Radiotracer medical imaging technologies applied to environmental remediation systems

We demonstrate an alternate application of high-sensitivity radiotracer imaging technologies developed for nuclear medical imaging. There are several available radioisotopes, namely ⁵¹Cr and ^99mTc, that are particularly appealing for studying environmental remediation techniques, notably for modeling toxic element runoff through the soil near former nuclear facilities such as the Hanford reactors in Washington state (USA). ⁵²Cr (stable) and ⁹⁹Tc (2.3?10⁶ year half-life) are important reactor-generated contaminants that have entered the groundwater. There are numerous studies being conducted to model transport of these compounds in different types of soil such as sand, clay, dirt and gravel. The speed and character of contaminant transport through medium depends on chemical composition of the particles, chemical composition of water, physical properties of the medium (particle size, homogeneity, temperature) and on content of different types of microorganisms. Measurements are typically performed by flowing water containing ⁵²Cr or ⁹⁹Tc through sediment columns (tubes a few cm in diameter and 0.5-1 meter long) and monitoring the in-and out- flows of contaminants. We will support the effort to develop different methods of reducing the contaminant transport speed by using SPECT imaging to study transport of the singlephoton emitting surrogates ⁵¹Cr and ^99mTc. By quantitatively imaging the contaminant distribution in the sediment column as a function of time, a much richer set of data can be obtained. We will compare contaminant transport in various media under different conditions including standard diffusion and flow at different speeds and volumes. Experimental work will be supplemented with theoretical analysis and modeling of transport processes, including studies of diffusion and chemical exchange using a standard multi-compartment model. In this conference record, w- - e present the results of two studies of technetium 99m transport in hydrated sand, including both planar and tomographic SPECT images of the columns acquired at different conditions.