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Measuring and Units : Is it Radioactive?

With the Measuring Laboratory, students gain a better understanding of radioactivity and radiation. Students are able to visualize what is meant by radiation and background radiation.

geigers

Grade Level
5-12

Disciplinary Core Ideas (DCI, NGSS)
5-PS1-1, 3-5ETS1-2, MS-PS1-1, MS-PS1-4, MS-PS3-2, MS-ETS1-1, MS-ETS1-3, HS-PS1-8, HS-PS3-2, HS-PS4-1, HS-PS4-4, HS-ESS1-2, HS-ESS2-3, HS-ESS3-6

Time for Teacher Preparation
30-60 minutes – Clear the room of any unnatural radioactive sources. Create identifiable “locations” within the room – to correspond to the number of lab groups you will have. Code each of these locations in some way for easy reference.

Activity Time:
30-60 minutes (1 Class Period)

Materials
Use as many Geiger counters as you have available. We will assume for this experiment that you are using Geiger counters which are not calibrated (they may not provide the same readings under the same circumstances). So, you may want to label each Geiger counter with a code number or letter; then, each group can record the code of the Geiger counter being used and use it for future activities.

Number each sample and record which category they fall into in a spreadsheet.

The students love testing the “hotter” items, but having the three categories of objects assures that everyone tests at least two each of clearly radioactive, marginally radioactive (would really need more counting time than available during lab to be sure), and essentially non-radioactive. The point is to have the students struggle with and face the uncertainty concerning whether or not items are radioactive.

Safety

Science and Engineering Practices (NGSS)

Cross Cutting Concepts (NGSS)

Objectives

The key ideas for students to understand upon completing this lab are:


Background
Introductory Information
We live in a radioactive world, as did our earliest ancestors. The radiation in our world comes from many sources – cosmic radiation (outer space), terrestrial sources (the earth), radon in the air, etc. In addition, we live and work in buildings made from materials (stone, adobe, brick, concrete) which contain elements that are naturally radioactive. The amount of naturally occurring background radiation we experience varies, depending upon location.

Background Radiation
Geiger counters will register the presence of some radiation even if you have not placed them near a known radiation source. This is a measure of the background radiation that is always present at a given location. In order to make meaningful measurements of the radioactive nature of specific objects or materials, we will need to know how much radiation is naturally present in the  environment.

The difference between background radiation and the radiation measured near a specific object will give us the level of radiation due to the object. Although background radiation is quite steady on average, you would never conclude that by listening to or watching a Geiger counter. The amount of radiation will appear to vary, depending upon the specific time at which you take a measurement.

The covert theme of this lab is dealing with ambiguity. Because there is background radiation always giving a background signal, and a non-constant signal at that, measuring a sample for a minute or two (with ordinary Geiger counters) just cannot determine with certainty if the sample is weakly radioactive or not.


Teacher Lesson Plan

Traditional
Before beginning, make sure students have some familiarity with the Geiger counter and how it will be used. Predetermine whether measurements are to be made with the “window” on the Geiger tube open or closed. Give students an overview of how and where to set the sensitivity level, etc.

  1. Have the students measure background counts for one minute.
  1. Have each lab group enter the results of all the groups into the proper space on the table you provide.
  1. Have students run a second and third trial and enter only the data for their own group into the table.
  1. Then, have the students enter the data for all of the groups into the table.

NOTE: If you are doing this activity in a one-period time slot, it is difficult to include measurement of background. Thus, most teachers use an average value for background, measured on a previous day. (Background varies little over time.)

Geiger Counter Resources:

How to attach speakers or head phones to a  CD V-700

CD V-700 Instruction and Maintenance Manual

Troubleshooting for your CD-V700

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