Design of a new neutron delivery system for high flux source

La construcción en la actualidad de nuevas fuentes para el uso de haces de neutrones así como los programas de renovación en curso en algunas de las instalaciones experimentales existentes han evidenciado la necesidad urgente de desarrollar la tecnología empleada para la construcción de guías de neutrones con objeto de hacerlas mas eficientes y duraderas. Esto viene motivado por el hecho de que varias instalaciones de experimentación con haces de neutrones han reportado un número de incidentes mecánicos con tales guías, lo que hace urgente el progresar en nuestro conocimiento de los susbtratos vítreos sobre los cuales se depositan los espejos que permiten la reflexión total de los neutrones y como aquellos se degradan con la radiación. La presente tesis se inscribe en un acuerdo de colaboración establecido entre el Institut Max von Laue - Paul Langevin (ILL) de Grenoble y el Consorcio ESS-Bilbao con objeto de mejorar el rendimiento y sostenibilidad de los sistemas futuros de guiado de neutrones. El caso de la Fuente Europea de Espalación en construcción en Lund sirve como ejemplo ya que se contempla la instalación de guías de neutrones de más de 100 metros en algunos de los instrumentos. Por otro lado, instalaciones como el ILL prevén también dentro del programa Endurance de rejuvenecimiento la reconstrucción de varias líneas de transporte de haz. Para el presente estudio se seleccionaron cuatro tipos de vidrios borosilicatados que fueron el Borofloat, N-ZK7, N-BK7 y SBSL7. Los tres primeros son bien conocidos por los especialistas en instrumentación neutrónica ya que se han empleado en la construcción de varias instalaciones mientras que el último es un candidato potencial en la fabricación de substratos para espejos neutrónicos en un futuro. Los cuatro vidrios tiene un contenido en óxido de Boro muy similar, approximadamente un 10 mol.%. Tal hecho que obedece a las regulaciones para la fabricación de estos dispositivos hace que tales substratos operen como protección radiológica absorbiendo los neutrones transmitidos a través del espejo de neutrones. Como contrapartida a tal beneficio, la reacción de captura 10B(n,_)7Li puede degradar el substrato vítreo debido a los 2.5 MeV de energía cinética depositados por la partícula _ y los núcleos en retroceso y de hecho la fragilidad de tales vidrios bajo radiación ha sido atribuida desde hace ya tiempo a los efectos de esta reacción. La metodología empleada en esta tesis se ha centrado en el estudio de la estructura de estos vidrios borosilicatados y como esta se comporta bajo condiciones de radiación. Los materiales en cuestión presentan estructuras que dependen de su composición química y en particular del ratio entre formadores y modificadores de la red iono-covalente. Para ello se han empleado un conjunto de técnicas de caracterización tanto macro- como microscópicas tales como estudios de dureza, TEM, Raman, SANS etc. que se han empleado también para determinar el comportamiento de estos materiales bajo radiación. En particular, algunas propiedades macroscópicas relacionadas con la resistencia de estos vidrios como elementos estructurales de las guías de neutrones han sido estudiadas así como también los cambios en la estructura vítrea consecuencia de la radiación. Para este propósito se ha diseñado y fabricado por el ILL un aparato para irradiación de muestras con neutrones térmicos en el reactor del ILL que permite controlar la temperatura alcanzada por la muestra a menos de 100 °C. Tal equipo en comparación con otros ya existences permite en cuestión de dias acumular las dosis recibidas por una guía en operación a lo largo de varios años. El uso conjunto de varias técnicas de caracterización ha llevado a revelar que los vidrios aqui estudiados son significativamente diferentes en cuanto a su estructura y que tales diferencias afectan a sus propiedades macroscópicas asi como a su comportamiento bajo radiación. Tal resultado ha sido sorprendente ya que, como se ha mencionado antes, algunos de estos vidrios eran bien conocidos por los fabricantes de guías de neutrones y hasta el momento eran considerados prácticamente similares debido a su contenido comparable en óxido de Boro. Sin embargo, los materiales N-BK7 and S-BSL7 muetran gran homogeneidad a todas las escalas de longitud, y más específicamente, a escalas nanométricas las subredes de Sílice y óxido de Boro se mezclan dando logar a estructuras locales que recuerdan a la del cristal de Reedmergnerita. Por el contrario, N-ZK7 y Borofloat muestran dominios separados ricos en Sílice o Boro. Como era de esperar, las importantes diferencias arriba mencionadas se traducen en comportamientos dispares de estos materiales bajo un haz de neutrones térmicos. Los resultados muestran que el N-BK7 y el S-BSL7 son los más estables bajo radiación, lo que macroscópicamente hace que estos materiales muestren un comportamiento similar expandiéndose lentamente en función de la dosis recibida. Por el contario, los otros dos materiales muestran un comportamiento mucho más reactivo, que hace que inicialmente se compacten con la dosis recibida lo que hace que las redes de Silicio y