Probe at a height of 40 meters on top of Kiel lighthouse, an extraordinary site within the GDR measuring network

At very exposed locations it is possible that the wind causes the probe to vibrate. The sensitive Geiger-Mueller tubes in the probes may then be triggered to produce additional impulses which are wrongly interpreted as gamma counts. When the data is validated by BfS experts, these values are marked as implausible. They are not reported in the time series.

The BfS is reducing this effect to the best possible extent using reinforced standpipes. The "Kiel Lighthouse" site that has been taken as an example, however, is an about 40 meter high aluminium tower which starts to vibrate easily. In this case there is no remedy available.

Various other reasons, for example maintenance, reconstruction works at the site, faulty data loggers, malfunctioning probes, problems with data transfer and regular tests with a radioactive check source, may also explain data gaps.

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• Information on the interpretation of ODL measuring results

Type "GS07" probe

Many stations are on private property, (e.g. schools and kindergardens) some are in restricted areas. The Federal Office for Radiation Protection is authorized to use the property free of charge for measuring the gamma dose rate. In order to protect the owner's privacy the exact location is not given.

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• ODL probe: Design / Maintenance

GDR probe (on the right) near the decommissioned nuclear power plant in Stade

The measurement network is comprised of a basic grid that homogeneously covers Germany.

The mean distance between stations is between 30 and 40 kilometres. Within a radius of 100 kilometres around nuclear reactors the network is denser with a mean distance of about 20 kilometres between stations. Additional 12 stations are installed in each sector of the 25 kilometres emergency planning zones.

As all active German nuclear reactors are located in the "old" federal states, the monitoring density is higher in western part of Germany.

The Federal Office for Radiation Protection (BfS) provides the data of the ODL measuring network free of charge via a standardised data interface.

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• Data interface

Components of the ambient dose rate: terrestrial, cosmic and artificial radiation

The natural gamma dose rate is composed of

• the radiation from the ground (terrestrial component) and
• the radiation from space (cosmic component).

If large quantities of snow lie on the ground surrounding a ODL probe, the terrestrial component is shielded and the measured gamma dose rate decreases. With the onset of thawing in spring the dose rate increases and returns to the level of the previous year when the snow cover has disappeared.

Emergency response, the function of the measurement network, deals with the artificial component, possibly released by a nuclear accident.

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• ODL values: Impact of external factors

The measured gamma dose rate values are not censored. The data is checked for plausibility in order to find technical defects in the measuring technology. This process serves to ensure that the published data is not distorted by technical defects. The BfS staff only add status information to the published data so that the data can still be verified later on. The measured values are not modified in any case.

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• Information on the interpretation of ODL measuring results

Time series of the increased local dose rate due to the Chernobyl reactor accident at five different measuring stations in Germany Source: source of data: SSK-Volume 7 / Visualisation BfS

The ambient dose rate in Germany is between 0.05 microsievert per hour (at some measuring stations in Schleswig-Holstein and Lower Saxony) and up to 0.2 microsievert per hour in parts of Thuringia, Baden-Württemberg and Bavaria. The average ambient dose rate in Germany is around 0.08 microsievert per hour. The geographical differences result from the different composition of the soil in the respective regions.

In case of rain, local values may be temporarily twice as high, since the naturally occurring radon products are washed out of the atmosphere.

The release of radioactive substances in the Chornobyl (Russian: Chernobyl) reactor accident contributes today roughly 0.001 microsievert per hour to the ambient dose rate in Germany. In some parts of Bavaria that were particularly affected by the Chornobyl fallout the contribution reaches values of 0.01 to 0.02 microsievert per hour at individual locations. Any increase of the local dose rate in Germany due to the Fukushima accident could be detected.

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• Information on the interpretation of ODL measuring results

In addition to the nationwide ODL measuring network operated by BfS , there are indeed other networks that measure the gamma dose rate: The German federal states have measuring networks around their nuclear facilities. The relevant costs are borne by the operators of these nuclear facilities. The offices responsible for the Remote Monitoring of Nuclear Power Plants (KFÜ) publish the values measured on their own internet pages. The values registered by ODL probes within the BfS network that are located in the immediate vicinity of nuclear facilities are included in the databases operated by KFÜ. However, the KFÜ data are also included in BfS ' gamma dose rate database.

