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

Recursos marinhos de Moçambique

This work aims to be a systematic description of marine fisheries of Mozambique, analysing old and new data. The various fish resources were divided in crustaceans, fish and other resources. The latest revision was presented during the Mozambique/NORAD Seminar on marine resources (1984), which also included fishing potential estimates. Mozambique does not have a national system of statistical data collection that covers all fisheries and this affects in particular the artisanal sector. The industrial and semi-industrial fisheries, however, are well covered and produce reliable data on catch and effort for resources evaluation

Características físicas dos ovos da perdiz vermelha (Alectoris rufa) criada em cativeiro

The objective of the present study was to evaluate the effects of female age (1, 2 and 3-year-old) and month of laying (March, April and May) on the physical characteristics of the red-legged partridge eggs reared in captivity. O objetivo do presente estudo foi avaliar os efeitos da idade das fêmeas (um, dois e três anos) e do mês de postura (março, abril e maio) sobre as características físicas dos ovos da perdiz vermelha (Alectoris rufa) criada em cativeiro. O peso (W), o comprimento máximo (L) e a largura máxima (B) de 2878 ovos foram determinados diretamente, enquanto o índice de forma (B/L), o volume (V) e a superfície (S) foram calculados com base nos parâmetros determinados diretamente. A análise mostrou diferenças significativas (P0,05). Observaram-se diferenças significativas (P<0,01) na largura máxima e no índice de forma do ovo entre as diferentes classes de idades, com valores mais elevados nas fêmeas mais velhas e no período de postura mais tardio. O volume dos ovos estimados por meio de V1 = 0,51LB2 e V2=0,913W foi afetado significativamente (P<0,01) pela idade e pelo mês de postura, bem como as áreas, S1=4.835W0,662, S2=4,951V10,666 e S3=4,951V20,666, as quais apresentaram os mesmos efeitos. Palavras-chave: perdiz vermelha, Alectoris rufa, características dos ovo

Variação do valor nutricional de caprinos Serranos ecótipo Jarmelista com diferentes graus de maturidade

O teor de gordura da carne dos caprinos é inferior em 47 e 54% relativamente à da carne dos bovinos e dos ovinos, respectivamente. A maior parte da gordura daqueles animais situa-se na cavidade abdominal, sendo retirada aquando da obtenção da carcaça, reduzindo desta forma o teor de gordura subcutânea o que, sob o ponto de vista de saúde, pode ter efeitos benéficos em relação à carne de bovinos e de suínos. Este estudo teve como objectivo caracterizar a carne de carcaças de caprinos machos e fêmeas desde os 10% até aos 40% de maturidade. Utilizaram-se 21 machos e 21 fêmeas, da raça caprina serrana ecótipo jarmelista, alimentados em prado de sequeiro natural. Quando os animais atingiram o grau de maturidade para abate, este foi efectuado após um jejum de 24 horas. As amostras de cada carcaça foram obtidas por dissecação, sendo o músculo e a gordura triturados e homogeneizados por forma a obter uma amostra de músculo e de gordura (gordura subcutânea com a gordura intermuscular). As amostras foram armazenadas a -18ºC até as análises serem efectuadas. A determinação da Humidade foi realizada pelo método II da NP– 1614 (1979). A determinação da proteína bruta foi efectuada pelo método de Kjeldhal, segundo a NP– 1612 . Para a determinação da gordura utilizou-se método de Soxhlet, segundo a NP– 1224 (1982). Com os resultados obtidos verifica-se que os caprinos são animais com baixo teor de tecido adiposo, apresentando os machos ligeiramente mais músculo, mais osso e menos gordura do que as fêmeas. Os teores de gordura na carcaça de caprino foram de 12,5% e 14,5% para os machos e as fêmeas respectivamente. Nas fêmeas, contrariamente aos machos, a distribuição da gordura, faz-se tanto no músculo como no tecido adiposo. Constatou-se também que as fêmeas apresentavam teores de proteína ligeiramente mais elevados (21,7%) do que os machos (20,9%) sem contudo haver diferença significativa entre os grupos. Quanto ao conteúdo mineral também não se observaram diferenças estatisticamente significativas Verifica-se assim que a carne dos caprinos é uma fonte de carne magra e quando consumida como parte integrante de uma dieta variada, equilibrada e em associação com o exercício físico, esta carne é saudável e benéfica, podendo contribuir para a prevenção de algumas patologias, nomeadamente as doenças cardiovasculares

Anisotropic splitting of intersubband spin plasmons in quantum wells with bulk and structural inversion asymmetry

In semiconductor heterostructures, bulk and structural inversion asymmetry and spin-orbit coupling induce a k-dependent spin splitting of valence and conduction subbands, which can be viewed as being caused by momentum-dependent crystal magnetic fields. This paper studies the influence of these effective magnetic fields on the intersubband spin dynamics in an asymmetric n-type GaAs/AlGaAs quantum well. We calculate the dispersions of intersubband spin plasmons using linear response theory. The so-called D'yakonov-Perel' decoherence mechanism is inactive for collective intersubband excitations, i.e., crystal magnetic fields do not lead to decoherence of spin plasmons. Instead, we predict that the main signature of bulk and structural inversion asymmetry in intersubband spin dynamics is a three-fold, anisotropic splitting of the spin plasmon dispersion. The importance of many-body effects is pointed out, and conditions for experimental observation with inelastic light scattering are discussed.Comment: 8 pages, 6 figure

