Neutron Computed Tomography

(with M.S. student Nik Huerta)

Computed tomography (CT) provides a 3D model of features in the imaged sample. Images of the amount of radiation transmitted through a sample that are taken at different angles can be mathematically reconstructed into a 3D model of the interaction of the radiation with the sample as a function of space (Kak & Slaney 2001). If the features of interest interact differently with the radiation than the bulk of the sample, these features will be visible in the reconstructed model. For fenestrate microbialites that are composed of calcite with organic inclusions, the main element that interacts with neutrons is hydrogen associated with the organic inclusion. When these rocks are imaged, the microbial features defined by organic inclusions appear as zones with less neutron transmission than areas composed exclusively of calcite. Results to date demonstrate that this technique can image the basic structure of fenestrate microbialites, but precision needs to be improved and noise needs to be reduced to produce models of the 3D structure on a sub-millimeter scale (Tabor 2004). We use neutron imaging facilities at McClellan Nuclear Radiation Center. On June 6, 2005, an upgraded tomography system will provide low-noise, 100 Ám resolution images. However, neutron scatter is a significant source of distortion in hydrogen-rich samples and needs to be addressed during image reconstruction. We are working on developing these technqiues (see NCT on the Geology web site).

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Dawn Y. Sumner
Department of Geology
University of California
Davis, CA 95616