Navigation and service

Go to:

Radon measuring devices

  • Basically, there are two types of radon measuring devices: passive radon detectors (which do not need electricity to measure) and electronic measuring devices (which do use electricity).
  • Passive devices are inexpensive and small and used only once. They provide an average value after a long-term measurement and subsequent evaluation in the laboratory.
  • Electronic devices are well-suited for snapshots, too. They can be used several times and usually show the results immediately.
  • BfS provides advice on what to consider depending on the purpose of the measurement.

Three passive and three electronic radon measuring devices Radon-MessgerätePassive and electronical radon measuring devices (examples)

The radioactive gas radon (radon-222) cannot be seen, smelled, or tasted – and is thus rather difficult to detect. However, the radiation produced by the radioactive decay of radon and its decay products (polonium, bismuth and lead) can be easily detected and measured.

Special measuring devices register this radiation on site (e.g. in living and working spaces) and then use the data to determine the concentration of radon.

Types of measuring devices

Passive detectors and electronic measuring devices can be used to measure the radiation emitted by radon and its decay products.

Passive radon measuring devices

Seven passive radon measuring devices Passive radon measuring devicesPassive radon measuring devices (examples)

Passive detectors are small plastic containers that do not require electricity. They emit neither light nor sound. They are merely placed. The measurement result is determined in the laboratory after the end of the measurement period.

Passive radon measuring devices are particularly suitable for long-term measurements in order to find out the average radon concentration in a room over a longer period.

Structure and mode of operation

Passive radon measuring devices typically consist of a special plastic film (detector film) enclosed by a protective housing. Radon from the ambient air can penetrate this protective housing (also referred to as a diffusion chamber). Unlike radon, dust and aerosols (i.e. suspended particles) as well as radon decay products cannot enter the diffusion chamber.

During its radioactive decay, each radon atom emits an alpha particle. If this happens inside the diffusion chamber, and the ejected alpha particle strikes the detector film, it leaves a tiny trace of only a few nanometres on the film. The radon decay products produced during the radioactive decay of radon in the diffusion chamber also produce such traces during their own decay.

A device that records radiation with the help of traces on detector films is also referred to as a “solid-state nuclear track detector”.

Measuring period

A measurement with a passive radon measuring device usually takes place over a longer period (i.e. from several weeks and months to one year).

Evaluation

After completion of the measurement, the detector film is removed from the diffusion chamber in a laboratory. All traces that have accumulated on the detector film over time are counted. The more traces found on the detector film, the more radon there was on site during the measurement period.

In order to visualise the tiny traces on the film, they are enlarged in the laboratory using a chemical or electrochemical etching process: Although still quite small (in the micrometre range), they are now visible and countable under the microscope. The result is always the sum of all traces of decays in the entire measurement period. This summation is also referred to as the “integrating method”.

In the evaluation system of the laboratory, the average radon concentration resulting from the total quantity of traces during the specified measurement period (average value) is stored. Based on the measurement result alone, it is not evident whether there were fluctuations in the radon concentration in the course of the measurements.

Variants

Electret ionization chamberElectret detector (example)

Besides the solid-state nuclear track detectors described here, electret detectors are also used in practice - but less frequently.

In these detectors (also called “electrets” or “electret ionisation chambers”) an electrically charged detector disc made of Teflon is used. The voltage of this decreases minimally with each radioactive decay in the diffusion chamber. At the end of the measurement period, no traces are counted here. Instead, a voltage drop is measured.

Electronic radon measuring devices

Electronic radon measuring devices

Three electronic radon measuring devices Electronic radon measuring devicesElectronic radon measuring devices (examples)

Electronic radon measuring devices require a power supply for the measurements. The measurement result can be read directly on the display or with a computer connected to the measuring device.

Electronic radon measuring devices are particularly suitable for finding out how high the radon concentrations currently are in a room (snapshot) and how they change (e.g. as a result of protective measures or over the course of the day, month, or year).

Structure and mode of operation

The protective housing of electronic radon measuring devices contains the detector, measuring electronics, and a chamber. Radon from the ambient air can enter this chamber. Ambient air can also be actively pumped into the chamber. The ambient air always contains radon because it occurs everywhere in the environment. Unlike radon, dust and aerosols (suspended particles) as well as radon decay products cannot enter the chamber.

