Articoli di riviste: "Very high energy electrons"

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Clements, Nathan, Nolan Esplen, Magdalena Bazalova-Carter, Pierre Korysko, Joseph Bateman, Wilfrid Farabolini, Manjit Dosanjh e Roberto Corsini. "271 Grid Therapy with Very-High Energy Electrons". Radiotherapy and Oncology 186 (settembre 2023): S115—S116. http://dx.doi.org/10.1016/s0167-8140(23)89363-x.

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Fuchs, T., H. Szymanowski, U. Oelfke, Y. Glinec, C. Rechatin, J. Faure e V. Malka. "Treatment planning for laser-accelerated very-high energy electrons". Physics in Medicine and Biology 54, n. 11 (8 maggio 2009): 3315–28. http://dx.doi.org/10.1088/0031-9155/54/11/003.

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Papiez, Lech, Colleen DesRosiers e Vadim Moskvin. "Very High Energy Electrons (50 – 250 MeV) and Radiation Therapy". Technology in Cancer Research & Treatment 1, n. 2 (aprile 2002): 105–10. http://dx.doi.org/10.1177/153303460200100202.

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Isravel, Hebzibha, Asaf Pe’er e Damien Bégué. "Proton Synchrotron Origin of the Very-high-energy Emission of GRB 190114C". Astrophysical Journal 955, n. 1 (1 settembre 2023): 70. http://dx.doi.org/10.3847/1538-4357/acec73.

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Abstract We consider here a proton-synchrotron model to explain the MAGIC observation of GRB 190114C afterglow in the energy band of 0.2–1 TeV, while the X-ray spectra are explained by electron-synchrotron emission. Given the uncertainty of the particle acceleration process, we consider several variations of the model, and show that they all match the data very well. We find that the values of the uncertain model parameters are reasonable: isotropic explosion energy ∼1054.5 erg, ambient density ∼10–100 cm−3, and the fraction of electrons/protons accelerated to a high-energy power law is of a few percent. All these values are directly derived from the observed teraelectronvolt and X-ray fluxes. The model also requires that protons be accelerated to observed energies as high as a few 1020 eV. Further, assuming that the jet break takes place after 106 s gives the beaming-corrected energy of the burst to be ≈1053 erg, which is one to two orders of magnitude higher than usually inferred, because of the small fraction of electrons accelerated. Our modeling is consistent with both late time data at all bands, from optical to X-rays, and with numerical models of particle acceleration. Our results thus demonstrate the relevance of proton-synchrotron emission to the high-energy observations of gamma-ray bursts during their afterglow phase.

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Tibolla, Omar, Sarah Kaufmann e Paula Chadwick. "Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources". J 5, n. 3 (19 luglio 2022): 318–33. http://dx.doi.org/10.3390/j5030022.

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The riddle of the origin of Cosmic Rays (CR) has been an open question for over a century. Gamma ray observations above 100 MeV reveal the sites of cosmic ray acceleration to energies where they are unaffected by solar modulation; recent evidence supports the existence of hadronic acceleration in Supernova Remnants (SNR), as expected in the standard model of cosmic ray acceleration. Nevertheless, the results raise new questions, and no final answer has been provided thus far. Among the suggested possible alternative accelerators in the Very High Energy (VHE) gamma ray sky, pulsar wind nebulae (PWNe, which together with dark matter are the main candidates to explain the local positron excess as well) are the dominant population among known Galactic sources. However, the most numerous population in absolute terms is represented by unidentified sources (~50% of VHE gamma ray sources). The relationship between PWNe and unidentified sources seems very close; in fact, in a PWN, the lifetime of inverse Compton (IC) emitting electrons not only exceeds the lifetime of its progenitor pulsar, but also exceeds the age of the electrons that emit via synchrotron radiation. Therefore, during its evolution, a PWN can remain bright in IC such that its GeV-TeV gamma ray flux remains high for timescales much larger than the lifetimes of the pulsar and the X-ray PWN. In addition, the shell-type remnant of the supernova explosion in which the pulsar was formed has a much shorter lifetime than the electrons responsible for IC emission. Hence, understanding PWNe and VHE unidentified sources is a crucial piece of the solution to the riddle of the origin of cosmic rays. Both theoretical aspects (with particular emphasis on the ancient pulsar wind nebulae scenario) and their observational proofs are discussed in this paper. Specifically, the scientific cases of HESS J1616-508 and HESS J1813-126 are examined in detail.

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Kifune, T. "Very High Energy Gamma Rays from Plerions: CANGAROO Results". Symposium - International Astronomical Union 188 (1998): 125–28. http://dx.doi.org/10.1017/s0074180900114597.

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The current status of very high energy gamma ray astronomy (in ~ 1 TeV region) is described by using as example results of CANGAROO (Collaboration of Australia and Nippon for a GAmma Ray Observatory in the Outback). Gamma rays at TeV energies, emitted through inverse Compton effect of electrons or π0 decay from proton interaction, provide direct evidence on “hot” non-thermal processes of the Universe, as well as environmental features, such as the strength of magnetic field in the emission region, for the non-thermal processes.

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Seitz, B. "166 RADIOTHERAPY WITH VERY HIGH ENERGY ELECTRONS GENERATED BY WAKEFIELD ACCELERATORS". Radiotherapy and Oncology 102 (marzo 2012): S77—S78. http://dx.doi.org/10.1016/s0167-8140(12)70137-8.

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XU, Wangwen, Zhanghu HU, 章虎胡, Dexuan HUI e Younian WANG. "High energy electron beam generation during interaction of a laser accelerated proton beam with a gas-discharge plasma". Plasma Science and Technology 24, n. 5 (19 aprile 2022): 055001. http://dx.doi.org/10.1088/2058-6272/ac4d1d.

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Abstract The study of the interaction between ion beam and plasma is very important to the areas of inertial fusion energy and high energy density physics. With detailed one-dimensional electromagnetic particle-in-cell simulations, we investigate here the interaction of a laser-accelerated proton beam assuming an ideal monoenergetic beam with a gas-discharge plasma. After the saturation stage of the two-stream instability excited by the proton beam, significant high energy electrons are observed, with maximum energy approaching 2 MeV, and a new two-stream instability occurs between the high energy electrons and background electrons. The trajectories of plasma electrons are studied, showing the process of electron trapping and de-trapping from the wakefield.

