Feasibility of high frame-rate neutron radiography by using a steady thermal neutron beam with 10⁶ n/(cm² s) flux

The feasibility of high frame-rate neutron radiography by using a steady thermal neutron flux on the order of 10⁶ n/(cm² s) was investigated and the application of this technique to fluid visualization was examined. The Kyoto University Research Reactor, whose neutron flux at the imaging plate was 1.2 × 10⁶ n/(cm² s), was used as a neutron source. The imaging system for the high frame-rate neutron radiography with the steady thermal neutron beam was constructed by combining a high sensitivity scintillator ⁶LiF/ZnS:Ag, a high-speed video which could take images with the light intensity of 1.5 lux at the recording speed of 1000 frames/s and an image booster whose gain was about 100. Visualization of air-water two-phase flows in a rectangular duct with 2.4 mm gap and 40 mm width were successfully performed with the steady thermal neutron beam and this imaging system at the recording speed of up to 500 frames/s. The limit of high frame-rate neutron radiography in an ideal system without background radiation such as scattered neutron and with neutron detection efficiency of 100% was preliminarily investigated by calculating the measurement error of neutrons due to the natural statistics of neutrons in the low neutron flux field. It was shown from this study that the high frame-rate neutron radiography by the steady neutron flux on the order of 10⁶ n/(cm² s) has a good possibility.