Bulk segregation in rotated granular material measured by magnetic resonance imaging

Many mixtures of granular materials tend to segregate when tumbled in a rotating horizontal cylinder, with the different components separating into bands of relatively pure single concentration along the rotational axis. The use of magnetic resonance imaging (MRI) to study concentration variations within a mixture of different sized spheres segregated in this manner indicates a more complicated structure within the bulk than can be observed or even inferred from surface measurements. Moreover, when the rotation speed is reduced and the homogeneous mixed state appears to be restored on the surface, the MRI data reveals that the radially segregated state persists.