How does a Geiger counter work? Discover its 6 characteristics

Last modified December 2, 2020

Have you ever wondered how a Geiger counter and how do you measure radioactivity? In this article we are going to see how it works in a way that everyone can understand.

What is a Geiger counter?

A meter or Geiger counter-Müller is a device used to measure and detect ionizing radiation.

Homemade Geiger Counter Radioactivity

When the ions that produce these radiations pass through the active volume of the detector they are accelerated by an electric field, producing a current pulse that signals the passage of radiation.

Geiger counters are part of a family of radiation detectors called «gas detectors«. These detectors, as the name suggests, are full of gas (some kind of inert gas at low pressure, over 0.1 atmospheres).

They have an electrode in the center of the chamber and are configured so that there is a electrical voltage between the electrode and the metal wall of the chamber

This is how a Geiger counter works

The moment the radiation hits the gas molecules in the tube, separates electrons from atoms, this process is called ionization. The electron is attracted by the effective charge of the anode and the rest of the atom (a positively charged ion) is thrown towards the wall of the tube. The electron then travels through the wires that make up the electrical circuit and recombines with the ion. One part of the Geiger counter is a device that measures that flow of electrons.

Geiger-Mueller tube

Of course, it is very difficult to measure a single electron, fortunately the instruments should not. At the moment when the electron and ion are accelerated towards the electrode and the walls of the chamber gain Lots of energy Due to the high voltage, they collide with other atoms and suppress electrons in a process called secondary ionization. Those electrons and also ions, meanwhile, cause even more ionizations and so on repeatedly, this amplifies the original signal to a colossal level, up to a point where it can be measured.

The creation of discrete avalanches on a proportional counter

In a Geiger counter, the voltage is so high that the entire gas chamber is ionized, this provides a very high sensitivity to incoming radiation. In other detectors (called ion chamber and proportional counters) the voltage is lower and the gas amplification ratio is also lower; only a few gas atoms are ionized in these detectors. The amplification ratio with increasing voltage is shown in the following graph.

Geiger-Mueller region

To make sense of this graph, trying mainly to understand how a Geiger counter works and some of its limitations, it is useful to know that alpha particles have considerably more energy than beta particles.

Furthermore, it helps to know that the radiation dose is a measure of the proportion of energy that is deposited by radiation on an element, more energy means more dose.

In this way, when we see this graph, we can see that high-energy radiation striking a detector leaves a larger signal than low-energy radiation.

Now look at the right part of the graph, the Geiger-Muller region; In this region, high-energy radiation generates exactly the same signal as low-energy radiation. So we don't have the ability to distinguish between high-energy and low-energy radiation, which means that we don't have the ability to always tell how much radiation dose an individual was exposed to if we only found ourselves measuring with a Geiger counter. This is one reason why not in all cases we have the possibility to use a Geiger counter to measure the radiation dose rate accurately.

If a Geiger counter, among other things, is calibrated to measure the radiation dose rate of radionuclide Cs-137, it will be really useful as long as you try to measure the radiation dose of this nuclide.

So far we have seen how a Geiger counter works in a simple way but it is important to know that these types of radiation meters have drawbacks.

Limitations of Geiger counters

But what if you are trying to measure cobalt 60 (Co-60) radiation?

Well then you are going to have a slight drawback: radiation from Co-60 has twice the energy of Cs-137, so whatever the detector reads it will only be half the actual radiation dose. On the other hand, various radionuclides have lower energy. In such a case, your meter is going to read a higher dose rate than it is, anyway. The bottom line is that A Geiger counter is only going to give an accurate reading of the radiation dose rate if it is measuring the exact same radioactive material with which it was calibrated. Hence, Geiger counters are not in all cases the appropriate instruments for measuring radiation dose rates.

It turns out that there is a type of Geiger tube that is going to give very accurate readings of a wide range of radiation energies, they are known as Geiger energy compensated counters. These are designed to provide a constant reading over a wide range of radiation energies, so if you are using an energy compensated GM detector you can take accurate dose rate readings. If not, it may be better to carry out dose rate measurements with an ion chamber.

One more thing about Geiger counters: They are large general purpose radiation detectors because they have the possibility to measure the alpha, beta and gamma radiation. If you are measuring gamma radiation, you may be more interested in measuring the dose rate (measured in mR / hr or, for really low scenarios, in µR / hr - microR per hour). If you are measuring alpha or beta radiation, then you may be trying to find contamination and you should measure either the counts per minute (cpm) or the counts per second (cps), depending on the type of meter you are using.

