Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2001. / Includes bibliographical references (leaves 215-220). / This thesis describes a new microwave output window for megawatt power level, 110 GHz gyrotrons. The window uses two spherically polished sapphire elements separated by a nearly uniform gap of about 1 mm. Pressurized, microwave transpar- ent coolant flows through this gap and across the transmitting aperture, removing absorbed energy at the element face. The design differs from previous face-cooled windows because the sapphire elements have a modestly curved dome, rather than flat shape. This curved shape increases the element's capability to withstand coolant pressures without significantly increasing stresses from differential heating. Conse- quently, window power can be increased either through enhanced, high pressure cool- ing or by using thinner elements with reduced microwave absorption. A model was developed to predict window power capability as a function of design geometry. This model predicted an increase from 0.5 to 2.1 MW when flat elements were changed to curved. Both designs used full size, 100 mm clear apertures, but the curved elements with 214 mm curvature radii were 1.3 rather than 1.75 mm thick. The model was also used to design a half size prototype experiment. This 50 mm clear aperture system used 60 mm OD x 0.47mm thick x 107mm surface radius elements. An initial piece was fabricated and statically tested to a pressure of 1.1 MPa well above the 0.5 MPa analytically predicted to be required for megawatt operation. The complete window structure was then fabricated, including instrumentation to simulate microwave heat- ing and to measure induced temperatures and strains. Test results demonstrated an equivalent continuous Gaussian beam power capability of 700 kW using a coolant flow of 1.1 lps. Scaling from this measurement, full size boiling limited power is expected to be 1.1 MW for a Gaussian microwave intensity profile, or 2.3 MW for a shaped profile typical of previous flat, face-cooled designs. / by George Stephenson Haldeman. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1999. / Includes bibliographical references (p. 129-137). / As one result of this thesis, a single slab 3D fast spin echo imaging (3DFSE) method has been implemented and optimized. This involved sequence design and implementation, SAR considerations, parameter adjustments and clinical testing. The method can deliver 3D Tl or T2 weighted brain image with isotropic Imm3 voxel resolution in approximately 10 minutes. The ability to obtain high spatial resolution in reasonable time periods has wide clinical applications such as improvement of treatment planning protocols for brain tumor patients, precise radiotherapy planning, and tissue segmentation for following the progression of diseases like multiple sclerosis. The other part of this thesis is devoted to developing and implementing spectroscopic imaging methods, which include 20 chemical shift imaging(2DCSI) methods, 20 line scan spectroscopic imaging(2D LSSI) methods, spin echo planar spectroscopic imaging(SEPSI) methods and ~ingle shot line scan spin echo planar spectroscopic imaging(SSLSEPSI) method. The former two methods are applied to oil phantoms and bone marrow studies. The SEPSI method can provide simultaneous spectroscopic measurements, R2 and R2' images and field distribution images. A time domain spectral analysis method, LP-HSVD was implemented and applied to spectroscopic imaging studies. The SEPSI method was applied to get lipid characterization of bone marrow as well as to get the R2 and R2' brain images. The SSLSEPSI method can provide instant line spectroscopic imaging which might be useful to image moving objects and can provide high temporal resolution for dynamic studies. With further development, both SEPSI and SSLSEPSI methods may prove useful for trabecular bone studies as well as functional magnetic resonance imaging( tMRI) studies. / by Sumi Bao. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1999. / Includes bibliographical references (leaves 96-100). / This thesis describes the design and applications of an improved Nuclear Magnetic Resonance (NMR) microscope, which permits MRI to study small sample sizes ( < 2mm) at high resolution (up to 2[mu]m). The effects of molecular diffusion and local variations in the magnetic susceptibility in NMR microscopy are described, which, along with the intrinsic low sensitivity of NMR, are the fundamental limitations to resolution. Molecular diffusion in the presence of a magnetization grating not only broadens the point spread function but also reduces the signal intensity. The significance of these effects depends strongly on the magnetic field gradient strengths and imaging protocols. A NMR microscope for a standard bore 14.lT magnet was developed, it is equipped with a highly efficient. solenoidal RF coil and three orthogonal gradients with strengths of 1260G / cm for Gz , 760G/cm for Gy , and 410G/cm for Gx at 15A. A modified CTI sequence is presented which incorporates strong pulsed gradients, Ernst angle excitation, CP coherent detection and reduced k-space sampling. It is the optimal pulse sequence for acquiring high-resolution ( < 5[mu]m) NMR images (best signal-to-noise ratio per unit time) when the effect of molecular diffusion is significant. It is demonstrated that this new sequence makes it possible to acquire images with a high resolution of 2[mu]m x 2[mu]m x 8[mu]m within a few hours. A wide variety of images have been acquired using the new microscope, and representative images are presented to demonstrate the potential of NMR microscopy as a new tool in developmental biology research. In particular, used in combination with other biological techniques, NMR microscopy can provide a robust, non-invasive, 3D imaging approach to quantifying changes in structure due for instance to radiative exposure, therapy, and natural growth or genetic modifications. / by Xiao-wu Tang. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1990. / Includes bibliographical references. / by Maureen J. Psaila-Dombrowski. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1989. / Includes bibliographical references (leaves 169-178). / by Warren Michael Stern. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1989. / Includes bibliographical references (leaves 205-209). / by Tue Nguyen. / Ph.D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1987. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 209-217. / by Andrew Joseph Wolford. / Sc.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1984. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Bibliography: leaves 355-360. / by Derek Bram Ebeling-Koning. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1984. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Sang-Nyung Kim. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2003. / Includes bibliographical references (leaves 146-147). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Boron Neutron Capture Synovectomy (BNCS) is a novel application of the ¹⁰B(n,α) reaction for potential treatment of rheumatoid arthritis. During BNCS clinical trials, real-time knowledge of boron dose delivered to the synovium is necessary so that the remaining irradiation time can be determined. A 478 keV photon is emitted following 94% of boron neutron capture reactions, and detection of 478 keV photons emitted from the synovium provides a potential approach for online monitoring of the accumulated synovial boron dose. This thesis explores the feasibility of developing a telescope system for online determination of synovial boron dose for accelerator-based BNCS. The Monte Carlo code MCNP was used to design the telescope system. The neutron and photon background distributions in the radiation vault at the Laboratory for Accelerator Beam Applications (LABA) at MIT were explored via Monte Carlo simulations, and an optimum position for the photon detector was determined. Collimator and detector shields were designed, and significant reduction of neutron flux and background count at the detector location was observed. Sufficient boron photon counts from the synovium were predicted, and the feasibility of using a NaI detector instead of an HPGe detector was also confirmed. Next, a telescope system was built in the radiation vault at LABA. A background peak overlapping the energy region of 478 keV photons was observed in the measured spectrum by a 10.2 cm x 10.2 cm NaI(Tl) detector. Origin and direction of background particles entering the detector were explored, and further background reduction was achieved. The composition of the background peak was also analyzed. / (cont.) Experimental characterization of the telescope system was performed. It was confirmed that boron photons from the synovium could be detected in the presence of background counts. The count saturation became significant when the boron concentration was over 10,000 ppm, as predicted by simulations. Experimental results were compared with simulation results, and the overall agreement was within 10-20%. Reconstruction approaches for determination of the synovial boron dose based on the measured boron photon count and additional information such as anatomic configuration of the joint and boron compound distribution were generated. / by Hongyu Jiang. / Ph.D.