Mind over antimatter
15 Jan 2000
Studying what happens inside a piece of process equipment can be daunting, but a technique being used at the University of Birmingham may help. Positron emission particle tracking uses antimatter to follow the paths of single particles inside mixers and reactors.
PEPT uses `tracer' particles that emit positrons (the antimatter equivalent of an electron). Every time a positron meets an electron, the pair annihilate each other with a burst of gamma radiation. A `positron camera', which detects this radiation, can follow the path of the tracer particles.
The Birmingham researchers are using PEPT to study the dispersion of particles inside rotary kilns, such as those used in the cement industry. These are inclined tubes that rotate slowly around their axis. The material inside the kiln is lifted by the rotation, then `slumps' down the surface of the bulk material in an `active layer'. Such kilns do not produce an even quality of product, as the particles take different paths through the kiln. The Birmingham team was attempting to determine whether a particle's path depends on its size.
Experiments with model kilns showed that the particle can only move along the kiln when it is in the active layer. Here, small particles percolate between larger ones, and congregate in the centre of the bed. Moreover, the team adds, the small particles form `a kind of dead zone' at the exit end of the drum, which stops them escaping.
