Radioactive tracers Fluidized beds 18 Radioactive particle tracking 14 Bubble columns 12 Fluidization 8 Radioactivity 8 Turbulence 8 Axially aligned detectors 6 Liquids 6 Velocity 6 Atmospheric movements 4 Axial dispersion coefficients 4 Bubble wakes 4 Calcium 4 Calcium alginate beads 4 Chaos theory 4 Chemical reactors 4 Detectors 4 Dynamics 4 Flow of solids 4 Flow regimes 4 Fluid dynamics 4 Hydrodynamics 4 Mixing 4 Operating condition 4 Radioactive Particle Tracking 4 Shear stress 4 Solid motion 4 Solid motions 4 Trajectories 4