The electronic detector in the chamber detects the radiation produced by each decay of radon and its decay products. Electronic detectors use various physical effects for this purpose:

  • Using the photoelectric effect, the radiation releases electrons in the detector chamber of the measuring device. This happens in electronic radon measuring devices with ionisation chambers.
  • In semiconductor materials such as silicon, the radiation generates free charges. The electric field built into the detector directs these charges to the metal contacts and generates a measurable current pulse. This is done in electronic radon measuring devices equipped with semiconductor detectors.
  • Using the luminescence effect, the radiation stimulates certain materials (scintillators) to glow. The optical effects (light flashes) thus created in the measuring chamber are amplified and registered by the detector. This is done in electronic radon measuring devices equipped with scintillation detectors (e.g. a Lucas cell).

Measuring period

Electronic radon measuring devices allow snapshots in the form of a measurement over a rather short period of time. Long-term measurements are also possible.

Evaluation

The effects qualitatively and quantitatively detected by the detectors are recorded in electronic radon measuring devices, converted, and directly shown as radon concentration in the display of the measuring device and/or stored in a file.

Based on a sequence of short measurements, these devices can also be used to determine the radon concentration over time. This allows conclusions to be drawn about daily patterns or the effects of mitigation such as ventilation. However, the shorter the measurement, the larger the measurement uncertainty. In general the measurement accuracy depends not only on the measurement duration but also on the built-in detector.

Possible applications (depending on model)

Electronic radon measuring devices can be operated with a suction pump in order to specifically measure air samples from specific areas that may be radon entry paths (e.g. service pipe penetrations in the floor) or to determine the radon concentration in the soil air using a measuring probe in the ground.

Long-term measurements are also possible. Special attention has to be paid that the power supply to the device is guaranteed over the entire period in order to obtain a reliable measurement result. For a long-term measurement, battery operation is usually dispensed with, and measurements are taken in mains operation instead.

The measurement signal from electronic radon measuring devices can also be used to control ventilation equipment.

In addition to the pure counting of decays to determine the radon concentration, an analysis of the decay energy is also possible – depending on the detector installed. This enables "sorted" measurements that distinguish between the occurrence of radon (radon-222) and the radon isotope thoron (radon-220) and their decay products.

Incidentally, commercially available Geiger counters (colloquial: "Geiger-Müller-counters") are not well suited for determining radon concentrations because they do not specifically measure only the radiation emitted by radon and/or radon decay products as the measuring devices specialising in radon do.

Areas of application

Not every radon measuring device available on the market is suitable for every application. Some measurements also require extensive specialist knowledge. These include measurements to determine radon in soil air, radon in water, or the release of radon from building materials. These measurements are usually reserved for specialists.

In contrast, measuring radon in indoor air is comparatively simple. Depending on the purpose of the measurement, the BfS recommends different measurement methods. However, for reasons of competitive neutrality, the BfS cannot recommend any specific products and/or providers.

In any case, it is advisable for interested consumers to consider which measurement purposes and operating requirements meet their needs before purchasing a measuring device.

Measurement purposes and methods

Determination of the long-term or annual mean value in an indoor roomShow / Hide

Typical criteria for the operation of the measuring device
  • Quiet in operation
  • Suitable for long-term operation
  • Small size so as not to interfere at the installation site
  • Inexpensive as the device cannot be used for other measurement tasks during the measurement period
  • Reliable/fail-safe over the entire measurement period
  • Sufficient (data) storage over the entire measurement period

Radon measuring device on a cupboard in a recreation room. radon measuring deviceRadon measuring devices are small plastic boxes which can be placed all over the room.

Recommendation

Passive radon measuring devices are ideal for long-term measurements: They are noiseless, small, inexpensive, and fail-safe because they do not require electricity. Low power-consuming electronic devices with appropriate battery and storage capacity can also be used for long-term measurements.

