Areal dosimetry

Radon is said to be the second most common risk factor for lung cancer besides tobacco smoke. A majority of cases could be avoided through easy preventive measures.

Source: Bundesamt für Strahlenschutz

What is radon?

The radioactive inert gas radon is a product of the uranium radium decay chain and can be found naturally in soils and rocks. Uranium and as a consequence also radon can be found in all soils of the earth – although in different concentrations. Thus granitic and volcanic regions show rather high levels of uranium whereas regions where gravel and shell limestone are dominant, the uranium levels are rather low.

Radon is the only intermediate gaseous product of the uranium radium decay chain. It is invisible as well as odorless and tasteless. Radon can penetrate our housing spaces via leakages in the parts of the house which are touching the ground (cracks, joints, piping shafts) and accumulate there. Due to the different conditions of the ground there are core areas with regards to the pollution. It depends on the basic structure of the building whether the concentration of radon is thus also high in the living areas. Leaky old buildings or even houses without base plate are particularly at risk.

Which effects does radon have on health?

Besides tobacco smoke, radon is the most important reason for lung cancer. The radioactive radiation of radon is due to the decomposition of its atom nucleus. Radon forms a series of short-lived decomposition products, which attach themselves to aerosol particles (little particles existing everywhere in the air) and thus reach the lungs via the breathing air. In the lungs they decompose by emitting alpha radiation, which damages especially the sensitive tissue in the bronchial tubes. The higher the concentration of radon in the room air and the longer you stay there, the higher is the risk to come down with lung cancer. However it is possible that years pass until the sickness breaks out.

Thereby it is important to pay attention to the fact that radon and the consume of tobacco mutually strengthen their effectiveness, so that an increased concentration of radon has a much higher effect on smokers. The following graph vividly demonstrates this effect. By means of this illustration you can assess the individual risk to develop a lung tumor due to an increased concentration of radon. The risk for non-smokers is still less than one percent at a radon concentration of 800 Bq/m3.

It was not possible to prove a connection between radon and other cancer types up to now. It is impossible that acute health problems such as headache, bronchitis or asthma are caused by radon.

Statistics taken from: BMJ 2005: S.  Darby et. al.: Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European casecontrol studies

Statistics taken from: BMJ 2005: S. Darby et. al.: Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European casecontrol studies

Where is radon to be found and in which concentration?

The radioactive concentration of radon is specified in the measuring unit ‘becquerel per cubic meter ambient air (Bq/m³). One Becquerel equals one radioactive decay per second.

In Germany the average concentration in flats is at approx. 50 Bq/m³. In about ten percent of the habitable rooms you can find values higher than 100 Bq/m³.

You can get an overview of especially affected regions on the radon-map: For example the radon concentration in the Ore Mountains (Erzgebirge) and in parts of the Bavarian Forest, and also in parts of the Saarland is higher than in many other regions in Germany.

Please note that the maps only show the according average value of a certain region. However it is important to emphasize the big fluctuation range in the different habitable rooms, the values can vary from approx. 10 to 1000 becquerel per cubic meter ambient air. This circumstance can be explained through the diverse consistencies of the ground and other factors, such as the condition of the building and also the ventilation habits of the residents.

It can only be clarified by a measurement if there is problem with radon in a certain building.

Source: Bundesamt für Strahlenschutz

Source: Bundesamt für Strahlenschutz

How is radon measured?

Basically there are various methods to measure the concentration of radon.

The monitoring service lends out specific electronic measuring instruments of the type Canary in order to define the average concentration of radon in the ambient air or in office buildings. The big advantage of these measurement instruments is that they already show continuously measured values during the current measurement. When using passive measurement instruments it often occurs that you only receive the result weeks after completion of the measurement. The measuring instruments are very suitable in order to determine an average value throughout a longer time period. We recommend a measurement period of at least one month during the heating period, in order to get a general outline if there is a problem with radon at all. Since the measuring instruments show only very slow reactions to sudden changes of the radon concentration they are only partly suitable for shorter measurement periods. Thus the significance of the average value of the last day is only of limited significance. However it can be used to examine the effects of ventilation measures.

The handling is rather easy, you only have to insert the batteries and then you can start straight away with the measurement.

The rental price is 24,50 EUR for a time period of four weeks, plus delivery costs of 3,95 EUR. You can also rent the measuring instrument for several months, whereby you have to pay the rental fee again after the course of four further weeks. Please note the rental terms as well as the recommendations on how to perform a measurement.

Download the measurement instructions now! (german only)

Here you can find the order form for the electronic measuring instrument. (german only)

Source: Auswertungsstelle, Helmholtz Zentrum München

Source: Auswertungsstelle, Helmholtz Zentrum München

Recommendations on how to perform a radon-measurement

The biggest source for radon is the surrounding construction underground of a building. In most cases the transport of radon from the soil into the building can be attributed to two reasons: a leak in the building cover and the so-called ‘chimney-effect’.

Warm air which is rising in the house causes a hardly noticeable vacuum of only a few pascals in the lower floors and in the cellar (the atmospheric air pressure is approx. 100 000 pascal), which has a suction effect on radon: cold, radon-bearing air is sucked inside. In the cold time of the year this suction effect increases in the cellar, when the house is heated and the temperature difference between the indoor- and outdoor walls increases. Due to this you can find strong seasonal fluctuations in the concentration of radon: in winter you can generally find a higher radon concentration than in summer. Thus it is only possible to prove a problem with radon during the heating period.

Whether it is possible for Radon to penetrate the house is first of all dependent on the leak tightness of the building towards the underground.