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Klingelhöfer, G., e E. Kankeleit. "Conversion electron Mössbauerspectroscopy with very low energy (0 to 15 eV) electrons". Hyperfine Interactions 57, n. 1-4 (luglio 1990): 1905–10. http://dx.doi.org/10.1007/bf02405740.

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Liu, Qingyu, Qinhe Zhang, Min Zhang e Fazhan Yang. "Study on the Discharge Characteristics of Single-Pulse Discharge in Micro-EDM". Micromachines 11, n. 1 (1 gennaio 2020): 55. http://dx.doi.org/10.3390/mi11010055.

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To further study the discharge characteristics and machining mechanism of micro-electrical discharge machining (micro-EDM), the variation trends of the discharge energy and discharge crater size with actual discharge duration are discussed based on single-pulse experiments. The polarity effect of micro-EDM was analyzed according to the motion characteristics of electrons and ions in the discharge plasma channel. The results show that the discharge current and voltage of micro-EDM were independent of the discharge width and open-circuit voltage. The energy utilization rate of the short-pulse discharge was relatively high, and the energy utilization rate decreased gradually as the discharge duration increased. Even if the mass of the positive ion was much larger than that of the electron, the kinetic energy of the positive ion was still less than that of the electron when bombarding the surface of the electrode. The acceleration and speed of electrons were very high, and the number of times that electrons bombarded the surface of positive electrode was more than 600 times that of positive ions bombarding the surface of the negative electrode during the same time.

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Delorme, R., T. A. M. Masilela, C. Etoh, F. Smekens e Y. Prezado. "FIRST THEORETICAL DETERMINATION OF RELATIVE BIOLOGICAL EFFECTIVENESS OF VERY HIGH ENERGY ELECTRONS". Physica Medica 94 (febbraio 2022): S73. http://dx.doi.org/10.1016/s1120-1797(22)01598-8.

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H Kelley, Michael. "Uses of Spin-polarised Electrons in Fundamental Electron-Atom Collision Processes and the Analysis of Magnetic Microstructures". Australian Journal of Physics 43, n. 5 (1990): 565. http://dx.doi.org/10.1071/ph900565.

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Two experimental programs are discussed which exploit the use of polarised electrons for studies of fundamental processes and physical properties. In one program, collisions between spin�polarised electrons and optically pumped sodium atoms provide a very detailed characterisation of the spin-dependent interactions important in low-energy electron-atom collisions. The results of these measurements provide a critical test for the reliability of state-of-the�art electron scattering calculations. In the second program, the spin polarisation of secondary electrons ejected by high� energy electron impact is used to determine the magnetic structure of ferromagnetic materials with very high spatial resolution (-60 nm). This ability to perform such studies with high resolution has been exploited both in studies of the basic magnetic properties of ferromagnetic materials and in studies of how these basic properties affect the magnetic structure and performance of devices used for magnetic information storage.

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Ottensmeyer, F. P., e X. G. Jiang. "High-resolution electron spectrometers for molecular microanalysis". Proceedings, annual meeting, Electron Microscopy Society of America 46 (1988): 664–65. http://dx.doi.org/10.1017/s0424820100105382.

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The last decade has brought major advances in electron beam induced microanalytical capabilities, particularly with the utilization of energy loss electrons. These developments have been predicated primarily by the design and by the more ready commercial availabilty of better magnetic spectrometers, both for scanning transmission and fixed-beam transmission electron microscopy.Theoretical and experimental investigation of spatial resolution or localization possible for microanalysis and elemental mapping has indicated a potential of about 0.5 nm at an energy loss close to 100 eV, improving slowly with increasing energy loss. At lower energy loss the spatial resolution worsens due to an expected increase in impact parameter, but is still anticipated to be of the order of 1 nm at a 10 eV loss.Coupled with high spatial resolution is an experimentally observed very high sensitivity of detection and identification of a very small number of atoms at high concentration.

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Roshchupkin, S. P., e S. S. Starodub. "The effect of generation of narrow ultrarelativistic beams of positrons (electrons) in the process of resonant photoproduction of pairs on nuclei in a strong electromagnetic field". Laser Physics Letters 19, n. 11 (3 ottobre 2022): 115301. http://dx.doi.org/10.1088/1612-202x/ac9401.

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Abstract The generation of narrow beams of high-energy positrons (electrons) in the process of resonant photogeneration of ultrarelativistic electron–positron pairs by high-energy gamma quanta in the field of the nucleus and a strong electromagnetic wave is theoretically predicted. It is shown that if the energy of the initial gamma quanta significantly exceeds the characteristic energy of the process, then ultrarelativistic positrons (electrons) are emitted with energies very close to the energy of gamma quanta. Moreover, the resonant differential cross-section of such processes can exceed the corresponding differential cross-section without an external field by thirteen orders of magnitude. This effect makes it possible to obtain narrow beams of ultrarelativistic positrons (electrons) in strong electromagnetic fields with high probability.

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Vergados, J. D., Ch C. Moustakidis, Yeuk-Kwan E. Cheung, H. Ejiri, Yeongduk Kim e Jeong-Yeon Lee. "Light WIMP Searches Involving Electron Scattering". Advances in High Energy Physics 2018 (2018): 1–14. http://dx.doi.org/10.1155/2018/6257198.

