Authors: Tamra C. Ragland
Subject(s):
Life Science
Grade Level:
Seventh (7th)
Standards:
Science:
1. Explain that diversity of species is developed through gradual processes over many
generations (e.g., fossil record).
2. Investigate how an organism adapted to a particular environment may become extinct
if the the environment, as shown by the fossil record, changes.
Mathematics:
1. Create a visual representation of an equation-solving process that models the use of
radioactive decay.
2. Read, create and interpret a graph illustrating the concept of half-life.
3. Use a graphing calculator to analyze change.
Technology:
N/A
Objectives:
The student will be able to:
1.) Create a model of radioactive decay to more fully understand radiometric dating.
2.) Construct a graph illustrating the concept of half-life.
3.) Apply the concept of half-life.
Rationale (How this relates to engineering):
Integration of mathematics and science
Materials Required:
Shoe box or a similar container with lid, 100 pennies, graph paper, Student Data page, graphing calculator (optional)
Activities:
Absolute Time and Radiometric Dating (Making a Model of Radioactive Decay)
After class discussion of relative and absolute dating, half-life and its applications, the students will work in pairs to:
1. Create a data chart with two colums on a blank sheet of paper. Label one column
"Amount of Parent Element" and the other "Trial Number."
2. Count out 100 pennies and place them in a shoe box or similar container. The pennies
represent atoms of an imaginary radioactive element that we'll call Pennium. Under
"Amount of Parent Element" record that you start with 100 atoms. Under "Trial
Number" record "0."
3. Remove from the box those pennies that are heads up. They represent atoms of the
daughter element, Headium, that were created from decay of the parent element,
Pennium. In your data chart, record the number of pennies left in the box under
"Amount of Parernt Element." Also record that his was "Trial #1."
4. Place the lid back on the box and turn it over again as you did before. Remove the
pennies that are heads up, recording the number of pennies remaining in the box and
that this was "Trial #2."
5. Continue shaking and removing pennies as above, recording the number of pennies
remaining in the box and the trial number. Shake the box a total of seven times (seven
trials) or until there are no pennies left in the box.
6. Use your date to contruct a graph, "The Radioacitve Decay of Pennium." Plot "Trial
Number" on the horizontal axis and the "Amount of Parent Element" on the vertical
axis.
Observations and Conclusions:
A. Have two students draw their graphs on the board and compare them noting that they
have the same general shape but the points are not identical.
B. Students may arrive at their answers to questions 1 and 2 by direct reasoning or by
using their graphs. Show them how the graph can be used for interpretation.
1. Question: If each trial represents 10,000 years, what is the half-life of Pennium?
Answer: The half-life is 10,000 years.
2. Question: Suppose you are analyzing a sample in a radiometric dating lab and
determine that you have 75 atoms of Headium for every 25 atoms of radioactive
Pennium. How old is the sample? Answer: The sample is 20,000 years old.
3. Question: Could the radioactive decay Pennium be used to date a rock that is known
to be older than 100 million years old? Why? Answer: No, its half-life is too short.
All the Pennium would have developed to Headium long ago.
Adapted from the National Geographic Society, 1999
Assessment of student learning:
Students responses to the following questions:
1. What did you learn from this project? "I know what radioactive decay is and I understand it…I didn't even notice that it [using the pennies] was almost splitting exactly in half each time which is a half-life." "I learned how half life worked and that different elements like uranium are userd for half-life." "I learned that half-life of an object means half the sample size, not half the years." "That you can take and inanimate regular object and use it to experiment with a scientific process." " I learned how to graph an experiment."
2. What did you like about completing this project? "I liked the fact that we used regular items that you see everyday to prove a scientific experiment. I like the creativity." " I would recommend this for the 7th grade class next year." "I liked how the activity seemed realistic, and I liked simulating the decay of 'Pennium.' It helped me understand what half-life and absolute dating were, and I liked how we displayed the data on a graph." "I liked that we got to do the activity instead of just having the information taught."
Assessment of the activity:
The lesson went well. Based on the student comments, we learned a great deal about what the students learned. I would do this activity again, because the students seemed to really enjoy and it helped improve their understanding of the types of readioactive dating, half-life, and decay.