Boro se mezclen resultando en un incremento en densidad hasta alcanzar un valor límite, seguido por un proceso de expansión lenta que resulta comparable al observado para N-BK7 y SBSL7. Estos resultados nos han permitido explicar el origen de las notorias diferencias observadas en cuanto a las dosis límite a partir de las cuales estos materiales desarrollan procesos de fragmentación en superficie. ABSTRACT The building of new experimental neutron beam facilities as well as the renewal programmes under development at some of the already existing installations have pinpointed the urgent need to develop the neutron guide technology in order to make such neutron transport devices more efficient and durable. In fact, a number of mechanical failures of neutron guides have been reported by several research centres. It is therefore important to understand the behaviour of the glass substrates on top of which the neutron optics mirrors are deposited and how these materials degrade under radiation conditions. The case of the European Spallation Source (ESS) at present under construction at Lund is a good example. It previews the deployment of neutron guides having more than 100 metres of length for most of the instruments. Also, the future renovation programme of the ILL, called Endurance, foresees the refurbishment of several beam lines. This Ph.D. thesis was the result of a collaboration agreement between the ILL and ESS-Bilbao aiming to improve the performance and sustainability of future neutron delivery systems. Four different industrially produced alkali-borosilicate glasses were selected for this study: Borofloat, N-ZK7, N-BK7 and SBSL7. The first three are well known within the neutron instrumentation community as they have already been used in several installations whereas the last one is at present considered as a candidate for making future mirror substrates. All four glasses have a comparable content of boron oxide of about 10 mol.%. The presence of such a strong neutron absorption element is in fact a mandatory component for the manufacturing of neutron guides because it provides a radiological shielding for the environment. This benefit is however somewhat counterbalanced since the resulting 10B(n,_)7Li reactions degrade the glass due to the deposited energy of 2.5 MeV by the _ particle and the recoil nuclei. In fact, the brittleness of some of these materials has been ascribed to this reaction. The methodology employed by this study consisted in understanding the general structure of borosilicates and how they behave under irradiation. Such materials have a microscopic structure strongly dependent upon their chemical content and particularly on the ratios between network formers and modifiers. The materials have been characterized by a suite of macroscopic and structural techniques such as hardness, TEM, Raman, SANS, etc. and their behaviour under irradiation was analysed. Some macroscopic properties related to their resistance when used as guide structural elements were monitored. Also, changes in the vitreous structure due to radiation were observed by means of several experimental tools. For such a purpose, an irradiation apparatus has been designed and manufactured to enable irradiation with thermal neutrons within the ILL reactor while keeping the samples below 100 °C. The main advantage of this equipment if compared to others previously available was that it allowed to reach in just some days an equivalent neutron dose to that accumulated by guides after several years of use. The concurrent use of complementary characterization techniques lead to the discovery that the studied glasses were deeply different in terms of their glass network. This had a strong impact on their macroscopic properties and their behaviour under irradiation. This result was a surprise since, as stated above, some of these materials were well known by the neutron guide manufacturers, and were considered to be almost equivalent because of their similar boron oxide content. The N-BK7 and S-BSL7 materials appear to be fairly homogeneous glasses at different length scales. More specifically, at nanometre scales, silicon and boron oxide units seem to mix and generate larger structures somewhat resembling crystalline Reedmergnerite. In contrast, N-ZK7 and Borofloat are characterized by either silicon or boron rich domains. As one could expect, these drastic differences lead to their behaviour under thermal neutron flux. The results show that N-BK7 and S-BSL7 are structurally the most stable under radiation. Macroscopically, such stability results in the fact that these two materials show very slow swelling as a function or radiation dose. In contrast, the two other glasses are much more reactive. The whole glass structure compacts upon radiation. Specifically, the silica network, and the boron units tend to blend leading to an increase in density up to some saturation, followed by a very slow expansion which comes to be of the same order than that shown by N-BK7 and S-BSL7. Such findings allowed us to explain the drastic differences in the radiation limits for macroscopic surface splintering for these materials when they are used in neutron guides.