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In the present work we examine the possibility of detecting electrons in light dark matter searches. These detectors are considered to be the most appropriate for detecting dark matter particles with a mass in the MeV region. We analyze theoretically some key issues involved in such detection. More specifically we consider a particle model involving WIMPs interacting with fermions via Z-exchange. We find that for WIMPs with mass in the electron mass range the cross section for WIMP-atomic electron scattering is affected by the electron binding. For WIMPs more than 20 times heavier than the electron, the binding affects the kinematics very little. As a result, many electrons can be ejected with energy which increases linearly with the WIMP mass, but the cross section is somewhat reduced depending on the bound state wave function employed. On the other hand for lighter WIMPs, the effect of binding is dramatic. More specifically at most 10 electrons, namely, those with binding energy below 10 eV, become available even in the case of WIMPs with a mass as large as 20 times the electron mass. Even fewer electrons contribute if the WIMPs are lighter. The cross section is, however, substantially enhanced by the Fermi function corrections, which become more important at low energies of the outgoing electrons. Thus events of 0.5–2.5 per kg-y become possible.

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Richter, Burton. "Very High Energy Colliders". IEEE Transactions on Nuclear Science 32, n. 5 (ottobre 1985): 3828–33. http://dx.doi.org/10.1109/tns.1985.4334517.

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Papiez, L. "TU-D-224A-07: Image-Guided IMRT and Very High Energy Electrons (VHEE)". Medical Physics 33, n. 6Part17 (giugno 2006): 2204. http://dx.doi.org/10.1118/1.2241584.

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Poblet, Josep M. "(Invited) Computational Modelling of Super-Reduced Polyoxometalates for Energy Storage". ECS Meeting Abstracts MA2023-01, n. 11 (28 agosto 2023): 1251. http://dx.doi.org/10.1149/ma2023-01111251mtgabs.

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It is well know that polyoxometalates can be reduced at relatively potentials and can act as reservoir of electrons. Very recently, it has been reported that polyoxometalates clusters like Li6[P2W18O62] can achieve very high proton–electron storage capacities in aqueous solution. DFT calculations in combination with classical MD and CPMD simulations were able to substantiate that the physical properties of classical polyoxotungstates, like those of the prototypical Dawson anion [P2W18O62]6-, strongly depend on the presence of collective forces associated to POM concentration, pH and countercation nature. At low POM concentration and neutral pH only four electrons are reversibly incorporated to the POM. However, in acidic media, the POM framework begins to protonate after the third electron reduction. The salt concentration is also very relevant, since it favours the POM aggregation, which induces an additional stabilization of molecular orbitals. These and another features of reduced polyoxometales will be discussed in the present communication.

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Liu, Jingyue. "Imaging and Microanalysis of Non-Conducting Materials in the Lowvoltage FE-SEM: Challenges and Strategies". Microscopy and Microanalysis 6, S2 (agosto 2000): 754–55. http://dx.doi.org/10.1017/s1431927600036266.

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Under high-energy electron bombardment, electrical charge can rapidly build up in non-conducting materials. The electron-induced charging process is very complex and is still not well understood. Injection of energetic electrons into insulators generates electron-hole pairs which can be localized at pre-existing or newly created charge-trap centers. Charging of insulators results from a balance between the emission of secondary electrons and the diffusion and trapping of incident electrons. In the SEM, charging is usually a dynamic process: the degree of specimen charging depends on the energy and the dose of the incident electrons, the image magnification, the pixel dwell time (PDT), and the history of the electron irradiation of the specimen. Although the degree of charging can be reduced by varying the energy of the incident electrons, charging of non-conducting specimens cannot be completely eliminated due to variations in the local SE yield across the specimen surface and the presence of charge-traps inside the specimen.

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Hirotani, Kouichi. "Very High-Energy Emission from the Direct Vicinity of Rapidly Rotating Black Holes". Galaxies 6, n. 4 (22 novembre 2018): 122. http://dx.doi.org/10.3390/galaxies6040122.

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When a black hole accretes plasmas at very low accretion rate, an advection-dominated accretion flow (ADAF) is formed. In an ADAF, relativistic electrons emit soft gamma-rays via Bremsstrahlung. Some MeV photons collide with each other to materialize as electron-positron pairs in the magnetosphere. Such pairs efficiently screen the electric field along the magnetic field lines, when the accretion rate is typically greater than 0.03–0.3% of the Eddington rate. However, when the accretion rate becomes smaller than this value, the number density of the created pairs becomes less than the rotationally induced Goldreich–Julian density. In such a charge-starved magnetosphere, an electric field arises along the magnetic field lines to accelerate charged leptons into ultra-relativistic energies, leading to an efficient TeV emission via an inverse-Compton (IC) process, spending a portion of the extracted hole’s rotational energy. In this review, we summarize the stationary lepton accelerator models in black hole magnetospheres. We apply the model to super-massive black holes and demonstrate that nearby low-luminosity active galactic nuclei are capable of emitting detectable gamma-rays between 0.1 and 30 TeV with the Cherenkov Telescope Array.

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Zhang, Lu-Lu, Jia Ren, Yun Wang e En-Wei Liang. "Very-high-energy Gamma-Ray Afterglows of GRB 201015A and GRB 201216C". Astrophysical Journal 952, n. 2 (21 luglio 2023): 127. http://dx.doi.org/10.3847/1538-4357/acd190.

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Abstract Gamma-ray bursts (GRBs) 201015A and 201216C are valuable cases where very-high-energy (VHE) gamma-ray afterglows have been detected. By analyzing their prompt emission data, we find that GRB 201216C is an extremely energetic, long GRB with a hard gamma-ray spectrum, while GRB 201015A is a relative subenergetic, soft-spectrum GRB. Attributing their radio–optical–X-ray afterglows to the synchrotron radiation of the relativistic electrons accelerated in their jets, we fit their afterglow lightcurves with the standard external shock model and infer their VHE afterglows from the synchrotron self-Compton scattering process of the electrons. It is found that the jet of GRB 201015A is midrelativistic (Γ0 = 44), surrounded by a very dense medium (n = 1202 cm−3), and the jet of GRB 201216C is ultrarelativistic (Γ0 = 331), surrounded by a moderate dense medium (n = 5 cm−3). The inferred peak luminosity of the VHE gamma-ray afterglows of GRB 201216C is approximately 10−9 erg cm−2 s−1 at 57–600 s after the GRB trigger, making it detectable with the MAGIC telescopes at a high confidence level, even though the GRB is at a redshift of 1.1. Comparing their intrinsic VHE gamma-ray lightcurves and spectral energy distributions with GRBs 180720B, 190114C, and 190829A, we show that their intrinsic peak luminosity of VHE gamma-ray afterglows at 104 s after the GRB trigger is variable from 1045 to 5 × 1048 erg s−1, and their kinetic energy, initial Lorentz factor, and medium density are diverse among bursts.

