Optimisation of systems to locate discrete gamma-ray sources within a large search area

Design and development of a detector system and software tool installed on a mobile laboratory to provide both radiological characterisation of large areas and a simple tool for localising radioactive sources

In emergency situations where an immediate response is required to make appropriate decisions by the competent authorities, it is essential to have measurement tools that provide results as accurate as possible in real-time. This paper presents the description of the upgrade of the mobile laboratory of the Radiological Alert Network of Extremadura, focusing on the characterisation of radioactive-contaminated land during emergency situations and the detection of radioactive sources. The detector system is based on two scintillation detectors and a car-borne dose rate monitor. Additionally, a software tool has been developed to collect information from the different devices involved (detectors, GPS, etc) and display it in an intuitive manner. This system has been tested in an area of a former phosphate facility where soils remain contaminated to varying degrees with radionuclides of TE-NORM origin.

Near real-time soil erosion mapping through mobile gamma-ray spectroscopy

Soil erosion has been associated with various negative environmental impacts foremost of which is the potential pressure it could impose on global food security. The poor conditions of our agricultural soil can be attributed to years of unsustainable farming practices occurring throughout history that has placed significant pressure on the environment. Moreover, climate change scenarios indicate further intensification which is likely making prediction and assessment of erosion processes critical for long term agricultural sustainability. This study demonstrates the potential of mobile gamma-ray spectrometry with large volume NaI(Tl) detectors to identify, at high spatial resolution, changes in ¹³⁷Cs soil concentration within the ploughed layer of soil and enabling the soil erosion processes to be quantified. This technique represents a significant advantage over conventional spatially-isolated point measurements such as soil sampling as it offers real time mapping at the field scale. However, spectral signal derived from measurements in the field are highly dependent on the calibration procedure used and are particularly sensitive to source-detector changes such as the presence of a vehicle, ground curvature and soil moisture content. Conventional calibration procedures tend to not consider these potential sources of uncertainty potentially leaving the system vulnerable to systematic uncertainties, especially when 137Cs concentrations are low. This study used Monte Carlo simulations to investigate such changes utilising additional information including a high-resolution digital terrain model. The method was demonstrated on a ploughed site in Scotland, revealing a mixture of tillage and water erosion patterns supported by soil core data. Findings showed that the sites topography had relatively little effect (<10%) on calculated erosion rates, but moisture content could be the determining factor, albeit very difficult to measure reliably throughout a survey.

A 4-point in-situ method to locate a discrete gamma-ray source in 3-D space

The determination of the source position (x,y,z) of a discrete gamma-ray source using peak count rates from four measurement points was studied. We derived semi-empirical formulas to find the position under the condition to neglect attenuation effects by obstacles between the target source and the detector. To validate the methodology, we performed the locating experiments for a (137)Cs small volume source placed at 10 different positions on the floor of a laboratory using the formulas derived in this study. In this study, a portable HPGe gamma spectrometry system with a virtual point detector concept was used. The calculation results for the source positions were compared with reference values measured with a rule. The applicability of the methodology was estimated based on the differences of the results.