Search results for "Instrumentation"
showing 10 items of 4914 documents
High-precision x-ray spectroscopy of highly charged ions with microcalorimeters
2013
The precise determination of the energy of the Lyman α1 and α2 lines in hydrogen-like heavy ions provides a sensitive test of quantum electrodynamics in very strong Coulomb fields. To improve the experimental precision, the new detector concept of microcalorimeters is now exploited for such measurements. Such detectors consist of compensated-doped silicon thermistors and Pb or Sn absorbers to obtain high quantum efficiency in the energy range of 40–70 keV, where the Doppler-shifted Lyman lines are located. For the first time, a microcalorimeter was applied in an experiment to precisely determine the transition energy of the Lyman lines of lead ions at the experimental storage ring at GSI. T…
Axial behaviour of Cantor ring diffractals
2003
Cantor ring diffractals describe rotationally symmetric pupils constructed from a one-dimensional polyadic Cantor set. The influence on the axial irradiance of several fractal descriptors of such pupils, including fractal dimension, number of gaps and lacunarity, are investigated. It is shown that, contrary to their transversal response, the axial behaviour of these pupils does not resemble the fractal structure of the aperture. The sensitivity of such pupils to the spherical aberration is also analysed.
Development of a High Precision Axial 3-D PET for Brain Imaging
2009
We describe a PET device based on a novel method to extract the coordinates of the interaction point of the 511keV γ rays from 100 mm long and thin LYSO (Lutetium Yttrium OxyorthoSilicate) scintillator bars, positioned axially in the tomograph. The coordinate along the hit crystal is measured by using a hodoscope of Wave Length Shifting (WLS) plastic strips mounted perpendicularly to each plane of scintillators. As photodetectors, new Geiger mode Avalanche PhotoDetectors (G-APDs) with integrated electronics are being used to detect both the hit crystal in a block (x and y coordinates) and the interaction point in the crystal (z coordinate) through the light escaping from the crystal and tra…
Formation Conditions of Titan's and Enceladus's Building Blocks in Saturn's Circumplanetary Disk
2021
Abstract The building blocks of Titan and Enceladus are believed to have formed in a late-stage circumplanetary disk (CPD) around Saturn. Evaluating the evolution of the abundances of volatile species in this disk as a function of the migration, growth, and evaporation of icy grains is then of primary importance to assess the origin of the material that eventually formed these two moons. Here we use a simple prescription of Saturn’s CPD in which the location of the centrifugal radius is varied, to investigate the time evolution of the icelines of water ice, ammonia hydrate, methane clathrate, carbon monoxide, and dinitrogen pure condensates. To match their compositional data, the building b…
The milliarcsecond-scale radio structure of AB Dor A
2020
Context: The fast rotator, pre-main sequence star AB Dor A is a strong and persistent radio emitter. The extraordinary coronal flaring activity is thought to be the origin of compact radio emission and other associated phenomena as large slingshot prominences. Aim: We aim to investigate the radio emission mechanism and the milliarcsecond radio structure around AB Dor A. Methods: We performed phase-referenced VLBI observations at 22.3 GHz, 8.4 GHz, and 1.4 GHz over more than one decade using the Australian VLBI array. Results: Our 8.4 GHz images show a double core-halo morphology, similar at all epochs, with emission extending at heights between 5 and 18 stellar radii. Furthermore, the seque…
Study of the γ decay of high-lying states in 208Pb via inelastic scattering of 17O ions
2014
A measurement of the high-lying states in 208Pb has been made using 17O beams at 20 MeV/u. The gamma decay following inelastic excitation was measured with the detector system AGATA Demonstrator based on segmented HPGe detectors, coupled to an array of large volume LaBr3:Ce scintillators and to an array of Si detectors. Preliminary results in comparison with (γ,γ’) data, for states in the 5-8 MeV energy interval, are presented.
Blendensysteme für Streulichtphotometer
1973
The geometrical arrangement of slits in the secondary beam of light scattering photometers has been investigated. The hitherto applied configuration of slits, vertically fixed on the secondary beam, requires a volume correction-sinϑ-for the determination of the angle-dependent scattered intensity. Arrangements of slits with varying width which depends on the angle of observation ϑ are proposed. They avoide the volume correction, or render the scattering volume independent of ϑ, and at the same time increase the measuring accuracy.
The methods of XLOOPS An introduction to parallel space techniques
1997
Abstract The package XLOOPS presented in this workshop relies on the application of parallel space techniques. We introduce these techniques covering the following topics: • - The generation of integral representations for massive two-loop diagrams. • - The treatment of tensor structures. • - The handling of the γ-algebra in this scheme. • - The separation of UV and IR divergences in analytic expressions. We present two-loop examples taken from Standard Model calculations.
Ageing studies of TPB in noble gas detectors for dark matter and neutrinoless ββ decay searches
2017
Noble gases (Xe, Ar, Kr) are very attractive as detector media in Dark Matter search and neutrinoless double-beta decay experiments. However, the detection of their scintillation light (in the VUV spectral region) requires shifting the VUV light to visible light, where standard photosensors are more efficient. Tetraphenyl butadiene (TPB) is widely used as wavelength shifter, absorbing the VUV light and re-emitting in the blue region (~430nm). TPB is an organic molecule that may degrade due to exposure to environmental agents and also to ultraviolet light. In this work, we present TPB ageing studies due to exposure to VUV light, aiming at quantifying the reduction of the absolute fluorescenc…
The X-ray gas scintillation spectrometer experiment on the first spacelab flight
1985
The First Spacelab mission, launched on Space ShuttleFlight STS-9 in November 1983 carried a multidisciplinary payload which was intended to demonstrate that valuable scientific results can be achieved from such short duration missions. The payload complement included a spectrometer to undertake observations of the brighter cosmic X-ray sources. The primary scientific objectives of this experiment were the study of detailed spectral features in cosmic X-ray sources and their associated temporal variations over a wide energy range from about 2 up to 30 keV. The instrument based on the gas scintillation proportional counter had an effective area of some 180 cm2 with an energy resolution of ∼9…