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Lee, Youngrok, Jihhwan Lee e Sunghyun Kim. "Solar Energy Is Effectively Converted to Electricity and Hydrogen Using Cyanobacteria". ECS Meeting Abstracts MA2023-02, n. 61 (22 dicembre 2023): 3283. http://dx.doi.org/10.1149/ma2023-02613283mtgabs.

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We present solar energy conversion for electricity generation and hydrogen production from water using Anabaena variabilis (A. variabilis), an oxygenic photosynthetic cyanobacterium. Electrons from water oxidation by the light reactions that take place in thylakoid membranes (TMs) undergo a series of electron transfer pathway called Z-schme. We devised a method in which electrons are directed to the external electrode. In order to extract electrons from TMs, we found that double mediators are very effective in transferring electrons to the electrode from TMs. Dimethylbenzoquinone, the first mediator, can take electrons from the Z-scheme and delivers them to ferricyanide, the second mediator. Thus transferred electrons move to the cathode where oxygen reduction reaction takes place. Figure shows how biosolar cell (BSC) is operating under illumination. Electricity generation was achieved by simply attaching an external load between the anode and the cathode. When A. variabilis was dispersed in solution, the maximum photocurrent up to 2.14 mA cm-2 upon one sun light intensity. A complete cell produced Pmaxof 160 mW cm-2 at 750 mA cm-2 with a quantum efficiency of 4.8% over a whole spectral range and turnover frequency of 17 per PSII for water molecule oxidation. The same concept was also applied to the hydrogen production. When operated in a double-chamber reactor under anaerobic condition, pure hydrogen gas was produced from water with high energy efficiencies and high production rates upon voltage bias. The maximum H2 production rate of 122 mmol H2(mg Chla)-1h-1 at anode potential of 0.4 V vs. Ag/AgCl was achieved. Energy efficiency exceeded 100% at lower anode potentials. We expect that this study opens a new way of utilizing cyanobacteria for appreciable electricity and hydrogen production. The same concept could be extended to other oxygenic cyanobacteria. Figure 1

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ZHOU, C. T., M. Y. YU e X. T. HE. "Electron acceleration by high current-density relativistic electron bunch in plasmas". Laser and Particle Beams 25, n. 2 (giugno 2007): 313–19. http://dx.doi.org/10.1017/s0263034607000171.

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Electron acceleration by a short high-current relativistic electron bunch (EB) in plasmas at three characteristic densities is studied by particle-in-cell simulation. It is found that if the EB is appropriately matched to the background plasma, the blowout space-charge field of the EB can accelerate the trailing bunch electrons at very high energy gain rate. This high energy gain, as well as the large-amplitude wakefield, the turbulent small-scale electron plasma waves, and the formation of large current peaks, are studied. The evolution of the EB, its blowout field, and other related parameters are shown to be self-similar.

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Ronga, Maria Grazia, Marco Cavallone, Annalisa Patriarca, Amelia Maia Leite, Pierre Loap, Vincent Favaudon, Gilles Créhange e Ludovic De Marzi. "Back to the Future: Very High-Energy Electrons (VHEEs) and Their Potential Application in Radiation Therapy". Cancers 13, n. 19 (30 settembre 2021): 4942. http://dx.doi.org/10.3390/cancers13194942.

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The development of innovative approaches that would reduce the sensitivity of healthy tissues to irradiation while maintaining the efficacy of the treatment on the tumor is of crucial importance for the progress of the efficacy of radiotherapy. Recent methodological developments and innovations, such as scanned beams, ultra-high dose rates, and very high-energy electrons, which may be simultaneously available on new accelerators, would allow for possible radiobiological advantages of very short pulses of ultra-high dose rate (FLASH) therapy for radiation therapy to be considered. In particular, very high-energy electron (VHEE) radiotherapy, in the energy range of 100 to 250 MeV, first proposed in the 2000s, would be particularly interesting both from a ballistic and biological point of view for the establishment of this new type of irradiation technique. In this review, we examine and summarize the current knowledge on VHEE radiotherapy and provide a synthesis of the studies that have been published on various experimental and simulation works. We will also consider the potential for VHEE therapy to be translated into clinical contexts.

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McEachran, Robert P., Kathryn R. Hamilton e Klaus Bartschat. "Low-Energy Elastic Electron Scattering from Helium Atoms". Atoms 9, n. 4 (18 ottobre 2021): 82. http://dx.doi.org/10.3390/atoms9040082.

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We reinvestigate a key process in electron-atom collision physics, the elastic scattering of electrons from helium atoms. Specifically, results from a special-purpose relativistic polarized-orbital method, which is designed to treat elastic scattering only, are compared with those from a very extensive, fully ab initio, general-purpose B-spline R-matrix (close-coupling) code.

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Čadež, Andrej. "The role of electromagnetism in tidal disruption events". Proceedings of the International Astronomical Union 12, S324 (settembre 2016): 107–10. http://dx.doi.org/10.1017/s1743921316013119.

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AbstractTidal disruption events are characterized by the prompt release of very high energy electromagnetic radiation, which rapidly carries away a significant fraction of mass-energy. The time scale od prompt release is quite comparable to the time scale of gravitational collapse. We suggest that generation of very high energy radiation from pulsar nebulae may be an example of the relativistic coupling between gravity and electromagnetism. The main ingredient of our picture comes from the observation that the electron - ion energy exchange time scale is much longer than the electron ion energy exchange time scale, which leads to thermodynamic decoupling of electron and ion gases, and thus to their different temperatures. Under such conditions the dominating hotter component pushes the colder component further out and thus generates a global electric field which constrains electrons and ions by their mutually generated electric field, yet allows them to reach very high kinetic energies

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Guo, L., H. W. Zhang e H. C. Wu. "High-frequency radio-wave emission by coherent transition radiation of runaway electrons produced by lightning stepped leaders". Physics of Plasmas 29, n. 9 (settembre 2022): 093102. http://dx.doi.org/10.1063/5.0102132.

