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Uranium mining and processing had been widespread in Central Asia since the mid-1940s. However, with the establishment of the newly independent states in the 1990s, many of the former uranium mining and processing facilities and their associated wastes (dumps and tailings) were abandoned and have since posed a threat to the environment. The fact that the sites were left behind without proper remediation for a long time has led to the uncontrolled spread of radioactive and toxic contaminants in the environment due to landslides or flooding. Knowledge of the exact location of some waste facilities was lost as a result of social disruptions during the 1990s. In order to assess radiological risks and plan and implement adequate, sustainable, and environmental remediation measures, the radiological situation at the uranium legacy sites must be repeatedly mapped with the best possible accuracy in terms of both sensitivity and spatial resolution. In this paper, we present the experimental use of an unmanned aerial vehicle (UAV) equipped with gamma spectrometry systems as a novel tool for mapping, assessing, and monitoring radioactivity at sites affected by uranium mining and processing and other activities related to enhanced natural radioactivity. Special emphasis is put on the practical conditions of using UAV-based gamma spectrometry in an international context focusing on low- and medium-income countries. Challenges and opportunities of this technology are discussed, and its reliability and robustness under field conditions are critically reviewed. The most promising future application of the technology appears to be the radiological monitoring, institutional control, and quality assurance of legacy sites during and after environmental remediation. One-off administrative and logistical challenges of the technology are outweighed by the significant amount of time and cost saved once a UAV-based gamma spectrometry survey system is set up.

<p>In the Central Asian countries of Kyrgyzstan, Tajikistan, Uzbekistan and Kazakhstan, uranium production activities during the Soviet era have led to a large number of mining legacies. The mining residues can show significant levels of radioactive contamination. Due to the mountainous landscape and the geotechnical conditions at these sites, there is a risk of uncontrolled release of radioactive contaminants into the environment and into cross-border rivers in the region. The situation is exacerbated further by the fact that the countries are prone to natural hazards such as earthquakes, floods, mudflows and landslides. There is an urgent need to map locations, extent and inventory of the contaminated areas in order to be able to support remediation measures and monitor the long-term stability of the remediated legacies.<br>The research project DUB-GEM funded by the German Federal Ministry of Education and Research (grant no. 01LZ106A-C) deals with the development of a UAV-based gamma spectrometry for the exploration and monitoring of uranium mining legacies. The aim of the three-year project is to develop and apply a method that allows regulatory authorities and operators to map contaminated sites rapidly and economically using gamma spectrometers mounted on a UAV (unmanned aerial vehicle). The main tasks of the project are to select and configure suitable detectors, to develop flight, measurement, and data processing strategies and to design an airframe that is ideally suited to carry out the surveys. In this contribution we present the current status of the project, including the design of the UAV prototype, results of the first test and calibration measurements with the selected gamma spectrometers and an outlook on upcoming project activities.</p>

The rapid technical development of drones (UAV; unmanned aerial vehicle) in combination with improved and miniaturised measurement technology enables a cost-effective and fast deployment in post-mining areas. Drone-based geophysical methods can be used to assess post-mining areas to facilitate remediation planning, and to monitor them as part of long-term institutional control in the post-closure phase.A case study of drone-based gamma spectrometric investigations is presented, using the example of legacies of former uranium mining. This type of legacy poses a direct threat to humans and the environment and is still present in the Central Asian countries of Kyrgyzstan, Kazakhstan, Uzbekistan and Tajikistan. In the DUB-GEM project (Development of a UAV-Based Gamma Spectrometry for the Exploration and Monitoring of Uranium Mining Legacies), a drone-based detector system was developed to investigate and monitor these legacies. Two scintillation detectors (CeBr3, NaI) with different crystal volumes can be used alternately. The drone is a custom-built heavy lift system with a maximum take-off mass of 25 kg. The measurement data can be displayed in real time at a ground station. This allows locating hotspots during the survey and planning subsequent detailed measurements. The use of drone-based systems is particularly advantageous in mining regions that are difficult to access and potentially harmful for human health. This paper shows the results of drone-based gamma spectrometry investigations obtained during a measurement campaign in Central Asia in 2021.The drone prototype developed in the project is also capable of carrying other sensors with a payload of up to 7 kg. In subsequent projects, a new department of the Federal Institute for Geosciences and Natural Resources (BGR) -Research and Development Centre for Post-Mining Areas (FEZB) -will investigate the post-mining areas of former lignite mining in Germany using further geophysical sensor technology.

<p>Legacies from uranium mining pose an acute risk to human health and the environment in Central Asia in the countries of Kyrgyzstan, Tajikistan, Uzbekistan and Kazakhstan. This risk is due to the emission of radioactive radiation and the potential contamination of groundwater with radionuclides from the mining residues. A precise knowledge of the location and the contained concentrations of these contaminated sites is necessary in order to obtain an assessment of the hazard and to define areas with the highest remediation priority.</p><p>The Federal Institute for Geosciences and Natural Resources in Germany (BGR) currently carries out the project DUB-GEM (Development of a UAV-based Gamma spectrometry for the Exploration and Monitoring of Uranium Mining Legacies), funded by the German Federal Ministry of Education and Research. Within the project, an Unmanned Aerial Vehicle (UAV) based system is to be developed with which the exploration of contaminated sites can be carried out both with low risk for the measurement technician and quickly and cheaply. The challenge lies in the nuclide-specific determination and differentiation of heap and tailing materials with airborne measurements and scintillation detectors. Due to the low spectral resolution of such detectors, this was not possible for a long time. However, with new technologies, scintillation materials and better computer algorithms there is now a potential to solve the problem.</p><p>In the DUB-GEM project, one of the detectors to be used will be a large volume (600 ml) CeBr3-detector. In preparation for the field campaign in 2021, we calculated theoretical gamma spectra for this detector using Monte Carlo simulations with the program MCNP6. The simulations were done for varying survey parameters such as flying height and speed, as well as for varying source parameters such as nuclide-specific composition and ground distribution of the mining residues to be mapped. The results of the theoretical investigations will be used to design and optimize survey parameters and to estimate minimum detectable activities.</p>