Examples for leaking spots in the outer shell of a building are the following: 

  • Cracks and joints in walls and floors
  • Openings for the implementation of cables and pipes
  • Cellar floors without solid baseplate made of soil or gravel

Due to the before mentioned reasons it is recommended to make the measurements during the heating period. A measuring of this sort can give a first overview on whether there is a problem with radon at all. A measuring in order to receive a general outline should last at least three months in order to compensate short-term fluctuations. The room in which the measuring instrument for radon is to be located should be used as usual and should be ventilated at least once per day. Execute the measurement in the room which is mainly used by you, i.e. bedroom, living-room, children’s room). You should only take measuring actions in the cellar if you should have a room there which is regularly used, i.e. office or bedroom.

The measuring device should be located at a fixed position for the whole time, or you could also place it in the main living-room during the day and in the sleeping-room during the night. The measuring device should not be located close to doors or windows, since the measurement result could be falsified through air streams.

The longer the measuring device stays at the same place, the more precise the measurement result will be. The concentration of radon can suddenly change due to changes in the weather. However the measuring devices only react very slowly to these changes. Due to that it is difficult to execute comparing short-term measurements in different rooms with a single measurement device, in order to find out the main entry of Radon.

In most cases if the measurement is made in offices which are only temporarily used, the measured concentration of radon is too high. Normally the windows are closed when the room is not used and during this time the concentration of radon is increasing. It is possible to avoid this effect by placing the measurement device at a place with a low radon concentration during times outside the utilization period, i.e. in another room with good ventilation.  

Source: Dr. Thomas Haninger, Auswertungsstelle, Helmholtz Zentrum München

Source: Dr. Thomas Haninger, Auswertungsstelle, Helmholtz Zentrum München

Is it possible that Radon comes off construction material?

The emissions of radon coming off construction material are usually insignificant compared to the emissions coming off the construction underground. However there are few exceptions, for instance when natural stones (granite) or burden material out of overburden-piles are used as building material or padding material. In order to eliminate the building material as source of radon it is possible to execute a measurement with a passive local dosimeter. This device is measuring the dose output (dose per time unit) of the gamma radiation of the building material. An increased local dose output is a hint for an increased concentration of natural radionuclides of the uranium radium decay, in the course of which Radon is resulting as decay product. For this purpose the measurement point is offering local dosimeters of the type SC-2, which can be hang-up in contact with the construction material.

Which reference values are to be considered?

After evaluating all available health surveys, the scientific advisory board of the Federal Environment Ministry, the Commission on Radiological Protection, has determined in a statement of May 12th 2005 that a statistical significant increase of lung cancer due to Radon is given in the area from 100 up to 200 Bq/m³.

The European council has determined the guidelines 2013/59/Euratorm in December 2013. In chapter VIII you can find the regulations with regards to the radiation exposure of the population.

In the article 74 – indoor radon exposure – the following has been determined: ‘the member states define national reverence values for the concentration of radon indoors. The reverence value for the activity concentration in the air must not exceed 300 Bq m-3 in the annual average.

In the article 75 – gamma radiation coming off building material – the following has been determined: ‚The reference value for the external exposure in interior rooms through gamma radiation coming off building material is 1 mSv per year in addition to the external exposure outdoors.’

The EURATOM-guideline has to be converted into national right. This means that the reference values mentioned above have yet to be included in the German Radiation Protection Ordinance.

How do I interpret the measurement values?


If the concentration of Radon is measured during the heating period it is likely to receive a high estimated value, meaning that the annual average is very likely below it.

However, it is important to take additional measurements in order to clarify if the yearly average value is really exceeding the reference value, before taking elaborate remediation measures into consideration. Passive dosimeters for radon based on the nuclear track procedure (DIN 25706-1) which can be laid out for a year, are appropriate for this measurement purpose. In Germany this kind of dosimeter is offered by various institutions. The measurement point should be certified and acknowledged by the Federal Office for Radiation Protection.

You can find a list of measurement points which have participated in a cross-validation at the Federal Office for Radiation Protection with their radon dosimeters in the internet (german only).

Local gamma dose

The natural local dose rate of gamma radiation is approx. 0,06 mSv per month. This underground dose is included in the gross measured value of a measurement carried out with a local dosimeter of the type SC-2 and therefore needs to be deducted in order to calculate the share of the dose caused by the building material. The share of the local dose caused by the building material is only exceeding the reference value of 1mSV per year if the monthly gross measurement value of the local dosimeter exceeds 0,14 mSV.

How can I reduce the radon concentration?

The easiest method is a regular and intermittent ventilation of the room. If the ventilation alone is not sufficient, it is important to consider the elimination of leakages. Possible entry points for radon like cracks and joints in the floor and walls, pipe openings but also wiring ducts and pipes should be sealed with materials impervious to radon.

If these actions should also fail to bring success it is necessary to take more complex constructional actions into consideration.

It is especially important to consider the protection against radon already during the new construction of a building. This applies especially for areas where the concentration of radon is known to be high more frequently.

Where can I get information regarding radon and possible remedial actions?

The bavarian regional authorities for environment have founded the so-called ‘radon-network Bavaria’ in cooperation with the ‘Bauzentrum Munich’. Through this network people with expert knowledge in the fields of radon measurement, the prevention of radon in new constructions and also in the execution of renovations due to radon have joined forces. On the homepage of the LfU you can find members of this radon-network, who have absolved an education as ‘radon expert’. 

You can find further information on the following websites (german only):