Summary of the characteristics of a Geiger counter

  1. Gas-filled detectors (such as Geiger counters and ion chambers) are filled with a gas to which an electrical voltage is applied.
  2. At the moment when the radiation interacts with the gas it causes ionizations, and this small signal is amplified by the electrical voltage. The amplification ratio is voltage dependent.
  3. Ion chambers have the possibility of measuring the difference in radiation energy, for this reason they are special for measuring radiation dose rate.
  4. Geiger counters, on the other hand, have full signal amplification for whatever radiation energy reaches them. For that reason, not in all cases give accurate dose rate readings, mainly if the radiation energy is different from the one that was calibrated.
  5. With the above mentioned, GM energy compensated detectors are designed to help address this issue, now that they offer very accurate dose rates over a wide range of radiation energies.
  6. And in the end, Geiger counters also have the possibility to measure not only the radiation dose gamma (measured in mR / hr or µR / hr), but rather also contamination alpha and beta (measured in cps or cpm).

I hope you liked this basic explanation. If you have fallen short and want to expand your knowledge of how a Geiger counter works, I recommend that you see this wikipedia article.

Do you want to have your own Geiger-Müller counter?

Here is one selection with best-selling Geiger counter kits so that it is easy for you to find the ideal one for you.

Bestseller No. 1
Kedelak DIY Geiger Counter Kit Module Assembled Nuclear Radiation Detector With LCD Display
  • For the detection of 20mR / h-120mR / h of gamma rays and 100-1800 of soft beta ray variables / spots.
  • Equipped with sound and alarm light.
  • Interrupt the output interface, through this interface can connect to the microcontroller, and then display on the LCD screen.
  • Supports most Geiger s: M4011, STS-5, SBM20, J305, etc. (Geiger 330-600V operating voltage can be supported).
  • Supports computer (PC) data acquisition, analysis and Matlab processing.
Bestseller No. 2
ILS - Geiger counter module Kit Miller tube GM tube nuclear radiation detector
  • Safe shipping and tracing
  • For more information or product specifications, read the description below.
Bestseller No. 3
Baugger Diy Geiger Counter Kit - Geiger Diy Counter Kit Module Assembled Nuclear Radiation Detector with Lcd Display
  • ☛ Supports Most Geiger Tubes: M4011, Sts-5, Sbm20, J305, Etc. (330-600V Operating Voltage of Geiger Tube Can Be Supported).
  • ☛ Equipped with Alarm Sound and Light.
  • ☛ Interrupt the output interface, through this interface can be connected to the microcontroller and then displayed on the lcd screen.
  • ☛ for the Detection of 20Mr / H-120Mr / H of Gamma Rays and 100-1800 of Variables / Points of Soft Beta Rays.
  • ☛ Supports Computer (Pc) Data Acquisition, Analysis and Matlab Processing.
Bestseller No. 4
KKmoon DIY Geiger Counter Parts Kit Core Radiation Detector Module with LCD Display
  • 5V power supply or 3 x 1.5V batteries; 4 batteries of 1.2 V; current: 30 mA - 120 mA.
  • For the detection of 20 mR / h / h of 120 mR / h of gamma rays and 100 - 1800 variables / points of the Soft Beta beam.
  • Equipped with sound and light alarm.
  • Disconnect the output interface, through this interface the microcontroller can be connected, and then displayed on the LCD.
  • Compatible with most Geiger tubes: M4011, STS-5, SBM20, J305, etc. (The working voltage of the Geiger tube can be supported from 330 to 600 V).
Bestseller No. 5
DIY Geiger Counter Kit Module Assembled Nuclear Radiation Detector With LCD Display
  • This is a kind of good quality nuclear radiation detection module, plug it in and you can directly measure nuclear radiation. For the detection of 20mR / h-120mR / h of gamma rays and 100-1800 of soft beta ray variables / spots. You can try.
  • For the detection of 20mR / h-120mR / h of gamma rays and 100-1800 of soft beta ray variables / spots.
  • Equipped with sound and alarm light.
  • Interrupt the output interface, through this interface can connect to the microcontroller, and then display on the LCD screen.
  • Supports most Geiger tubes: M4011, STS-5, SBM20, J305, etc. (Geiger tube 330-600V working voltage can be supported).
Bestseller No. 6
KKmoon Geiger Counter Kit Assembled Nuclear Radiation Detector Module
  • For the detection of 20 mR / h ~ 120 mR / h of gamma rays and 100 ~ 1800 variables / turn-off points of soft beta rays.
  • Sound and light alarm.
  • Interrupt the output interface, through this interface can be connected to the microcontroller and then displayed on the LCD.
  • Supports most Geiger tubes: M4011, STS-5, SBM20, J305, etc. (330 ~ 600V working voltage of Geiger tube can be supported.)
  • Compatible with MatLab computer (PC) data acquisition, analysis and processing.
Bestseller No. 7
Kshzmoto Unassembled Geiger Counter Parts Kit Module, Nuclear Radiation Detector with LCD Display
  • 5V power supply or 3 * 1.5V battery; 4 * 1.2V battery, current: 30mA - 120mA.
  • For the detection of 20mR / h-120mR / h of gamma rays and 100-1800 of soft beta ray variables / spots.
  • Equipped with sound and alarm light.
  • Interrupt the output interface, through this interface can connect to the microcontroller, and then display on the LCD screen.
  • Supports most of Geiger tube: M4011, STS-5, SBM20, J305, etc. (Geiger tube 330-600V working voltage can be supported.)
Bestseller No. 9
JISHIYU DIY Module Geiger Counter Kit Miller Module Tube GM Tube Atomic Radiation Detector for Arduino
  • Legal and light alarm.
  • 1 x power cord
  • For detection of 20MR / H ~ 120MR / h of gamma rays and 100 ~ 1800 discount
  • Support MATLAB computer (PC) data acquisition, analysis, and processing
  • Clients using our Geiger Roying to record the video:

