Radiating from the earthquake-caused nuclear plant accident in Japan is a renewed interest in Geiger counters. People are generally aware that radiation is potentially harmful, can cause cancer and kill. While you likely know a Geiger counter can detect radiation, you may want more detailed information about how the detector works and in what situations it can be used.
Radiation is a process: energy or particles or waves are emitted from a source, and spread out in straight lines in all directions. Geiger counters detect a specific type, which is called ionizing radiation. Ionizing radiation has a higher energy level than non-ionizing, creates electrically unstable atoms, and is the more potentially harmful of the two.
A Geiger counter operates by using a tube filled with an inert gas, which conducts electricity. The gas is usually helium, argon, or neon with added halogens. Running down the middle of the tube is a thin wire or metal plate. When a photon or particle of radiation passes through the tube it makes the gas conductive. The charge is picked up by the wire or plate. This conduction is amplified and emits a current pulse, which can be demonstrated by a needle movement, lamp, electronic display, or the classic clicking sound. Since the gas loses the charge rapidly, the Geiger counter is very sensitive and permits technicians to precisely measure radiation levels.
What we call the Geiger counter today is actually termed the halogen counter. Invented in 1908 by Hans Geiger, the halogen counter version was developed in 1947 by Sidney Liebson and has a longer life while using a lower operating voltage.
What uses does a Geiger counter have? We naturally think of military and nuclear physics applications. Medical professionals can use them to track radioactive tracers and recognize certain diseases. Also, geologists can locate radioactive minerals, and astronomers can measure low level cosmic rays to study the origins of the universe. Today, regular people are using Geiger counters to test whether other people or objects are safe to be around: if food is not safe to consume, water to drink, or a workplace unsafe to be in, for instance.
The common units found on Geiger counters calibrate in the following:
- CPH, or Counts/Clicks Per Hour
- mrem per hour, or millirems per hour, an outdated unit used on older models (now replaced by mSv)
- mSv per hour, or millliseverts per hour.
100 mrem = 1 mSv
Radiation is always present around us and, according to the United States Nuclear Regulatory Commission (NRC), every year the average American receives a dosage of 620 mrem or 6.2 mSv, mostly from natural sources and medical procedures. The US Environmental Protection Agency puts the figure at 360 mrem or 3.6 mSv. In addition to this average background exposure, the NRC requires its licensees to limit the maximum exposure of individual members of the public to another 100 mrem or 1 mSv per year. If the individual works with radioactive materials, that limit is increased to 5000 mrem or 50 mSv annually.
Why does radiation scare people? High doses usually kill cells including organs, and lower doses can alter DNA of cells. Low doses of 100 mSv or less experienced over many years may not result in observable results for a considerable time following exposure. Unfortunately, just as in the cases of higher doses, radiation exposure often leads to many forms of cancer.
Knowing the usual background radiation level is therefore important. It is generally considered that significant cancer risks begin at a level of 12.5 mSv, and the earliest onset of radiation sickness at 750 mSv. Keep in mind that stone, just like all natural products, emits radiation—leading many people to become unnecessarily alarmed at the reading of their granite countertops! Make sure you calibrate your Geiger counter annually if not more frequently.
You are welcome to publish this article for free of charge on your website, newsletter or e-zine provided:
- You do not alter the article in any way,
- You include the entire article, including the About the author section,
- All hyperlinks remain intact,
- You agree to indemnify the author,
- You provide a courtesy copy of your publication to the author.
Jason Kanigan is a technical writer for Global Test Supply, a distributor of test and measurement equipment.