Aeroradiometric Measurements in the Framework of the Swiss Exercise ARM19

The flights of the civil part ARM19z of the exercise were performed between June 2nd and June 6th, 2019, covering the recurrent measuring areas around the nuclear power plants Gösgen and Mühleberg, a transversal from Chur to Torre (TI) and an altitude profile over lake Neuchâtel. A short report of the measurement results of ARM19z was placed on the NEOC website https://www.naz.ch/ on June 7th, 2019. The flights of the military part of the exercise ARM19m were performed from September 2nd to September 5th. ARM19m contained source search exercises ver the Spiez military training area, measurements over a prospective reference area at the Thun military training area and measurements in the vicinity of the towns Bulle, Köniz and Vevey. The survey of the environs of the Swiss nuclear power plants Gösgen (KKG) and Mühleberg (KKM) showed no artificial radionuclides outside of the plant premises. The measurements over the towns of Bulle, Köniz and Vevey expanded the database of radiation background over Swiss cities. No unusual values of the radiological quantities were observed. An altitude profile over lake Neuchâtel lead to a revision of a model planned to be used for compensating the influence of airborne radon progeny on the measurement. The deterioration of the energy resolution of several NaI(Tl) crystals used in the RLL detectors continues to downgrade system performance. The analysis of cosmic dose rate data measured over the boiling water reactor of KKM indicates a misinterpretation of high energy photons emitted by the radionuclide 16N using the evaluation software developed by the manufacturer of the RLL system (Mirion). Results of training flights over radionuclide sources demonstrated the advantage of the online identification of radionuclides by the Mirion software and the subsequent alert to the operators. Nevertheless, in cases with several sources of different radionuclides, a visual inspection of the associated photon spectra by operators well acquainted with gammaspectrometry is advisable. First estimates of correction factors for 232Th and 40K activity concentrations were determined from results of current and past measurements to align data evaluations with ARM and Mirion software.