Doctor of Philosophy (PhD)
Physics and Astronomy
A hard x-ray/gamma-ray telescope with high sensitivity and wide field of view would be capable of performing an all-sky census of black holes over a wide range of obscuration and accretion rates. As an example, NASA's Black Hole Finder Probe mission was designed to provide a 5-sigma flux sensitivity in a 1-year observation of ~0.02 mCrab in the 10 - 150 keV energy range and 0.5 mCrab in the 150 - 600 keV energy range with 3 - 5 minutes of arc angular resolution. These are significantly higher sensitivity and resolution goals than those of current instruments. The design focus on sensitivity would make the instrument equally suitable for national security applications in the detection of weak shielded illicit radioactive materials at large distances (100 m - 1 km). X-ray and gamma-ray imaging designs for astrophysics and security applications typically utilize a coded aperture imaging technique. The spatial resolution necessary, however, coupled with the specification of high sensitivity, requires a large number of readout channels (resulting in high cost and complexity) and limits the use of this technique to relatively low energies. As an alternative approach, an investigation is made here of the rotating modulator (RM), which uses primarily temporal modulation to record an object scene. The RM consists of a mask of opaque slats that rotates above an array of detectors. Time histories of counts recorded by each detector are used to reconstruct the object scene distribution. Since a full study of RM characterization and capabilities has not been performed prior to this work, a comprehensive analytic system response is presented, which accounts for realistic modulation geometries. The RM imaging characteristics and sensitivity are detailed, including a comparison to more common hard x-ray imaging modalities. A novel image reconstruction algorithm is developed to provide noise-compensation, super-resolution, and high fidelity. A laboratory prototype RM and its measurement results are presented. As a pathfinder mission to an eventual astrophysics campaign, a one-day high-altitude balloon-borne RM is also described, including expected performance and imaging results. Finally, RM designs suitable for next-generation astrophysics and security applications are presented, and improvements to the RM technique are suggested.
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Budden, Brent, "Characterization and prototyping of the rotating modulator hard x-ray/gamma-ray telescope" (2011). LSU Doctoral Dissertations. 454.
Cherry, Michael L.