II. The German gamma dose rate network
From Intamap
II. The German gamma dose rate network
The protection of the general public against radioactive radiation is an important component of the state precautionary and protective system. To fulfil this task BfS (Federal Office for Radiation Protection) operates the comprehensive Measuring and Information System for Environmental Radioactivity (IMIS). The task of IMIS is to monitor the environmental radioactivity continuously and, in case of an accident, to register rapidly the radioactive contamination of the environment and to assess the radiation exposure to be expected.
All measurement results are registered, evaluated and displayed in IMIS. The results are published and evaluated technically in the annual report "Environmental radioactivity and radiation exposure" of the BMU (Federal Ministry for the Environment, Nature Conservation and Nuclear Safety). In case of an accident the measurement results form the basis for decisions for the benefit of public health and the protection of the environment.
An important measuring facility of the BfS is the nation-wide measuring network for the measurement of external radiation exposure (gamma dose rate, GDR).
Currently the measuring network consists of 2150 stationary measuring points which have been distributed over Germany area-wide in a raster of 15 km x 15 km each.
In routine operation, the natural radiation exposure which man is permanently exposed to is measured with the measuring network. It is composed of the radiation of the radioactive substances occurring overall in the soil (radionuclides) such as uranium, thorium or potassium (K-40) (terrestrial radiation) and of the radiation which has its origin in space and part of which also reaches the earth´s surface (cosmic radiation).
The natural dose rate in Germany is in the range between 50 and 170 nSv/h, depending on local conditions. The external radiation exposure is widely constant at one site. Smaller, short-term increases occur when radioactive decay products of the naturally occurring radioactive noble gas radon are washed out by precipitation and deposited on the ground. The terrestrial radiation is weakened in case it is covered by snow.
Operation of the gamma dose rate network
The permanent operability of the total network for the measurement of the dose rate is ensured by six so-called measuring and service centres. Measuring and service centre sites are:
- inline:Grafik2.jpg Berlin for Brandenburg, Saxony-Anhalt, Saxony and Berlin
- Bonn for Northrhine-Westphalia, Rhineland-Palatinate and Saarland
- Freiburg for Baden-Wurttemberg and Hesse
- Oberschleißheim for Bavaria
- Rendsburg for Hamburg, Schleswig-Holstein and Mecklenburg-Vorpommern
- Salzgitter for Lower Saxony, Bremen and Thuringia
Technical Equipment of the GDR measuring network
The technical equipment of an GDR measuring point consists of the following components
- Measuring probe equipped with G.-M.-counters mounted on a standpipe in the open air
- Earth-run probe cables for the connection ot the probe to the in-house data logger
- Data logger for the registration and transfer of the data to the measuring and service centres requiring an analogue telephone mainline, a 230-V-mains operated and possibly a grounding device.
The measuring point measures automatically and continuously the environmental radiation as gamma dose rate. The measuring probe registers this in a reference height of about 1 m above the ground. The microprocessor-controlled data logger saves the results of the probe, forms mean values of them and transfers these data via the public telephone network to the respective measuring and service centre. For each measuring point site-specific thresholds have been determined. In case they are exceeded a spontaneous message is automatically sent from the measuring point to the measuring and service centres.
The thresholds take into account the level of the environmental radiation in situ which, as shown, predominantly depends on the level of natural radioactivity in the soil and on the intensity of cosmic radiation.
Site criteria and technical information
Premises owned by public authorities, e. g. a school, fire brigade, a reservoir, hospital or airport, are predominantly selected as a site for the installation of an GDR measuring point. A surface as even as possible and without buildings on it must be chosen for the erection of a measuring probe (e. g. lawn, meadow, waste land, but no agricultural crop land). It is avoided to chose large sealed surfaces such as asphaltic or plastered surfaces, as probe sites. The distance to larger objects (buildings, walls, trees) should be such that the measurement is not impaired by the shielding caused by the building development. This requires an undeveloped area of at least 20 m radius around the probe. In the local main wind direction the area should not be developed. Furthermore, there must be no open water reservoirs (e. g. clarifiers) within a radius of 100 m. Between the probe and the data logger a probe cable is laid in a 60 cm deep cable trough. For technical reasons, the length of the cable must be 180 m at maximum.
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