Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2002. / Includes bibliographical references (leaves 69-74). / This thesis reports on the first measurement of the spin diffusion rate of a two-spin correlated state, known as dipolar order, in a single crystal of calcium fluoride. The experimental results for the component of the spin diffusion rate parallel with the azimuthal axis are ... for the [001] direction and ... for the [111] direction. These rates are significantly faster than those for Zeeman order and are also faster than theories have predicted. The standard method of measuring diffusion in magnetic resonance is to encode a spatial modulation of magnetization in a sample and then measure it's attenuation over time. The difficulty in measuring spin diffusion in solid crystals by these scattering methods is that the spin diffusion rate is very slow (of order 1 x 10⁻¹² cm²/s) and hence the displacement of coherence is very small. The experimental challenge for probing these dynamics is that a modulation must be created with a wavelength on these length scales. To perform the measurement a special probe was developed with a gradient coil constant of 370±10.5[G/cmA]. A special holder was designed for holding the 1mm³ sample in addition to a gradient switcher for switching pulsed currents through the coil. The peak pulsed gradient strengths ranged from 28 to 85 T/m and the spatial wavelengths generated ranged from 1[mu] to 0.5 [mu]/tm. / (cont.) Additional work focuses on correcting for finite pulse widths effects, phase transients and other pulse errors in a time-reversal multiple-pulse cycle known as the magic-echo sequence. The highest resolution achieved was a line-width of 0.5 Hz in a single crystal of calcium fluoride whose natural line-width was approximately 45 kHz, a reduction by 5 orders of magnitude. A phase alternating scheme for generating and detecting high order n-spin azimuthal spin correlations ... was also investigated. The relaxation times of 2, 3 and 4 spin correlations were was found to be comparable to that of dipolar order. / by Gregory Steven Boutis. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2004. / Includes bibliographical references (leaves 75-76). / Bolometry is a diagnostic technique common to most tokamak fusion experiments. Bolometers are so widespread because they provide an important measure of the energy lost from confined plasmas as radiation, as well as being relatively simple and resilient in their construction. Here the bolometric diagnostics of the Alcator C-mod tokamak, their function, limitations, and the details of their calibration, operation, and maintenance are covered. In addition, the results of a variety of investigations into the behavior of C-mod plasmas as observed by bolometers are presented and discussed. The measurements dealt with are either measurements of total power radiated by the plasma or measurements of radial emissivity profiles. Measurements of the first kind are suitable for studying the effects of factors like net input power while measurements of the second kind are useful for studying the effects of factors like local temperature profiles and plasma composition. / by Brian Joaquin Youngblood. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / Includes bibliographical references (p. 275-282). / Proliferation is the results of a competition between the proliferating country (proliferation) and the party to resist the proliferation efforts (safeguarder). An integrated evaluation methodology to evaluate proliferation resistance of nuclear energy systems is outlined and demonstrated focusing upon the proliferation competition. The methodology consists of four steps: actor characterization, proliferation competition model development, model input evaluation, and pathway assessment. A success tree method is used to structure the proliferation. The method permits integration of all aspects of proliferation resistance of a nuclear energy system, both intrinsic and extrinsic, in evaluating an integrated proliferation probability measure. Most of the input data obtained in a subjective form are viewed as the current state of knowledge of an evaluator for a system, reflecting an evaluator's beliefs. A modular pebble bed reactor (MPBR) design was chosen as the reference system for demonstration of the methodology. The demonstration study follows the integrated evaluation methodology, and gives a particular assessment of the proliferation resistance associated with a proliferating host State focusing upon the diversion from the spent fuel storage of a MPBR plant. / In order to evaluate the probability value of the diversion success, the study has provided: three top-level proliferation resistance measures addressing the inherent features of the system; a hypothesized safeguards approach for the system and a set of the plausible concealment tactics of the proliferator; an expert elicitation approach for evaluation of key model inputs; identification of the most attractive diversion pathway; uncertainty propagation of experts' inputs, sensitivity analyses of an ultimate outcome to input variables, and importance analyses of minimal path sets of success trees. Consequently, the study showed that the proposed methodology is an effective evaluation tool for comparison of advanced nuclear systems in terms of proliferation resistance. In addition, some limitations of the study and future work were also determined. / by Hyeongpil Ham. