Gamma ray tomography
Gamma ray tomography is a non-invasive imaging technique primarily used to characterize multiphase flows within industrial processes. Utilizing gamma radiation attenuation, this technique allows for visualization and detailed analysis of the internal structure and dynamics of materials flowing through pipelines or vessels.
Background
Gamma ray tomography experienced substantial advancements starting in the 1990s, notably driven by research conducted at the University of Bergen, Norway. The university pioneered high-speed gamma-ray tomography setups optimized for studying complex multiphase flows, establishing itself as a leader in industrial tomography research.A significant development occurred with the second-generation gamma ray tomography system, collaboratively designed by the University of Bergen and for the Saskatchewan Research Council. Delivered in 2016, this advanced unit significantly enhanced real-time imaging capabilities, capturing up to 100 frames per second with improved spatial resolution. This unit has since become integral to SRC's Pipe Flow Technology Centre, facilitating advanced analysis of slurry pipeline dynamics and predictive modeling of multiphase flows.
Operational principle
Gamma ray tomography operates based on gamma-ray densitometry, governed by Beer–Lambert's law:Here, is the measured intensity, is the source intensity, is the build-up factor, is the linear attenuation coefficient, and is the path length between the source and detector.
According to this principle, a narrow beam of monochromatic gamma radiation emitted from a source attenuates exponentially when passing through a material, enabling measurement of the material's density distribution along defined paths. Multiple gamma-ray sources and detectors arranged around the investigated material facilitate detailed cross-sectional image reconstruction using algorithms such as the Iterative Least Squares Technique.
The linear attenuation coefficient depends on material properties and photon energy. To optimize measurement accuracy, careful selection of the geometry dimensions and radioactive source with an appropriate photon energy level is crucial. The relative uncertainty in gamma densitometry measurements can be expressed as:
where is the absolute uncertainty of, is the distance between the source and detector, and is the integration time. Since the function has a minimum at, selecting the product close to this value minimizes uncertainty.