Combined measurements are optimal for determining the long-term or annual mean value in an indoor space: An initial measurement with an electronic radon measuring device provides an initial assessment of the situation in order to clarify the immediate need for action. With the help of a subsequent long-term measurement, the annual mean value is determined with a passive radon measuring device.

Permanent observation of the ambient air concentrationShow / Hide

Typical criteria for the operation of the measuring device
  • Quiet in operation
  • Display of the value in order to be able to read both current values and mean values over longer periods of time
  • Time history can be read out via software in order to evaluate one’s own ventilation behaviour
  • Sufficient time resolution with a minimum measurement duration of usually at least one hour
  • Small size so as not to interfere at the installation site
  • Inexpensive as the device cannot be used for other measurement tasks during the measurement period
Recommendation

Electronic radon measuring devices with power supply via mains adapter and direct readout with large display are ideal for permanent observations of radon concentrations in indoor air: They are quiet and easy to read.

Short measurements such as those needed to analyse radon entry paths (sniffing)Show / Hide

Typical criteria for the operation of the measuring device
  • High measuring sensitivity
  • Fast response
  • Direct display of measurement results
  • Active air intake via suction pump
  • Wearable
Recommendation

Wearable electronic radon measuring devices with a sensitive detector and direct readout with display are ideal for short measurements to detect radon entry pathways.

Measurements for monitoring people who spend prolonged periods of time in areas with high radon concentrations (radon-exposed persons)Show / Hide

Typical criteria for the operation of the measuring device

Diffusion chamber Diffusion chamberExample of a passive radon measuring device (Diffusion chamber)

Recommendation

Passive radon measuring devices with a clip to attach the device to clothing are ideal for monitoring people who spend prolonged periods of time in areas with high radon concentrations. For this application, passive radon measuring devices with on-off mode are also available on the market.

Lightweight, wearable electronic radon measuring devices can also be used for the monitoring of people.

Room monitoring and control of room air systemsShow / Hide

Typical criteria for the operation of the measuring device
  • Short measurement intervals (e.g. hourly)
  • Fast response
  • Direct display of current measurement results
  • Interfaces for linking the measurement results with electronically controlled room air systems
Recommendation

Electronic radon measuring devices with alarm threshold and switching outputs are ideal for short measurements for room monitoring and the control of indoor air systems.

Investigation for radon and additional occurrence of thoron (e.g. in buildings with clay plaster)Show / Hide

Typical criteria for the operation of the measuring device
  • Direct display of current measurement results
  • Measurement with an evaluation method that can distinguish between the individual radon isotopes (e.g. via the level of decay energy or the half-life)
  • Ideally, the possibility to measure the radon and thoron decay products produced during the radioactive decay of radon and thoron based on their characteristic decay energy
  • Active air intake via suction pump
Recommendation

Electronic radon measuring devices with a suction pump and a sensitive detector mapping the energy spectrum (e.g. semiconductor detectors) are ideal for measurements to test for radon and additional occurrences of thoron in e.g. buildings with clay plaster.

Measurements of the soil air to determine ground contaminationShow / Hide

Typical criteria for the operation of the measuring device
  • Measurement of high radon activity concentrations possible
  • Device for drawing air into a measuring chamber
  • Suitable for outdoor use
Recommendation

Electronic radon measuring devices with a large measuring range, suction pump, and additional equipment for taking the soil gas sample are ideal for measuring the soil gas to clarify possible radon contamination in the subsoil.

Quality criteria of measuring devices

In order to ensure the quality of the measurement results, measuring devices of any kind should be

  • acquired only if they meet quality requirements
  • operated only if they are regularly checked for their functional capability

This also applies to radon measuring devices. For these, the BfS recommends:

Passive radon measuring devices

Quality criteria for passive radon measuring devices

Seven passive radon measuring devices Passive radon measuring devicesPassive radon measuring devices (examples)

Passive radon measuring devices are used only once. What is purchased is the actual measurement for which such a device is provided; this is returned to the measurement laboratory for evaluation.

Consumers should make sure that the measurement providers carry out quality assurance (i.e. that the evaluation laboratory participates in interlaboratory comparison and proficiency testings or that it is accredited for such measurements by the DAkkS, the German Accreditation Body).

