Search results for "Absorption"
showing 10 items of 2701 documents
Spectral broadening by incomplete thermalization of the energy in X-ray microcalorimeters with superconducting absorber and NTD-Ge thermal sensor
2004
Abstract We present a model of the response of a cryogenic microcalorimeter with superconducting absorber and phonon sensitive thermal sensor to the absorption of X-ray photons. The model is based on the main microscopic processes responsible for the thermalization of the deposited energy. We use a system of rate equations to describe the energy downconversion in the superconductor and transport to the thermal sensor. The model is a tool to investigate the thermalization efficiency with respect to the device characteristics (i.e. absorber material, geometry), in order to optimize the performances of these detectors. As a first case study, we report results of simulations for a microcalorime…
Determination of the high-pressure crystal structure ofBaWO4andPbWO4
2006
We report the results of both angle-dispersive x-ray diffraction and x-ray absorption near-edge structure studies in $\mathrm{Ba}\mathrm{W}{\mathrm{O}}_{4}$ and $\mathrm{Pb}\mathrm{W}{\mathrm{O}}_{4}$ at pressures of up to $56\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $24\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, respectively. $\mathrm{Ba}\mathrm{W}{\mathrm{O}}_{4}$ is found to undergo a pressure-driven phase transition at $7.1\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ from the tetragonal scheelite structure (which is stable under normal conditions) to the monoclinic fergusonite structure whereas the same transition takes place in $\mathrm{Pb}\mathrm{W}{\mathrm{O}}_{4}$ at $9\phantom{\rule{0…
Basic Physical Concepts
2010
Mossbauer spectroscopy is based on recoilless emission and resonant absorption of γ-radiation by atomic nuclei. The aim of this chapter is to familiarize the reader with the concepts of nuclear γ-resonance and the Mossbauer effect, before we describe the experiments and relevant electric and magnetic hyperfine interactions in Chaps. 3 and 4. We prefer doing this by collecting formulae without deriving them; comprehensive and instructive descriptions have already been given at length in a number of introductory books ([7–39] in Chap. 1). Readers who are primarily interested in understanding their Mossbauer spectra without too much physical ballast may skip this chapter at first reading and p…
Enhancedγ-Ray Emission from Neutron Unbound States Populated inβDecay
2015
Total absorption spectroscopy is used to investigate the β-decay intensity to states above the neutron separation energy followed by γ-ray emission in (87,88)Br and (94)Rb. Accurate results are obtained thanks to a careful control of systematic errors. An unexpectedly large γ intensity is observed in all three cases extending well beyond the excitation energy region where neutron penetration is hindered by low neutron energy. The γ branching as a function of excitation energy is compared to Hauser-Feshbach model calculations. For (87)Br and (88)Br the γ branching reaches 57% and 20%, respectively, and could be explained as a nuclear structure effect. Some of the states populated in the daug…
Carbon coatings for soft-x-ray reflectivity enhancement
2007
In X-ray astronomical telescopes, the focalization of the radiation is achieved by means of grazing incidence Wolter I (parabola + hyperbola) optics in total reflection regime. In general, high density materials (e.g. Au, Pt, Ir, W) are used as reflecting coatings, in order to increase as much as possible the cut-off angles and energies for total reflection. However these materials present an important reduction of the reflectivity between 0.2 and 5 keV, due to the photoabsorption, and this phenomenon is particularly enhanced in correspondence of the M absorption edges (between 2 and 3.5 keV). In general, this determines a strong decrease of the telescope effective area. To overcome the pro…
X-ray absorption spectra at the CaL2,3edge calculated within multichannel multiple scattering theory
2004
We report a theoretical method for x-ray absorption spectroscopy (XAS) in condensed matter which is based on the multichannel multiple scattering theory of Natoli et al. and the eigen-channel $R$-matrix method. While the highly flexible real-space multiple scattering (RSMS) method guarantees a precise description of the single-electron part of the problem, multiplet-like electron correlation effects between the photoelectron and localized electrons can be taken account for in a configuration interaction scheme. For the case where correlation effects are limited to the absorber atom, a technique for the solution of the equations is devised, which requires only little more computation time th…
Element-specific magnetic moments and spin-resolved density of states in CoFeMnZ(Z=Al, Ga; Si, Ge)
2011
Using circular dichroism in x-ray-absorption spectroscopy (XAS/XMCD), we determined element-specific magnetic moments and spin-resolved unoccupied densities of states (DOS) for Co, Fe, and Mn in the quaternary Heusler compounds CoFeMn$Z$ ($Z=\text{Al}$, Ga; Si, Ge). These compounds belong to a class of highly spin-polarized materials with cubic LiMgPdSn-type structure. Different structure models for the sublattice occupation leading to similar average magnetization values can be distinguished by comparison of element-specific moments with theory. We find that the compounds form similar structures, where Co, Fe, Mn, and $Z$ occupy the $X$, ${X}^{\ensuremath{'}}$, $Y$, and $Z$ sublattice of t…
Total Absorption Spectroscopy of Fission Fragments Relevant for Reactor Antineutrino Spectra Determination
2015
8 pags., 3 figs., 1 tab. ; Presented at the XXXIV Mazurian Lakes Conference on Physics, Piaski, Poland, September 6–13, 2015.
Refractive index change dependence on Ge(1) defects inγ-irradiated Ge-doped silica
2009
We present an experimental study regarding the effects of the $\ensuremath{\gamma}$ radiation on silica glass doped with Ge up to $10\text{ }000$ ppm molar produced by the sol-gel technique. We have determined the irradiation-induced changes in the refractive index $(\ensuremath{\Delta}n)$ as a function of the oxygen deficiency of the samples, evaluated from the ratio between the germanium lone pair centers (GLPC) and the Ge content. $\ensuremath{\Delta}n$ at 1500 nm have been estimated using optical-absorption spectra in the range 1.5--6 eV. We have found that $\ensuremath{\Delta}n$ is independent of Ge differences for GLPC/Ge values $l{10}^{\ensuremath{-}4}$, while it depends on Ge for la…
Electromagnetic energy within dielectric spheres
1987
We present exact and approximate analytic expressions for the time-averaged electromagnetic energy within dielectric spheres on the basis of rigorous Mie theory. Such information is of importance for the study of photochemical reactions within atmospheric water spheres. Numerical results show that on the average the energy inside a cloud droplet is enlarged by a factor exceeding 2 compared with that of a sphere of the same radius of the surrounding medium. In regions of resonance peaks the electromagnetic energy may be increased by more than 2 orders of magnitude.