  We have demonstrated the feasibility of performing high-frame-rate, fast
neutron radiography of air-water two-phase flows in a thin channel with
rectangular cross section. The experiments have been carried out at the
accelerator facility of the Physikalisch-Technische Bundesanstalt. A
polychromatic, high-intensity fast neutron beam with average energy of 6 MeV
was produced by 11.5 MeV deuterons hitting a thick Be target. Image sequences
down to 10 millisecond exposure times were obtained using a fast-neutron
imaging detector developed in the context of fast-neutron resonance imaging.
Different two-phase flow regimes such as bubbly slug and churn flows have been
examined. Two phase flow parameters like the volumetric gas fraction, bubble
size and bubble velocities have been measured. The first results are promising,
improvements for future experiments are also discussed.
