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Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538

Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography


Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.

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 Quantum Effects
 Atomic Physics
 Nuclear Physics
 Geiger counter
  video  - Mouse Trap Atomic Bomb
 Daedalon Geiger Counter
 Spark Detector for Alpha Particles
 Diffusion Cloud Chamber
 Larmor Precession/NMR

Geiger counter


To demonstrate radioactivity and the Geiger counter.


A Geiger counter detector is placed near everyday objects containing radioactive elements. The count rate is heard using the audio output connected to the room's sound system.

Geiger counters are used for the detection of alpha and beta (charged) particles. Geiger counters are also used for gamma photon detection, although efficiency is generally low (1%) due to the poor interaction of gamma rays compared with alpha and beta particles. For high energy gammas, the counter largely relies on interaction of the photon radiation with the tube wall material, usually 1–2 mm of chrome steel on a "thick-walled" tube, to produce electrons within the wall which can enter and ionize the fill gas.

Some radioactive objects we provide include "Fiesta" dinnerware with orange-red Uranium Oxide in its glaze, Gas Mantles with Thorium Dioxide (today mantles have yttrium instead), Yellow Uranium Glass Beads, and a Watch Dial with "glow-in-the-dark" Radium paint. See the Environmental Assessment of Consumer Products Containing Radioactive Material report.

Uranium and Thorium decay to many different radioactive elements until they reach a stable isotope of lead. These are known as decay chains and are referred to as the Uranium and Thorium Series. The first decay of each series and its half life are listed below (in the case of Ra, it is actually part of the U-series):
  • 238U ➞ 234Th + alpha (4.5 billion yr)
  • 232Th ➞ 228Rn + alpha + gamma (14 billion yr)
  • 226Ra ➞ 222Rn + alpha (1600 yr)

LUDLUM MODEL 3: The light brown Ludlum Model 3 Survey Meter comes with a Model 44-9 pancake geiger counter probe.

CIVIL DEFENSE V-700: The yellow CD V-700 model no. 6b geiger counter is described on the Civil Defense Museum pages. This UVa unit was manufactured by Lionel Electronic Laboratories, Brooklyn, NY. This unit was designed to detect betas but actually measure gammas.


Make sure the beta shield "window" on the chrome colored Geiger probe is open in order to detect alpha & beta radioactivity. Just "twist" the handle to slide the "window" open/close.

The beta shield "window" in the closed position is used to detect gammas (see Civil Defense Museum for CD V-700).