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Lightning can produce multiband radio waves and high-energy radiations. Some of them are associated with the formation of lightning leaders. However, their generation mechanisms are not fully understood yet. Based on the understanding of thermal runaway electrons generated at the leader tip, we propose transition radiation of these runaway electrons as an alternative mechanism for producing very-high-frequency radio signals. Transition radiations are induced when runaway electrons cross the interfaces between lightning coronas and the air. By the use of estimated parameters of electron beams emerging from the leader tips, we calculate their coherent transition radiation and find that the energy spectra and radiation powers are consistent with some detection results from stepped leaders and even narrow bipolar events. Moreover, our model also predicts strong THz radiation during the stepped-leader formation. As a standard diagnosis technique of electron bunches, the proposed coherent transition radiation here may be able to reconstruct the actual properties of electron beams in the leader tips, which remains an open question.

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Li, Bochao, Hao Li, Chang Yang, Boyu Ji, Jingquan Lin e Toshihisa Tomie. "Picosecond Lifetime Hot Electrons in TiO2 Nanoparticles for High Catalytic Activity". Catalysts 10, n. 8 (10 agosto 2020): 916. http://dx.doi.org/10.3390/catal10080916.

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A large number of studies have examined the origins of high-catalytic activities of nanoparticles, but very few have discussed the lifetime of high-energy electrons in nanoparticles. The lifetime is one of the factors determining electron transfer and thus catalytic activity. Much of the lifetime of electrons reported in the literature is too short for a high transfer-efficiency of photo-excited electrons from a catalyst to the attached molecules. We observed TiO2 nanoparticles using the femtosecond laser two-color pump-probe technique with photoemission electron microscopy having a 40 nm spatial resolution. A lifetime longer than 4 ps was observed together with a fast decay component of 100 fs time constant when excited by a 760 nm laser. The slow decay component was observed only when the electrons in an intermediate state pumped by the fundamental laser pulse were excited by the second harmonic pulse. The electronic structure for the asymmetry of the pump-probe signal and the origin of the two decay components are discussed based on the color center model of the oxygen vacancy.

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Khangulyan, Dmitry, Andrew M. Taylor e Felix Aharonian. "The Formation of Hard Very High Energy Spectra from Gamma-ray Burst Afterglows via Two-zone Synchrotron Self-Compton Emission". Astrophysical Journal 947, n. 2 (1 aprile 2023): 87. http://dx.doi.org/10.3847/1538-4357/acc24e.

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Abstract Electron Compton scattering of target photons into the gamma-ray energy band (inverse Compton scattering; IC) is commonly expected to dominate the very high energy (VHE) spectra in gamma-ray bursts (GRBs) especially during the afterglow phase. For sufficiently large center-of-mass energies in these collisions, the effect of the electron recoil starts reducing the scattering cross-section (the Klein–Nishina regime). The IC spectra generated in the Klein–Nishina regime is softer and has a smaller flux level compared to the synchrotron spectra produced by the same electrons. The detection of afterglow emission from nearby GRB190829A in the VHE domain with H.E.S.S. has revealed an unexpected feature: the slope of the VHE spectrum matches well the slope of the X-ray spectra, despite expectations that, for the IC production process, the impact of the Klein–Nishina effect should be strong. The multi-wavelength spectral energy distribution appears to be inconsistent with predictions of one-zone synchrotron–self-Compton models. We study the possible impact of two-zone configuration on the properties of IC emission when the magnetic field strength differs considerably between the two zones. Synchrotron photons from the strong magnetic field zone provide the dominant target for cooling of the electrons in the weak magnetic field zone, which results in a formation of hard electron distribution and consequently of a hard IC emission. We show that the two-zone model can provide a good description of the Swift's X-ray Telescope and VHE H.E.S.S. data.

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Peretti, Enrico, Pasquale Blasi, Felix Aharonian e Giovanni Morlino. "Cosmic ray transport and radiative processes in nuclei of starburst galaxies". Monthly Notices of the Royal Astronomical Society 487, n. 1 (27 aprile 2019): 168–80. http://dx.doi.org/10.1093/mnras/stz1161.

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Abstract The high rate of star formation and supernova explosions of starburst galaxies make them interesting sources of high-energy radiation. Depending on the level of turbulence present in their interstellar medium, the bulk of cosmic rays produced inside starburst galaxies may lose most of their energy before escaping, thereby making these sources behave as calorimeters, at least up to some maximum energy. Contrary to previous studies, here we investigate in detail the conditions under which cosmic ray confinement may be effective for electrons and nuclei and we study the implications of cosmic ray confinement in terms of multifrequency emission from starburst nuclei and production of high-energy neutrinos. The general predictions are then specialized to three cases of active starbursts, namely, M82, NGC 253, and Arp220. Both primary and secondary electrons, as well as electron–positron pairs produced by gamma-ray absorption inside starburst galaxies are taken into account. Electrons and positrons produced as secondary products of hadronic interactions are found to be responsible for most of the emission of leptonic origin. In particular, synchrotron emission of very high energy secondary electrons produces an extended emission of hard X-rays that represents a very interesting signature of hadronic process in starburst galaxies, potentially accessible to current and future observations in the X-ray band. A careful understanding of both the production and absorption of gamma-rays in starburst galaxies is instrumental to the assessment of the role of these astrophysical sources as sources of high-energy astrophysical neutrinos.

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31

Delorme, R., T. Masilela, C. Etoh, F. Smekens e Y. Prezado. "OC-0080 First theoretical determination of relative biological effectiveness of very high energy electrons". Radiotherapy and Oncology 161 (agosto 2021): S53—S54. http://dx.doi.org/10.1016/s0167-8140(21)06774-8.

