Lesson 1: Radioactive Decay
Radioactive decay is the spontaneous disintegration of isotopes of certain atoms, such as Uranium, Potassium, and Thorium, into new isotopes and the process continues until a stable isotope is reached. Some by-products of the decay process are Alpha particles, Beta particles, Gamma rays, and heat. Radioactive decay is expressed in half-lives, the time it takes for half of the parent atoms to disintegrate into daughter atoms. As the parent decays, the stable daughter atoms increase proportionally, always maintaining the total ratio of one. The rate of decay can be shown by use of a decay curve. Most decay takes place within the first three half-lives.
Activity 1 Radioactive Isotopes
Objectives
To identify half-lives of certain radioactive isotopes. To draw and use Decay Curves. To use half-lives in dating rocks.
Vocabulary
Radiometric dating, radioactive decay, half-life, alpha particles, beta particles, gamma rays, exponential function, isotope, atomic mass, atomic number.
Materials
A reference source of radioactive isotopes, paper, pen, graph paper, graphing calculator.
Procedures: In Activity 1,the students will make a list of five radioactive isotopes and place them on the chart.They will graph a decay curve of the isotopes from the chart. The student will make a statement about the shape graph of the half life of any isotope. Each student will complete the chart for this activity. In Activity 2 students will complete the exercises on dating rocks using the decay process.
Radioactive Isotopes
| Name of Radioactive Isotope | Half-Life (years) |
| 1) | |
| 2) | |
| 3) | |
| 4) | |
| 5) |
Activity 2: Dating Rocks Using the Decay Process.
- Parent isotope X has a half-life of 100 millions. A rock sample has a ratio of 3/4 isotope X and 1/4 daughter isotope Y. What is the age of that rock? (Show work)
- Parent isotope A has a half-life of 200 million years. A rock sample has 1/8 parent A and 7/8 daughter isotope B. What is the age of that rock? (Show work)
- . A Rock contains 50% parent isotope X and 50% daughter isotope Y. The age of this rock has been determined to be 800 millions years old. What is the half life of that rock?
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