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Electron Energy (electron + energy)
Terms modified by Electron Energy Selected AbstractsAnalyses of the factors for the demagnetization of permanent magnets caused by high-energy electron irradiationJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2009Yoshihiro Asano Demagnetization owing to high-energy electron irradiation has been analyzed for permanent magnets used in insertion devices of synchrotron radiation sources, using the Monte Carlo code FLUKA. The experimental data of a thermally treated Nd2Fe14B permanent magnet with a copper or a tantalum block at electron energies ranging from 2 to 8,GeV were compared with the calculation data of the absorbed doses, photoneutron production distributions and star densities. The results indicate that low-energy photoneutrons and bremsstrahlung photons are not involved in the demagnetization process, and suggest that the star density owing to the photoneutrons is strongly correlated with the demagnetization process. [source] Phenol, chlorobenzene and chlorophenol isomers: resonant states and dissociative electron attachment,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2003Roustem V. Khatymov This paper reports a study of resonant dissociative electron attachment (DEA) to the phenol, chlorobenzene, p- , m- , and o- chlorophenol molecules. On the basis of spectroscopic and thermochemical approaches the resonant states of the molecular negative ions (NIs) and the structures of some dissociative decay products are assigned. In the electron energy range up to 3,eV, DEA processes are determined by the two 2[,*]-shape resonances resulting mainly in formation of [MH], and/or Cl, ions. At higher electron energies the energy correlation between peaks in the negative ion effective yield curves and bands of UV spectra allowed identification of the core-excited resonances. The peculiarities of Cl, ion formation and the vibrational fine structure on the effective yield curves of the [MH], ions are discussed. The mass spectrometric procedures for measurement of relative cross sections for NI formation are described. Copyright © 2003 John Wiley & Sons, Ltd. [source] Chemical modification of polystyrene by low-energy (<100 eV) electron irradiation studied by mass spectrometryJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008S. Massey Abstract Dip-coated thin films of polystyrene were chemically modified (degraded) by low-energy electron irradiation (0,100 eV). The resulting degradation was studied by mass spectrometry with variable electron energy. In the negative-ion mode, H, was observed and was associated with two phenomena. The resonant structure at 9.1 ± 0.4 eV was associated with dissociative electron attachment. The energy of the resonance peak agreed with the results obtained for organic molecules. At a higher energy, a monotonic rise of the emission yield was observed and was associated with nonresonant dipolar dissociation. More mass fragments were observed in the positive-ion mode. The predominant ion was H+ at 100 eV of electron irradiation, and alkyl ions were detected at higher masses. Emission thresholds were measured for the most predominant positive ions. The shape of the emission curve showed that there was no resonant process in the formation of these ions. The energy threshold was measured at about 20 eV, and this meant that the carbon structure of the polymer broke with a recombination of the degradation products with hydrogen atoms before the emission occurred. Below 19 eV, there was only hydrogen loss; this implied that the possible degradation mechanisms did not break the general carbon structure of the material, leading to crosslinking. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Sonographic guidance for electron boost planning after breast-conserving surgeryJOURNAL OF CLINICAL ULTRASOUND, Issue 7 2004Antje Warszawski MD Abstract Purpose This study was conducted to determine the feasibility of using sonography for electron boost planning in breast cancer treatment and to define the factors that influence the accuracy and reproducibility of this technique. Patients and Methods Seventy-seven patients underwent 102 sonographic examinations after breast-conserving surgery and before and after radiotherapy. The size of the electron boost field was defined by measuring the postoperative cavity. Reproducibility of the sonographic findings was investigated in 25 of the patients who were examined before and after radiotherapy (at a total dose of 46,50.4 Gy). Depth (distance from the skin surface to the posterior aspect of the postoperative cavity) was measured, and sonographic appearance of