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Hand-held instruments with the ability to passively detect and identify sources of neutron radiationeither bare or obscured by neutron moderating and/or absorbing material(s)-in real time are of interest in a variety of non-proliferation and health physics applications. Such an instrument must provide a means to high intrinsic detection efficiency and energy-sensitive measurements of free neutron fields, for neutrons ranging from thermal energies to the top end of the evaporation spectrum. To address and overcome the challenges inherent to the aforementioned applications, four solid-state moderating-type neutron spectrometers of varying cost, weight, and complexity have been designed, fabricated, and tested. The motivation of this work is to introduce these novel human-portable instruments by discussing the fundamental theory of their operation, investigating and analyzing the principal considerations for optimal instrument design, and evaluating the capability of each of the four fabricated spectrometers to meet the application needs.

This paper establishes a method for force filtering, develops a dynamic process model, and designs and implements a general tracking controller to regulate the axial force for a variety of reference signals in Friction Stir Welding processes. Steady state and dynamic models are used to relate the input process parameters to the axial force. The general tracking controller is implemented in a Smith Predictor-Corrector Structure to compensate for a pure communication delay. The controller successfully performs bead-on-plate welds using a 6061 aluminum alloy. Both constant and sinusoidal reference forces are tracked.

The high thermal neutron capture cross section of boron provides a unique opportunity for the construction of solid state neutron detectors with application to the identification of nuclear fuels and non-proliferation activities. The ionization resulting from the neutron capture products, lO B+n� 7 Li+a, is deposited within a short range of the initial interaction, thus allowing the location of the capture event to be determined. Construction of a system consisting of alternating layers of thin sensitive detector and moderating materials in a geometrically regular shape that allows coordinate dependence of neutron thermalization to be determined results in a novel solid state neutron spectrometer. A GEANT4 model has been developed to study neutron thermalization as a function of detector geometry, neutron moderation materials, and radial sensitivity. The simulation results indicate that a unique relationship exists between the incident neutron energy and the statistical pattern of energy deposition. This allows the geometrical configuration and moderator identity to be tuned to match the neutron energy spectrum of interest. The detector response is found empirically to match the shape of the Fisher statistic distribution allowing the incident neutron spectrum to be extracted without unfolding.Furthermore, the pattern of energy deposition is strongly dependent on the direction of incidence of the neutrons.Ultimately, this instrument can be used to spectroscopically differentiate localized neutron sources from a cosmic background.