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 a Geiger counter 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?

I bought my Geiger counter in a kit several years ago and it was very easy to assemble. Since then it has been working great.

If you want to have yours, 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
GQ GMC300EPLUS COMPLUSE GEIGER DIGITAL Nulcear Counter Nulcear Radiation Detector Monitor Meter Beta Gamma Dosimeter Radiography Data Data Data Rays Monitoring
  • 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.
Bestseller No. 3
F Fityle DIY Geiger Counter Kit Nuclear Radiation Detector Beta Gamma X-ray Test Equipment for Stone
  • Supports computer (PC) data acquisition, analysis and processing.
  • 5V power supply or 3 * 1.5V battery; 4 * 1.2V battery, current: 30mA - 120mA.
  • Supports most of Geiger tube: M4011, STS-5, SBM20, J305, etc. (Geiger tube 330-600V working voltage can be supported.)
  • For the detection of 20mR / h-120mR / h of gamma rays and 100-1800 outside variables / points of the soft beta ray.
  • Equipped with sound and light alarm. Interrupt the output interface, through this interface can be connected to the microcontroller and then displayed.
Bestseller No. 4
Assembled DIY Geiger Counter Kit Weytoll Nuclear Radiation Detector Module with LCD Display
  • It is used to detect 20mR / h-120mR / h gamma rays and 100-1800 soft beta ray variables / spots.
  • Equipped with warning lights and sound. Interrupt the output interface, through this interface can be connected to the microcontroller, and then displayed on the LCD screen.
  • Supports most Geiger tubes: M4011, STS-5, SBM20, J305, etc. (Supports Geiger tube 330-600V working voltage.)
  • Supports most Geiger tubes: M4011, STS-5, SBM20, J305, etc. (Supports Geiger tube 330-600V working voltage.)
  • 5V power supply or 3 * 1.5V battery; 4 * 1.2V battery, current: 30mA-120mA.
Bestseller No. 5
Lepeuxi 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. 6
Sharplace DIY Geiger Counter Kit Nuclear Radiation Detector Radioactive Detector for Marble
  • . For detection of 20mR / h-120mR / h gamma rays and 100-1800 out of soft beta ray variables / spots.
  • . 5V power supply or 3 * 1.5V battery; 4 * 1.2V battery, current: 30mA - 120mA.
  • . Equipped with sound and light alarm. Interrupt the output interface, through this interface can be connected to the microcontroller and then displayed.
  • . Supports most of Geiger tube: M4011, STS-5, SBM20, J305, etc. (Geiger tube 330-600V working voltage can be supported.)
  • . Supports computer (PC) data acquisition, analysis and processing.
SaleBestseller No. 7
Bestseller No. 8
skrskr DIY Geiger Counter Kit Module Assembled Nuclear Radiation Detector With LCD Display
  • Interrupt the output interface, through this interface can connect to the microcontroller, and then display on the LCD screen.
  • For the detection of 20mR / h-120mR / h of gamma rays and 100-1800 of soft beta ray variables / spots.
  • Equo with sound and light alarm.
  • Supports computer (PC) data acquisition, analysis and Matlab processing.
  • Supports most Geiger tubes: M4011, STS-5, SBM20, J305, etc. (Geiger tube 330-600V working voltage can be supported).
Bestseller No. 9
Colcolo DIY Geiger Counter Kit Nuclear Radiation Detector for Him
  • For the detection of 20mR / h-120mR / h of gamma rays and 100-1800 outside variables / points of the soft beta ray.
  • Supports computer (PC) data acquisition, analysis and processing.
  • Supports most of Geiger tube: M4011, STS-5, SBM20, J305, etc. (Geiger tube 330-600V working voltage can be supported.)
  • 5V power supply or 3 * 1.5V battery; 4 * 1.2V battery, current: 30mA - 120mA.
  • Equipped with sound and light alarm. Interrupt the output interface, through this interface can be connected to the microcontroller and then displayed.

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

GQ GMC300EPLUS COMPLUSE GEIGER DIGITAL Nulcear Counter Nulcear Radiation Detector Monitor Meter Beta Gamma Dosimeter Radiography Data Data Data Rays Monitoring
  • 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-500 + Plus - Geiger counting nuclear radiation detector, for X, beta and gamma rays
  • Independent detection mode
  • Continuous monitoring mode
  • Quick read in seconds after power on
  • Accurate and real-time data
  • Display CPM, USV / H, MR / H on one display
GQ GMC-320 + V5-UK Digital Geiger Wireless WiFi Counter Data Wireless Dosimeter Radiation Detector
  • Record data through wireless WiFi connection server and internal memory at the same time.
  • Edifi WiFi ready, keep in touch with Geiger Counter World Map
  • Free history of unlimited online data storage and Geiger Wold map counter service.
  • Real-time evaluation tests, scientific tests on the sample such as: Necessary for the construction of the Hospital Radiation therapy for Cancer Monitoring, food, water, indoor / outdoor, radiography, and more ..
  • Real-time graphic, text and large font mode (recording radiation data and playback again later)
Smart Geiger Pro SGP-001 Radiation Meter for Smartphone iOS Andriod Geiger Counter Measure Radiation Counter Radiation Detector Geiger Counter
  • Smart 001 001.) is 10 times more accurate predecessor fsg SGP Geiger Pro (SGP 001 only 13.5 g is easy, 75 x 24 x 10 mm, Large size, angeschloßen in the headphone jack can transform your smartphone in seconds into a full-fledged injection meter
  • 001 SGP with 10 built-in semiconductor sensors now 10 times delicate. Useful measurement Adjustable to 3/5/10 minutes.
  • With SGP 001 you can now also radioactive injection measure charge in the air.
  • Beam measurement: Gamma, X-ray - Measurement range: 0.05 ~ 200 µSv / h - ehler measurement: <± 15% - User Interface: Smartphone (Headphone Jack) - Size: 75 x 24 x 9.9mm - Weight: 13.5g
  • '' Compatible with smartphones: iOS 7.0, Andriod 4.3. Check before ordering if you can install the application "Smart Geiger Pro on your smartphone
RADEX RD1503 + Outdoor Edition Dosimeter, Geiger Counter, High Precision Nuclear Radiation Detector
  • Updated exterior edition - better protection
  • Combined detection of Beta, Gamma and X-ray radiation.
  • Detection range of 0.05 ~ 9.99 µSv / h (Micro Sieverts per hour) or millirems
  • Audio alarm - vibration alarm - backlight
  • Precalibrated, accurate (+/- 15%), fast (40 second cycle if low, immediate if high)
GQ GMC-600 Plus Geiger Detector 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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