Time-of-flight neutron radiography for differentiating ice and water during phase transitions in natural porous media

Measurement of coexistent liquid water and ice distributions is useful for many materials and systems such as fuel cells, concrete, snow, and soil. Energy-resolved neutron imaging is a promising technique for these measurements by exploiting differences in neutron cross-section between ice and water at cold neutron energies. Until now, energy-resolved neutron imaging techniques have only been used with relatively thin and non-natural samples. Given the importance of liquid water and ice distributions in many natural porous materials, we investigated the feasibility of using time-of-flight neutron radiography for two natural porous materials. Two exploratory experiments were performed with a model system of glass beads (simple soil analogue) and a natural snow sample with sample thicknesses of 5 mm. The experiments demonstrated that the relative attenuation could be used to distinguish between liquid and solid water phases as well as to dynamically track the phase transition within these porous materials. The results also demonstrated that significant challenges with respect to the scattering in thick samples, inconsistent thicknesses associated with spatial variations of the porosity, and time-variant structures of the porous matrix remain.