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How Do Geiger Counters Work?

Updated on May 6, 2013
Geiger counters consist of a tube (probe) that picks up the radiation and sends the information in pulses to the Geiger counter.
Geiger counters consist of a tube (probe) that picks up the radiation and sends the information in pulses to the Geiger counter. | Source

By Joan Whetzel

Geiger counters, a 20th century invention, are used to detect radiation. Before purchasing a Geiger counter or using one its best to be aware of how they work and have a basic understanding of how to operate one.

What Are Geiger Counters?

Geiger counters are a form of particle detector used for measuring ionizing radiation, which is generated through nuclear radiation. Nuclear radiation produces so much heat that the atoms release an electron from their atoms, which makes them ionized (hence the name ionizing radiation). Geiger counters detect and measure alpha particles, beta particles, or gamma rays, each of which produces a pulse current. Unfortunately, Geiger counters cannot differentiate between the types of energy being produced. Today, Geiger counters are used professionally to measure radiation in the fields pf health, physics, industry, and geology to name a few. They can also be used by individuals to test their environment or household items for radioactivity and for the presence of radon. Amateur rock hunters have been known to use Geiger counters to prospect for uranium and other radioactive minerals, though I wouldn't recommend this, for health reasons.

Measurement of Radiation

Geiger counters detect three types of radioactive discharges, collectively known as ionizing radiation:

1. Alpha Particles: the milder form or radiation with the least penetration; it can be stopped with a piece of paper or a few inches of air used as a barrier; found in the nucleus of helium atoms, thorium and uranium.

2. Beta Particles: stronger than alpha particles; can be blocked by barriers made from aluminum and other metals.

3. Gamma Rays: strongest form of the detectable radiations; can penetrate steel barriers that are several inches thick and travel through the air for hundreds of feet; usually generated together with alpha rays or with beta ways.

Geiger counters have a wand or an electric eye containing a tube filled with an inert gas (helium, neon, or argon) which conducts electricity when the free electrons (produced from the ionizing radiation) enter the gas chamber and ionize the gas. The ionized gas transmits a current pulse, which is then displayed either on a digital readout or an analog readout where a swiveling needle displays the radiation level. The visual display is accompanied by audible clicks which increase in rate as the level of radiation increases. Geiger counters can be purchased that will detect only alpha particles, beta particles, or gamma rays. However, the all-purpose Geiger counters are generally preferred because they detect all three types of contamination and provide a dose rate. In addition these multi-purpose Geiger counters tend to be sturdier and lower in cost.

How to Use a Geiger Counter

What You Will Need:

· Geiger counter

· Objects and substances to be tested for radioactivity

The Steps for Using a Geiger Counter:

a) Switch on the Geiger counter. This will activate the anode wire (the probe) and produce a click sound or flash on the digital screen occurring approximately 10 to 20 times per minute, indicating that background radiation is being detected.

b) Pass the tube (a.k.a. the probe or sensor) over the test objects or substances, one at a time. If the object or substance contains any radiation, it will pass through the mica probe covering (looks something like an opaque window) and trigger the gas inside the tube (ionizing the gas).

c) Examine the digital or analog readout and listen for the clicking. Any testing materials containing a radiation level greater than the background radiation will produce a reaction on the meter, indicating that it is radioactive.

d) Count the clicks heard or flashes seen on the digital readout over a 10 to 15 second period and do the math to determine the number of clicks / flashes per minute. This will help establish the level of radioactivity for each material tested.

Geiger Counter Tips:

· Typically, a GM-10 Geiger counter will pick-up a background level of radiation at around Clicks Per Minute (CPM).

· Radiation levels may be considerably higher in basements or in homes with high radon levels.

· GM-10 and GM-45 Geiger counters (which detect alpha, beta, and gamma radiation) can be plugged into a computer serial port (both PC with Windows and Mac), which uses the software included in the package.

· The software collects, chronicles, and displays radiation readings recorded over time, and stores it on the computer.

· The software is a great feature for science fair experiments or for anyone who needs to collect this data as evidence.


Wikipedia. Geiger Counter.

About Geigers. Geiger Counters

Softpedia. How Geiger Counters Work.

Black Cat Systems. Geiger Counter Nuclear Radiation Monitor Detector for Windows and Mac.

Big Site of Amazing Facts. How Does a Geiger Counter Work?

The Geiger Counter

Geiger Counter

Geiger Counter Demonstration

Geiger Counter iPhone App

how to build a geiger counter / radiation detector from household materials


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