Determination of air/water ratio in pipes by fast neutrons: Experiment and Monte Carlo simulation

Fast neutron dose attenuation from a ²⁵²Cf neutron source is used for the determination of air to water ratio in pipes. Such measurement of the two-phase flow volume fraction is important for many industrial plants such as desalination plants and oil refineries. Fast neutrons penetrate liquid more than slow neutrons or gamma rays. Using diameters from 11.5 cm to 20.76 cm and with wall thicknesses from 0.45 to 1.02 cm, attenuation was independent of pipe wall thicknesses and diameters. Experimental data was in good agreement with values calculated using MCNP codes. The measured neutron flux values decreased with increasing water levels in pipes up to about 14 cm, indicating that our system can be used successfully in desalination plants in pipes of different sizes. The experimental sensitivity was found to be about 0.015 mSv/h cm and the system can be used to measure water level changes down to few millimeters. Use of such a system in fixed positions in the plant can provide information on plant's overall performance and can detect loss of flow immediately before any consequences. A portable system could be designed to measure the air to water ratio in different locations in the plant in a relatively short time.