Decay of Carbon 14

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? _________________________________________________ _________________________________________________ _________________________________________________ 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. _________________________________________________ 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