  We study the packing fraction of clusters in free-falling streams of
spherical and irregularly shaped particles using flash X-ray radiography. The
estimated packing fraction of clusters is low enough to correspond to
coordination numbers less than 6. Such coordination numbers in numerical
simulations correspond to aggregates that collide and grow without bouncing.
Moreover, the streams of irregular particles evolved faster and formed clusters
of larger sizes with lower packing fraction. This result on granular streams
suggests that particle shape has a significant effect on the agglomeration
process of granular materials.
