Abstract
When a nuclear or radiological accident results in a release of a radioactive plume, AGS (Aerial Gamma Spectrometry) systems used in many countries, equipped with passive detectors, can help in giving quantitative assessment on the radiological situation (land surface contamination level) only when the air contamination due to the passage of the travelling plume has become negligible. To overcome this limitation, the Italian Institute of Health has developed and implemented a multi purpose air sampling system based on a fixed wing aircraft, for time-effective, large areas radiological surveillance (to face radiological emergency and to support homeland security). A fixed wing aircraft (Sky Arrow 650) with the front part of the fuselage properly adapted to house the detection equipment has been equipped with a compact air sampling line where the isokinetic sampling is dynamically maintained. Aerosol is collected on a Teflon® filter positioned along the line and hosted on a rotating 4-filters disk. A complex of detectors allows radionuclide identification in the collected aerosol samples. A correlated analysis of these two detectors data allows a quantitative measurement of air as well as ground surface concentration of gamma emitting radioisotopes. Environmental sensors and a GPS receiver support the characterization of the sampling conditions and the temporal and geolocation of the acquired data. Acquisition and control system based on compact electronics and real time software that operate the sampling line actuators, guarantee the dynamical isokinetic condition, and acquire the detectors and sensor data. The system is also equipped with other sampling lines to provide information on the concentration of other chemical pollutants. Operative flights have been carried out in the last years, and performances and results are presented.
Highlights
With aerial monitoring systems in use, equipped with large volume NaI(Tl) or high purity germanium (HPGe) detectors, the quantification of the source activity, or the ground contamination, through the analysis of the measured gamma ray spectra, is only possible with the assumption of a source pattern
The lack of quantitative measurements and the derived uncertainty in forecasting the propagation of the radioactive contamination, do not help the emergency management in the most critical phase, i.e. when countermeasures have to be decided in a preventive way and some risk of negative effects is inevitably linked to their enforcement
The provided information is of relative use during the plume phase of an accident when, instead, the measurement of the concentration of gamma emitters in air, the extension of the plume, and in situ environmental and meteorological parameters would be an invaluable help in order to forecast transport and dispersion of the plume and ground contamination levels
Summary
With aerial monitoring systems in use, equipped with large volume NaI(Tl) or high purity germanium (HPGe) detectors, the quantification of the source activity, or the ground contamination, through the analysis of the measured gamma ray spectra, is only possible with the assumption of a source pattern (localized for a point-like source, diffused for ground surface contamination). In case of a more complex situation, when there is no suitable knowledge to model the radiation source, the measurements can only supply qualitative information. This is the case, both in near and far field, when the radioactive plume released by an accident is passing over the country. The lack of quantitative measurements and the derived uncertainty in forecasting the propagation of the radioactive contamination, do not help the emergency management in the most critical phase, i.e. when countermeasures have to be decided in a preventive way and some risk of negative effects is inevitably linked to their enforcement. The provided information is of relative use during the plume phase of an accident when, instead, the measurement of the concentration of gamma emitters in air, the extension of the plume, and in situ environmental and meteorological parameters would be an invaluable help in order to forecast transport and dispersion of the plume and ground contamination levels
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