What you need to know before proceeding:
- Background radiation - what it is and where it comes from.
- The difference between a count and a rate, and what a Bq is...
- How to perform an accurate count..
What to do:
- Set up the GM Tube and the Counter/Scaler as shown in photo at right.
Ensure the GM tube voltage is set for 400 V.
Note that the display has a decimal place so displays results in
"thousands"... if you just ignore the decimal it gives actual counts.
CAUTION:
Do not press against
the blue plastic mesh screen "window" of the GM tube. Do not allow anything to
enter the mesh (i.e. wires etc.) since the mica window is very delicate -
we've already broken one of these $450 tubes... :-(
- Take a 120 s background count at an "empty" location in the
room. Record the results.
- Count the radiation coming from a lantern mantle and a smoke detector:
a) When testing the lantern mantle, just hold it
over the end of the detector and count for 120 s.
b) When testing the smoke detector, hold the
meter as close as possible to the openings in the metal chamber inside the
smoke detector and count for 120 s.
- Measure the radiation given off by the fluorescent lights, your
laptop, and some other objects you think might be a source of nuclear
radiation. See if you can find any notably radioactive material in
the room.
- Clean up:
leave your GM tube and counter on your desk, return all other objects
to where you got them.
- Homework:
a) Convert all your results to counts per second (Bq) and put in table
form.
b) Compare the activity for each of your measured objects. How
radioactive are these objects? Discuss.
c) Look over these two web pages:
Radioactivity in
Lantern Mantles
How
Ionization Smoke Detectors Work
Do these links explain and/or agree with your results? Discuss.
Explain briefly how a smoke detector works .
d) Research the Geiger-Muller tube... start
here!
i)
Explain how it works.
ii)
Explain how it detects what it detects
(and why it cannot detect other
things...)
iii)
Explain why it is important to place the sample
near the "window" at the
end of the GM tube.
For fun:
How to build your own GM
Tube radiation detector!
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< Click to see settings & connections on Timer/Scaler.
What to hand in:
Answers to the questions.
Each student must do their own report.
Submit them to www.turnitin.com as
instructed in class (on daybook).
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