7D10.10 Geiger Counter


Radioactivity, nuclear physics


Various radioactive objects can be examined using a Geiger counter. Paper, aluminum foil, aluminum plate, and lead plate can be used to block emissions from the objects.



  • [1] Geiger Counter
  • [1] Overhead projector meter
  • [1] Fiestaware piece
  • [1] Trinitite sample
  • [1] Radium watch dial
  • [1] Smoke detector source
  • [1] Smoke detector prop
  • [1] Lantern mantle
  • [1] Cobalt-60 sample
  • [1] Strontium-90 sample
  • [1] Thallium-204 sample
  • [1] Lab stand
  • [1] 90-degree clamp
  • [1] 3-finger clamp
  • [1] Piece of paper
  • [1] Piece of aluminum foil
  • [1] Piece of aluminum plate
  • [1] Piece of lead

Classroom Assembly

  1. Place the source on the bench.
  2. Attach the Geiger counter detector to the lab stand and place it directly over the source.


  1. Attach the Geiger counter to the unity gain buffer on the overhead projection meter (to avoid overloading 1 V full scale survey meter output).
  2. Place the overhead projection meter on the overhead projector. The projection meter reading will vary with time and different sources.

Important Notes

  • Use caution when handling all radioactive sources. Wash hands after handling.
  • The Coleman propane lamp mantle is unsealed. Handle with extreme care.
  • The audio on the Geiger counter can be heard throughout a large lecture hall.
Item Primary Decay Notes
Fiestaware Uranium-238, alpha Bright orange glaze on plate (!) is uranium oxide. Alpha and beta emitters down the decay chain.
Radium watch dial Radium-226, alpha Radium girls painted glowing watch dials for military use and licked the brushes (!) to get a fine point. Alpha and beta emitters down the decay chain.
Smoke detector Americium-241, alpha Some smoke detectors work by detecting ionization of air from radioisotopes. Detected ionization decreases when smoke particles absorb the ions. Alpha and beta emitters down the decay chain.
Propane lantern mantle Thorium-232, alpha Contains hydroxides and nitrates of thorium. Low emissivity in IR and high emissivity in visible wavelengths help enhance lantern glow. Alpha and beta emitters down the decay chain.
Cobalt-60 Cobalt-60, beta and gamma Decay products stable.
Strontium-90 Strontium-90, beta Beta emitters down the decay chain.
Thallium-204 Thallium-204, beta Decay products stable.
Trinitite Various, alpha and beta Glassy rock from first fission bomb tests. Fission bomb isotope plutonium-239.
Electrical shunt tube Krypton-85?,  beta and gamma
Used in electrical power stations to protect equipment from transients or surges. Decay products stable.


  1. Turn on the Geiger counter speaker. The Geiger counter will emit clicks that correspond to radioactive events.
  2. Show the Geiger counter display on the document camera.
  3. Place paper, foil, plate, or lead between the counter and the radioactive source. Ask students if they hear the any difference in the count rate.
  4. Change samples as desired and repeat.
  5. Turn off the Geiger counter.


Additional Resources


  • PIRA 7D10.10, 7D10.12, 7D10.61, 7D30.05


  • Don't attempt this at home!

Last revised

  • 2020


  • The counter is a Ludlum Model 3 Survey Meter.
  • From the manual for this instrument: 3. Description of controls and functions: Range Multiplier Selector Switch is a 6-position switch marked OFF, BAT, X100, X10, X1, X0.1. Turning the range selector switch from OFF to BAT position provides the operator a battery check of the instrument. A BAT check scale on the meter provides a visual means of checking the battery status. Moving the range selector switch to one of the range multiplier positions (X100, X10, X1, X0.1) provides the operator with an overall range of 0-500K counts per minute. Multiply the scale reading by the multiplier for determining the actual reading. AUDIO ON-OFF Toggle Switch in the ON position operates the unimorph speaker, located on the left side of the instrument. The frequency of the clicks is relative to the rate of incoming pulses. The higher the rate is, the higher the audio frequency. The audio should be turned OFF when not required to reduce battery drain. Fast-Slow Toggle Switch provides meter response. Selecting the "F" position of the toggle switch provides 90% of the final reading in 4 seconds. In "S" position, 90% of the final meter reading takes 22 seconds. In "F" position there is fast response and large meter deviation. In "S" position there is a slow response and damped meter deviation.

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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.