Semiconductor Pixel Detectors for Imaging Applications

In this thesis the work is presented as follows: Chapter 1 introduces the ideal detector characteristics for medical imaging. The requirements of the ideal diagnostic method are related to the various types of medical examinations, comparing the existing techniques and discussing results of Monte Carlo simulation studies. A review of existing detectors based on semiconductor microstrip and semiconductor pixel detectors introduces the hybrid Omega family, the pixel readout electronics used by the author for the tests presented in the following chapters. Chapter 2 describes a material defect characterisation study of semi-insulating gallium arsenide using a near-infrared absorption technique. Generally this technique is applied to "as-grown" materials but in this case, using a set-up proposed by the author, the concentration of the deep defect EL2 was monitored in a biased detector for different values of the applied electric field. The results obtained seem to support a theoretical model which predicts the presence of a "quasi"-neutral region inside the detector active volume. The tests performed by the author using silicon and gallium arsenide pixel detectors coupled with the Omega2 and Omega3 read-out electronics are discussed in Chapter 3. The results reported include images of phantoms of different contrasts illuminated by X-ray sources, biological samples traced with beta- emitters and pixel detector characterisation using particle beams. Chapter 4 describes the characterisation made by the author of a photosensitive version of the silicon pixel detector associated with the OmegaD and Omega2 read-out electronics. The tests were performed using light sources at different wavelengths, scintillating plastic fibres and scintillating crystals excited by radioactive sources and particle beams. The aim of this study was the search for a fast, high spatial resolution alternative to CCDs and multi-anodes photomultipliers for scintillating fibre particle tracking and for nuclear medicine based on scintillating crystals. The advantages and limitations of the present system are discussed with possible future improvements The final chapter draws some conclusions about the work reported and offers some considerations for future developments. In particular, a description is given of a new pixel detector electronics chip with single photon counting capabilities, which followed the experience gained with the present versions of the Omega family electronics. The new electronics chip consists of a 64 x 64 array of pixels, each measuring 170 x 170 mum2 and including a 15-bit binary counter. This chip is therefore extremely well-matched to a wide range of X-ray imaging applications, some of which are reviewed here

First fabrication of full 3D-detectors at SINTEF

International audienceA knowledge of the mechanical properties of bacterial biofilms is required to more fully understand the processes of biofilm formation such as initial adhesion or detachment. The main contribution of this article is to demonstrate the use of homogenization techniques to compute mechanical parameters of Pseudomonas aeruginosa PAO1 biofilms. For this purpose, homogenization techniques are used to analyze freeze substitution electron micrographs of the biofilm cross-sections. The concept of a representative volume element and the study about his representativeness allows us to determine the optimal size in order to analyze these biofilm images. Results demonstrate significant heterogeneities with respect to stiffness and these can be explained by varying cell density distribution throughout the bacterial biofilms. These stiffness variations lead to different mechanical properties along the height of the biofilm. Moreover, a numerical shear stress test shows the impact of these heterogeneities on the detachment process. Several modes of detachment are highlighted according to the local strain energy in the different parts of the biofilm. Knowing where, and how, a biofilm may detach will allow better prediction of accumulation and biomass detachment

3D active edge silicon sensors: Device processing, yield and QA for the ATLAS-IBL production

n/

R&D Paths of Pixel Detectors for Vertex Tracking and Radiation Imaging

This report reviews current trends in the R&D of semiconductor pixellated sensors for vertex tracking and radiation imaging. It identifies requirements of future HEP experiments at colliders, needed technological breakthroughs and highlights the relation to radiation detection and imaging applications in other fields of science.Comment: 17 pages, 2 figures, submitted to the European Strategy Preparatory Grou

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Determination of the strong coupling constant αs from transverse energy–energy correlations in multijet events at s√=8 TeV using the ATLAS detector

Measurements of transverse energy–energy correlations and their associated asymmetries in multi-jet events using the ATLAS detector at the LHC are presented. The data used correspond to s√=8 TeV proton–proton collisions with an integrated luminosity of 20.2 fb−1 . The results are presented in bins of the scalar sum of the transverse momenta of the two leading jets, unfolded to the particle level and compared to the predictions from Monte Carlo simulations. A comparison with next-to-leading-order perturbative QCD is also performed, showing excellent agreement within the uncertainties. From this comparison, the value of the strong coupling constant is extracted for different energy regimes, thus testing the running of αs(μ) predicted in QCD up to scales over 1 TeV . A global fit to the transverse energy–energy correlation distributions yields αs(mZ)=0.1162±0.0011(exp.) +0.0084−0.0070(theo.) , while a global fit to the asymmetry distributions yields a value of αs(mZ)=0.1196±0.0013(exp.) +0.0075−0.0045(theo.)