Tom McNulty
April 7, 1999

Lesson Plan








Title: An Introduction to Radioactivity.

Audience: 11th Grade Physics.

Duration: Approx. 45 minutes.

References: Physical Science, Holt, etal. Ch. 11, pp. 251-262.
                       Physics: A General Introduction, 2nd ed. Van Heuvelen. Ch. 34-35, pp. 709-756.

Specific Behavioral Objectives:

  1. Students will be able to define the terms radiation, radioactivity, radioactive decay, fission, and fusion.
  2. Students will be able to identify key events/discoveries and scientists who played important roles in the discovery and development of the concept of radioactivity.
  3. Students will be able to identify the four types of radiation and radioactive decay and give an example of each by writing nuclear reaction formulas.
Materials:
  1. Definitions/terminology handout
  2. Charts of selected isotopes
  3. Periodic chart handouts
  4. Nuclear reaction worksheet
Anticipatory Set:  Ask students, "When you hear the word 'radiation,' what do you think of?"  Take responses from students.  Students may mention many negative ideas.  Radioactivity can be very dangerous and it must be treated with care and respect.  However, it can be very useful.  Ask students, "Can you think of any positive uses for radioactive materials?"  Take responses from students.  Point out practical uses that students do not mention, such as carbon and potassium dating, X-rays, nuclear power production, cancer treatment, and medical tracers.  We will talk more about all of these applications as well as why radiation behaves as it does.

Main Body:
 

HISTORY OF WORK IN THE FIELD OF RADIATION
  1. Henri Becquerel discovered radioactivity by accident in 1896. He was doing experiments using uranium salt crystals and photographic plates wrapped in heavy black paper. He believed that placing the crystals on the film plate and exposing them both to sunlight caused the crystals to emit something that caused the plate to be exposed in the area where the crystals were. A stretch of bad weather caused Becquerel to postpone his experiments, as there was no direct sunlight. So he placed the film and salt crystals in his desk drawer until the weather cleared. When he checked the film several days later, he was amazed to find that it was exposed in the places where the salt crystals were in contact with the plate. He concluded that the uranium salt crystals emitted an invisible radiation that could penetrate objects and cause photographic plates to be exposed. He had discovered radiation by accident!
  2. Marie and Pierre Curie discovered two new radioactive elements- polonium and radium- in 1898.
  3. These scientists had no idea what was causing the radiation. The electron had just been discovered by J.J. Thomson one year before the Curies made their discoveries and the atomic nucleus would not be discovered until 1908 by a scientist named Ernest Rutherford. Not only were they unaware of the cause of radiation, they also didn't know any of the effects radiation could have on the human body, since most radiation cannot be detected by humans (except for visible light and infrared).
  4. We now know that radioactivity is the result of some instability within the nucleus of an atom. This instability causes the nucleus to emit particles or to split into smaller particles. Nuclear instability results from a high proton to neutron ratio within the nucleus of an atom.
DEFINITIONS AND TERMINOLOGY
  1. Radioactivity- the emission of energy in the form of particles or electromagnetic waves as a by- product of a nuclear reaction (i.e. nuclear fission or fusion) or by spontaneous radioactive decay.
  2. Radiation- energy given off when certain substances undergo either radioactive decay or some other nuclear reaction.
  3. Radioactive Decay- the spontaneous breakdown of an unstable atomic nucleus.
  4. Isotopes- nuclei with the same number of protons but different numbers of neutrons.
  5. Nuclear Reaction Equation- equations which use atomic symbols to describe nuclear processes.
  1. Nuclear Fission- the splitting of an atomic nucleus into two smaller nuclei of approximately equal mass, during which, energy is released. Illustrate with drawing on the board.
  2. Nuclear Fusion- the joining of two atomic nuclei of smaller masses to form a single nucleus of larger mass. Illustrate with drawing on the board.
  3. Types of Radiation:
  1. Types of Radioactive Decay:
Evaluation:  Students will receive verbal feedback on concept mastery by responding to questions and participating in a brief review session. Areas of confusion will be retaught or clarified.
 
ACTIVITY
  1. Students get into pairs.
  2. Students will find one isotope for each type of radioactive decay on their chart of selected isotopes.
  3. Students will draw each reaction using proper nuclear reaction equation format.
  4. Students will be selected to put their decay process on the board.
Assignments:
  1. Problems #14-16 on pg. 736 in Van Heuvelen
  2. Nuclear Reaction Worksheet
  3. Read pg. 730-735 in Van Heuvelen
Summary/Closing Statement:  Today, we learned about radiation: what it is, where it comes from, and who discovered it. We also learned about the four types of radiation. What were they? (Gamma, alpha, beta, and neutron) And we learned about the four types of radioactive decay. What are they? (Gamma, alpha, beta minus, and beta plus) We all know that radiation can be dangerous, right? Do you think that the type of radiation has anything to do with how dangerous it is? Well, it does, and next time we'll find out why different types of radiation are more dangerous than others. We'll also look at some of the ways we detect and measure radiation, as well as some of the uses of radiation.

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Copyright 1999, Thomas McNulty
Last updated 9 August 1999