps 2 – 4 until all the “isotopes” have “decayed”.
6. Record your complete data set on the overhead machine (front of class, big
bright light thingy)
7. Calculate the number of accumulating decayed candies based on the class
average.
8. Graph the class averages for parent and decay product on a single set of
axes. Use different colored pencils for each line. Provide a key, title etc.
DATA TABLE
Number of Unchanged Candies
Flipped
Candies
Your
Data
100
Class
Average
0
TRIAL
(shake) #
0
1
2
3
4
5
6
7
8
Class
Average
100
Define Half-life:_____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
Discussion Questions:
1. State what each of the following parts of the model represent in real
radioactive decay.
a) A single candy FACE DOWN in the box.
___________________________________________________________
b) A single candy, letter facing UP. (you removed them)
___________________________________________________________
c) A trial (when you shook the box).
___________________________________________________________
2. Predict what the half-life of 100,000 candies would be if you were fortunate
enough to have that many. __________________________________________
3. Assume that each trial on the horizontal axis of your graph represents 1000
years of time. Using the class averages UNCHANGED line on the graph,
indicate the absolute age of a radioactive sample with:
80 percent unchanged “atoms”________________
40 percent unchanged “atoms” _______________
10 percent unchanged “atoms” _______________