Geiger counters are devices that detect radioactivity, another term for ionizing radiation, the four major types of which include Gamma, X-rays, Beta, and Alpha radiation. Virtually all Geiger counters detect Gamma and X-rays, while some models detect Alpha and Beta radiation as well. Select the navigation button above or click here to learn more About Radiation.
A typical Geiger counter consists of a Geiger-Mueller tube, a visual readout, and an audio readout. The Geiger-Mueller tube or detector is the heart of a Geiger counter. It is a type of ionization chamber that counts particles of radiation. That count is read by the user through a visual readout in the form of a traditional analog meter, or an electronic LCD (liquid crystal display) readout. These meters are available in different units, including mR/hr, or milli-Roentgens per hour (popular in the US and Israel), and ÁSv/hr, or micro-Sieverts per hour (popular in Canada and overseas ).
Most Geiger counters also have an audio readout that sounds one "click" for each particle count. These particles are emitted at random intervals, and a large number of particles produced in a short span of time sound almost like static from a radio. Play this sound file as an example. Geiger counters that have meter readouts in CPM, that is, Counts or Clicks per Minute, mimic the audible clicks in visual form. CPM is the unit normally used to measure Alpha and Beta radiation.
Digital Geiger counters not only offer visual digital readouts on an LCD display, but they typically also have audio ports for external speakers, as will as data ports for readout on computers and data loggers.
In contrast to vintage 1950's civil defense models, modern Geiger counters are built around transistorized, solid state electronics, and are powered by easily replaceable batteries.
Another feature found on some Geiger counters is an open window over the Geiger-Mueller tube. This allows for energy discrimination, that is, the determination of what type of radioactivity the unit is measuring, between Gamma and X-rays that are strong enough to pass right through the housing of the Geiger counter, versus Beta and Alpha radiation, which are too weak to pass through the housing, but can be read through the open window of the detector. Geiger counters don't incorporate any type of switch to discriminate between Gamma, X, Beta, or Alpha radiation, but instead make that distinction by the process described below:
How do I determine the type of radioactivity?
In the course of your readings, be careful not to contaminate the detector with radioactivity by physically touching the radioactive source or by holding the source above the open window of the Geiger counter.
Unless otherwise mentioned, all of our Geiger counters come pre-calibrated from the factory. You should re-calibrate your Geiger counter as often as your regulations require, or in any case, at least once a year. Follow the manufacturer's instructions in the operating manual that comes with your unit for guidance on re-calibration.
Select the navigation button above or click here to learn about some Applications for Geiger counters.