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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.

A determination of the resonance escape probability of thorium as thorium nitrate in aqueous solution has been made as a function of thorium concentration. The physical system used was an aluminum box surrounded by successive layers of cadmium, paraffin and borated paraffin to keep out neutrons scattered by objects in the laboratory. Neutrons were obtained from a Cockcroft-Walton type accelerator by the D(d,n)He³ reaction. The drive-in target was located at the center of one of the faces of the aluminum box. Neutron density was measured at nine spatial positions in the direction of the neutron beam with a bare boron trifluoride detector. The area under a curve of neutron density versus spatial position was obtained for various concentrations of absorber. The above process was carried out for the thorium solution and for a “mock solution," whose cross-section was similar to that of thorium except that it had no resonances in the thorium resonance region. By taking ratios of the neutron densities (area under curves of neutron density versus spatial position) in the thorium solution to the neutron density in the mock solution, it was possible to determine the resonance escape probability of neutrons in a homogeneous, aqueous solution of thorium nitrate. It is shown that, for the absorber concentrations used in the experiment, the resonance escape probability for an infinite geometry may be obtained by the above ratio method. The difference between a finite system and an infinite one is exhibited as leakage of neutrons from the system in the finite case. If one can compare neutron densities for systems which are large enough so that leakage is negligible or for systems with corresponding leakage rates, the effect of leakage can be overcome and the resonance escape probability for the infinite geometry obtained. Before taking the above ratios of neutron densities, it was necessary to compensate for the spectral shift of the thermal flux in the two solutions. After such a correction, the resonance escape probability so obtained shows good correlation with the results of the Monte Carlo prediction for this system. Over the range covered by the experiment (0 - 1 x 10²¹ atoms of thorium per cubic centimeter), experimental results agree with Monte Carlo predictions to within one percent. Counting statistics were good, with 10⁶ counts normally taken per spatial position. The curves from which the value of neutron density were determined were formed by nine points, each of which represented at least 10⁶ counts. Reproducibility of the neutron density at a point was of the order of one percent. Various changes made in the analysis of the data have caused corresponding changes in the values obtained for the resonance escape probability of less than one percent. These facts all indicate that the uncertainty in the experimental determination is of the order of one percent. Calculations of effective resonance integrals from the experimentally determined values of the resonance escape probability show good agreement with published measurements on other systems. / Ph. D.

Tunneling phenomenon has been studied since the time of Sir Isaac Newton. In the case of neutron tunneling phenomenon, it is the quantum mechanics wave-particle duality which manifests itself. In this case, particularly, the neutron wave-packet under total reflection condition suffers the so-called frustrated total reflection as known in standard optics. More accurately, this tunneling phenomenon shows itself via sharp dips in the plateau of total reflection. The prerequisite to observe such quantum mechanics phenomenon lies within a thin film Fabry-Perot resonator configuration. This thin film Fabry-Perot resonator geometry consists of two reflecting mirrors separated by a transparent material from a neutron optics viewpoint. In view of the specific neutron scattering properties related to the spin of the neutron wave-packet. As a direct proof, isotopic nickel based thin films Fabry-Perot resonator have been fabricated by depositing thin film of nickel by ion beam sputtering. The vacuum chamber was pumped down to the pressure of 10-8 mbar and deposition was performed at pressure of 2x10-4 mbar. The deposition rate was kept at 1.5 nm / minute and thickness layers were monitored by a calibrated quartz microbalance. Unpolarized neutron reflectometry measurements were carried out at the ORPHEE reactor using the time-of-flight EROS reflectometer. The incidence neutron wavelength varied between 3 – 25 Å. The grazing angle and angular resolution were of the order of 0.8˚ and 0.05 respectively. The software program, a Matlab routine for the simulation of specular X-ray and neutron reflectivity data with matrix technique, was employed to simulate the phenomenon and thereafter the experimentally obtained data and calculated (theoretical) data were compared. From the analysis of the comparison, a conclusion was drawn about the agreement between experimental data and theoretical data. The tunneling phenomenon has been observed in nanostructured isotopic nickel based thin film Fabry-Perot resonator. It manifested itself by the existence of dips, tunneling resonances, in the total reflection plateau due to quasi-bound states in the isotopic nickel based thin film Fabry-Perot resonator. In total, there were 7 tunneling resonances. The full widths at half maximum of these dips were found to decrease with increasing momentum wave vector transfer (Q) and this correlated to the neutron lifetime in the nanostructured isotopic nickel based thin film Fabry-Perot resonator. / Physics / M. Sc. (Physics)