International measuring exercise 2017 in Switzerland

In order to be able to act swiftly and routinely in the event of an emergency, teams from four countries practised the joint measurement of radioactivity on the ground from a helicopter. Together with colleagues from Switzerland, France, and the Czech Republic, specialists of the Federal Office for Radiation Protection (BfS) and the federal police force (BPol) took part in the international exercise "ARM 17" which was performed in Dübendorf, Switzerland, from 26 June to 30 June. The exercise was organised by the Swiss National Alarm Centre (NAZ).

The main objective of this exercise was to co-ordinate the measuring teams such that they are instantaneously ready for operation across borders in a nuclear emergency.

Measuring areas of the international measuring exercise: The German team flew over the areas highlighted in green and orange; the stars show the hiding places of the radioactive sources to be found in the exercise. Source: NAZ

International measuring exercises as a component of emergency preparedness

Aero-gamma spectrometry exercises are carried out annually in co-operation between the BfS and the federal police force at different locations in Germany. Additionally, the BfS and the federal police force organise international measuring campaigns in co-operation with neighbouring countries.

These exercises are an essential component of the participating countries’ emergency preparedness because it is vital that the cross-national co-operation in the event of an emergency functions effectively without a long timeframe.

Challenge

One particularity of the exercise in June 2017 was the size of the flight area extending between Lake Constance in the north and Lake Zug in the south covering about ten per cent of Switzerland. This area was to be fully mapped radiologically by all participating measurement teams in only one day within a period of six hours. At the same time, two hidden radioactive sources with activities of 19 and 47 gigabecquerel had to be located in the measuring area.

Flight paths and gamma dose rate (ODL) handed over to the organiser immediately after the measuring flights Source: NAZ

Given that the approach to the radiological mapping of the areas overflown and to the search for hidden radiological sources is different, this type of task was extremely challenging in terms of both aeronautical and measurement technology. Mapping usually requires high flying velocity and a large distance between the flight paths. Typical distances between the paths are 500 metres up to several kilometres. When searching a source, one usually chooses lower flying velocity and smaller distances between the flight paths. In order to comply with both requirements, a compromise had to be found.

Like in previous exercises, flight procedures with parallel paths (search-and-rescue pattern) were chosen. On the German side a procedure was applied where the helicopter approaches the centre of the measuring area in a spiral from the outside to the inside. With this flight procedure the German team could clearly identify and verify both the radionuclide distribution and the position of the caesium-137 source that was hidden in the measurement area.

Reference measuring areas

Furthermore, two reference measuring areas had to be flown in previously defined flight procedures during the exercise in June 2017. The first reference area is located in a large valley – the Linthebene –, a nearly plain area except for a small hill. The second, clearly hillier reference area is located in the area of Murgtal-Mürtschenalp.

Subsequently, the data measured by the measuring teams in the respective reference areas was compared in order to ensure a uniform standard of quality of the data measured by the helicopter measuring teams involved. This is vital, since in a real operation, where also measuring teams from neighbouring European countries are requested for support, the measuring flights need to start immediately and deliver reliable data.

At different distances between the flight paths and different altitudes, the thorium distributions in the Linthebene measured by both German teams are comparable. As a follow-up to the exercise, the data will be re-evaluated in more detail in relation to the other measuring teams' results.

Thorium distribution in the reference area Linthebene, determined by using different flight parameters

Results

• The six measuring teams succeeded in mapping a measuring area extending to 2,800 square kilometres within six flight hours only. Thus, the teams have shown that they are capable of acting swiftly in the event of an emergency.
• Both hidden sources were identified by the measuring teams and their geographical position was submitted to the operations centre within the defined exercise period on 27 June 2017. In the German measuring area, a caesium-137 source with an activity of 19 gigabecquerel had been hidden.