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32

Wen, Lu, Ke-Yao Wu, Huan Yu e Jun Fang. "Investigating the energy distribution of the high-energy particles in the Crab nebula". Research in Astronomy and Astrophysics 21, n. 11 (1 dicembre 2021): 286. http://dx.doi.org/10.1088/1674-4527/21/11/286.

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Abstract The Crab nebula is a prominent pulsar wind nebula detected in multiband observations ranging from radio to very high-energy γ-rays. Recently, γ-rays with energies above 1 PeV have been detected by the Large High Altitude Air Shower Observatory, and the energy of the most energetic particles in the nebula can be constrained. In this paper, we investigate the broadest spectral energy distribution of the Crab nebula and the energy distribution of the electrons emitting the multiwavelength nonthermal emission based on a one-zone time-dependent model. The nebula is powered by the pulsar, and high-energy electrons/positrons with a broken power-law spectrum are continually injected in the nebula as the pulsar spins down. Multiwavelength nonthermal emission is generated by the leptons through synchrotron radiation and inverse Compton scattering. Using appropriate parameters, the detected fluxes for the nebula can be well reproduced, especially for the γ-rays from 102 MeV to 1 PeV. The results show that the detected γ-rays can be produced by the leptons via the inverse Compton scattering, and the lower limit of the Lorentz factor of the most energetic leptons is ∼ 8.5 × 109. It can be concluded that there exist electrons/positrons with energies higher than 4.3 PeV in the Crab nebula.

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33

Frank, Luděk, Miloš Hovorka, Ivo Konvalina, Šárka Mikmeková e Ilona Müllerová. "Very low energy scanning electron microscopy". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 645, n. 1 (luglio 2011): 46–54. http://dx.doi.org/10.1016/j.nima.2010.12.214.

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34

KALASHEV, O. E., V. A. KUZMIN e D. V. SEMIKOZ. "ULTRA HIGH ENERGY COSMIC RAYS: PROPAGATION IN THE GALAXY AND ANISOTROPY". Modern Physics Letters A 16, n. 39 (21 dicembre 2001): 2505–15. http://dx.doi.org/10.1142/s0217732301005990.

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We considered propagation of Ultra High Energy Cosmic Rays (UHECR) through the galaxy. We investigated models with sources of UHECR distributed in the same way as Cold Dark Matter (CDM) in a self-consistent way, taking into account both extra-galactic and Galactic contributions. Using a very simple toy model of galactic magnetic field we showed that in the case of galactic origin of UHECRs the anisotropy can reach considerable values. In the case of extragalactic UHECRs origin, the anisotropy appears to be nonvanishing only for electron and photon components due to synchrotron losses, but it can hardly be reassured. The reason is an extremely low flux of UHE electrons and a too low level of γ-ray anisotropy.

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BOULWARE, C. H., J. D. JARVIS, H. L. ANDREWS e C. A. BRAU. "NEEDLE CATHODES FOR HIGH-BRIGHTNESS BEAMS". International Journal of Modern Physics A 22, n. 22 (10 settembre 2007): 3784–93. http://dx.doi.org/10.1142/s0217751x07037421.

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At the tips of sharp needles, the surface electric field is enhanced by many orders of magnitude. This intensifies thermionic emission and photoemission of electrons through the Schottky effect, and reduces the effect of space charge. The increased current density improves the brightness of electron sources by orders of magnitude. In addition, at very high fields (>109 V/m ), field emission and photo-field emission produce very high current density. Arrays of needles can be used to achieve high total current.

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36

Aleksandrov, A. V., R. Calabrese, G. Ciullo, N. S. Dikansky, V. Guidi, N. Ch Kot, V. I. Kudelainen et al. "Very-high-resolution energy analyser for electron beams". Measurement Science and Technology 4, n. 7 (1 luglio 1993): 764–68. http://dx.doi.org/10.1088/0957-0233/4/7/008.

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37

Wu, Jin-tao, Ming-jun Feng e Jian-hong Ruan. "Research on electron and positron spectrum in the high-energy region based on the gluon condensation model". Journal of Cosmology and Astroparticle Physics 2023, n. 10 (1 ottobre 2023): 059. http://dx.doi.org/10.1088/1475-7516/2023/10/059.

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Abstract Electron (positron), proton and nuclei can be accelerated to very high energy by local supernova remnants (SNR). The famous excesses of electron and proton (nuclei) potentially come from such kind of local sources. Recently, the DAMPE experiment measured the electron spectrum (including both electrons and positrons) of cosmic rays with high-accuracy. It provides an opportunity to further explore the excess of electrons. According to the gluon condensation (GC) theory, once GC occurs, huge number of gluons condense at a critical momentum, and the production spectra of electron and proton showing typical GC characteristics. There are exact correlations between the electron and proton spectrum from a same GC process. It is possible to interpret the power-law break of cosmic rays in view of GC phenomenon, and predict one from another based on the relations between electron and proton spectrum. In this work, we point out the potential existence of a second excess in the electron spectrum, the characteristics of this excess is derived from experimental data of proton. We hope that the future DAMPE experiments will confirm the existence of this second excess and support the result of GC model.

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38

Reichelt, R., A. Engel e R. Leapman. "Electron energy loss spectroscopy (EELS) by scanning transmission electron microscopy (STEM) at low doses". Proceedings, annual meeting, Electron Microscopy Society of America 45 (agosto 1987): 116–17. http://dx.doi.org/10.1017/s0424820100125518.

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A scanning transmission electron microscope (STEM) has the unique feature to record simultaneously two types of images with high collection efficiencies. The first type, collected by an annular detector (AD), contains high resolution structural information which is primarily transmitted by elastically scattered electrons. The second type, formed by an electron spectrometer (SP), yields information on the local energy loss spectrum of the inelastically scattered electrons at lower structural resolution. Thus useful quantitative information from biological matter can be obtained: the AD-signal provides the basis for mass mapping and the inelastic one allows the estimation of the local chemical element concentration.For a very thin specimen (T<< ^, T: thickness, A: mean free path between two scattering events) the signal S of the imaging modes mentioned above can be linearly related to the properties of the sample:

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39

Liu, Jingyue. "Contrast of Highly Dispersed Metal Nanoparticles in High-resolution Secondary Electron and Backscattered Electron Images of Supported Metal Catalysts". Microscopy and Microanalysis 6, n. 4 (luglio 2000): 388–99. http://dx.doi.org/10.1017/s143192760200065x.

