Remote detection of alpha and gamma radioactivity using unmanned aerial vehicles

By Dr. Arturo Vargas, INTE Director and Chair of the Working Group 3 of the European Radiation Dosimetry Group, Technical University Catalonia (UPC), Spain

The protection of first responders and the public against radioactive contamination caused by radiological accidents is a matter of enormous importance, especially in the event of terrorist attacks and war scenarios such as the invasion of Ukraine, where radiological facilities and nuclear power plants were affected by the attacks of Russian troops.

Following a nuclear or radiological event, knowledge of how contamination spreads and the area it covers is essential for decision makers who must determine the most appropriate response. In the immediate vicinity of a nuclear or radiological scenario, as well as in case of a large-area ground contamination, and before first responders can enter in the contaminated area, remote detection of alpha and gamma radioactivity by using unmanned aerial vehicles (UAVs) are an excellent solution to protect operators and early responders against contamination and irradiation.

Since the radionuclides in the scenario are usually unknown and there is no optimal detector-UAV configuration, the end-user should analyze the most likely radiological situation in terms of type of radionuclides and dose rates in order to select the most convenient configuration. In such context, spectrometric gamma detectors that can identify radionuclides are recommended to be mounted on the UAVs. “Classical” dose rate monitors such as Geiger-Muller (GM) tubes can be used for a fast screening to evaluate the dose rate map for further analysis with spectrometric detectors. In the European project “Preparedness” spectrometric detectors were adapted and mounted on selected UAVs based on their flight capabilities. The airborne detectors mounted on the UAVs were tested and calibrated in measurement campaigns. In case of a radiological scenario involving dispersion of alpha emitting radionuclides in the environment, the situation is more complex because, there is no available detection system to measure remotely alpha particle at present. In case of such an emergency, the only option is to evacuate the population from the affected areas and then run diagnostics by hand, thus exposing the emergency teams to considerable risk. Even then, the results of emergency field applications are notoriously ambiguous, time consuming and tedious due to the centimetre range of the alpha particles in air. Currently, in the European project “remoteALPHA”, a remote alpha airborne monitor to be mounted in UAVs will be tested in experimental campaigns during the next months.

The Preparedness Project consortium comprises 17 institutions from 12 European countries: Six leading National Metrological Institutions od Designated Institutions, ten external partners, including the European Commission Joint Research Centre (JRC), three private companies and one unfunded partner.

In the project the weight and size of different commercial gamma detectors to be mounted in UAVs, flight endurance, capacity to flight in adverse meteorological conditions, latitude, longitude and altitude position and other auxiliary components, have been analyzed and published in a “Good practice guide on measurement of dose rates and radioactivity concentrations using rotary-wing unmanned aerial detection systems (RWUAS)”.

Based on the size of the carrier and the detector, the developed RWUAS can be divided into three categories: small, medium, and big. Several spectrometric detectors were adapted and mounted on selected UAVs based on their flight capabilities and some of them are shown in Fig. 1. It should be highlighted that one of the medium-sized RWUAS is mounted with an angular sensitivity detector (“source-localizer”). While spectrometers installed on UAVs need to scan the whole affected area to find radioactive sources, the source-localizer detector can identify the direction of a hotspot of radioactivity on ground in real-time and optimizes the scanning process by adjusting the flight path towards the direction of the source position.

The airborne detectors mounted on the UAVs were tested and calibrated in measurement campaigns. In addition, a measurement campaign was carried out in a former uranium mine of to test the developed systems in operational conditions. The flights in operation conditions can be seen here and main results are documented in the paper of Vargas et al. (2021).

Figure 1. Top left: medium DJI Matrice 600 Pro with a NaI detector (“5 cm x 5 cm”)*; Top right: Huge SWISSDRONES SDO 50 UAV with a HPGe detector. Bottom left: DJI Matrice 600 Pro with a CeBr3 detector (“3.8 cm x 3.8 cm”). Bottom middle: small DJI F550 with a CZT 1.5 cm3 detector (mounted on top). Bottom right: Medium DJI Matrice 600 Pro UAV and gimbal with a source locator detector. Note: For cylindrical detectors, the dimensions of the crystals are given in “diameter x height“.

