ENRICHMENT DETERMINATION OF URANIUM METAL IN SHIELDED CONFIGURATIONS WITHOUT CALIBRATION STANDARDS

The determination of the enrichment of uranium is required in many safeguards and security applications. Typical methods to determine the enrichment rely on detecting the 186 keV gamma ray emitted by uranium-235. In some applications the uranium is surrounded by external shields, and removal of the shields is undesirable. In these situations, methods relying on the detection of 186 keV gamma rays fail because these gamma rays are shielded easily. This research presents a novel method to estimate the enrichment of uranium metal when heavily shielded by high-Z materials. The method uses fast neutron tomography to estimate the geometry and materials inside the shielding. With the geometry and materials information, the components suspected of being enriched uranium metal are modeled with different enrichments in Monte Carlo simulations. For each modeled enrichment, a simulation predicts the time correlations expected from plastic scintillation detectors following interrogation of the uranium with a deuterium-tritium neutron generator. The simulated time correlations that best match the measured time correlations are used to estimate the actual enrichment. The method was demonstrated with measurements of a 93% enriched storage casting surrounded by different combinations of depleted uranium shields. For each combination, the fast neutron imaging techniques provided reasonable estimates of the known geometry and materials. Using the estimated geometry, the storage casting was modeled with several enrichments. The comparison of the measured time correlations to the predicted ones for each shielding combination clearly shows that the enrichment of the casting is greater than 80%. By comparing the total doubles measured to the total doubles predicted from the simulations, the estimated enrichment of the casting is between 82% and 95% for the shielding combinations considered. Even though the worst estimate differs from the actual enrichment by 11%, the accuracy of the method is likely acceptable for many nonproliferation applications, including arms control and treaty verification where the goal may be simply to identify the presence of highly enriched uranium

Measurement of the heat transfer coefficient and viscous pressure loss for mercury flowing in narrow channels

The Spallation Neutron Source (SNS) is a new linear accelerator that is being designed for neutron scattering experiments. The SNS will supply pulses of high-energy protons to a flowing liquid mercury target. The spallation reaction resulting from the bombardment of the protons on the mercury target produces 1.3 MW of thermal power, which must be absorbed by the mercury and structural materials. To prevent excessive temperatures and thermal stresses in the structural materials, the liquid mercury must also serve as a coolant in addition to being the source of neutrons. To provide additional cooling to the target container, cool mercury flows in narrow, rectangular channels around the nose of the target container. This area is directly exposed to the proton beam. Three test sections are used in the Mercury Thermal Hydraulic Loop (MTHL) to investigate heat transfer in the window-cooling channels. The Water-Cooled Test Section is used to detect nonwetting spots. The Electrically-Heated Straight Test Section provides high quality data on the heat transfer coefficient and friction factor for flow velocities from 1 to 4 m/s and heat fluxes from 192 kW/m2 to 1.14 MW/m2 at mercury bulk temperatures ranging from 67 to 143 °C. Finally, A Curved Electrically Heated Test Section provides investigation of the effect of curvature on the heat transfer and friction factor performance. Results from the experiments indicate that no non-wetting spots appeared. Observed friction factors are slightly lower than those obtained from a Moody Curve for a smooth pipe, but they agree well at the SNS nominal velocity. Inferred heat transfer coefficients lie well with world tube data when compared on a Nusselt vs. Peclet number plot. Due to fabrication difficulties with the Curved Electrically Heated Test Section, no effects of curvature are discernable

The Effects of Monitoring and Incompatible Contingencies on Say/Do Correspondence.

This study investigated effects of monitoring on correspondence between nonverbal responding and verbal descriptions of those contingencies, when verbal descriptions and contingencies were compatible and when incompatible. In the Nonverbal Component, the contingency for key pressing was either on a 0.8 s IRT or a 3.4 s IRT. In the Verbal Component, subjects made responses to a statement about the contingency for reinforcement in the Nonverbal Component. Shaping was used to establish targets of 0.8 s and 3.4 s in this component. Results indicated that across 7/8 opportunities subjects exhibited nonverbal and verbal behavior that was sensitive to their respective contingencies regardless of compatibility. This sensitivity to contingencies was not affected by the presence of a monitor

Instruction and Assessment in Special Collections: An Exploratory Study of Student, Staff, and Faculty Perceptions

This exploratory study discusses the perceptions of faculty, library staff, and students involved in special collections instruction sessions. Students completed surveys in four sessions of three different classes visiting the collections, and the faculty teaching the courses were interviewed about the sessions. Library staff members were also interviewed about their current and past practices in instruction. Surveys revealed that most students felt competent to begin their research after their sessions, but many students also desired further information about how to approach the collections and in the case of one class, a closer connection to their research projects. Staff members and faculty felt that hands-on activities for students during visits were very important, reflecting the move toward active learning principles in the literature on special collections instruction. The specific challenges faced by assessment programs in special collections are discussed, as well as recommendations for future projects

Electrochemically Generated Acid and Its Containment to 100 Micron Reaction Areas for the Production of DNA Microarrays

An addressable electrode array was used for the production of acid at sufficient concentration to allow deprotection of the dimethoxytrityl (DMT) protecting group from an overlaying substrate bound to a porous reaction layer. Containment of the generated acid to an active electrode of 100 micron diameter was achieved by the presence of an organic base. This procedure was then used for the production of a DNA array, in which synthesis was directed by the electrochemical removal of the DMT group during synthesis. The product array was found to have a detection sensitivity to as low as 0.5 pM DNA in a complex background sample

Non-clinical obsessions in a young adolescent population: Frequency and association with metacognitive variables

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The prevelance of obsessions in a non-clinical adolescent sample

The aim of the current study was to identify the prevalence of obsessional thoughts and impulses in a sample of non-clinical adolescents. Additional hypotheses explored the relationship between general obsessional symptoms, metacognitive beliefs and obsessions in this sample. The impact of normalising information, about obsessions in non-clinical samples, on participants' unhelpful metacognitive beliefs was also examined.EThOS - Electronic Theses Online ServiceGBUnited Kingdo