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Definition of ODL

The ODL measuring network

Everyone is subject to external radiation exposure caused by natural radioactivity at all times. This is due to natural radioactive substances (radionuclides) such as uranium, thorium and potassium (K-40) contained everywhere in the soil, in building materials and in space.

What do we measure?

The BfS measuring network routinely measures the natural radiation exposure. The measured local dose rate or ambient dose rate (Ortsdosisleistung, ODL) is expressed in microsievert per hour (μSv/h). This value describes the gamma radiation from the ambient air received per hour at a specified location.

The natural ambient dose rate in Germany is roughly between 0.05 μSv/h and 0.18 μSv/h, depending on local conditions. This external radiation exposure remains largely constant. Small and short-term increases occur where radioactive decay products of radon, a natural radioactive gas, are washed out of the atmosphere by precipitation and are deposited on the ground. A reduction of natural radiation is also possible, e.g. when the ground is covered by snow.

Why do we measure?

The ODL measuring network is an essential element of emergency preparedness. If the level of radioactivity measured at two adjacent measuring stations exceeds certain threshold values for a certain period of time, a notification is automatically triggered.

The BfS on-call service team processes and analyses such notifications without delay 24 hours a day, 365 days a year. The BfS team will check to see if there is a natural cause of the ambient dose rate increase or if it is e.g. caused by an accident.

Where do we measure?

The ODL measuring network comprises 1,800 stationary, self-controlled measuring stations which are spread all over Germany in a basic grid of roughly 20 x 20 km. Nuclear installations are surrounded by a much denser grid up to a distance of 100 km from the installations.

Locations of ODL measuring stations

In order to ensure standardised comparability of the measured ambient dose rate values, the measuring probes are positioned at a rather flat and unoccupied area.

The BfS does not only have stationary measuring systems. Mobile measuring systems installed in six vehicles supplement the stationary ambient dose rate measurements. The use of helicopters also makes it possible to perform airborne measurements (aero gamma measurements). This enables us to detect even small-scale distributions.

Nuclear emergency preparedness

The ODL measuring network is a key early warning system to rapidly detect increased levels of radiation caused by radioactive substances in the air in Germany. In the event of a radioactive cloud it would be possible to follow its dispersion almost in real time. This is an essential prerequisite for initiating targeted measures to protect the population within a very short delay.

The importance of an ODL measuring network became clear at the occasion of the Fukushima reactor accident. For Japan the ambient dose rate measurements (which were performed both in the early phase of the release and in the following days) were an important source of information so that they were able to estimate the progression and the impact on the environment. Since Germany is at a large distance from Japan and the concentration of radioactive substances was very low, the ODL measuring network did not register any increase.

Relevant information on www.bfs.de

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