Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed February 25, 2010). PDF text: xii, 92 p. : col. ill. ; 29 Mb. UMI publication number: AAT 3386942. Includes bibliographical references. Also available in microfilm and microfiche formats.

Modeling and understanding the doses around the neutron generator provides insightful data in regard to radiation safety and protection precautions. Published data can be used to predict doses, but realistic data for the Nuclear Engineering Teaching Laboratory’s Thermo MP 320 Neutron Generator helps health physicists more accurately predict dose rates and protect experimenters against exposure. The goal was to create a model inclusive of the entire setup and room where the neutron generator is housed. Monte Carlo N-Particle (MCNP) Code reigns as the preferred method for modeling radiation transport and was utilized to model the transport of neutrons within the current configuration of the 14 MeV neutron generator facility. This model took into account all shielding materials and their respective dimensions and locations within the concrete room. By utilizing tallies and tally modifiers, the model predicts dose rates that can be used with experimental factors such as irradiation time and flux to predict a dose in millirem. Validation experiments were performed in the current setup using Landauer Luxel®+ with Neutrak dosimeters placed in strategic locations to record the neutron dose vi received as well as a Ludlum Model 42-41 PRESCILA neutron probe to predict dose rates. The dosimeters and PRESCILA measurement locations matched the positions of the point detector tallies in MCNP. After laboratory analysis, a comparison was performed between the model output and the dosimeter and PRESCILA values to successfully validate the accuracy of the model. / text

The work described in this thesis was carried out at the Institut Laue Langevin, Grenoble, France as a member of the group searching for the electric dipole moment (EDM) of the neutron. The first chapter is an introduction to ultra-cold neutrons (UCN) and their use in the search for an EDM. In chapter two a description is given of the data acquisition procedure and the data analysis method as well as a discussion of the various sources of spurious EDM signals. The data taken by the author yielded the result I-fe/e = ( -3.7 ± 5.4 )xl0-25 cm, which together' with all the other data previously and subsequently collected on PN5 gives I-fe/e = ( -3.7 ± 5.4 )xlO- 25 cm. The third chapter contains some calculations, based on a simple model of the polarizer's properties, of the time dependence of the polarized UCN density in the apparatus during a data ~cquisition cycle. It. also includes the results of the experiments made in an attempt to determine experimentally the model's parameters. The other two chapters are concerned with the problem of transferring efficiently UCN from the 0.6 K volume of the 4He superthermal source to thf! 300 K EDM apparatus without allowing the heat transfer by radiation to overload the source's refrigerator. The possibility of using metal coated polypropylene windows to achieve this aim is investigated in the fourth chapter. In chapter five the infra-red transmission of the stainless steel neutron guides is estimated by calculation and then determined experimentally with a view to using lengths of cold guides to attenuate the radiation heat transfer from the apparatus to the source.

The Best M.Phil Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,1993-1995 / published_or_final_version / Physics / Master / Master of Philosophy

Integral transport theory is used to compute transfer matrix elements for neutral particle streaming through r-z rectangular voids. The transfer matrix is utilized in a hybrid method; it interfaces with a conventional discrete ordinates calculation outside the void. Since the hybrid interface is accomplished within the inner iteration of an existing discrete ordinates code, standard sweeping schemes used in SN codes are not adversely affected. The resulting transfer matrix is independent of the multigroup energy structure used in a calculation. Further, the transfer matrix is not affected by changes in materials or cross sections outside the void. For these reasons, once a transfer matrix is calculated it can be used in a wide variety of problems containing a similar void. In this study, the transfer matrix hybrid, standard discrete ordinates, and Monte Carlo methods are applied to two sample problems to compare the accuracy of these methods. The Monte Carlo results are considered correct in order to compute errors in the deterministic calculations. The transfer matrix hybrid method is more accurate than conventional SN methods; the ray effect, persistent in discrete ordinates calculations, is substantially reduced. In addition, the transfer matrix hybrid executes faster than higher order SN calculations.

No description available.

There has been a strong international interest in using pyroprocessing to close the fast nuclear reactor fuel cycle and reprocess spent fuel efficiently. To commercialize pyroprocessing, safeguards technologies are required to be developed. In this research, the use of Self-Interrogation Neutron Resonance Densitometry (SINRD) has been investigated as a method to safeguard the process and more precisely quantify the 239Pu content of pyroprocessing materials. This method uses a detector array with different filters to isolate the low-energy resonance in 239Pu neutron fission cross section. The relative response of the different detectors allows for the quantification of the amount of 239Pu in the pyroprocessing materials. The Monte-Carlo N-Particle (MCNP) code was used to design a prototype SINRD instrument. This instrument is composed of a neutron source pod and a SINRD detector pod. Experimental measurements were also performed to validate the MCNP model of the instrument. Based on the results from simulations and experiments, it has been concluded that the MCNP model accurately represents the physics of the experiment. In addition, different SINRD signatures were compared to identify which of them are usable to determine the fissile isotope content. Comparison of different signatures allowed for reduction in the uncertainty of the 239Pu mass estimate. Using these signatures, the SINRD instrument was shown to be able to quantify the 239Pu content of unknown pyroprocessing materials suitable for safeguards usage.

No description available.

Hyperflares from Soft Gamma Repeaters have revealed quasi-periodic oscillations, suggested to be torsional modes of the neutron star crust produced during starquakes. We study how a magnetic field affects these modes. We make a plane-parallel model of the neutron star crust with a vertical and non-vertical field and solve for the eigenvalues and eigenfunctions. In the vertical field case we find a discrete set of modes comparable to the observed frequencies giving evidence for this theory. We find that the lower order modes do not depend on B while the higher order modes do when the field strength is low or extremely high. We make a simple analytic model of a non-vertical field in a closed box representing the neutron star crust. The mode spectrum in this model is continuous rather than discrete, raising the puzzle of why only specific modes are excited during the hyperflare.

Future fundamental physics experiments in neutron beta-decay require highly efficient detection of protons. Many of the experiments use electrostatic acceleration of the recoil protons into large-area silicon detectors for this purpose. A 30~keV proton accelerator was designed, created, and commissioned in order to characterize silicon detectors of this type. Final construction and initial results on the performance of the accelerator are presented. A unique aspect of the work is the use of a Penning ion generator as an ion source. The accelerator produced protons with momentum resolution ~1%. The ion source produced current stably, over a range of parameters, and over long periods of time. The accelerator achieved proton rates sufficient to calibrate silicon detectors.