  The unique ability of magnetic resonance imaging (MRI) to provide spatial and
temporal information from optically opaque systems, in three dimensions, make
it an ideal tool to study the internal motion of rapid granular flows. This
paper will focus on the use of ultra-fast velocity compensated MRI measurements
to study particle velocity and density distributions in a granular gas,
produced by vibrating vertically a bed of mustard seeds at 40 Hz. Specifically,
a velocity compensated, double spin-echo, triggered, one-dimensional MRI
profiling pulse sequence was developed. This gives an MRI temporal resolution
of approximately 2 ms and also minimises MRI velocity artefacts. 12 phase
measurements per vibration cycle were used. The data can be used to extract
values of the mustard seed average velocity and velocity propagators
(probability distributions functions) as a function of the phase of the
vibration cycle and vertical height within the cell. The data show strong
transient effects during the impact phase of the vibration. A detailed
discussion of the temporal passage of the individual phase resolved, height
resolved velocity distributions, along with seed velocity propagators at a fix
height from the vibrating base is presented.
