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Monitoring of the ambient gamma dose rate

ODL-INFO - Radioactivity in Germanyhttps://odlinfo.bfs.de provides online monitoring data of radiactivity in Germany

  • The BfS operates a national monitoring network for the large-scale determination of external radiation exposure by continuously measuring the ambient gamma dose rate (ODL).
  • The ODL Measuring Network consists of 1,700 stationary measuring probes in automatic operation across Germany.
  • The ODL Measuring Network has an important early warning function to quickly recognise increased radioactive contamination in the air in Germany.
  • The BfS website https://odlinfo.bfs.de provides online monitoring data.

The BfS, being one of the key measuring institutions, operates a national monitoring network on the basis of the Radiation Protection Act (Strahlenschutzgesetz) for the large-scale determination of external radiation exposure by continuously measuring the ambient gamma dose rate (ODL).

Map of Germany with ODL measuring points ODL-MapODL Measuring Network comprises 1,700 probes nation-wide.

The ODL Measuring Network consists of 1,700 stationary measuring stations in automatic operation that are installed in a grid of about 20 x 20 km across Germany. In a radius of 25 kilometres, respectively, 100 kilometres around nuclear facilities, the network’s density is greater.

Measurement of natural radiation exposure

In routine operation, the Network determines the natural radiation exposure man is constantly exposed to. It is composed of the radiation from radioactive substances occurring everywhere in the ground (radionuclides), such as uranium, thorium, potassium-40 (terrestrial radiation). These are more pronounced in regions with old rock formations (e.g. granite). Therefore, terrestrial radiation is higher in Germany's lower mountain ranges (e.g. Black Forest and Ore Mountains) than in northern parts of Germany and in limestone alps. Among others, radon is one element in the natural uranium-238 decay chain. Being a gas, it diffuses from the ground and enters the biosphere as a natural emitter.

Furthermore, man is exposed to natural radiation originating from space and reaching the Earth’s surface after it has weakened in the atmosphere (cosmic radiation).

ODL is determined in the measurand "ambient equivalent dose rate" and given in the unit "microsievert per hour". In Germany, the natural ODL ranges from 0.05 to 0.18 microsievert per hour, depending on local conditions.

Influence of natural processes on dose rates

External radiation exposure at a place is largely constant. However, two natural processes influence the measured dose rate significantly. Short-term increases of up to about twice the natural level occur when radioactive decay products of the naturally occurring radioactive gas radon are washed out of the atmosphere by precipitation and deposited on the ground.

Snow covering on the ground might reduce the previously measured dose rate considerably, as the snow partly shields terrestrial radiation.

Measurement Data

Probe for measuring the local dose rate (Ortsdosisleistung/ODL) Dose rate probeProbe for measuring the local dose rate (Ortsdosisleistung/ODL)

Dose rate probes, which are normally installed 1 meter above flat grassland, measure the ambient dose rate every ten minutes. Generally every hour, measured data are transferred to the central units of the monitoring network.

They are analyzed using automatic validation procedures. Conspicucous data are checked on workdays. Thus, faulity probes can be identified in time and, if necessary, be replaced.

Important early warning function

The ODL Measuring Network is important for emergency preparedness. The probes are in non-stop measurement operation. In addition to the regular data transmission, the probes are equipped with a notification function. They transfer enhanced data to the central units of the monitoring network as soon as the measured dose rate at one measurement point exceeds the predefined threshold. In case of an internal alert, BfS experts analyse enhanced dose rate data. This ensures that an increase in radiation is detected immediately.

The thresholds take into account the natural local underground, the statistical fluctuations of the detector, as well as long-term fluctuations, e.g. when the ground is covered by snow.

Emergency preparedness - quickly recognise affected areas

In case of an emergency, the ODL Measuring Network helps to quickly recognize increased levels of radioactivity in air. Affected areas with enhanced dose rate levels can be identified quickly. If required, it is possible to query the probes every 10 minutes. This puts the BfS experts in a position to monitor the dispersion of a radioactively polluted cloud almost in real-time. Measured data enable dose assessment procedures for the affected areas.

To be prepared for all scenarios, the installed system enables ODL measurements in an extremely wide range of 0.05 microsievert per hour up to 5 sievert per hour.

Extension of the monitoring network using spectroscopic probes

Probe for measuring the ambient gamma dose rate (Ortsdosisleistung/ODL) ODL-Twin-ProbeTwin-probe for measuring the ambient gamma dose rate in German border area in front of Swiss NPP Leibstadt (left side: spectroscopic probe with intrinsic Lanthanum Bromide detector)

In the vicinity of nuclear installations, about 20 monitoring stations were equipped with additional spectroscopic probes. These probes use Lanthanum Bromide detectors and are able to provide gamma spectra data every 10 minutes.

Using these probes, the nature of enhanced radiation can be identified even during events of only slightly enhanced dose rate. Thus, the early warning function of the monitoring network can be improved. In case of an emergency, the information from these systems provide early helpful information about nuclide mixture.

Forecast models

With the help of forecast models based on weather and release forecasts, the BfS would be able to forecast in the event of a nuclear emergency in Germany how a radioactive cloud would spread in the following three days and what radiation levels man and the environment could be exposed to in the affected areas as a result. In detail, the following information is important:

  • What areas are affected?
  • What radionuclides play a role and how high are the activity levels in the environment?
  • What are the levels tor actual and expected radiation exposure to the population in the affected areas?

The competent federal and Länder authorities could then swiftly decide as to what measures are necessary to protect the population from the harmful effects of radioactivity.

In such situations, the ODL measuring network’s data could be combined quickly with the results of these prognostic calculations. In an emergency, this helps to see whether protection and precautionary measures that had already been recommended, are sufficient.

View current measurements online

ODL-INFO - Radioactivity in Germanyhttps://odlinfo.bfs.de provides online monitoring data of radiactivity in Germany

The BfS website odlinfo.bfs.de provides online monitoring data. Up-do-data are available from an interactive map and from charts of the time evolution of observed dose rate:

  • For one week, respectively, the most up-to-date 1-hour mean values are displayed (some of them not validated). In combination with the information from the precipitation radar system of the German Weather Service, ODL increases because of precipitation may be recognised.
  • For a period of one year, daily mean values are displayed. In winter, time series from measuring points put up in higher elevation often show lower ODL values because of snow.

European information platform

European countries have similar networks for the monitoring of the ambient gamma dose rate. Their data can be retrieved via the European information platform EURDEP (European Radiological Data Exchange Platform). In the event of an accident abroad, these measuring networks too, would provide important information about the emergency incident as well.

State of 2023.02.27

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