Name
Class
Date
The Decay of Carbon-14
Enrichment Activity
Skills: interpreting graphs, predicting, making graphs
Over time, the nuclei of radioactive elements decay. When this occurs, the element
turns into a new element. For example, carbon-14 decays into nitrogen-14. The half-life
of a radioactive element is the time it takes for half of the atoms in a sample of the
element to decay. The graph below shows the decay of carbon-14 into nitrogen-14.
Study the graph. Then, answer the questions.
1. What is the half-life of carbon-14? How do you know?
_________________________________________________
_________________________________________________
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2. What percentage of carbon-14 remains after 17,190
years? ___________________________________________
3. Predict what percentage of the original carbon-14
sample will remain after 28,650 years.
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4. Uranium-238 has a half-life of 4.5 billion years. Draw a
decay graph for uranium-238 in the space below.
Show how uranium-238 decays over a period of 18
billion years.
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
(c) by Pearson Education, Inc./Globe Fearon/Pearson Learning Group. All rights reserved.
Nonmetals, Metalloids, and Radioactive Elements
Answer Key
The Decay of Carbon-14
Enrichment Activity
1. 5,730 years; The graph shows that 50 percent of
the carbon-14 atoms have decayed after 5,730 years,
so 5,730 is the half-life of carbon-14.
2. 12.5%
3. 3.125% 4. Students’ graphs should be identical to
the graph for carbon-14, but the labels on the
horizontal axis should be as follows: 4.5 billion (for
50%); 9 billion (for 25%); 13.5 billion (for 12.5%), and
18 billion (for 6.25%).
Concepts and Challenges in Physical Science, Teacher’s Resources CD-ROM
(c) by Pearson Education, Inc./Globe Fearon/Pearson Learning Group. All rights reserved.
Nonmetals, Metalloids, and Radioactive Elements