Footprint and height corrections for UAV-borne gamma-ray spectrometry studies

Advancements in the development of gamma-ray spectrometers (GRS) have led to small and lightweight spectrometers that can be used under unmanned aerial vehicles (UAVs). Airborne GRS measurements are used to determine radionuclide concentrations in the ground, among which the natural occurring radionuclides K-40, U-238, and Th-232. For successful applications of these GRS sensors, it is important that absolute values of concentrations can be measured. To extract these absolute radionuclide concentrations, airborne gamma-ray data has to be corrected for measurement height. However, the current analysis models are only valid for the height range of 50-250 m. The purpose of this study is to develop a procedure that correctly predicts the true radionuclide concentration in the ground when measuring in the UAV operating range of 0-40 m. An analytical model is developed to predict the radiation footprint as a function of height. This model is used as a tool to properly determine a source-detector geometry to be used in Monte-Carlo simulations of detector response at various elevations between 0 and 40 m. The analytical model predicts that the smallest achievable footprint at 10 m height lies between 22 and 91 m and between 40 and 140 m at 20 m height. By using Monte-Carlo simulations it is shown that the analytical model correctly predicts the reduction in full energy peak gamma-rays, but does not predict the Compton continuum of a spectrum as a function of height. Therefore, Monte-Carlo simulations should be used to predict the shape and intensity of gamma-ray spectra as a function of height. A finite set of Monte-Carlo simulations at intervals of 5 m were used for the analysis of GRS measurements at heights up to 35 m. The resulting radionuclide concentrations at every height agree with the radionuclide concentration measured on the ground

Contextualising Liberal Peacebuilding for Local Circumstances: Unmiss and Local Peacebuilding In South Sudan

In recent literature on international peacekeeping and peacebuilding interventions, attention has been drawn increasingly to local level dynamics and the reciprocal relationships with national conflict dynamics. This article places local social structures and networks at the centre of analysis and action, while unpacking the category of the ‘external actor’. Through a case study of UN civilian peacekeeping support to local peacebuilding in South Sudan, it argues that there are important efforts being made to contextualise peacebuilding activities for local circumstances, notwithstanding significant institutional obstacles limiting the impact of these efforts. It also argues for further empirical scrutiny of if and how international peacebuilders are engaging with the local dynamics of conflict, seeking to improve the understanding of the heterogeneity of and interaction between actors at these levels