This paper presents the application of gamma ray scanning technique to distillation/absorption columns and FCC risers. The flow regime transition, clear liquid height, froth height, crest liquid height over the exit weir on a V-1 type valve tray and downcomer hydraulics were investigated using the scanning device previously developed. The solid distribution and coke deposition were experimentally simulated in a FCC riser simulator by employing a three-dimensional scanning device developed for the present investigation. The success of this investigation should shed a light for quantifying two-phase contact phenomena in various gas-liquid and gas-solid two phase flow system.