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AbstractPlatinum nanoparticles finely dispersed in activated carbon powders have been observed with high contrast in secondary electron (SE) and backscattered electron (BE) images. The factors that contribute to the visibility of small metal particles in high-resolution BE and SE images are discussed. Monte Carlo simulations provided insight into the scattering of electrons by small, heavy-element particles located on, or embedded in, light-element supports. The visibility of Pt nanoparticles in BE images depends on many factors including the size and the location of the Pt particles, the energy of the incident electrons, and the size of the electron probe. The SE signals generated by backscattered electrons may not significantly contribute to the visibility of small Pt particles in high-resolution SE images of carbon supported Pt catalysts. Only those small Pt particles that are located on or very close to the surface of the carbon support can be revealed in high-resolution SE images.

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40

Liu, Jingyue. "Contrast of Highly Dispersed Metal Nanoparticles in High-resolution Secondary Electron and Backscattered Electron Images of Supported Metal Catalysts". Microscopy and Microanalysis 6, n. 4 (luglio 2000): 388–99. http://dx.doi.org/10.1007/s100050010033.

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Abstract (sommario):

Abstract Platinum nanoparticles finely dispersed in activated carbon powders have been observed with high contrast in secondary electron (SE) and backscattered electron (BE) images. The factors that contribute to the visibility of small metal particles in high-resolution BE and SE images are discussed. Monte Carlo simulations provided insight into the scattering of electrons by small, heavy-element particles located on, or embedded in, light-element supports. The visibility of Pt nanoparticles in BE images depends on many factors including the size and the location of the Pt particles, the energy of the incident electrons, and the size of the electron probe. The SE signals generated by backscattered electrons may not significantly contribute to the visibility of small Pt particles in high-resolution SE images of carbon supported Pt catalysts. Only those small Pt particles that are located on or very close to the surface of the carbon support can be revealed in high-resolution SE images.

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41

Phifer, D., L. Tuma, T. Vystavel, P. Wandrol e R. J. Young. "Improving SEM Imaging Performance Using Beam Deceleration". Microscopy Today 17, n. 4 (26 giugno 2009): 40–49. http://dx.doi.org/10.1017/s1551929509000170.

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Beam Deceleration is a relatively simple method to reduce electron beam energy and improve imaging parameters such as resolution and contrast. The scanning electron microscope (SEM) uses a sharply focused electron beam to probe the specimen surface. The energy of the electrons forming such a probe is determined by the electrical potential of the electron source, referred to as accelerating voltage or high voltage (HV). No matter how many times the electrons are accelerated or decelerated inside the column, they leave the column with an energy corresponding to the high voltage. The high voltage is usually controllable within a range of 200 V to 30 kV for most commercially available SEMs, allowing the operator to select the electron beam energy suitable for the application. Imaging with very low electron beam energy has great importance, which is illustrated by SEM instrumentation development over the last few decades [1–2]. Low voltage microscopy is a topic discussed at most microscopy-related conferences these days, but generally, it is approached with an immersion lens and field emission gun (FEG) SEM system because of the better beam current densities. However, beam deceleration is also a means to bring low kV improvement to SEMs with thermionic electron sources.

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42

Slaughter, J. M., W. Weber, Gernot Güntherodt e Charles M. Falco. "Quantitative Auger and XPS Analysis of Thin Films". MRS Bulletin 17, n. 12 (dicembre 1992): 39–45. http://dx.doi.org/10.1557/s0883769400046947.

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In 1925, P. Auger first observed the so-called Auger electrons in a Wilson cloud chamber. He explained this occurrence as being due to a radiationless transition in atoms excited by a primary x-ray photon source. In 1953, Lander first pointed out that Auger electrons arising from solid samples can be detected in the energy distribution curve of secondary electrons from surfaces subjected to electron bombardment. Moreover, low-energy Auger electrons (∼1 keV kinetic energy) can escape from only the first several atomic layers of a surface since they are strongly absorbed by even a monolayer of atoms. Thus Auger electron spectroscopy (AES) possesses high surface sensitivity. This is one characteristic that makes AES very useful for the study of thin films. For such applications, an important development in AES occurred when Harris showed that the sensitivity of the detection of Auger electrons can be improved by differentiating the electron energy distribution curve with respect to the energy. Furthermore, Weber and Johnson demonstrated that, provided the Auger line profile does not change, the peak-to-peak height in the differentiated energy distribution curves is proportional to the Auger current in the peak. Therefore, in addition to its surface sensitivity, AES also can be used for quantitative studies of thin films.Like AES, x-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique that uses the energy distribution of electrons ejected from a thin film for quantitative analysis. However, in many ways the information provided by AES and XPS is complementary.

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43

Lacki, Brian C., e Todd A. Thompson. "DIFFUSE HARD X-RAY EMISSION IN STARBURST GALAXIES AS SYNCHROTRON FROM VERY HIGH ENERGY ELECTRONS". Astrophysical Journal 762, n. 1 (13 dicembre 2012): 29. http://dx.doi.org/10.1088/0004-637x/762/1/29.

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44

De Gregorio, A., D. Carlotti, M. Fischetti, G. Franciosini, M. Marafini, I. Mattei, A. Muscato et al. "PO-2031 Development of a TPS for Very High Energy Electrons delivered at FLASH rates". Radiotherapy and Oncology 182 (maggio 2023): S1804—S1805. http://dx.doi.org/10.1016/s0167-8140(23)66946-4.

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45

MERDJI, H., S. GUIZARD, P. MARTIN, G. PETITE, F. QUÉRÉ, B. CARRÉ, J. F. HERGOTT et al. "Ultrafast electron relaxation measurements on α-SiO2 using high-order harmonics generation". Laser and Particle Beams 18, n. 3 (luglio 2000): 489–94. http://dx.doi.org/10.1017/s0263034600183193.

