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Monitoring of the ambient gamma dose rate
- 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 1,800 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, being one of the key measuring institutions, operates a national monitoring network on the basis of the Radiation Protection Act (StrSchG) for the large-scale determination of external radiation exposure by continuously measuring the ambient gamma dose rate (ODL).
The ODL Measuring Network consists of 1,800 stationary measuring stations in automatic operation that are installed in a grid of about 20x20 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 Erzgebirge) 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 noble gas, it diffuses from the ground and enters the biosphere as a natural emitter.
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 noble gas radon are washed out of the atmosphere by precipitation and deposited on the ground.
Dose rates probes, which are normally installed 1 meter above flat grassland, measure the ambient dose rate every ten minutes. Measured data are transferred to the central units of the monitoring network at least four times a day. They are analyzed on workdays and checked for abnormalities to be able to identify and, if necessary, replace faulty probes.
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.
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 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
A map on the BfS website odlinfo.bfs.de of the BfS depicts the gamma dose rate at approx 1,800 measuring probes of the BfS radioactivity measuring network as daily average values, averaged over 24 hours. The measurements are checked daily by experts for potential peculiarities and errors due to defective probes and then forwarded to IMIS. Then the measurements on ODL-Info are updated automatically.
Furthermore, ODL time series of the respective measuring points can be displayed.
For one week, respectively, the most up-to-date 1-hour mean values are displayed (some of them not yet evaluated). 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 preiod of one year, daily mean values are displayed. 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.
State of 2018.04.19