82 research outputs found
Effects of High Charge Densities in Multi-GEM Detectors
A comprehensive study, supported by systematic measurements and numerical
computations, of the intrinsic limits of multi-GEM detectors when exposed to
very high particle fluxes or operated at very large gains is presented. The
observed variations of the gain, of the ion back-flow, and of the pulse height
spectra are explained in terms of the effects of the spatial distribution of
positive ions and their movement throughout the amplification structure. The
intrinsic dynamic character of the processes involved imposes the use of a
non-standard simulation tool for the interpretation of the measurements.
Computations done with a Finite Element Analysis software reproduce the
observed behaviour of the detector. The impact of this detailed description of
the detector in extreme conditions is multiple: it clarifies some detector
behaviours already observed, it helps in defining intrinsic limits of the GEM
technology, and it suggests ways to extend them.Comment: 5 pages, 6 figures, 2015 IEEE Nuclear Science Symposiu
Charge Transfer Properties Through Graphene for Applications in Gaseous Detectors
Graphene is a single layer of carbon atoms arranged in a honeycomb lattice
with remarkable mechanical and electrical properties. Regarded as the thinnest
and narrowest conductive mesh, it has drastically different transmission
behaviours when bombarded with electrons and ions in vacuum. This property, if
confirmed in gas, may be a definitive solution for the ion back-flow problem in
gaseous detectors. In order to ascertain this aspect, graphene layers of
dimensions of about 2x2cm, grown on a copper substrate, are transferred
onto a flat metal surface with holes, so that the graphene layer is freely
suspended. The graphene and the support are installed into a gaseous detector
equipped with a triple Gaseous Electron Multiplier (GEM), and the transparency
properties to electrons and ions are studied in gas as a function of the
electric fields. The techniques to produce the graphene samples are described,
and we report on preliminary tests of graphene-coated GEMs.Comment: 4pages, 3figures, 13th Pisa Meeting on Advanced Detector
Increased strontium uptake in trabecular bone of ovariectomized calcium-deficient rats treated with strontium ranelate or strontium chloride
Based on clinical trials showing the efficacy to reduce vertebral and non-vertebral fractures, strontium ranelate (SrR) has been approved in several countries for the treatment of postmenopausal osteoporosis. Hence, it is of special clinical interest to elucidate how the Sr uptake is influenced by dietary Ca deficiency as well as by the formula of Sr administration, SrR versus strontium chloride (SrCl2). Three-month-old ovariectomized rats were treated for 90 days with doses of 25 mg kg-1 d-1 and 150 mg kg-1 d-1 of SrR or SrCl2 at low (0.1% Ca) or normal (1.19% Ca) Ca diet. Vertebral bone tissue was analysed by confocal synchrotron-radiation-induced micro X-ray fluorescence and by backscattered electron imaging. Principal component analysis and k-means clustering of the acquired elemental maps of Ca and Sr revealed that the newly formed bone exhibited the highest Sr fractions and that low Ca diet increased the Sr uptake by a factor of three to four. Furthermore, Sr uptake in bone of the SrCl2-treated animals was generally lower compared with SrR. The study clearly shows that inadequate nutritional calcium intake significantly increases uptake of Sr in serum as well as in trabecular bone matrix. This indicates that nutritional calcium intake as well as serum Ca levels are important regulators of any Sr treatment
Charge transfer properties through graphene for applications in gaseous detectors
Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical and electrical properties. Regarded as the thinnest and narrowest conductive mesh, it has drastically different transmission behaviours when bombarded with electrons and ions in vacuum. This property, if confirmed in gas, may be a definitive solution for the ion back-flow problem in gaseous detectors. In order to ascertain this aspect, graphene layers of dimensions of about 2 x 2 cm(2), grown on a copper substrate, are transferred onto a flat metal surface with holes, so that the graphene layer is freely suspended. The graphene and the support are installed into a gaseous detector equipped with a triple Gaseous Electron Multiplier (GEM), and the transparency properties to electrons and ions are studied in gas as a function of the electric fields. The techniques to produce the graphene samples are described, and we report on preliminary tests of graphene-coated GEMs.UK Research & Innovation (UKRI) - Engineering & Physical Sciences Research Council (EPSRC) - EP/H020055/1 / EP/N004159/
Synchrotron radiation micro X-ray fluorescence spectroscopy of thin structures in bone samples: comparison of confocal and color X-ray camera setups
Aerosol particle chemical characteristics measured from aircraft in the lower troposphere during ACE-2
Tellus (ACE-2 Special Issue), 52B, 185-200.During the Aerosol Characterization Experiment (ACE-2), filter samples were collected aboard
the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Pelican aircraft
near Tenerife in June and July of 1997. The flights included constant altitude measurements in
the boundary layer as well as profiles up to 3800 m providing detailed chemical information
about the composition of the aerosol distribution in the lower troposphere. Three cases with
different air mass origins — clean marine air, anthropogenically-influenced air from the
European continent, and dust-laden air from the Sahara — were identified. The samples were
analyzed by ion chromatography (IC) for ionic species, by combined thermal and optical
analysis (TOA) for organic carbon, and by total reflection X-ray fluorescence (TXRF) for
elemental composition. Particle composition and size distributions for the range of air masses
encountered illustrate links in the chemical and microphysical characteristics of aerosol from
different sources. Clean marine air masses were characterized by low particle number and mass
concentrations with no detectable metals, while anthropogenically-influenced and dust-laden
air had high number, mass, and trace metal concentrations. Anthropogenic sources were characterized
by high concentrations of submicron particles and some Fe and Cu, whereas dust particle
loadings included a significant mass of micron-sized particles and significant loadings of Fe, in
addition to small amounts of Mn, Cu, and Ni. These results showed similar tracers for air mass
origin as those found in other measurements of oceanic and continental air masses. Aerosol
optical properties were estimated with a simplified model of the aerosol based on the measured
compositions. The real and imaginary refractive indices and single scattering albedos differed
significantly among the three types of aerosol measured, with clean marine aerosol properties
showing the least absorption and dust-containing aerosols showing the most. There were only
small differences in optical properties for the two different cases of clean marine aerosol, but
some significant differences between the two dust cases. Since measurement uncertainties affect
these calculations, we studied the type of mixing and the fraction of absorbing species and
found the calculation was sensitive to these variations only for the dust-containing aerosol case,
probably due to the small amount of water present. While the optical properties varied little with composition for clean marine and anthropogenically-influenced cases, they showed a strong
dependence on variations in particle composition and mixing state for the dust-containing cases
Total reflection x-ray fluorescence analysis of light elements under various excitation conditions
Total reflction x-ray fluorescence (TXRF) analysis was tested for its suitability for the photon-induced energy dispersiver analysis of light elements such as B, C, N, O, F, Na and Mg using a special spectrometer meeting the requirements for the detection of low-energy fluorescence radiation. The influence of different spectral modification devices such as a high-energy cut-off reflector and a multilayer monochromator were compared using excitation by a Cr tube and also synchrotron radiation. The effects on intensity, background and detection lilmits are compared and discussed. A new method of monitoring the x-ray beam to adjust total reflection by a CCD camera is introduced. Considerations on the penetration depth and information depth of light elements are presented
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