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Monitoring of the ambient gamma dose rate
The BfS, being one of the key measuring institutions, operates a national monitoring network on the basis of the Precautionary Radiation Protection Act (StrVG) 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 distributed in a basic pattern of about 20 km by 20 km across Germany. In a radius of 25 kilometres or, respectively, 100 kilometres around nuclear facilities, the network’s density is greater.
Measurment of natural radiation exposure
In routine operation, the Measuring Network measures the natural radiation exposure man is continually exposed to. It is composed of the radiation of the radioactive substances occurring everywhere in the ground (radionuclides), such as uranium, thorium, potassium-40 (terrestrial radiation). 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 natural emitter.
The ODL is determined in the measurand ambient equivalent dose rate and given in the unit microsievert per hour. In Germany, the natural ODL is between 0.05 and 0.18 microsievert per hour, depending on local conditions.
The external radiation exposure at a place is largely constant. 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. For example, the terrestrial radiation is weakened when a snow cover shields part of the radiation of the ground.
The ODL measuring probe measures the ambient radiation levels in a reference height of one metre above the ground. The transmitter of measurement values controlled by a microprocessor stores the values measured by the probe and calculates mean values.
On a daily basis, the measured data determined in situ is automatically transferred to the monitoring network stations. Following a quality assurance procedure (e.g. adjusting by data from defective probes), the data is thus available in IMIS for further analysis and evaluation.
Important early warning function
The ODL Measuring Network is important for emergency planning. The probes are in non-stop measurement operation. In addition to the daily data transmission, the probes are equipped with a notification function. They immediately notify the BfS data centres automatically once the measured radioactivity level exceeds certain thresholds. The BfS experts analyse the reports promptly. 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.
Fast recognition of radioactive contamination in the air
Thus, the ODL Measuring Network has an important early warning function to quickly recognise enhanced radioactive contamination in the air in Germany. If required, it is possible to query the probes every 10 minutes. This puts the BfS experts in a position to obtain nearly real-time information about the dispersion of a radioactively polluted cloud, so that the affected areas and the seriousness of an event can be determined very rapidly. This is a key prerequisite for initiating targeted, timely action to protect the population.
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 forecast, 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 and what are the exposure levels?
- What radionuclides play a role and how high are the activity levels in the environment?
- How high is the resulting current and the 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 damaging effects of radioactivity.
View current measurements online
A map on the ODL-Info website of the BfS depicts the gamma dose rate at ca. 1,800 measuring probes of the BfS radioactivity measuring network as daily average values, averaged over 24 hours. On a daily basis, experts examine the measurements for potential peculiarities and faults due to defective probes and then forward the measurements to the IMIS. Then the measurements on ODL-Info are updated automatically.
European information plattform
All neighbouring countries have similar monitoring 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 issue a timely warning before the radioactivity reaches the German monitoring network.
State of 2016.09.21