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / Includes bibliographical references (p. 107-112). / Recently, it has been suggested that an array of small quantum information processors sharing classical information can be used to solve selected computational problems, referred to as a type-II quantum computer. The first concrete implementation demonstrated here solves the diffusion equation, and it provides a test example from which to probe the strengths and limitations of this new computation paradigm. The NMR experiment consists of encoding a mass density onto an array of 16 two-qubit quantum information processors and then following the computation through 7 time steps of the algorithm. The results show a good agreement with the analytic solution for diffusive dynamics. From the numerical simulations of the NMR implementations, we explore two major error sources (1) the systematic error in the collision operator and (2) the linear approximation in the initialization. Since the mass density evolving under the Burgers equation develops sharp features over time, this is a stronger test of liquid state NMR implementations of type-II quantum computers than the previous example using the diffusion equation. Small systematic errors in the collision operator accumulate and swamp all other errors. We propose, and demonstrate, that the accumulation of this error can be avoided to a large extent by replacing the single collision operator with a set of operators, that have random errors and similar fidelities. / (cont.) Experiments have been implemented on 16 two-qubit sites for eight successive time steps for the Burgers equation. The improvement in the experimental results suggests that more complicated modulation of error terms may offer further improvement. An alternative approach has been suggested to encode in the Fourier space (k-space) to remove the usage of this linear approximation. This new method also provides us a simple means to implement the streaming operation quantum mechanically by controlling magnetic field gradients sandwiched with RF pulses. Therefore, this method might serve as a new tool to probe the implementations of quantum lattice gas (QLG) algorithms. Experimental demonstration of the diffusion equation has been performed on 16 two-qubit sites for four successive time steps. Recently, much attention has been focused on constructing many identical simple processing elements arranged in a cellular automata architecture recently. It is likely that the early quantum hardware will be built in a similar manner. Quantum lattice gas algorithms therefore provide a bridge between such hardware and potential early algorithms. We propose a quantum lattice gas model similar to the one proposed by Margolus for the classical setting. / (cont.) This quantum algorithm simulates the one-particle quantum random walk. The preliminary experimental design associated with the lattice gas model on a ring molecule is presented. The searches for the suitable pulses to construct the unitary operators, used in the implementations of the lattice gas model, are done and the results are encouraging. / y Zhiying Chen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, February 2005. / Includes bibliographical references (p. 93-102). / This thesis describes the development, investigation and experimental implementation via liquid state nuclear magnetic resonance techniques of new methods for controlling open quantum systems. First, methods that improve coherent control through the use of both strong control fields and detailed knowledge of the subsystem's Hamiltonian are demonstrated. With the aid of numerical search methods, pulsed irradiation schemes are obtained that perform accurate, arbitrary, selective gates on multi-qubit systems. For systems of 3 and 4 qubits, simulations show that the control sequences faithfully implement unitary operations with gate fidelities on the order of 0.999 while experimentally determined correlations of 0.99 were obtained. The technique is then extended to account for the incoherent errors arising from the slow variation of control parameters. It is demonstrated in this study that such errors can be greatly counteracted directly from the design of the time-dependent control fields if some knowledge about the incoherence source is available. The results obtained show a substantial decrease of the non-unitary features normally caused by incoherent noise. The methods are applicable to a variety of experimental studies in quantum information processing. / (cont.) To test the control techniques, we carried out two benchmark experiments, namely an entanglement transfer and an entanglement swapping experiment performed on a 4-qubit system. The second experiment, while more complex, yields significantly better results, thereby showing the improvement made by the further development of the control techniques. To optimally protect a quantum system against various decoherent errors, it is essential to design methods to acquire knowledge about them. It is in this context that we then develop a robust method for quantum process tomography for measuring relaxation superoperators and Lindblad operators, which is experimentally tested. Finally, we explore both theoretically and experimentally the concatenation of a quantum error correction code with a decoherence-free subspace scheme. Using the two techniques, a 4-qubit quantum system is efficiently protected against a noise containing partial symmetry. To date, this is the first experimental demonstration of such a concatenation scheme. / by Nicolas Boulant. