Gamma Who? Gamma What?.

A tool for measuring fluid contents and solid mass densities in porous media is radiation attenuation. Gamma rays are potentially strong enough to pass through water-saturated porous media 6-8 cm thick. Two gamma sources, each with a different energy band, can be used to measure two properties simultaneously, such as water content and bulk density. Jacob Dane was an early pioneer in developing dual-energy, gamma-radiation attenuation experimental systems. Initially, the experimental systems were used to measure water content and soil bulk density in systems with expanding clays where the bulk density can change as a function of water content. Later, he applied the dual gamma measurement technique for studying the behavior of nonaqueous-phase liquid (NAPL) in porous media. If the mass density of a porous medium is invariant along the gamma ray path, then the two gamma energy sources can also be used to measure both water and NAPL saturations simultaneously. Assuming that there is negligible radiation attenuation by the gas phase, then a dual-energy, gamma-radiation attenuation system can be employed for measuring air, NAPL, and water contents simultaneously in porous media with an invariant bulk density. With quantitative measurements using a dual-gamma system, experiments could be conducted and used to test theoretical and numerical models for three-phase air-NAPL-water movement in porous media. Jacob Dane was again a pioneer in employing dual-gamma systems to test numerical codes for predicting the subsurface movement of NAPLs. In 1987, Jacob Dane published a seminal paper quantifying the downward migration of NAPL through a porous medium column. The paper stimulated others to build dual-gamma systems and to conduct experiments with which to test numerical models. Today, there are several dual-gamma systems at different institutions that were built utilizing the pioneering work of Jacob Dane.