For the motion is a relative phenomenon,
one, instead of moving the source, may put the sample on
a moving train and sweep it with respect to the source position thus achieving the same effect.
Moreover it will be more efficient from a radiological protection point of view, because the localized source does not create the risk of radiation leaks and environment ionization or radiation pollution.
Speeds of sound are feasible but safety is more important than the science. What must be taken into account firstly, is that the entire experimental setup is shatter-proof, the sample can be easily mounted and some electronic read-out system is foreseen (Doppler effect strongly involved for relative source-target velocities).