Search results for "electromagnetic"
showing 10 items of 1595 documents
Theoretical simulations of the radiation-induced defect processes in insulating materials
1994
Abstract The results of two basic kinds of computer simulations of radiation-induced processes in insulating materials, one based on quantum-mechanical and pair-potential (atomistic) approaches, and the other a phenomenological theory of diffusion-controlled reactions, are presented. It is shown that, by combining different techniques (atom-atom potentials and semi-empirical quantum chemical methods) the optimized geometry and the electronic structure of a family of hole centres in crystalline corundum (α-Al2O3) could be found. Their energetics are analyzed; V2−, V−V−Mg hole centres all have a common basic element, namely the diatomic molecule O23−, which is responsible for their similar ab…
The model of recombination process in TlBr
2002
The time-resolved luminescence was used as a tool in the study of recombination process in several undoped TlBr crystals. The spectra and decay kinetics observed under electron beam excitation were investigated. Observation of several luminescence bands with different decay rates shows that more than one recombination center is involved and the recombination process is quite complicated. The band at ∼2.5 eV is dominant under 10 ns excitation pulse (electron beam or nitrogen laser pulses). The results of short-lived absorption and luminescence are used for analysis of possible mechanisms of recombination processes in TlBr.
Vacuum correlators at short distances from lattice QCD
2021
Non-perturbatively computing the hadronic vacuum polarization at large photon virtualities and making contact with perturbation theory enables a precision determination of the electromagnetic coupling at the $Z$ pole, which enters global electroweak fits. In order to achieve this goal ab initio using lattice QCD, one faces the challenge that, at the short distances which dominate the observable, discretization errors are hard to control. Here we address challenges of this type with the help of static screening correlators in the high-temperature phase of QCD, yet without incurring any bias. The idea is motivated by the observations that (a) the cost of high-temperature simulations is typica…
Measurement of the phase between strong and electromagnetic amplitudes of J/ψ decays
2019
Kolcu, Onur Buğra (Arel Author)
Magnetic resonance imaging of (1)H long lived states derived from parahydrogen induced polarization in a clinical system.
2015
Hyperpolarization is a powerful tool to overcome the low sensitivity of nuclear magnetic resonance (NMR). However, applications are limited due to the short lifetime of this non equilibrium spin state caused by relaxation processes. This issue can be addressed by storing hyperpolarization in slowly decaying singlet spin states which was so far mostly demonstrated for non-proton spin pairs, e.g. 13C-13C. Protons hyperpolarized by parahydrogen induced polarization (PHIP) in symmetrical molecules, are very well suited for this strategy because they naturally exhibit a long-lived singlet state. The conversion of the NMR silent singlet spin state to observable magnetization can be achieved by ma…
Optical absorption and Raman studies of neutron-irradiated Gd3Ga5O12 single crystals
2018
Abstract In this work we have performed a comparative analysis of optical absorption and micro-Raman spectra for series of Gd3Ga5O12 (GGG) single crystals irradiated by fast neutrons with fluences from 1016 n/cm2 to 1018 n/cm2. It was found that the optical absorption spectra of non-irradiated Czochralski grown GGG consist of the relatively narrow lines in the UV spectral range related to the 4f–4f transitions in Gd3+. Transitions from the 6S7/2 ground state to the 6P, 6J and 6D states in a Gd3+ cation are clearly detected. For a GGG crystal containing Ca impurity ions, additional absorption band at 350 nm is observed, and it is tentatively ascribed to oxygen vacancies associated with Ca im…
Oxygen-excess-related point defects in glassy/amorphous SiO2 and related materials
2012
Abstract An insight is given into recent experimental advances in the spectroscopic studies of oxygen-excess intrinsic defects, in glassy SiO 2 and α-quartz. By controlling excess oxygen in a-SiO 2 , and the conditions of F 2 -laser irradiation, SiO 2 glass samples can be obtained with optical absorption almost exclusively dominated by single defect, oxygen dangling bonds (“non-bridging oxygen hole centers” or NBOHCs), without the presence of complementary Si dangling bonds (generic “E′-centers”). This allows for a more accurate determination of the spectral shape of NBOHC optical absorption in UV and vacuum UV spectral regions. The temperature dependence of NBOHC electron paramagnetic reso…
Theoretical and experimental study of primary radiation defects in KNbO3 perovskite crystals
2000
Abstract The results of large-scale computer simulations of point defects – F-type electron centers and hole polarons bound to a potassium vacancy – in perovskite KNbO3 crystals are presented. One-site polarons and two-site (molecular) polarons are expected to coexist, both are characterized by close absorption energies around 1 eV. The transient absorption spectra and decay kinetics observed after ns-pulsed electron beam irradiation have been measured for different KNbO3 crystals. The relaxation kinetics of the optical density vary considerably for different impurity concentrations and sample stoichiometries. Experimental data are discussed in the light of the presented calculations.
Quantitative analysis of rhenium in irradiated tungsten
2021
Abstract Pure tungsten (W), irradiated to 3.5 dpa in a target of the Swiss neutron spallation source (SINQ), was characterized using high-sensitivity HPGe gamma ray spectroscopy to identify the present radionuclides. Synchrotron X-ray absorption spectroscopy was used to quantify the amount of Re produced in the irradiated W. An atomic concentration of 0.61% Re in the irradiated W was determined from the height of the L3-edge X-ray absorption edge jump. Analysis of the local atomic structure from the extended X-ray absorption fine structure (EXAFS) spectra indicates that rhenium (Re) produced in the system is mainly coordinated by W atoms and partly coordinated by void defects. First-princip…
Recent developments in the evaluation of Mössbauer line intensities
1985
The angular dependence of the intensities of pure or mixed multipole transitions is formulated in a new fashion, which takes into account arbitrary texture of the Mossbauer absorber ranging from complete orientation (single crystals) over preferred orientation to random powders and an anisotropic absorption fraction of the nuclei. The application of the theory is demonstrated by means of typical examples from the literature.