Measurement exercise 2016 in Bavaria - Upper Franconia / Upper Palatinate

From 20 to 22 September 2016, the Federal Office for Radiation Protection (BfS) and the Federal Police (BPOL) jointly conducted a measurement exercise in the northern and eastern vicinity of Bayreuth. Prior to the measurement exercise, a total of eight measurement areas was selected for possible survey flights. As part of the exercise, five of the selected measurement areas were completely, and two partially, surveyed by helicopter. An area of 700 square kilometres altogether was investigated during a flight duration of 24 hours.

Overview of the areas surveyed by helicopter; a quarry located in the "Fuchsbau" forest compartment west of Tröstau (Echo measurement area) providing the most striking results is additionally marked by a blue circle.

Characteristic features of the region

This region was selected because of the comprehensive radiological surveys [1] on the near-surface distribution of natural uranium and thorium conducted there from the 1950s to 1970s. The results of those surveys can be compared with the recent airborne gamma spectrometry surveys.

Moreover, the region provides the opportunity to investigate whether the Caesium-137 deposited there 30 years ago after the Chernobyl reactor accident can be still detected today from the helicopter.

Besides, flying in the mountainous surroundings of Bayreuth is challenging for the pilot. Various flight procedures were used for the rapid mapping of large measurement areas and were compared with one another..

The measurement results: brief overview

Representation of the results from the measurement flights (specific activity Aw of thallium-208) and the results from the report by Gudden et al. published in 1974 (uranium and thorium deposits highlighted in black and white) [1]

The ambient dose rates (ODL) calculated from the current measurements are mostly within the range of the levels typically occurring in Germany, that is about 100 to 200 nanosieverts per hour. One single locally increased level of 320 nanosieverts per hour was determined in a quarry located in the "Fuchsbau" forest compartment west of Tröstau-Leupoldsdorf. This increase is due to potassium- and uranium-containing minerals exposed in the quarry.

Radiation anomalies identified in radiological surveys during the period from the 1950s to 1970s [1] were confirmed by the airborne gamma spectrometry surveys conducted in 2016. In the same areas, elevated levels of natural radionuclides of the thorium-232 and uranium-238 decay series were detected.

Representation of the results from the measurement flights (ambient gamma dose rate ODL, in nanosieverts per hour)

Only very low levels were determined in almost all measurement areas for caesium-137 deposited on the ground. They were in the range from three to eight kilobecquerels per square metre.

All measurement results were represented on maps as colour-coded dots showing the spatial distribution of the parameters considered. In addition to the ambient gamma dose rate ODL, the specific activities of the natural radionuclides thallium-208 (thorium decay series), bismuth-214 (uranium-radium decay series) and potassium-40 as well as artificial caesium-137 were determined. Values falling below the particular limit of detection were not represented in the result maps.

Characteristics of the measuring areas

The applied flight procedures

The tasks of the measurement teams and the helicopter crews were to jointly determine the measurement area to be surveyed as well as the flight procedure to be applied on site and to create corresponding aeronautical maps during the exercise. This approach was aimed at identifying the most appropriate flight procedure for rapid and efficient gamma spectrometry mapping of an area.

The following flight procedures were available: the search-and-rescue pattern using parallel paths and the Hawk procedure where the centre of the measurement area is evenly approached in a spiral path from the outside towards the inside.

The hawk procedure has proved to be the most appropriate for the high spatial resolution mapping of large measurement areas, considering both aeronautical as well as metrological aspects.

Literature:

[1] H. Gudden, H. Schmid; URAN IN BAYERN Bericht über natürliche Uran-Vorkommen in Bayern insbesondere über die mit Bundesmitteln geförderte Uran-Prospektion in Bayern 1956 – 1974; Bayerisches Geologisches Landesamt; München, November 1974 (Report on natural uranium deposits in Bavaria, in particular on federally funded uranium prospection in Bavaria 1956-1974)