Erosion and deposition processes have a critical impact on material lifetime and fuel inventory. The assessment of such effects is therefore of primary importance for the steadystate operation of a reactor-class device fuelled with a deuterium-tritium mixture. The experimental approach to studies of material transport involves spectroscopic methods, surface probes and tracer techniques. The term "tracer" denotes an agent not usually present in the system introduced deliberately in minute quantities. In controlled fusion devices, material migration studies by means of tracer techniques are essential to the assessment of erosion, re-deposition and tritium retention. An important issue at JET is to understand the transport of carbon and its co-deposition with fuel species in shadowed areas of the inner divertor where the massive fuel accumulation has been observed in the past [1]. One way in which this is being done is via injection of 13CH4 and other species at the end of campaigns preceding major shut-downs, followed by detailed ex-situ surface studies of plasma facing components (PFC) retrieved from the torus.