Theoretical and experimental investigations in characterizing and developing multiplexed diamond-based neutron spectrometers

Title from PDF of title page (University of Missouri--Columbia, viewed on August 29, 2012).The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Dissertation advisor: Dr. Mark PrelasIncludes bibliographical references.Vita.Ph.D. University of Missouri--Columbia 2012"May 2012"In this work a novel technique of multiplexing diamond is presented where electronic grade diamond plates are connected electrically in series and in parallel to increase the overall detection efficiency of diamond-based neutron detection systems. Theoretical results in MCNPX indicate that further development in this software is required to accurately predict the response of diamond-based neutron spectrometers. However, the results accurately indicate that an equivalent diamond plate 1cm thick only lowers the energy resolution of the 12C(n,αo)9Be peak from a 14.1 MeV interrogating neutron by a factor of two compared to a single diamond plate 0.5mm thick while increasing the detection efficiency from 1.34 percent for a single diamond plate to 25.4 percent. Further, the number of secondary neutron interactions is approximately 5.3 percent for a 1cm thick diamond plate. In addition, photons can interfere with lower energy neutron signals when multiplexing is used, especially at low photon energies, although the full energy peak still does not dominantly present itself in the pulse height spectrum for multiplexed arrays approaching 1cm with respect to the incident neutron vector. Experimental results indicate that series multiplexing is not capable for use as a means of increasing the active detection volume because of the interaction of the diamond plates in series with each other, where severe signal degradation is seen due to the equal impedances of the single crystal diamond plates. However, parallel multiplexing is shown to have great promise, although there are limitations to this technique due to the large capacitance at the preamplifier input for a large parallel multiplexed array. Still, the latter multiplexing technique is shown here to be capable of producing the largest diamond detection medium in a single detector with spectroscopic capabilities reported to date.Includes bibliographical reference

Neutron and gamma ray spectroscopic detection system

The Domestic Nuclear Detection Office's mission is to improve the nation's ability to detect unauthorized nuclear importation, and the office was allocated $1.2 billion to accomplish its goal. The office has invested heavily in advanced spectroscopic portals, but these have turned out to have very low detection efficiencies despite the fact that they cost nearly$400,000 a piece. However, the office continues to search for new technologies that adequately detect neutrons. This invention, developed at this premier nuclear engineering school with the largest research reactor in the country, proposes a novel solution for neutron detection. Diamond based detection systems are becoming popular with the technological advances in CVD diamond film growth technologies. Within the past ten years, diamond film purities have reached levels that allow undoped diamond plates to be used as an intrinsic semiconductor. With this, several charged particle and ultra-violet detection systems have been developed, along with a few neutron detection systems. Neutron detection utilizing diamond use neutron absorption into carbon for fast neutron detection. However, the cross section for this detection mechanism is small and so these detection systems are limited in their active detection volume. If the volume of the diamond detection medium were increased, then this detection mechanism would become advantageous. Even more so, the elastic scattering cross section of neutrons from diamond is higher than that of neutron absorption and does not have a 5.7 MeV threshold. Therefore, by increasing the diamond detection volume, another avenue of detection and spectroscopic determination of neutron sources becomes available. There are two ways of doing this, through advancing the CVD growth technology limitations, or through innovation. Here, a plate combination mechanism is proposed that allows the increase in the active detection volume while maintaining all other characteristics of single diamond plates. Potential Areas of Applications: * Homeland Security (sea ports, airports, border crossings) * Nuclear reactor design and managemen

Photonuclear activation of pure isotopic mediums.

This work simulated the response of idealized isotopic U-235, U-238, Th-232, and Pu-239 mediums to photonuclear activation with various photon energies. These simulations were conducted using MCNPX version 2.6.0. It was found that photon energies between 14-16 MeV produce the highest response with respect to neutron production rates from all photonuclear reactions. In all cases, Pu-239 responds the highest, followed by U-238. Th-232 produces more overall neutrons at lower photon energies then U-235 when material thickness is above 3.943 centimeters. The time it takes each isotopic material to reach stable neutron production rates in time is directly proportional to the material thickness and stopping power of the medium, where thicker mediums take longer to reach stable neutron production rates and thinner media display a neutron production plateau effect, due to the lack of significant attenuation of the activating photons in the isotopic mediums. At this time, no neutron sensor system has time resolutions capable of verifying these simulations, but various indirect methods are possible and should be explored for verification of these results

Engineering elevator pitches

The slides for the panelists' presentations can be found by going to Presentations collection for the Missouri Technology Expo 2010: https://mospace.umsystem.edu/xmlui/handle/10355/9623This video presents the elevator pitches given in the field of engineering. Each elevator pitch consists of a presentation from the faculty/student innovator, followed by questions/answers from the audience

Sporadic neutron production by pressure-loaded D/Ti systems under high rates of temperature change

The mechanisms of low energy nuclear reactions (LENR) phenomena are poorly understood. If these phenomena are the consequence of commonly understood nuclear interactions, they should produce some nuclear byproducts such as gamma rays, neutrons, or charged particles. The unpublished results of a 1991 thermal shock experiment with high D/Ti loading observed a high rate of neutron emission while a recent attempt to recreate the 1991 results showed no evidence of neutrons produced by interactions within the D/Ti lattice. This work recreates the 1991 experiment and continues the previous recent investigation with improved methodology. In addition to control of deuterium pressure, system temperature, and duration of cryogenic exposure, this new setup also offers continuous data-logging and automated analysis routines. Although it has been suggested that the appearance of LENR phenomena is intimately related to specific characteristics of the material, the experimental system described herein has recorded anomalous numbers of neutrons on several occasions using materials of unspecified origin. Helium-3 data indicate neutrons are periodically emitted by reactions occurring within the D/Ti lattice, with a recorded maximum of 1800 neutrons per second, but these neutron releases do not appear to coincide with thermal shock events

Neutron Imaging with Timepix Coupled Lithium Indium Diselenide

The material lithium indium diselenide, a single crystal neutron sensitive semiconductor, has demonstrated its capabilities as a high resolution imaging device. The sensor was prepared with a 55 μ m pitch array of gold contacts, designed to couple with the Timepix imaging ASIC. The resulting device was tested at the High Flux Isotope Reactor, demonstrating a response to cold neutrons when enriched in 95% 6 Li. The imaging system performed a series of experiments resulting in a <200 μ m resolution limit with the Paul Scherrer Institute (PSI) Siemens star mask and a feature resolution of 34 μ m with a knife-edge test. Furthermore, the system was able to resolve the University of Tennessee logo inscribed into a 3D printed 1 cm 3 plastic block. This technology marks the application of high resolution neutron imaging using a direct readout semiconductor

Progress in diamond sensor development for use in LENR experiments

Electronic grade single crystal diamonds have recently become available, and the characteristics of these diamonds are ideal for the detection of various types of nuclear radiation. Previous work demonstrated the usefulness of diamond detectors in low energy nuclear reaction systems and exposed their fragile nature when used in situ. This work describes the use of different material combinations and fabrication techniques in an effort to improve the sensitivity and durability of these diamond sensors. We have successfully fabricated Palladium electrode diamond sensors using two additional material combinations. Their behavior was characterized using common I-V techniques. The spectroscopic response of the sensors was calibrated using a Pu-239 alpha source