Abstract: A numerical control scanning Gamma ray attenuation technique is developed and applied to the study of two phase fluid characteristics on distillation trays. It is sensitive, reliable and quick in measurement. Dispersion densities, integrated clear liquid height, froth height, horizontal dispersion density profiles, perpendicular dispersion density profiles, liquid height gradients, crest over the weir and so on can be measured. Integrated clear liquid height and froth height in the downcomer may also be examined. A "pulse spray" mechanism is proposed to explain the flexion observed pn the density profile of disperson.