Reflectance of Polytetrafluoroethylene (PTFE) for Xenon Scintillation Light

Gaseous and liquid xenon particle detectors are being used in a number of applications including dark matter search and neutrino-less double beta decay experiments. Polytetrafluoroethylene (PTFE) is often used in these detectors both as electrical insulator and as a light reflector to improve the efficiency of detection of scintillation photons. However, xenon emits in the vacuum ultraviolet wavelength region (175 nm) where the reflecting properties of PTFE are not sufficiently known. In this work we report on measurements of PTFE reflectance, including its angular distribution, for the xenon scintillation light. Various samples of PTFE, manufactured by different processes (extruded, expanded, skived and pressed) have been studied. The data were interpreted with a physical model comprising both specular and diffuse reflections. The reflectance obtained for these samples ranges from about 47% to 66% for VUV light. Fluoropolymers, namely ETFE, FEP and PFA were also measured

La primauté du droit : la situation des immigrants et des réfugiés en droit canadien au regard des Chartes et des textes internationaux

The « rule of law » which for a long time was considered as an unwritten part of the Constitution now enjoys full constitutional status. Its enshrining in the preamble of the Canadian Charter sheds considerable light on the manner in which the rights and freedoms of the Charter should be perceived. The author opens his discussion by examining the impact that the constitutionalization of the « rule of law » has had on immigrants and refugees in Canada. As the Immigration Act of 1976 confers numerous discretionary powers which could result in their abusive use, the author analyses how the Human Rights charters applicable in Canada and in Quebec can insure the legal protection of immigrants and refugees. In the second part of his study, the author discusses the principal international texts ratified by Canada which have as their purpose the protection of the rights of immigrants and refugees. As international law is not « self-enforcing » in Canada, the author shows how the internal legal community conforms to the international obligations contracted by Canada

A model of the reflection distribution in the vacuum ultra violet region

A reflection model with three components, a specular spike, a specular lobe and a diffuse lobe is discussed. This model was successfully applied to describe reflection of xenon scintillation light (175 nm) by PTFE and other fluoropolymers and can be used for Monte Carlo simulation and analysis of scintillation detectors. The measured data favors a Trowbridge-Reitz distribution function of ellipsoidal micro-surfaces. The intensity of the coherent reflection increases with increasing angle of incidence, as expected, since the surface appears smoother at grazing angles. The total reflectance obtained for PTFE is about 70% for VUV light at normal incidence in vacuum and estimated to be up to 100% in contact with liquid xenon

Estudo de solos do município de Encruzilhada do Sul - RS.

bitstream/item/30598/1/Circular-45.pdf; bitstream/item/30600/1/aptidao-bmp-final.pdf; bitstream/item/30616/1/capacidade-bmp-final.pdf; bitstream/item/30623/1/relevo-bmp-final.pdf; bitstream/item/30634/1/vegetacao-bmp-final.pd

Estudo de solos do município de Esperança do Sul - RS

bitstream/item/30800/1/Circular-49.pdf; bitstream/item/33471/1/aptidao.pdf; bitstream/item/33473/1/vegetacao.pd

Avaliação de metodologias para estimativa da temperatura do ar para áreas de canola no Rio Grande do Sul.

Orientador: Genei Antonio Dalmago

NDVI da canola obtido com sensor Green Seeker e calculado a partir de dados hiperespectrais.

Orientador: Genei Antonio Dalmago

LUX Cryogenics and Circulation

We report the effciency of a thermosyphon-based cooling system for a liquid xenon (LXe) time projection chamber (TPC), as well as the effciency of a unique internal heat exchanger with standard gas phase purification using a heated getter, which allows for very high flow purification without requiring large cooling power.Peer Reviewe

Radioactivity Backgrounds in ZEPLIN-III

We examine electron and nuclear recoil backgrounds from radioactivity in the ZEPLIN-III dark matter experiment at Boulby. The rate of low-energy electron recoils in the liquid xenon WIMP target is 0.75$\pm$0.05 events/kg/day/keV, which represents a 20-fold improvement over the rate observed during the first science run. Energy and spatial distributions agree with those predicted by component-level Monte Carlo simulations propagating the effects of the radiological contamination measured for materials employed in the experiment. Neutron elastic scattering is predicted to yield 3.05$\pm$0.5 nuclear recoils with energy 5-50 keV per year, which translates to an expectation of 0.4 events in a 1-year dataset in anti-coincidence with the veto detector for realistic signal acceptance. Less obvious background sources are discussed, especially in the context of future experiments. These include contamination of scintillation pulses with Cherenkov light from Compton electrons and from $\beta$ activity internal to photomultipliers, which can increase the size and lower the apparent time constant of the scintillation response. Another challenge is posed by multiple-scatter $\gamma$-rays with one or more vertices in regions that yield no ionisation. If the discrimination power achieved in the first run can be replicated, ZEPLIN-III should reach a sensitivity of $\sim 1 \times 10^{-8}$ pb$\cdot$year to the scalar WIMP-nucleon elastic cross-section, as originally conceived.Peer Reviewe

Coquetel vegetal: produção de fitomassa e teores de macro e micronutrientes de espécies para adubação verde e/ou cobertura do solo.

A fitomassa produzida por coquetéis vegetais tem influência direta na melhoria das condições do solo contribuindo com a diminuição das perdas de nutrientes por lixiviação e diminuição da erosão; com a manutenção da umidade e melhoria da infiltração, além de colaborar no controle de ervas espontâneas; auxiliam na disponibilização de nutrientes, principalmente as espécies leguminosas, e na melhoria da estruturação do solo pelas gramíneas. Diante do exposto, o presente trabalho teve como objetivo avaliar a produção da fitomassa e os teores de macro e micronutrientes de espécies vegetais para adubação verde e/ou cobertura do solo. A pesquisa foi desenvolvida na Estação Experimental de Agricultura Irrigada da Embrapa Semiárido, em Petrolina, PE. Foram avaliadas 14 espécies vegetais em diferentes opções de coquetéis vegetais que constituíram cinco tratamentos mais o tratamento referência. Os resultados demonstram que o coquetel vegetal é uma alternativa de manejo que contribui para aumentar a biodiversidade (diversificação de espécies) dentro e acima do solo, estabelecendo um ambiente onde as espécies convivem harmoniosamente. Os tratamentos T3 e T4 apresentaram as melhores produções de fitomassa para as condições de solo e clima do Polo Petrolina, PE/Juazeiro, B