Lesson 2 Plan

Radioactive Decay, the Natural Decay Series, and Half-Lives

Purpose:

This lesson will explain how radioactive materials become less radioactive over time through the process of radioactive decay. Additionally, students will learn that the half-life of a radionuclide is the time it takes for a quantity of that radionuclide to lose half of its radioactivity, and that every radionuclide has a unique half-life. Students will learn that the time for radioactive materials to lose essentially all their radioactivity can vary from seconds to billions of years. The lesson also provides students the opportunity to practice reading charts and calculating their own overall exposure to cosmic radiation. Students also will have the opportunity to estimate how much extra radiation a person receives by traveling on a jet plane for various distances.

Concepts:

1. Radioactive materials become less radioactive over time through the process of radioactive decay.
   
   
2. Each radionuclide has its own distinct half-life.
   
   
3. The time for radioactive materials to lose essentially all their radioactivity can vary from seconds to billions of years.
   
   
4. Radioactive decay always releases a charged particle; in some cases a gamma ray is also released.

Duration of Lesson:

One to two 50-minute class periods

Objectives:

After participating in the lesson “Radioactive Decay, the Natural Decay Series, and Half-Lives,” students will be able to

1. discuss the nature of radioactive decay;
   
   
2. explain the difference between alpha particles, beta particles, and gamma rays;
   
   
3. discuss nuclear transformations caused by radioactive decay;
   
   
4. estimate their own exposure to cosmic radiation (optional);
   
   
5. calculate amounts of extra cosmic radiation a person receives by flying on a jet plane (optional).

Skills:

Analyzing, calculating, critical thinking, drawing conclusions, evaluating, interpreting, using an atlas (optional)

Vocabulary:

Alpha particle, beta particle, decay products, fission, gamma ray, helium nucleus, radioactive decay, radioactive decay series (chain), radionuclide, spent nuclear fuel, X-ray

Materials:

Reading Lesson: “Radioactive Decay, the Natural Decay Series, and Half-Lives”

Student Activity 1: “Jet Flight Exposure”

Student Activity 2: “Cosmic Radiation: Living in Different Cities”

Answer Key for Student Activity 1: “Jet Flight Exposure”

Answer Key for Student Activity 2: “Cosmic Radiation: Living in Different Cities”

Background Notes: “The Periodic Table Versus the Chart of the Nuclides”

Suggested Procedure:

1. Assign the reading lesson “Radioactive Decay, the Natural Decay Series, and Half-Lives.”
   
   
2. After students have read the assignment, lead a discussion on the major points in the reading.
   
   
3. As appropriate, and as time permits, have students participate in the activities.

For Class Discussion:

1. Is it possible to predict when a radionuclide will decay and produce radiation?
   
   (Radionuclides decay at random — it is impossible to predict which one will decay next. However, when these atoms are gathered together, it is possible to measure clear patterns of decay. The patterns of decay turn out to be consistent and statistically predictable, even though we can’t predict which particular atom out of the group of identical radionuclides will be the next to undergo decay. This statistically consistent pattern is called the half-life of the radioisotope.)
   
   
2. What is half-life?
   
   (The amount of time it takes for a quantity of a given radionuclide to lose half of its radioactivity is the halflife of the particular radionuclide. Each radionuclide has a definite and unique half-life not shared with any other radionuclide.)
   
   
3. Discuss the meaning of the term “decay series (chain).”
   
   (This is the ordered process that radioactive elements pass through as they spontaneously emit radiation in order to become stable. For instance, the radionuclide uranium-238 transforms into many different radionuclides before it becomes stable lead-206. Some radionuclides may decay to stability in the next second, some in the next hour, some tomorrow, and some next year; others will not reach a stable, nonradioactive state for billions of years. Half-lives range from fractions of a second to several billion years.)

Teacher Evaluation of Student Performance:

Student completion of activities and participation in discussion will indicate level of comprehension.