Characterization of Thin p-on-p Radiation Detectors with Active Edges

Active edge p-on-p silicon pixel detectors with thickness of 100 $\mu$m were fabricated on 150 mm Float zone silicon wafers at VTT. By combining measured results and TCAD simulations, a detailed study of electric field distributions and charge collection performances as a function of applied voltage in a p-on-p detector was carried out. A comparison with the results of a more conventional active edge p-on-n pixel sensor is presented. The results from 3D spatial mapping show that at pixel-to-edge distances less than 100 $\mu$m the sensitive volume is extended to the physical edge of the detector when the applied voltage is above full depletion. The results from a spectroscopic measurement demonstrate a good functionality of the edge pixels. The interpixel isolation above full depletion and the breakdown voltage were found to be equal to the p-on-n sensor while lower charge collection was observed in the p-on-p pixel sensor below 80 V. Simulations indicated this to be partly a result of a more favourable weighting field in the p-on-n sensor and partly of lower hole lifetimes in the p-bulk.Comment: 23 pages, 16 figures, 1 tabl

Shock Deformation in Zircon, a Comparison of Results from Shock-Reverberation and Single-Shock Experiments

The utility of the mineral zircon, ZrSiO4, as a shock-metamorphic geobarometer and geochronometer, has been steadily growing within the planetary science community. Zircon is an accessory phase found in many terrestrial rock types, lunar samples, lunar meteorites, martian meteorites and various other achondrites. Because zircon is refractory and has a high closure temperature for Pb diffusion, it has been used to determine the ages of some of the oldest material on Earth and elsewhere in the Solar System. Furthermore, major (O) and trace-element (REE, Ti, Hf) abundances and isotope compositions of zircon help characterize the petrogenetic environments and sources from which they crystallized. The response of zircon to impact-induced shock deformation is predominantly crystallographic, including dislocation creep and the formation of planar and sub-planar, low-angle grain boundaries; the formation of mechanical {112} twins; transformation to the high pressure polymorph reidite; the development of polycrystalline microtextures; and dissociation to the oxide constituents SiO2 and ZrO2. Shock microstructures can also variably affect the U- Pb isotope systematics of zircon and, in some instances, be used to constrain the impact age. While numerous studies have characterized shock deformation in zircon recovered from a variety of terrestrial impact craters and ejecta deposits and Apollo samples, experimental studies of shock deformation in zircon are limited to a handful of examples in the literature. In addition, the formation conditions (e.g., P, T) of various shock microstructures, such as planar-deformation bands, twins, and reidite lamellae, remain poorly con-strained. Furthermore, previous shocked-zircon experimental charges have not been analyzed using modern analytical equipment. This study will therefore under-take an new set of zircon shock experiments, which will then be microstructurally characterized using state-of-the-art instrumentation within the Astromaterials Research and Exploration Science Division (ARES), NASA Johnson Space Center

Real-time in-vivo μ-imaging with Medipix2

Abstract An X-ray micro-radiographic system based on the Medipix2 semiconductor pixel detector for dynamic high spatial resolution and for high contrast imaging has been developed. Our system is based on a micro-focus and nano-focus X-ray tube and the hybrid single-photon counting silicon pixel detector Medipix2 (matrix 256×256 sq. pixels of 55 μm pitch). This compact table-top system stands promising as a new tool in the field of small animal imaging as well as in the in-vivo observation of dynamic processes inside living organisms. The main advantages of these Medipix2 pixel detectors include: high sensitivity to low-energy X-ray photons; position sensitive and noiseless single-photon detection with preselected photon energies; single-quantum counting in each pixel performed by digital counter (therefore there is no dark current); digital integration (providing unlimited dynamic range and absolute linearity in device response to number of photons, high sensitivity and high contrast); real-time digital information, high-speed digital communication and data transfer. We improve the picture quality with the help of statistical data analysis and extended the calibration of individual pixels response. 2D and 3D radiographic images of samples demonstrate the potential and applicability of our system for precise in-vivo X-ray high-resolution dynamic diagnostic and biological studies. Obtained results are shown on small animal and organic samples

Effectiveness verification of an educational program about hearing protection for noise-exposed workers

OBJETIVO: Verificar a efetividade de uma ação educativa de treinamento, com ênfase na importância da proteção auditiva, para trabalhadores expostos a ruído ocupacional. MÉTODOS: Participaram 78 funcionários do gênero masculino. Todos os indivíduos passaram por avaliação audiológica completa e responderam a um questionário no momento do início do atendimento. Para a segunda aplicação do questionário, os participantes foram randomicamente divididos em dois grupos: Grupo Pesquisa, constituído por 44 funcionários, que responderam ao questionário após passarem por treinamento educativo, e Grupo Controle, constituído por 34 funcionários, que responderem ao questionário antes de passar por treinamento educativo. O treinamento foi feito com base em material gráfico com figuras e textos, sob a forma de conversa. Os temas abordados foram: importância da audição, efeitos do ruído sobre a saúde, importância da prevenção da perda auditiva e da utilização do protetor auditivo, conservação e higienização dos protetores, níveis de ruído no ambiente de trabalho e atenuação do ruído fornecida pelos protetores auditivos. O questionário continha 14 perguntas de múltipla escolha que abordavam os mesmos temas explorados no treinamento educativo. RESULTADOS: Houve aumento significativo do número de acertos durante a 2ª aplicação do questionário, somente para o Grupo Pesquisa, em todas as comparações realizadas. CONCLUSÃO: Ações educativas realizadas com trabalhadores expostos a ruído ocupacional são efetivas. Além disso, o questionário é uma ferramenta estável e viável para a verificação da efetividade de programas educativosPURPOSE: To verify the effectiveness of an educational action in the form of training, emphasizing the importance of hearing protection for workers exposed to occupational noise. METHODS: The study included 78 male individuals. All participants answered a questionnaire before they were submitted to audiological evaluation. For the second application of the questionnaire, participants were randomly divided into two groups: Research Group, constituted by 44 subjects that received educational training before the second questionnaire application, and Control Group, comprising 34 individuals that answered the questionnaire before the educational training. Training was based on material with graphic images and text, in the form of conversation. The topics covered included: the importance of hearing, noise effects on health, importance of preventing hearing loss and using hearing protection, conservation and cleaning of hearing protectors, levels of noise in the workplace and noise attenuation provided by hearing protectors. The questionnaire contained 14 multiple choice questions that addressed the same themes explored in the educational training. RESULTS: There was a significant increase of correct responses in the second application of the questionnaire, only in the Research Group, in all comparisons. CONCLUSION: Educational action performed with workers exposed to occupational noise are effective, and the questionnaire is a stable and viable tool to evaluate the effectiveness of educational program

