1. Place 80 Pennies HEADS-UP in a Box. These Pennies Represent the Starting Composition

Name: ______Date: ______Period: ______

Half-Life Lab

Discussion: Carbon-14 is a radioactive element that breaks down, or decays, into nitrogen. The time it takes for one-half of the carbon-14 to break down into nitrogen is called its half-life. The carbon-14 in an organism begins to decay into nitrogen when the organism dies. For this reason, the half-life of carbon-14 can be used to find the absolute age of a fossil by comparing the amount of carbon-14 with the amount of nitrogen in the fossil. A disadvantage to using carbon-14 dating is that it can only be used on fossils younger than 60,000 years. Radioisotopes like Uranium and Potassium must be used on fossils older than 60,000 years.

Purpose: In this activity you will simulate radioactive decay using pennies. The pennies represent atoms of a radioactive element. They will be used to discover the relationship between the passage of time and the number of atoms that decay. Each trial represents one half-life. Heads-up coins represent un-decayed atoms. Tails-up coins represent atoms that have undergone radioactive decay.

Procedure:

1. Place 80 pennies HEADS-UP in a box. These pennies represent the starting composition.

2. Close the box and shake vigorously (making sure the top of the box doesn’t open).

3. Open the box. Remove all the TAILS-UP coins, count them and record the number in your table.

4. Count and record the number of HEADS-UP coins that remain (half-life # 1)

5. Repeat steps 2, 3 and 4 three more times. These trials represent half-lives #2, 3, and 4. You must

record the number of TAILS-UP coins produced and the number of HEADS-UP coins for each trial

(half-life).

6. Pool the class data and determine the number of decayed and un-decayed atoms for each half-life.

Record in your data table.

7. Prepare 2 graphs. 1) Graph showing your results. 2) Graph showing the pooled class results.

a. X-axis = number of half lives (start at 0 and number 1-4)

b. Y axis = number of un-decayed atoms (heads-up coins) that remain for each half-life

c. Label your axes and include a title for each graph.

Data Tables:

Analysis Questions:

1. What did the pennies represent in this activity? ______

2. What did the heads-up pennies represent? ______

3. What did the tails-up pennies represent? ______

4. What did shaking the box represent? ______

5. Are your graphs straight or curved? ______Why do you think that is?

______

6. Which set of data, your own or pooled class provides the better demonstration of the concept of

half-life? ______Why? ______

______

7. In this simulation is there any way to predict when a particular penny (atom) will decay? ______

8. Which of the following fossils do you think is older: a fossil containing 25% carbon-14 and 75% nitrogen OR a fossil containing 50% carbon-14 and 50% nitrogen? How do you know?

______

______

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9. Do you think carbon-14 dating could be used to find the age of a dinosaur fossil? Why or why not?

______

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10. If a half-life is equal to 20 minutes,

a. How many un-decayed atoms (from the lab) remained after 40 minutes? ______

b. How many un-decayed atoms remained after one hour? ______

c. How many un-decayed atoms remained after 30 minutes? ______

d. How many un-decayed atoms would remain after 1 hour and 20 minutes? ______