Experiments with the Geiger Counter

You can perform radiation experiments safely with a Geiger Counter.

A Geiger Counter is a portable electronic device that detects ionizing radiation with a small high-voltage vacuum tube. X-rays and the products of radioactive decay, such as alpha particles, beta particles and gamma rays, will set off a Geiger Counter. It registers the amount of radiation as a number on a display and as a series of audible clicks. You can use one to safely conduct experiments involving radiation and radioactivity.

Background Radiation

Every place on Earth has a small amount of natural radiation that comes from the sky and minerals in the ground. Scientists call this background radiation, and you can measure it with a Geiger Counter. Simply turn the Geiger Counter on away from any strong sources of radiation. It will measure the background radiation in units of microsieverts per hour or millirems per hour. Since radioactive decay has a random nature, you will see the measured radiation increase and decrease slightly over time.

Radioactive Decay

Prepare a solution of pure water and .9 percent sodium chloride (table salt) by weight. Obtain a radioactive decay kit from a scientific supply house that has a cesium-137 generator. These are safe enough to ship through the U.S. mail. Fill the generator's syringe with 5 milliliters of the salt water, screw it to the capsule and pump the water though into a small beaker. Immediately begin measuring the water's radioactivity with the Geiger Counter. Record the measured radioactivity rate at every full minute, repeating for 20 minutes. Plot the results on a graph, with the rate on the Y-axis and minutes on the X-axis. You can pour the water down the drain, as it will have extremely low radioactivity after 20 minutes.

Radiation Shielding

Obtain small "button" type radioactive sources from a scientific supply house. Have a variety of materials handy, including paper, wood, steel and if possible, lead. Using a Geiger Counter, measure the radiation from one of the button sources from 8 inches away and write down the results. Place a piece of wood or metal between the source and the counter. Some materials will reduce the radiation greatly, others to lesser degrees. Perform this experiment with each of your radiation sources.

Cosmic Rays

Part of the background radiation, called cosmic rays, comes from stars and the sun. Its intensity changes with altitude. If you live in a mountainous area, obtain a global positioning system (GPS) receiver. With the Geiger Counter, record the background radiation at ground level as in the section above. Drive up a mountain road and take outdoor background radiation readings at 20-meter height intervals using the GPS to measure altitude. Note that the higher you go, the more radiation you receive. The atmosphere acts as a natural shield.

References

• Georgia State University: Geiger Counters
• Cornell University: "Educational Cosmic Ray Experiments with Geiger Counters"

Resources

• North American Technical Services: Radioactive Sources for Instrument Calibration