Tom McNulty
June 28, 1999

Lesson Plan

Title: Effects of Radiation on Living Organisms.

Audience: 11^th Grade Physics.

Duration: Approx. 45 minutes.

References: Physical Science, Hurd, etal. Ch. 11, pp. 256-262.
Physics: A General Introduction, 2^nd ed. Van Heuvelen, Alan. Ch. 34, pp. 727-730.

Specific Behavioral Objectives:

Students will be able to explain how radiation damages living tissue.
Students will be able to differentiate between RAD, Roentgen, and REM, and give the definition of each.
Students will be able to determine the amount of biological damage in REM that a particular radiation will do.
Students will be able to describe the three ways to minimize one's exposure to radiation.

Materials:

Personnel radiation detector
Videotape on Chernobyl nuclear disaster
TV and VCR

Anticipatory Set: Show students a TLD (thermoluminescent dosimeter) or other type of personnel radiation detector, and explain that I had to wear one everyday while I was in the Navy. "We just learned yesterday that radiation is all around us - in building materials, some foods, etc. - so shouldn't we all be wearing these TLD's? Why or why not?" Tell students that about 100 REM of radiation is the smallest amount needed to cause noticeable effects on the human body. "The sources we talked about yesterday are much too weak to cause us any harm."

Main Body:

DEFINITIONS

Ionization - the removal of an electron from its orbit around the nucleus of an atom, resulting in a particle with a net charge (i.e. an ion).
RAD (Radiation Absorbed Dose) - that amount of radiation that deposits 10^-2 Joules of energy into 1 kg of absorbing material.
Roentgen - that amount of ionizing radiation that produces an electric charge of 0.333 x 10^-19 Coulombs in 1 cm³ of air at STP.
RBE (Relative Biological Effectiveness) - the number of RADs of X-radiation or g-radiation that produces the same biological damage as 1 RAD of the radiation being used.

RBE FOR SEVERAL TYPES OF RADIATION:

        Radiation                         RBE Factor
X-ray or g-ray                              1.0
b particles                                     1.0 to 1.7

a particles 10 to 20

Slow neutrons 4 to 5

Protons and fast neutrons 10

Heavy ions 20

5. REM (Radiation Equivalent in Man) - standardized unit for measuring the biological damage caused by different types of radiation.

REM = RAD x RBE factor

Biological damage depends not only on dose rate in RADs, but also on the type of radiation being received.

Example: One RAD of g radiation vs. one RAD of a radiation.

(RAD_g)(1.0) = 1.0 REM

(RAD_a)(15) = 15 REM

Radiation damages living tissue by penetrating cells and, through ionization, either kills the cell by damaging its nucleus or other vital organelles, or it alters the cell's genetic material such that the cell mutates upon subsequent divisions.

WAYS TO MINIMIZE THE DOSE YOU RECEIVE

Time - minimize the time spent in the vicinity of the radiation source.
Distance - increase your distance from the radiation source.
Shielding - use appropriate shielding between you and the radiation source.

ACTIVITY

Show clip of video on Chernobyl nuclear accident
Discuss the video with the class

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.

Assignment:

Problems #48-53 on pages 737 and 738.
Read pp. 720-726.

Summary/Closing Statement: Today, we discussed the ways in which radiation interacts with biological tissue as well as the relative damage each particular type of radiation can cause. If we apply what we learned yesterday about the penetrating abilities of the different types of radiation, we can get a good idea of which radiation types are the most dangerous to humans. (Use "4 Radioactive Cookies" example) Next time, we'll take a look at some relationships between radioactive decay rate and time, as well as how the measured activity of a source decreases as distance from it increases.

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