Tip: If measuring laboratories offer radon measurements at the workplace, they must be recognised by the BfS as a "recognised body in accordance with Section 155 Radiation Protection Ordinance". This ensures the quality of the providers. Those providers that have this recognition from the BfS are shown at www.bfs.de/radon-messen. The BfS recommends applying this quality standard to radon measurements in general.

Electronic radon measuring devices

Quality criteria for electronic radon measuring devices

Calibration mark of ar adon measuring device Calibration mark of a radon measuring deviceCalibration mark of a radon measuring device

Electronic radon measuring devices can be used multiple times and permanently.

When purchasing such a device, consumers should make sure that it is calibrated (i.e. that it has been checked whether and to what extent the displayed value deviates from the actual value).

In order to ensure that the measured value is displayed correctly throughout the lifetime of the measuring device, the measuring device should be recalibrated approximately every two years. The background level should also be checked regularly: What does the device show when there is (almost) no radon (e.g. in fresh air)?

Tips and hints for the use of radon measuring devices

How can I recognise a good radon measuring device?

Good passive radon measuring devices have achieved good results in interlaboratory comparison and proficiency testing (i.e. the measurement results obtained deviate from the reference value only within permissible limits).

Good electronic radon measuring devices are optimally suited for the intended use (e.g. they have a sufficient measuring sensitivity (minimum detection limit) and sufficient measuring range). A suitable energy supply (mains adapter for longer and/or stationary measurements, battery for shorter and/or mobile measurements) and data storage capacity are also important criteria. Measuring devices should be also designed for the temperature and humidity conditions at the measurement site. It is important to pay attention to the manufacturer's instructions for calibrating the device.

How can I recognise good providers for radon measurements?

Good providers of radon measurements

  • have a radon continuing education certificate
  • work with calibrated devices (if they use electronic devices)
  • provide understandable guidelines for the installation and handling of passive radon measuring devices
  • document the procedure for determining the radon concentration
  • are accredited for the measurement method used (e.g. by the DAkkS, the German Accreditation Body)
  • are recognised by the BfS if they offer legally required compulsory measurements at workplaces

What do I have to pay attention to when using radon measuring devices?

Read the operating instructions and follow the manufacturer's instructions before unpacking, setting up, and operating a radon measuring device. The radon measuring device should be

  • located at an undisturbed placement area so that you can continue to use the room in the usual way even with the measuring device set up
  • in permanent contact with the room air
  • located away from the heating or window in order to prevent air currents and outside air from influencing the measurement results
  • located at a place which is representative of the use of the room

One such undisturbed placement area could be a bookshelf. Do not cover the radon measuring devices or place it in a closed cabinet. If you are using electric radon measuring devices, ensure that the power supply is on for the entire measurement period.

If possible, the radon measuring device should not be moved during the entire measuring period. However, it is possible to move the device carefully for a short time (e.g. when dusting).

Ideally, each indoor space should be equipped with its own measuring device. If this is not possible, the main common rooms (e.g. the living room, bedroom, children's room, workshop, and kitchen) should be selected as the most important rooms. Traffic areas such as corridors, entrance areas, or sanitary rooms are not considered common rooms.

The highest radon concentrations are typically found in the basements of buildings.

How can I tell whether my radon measuring device is working correctly?

Whether a measuring device is functional and provides correct measurement results is usually difficult for laypersons to recognise.

In the case of passive radon measuring devices, the protective housing (diffusion chamber) should always be intact. For electronic measuring devices, a test in the fresh air provides some indications: If, when used outdoors, the device does not show the expected low values within the average radon concentration in Germany (about 3–31 becquerel per cubic metre) but rather values of over 100 becquerel per cubic metre, this could suggest that the device is contaminated. Possible indications of malfunctions can usually be found in the operating instructions.

Can I measure radon on my own – or would it be better to hire a specialist?

Consumers can set up passive radon measuring devices on their own if they follow the instructions provided. At the end of the measurement period, the measuring devices are returned to the evaluation laboratory of the measurement provider as described in the instructions supplied.

Consumers can also independently set up simple electronic radon measuring devices for long-term measurements and take readings if they follow the instructions.