Ultracold-neutron infrastructure for the gravitational spectrometer GRANIT

The gravitational spectrometer GRANIT will be set up at the Institut Laue Langevin. It will profit from the high ultracold neutron density produced by a dedicated source. A monochromator made of crystals from graphite intercalated with potassium will provide a neutron beam with 0.89 nm incident on the source. The source employs superthermal conversion of cold neutrons in superfluid helium, in a vessel made from BeO ceramics with Be windows. A special extraction technique has been tested which feeds the spectrometer only with neutrons with a vertical velocity component v < 20 cm/s, thus keeping the density in the source high. This new source is expected to provide a density of up to 800 1/cm3 for the spectrometer.Comment: accepted for publication in Proceedings International Workshop on Particle Physics with Slow Neutron

BrachyView, A novel inbody imaging system for HDR prostate brachytherapy: Design and Monte Carlo feasibility study

Purpose: High dose rate (HDR) brachytherapy is a form of radiation therapy for treating prostate cancer whereby a high activity radiation source is moved between predefined positions inside applicators inserted within the treatment volume. Accurate positioning of the source is essential in delivering the desired dose to the target area while avoiding radiation injury to the surrounding tissue. In this paper, HDR BrachyView, a novel inbody dosimetric imaging system for real time monitoring and verification of the radioactive seed position in HDR prostate brachytherapy treatment is introduced. The current prototype consists of a 15 × 60 mm2 silicon pixel detector with a multipinhole tungsten collimator placed 6.5 mm above the detector. Seven identical pinholes allow full imaging coverage of the entire treatment volume. The combined pinhole and pixel sensor arrangement is geometrically designed to be able to resolve the three-dimensional location of the source. The probe may be rotated to keep the whole prostate within the transverse plane. The purpose of this paper is to demonstrate the efficacy of the design through computer simulation, and to estimate the accuracy in resolving the source position (in detector plane and in 3D space) as part of the feasibility study for the BrachyView project. Methods: Monte Carlo simulations were performed using the GEANT4 radiation transport model, with a 192Ir source placed in different locations within a prostate phantom. A geometrically accurate model of the detector and collimator were constructed. Simulations were conducted with a single pinhole to evaluate the pinhole design and the signal to background ratio obtained. Second, a pair of adjacent pinholes were simulated to evaluate the error in calculated source location. Results: Simulation results show that accurate determination of the true source position is easily obtainable within the typical one second source dwell time. The maximum error in the estimated projection position was found to be 0.95 mm in the imaging (detector) plane, resulting in a maximum source positioning estimation error of 1.48 mm. Conclusions: HDR BrachyView is a feasible design for real-time source tracking in HDR prostate brachytherapy. It is capable of resolving the source position within a subsecond dwell time. In combination with anatomical information obtained from transrectal ultrasound imaging, HDR BrachyView adds a significant quality assurance capability to HDR brachytherapy treatment systems. © 2013 American Association of Physicists in Medicine

Formation and dynamics of van der Waals molecules in buffer-gas traps

We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxations are too slow to affect trap lifetimes. However, helium-3-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag3He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps.Comment: 20 pages, 13 figure

Experimental Tests of Neutron Shielding for the ATLAS Forward Region

Experimental tests devoted to the optimization of the neutron shielding for the ATLAS forward region were performed at the CERN-PS with a 4 GeV/c proton beam. Spectra of fast neutrons, slow neutrons and gamma rays escaping a block of iron (40$\times$40$\times$80 cm$^3$) shielded with different types of neutron and gamma shields (pure polyethylene - PE, borated polyethylene - BPE, lithium filled polyethylene - LiPE, lead, iron) were measured by means of plastic scintillators, a Bonner spectrometer, a HPGe detector and a slow neutron detector. Effectiveness of different types of shielding agaisnt neutrons and $\gamma$-rays were compared. The idea of a segmented outer layer shielding (iron, BPE, iron, LiPE) for the ATLAS Forward Region was also tested

Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC

The uncertainty on the calorimeter energy response to jets of particles is derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the calorimeter response to single isolated charged hadrons is measured and compared to the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter response to specific types of particles (positively and negatively charged pions, protons, and anti-protons) is measured and compared to the Monte Carlo predictions. Finally, the jet energy scale uncertainty is determined by propagating the response uncertainty for single charged and neutral particles to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3% for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table, submitted to European Physical Journal

Standalone vertex finding in the ATLAS muon spectrometer

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011