Additional Resources
Teacher Notes
Hands-on Investigation: Testing “Everyday”
Items for Radioactivity
Teacher Notes
Introductory description of the investigation:
Students will measure ionizing radiation from “everyday” sources.
These sources of radiation are typically not regulated by the Nuclear
Regulatory Commission, because the amount of radiation they emit is
slightly above background radiation levels. Students will need to
measure the background radiation in the classroom so they can take this
into consideration when evaluating whether the “everyday” sources are
“radioactive” or not.
Student Handout
Student Handout
Solution
Detector Setup
Guide
Detector
Manufacturer Site
Radiation Safety
Poster
HPS Guidelines
Health Physicists
Society
One challenge in all measurements of radioactive processes is that the emission of radiation is
statistical in nature. At any instant a radioactive material may emit more or less than it emits
over an average number of measurements. When small levels of radiation are measured, the
values observed may fluctuate. Your students will be asked to observe the consistency of their
measurements (both background radiation and the everyday sources) and think about how these
fluctuations impact their determination of whether or not a specific material is “radioactive.”
Materials needed:
Radiation monitors, preferably digital radiation monitors are needed. In addition, each group
will need a stop watch. If you have checked out the Nuclear Forensics equipment set, you will
find 8 Vernier Digital Radiation monitors in the kit. Everyday radiation sources supplied by
students and in the classroom are very helpful. You may wish to have the following available for
the students to test:
• Orange Fiestaware plates/cups - pre-1970 era (available on e-bay)
• Thoriated tungsten welding rods – available in welding supply stores
• Uranium glass (marbles and beads are available on e-bay)
• Potassium based salt substitutes (in the grocery store)
• Kitty litter (high Potash content is key)
• Fertilizer (high potash content is key)
Preparing the students:
If students haven’t worked with the radiation monitors yet, consider allotting more time for
students to become familiar with the monitor.
Before handing the monitors to your students, demonstrate to the class how one works.
Show them the monitor and explain the parts. In particular, point out the thin mica window on
the front of the monitor where the small wire grid can be seen (see Figure 1). Emphasize that
this window is VERY fragile and that they should not only avoid poking it, but they should
simply not let anything touch that part of the monitor. If the window is broken, it must be sent
back to the manufacturer for repair. The repairs cost over $90. Should a monitor be damaged
more extensively (for example, if someone places it in a microwave and turns on the
microwave), it will have to be replaced at a cost of $250. If students exercise common sense and
use the detectors as directed in the activities in this curriculum, it is unlikely that the detectors
will be damaged.
Let students know that in the initial investigations, they will simply let the monitor count the
number of ionizing radiation particles that the GM tube registers. Describe to the students the
two counting modes of operation described below.
Total Count Mode: To start, slide the top “Mode” switch downward into the Total/Timer
position. Turn the monitor on by sliding the bottom switch upward into the Audio position.
When the display reads “TOTAL” and “0” or “1” the monitor will start counting radioactivity.
A clicking sound is made every time radiation is detected by the monitor. The digital counter
will also increase each time radiation is detected. After one minute passes, the counter will
make a very loud beep, but will continue to count and click. When they are ready to take
another measurement, they can turn the monitor on and off and repeat the process.
Timed Count Mode: To start, turn the monitor by sliding the bottom switch upward into the
Audio position. Then, slide the top “Mode” switch into the Total/Timer position (if it is
already in this position, slide it out and then back in). The display should show an hour glass
icon on the left and say “SET” on the top right. The number displayed is the length of time for
which it will count. To change the length of time over which they will count, press the “+”
button or “-“ button on the front face of the monitor (near the Mica window). We suggest
counting between 4 and 6 minutes for samples with low activities. When the students are
ready to record data, they should push the “Set” button on the front face of the monitor. The
monitor will beep loudly three times. A clicking sound is made every time radiation is
detected by the monitor. The digital counter will also increase each time radiation is detected.
After one minute passes, the counter will make a series of very loud beeps and the counter will
stop changing. It will, however, continue to click whenever radiation passes through the
Geiger tube. When they are ready to take another measurement, they should slide the mode
switch out of the Total/Timer position and back in. Then repeat the process above.
Procedure:
Distribute to each group a radiation monitor and a few potentially radioactive items they
identified on their “Sources of Radiation” worksheet. Many of the items students bring in will
not be radioactive therefore the measurements should be comparable values to the background
levels. A few items may emit low levels of radiation. In order for students to truly be certain
that these items are emitting low levels of radiation, they will need to know what background
levels are.
Let the class know how you want them to deal with background radiation for this investigation.
Consider the following: It is best if the background levels are measured in the same time frame
and location as they are doing this experiment. If you are limited for time and you have already
completed the “Using a GM Radiation Monitor” investigation, you may use the average
background values measured previously.
During and after the investigation discuss with students the following:
What does it mean if the CPM readings for an object are lower than background?
• Background averages are too high (perhaps the previous experiment had an error)
• Measured CPM is too low (statistical fluctuations had lower background counts than
average during the measurement period, the “source” was large enough to shield the
detector from background)
• If the number of counts is low, is it better to take lots of repeated measurements for 1
minute periods OR one very long measurement?
Tips: Some classes are very engaged with this activity, while other student groups quickly tire
of discovering that everything they thought was radioactive does not produce measureable levels
of ionizing radiation. As students become disengaged, break out the sources from your kit and
distribute various materials to each group such that they get at one item that is clearly above
background. While all of these items are at least slightly radioactive, the Fiestaware is notably
above background. The uranium glass and thoriated welding rods yield measurements above
background, but not as much as the Fiestaware. The remaining items are barely detectable.