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / "September 2005." / Includes bibliographical references. / The objective of this project is to establish a model system to study the direct effect, the bystander effect and the combinational effect of alpha-particle irradiations of human prostate tumor cells, toward the goal of improving the effectiveness of alpha-particle involved radiation therapies such as radioimmunotherapy and BNCT. This project consists of an engineering part and a biological part. In the engineering part, an apparatus for alpha-particle irradiation of cells was designed and constructed. Dosimetry of this irradiator was conducted. The average dose rate to the cell monolayer in the specially designed Mylar dish was calculated to be 1.2 Gy/min. In the biological part, three in vitro studies were carried out with the DU-145 human prostate tumor cells using the established alpha-particle irradiator. Firstly, the direct effects of the alpha-particle irradiation of DU-145 cells were studied using the clonogenic assay, the comet assay and the micronucleus assay. A novel co-culture system was then designed to study the bystander effect transmitted through the cell culture medium. The micronucleus assay was used as endpoint for the bystander studies. A bystander effect was observed. / (cont.) Mechanism studies suggested that the nitric oxide was not involved in the process and indicated a short effective lifetime (< min) of the bystander signal. In the combinational studies, the effects of two anticancer drugs (Taxol and Oxaliplatin) together with direct alpha-particle irradiation were studied and no synergistic effect was observed for both drugs. Finally, the combined effect of the bystander effect and drug Taxol was studied, which was the first time that a combined effect between an anticancer drug and the radiation-induced bystander effect was studied. The results of the model studies carried out in the two-dimensional monolayer of cells in this project can serve as a fundamental frame to be further applied to a three dimensional tumor micrometastasis model (spheroids) in the future. The understanding of the role the bystander effect plays in tumor cell killing, its mechanisms and its interaction with other agents, may make it possible to manipulate these factors to improve the effectiveness of alpha-particle involved therapies. / by Rong Wang. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, February 2005. / Includes bibliographical references (p. 94). / Enabling high power density in the core of Boiling Water Reactors (BWRs) is economically profitable for existing or new reactors. In this work, we examine the potential for increasing the power density in BWR plants by switching from the current solid fuel to annular fuel cooled both on its inside and outside surfaces. The GE 8x8 bundle dimensions and fuel to moderator ratio are preserved as a reference to enable applications in existing reactors. A methodology is developed and VIPRE code calculations are performed to select the best annular fuel bundle design on the basis of its Critical Power Ratio (CPR) performance. Within the limits applied to the reference solid fuel, the CPR margin in the 5x5 and 6x6 annular fuel bundles is traded for an increase in power density. It is found that the power density increase with annular fuel in BWRs may be limited to 23%. This is smaller than possible for PWRs due to the different mechanisms that control the critical thermal conditions of the two reactors. The annular fuel could still be a profitable alternative to the solid fuel due to neutronic and thermal advantages. / by Paolo Morra. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / Includes bibliographical references (p. 269-277). / The Supercritical Water-Cooled Reactor (SCWR) is a concept for an advanced reactor that will operate at high pressure (25MPa) and high temperature (500°C average core exit). The high coolant temperature as it leaves the reactor core gives the SCWR the potential for high thermal efficiency (45%). However, near the supercritical thermodynamic point, coolant density is very sensitive to temperature which raises concerns about instabilities in the supercritical water-cooled nuclear reactors. To ensure a proper design of SCWR without instability problems, the U.S. reference SCWR design was investigated. The objectives of this work are: (1) to develop a methodology for stability assessment of both thermal-hydraulic and nuclear-coupled stabilities under supercritical pressure conditions, (2) to compare the stability of the proposed SCWR to that of the BWR, and (3) to develop guidance for SCWR designers to avoid instabilities with large margins. Two kinds of instabilities, namely Ledinegg-type flow excursion and Density Wave Oscillations (DWO), have been studied. The DWO analysis was conducted for three oscillation modes: Single channel thermal-hydraulic stability, Coupled-nuclear Out-of-Phase stability and Coupled-nuclear