(Table 1) Elements at DSDP Section 93-605-66-1

The oldest sediments cored at Site 605 are upper Maestrichtian argillaceous limestone (Hole 605, Subunit VB). The terrigeneous silt content of the uppermost Maestrichtian is quite low, averaging about 3%, whereas the carbonate content is high, usually greater than 60%; the silt contains only traces of glauconite (Site 605 chapter, this volume). Within Subunit VB a K/T boundary was defined by planktonic foraminifers. It was expected to be spread over an extended vertical interval because of the continental margin depositional setting. Examination by the shipboard party showed that the K/T boundary occurs in Section 605-66-1, between 70 and 75 cm. At the contact, the foraminiferal Globigerina pseudobulloides Zone (PIc) and the Coccolith Cruciplacolithus primus Subzone (CPla) overlie, respectively, the Abathomphalus mayaroensis and Nephrolithus frequens zones (Site 605). However, the thin K/T boundary clay, which is always present in complete sections, was not found, indicating either that the K/T boundary clay was not present or, more likely, that it was washed away during the coring operation.

Capture cross sections for fast neutrons /

Work performed at the Argonne National Laboratory.

Capture cross sections of I¹²⁷, In¹¹⁵, Ag¹⁰⁹, Au¹⁹⁷, Ag¹⁰⁷ for neutrons of various energies /

"LADC 101"

Concentrations of chemical elements in bottom sediments from the Southeast Pacific

Data from the Appendix to the PhD Thesis of the author.

Assessing Surveillance Elements of the Zanzibar Malaria Elimination Program to Support Malaria Elimination in Zanzibar

Though significant progress has been made through control efforts in recent years, malaria remains a leading cause of morbidity and mortality throughout the world, with 3.2 billion people at risk of developing the disease. Zanzibar is currently pursuing malaria elimination through the Zanzibar Malaria Elimination Program (ZAMEP), and is working toward a goal of no locally acquired malaria cases by 2018. A comprehensive and well functioning malaria surveillance program is central to achieving this goal. Under ZAMEP’s current surveillance strategy, District Malaria Surveillance Officers (DMSOs) respond to malaria case notifications through the reactive case detection (RACD) system. Three malaria screening and treatment strategies are undertaken in response to this system, including household-level (HSaT), focal-level (FSaT), and mass-level (MSaT). Each strategy is triggered by a different case threshold and tests different-sized populations. The aims of this study were to (1) assess the cost effectiveness of three malaria screening and treatment strategies; (2) assess the timeliness and completeness of ZAMEP’s RACD system; (3) and qualitatively explore the roles of DMSOs.

Screening disposition and budget information for 2014 screening and treatment strategies was analyzed to determine prevalence rates in screened populations and the cost effectiveness of each strategy. Prevalence rates within the screened population varied by strategy: 6.1 percent in HSaT, 1.2 percent in FSaT, and 0.9 percent in MSaT. Of the various costing scenarios considering cost per person screened, MSaT was the most cost-effective, with costs ranging from $9.57 to $12.57 per person screened. Of the various costing scenarios considering cost per case detected, HSaT was the most cost-effective, at $385.51 per case detected.

