Half-Life Model (Nuclear Decay) Laboratory
Radioactive isotopes are unstable atoms that decompose spontaneously to the atoms of a different
element. The breakdown of atoms takes place at a set rate, called half-life, which differs for each
radioactive isotope. Half-life is the amount of time it takes for one-half of the atoms in a sample
of a radioactive isotope to decay to the atoms of a different element. Because it is not practical
for you to study the half-life of a real radioactive isotope, you will use a model of such an element
in this activity.
Purpose: The purpose of this lab is to use a model to study half-life. A decay curve of the model
atoms will be constructed.
Materials: split peas (100 per lab group), 2 small beakers, clock or watch
Procedure:
1. Label the beakers Decayed Atoms and Undecayed Atoms.
2. Obtain a sample of 100 split peas. Count your sample to make sure you have 100 split peas. Place
this sample into your beaker marked Undecayed Atoms. Each pea will represent one atom of the
imaginary element peanium.
3. Shake the Undecayed Atoms beaker and dump the split peas out onto the table.
4. Note that some peas landed curved side down and the others landed curved side up. Separate
the peas into two groups, according to the position up or down, of the curved side. The group with
the curved side down will represent the peanium atoms that have decayed to the atoms of a
different element. The group with the curved side up will represent the undecayed peanium atoms.
5. Count the undecayed peanium atoms and record the number in your data table.
6. Place the decayed peanium atoms in the Decayed Atoms beaker. Return the undecayed atoms to
the Undecayed Atoms beaker.
7. Repeat steps 4-7 until there are no more atoms in the Undecayed Atoms beaker.
Data and Analysis:
Create a data table in your lab book as shown below.
Data Table
Run #
Number of Undecayed
Atoms
0(start)
100
1
2
Note: You may have more than 3 runs
Conclusion:
1. Make a graph of your results. Place time (the run number), on the x-axis and the number of
remaining undecayed peanium atoms on the y-axis. Label this as “Graph A.”
2. Regraph your data using time on the x-axis and the natural logarithm of the number of remaining
peanium atoms on the y-axis. The natural logarithm of a number is 2.3 times the logarithm of the
number (ln x = 2.3 log x). Label this as “Graph B.”
3. Which of the graphs is linear?
4. What is the relationship between time and the number of remaining peanium atoms?
5. If each run represented 1 day, according to Graph A, what would be the half-life of peanium?