All European states operate their own measuring networks in order to monitor the environmental radioactivity. The European Atomic Energy Community stipulates in Article 35 of the EURATOM Treaty that each Member State shall establish the facilities necessary to carry out continuous monitoring of the levels of radioactivity in air, water and soil. All Member States have installed the relevant measuring networks that deliver their data to the central EU database (EURDEP, EUropean Radiological Data Exchange Platform) that is operated in Ispra (Italy). These data are published on the website of the EURDEP server. BfS operates the backup server for the EURDEP database.

Gamma dose rate is the dose per time unit from gamma radiation. It is given in units of Sievert per hour (Sv/h).

The radiation dose measured in a fixed location is the local ambient dose rate and in Germany commonly abbreviated by the acronym ODL.

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• Measuring radioactivity

An adequate site such as a large lawn area is essential for measuring the gamma dose rate

Several factors are important for measuring the environmental radioactivity: the location, the altitude and the measuring period, i.e. the interval of time over which the measured values are averaged. All probe locations within the measuring network comply with specific criteria. This makes it possible to obtain representative measuring results for the relevant region that can be compared with results measured in any other part of Germany:

• Measurements are performed at a height of 1.30 metre with the probe base being at a height of 1 m and the middle of the counter tube 30 cm above.
• Measurements are performed outside, if possible on an open meadow.
• The data is averaged to obtain hourly values.

Apart from this it is important to take the calibration into account: Potential calibrations may refer to the photon equivalent dose (Hx) or to the environmental equivalent dose H*(10). The latter includes a biological assessment factor. H*(10) is the dose value of environmental radioactivity prescribed by the Radiation Protection Ordinance.

A large number of measuring devices is also calibrated to a medium-level dose range with respect to a known emitter. For these relatively high doses the measuring values will be close to the expected value. However, the values obtained when measuring the environmental radioactivity are much smaller. Consequently, the relative errors are much larger so that a measured value may easily deviate by a factor of 2 or 3.

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• Measuring radioactivity

Transmitter within the GDR measuring network

Responsibility for monitoring radioactivity in the environment is shared between the federal government and the states (Länder). BfS operates a nation wide network of approximately 1.700 fixed stations monitoring gamma dose rate and six vehicles measuring nuclide specific soil contamination. In a radiological emergency, measurements can be supplemented with mobile measuring systems on the ground or in the air.

In the North and Baltic Seas, the Federal Maritime and Hydrographic Agency (Bundesamt für Seeschifffahrt und Hydrographie) operates six coastal stations and seven offshore stations in the MARNET network.

Domestic waterways are monitored by the Federal Institute of Hydrology (Bundesanstalt für Gewässerkunde) with 40 stations.

At 48 stations, the German Weather Service (Deutscher Wetterdienst) is monitoring air with on-line filter systems, measuring rain water in radio-chemical laboratories and with the help of gamma spectrometric measurements, a large number of radionuclides can be identified.

The laboratories of the federal states monitor continuously food, animal feed, drinking water and soil.

All these monitoring networks and laboratories are part of the Integrated Measurement and Information System for the Monitoring of Environmental Radioactivity (IMIS). In case of a nuclear accident these systems provide the data for decisions and recommendations to protect man and environment against radioactivity.

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• Measurement systems

Defective measuring station

Stations are not listed on the map if they provide corrupted readings or if they are out of order. In the station list, however, they are still listed with a corresponding status, e.g. unavailable or out of order.

If the measuring station had to be removed for whatever reason, it neither appears on the map nor in the station list.

As soon as possible a new location will then be found nearby in order to close the gap in the measurement network again. This can be a different municipality with different name.

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• Information on the interpretation of ODL measuring results

CTBTO station (on the left) on Schauinsland mountain near Freiburg im Breisgau

Single traces of radiators from the reactor in Japan have also been detected in Germany by aerosol samplers of the CTBTO measurement network (Comprehensive Nuclear-Test-Ban Treaty Organization). Only trace-analysis and air-monitoring systems were sensitive enough to measure those small concentrations of radioactive substances that were transported to Europe.

Radioactive substances transported from Japan to Europe added only an very small fraction to the normal radiation measured in Germany. The activity was of the order of few millibecquerel per cubic meter air (1 Becquerel equals one decay per second). The probes of the gamma dose rate measurement network, although being highly sensitive, cannot detect these low values. Therefore, no increase due to the accident in Japan could be reported by the German gamma dose rate network.

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• Trace analysis worldwide - Analysis of the Fukushima release