Name______________________________________________ Block_________Half-life Lab

Information: To determine the absolute (real) age of an item, scientists use radioactive decay. Radioactive decay is when atoms in an object decay and turn into a new substance. The rate of radioactive decay is measured in a half-life. A half-life is the length of time it takes for ½ of an object to change into a new substance.

Today, you and a partner will be completing an activity that represents Carbon-14 turning into Nitrogen-14 and the number of years and half-lives it will take for all of the Carbon-14 to turn into Nitrogen-14.

Materials: 1 cup 100 pennies calculator graph paper (1 piece for each person) ruler

Carbon-14 Nitrogen-14Undecayed Atoms Decayed Atoms

Procedure:1. Collect all lab materials and sit next to your partner at a lab table.2. Place all 100 undecayed atoms (pennies) into the cup. They represent the amount of Carbon-14 in

your sample.3. Cover the cup with your hand and shake it for 3 seconds.

For example Carbon-14 turns into Nitrogen-14

1 Half-life is 5730 years

4. Pour out the pennies onto the lab table. Be carful that they don’t fall onto the floor or get mixed with another group’s pennies.

5. Remove the decayed Nitrogen-14 atoms (the pennies that are tails side up), count them, and set them to the side.

6. Enter this number of decayed atoms you set off to the side from number 5 into Table 1 in the row labeled 1 half-life.

7. Count the number of undecayed atoms (the pennies that are heads side up) and enter this number into Table 1 in the row labeled 1 half life.

8. Add up the decayed and undecayed atoms and write this number in the “Total Atoms” column in Table 1.

9. Put ONLY the undecayed atoms (the pennies that are heads side up) back into the cup.10. On Table 1, add up the number of years for each half-life. The first 2 have been done for you.11. Repeat steps 3-9 until all of the atoms have decayed and the cup has no pennies in it.12. Do the entire experiment (all steps 2-11) to complete Table 2.13. Average your results of Table 1 and Table 2 in order to complete Table 3.

Graphing Table 3:1. Create a line graph to represent your data in Table 3.2. First, on the x-axis (horizontal axis) finish labeling the number of half-lives and years. The first

two have already been done for you as an example.3. Plot ONLY the undecayed atoms (Carbon-14) for each half-life on your graph. **Be sure to

make note that your ½ lives and years are on the x-axis (horizontal axis) and the undecayed atoms (number of pennies) are on the y-axis (vertical axis)**

a. For example, when plotting the first data point from Table 3 you would go over on the x-axis to 0, and up 100 on the y-axis. THEN plot your data point.

4. After you have plotted all of your data points onto the graph create a line of best fit.a. A line of best fit is a line that is smooth and curvy and goes through the center of your

data. DO NOT SIMPLY CONNECT THE DOTS. This means that you will have some data points above , some below, and some through the line of best fit.

Breaking News!!!

The remains of the elusive “Big Foot” have been found. The specimen has been tested, and it has been found to contain 37% of the Carbon-14 that would be expected in a living organism. The state Department of Really Extinct And Dead things (DREAD) is at a total loss, and has asked Miss Duba’s geoscience class to come to scientific conclusions about this animal.

Also, a log cabin has been found in Nemaha County, Nebraska, that is thought to be the summer home of the first cornhusker, thought to be alive 2,000 years ago.

The state of Nebraska needs you to answer the following questions. YOU WILL NEED TO USE YOUR FINISHED GRAPH, AND THE FOLLOWING INFORMATION, TO ANSWER THESE QUESTIONS.

*On the y-axis (labeled 1-100) each square = 4% of carbon-14

*On the x-axis (labeled 1-11) 4 squares= 1 half-life

1. How many years ago did this “Big Foot” die?

2. What would be the expected concentration of Carbon-14 in a log cabin, found in Nemaha County, that is thought to be 2,000 years old?