Factors That Affect a Geiger Counter
The Geiger counter, invented in the early 1900s, is an essential tool for safely managing radioactive materials. It's rugged, portable, and simple to operate. As with most equipment, its best performance depends on careful use. Learn its limitations. It won't pick up some forms of radiation. It needs to be aimed at where you expect radiation to be. To keep its readings accurate and its sensitivity sharp, it needs periodic maintenance.
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Description
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A Geiger counter consists of two main physical parts: the Geiger-Muller (G-M) tube and the counter. The tube is sensitive to ionizing radiation. It's encased in a rugged metal cylinder open at one end, usually with a plastic cap. A cable connects the tube to the counter. The counter is a metal box containing the electronics, battery, meter, and speaker. It indicates radiation as a meter dial reading and audible clicks. Some have a digital count display instead of a meter.
Orientation
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The counter is most sensitive to radiation coming into the front, open part of the G-M tube. This helps you locate unknown sources of radiation; by waving the tube part around, you'll notice where the stronger radioactivity comes from. On the other hand, if the tube is aimed incorrectly, radiation sources will be missed.
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Radiation
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Geiger counters are sensitive to ionizing radiation: alpha and beta particles, x-rays, gamma rays, and cosmic rays. Alpha and beta radiation are easily blocked; if they're in a closed cabinet or package, the Geiger counter will detect them poorly, if at all. X-rays and gamma rays penetrate strongly and are easily detected unless shielded by lead or concrete. Infrared, ultraviolet, and neutrons are non-ionizing radiation and won't be picked up by a Geiger counter.
Calibration
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Most Geiger counters, to stay accurate, need to have their electronics calibrated yearly. The Geiger-Muller tube itself needs no maintenance, but the circuits do. During calibration, a technician uses the Geiger counter to measure radioactive sources of precisely known strength. She makes adjustments to the circuit until the counter's readings match the source's intensity. If a unit sees a lot of use and has not been calibrated in several years, it may not be accurate.
Battery
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Portable Geiger counters are battery-powered; many use a single 9-volt battery. If the battery power is low, the unit may be inaccurate or not work at all. Most Geiger counters have a battery test switch that will show you its condition. When in doubt, replace the battery.
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References
- Photo Credit Leonardo Rizzi/creativecommons.org