In-Phase stability. / (cont.) Although the supercritical water does not experience phase change, the thermodynamic properties exhibit boiling-like drastic changes around some pseudo-saturation temperature. A three-region model consisting of a heavy fluid region, a heavy-light fluid mixture region and a light fluid region has been used to simulate the supercritical coolant flowing through the core. New non-dimensional governing parameters, namely, the Expansion Number (Nexp) and the Pseudo-Subcooling Number (Npsub) have been identified. A stability map that defines the onset of DWO instabilities has been constructed in the Nexp-Npsu,b plane based on a frequency domain method. It has been found that the U.S. reference SCWR will be stable at full power operating condition with large margin once the proper inlet orifices are chosen. Although the SCWR operates in the supercritical pressure region at steady state, operation at subcritical pressure will occur during a sliding pressure startup process. At subcritical pressure, the stability maps have been developed based on the traditional Subcooling Number and Phase Change Number (also called as Zuber Number). The sensitivity of stability boundaries to different two phase flow models has been studied. / (cont.) It has been found that the Homogcnouls-Nonequilibrium model (HNEM) yields more conservative results at high subcooling numbers while the Homogenous Equilibrium (HEM) model is more conservative at low subcooling numbers. Based on the stability map, a stable sliding pressure startup procedure has been suggested for the U.S. reference SCWR design. To evaluate the stability performance of the U.S. reference SCWR design, comparisons with a typical BWR (Peach Bottom ) have been conducted. Models for BWR stability analysis (Single channel, Coupled-nuclear In-Phase and Out-of-Phase) have been constructed. It is found that, although the SCWR can be stable by proper inlet orificing, it is more sensitive to operating parameters. such as power and flow rate, than a typical BWR. To validate the models developed for both the SCWR and BWR stability analysis, the analytical results were compared with experimental data. The Peach Bottom 2 stability tests were chosen to evaluate the coupled-nuclear stability analysis model. It was found that the analytical model matched the experiment reasonably well for both the oscillation decay ratios and frequencies. Also, the analytical model predicts the same stability trends as the experiment results. / (cont.) Although there arc plenty of tests available for model evaluations at subcritical pressure, the tests at supercritical pressure are very limited. The only test publicly found was for the single channel stability mode. It was found that the three-region model predicts reasonable results compared with the limited test data. / by Jiyun Zhao. / 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 Mark Steven Tillack. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1999. / Includes bibliographical references (leaf 122). / Organizations with large R&D activities must deal with a hierarchy of decision regarding resource allocation. At the highest level of allocation, the decision is related to the total allocation to R&D as some portion of revenue. The middle level of allocation deals with the allocation among phases of the R&D process. The lowest level of decisions relates to the resource allocation to specific projects within a specific phase. This study focuses on developing an R&D model to deal with the middle level of allocation, i.e., the allocation among phases of research such as basic research, development, and demonstration. The methodology used to develop the R&D model is System Dynamics. Our modeling concept is innovative in representing each phase of R&D as consisting of two parts: projects under way, and an inventory of successful but not-yet-exploited projects. In a simple world, this concept can yield an exact analytical solution for allocation of resources among phases. But in a real world, the concept should be improved by adding more complex structures with nonlinear behaviors. Two particular nonlinear feedbacks are incorporated into the R&D model. The probability of success for any specific project is assumed partly dependent upon resources allocated to the project. Further, the time required to reach a conclusion regarding the success or failure of a project is also assumed dependent upon the level of resources allocated. In addition, the number of successful projects partly depends on the inventory of potential ideas in the previous stage that can be exploited. This model can provide R&D management with insights into the effect of changing allocations to phases whether those changes are internally or externally driven. With this model, it is possible to study the effectiveness of management decisions in a continuous fashion. Managers can predict payoffs for a host of different policies. In addition, as new research results accumulate, a re-assessment of program goals can be implemented easily and allocations adjusted to enhance continuously the likelihood of success, and to optimize payoffs. Finally, this model can give managers a quantitative rationale for program evaluation and permit the quantitative assessment of various externally imposed changes. / by Namsung Ahn. / Ph.D.