Problem: How does half-life vary between isotopes? How can the radioactive isotopes be used to determine the age of rocks?

Background: In this investigation we will be modeling radioactive decay in three different elements. The

following is a list of the objects and what is being modeled.

  • Box = A rock or object being dated ●Shake = Time of decay (1 shake = 1000 yrs)
  • Corn Seeds = 100 atoms of a radioactive isotope (Parent) ● Sides of the box = Each different element
  • Removed Corn = Decayed atoms (Daughter)

Procedure: Part One:

  1. Obtain a laptop computer and open the excel file for this lab.
  2. Obtain a clear rectangular container with a lid, and 100 pieces of corn (markers).
  3. Choose one long side of the container and mark it.
  4. Place the corn markers in the box, replace the lid and shake gently.
  5. Remove the lid and count the corn markers that are pointing to the one marked side. Assume these markers have decayed.
  6. Record the number of decayed (taken out) and the number remaining in table 1 of the excel file.
  7. Replace the lid and repeat steps #3-#5, as many times as needed, until the box is empty.
  8. From excel, copy table 1 and paste in the blank space below.

Insert Table 1 here:

Procedure: Part 2:

  1. Repeat the procedure above with 2 sides marked and record your results in data table 2 in excel.
  2. From excel, copy table 2 and paste in the blank space below.

Insert Table 2 here:

Procedure: Part 3:

  1. Repeat the procedure above with 3 sides marked and record your results in data table 3 in excel.
  2. From excel, copy table 3 and paste in the blank space below.

Insert Table 3 here:

  1. Create a line graph comparing the number of undecayed markers verses time. Place time on the horizontal (x-axis) and the number of undecayed markers on the vertical (x-axis). Plot all three lines on one graph.

Insert the graph here:

Questions: Type your answer to each question in the space below the question.

  1. In modeling the process of radioactive decay, what did the corn seeds represent?
  1. In modeling the process of radioactive decay, what did the number of marked sides represent?
  1. In modeling the process of radioactive decay, what did each shake represent?
  1. From your graph, what was the half-life in years of each of your elements? (Hint: The time when the # decayed =50%)

Isotope A -

Isotope B -

Isotope C -

  1. Make a claim about the half-life length of various elements. Support your claim using your numerical data, as well as the information learned in class. Justify how your data supports your claim.
  1. Which of your Isotopes would you choose to date an object that is believed to be 30,000 years old? Why?
  1. In the space below, or on a separate sheet of paper, create a model or illustration to represent a sample of Potassium-40 going through two half-lives.