The study of the movement of solids in multiphase reactors using radioactive particle tracking is currently limited-to fairly modest particle velocities: because: of, count-rate limitations of the detection system. In this work, this restriction was overcome by increasing the activity of the radioactive tracer, by decreasing the sampling time interval and by modifying,the particle,tracking software to recognize which detectors, were saturated and to use only the data from the remaining unsaturated detectors. Higher tracer activity resulted in lower standard deviation of the calculated, tracer. coordinates.