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Time-resolved photoemission spectroscopy, using high order harmonics, is used to measure the energy relaxation rate of hot electrons in α-SiO2 with sub-picosecond time resolution. Our results indicate that electrons of 30 eV kinetic energy in the conduction band relax at a rate which is at least two orders of magnitude lower than the one of photo-excited carriers of a few eV. As a result, we give insight in the relaxation process of hot electrons and show that impact ionization probability per unit time is only of the order of 1/40 ps−1, in very strong contrast with the much higher value generally assumed in models of optical breakdown.

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46

Tschentscher, Th, e P. Suortti. "Experiments with Very High Energy Synchrotron Radiation". Journal of Synchrotron Radiation 5, n. 3 (1 maggio 1998): 286–92. http://dx.doi.org/10.1107/s0909049597014775.

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The use of synchrotron radiation with very high photon energies has become possible only with the latest generation of storage rings. All high-electron-energy synchrotron sources will have a dedicated program for the use of very high photon energies. The high-energy beamline ID15 at the ESRF was the first beamline built and dedicated to this purpose, and it has now been in user operation for more than three years. The useful energy range of this beamline is 30–1000 keV and the superconducting insertion device for producing the highest attainable photon energies is described in detail. The techniques most often used today are diffraction and Compton scattering; an overview of the most important experiments is given. Both techniques have been used in the investigation of magnetic systems, and, additionally, the high resolution in reciprocal space, which can be achieved in diffraction, has led to a series of applications. Other fields of research are addressed, and attempts to indicate possible future research areas of high-energy synchrotron radiation are made.

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47

Kohl, H. "The Contribution of Phonon-Scattered Electrons to High-Resolution Electron Micrographs of Crystals". Proceedings, annual meeting, Electron Microscopy Society of America 48, n. 1 (12 agosto 1990): 62–63. http://dx.doi.org/10.1017/s0424820100179063.

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High-Resolution Electron Microscopy is able to determine structures of crystals and interfaces with a spatial resolution of somewhat less than 2 Å. As the image is strongly dependent on instrumental parameters, notably the defocus and the spherical aberration, the interpretation of micrographs necessitates a comparison with calculated images. Whereas one has often been content with a qualitative comparison of theory with experiment in the past, one is currently striving for quantitative procedures to extract information from the images [1,2]. For the calculations one starts by assuming a static potential, thus neglecting inelastic scattering processes.We shall confine the discussion to periodic specimens. All electrons, which have only been elastically scattered, are confined to very few directions, the Bragg spots. In-elastically scattered electrons, however, can be found in any direction. Therefore the influence of inelastic processes on the elastically (= Bragg) scattered electrons can be described as an attenuation [3]. For the calculation of high-resolution images this procedure would be correct only if we had an imaging energy filter capable of removing all phonon-scattered electrons. This is not realizable in practice. We are therefore forced to include the contribution of the phonon-scattered electrons.

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48

DAVIES, J. R. "Proton acceleration by fast electrons in laser–solid interactions". Laser and Particle Beams 20, n. 2 (aprile 2002): 243–53. http://dx.doi.org/10.1017/s0263034602202141.

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The emission of high-energy protons in laser–solid interactions and the theories that have been used to explain it are briefly reviewed. To these theories we add a further possibility: the acceleration of protons inside the target by the electric field generated by fast electrons. This is considered using a simple one-dimensional model. It is found that for relativistic laser intensities and sufficiently long pulse durations, the proton energy gain is typically several times the fast electron temperature. The results are very similar to those obtained for proton acceleration by electron expansion into vacuum.

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49

Venables, J. A., G. G. Hembree e C. J. Harland. "Electron spectroscopy in SEM and STEM". Proceedings, annual meeting, Electron Microscopy Society of America 48, n. 2 (12 agosto 1990): 378–79. http://dx.doi.org/10.1017/s0424820100135496.

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Low energy electrons, in the energy range 0-2 keV, are very useful in surface science. Both secondary (0-100 eV nominally) and Auger (50-2 keV) electrons can be used as analytic signals in ultra-high vacuum (UHV) scanning (SEM) and scanning transmission (STEM) electron microscopes. This paper briefly reviews some ongoing projects, which are aimed at improving the spatial resolution and information content of these signals.Both secondary electron imaging (SEI) and Auger electrons spectroscopy (AES) have a long history. Reviews of AES and its microscopic counterpart scanning Auger microscopy (SAM) have been given previously in this International Conference Series; over the intervening period AES/SAM instruments have become widely available commercially. Simply biassing the sample up to a few hundred volts (-ve) has lead to a new technique (biassed-SEI) which is sensitive at the sub-monolayer level. In general biassing the sample is a useful additional experimental variable. It can be used to visualize thin films and surface topography, including steps; it can also be used to distinguish spectral features (eg Auger peaks) from the sample from those due to stray electrons, and to place such features in the best energy region for the electron spectrometer.

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Kahane, Sylvian. "Backscattered Electrons Spectra and Angular Distributions: Simulations with EGS5". European Journal of Engineering Research and Science 3, n. 10 (26 ottobre 2018): 95–102. http://dx.doi.org/10.24018/ejers.2018.3.10.917.

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The purpose of the present study is to compare numerical Monte Carlo simulations of backscattering of electrons, mainly in the keV range, with available experimental data. The final goal is to assess the ability of the Monte Carlo code to predict viable results, in view of the complexity and difficulty of performing experimental measurements. A specific code for simulating electrons backscattering was developed, based on the EGS5 electron-photon transport routines. The code was parallelized very efficiently for a common memory configuration. Simulation results for the backscattering coefficient h, the energy spectrum dh/dq, and the angle dependent energy spectrum dh/dqdW were obtained. Comparing with experiments shows agreement from very good to fair, especially in regions of high q (energy) values. For low values of q there are not experimental results due to difficulties in measurements. Hence, the Monte Carlo program can provide good estimates, in the range of energies from tens of keV up to 100-200 keV.

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