Systematic study of variation in radiation data in cluttered environments

There are many challenges to overcome during nuclear nonproliferation measurements, including a wide variety of clutter sources that may be introduced into a scene during acquisition. The ability to understand how the dissimilarity of various objects, or clutter, obscures a detector's field of view and affects the measured response of the detector improves the input to detection alarm and nuclide identification algorithms. Additionally, having the capability to input clutter variation into radiation transport models would allow for more real-world scenarios to be modeled and understood. Efforts at Oak Ridge National Laboratory have been exploring the ability to determine specific natural background radiation contributions from surroundings, such as buildings, soil, asphalt, and concrete, and use those source terms in large-scale (100+m²) models. The capability to quantify different clutter terms, ranging from humans to large vehicles, allows researchers to inject realistic noise into these models. This work seeks to explore the effects that clutter introduces to quantify the expected signal variation inherent to both controlled and uncontrolled scenarios, specifically how the introduction of clutter into a scene introduces a variation in signals due to the attenuation of naturally occurring radioactive material distributed within the scene or by introducing non-threatening radioactive materials into the scene. Controlled measurements aim to quantify how different types of clutter of varying size and composition affects the response of a radiation detector. Using results from various controlled tests, the systematic effects of clutter and its effect on radiation readings is analyzed.