The consortium includes 8 leading European institutions that bring competence, knowledge, and experience to successfully cover all relevant topics addressed by this project such as metrology of alpha particles, radioluminescence, radiological protection, etc.

The principle to measure remotely alpha particle is based on the radioluminescence signal produced by alpha particles in air. The light photons emission is mainly in the wavelength range of ultraviolet A (UV-A) and C (UV-C). A focal length of 424.5 mm was selected to detect these light photons by a system able to mount in a UAV an optical detection based on the PMMA Fresnel lenses with a lens diameter of 452.9 mm. In addition, carbon fibre reinforced polymer frame to reduce weight and ensure the required stability of the UAV was built. Since the system weighs less than 5 kg, the DJI Matrice 600 Pro was selected for this project.

Figure 2. DJI Matrice 600 Pro with the Fresnel lens during preliminary test flight.

The alpha remote airborne system will be tested and calibrated by using dedicated UV LEDs and three Am-241-point sources with activities of 1, 10 and 100 MBq in the recently built DroneLab of the Universitat Politècnica de Catalunya (Spain). Several measurement campaigns will be organized and carried out to analyse the performance of the systems. A selected campaign will also be a demonstration for invited stakeholders.

The use of UAVs to measure the radiological contamination in case of radiological accidents is increasing. In the EU’s Preparedness project, airborne spectrometric detectors carried by UAVs were analysed. Currently, these systems are already commercially available. On the other hand, source-locator and the alpha remote systems need still some developments to be in the market.

This increased use of UAVs for radiological measurement leads us to the need to create a metrological reference system with the objective of guaranteeing the quality of the measurements. Currently, there are no European reference standards for carrying out comparison exercises for this purpose on a regular basis and, therefore, it would be highly advisable to develop such a reference metrological system.

Combining the measured data from airborne detectors mounted in UAVs with other data such as manned airborne detectors, fix detectors, massive citizens networks, carborne detectors and others, to get a more precise picture of the contaminated area, is another file that is recommendable to advance on it. This means that the use of big data analysis and Artificial Intelligence could play an important role in the future.

REFERENCES AND ACKNOWLEDGMENTS

Vargas, A., Costa, D., Macias, M., Royo, P., Pastor, E., Luchkov, M., Neumaier, S., Stöhlker, U., Luff, R. Comparison of airborne radiation detectors carried by rotary-wing unmanned aerial Systems. Radiation Measurements, 145, 106595 (2021). DOI: 10.1016/j.radmeas.2021.106595

”Preparedness” and “remoteALPHA” projects have received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme.

AUTHOR

Dr. Arturo Vargas has a nuclear engineer PhD from the Technical University Catalonia (UPC). He joined the Institute of energy technologies (INTE) of the UPC in 1992, working in the research of radionuclide metrology and instrument development and, becoming the INTE Director in December 2021. Currently, he is in charge of the environmental radioactivity subgroup included in the research group “Dosimetry and Medical Radiation Physics”, part of the “Environmental dosimetry” Working Group 3 of the European Radiation Dosimetry Group (EURADOS). From February 2015, he has been the elected Chairperson of WG3. At the beginning of his research career, Dr. Vargas studied the radiological risk occurred as a result of inhaling the radon progeny. At this stage, he designed and set up equipment for the measurement of radon gas and the characterization of radioactive aerosol particles arising from its disintegration. Furthermore, he designed and set up the radon chamber at the UPC.

Additionally, Dr Vargas has carried out research in the use of unmanned aerial systems (UAS) for radiological emergency scenarios and has been involved in the European project “Metrology for mobile detection ionising radiation following a nuclear or radiological incident – preparedness”. At present, he is working in the European remoteAlpha project “Remote and real-time optical detection of alpha-emitting radionuclides in the environment“