Case data from 2013 through mid-2015 was used to assess the timeliness and completeness of the RACD system. The average number of RACD activities occurring within 48 hours of notification improved slightly between 2013 and the first half of 2015, from 90.7 percent to 93.1 percent. The average percentage of household members screened during RACD also increased over the same time period, from 84 percent in 2013 to 89.9 percent in the first half of 2015.

Interviews with twenty DMSOs were conducted to gain insights into the challenges to malaria elimination both from the health system and the community perspectives. Major themes discussed in the interviews include the need for additional training, inadequate information capture at health facility, resistance to household testing, transportation difficulties, inadequate personnel during the high transmission season, and community misinformation.

Zanzibar is now considered a low transmission setting, making elimination feasible, but also posing new challenges to achieving this goal. The findings of this study provide insight into how surveillance activities can be improved to support the goal of malaria elimination in Zanzibar. Key changes include reevaluating the use of MSaT activities, improving information capture at health facilities, hiring additional DMSOs during the high transmission season, and improving community communication.

Major element compositions, minerals and trace elements at DSDP Leg 67 Holes

Mineralogical (microprobe) and geochemical (X-ray fluorescence, neutron activation analyses) data are given for 18 samples of volcanic rocks from the Guatemala Trench area (Deep Sea Drilling Project Leg 67). Typical fresh oceanic tholeiites occur in the trench itself (Hole 500) and in its immediate vicinity on the Cocos Plate (Site 495). Several samples (often reworked) of "spilitic" oceanic tholeiites are also described from the Trench: their mineralogy (greenschist facies association - actinolite + plagioclase + chlorite) and geochemistry (alteration, sometimes linked to manganese and zinc mineralization) are shown to result from high-temperature (300°-475°C) hydrothermal sea water-basalt interactions. The samples studied are depleted in light rare-earth elements (LREE), with the exception of the slightly LREE-enriched basalts from Hole 500. The occurrence of such different oceanic tholeiites in the same area is problematic. Volcanic rocks from the Guatemala continental slope (Hole 494A) are described as greenschist facies metabasites (actinolite + epidote + chlorite + plagioclase + calcite + quartz), mineralogically different from the spilites exposed on the Costa Rica coastal range (Nicoya Peninsula). Their primary magmatic affinity is uncertain: clinopyroxene and plagioclase compositions, together with titanium and other hygromagmaphile element contents, support an "active margin" affinity. The LREE-depleted patterns encountered in the present case, however, are not frequently found in orogenic samples but are typical of many oceanic tholeiites.

Artificial Neural Network and Neutron Aplication in a Volume Fraction Calculation in Annular and Stratified Multiphase System

Multiphase flows, type oil–water-gas are very common among different industrial activities, such as chemical industries and petroleum extraction, and its measurements show some difficulties to be taken. Precisely determining the volume fraction of each one of the elements that composes a multiphase flow is very important in chemical plants and petroleum industries. This work presents a methodology able to determine volume fraction on Annular and Stratified multiphase flow system with the use of neutrons and artificial intelligence, using the principles of transmission/scattering of fast neutrons from a 241Am-Be source and measurements of point flow that are influenced by variations of volume fractions. The proposed geometries used on the mathematical model was used to obtain a data set where the thicknesses referred of each material had been changed in order to obtain volume fraction of each phase providing 119 compositions that were used in the simulation with MCNP-X –computer code based on Monte Carlo Method that simulates the radiation transport. An artificial neural network (ANN) was trained with data obtained using the MCNP-X, and used to correlate such measurements with the respective real fractions. The ANN was able to correlate the data obtained on the simulation with MCNP-X with the volume fractions of the multiphase flows (oil-water-gas), both in the pattern of annular flow as stratified, resulting in a average relative error (%) for each production set of: annular (air= 3.85; water = 4.31; oil=1.08); stratified (air=3.10, water 2.01, oil = 1.45). The method demonstrated good efficiency in the determination of each material that composes the phases, thus demonstrating the feasibility of the technique.

The role of nuclear physics in supernovae and the evolution of neutron stars, Neutrino Opacities, Equation of State, Transport Coefficients, and Dark Matter Production

Thesis (Ph.D.)--University of Washington, 2016-08