In order to use more specialised electronic radon measuring devices for specific measurement purposes, it is better for consumers to consult professionals.

Who can help me with a radon measurement?

Experts with further training in radon include radon specialists, radon measurement service providers, and radon experts. The state authorities responsible for protection against radon have also set up information services and radon specialist offices.

Radon measuring devices can be purchased directly from the manufacturer. If measuring laboratories offer legally required compulsory measurements of radon at workplaces, they must be recognised by the BfS as a "recognised body in accordance with Section 155 Radiation Protection Ordinance". This ensures the quality of the measurements. These providers recognised by the BfS can also provide devices for measurements in private rooms.

Read and interpret radon measurement results

Measurements with radon measuring devices have as a result either the radon exposure (in becquerel times hour per cubic metre) or the radon activity concentration (in becquerel per cubic metre); this is often shortened to "radon concentration".

The radon concentration is used to assess the radon situation in indoor spaces: If it is above the reference value of 300 becquerel per cubic metre of indoor air for common rooms and workplaces specified in the Radiation Protection Act, measures to reduce it must be examined.

If a measuring device shows the radon exposure as a result, this result must be divided by the measurement duration in hours in order to calculate the radon concentration.

Frequently asked questions about measurement results

Why does my electronic radon measuring device keep showing “0 becquerel per cubic metre”?Show / Hide

Radon measuring devices measure the radiation produced by the decay of radon and its decay products. Because radon decays randomly, no decay may be registered if the measurement times are short and the radon concentration is too low.

Why does the displayed current measured value of my electronic radon measuring device not change?Show / Hide

Each electronic radon measuring device has a certain sensitivity (i.e. a certain detection capability). This converts the individual measuring pulses registered by the measuring device into the current radon concentration shown in the display.

If the sensitivity is low and only a few individual pulses are generated in the device, the measuring device can display only exactly the concentration values that are assigned to these individual pulses. Only an extension of the measuring time in which more pulses can be registered allows a finer resolution of the concentration values displayed.

More powerful detection devices with high sensitivity show this effect only with extremely short measuring times.

What does it mean if the mean value of the measured values determined by my electronic radon measuring device shows 1,000 becquerel per cubic metre after only one month of measurement?Show / Hide

If the mean value of the radon concentration is already quite high after about one month, the room in which the electronic radon measuring device is installed will, in all probability, also have an annual mean radon concentration above the reference value of 300 becquerel per cubic metre of room air for common rooms and workplaces specified in the Radiation Protection Act. Reduction measures are highly recommended or even mandatory.

What does it mean if the measured values of the radon concentration rise sharply during the night hours?Show / Hide

If elevated readings can be observed in measurement series with electronic radon measuring devices during the night hours, this is probably because the affected room is used and ventilated only to a limited extent at night. As a result, radon can accumulate there and lead to higher concentrations.

As the simplest and most effective mitigation measure, the room should be regularly ventilated – in such a way that the entire interior air is exchanged after just a few minutes (shock ventilation). If possible, a window can also be left open/tilted in the affected room at night.

Should I take mitigation measures at radon concentrations above 100 becquerel per cubic metre of air?Show / Hide

There is no indication of a threshold below which radon would be harmless. For every 100 becquerel per cubic metre of indoor air with a long-term radon concentration, the risk of lung cancer increases by about 16 per cent.

Therefore, measures to reduce radon concentrations even below the reference value of 300 becquerel per cubic metre of indoor air for common rooms and workplaces specified in the Radiation Protection Act are reasonable as far as this can be achieved with reasonable effort.

What do I do if I receive a result report from my measurement provider certifying a radon concentration of over 300 becquerel per cubic metre?Show / Hide

Various measures help to reduce the concentration of radon in a building and thus protect against exposure to radon. Read more: Protective measures: What can I do? What do I have to do?

Further Information

How can I protect myself from radon?

State of 2024.04.22

How do you rate this article?

Ionising radiationFrequently asked

What is radon?

What radon concentrations are observed in buildings?

How does radon migrate and how does it enter buildings?

All questions

Site information and functions

© Bundesamt für Strahlenschutz