the postoperative cavity was evaluated. Type of surgical procedure, time elapsed since surgery, use of systemic therapy, menopausal status, breast size, and radiation dose were investigated for their influence on sonographic appearance and visualization of the postoperative cavity. Results The postoperative cavity was well visualized in 78% of patients and visualized with some difficulty in 22%. In all but 5 patients, it was hypoechoic and inhomogeneous. The mean depth of the postoperative cavity after radiotherapy was 27 ± 4 mm. Smaller breast (p < 0.001) and younger age (p < 0.05) were associated with decreased visibility of the postoperative cavity. Sonographic appearance was the same before and after radiotherapy, but the mean difference in postoperative cavity depth between the 2 measurements was 2 mm (range, 0,4 mm). In 43/77 (56%) of the patients, changes in electron energy or in field size were required after sonographic measurement. Conclusion Sonography is a useful and reproducible means of electron boost planning, helping to avoid underdosage of the postoperative cavity and overdosage of normal tissue. © 2004 Wiley Periodicals, Inc. J Clin Ultrasound 32:333,337, 2004 [source] Theoretical studies on the role of ,-electron delocalization in determining the conformation of N-benzylideneaniline with three types of LMO basis setsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2006Peng Bao Abstract To understand the role of ,-electron delocalization in determining the conformation of the NBA (Ph,NCH,Ph) molecule, the following three LMO (localized molecular orbital) basis sets are constructed: a LFMO (highly localized fragment molecular orbital), an NBO (natural bond orbital), and a special NBO (NBO-II) basis sets, and their localization degrees are evaluated with our suggesting index DL. Afterward, the vertical resonance energy ,EV is obtained from the Morokuma's energy partition over each of three LMO basis sets. ,EV = ,EH (one electron energy) + ,Etwo (two electron energy), and ,Etwo = ,ECou (Coulomb) + ,Eex (exchange) + ,Eec (or ,,En) (electron correction). ,EH is always stabilizing, and ,ECou is destabilizing for all time. In the case of the LFMO basis set, ,ECou is so great that ,Etwo > |,EH|. Therefore, ,EV is always destabilizing, and is least destabilizing at about the , = 90° geometry. Of the three calculation methods such as HF, DFT, and MPn (n = 2, 3, and 4), the MPn method provides ,EV with the greatest value. In the case of the NBO basis set, on the contrary, ,EV is stabilizing due to ,ECou being less destabilizing, and it is most stabilizing at a planar geometry. The LFMO basis set has the highest localization degree, and it is most appropriate for the energy partition. In the NBA molecule, ,-electron delocalization is destabilization, and it has a tendency to distort the NBA molecular away from its planar geometry as far as possible. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 809,824, 2006 [source] Spontaneous bremsstrahlung effect in the nonrelativistic electron scattering by a nucleus in the field of pulsed light waveLASER PHYSICS LETTERS, Issue 6 2009A.A. Lebed' Abstract The theory of nonresonant spontaneous bremsstrahlung by a nonrelativistic electron scattered by a nucleus in the field of a pulsed light wave is developed. The electron interaction with a Coulomb potential of a nucleus is considered in the first order of perturbation theory (the Born approximation), and the interaction with an external pulsed field is taken into account accurately. The approximation is examined when the pulsewidth is considerably greater than the characteristic time of wave oscillations. For the range of moderately strong fields the analytic expression for the nonresonant differential cross-section was obtained, which has the form of a sum over partial differential crosssections. It is shown, that in the case of nonrelativistic electron energy the partial cross-section is not factorable on the crosssection of electron-nucleus spontaneous bremsstrahlung in the absence of the external field and the emission-absorption probability of a certain number of wave photons. It is concluded, that the total cross-section of spontaneous bremsstrahlung of an electron scattered by a nucleus in the field of pulsed light wave summing over all possible partial processes differs essentially from the cross-section of electron-nucleus spontaneous bremsstrahlung in the absence of the external field. (© 2009 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Monoenergetic electron beam generation in a laser-driven plasma accelerationLASER PHYSICS LETTERS, Issue 2 2006M. Adachi Abstract We obtained a 7-MeV monoenergetic