Urban Dose Rate Estimation Using Distributed Static D3S Gamma-Ray Spectrometers

Dose rate monitoring is an important aspect of environmental monitoring, health physics, and radiological response preparedness. Dedicated monitoring networks already exist within the UK; however, distributed gamma-ray spectrometer networks deployed for nuclear-security purposes may provide a supplementary source of environmental radiation information. To estimate dose rates from spectral measurements recorded by these detectors, appropriate dose rate conversion factors are required. In this work, a method for obtaining dose rate conversion factors, based on previously published approaches, is outlined and applied to Kromek™ D3S CsI(Tl) detectors. A reusable codebase for calculating these conversion factors is made available alongside the work. The resulting conversion factors are validated using spectral measurements made with a D3S detector exposed to both 137Cs and 152Eu sources. These conversion factors are then applied to a static subset of D3S detectors deployed around Westminster during the 2017/18 AWE London SIGMA Pilot trial, a nuclear-security dataset that has not been widely analysed for environmental dose-rate estimation. The resulting dose rate estimates show measurable environmental and location-based effects, including spatial variations in urban background radiation and temporal increases associated with rainfall. Analysis across the wider trial period demonstrates the importance of energy calibration stability and indicates that relative temporal changes can be resolved more precisely than absolute dose rates. These results demonstrate that distributed spectrometer networks deployed for nuclear security applications can also contribute to environmental radiation monitoring while highlighting the need for careful treatment of calibration, detector geometry and systematic uncertainty.