archives@tulane.edu / This dissertation details a measurement of the n-$^{4}$He coherent scattering length to be $b_{4\rm{He}} = [3.0982 \pm\: 0.00214\; (\rm{stat}) \pm\: 0.00077\; (\rm{sys})]$ fm utilizing a perfect silicon crystal neutron interferometer. This measurement provides over a factor of 10 improvement in precision and differs by $0.162$ fm compared to the most commonly used value. Neutron interferometry provides a tool for precision scattering lengths measurements for a variety of isotopes. Examples include coherent scattering length measurements for $^{1}$H, $^{2}$H, $^{3}$He and the incoherent scattering length of $^{3}$He. Neutron scattering lengths of light nuclei provide useful tests of nuclear potential models and serve as inputs for nuclear effective field theories. A monolithic, perfect silicon neutron interferometer splits the wave function of a single neutron via Bragg diffraction into two coherent paths spatially separated to the extent of a few centimeters. A sample of $^{4}$He gas, contained within an aluminum cell, is introduced into one beam path which produces a phase shift directly proportional to $b_{4\rm{He}}$. Significant effort has been spent quantifying important systematic considerations that include thermal transfer from the gas cell to the interferometer crystal and deformation of the gas cell walls due to gas pressure which ranges from 7 bar to 13 bar which were calculated by an FEA simulation. Thermal transfer between the gas cell and interferometer crystal induces a change of the intrinsic interferometer phase which is dependent on sample position. This additional systematic phase has been named the shadow phase. A glycol cooling system was used to mitigate the shadow phase and a special measurement pattern was devised to account for possible shadow phase drift. This work was performed at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR). / 1 / Robert Haun

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 262-263). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 262-263). Also available on the Internet.

In this report, the effects of adding 11B4C as interlayers into Fe/Si multilayers is studied. Fe/Si multilayers are commonly used for neutron polarization at large research facilities, and improving the polarizing properties would improve their efficiency. To study this, DC magnetron sputtering was used to make different sets of samples varying interlayer thicknesses, period thicknesses, number of periods, layer thickness ratios and also testing it with steel instead of iron in the multilayers. The samples were then studied using a series of characterization techniques to study how different growth parameters affected the sample’s properties. X-ray diffraction(XRD) and selected area electron diffraction (ED) were used for studying the crystal structure of the samples. X-ray reflectometry (XRR) was used to for fitting layer thicknesses and interface widths, and also to compare reflectivities. Elastic recoil detection analysis (ERDA) was used to study the compositions changes of the samples. Vibrating sample magnetometry (VSM) gave information about how the magnetization changed between samples. Transmission electron microscopy (TEM) visualized the structure of the samples. Finally, polarized neutron reflectometry (PNR) was done at Institute Laue Langevin (ILL), revealing the actual polarization of the samples. The results of the measurements concluded that for a sample with 40 periods, a period thickness of approximately 16 Å and a thickness ratio of around 0.5 for iron and silicon, using 1 Å thick 11B4C interlayers improved the polarization between the Bragg peaks by 60 %, and at the angle of the spin up peak by 130 %. The results also indicate improved polarization for samples with more or thicker periods. Using low carbon steel instead of iron showed poor results for thin layers, however showed promise for thicker layers due to good reflectivity results, but further testing is required.

This thesis introduces reader to current knowledge of nanomaterials and their usage. It summarises production methods and usage of different materials in nuclear power plants, nuclear research and nuclear medicine. Theoretical part of this thesis is dedicated to possible usage of carbon nanotubes for neutron beam collimation and guides. In experimental part different materials were tested in measuring box connected to horizontal radial channel of VR-1 nuclear reactor and their influence on neutron flux was measured. Tested samples were non-oriented carbon nanotubes, carbon nanofibers, alumina nanowires, oriented carbon nanotubes with several angles of rotation and these samples were compared with results of graphite.