Positrons as in situ probes of transient phenomena

Techniques such as positron emission tomography (PET), positron emission particle tracking (PEPT) and positron emission profiling (PEP) are currently used to perform in situ studies of physical and chemical phenomena that occur within chemical reactors and other processing equipment under process conditions. PEPT is capable of measuring the flow patterns inside mixers and fluidized-bed reactors by tracking a labelled particle. Currently a particle as small as 500 mu moving at 0.1 m/s can be continuously located with a resolution of 5 mm. The ability to perform such measurements greatly aids in the development and optimisation of such systems. PET and PEP are being employed to perform measurements of the concentration of molecules labelled by C-11, N-13 and O-15 inside packed-bed reactors. The measured concentration distributions, as a function of position and time, are used as input for mathematical models based on the kinetics of the physical (e.g., diffusion, adsorption) or chemical processes occurring