7D10.10 - Radioactivity Demo

Code Number:
Demo Title:
Radioactivity Demo
Natural and Artificial Radioactive Sources
Area of Study:
Modern Physics
Geiger Counter with Special Cord (Cord Has a Low Pass Filter Built In), Radioactive Sources (All), Amplifier, Speaker, and Aero-Ektar Lens.

Video Credit: Jonathan M. Sullivan-Wood

Plug the speaker into the speaker outputs of the amplifier.  Plug the Geiger counter into the auxiliary input of the amplifier.  Turn the amplifier on and turn the Geiger counter on to the desired scale.  Bring the radioactive source close to the counter tube and hear the audible clicks.  The radioactive sources are all labeled except for the large rock.  The radioactivity is concentrated in the dark bands of the rock.

Salt substitute usually contains KCl as the active ingredient.  Natural potassium has a  significant amount of 40K which is one of the most abundant radioactive substances with a half-life of 1.277 billion years.  The counting rate heard should be 3 to 4 times background.

Many of the old style lantern mantles use thorium as the main ingredient.  The most abundant radioisotope of thorium is 232Th with a 14.05 billion year half-life.

Another cheap radioactive source can be purchased at the camera store.  This is an anti-static brush that is used to neutralizes the static charge on dust and then wipe it away.  A small amount of Polonium 210 is used for this neutralization.  This brush with source will last for several years before it needs to be replaced.  This is a very good source to use for the electrostatic discharge of a parallel plate capacitor (5D40.30).

The Aero-Ektar lens is a World War II aerial reconnaissance lens.  To get the high index of refraction needed for a fast lens two elements of the compound lens were doped with Thorium.  To test for radioactivity screw off the back mount part of the lens so that you can get the detector close to the back side of the lens.  A count rate similar to the uranium plate should be heard.

Commonly Found Radioactive Sources:

  1. Smoke Detector = Americium 241.
  2. Salt Substitute = Potassium 40.
  3. Radon = Can be collected on TV screens or with a statically charged balloon.  Common in the Midwest and upper eastern states.
  4. Coleman style Lantern Mantles = Thorium.
  5. Fiesta Ware = Uranium oxide.
  6. Antistatic Brushes = Polonium 210.
  7. Cigarettes = The tobacco plant concentrates Polonium 210 while it is growing and the smoke particles attract and collect Radon in the lungs when smoked.  Double Whammy.
  8. TIG welding rod  =  Thoriated rod = 2% Thorium, good for cloud chamber source.
  9. Thorium impregnated camera lenses = the Aero-Ectar lenses.
  10. Vaseline glass = Uranium oxide and also fluoresces under black light.
  11. Cosmic Rays.
  12. Natural sources = Uranium concentrated in the dark bands from many of the rock collected in the west and southwest.

Other natural sources and their locations:

Autunite - Montebras, France

Carnotite in Sandstone - Montrose Co., Colorado

Cyrtolite, uranium bearing - Bancroft , Ontario , Canada

Ellsworthite (Pyrochore in Calcite) - Hybla , Ontario, Canada

Euxenite - Voandelaka, Madagascar

Fergusonite - Madawaska, Ontario, Canada

Gummite with Uraninite, etc. - near Grafton Center, New Hampshire

Monazite - Elk Mtns., San Miguel Co., New Mexico

Monazite Sand - Idaho

Polycrase-Euxenite - Minas Gerais, Brazil

Samarskite - Mitchell County, North Carolina

Torbernite (Meta-Torbernite) - Mitchell County, North Carolina

Uraninite (Pitchblende) - Great Bear Lake, Northwest Territories

Uraninite - Mitchell County, North Carolina

Uranophane - Ruggles Mine, near Grafton Center, New Hampshire

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