Scintillation efficiency of liquid xenon for nuclear recoils with the energy down to 5 keV

The scintillation efficiency of liquid xenon for nuclear recoils has been measured to be nearly constant in the recoil energy range from 140 keV down to 5 keV. The average ratio of the efficiency for recoils to that for gamma-rays is found to be 0.19+-0.02.Comment: 13 pages, 5 figure

Identification of Radiopure Titanium for the LZ Dark Matter Experiment and Future Rare Event Searches

The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a detector containing a total of 10 tonnes of liquid xenon within a double-vessel cryostat. The large mass and proximity of the cryostat to the active detector volume demand the use of material with extremely low intrinsic radioactivity. We report on the radioassay campaign conducted to identify suitable metals, the determination of factors limiting radiopure production, and the selection of titanium for construction of the LZ cryostat and other detector components. This titanium has been measured with activities of $^{238}$U$_{e}$~$<$1.6~mBq/kg, $^{238}$U$_{l}$~$<$0.09~mBq/kg, $^{232}$Th$_{e}$~$=0.28\pm 0.03$~mBq/kg, $^{232}$Th$_{l}$~$=0.25\pm 0.02$~mBq/kg, $^{40}$K~$<$0.54~mBq/kg, and $^{60}$Co~$<$0.02~mBq/kg (68\% CL). Such low intrinsic activities, which are some of the lowest ever reported for titanium, enable its use for future dark matter and other rare event searches. Monte Carlo simulations have been performed to assess the expected background contribution from the LZ cryostat with this radioactivity. In 1,000 days of WIMP search exposure of a 5.6-tonne fiducial mass, the cryostat will contribute only a mean background of $0.160\pm0.001$(stat)$\pm0.030$(sys) counts.Peer Reviewe

Position Reconstruction in LUX

The (x, y) position reconstruction method used in the analysis of the complete exposure of the Large Underground Xenon (LUX) experiment is presented. The algorithm is based on a statistical test that makes use of an iterative method to recover the photomultiplier tube (PMT) light response directly from the calibration data. The light response functions make use of a two dimensional functional form to account for the photons reflected on the inner walls of the detector. To increase the resolution for small pulses, a photon counting technique was employed to describe the response of the PMTs. The reconstruction was assessed with calibration data including 83mKr (releasing a total energy of 41.5 keV) and 3H (β− with Q = 18.6 keV) decays, and a deuterium-deuterium (D-D) neutron beam (2.45 MeV) . Within the detector's fiducial volume, the reconstruction has achieved an (x, y) position uncertainty of σ = 0.82 cm and σ = 0.17 cm for events of only 200 and 4,000 detected electroluminescence photons respectively. Such signals are associated with electron recoils of energies ~0.25 keV and ~10 keV, respectively. The reconstructed position of the smallest events with a single electron emitted from the liquid surface (22 detected photons) has a horizontal (x, y) uncertainty of 2.13 cm.Peer Reviewe

Measurement of the absolute reflectance of polytetrafluoroethylene (PTFE) immersed in liquid xenon

The performance of a detector using liquid xenon (LXe) as a scintillator is strongly dependent on the collection efficiency for xenon scintillation light, which in turn is critically dependent on the reflectance of the surfaces that surround the active volume. To improve the light collection in such detectors the active volume is usually surrounded by polytetrafluoroethylene (PTFE) reflector panels, used due to its very high reflectance—even at the short wavelength of scintillation light of LXe (peaked at 178 nm). In this work, which contributed to the overall R&D effort towards the LUX-ZEPLIN (LZ) experiment, we present experimental results for the absolute reflectance measurements of three different PTFE samples (including the material used in the LUX detector) immersed in LXe for its scintillation light. The obtained results show that very high bi-hemispherical reflectance values (≥ 97%) can be achieved, enabling very low energy thresholds in liquid xenon scintillator-based detectors.Peer Reviewe

Ultralow energy calibration of LUX detector using 127^{127}Xe electron capture

We report an absolute calibration of the ionization yields (Qy) and fluctuations for electronic recoil events in liquid xenon at discrete energies between 186 eV and 33.2 keV. The average electric field applied across the liquid xenon target is 180  V/cm. The data are obtained using low energy Xe127 electron capture decay events from the 95.0-day first run from LUX (WS2013) in search of weakly interacting massive particles. The sequence of gamma-ray and x-ray cascades associated with I127 deexcitations produces clearly identified two-vertex events in the LUX detector. We observe the K-(binding energy, 33.2 keV), L-(5.2 keV), M-(1.1 keV), and N-(186 eV) shell cascade events and verify that the relative ratio of observed events for each shell agrees with calculations. The N-shell cascade analysis includes single extracted electron (SE) events and represents the lowest-energy electronic recoil in situ measurements that have been explored in liquid xenon.Peer Reviewe