Maybe you don't like electronics and gadget so much and prefer buy a more "finished" Geiger counter. If so, here are these options:

GQ GMC-300E-Plus Digital Geiger Counter Nullify Radiation Detector Monitor Beta Gamma Dosimeter Meter Detector Real Time Monitoring Recorder Data Recorder with UK Wall Charger
  • Small Geiger counter mount developed by gQ Electronics USA General indoor and outdoor sensing.
  • Auditory / visual indicator; Dot Matrix LCD screen; real-time recording of data per second to internal flash memory.
  • USB data port for connection to PC / GQ laptop, Geiger counter software.
  • It features large font text modes for easy reading and easier acquisition of information, e.g. CPM, date, time, elapsed time, USV / h, MR / h, etc.
  • Real-time graphing mode provides a real-time display of radiation level changes, to more easily observe radiation changes.
Geiger counter Mueller GQ GMC-320 Plus Geiger Counter Nuclear Radiation Detector Meter Beta Gamma X ray Europe wall charger
  • Portable hand-held Geiger counter developed by GQ Electronics USA
  • Audio / visual indication; Dot matrix LCD display; Real-time per second data recording
  • USB Data port for connection / charging with PC GQ Soft Geiger Counter software
  • Large font and text mode easy reading, maximum data information
  • If the product has a plug you may need a UK plug adapter. If the product has a keyboard, it is UK configuration
GQ GMC-320 + V5 Digital Geiger Counter WiFi Wireless Data Logger Dosimeter Radiation Detector
  • Log data to server via wireless WiFi connection and internal memory at the same time.
  • Built-in WiFi ready, stay connected with the Geiger world map
  • Free online history unlimited data storage and Geiger's Wold map service.
  • Real-time test evaluation, scientific tests on samples such as: building material, hospital radiation therapy for cancer, food, water, indoor / outdoor, X-ray and more.
  • Real-time graphic, text and large font mode (record radiation data and play back later)
Smart Geiger Pro SGP-001 Radiation Meter for Smartphone iOS Andriod Geiger Counter Measure Radiation Counter Radiation Detector Geiger Counter
  • Whether it is synthetic or naturally occurring - too much radioactive radiation is harmful. Not only in nuclear power plants, but also in other areas of everyday life. Life produces radioactive radiation in various concentrations. among others the food, construction and research sector to varying degrees of these rays hit.
  • For example, check the materials of your living spaces (for example, your own mineral collection enamel tiles), clay, some granite, pumice stone, gypsum, slag, bauxite or red mud contains uranium ...
  • Smart Geiger Pro (SGP-001) is 10 times more accurate than the previous FSG-001. SGP-001 is only slightly 13.5 g, size 75x24x10 mm, connected to the headphone jack, the Smartphone in seconds to a complete radiation meter transform.
  • SGP-001 with 10 built-in semiconductor sensors now 10 times more sensitive With previous FSG-001, you can now also measure radioactive radiation in air! radiation measurement: gamma, X-ray - Measurement range: 0.05 ~ 200 mSv / h - Accuracy: <15% - User interface: Smartphone (headphone jack) - Size: 75x24x9.9 mm - Weight: 13.5 g
  • FEATURE: practical, easy to carry, fast and accurate data, reasonable price, no battery required, Personal EMF monitor for smartphone, quick and easy inspector. Compatible with smartphones: iOS 7.0, Andriod 4.3. Check before ordering if you can install the "Smart Geiger Pro" app on your smartphone
RADEX RD1503 + Dosimeter, geiger counter, high precision nuclear radiation detector
  • Outdoor edition, better protected
  • Detection of combined beta, gamma and X-ray radiation.
  • Detection range of 0.05 ~ 9.99 µSv / h (micro sieverts per hour) or millremos
  • Audio alarm, vibration alarm, backlight
  • Precalibrated, accurate (+/- 15%), fast (40 second cycle if low, immediate if high)
GQ GMC-600 Plus Geiger Counter Dosimeter Alpha Beta Gamma XRay LND 7317
  • High sensitivity Pancake Geiger tube lnd 7317 installed
  • Large LCD Screen - Auto Source Large Horizontal and Vertical Screen
  • Built-in flash memory and built-in WIFI
  • Real-time, Unlimited log data log data storage server
  • Rechargeable battery installed and many more ...
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