Search results for "Absorption"
showing 10 items of 2701 documents
Origin of the visible absorption in radiation-resistant optical fibers
2013
In this work we investigated the point defects at the origin of the degradation of radiation-tolerant optical fibers used in the visible part of the spectrum for plasma diagnostics in radiation environments. For this aim, the effects of γ -ray irradiation up to the dose of 10 MGy(SiO2) and post-irradiation thermal annealing at 550◦C were studied for a Fluorinedoped fiber. An absorption peaking around 2 eV is mainly responsible for the measured radiation-induced losses, its origin being currently debated in the literature. On the basis of the unchanging shape of this band with the radiation dose, its correlation with the 1.9 eV photoluminescent band and the thermal treatment results we assig…
Time-resolved luminescence and absorption in CdWO4
1998
Abstract The luminescence and short-lived absorption are studied in CdWO 4 single crystals under pulsed laser beam as well as pulsed electron beam excitation. The luminescence spectrum and decay kinetics for CdWO 4 powder are studied. The short-lived absorption in single crystals arises from electron transitions from the luminescence center excited state to the conduction band. From luminescence and short-lived absorption spectra the energy depths of luminescence center excited and ground states are estimated.
Photoabsorption and MXCD in photoemission microscopy for characterisation of advanced materials
1999
Abstract We applied chemical and magnetic sensitive photoemission electron microscopy (PEEM) to investigate surfaces of advanced materials. PEEM at low photon energies provides a high spatial resolution, but suffers from the lack of information about the chemical composition of the imaged surface. Such information can be obtained by PEEM via tuning the photon energy to X-ray absorption edges. To apply spectromicroscopy we acquired and subtracted microscopic images using photon energies just below and at the edges. The resulting difference gives a micro-image of the lateral distribution of a specific element. Microspectroscopy is performed by recording the intensity of secondary electrons in…
Optical and magnetic resonance spectroscopy of stimulated recombination processes in defect studies
2004
Optical and magnetic resonance spectroscopy is widely used in the investigation of radiation-induced processes in wide-gap solids. This paper discusses the present understanding of applications of the experimental methods of optical and thermoactivation spectroscopy in the research of new materials, for applications in radiation dosimetry and digital imaging and in the basic research into the fundamental physics and chemistry of radiation. The advantages of the simultaneous use of optical and magnetic resonance techniques for the investigation of stimulated processes are considered.
The nature of radiohaloes in biotite: Experimental studies and modeling
2001
Several micro-techniques (confocal laser-Raman microprobe, optical absorption micro-spectroscopy, high-resolution transmission electron microscopy, electron microprobe analysis) were employed in the detailed characterization of radiohaloes in biotites from two Variscan rocks from Germany. The studied biotites are intermediate members of the phlogopite-annite series with Mg/Fe 2+ ratios in the range 1.6–1.0. Radiohaloes in biotite resulted from the impact of 4 He cores (α-particles) emitted from actinide-bearing inclusions. Monte Carlo simulations yielded α ( 238 U, 235 U, and 232 Th series) penetration ranges in biotite between 12.5 and 37.3 μm, which are in reasonable agreement with the ob…
A Novel Approach of a Low-Cost UWB Microwave Imaging System with High Resolution Based on SAR and a New Fast Reconstruction Algorithm for Early-Stage…
2022
In this article, a new efficient and robust approach—the high-resolution microwave imaging system—for early breast cancer diagnosis is presented. The core concept of the proposed approach is to employ a combination of a newly proposed delay-and-sum (DAS) algorithm and the specific absorption rate (SAR) parameter to provide high image quality of breast tumors, along with fast image processing. The new algorithm enhances the tumor response by altering the parameter referring to the distance between the antenna and the tumor in the conventional DAS matrices. This adjustment entails a much clearer reconstructed image with short processing time. To achieve these aims, a high directional Vivaldi …
Inter/intramolecular Cherenkov radiation energy transfer (CRET) from a fluorophore with a built-in radionuclide.
2014
The Cherenkov radiation (CR) from [(18)F]-FDG, [(177)Lu]-LuCl3 and [(90)Y]-YCl3 was detected and CR energy transfer (CRET) to several fluorophores was examined. Subsequent fluorescence emission was found to be a function of the position of absorption bands with respect to the CR peak, energy of emitted particles, radionuclide/fluorophore loading, and fluorophore brightness. A variant of the best fluorophore with a built-in radionuclide was synthesized to achieve inter- and intra-molecular CRET.
Temperature dependence of the absorption properties of silanol groups in amorphous : Are silanol groups organized in clusters?
2011
Abstract We present a study on the vacuum-ultraviolet (VUV) and infrared (IR) absorption of silanol groups in amorphous silicon dioxide ( a - SiO 2 ) in the range of temperature from 4 to 300 K. The observed temperature induced modifications of IR and VUV absorption spectra are interpreted as due to a process of conversion of free into H-bonded silanol groups. The changes of the amplitude of the VUV absorption spectra are shown to be linearly correlated to the changes of the IR absorption of free Si–OH groups. This point together with the evidence that the shape of the Si–OH VUV absorption does not depend on temperature demonstrates that the different silanol group sub-species have differen…
Absorption band at 7.6 eV induced by γ-irradiation in silica glasses
2001
Optical absorption of defects induced by γ-irradiation in both natural and synthetic silica is experimentally investigated in the vacuum-ultraviolet (UV) range. Our results show that γ-rays, in a dose range of 1000 Mrad, induce an absorption band centered at 7.6 eV, the so-called E band, whose growth kinetics is not related to γ-activated precursors but to defects of the glassy matrix directly induced via the breaking of Si–O bonds occurring under γ-irradiation. Moreover, we observe that γ-rays do not bleach the E band present in some silica samples before irradiation, so ruling out that the associated defects can be precursors of the paramagnetic E′ centers, also induced by γ-irradiation.
Evaluation of multiple-scattering contribution in extended X-ray absorption fine structure for MO4 and MO6 clusters
1994
Abstract We present a theoretical ab initio evaluation of the multiple-scattering contribution in the extended X-ray absorption fine structure for MO4 and MO6 clusters with M = Mg, Ca, Mn, Zn, Se, Sr, Mo, Ag, Te, Ba, Nd, Tb, W, Au or Bi. The dependence of the multiple-scattering signal on the absorber type, the photoelectron angular momentum and the local distortion is discussed. It is shown that the multiple-scattering contribution is significant in the photoelectron wave-vector range up to 6–7 A−1 and strongly depends on both the path geometry and the atomic species involved in the scattering process.