electron beam from a plasma with the electron density ne of 1.5 × 1020 cm,3 produced by a 2-TW 50-fs laser pulse. In both higher and lower sides of the density region of 4 × 1019 ÷ 4 × 1020 cm,3, energy spectra of electrons were bi-Maxwellian distribution function whose maximum electron energy and effective electron temperature were 30 MeV and approximately MeV, respectively. Observed first Stokes satellites in the forward scattering light spectra, and the density dependences of maximum electron energy and the effective temperature suggest that electrons are first accelerated by SMLWFA and are further accelerated by direct laser acceleration (DLA) in the ne region of more than 2 × 1020 cm,3; a cascade acceleration by SMLWFA and DLA. A Stokes satellite peak observed with the monoenergetic beam suggests that the monoenergetic beam would be accelerated by SMLWFA. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] The energy cascade from warm dark matter decaysMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008M. Valdés ABSTRACT We use a set of Monte Carlo simulations to follow the cascade produced by a primary electron of energy Ein in the intergalactic medium. We choose Ein= 3,10 keV as expected from the decay of one of the most popular warm dark matter (WDM) candidates, sterile neutrinos. Our simulation takes into account processes previously neglected such as free,free interactions with ions and recombinations, and uses the best available cross-sections for collisional ionizations and excitations with H and He and for electron,electron collisions. We precisely derive the fraction of the primary electron energy that heats the gas, ionizes atoms and produces line and continuum photons as a function of the ionization fraction. Handy fitting formulae for all the above energy depositions are provided. By keeping track of the individual photons, we can distinguish between photons in the Ly, resonance and those with energy E < 10.2 eV that do not interact further with gas. This separation is important because a Ly, background can heat or cool the gas depending on the nature of the photons, and can have effects on the 21-cm radiation emitted by neutral H, which will probably become detectable at z > 6 in the near future by the next generation radio interferometers. [source] E-beam pumped resonant periodic gain GaInP/AlGaInP VCSELPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2005V. Yu. Abstract 25-period Ga0.5In0.5P/(Al0.7Ga0.3)0.5In0.5P quantum well structure was grown by MOVPE on GaAs substrates misoriented by 100 from (001) to (111)A and fabricated into a microcavities with dielectric oxide mirrors. The structure period and mirror design were chosen to provide resonant periodic gain. A non-uniformity of 5% in the total structure thickness across the 2 inch wafer was used for studying laser characteristics depending on mismatching structure period from resonance condition. The laser wavelength, threshold and output power was found to depend critically on the alignment of QW period with both the cavity and the MQW gain spectrum. Lasing in the 625,650 nm spectral range with output power up to 9 W (0.45 MW/cm2) was achieved under scanning electron beam longitudinal pumping at room temperature. The minimum threshold current density for a 40 keV electron energy was 8 A/cm2 (0.32 MW/cm2). In order to control the lasing threshold to within 10 % of its minimum, the MQW period should be tuned to the optimum value with an accuracy of about 1 %. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Gas-phase tautomerism in 1-phenylazonaphthalene-4-ol: verification of the responses of individual tautomersRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2009Daniela Nedeltcheva Gas-phase tautomerism in 1-phenylazonaphthalene-4-ol (1) was studied by using electron ionization (EI) mass spectrometry on the basis of the fragmentations of the model enol and keto tautomers, where the movable proton is replaced by a methyl group. These fixed tautomers were obtained as an easy separable mixture by simple methylation of the cheap and easily accessible diazene (1). It was found that their EI mass spectral fragmentations are in full congruence with the already published theoretical predictions. The relative energies required for bond cleavage in 1 and its fixed tautomers were estimated by stepwise increasing of the electron energy of the ion source of the mass spectrometer. A simple equation for the approximate estimation of the molar fractions of the individual tautomers was suggested. It was shown that the enol form is dominant in the temperature range of 200,300°C. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||