[en] Nuclear spectroscopy has been successfully employed to monitor the operation and performance of a number of different pilot plant and production scale mass transfer systems. Unparalleled insights were gained in a few cases that would have been nearly impossible using conventional procedures. An external gamma scanning device is described that was used to obtain direct measurement of packed column, cold trap, and fixed bed concentration/loading profiles. A number of these operating scans are presented to demonstrate the analytical capability and general utility of the method. Current interest is being directed toward the development of a gamma spectroscopy-based process control system