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Gerry Skinner - One of the best experts on this subject based on the ideXlab platform.
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an asymmetric distribution of Positrons in the galactic disk revealed by gamma rays
Nature, 2008Co-Authors: G Weidenspointner, P. Jean, Gerry Skinner, J Knodlseder, Peter Von Ballmoos, G F Bignami, R Diehl, A W StrongAbstract:Antimatter is not an exotic rarity found only in the depths of the Universe: there are large quantities in our own Galaxy. We know this because we see the 511-keV γ-ray emission line, a signature of electron–Positron annihilation, coming from the general direction of the Galactic Centre. The origin of the Positrons has remained a mystery, but the distribution of the annihilation line radiation provides a clue. Astronomers now have the tools that can work out that distribution, and analysis of more than four years of spectroscopic data from the INTEGRAL satellite reveals an unexpected distribution of the 511-keV γ-ray emission from the inner Galactic disk, suggesting that the Positrons originate in binary stars containing black holes or neutron stars. Gamma-ray line radiation at 511 keV is the signature of electron–Positron annihilation, which comes from the general direction of the Galactic centre, but the origin of the Positrons was a mystery. This paper reports a distinct asymmetry in the 511 keV line emission coming from the inner Galactic disk, which resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies >20 keV, indicating that they may be the dominant origin of the Positrons. Gamma-ray line radiation at 511 keV is the signature of electron–Positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre1, but the origin of the Positrons has remained a mystery. Stellar nucleosynthesis2,3,4, accreting compact objects5,6,7,8, and even the annihilation of exotic dark-matter particles9 have all been suggested. Here we report a distinct asymmetry in the 511-keV line emission coming from the inner Galactic disk (∼10–50° from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies >20 keV (‘hard’ LMXBs), indicating that they may be the dominant origin of the Positrons. Although it had long been suspected that electron–Positron pair plasmas may exist in X-ray binaries, it was not evident that many of the Positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511-keV line. For these models, our result implies that up to a few times 1041 Positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter.
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an asymmetric distribution of Positrons in the galactic disk revealed by gamma rays
Nature, 2008Co-Authors: G Weidenspointner, P. Jean, Gerry Skinner, J Knodlseder, G F Bignami, Peter Von Ballmoos, R DiehlAbstract:Gamma-ray line radiation at 511 keV is the signature of electron-Positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the Positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles have all been suggested. Here we report a distinct asymmetry in the 511-keV line emission coming from the inner Galactic disk ( approximately 10-50 degrees from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies >20 keV ('hard' LMXBs), indicating that they may be the dominant origin of the Positrons. Although it had long been suspected that electron-Positron pair plasmas may exist in X-ray binaries, it was not evident that many of the Positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511-keV line. For these models, our result implies that up to a few times 10(41) Positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter.
Weiss A. - One of the best experts on this subject based on the ideXlab platform.
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Surface states and annihilation characteristics of Positrons trapped at the (100) and (111) surfaces of silicon [57]
2020Co-Authors: Fazleev N., Fry J., Weiss A.Abstract:Recent studies of Si(100) and Si(111) using Positron annihilation induced Auger-electron spectroscopy (PAES) reveal that experimental annihilation probabilities of surface trapped Positrons with relevant Si core-level electrons differ significantly for two faces of clean Si, an elemental semiconductor. These experimental results are investigated theoretically by performing calculations of the "image-potential" Positron surface states and annihilation characteristics of the surface trapped Positrons with relevant Si core-level electrons for the ideally terminated, nonreconstructed and reconstructed Si(100)-(2 X 1) and Si(111)-(7 X 7) surfaces. Computed Positron surface binding energies demonstrate their sensitivity to the specific atomic structure of the topmost layers of surfaces, and, when compared to Positron work functions, the stability of Positron surface states on all studied Si(100) and Si(111) surfaces. The Positron surface state wave function was found to be localized in a potential well on the vacuum side at both nonreconstructed semiconductor surfaces. The (2 X 1) reconstruction of the Si(100) surface causes the Positron surface state wave function to extend into the lattice in the regions where atoms are displaced away from their ideal terminated positions. A comparison of theoretical and experimental Positron surface binding energies for Si(100) shows that the best agreement is achieved when the reconstructed Si(100)-(2 X 1) surface is described within the asymmetric dimer model. Calculations indicate that the Positron surface state wave function is localized in all three dimensions in the corner hole regions of the reconstructed Si(111)-(7 X 7) surface. This localization provides an explanation for previous experiments that failed to show the anisotropy in the electron-Positron pair momentum density distribution expected for a Positron surface state delocalized in the plane of the surface. Positron annihilation characteristics are calculated for each surface and compared with experimental Positron spectroscopy data. These calculations reveal strong dependence of Positron annihilation characteristics on the crystal face of clean Si in contrast to the much smaller face dependence found on clean metal surfaces. Annihilation probabilities of surface trapped Positrons with Si 2s- and 2p-core-level electrons are found to be significantly smaller for the reconstructed Si(111)-(7 X 7) surface when compared with the results for the reconstructed Si(100)-(2 X 1) surface, in agreement with experimental PAES data. These results indicate that PAES intensities, which are proportional to core annihilation probabilities, are sensitive to the crystal face and surface structure of an elemental semiconductor
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Oxidation and thermal reduction of the Cu(1 0 0) surface as studied using Positron annihilation induced Auger electron spectroscopy (PAES)
2020Co-Authors: Fazleev N., Nadesalingam M., Maddox W., Mukherjee S., Rajeshwar K., Weiss A.Abstract:Changes in the surface of an oxidized Cu(1 0 0) single crystal resulting from vacuum annealing have been investigated using Positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 °C. The intensity then decreases monotonically as the annealing temperature is increased to ∼600 °C. Experimental probabilities of annihilation of surface-trapped Positrons with Cu 3p and O 1s core-level electrons are estimated from the measured intensities of the Positron annihilation induced Cu M2,3VV and O KLL Auger transitions. Experimental PAES results are analyzed by performing calculations of Positron surface states and annihilation probabilities of surface-trapped Positrons with relevant core electrons taking into account the charge redistribution at the surface, surface reconstructions, and electron-Positron correlations effects. The effects of oxygen adsorption on localization of Positron surface state wave function and annihilation characteristics are also analyzed. Possible explanation is proposed for the observed behavior of the intensity of Positron annihilation induced Cu M2,3VV and O KLL Auger peaks and probabilities of annihilation of surface-trapped Positrons with Cu 3p and O 1s core-level electrons with changes of the annealing temperature. © 2009 Elsevier B.V. All rights reserved
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Studies of Positrons trapped at quantum-dot like particles embedded in metal surfaces
2020Co-Authors: Fazleev N., Nadesalingam M., Weiss A.Abstract:Experimental studies of the Positron annihilation induced Auger electron (PAES) spectra from the Fe-Cu alloy surfaces with quantum-dot like Cu nanoparticles embedded in Fe show that the PAES signal from Cu increase rapidly as the concentration of Cu is enhanced by vacuum annealing. These measurements indicate that almost 75% of Positrons that annihilate with core electrons due so with Cu even though the surface concentration of Cu as measured by EAES is only 6%. This result suggests that Positrons become localized at sites at the surface containing high concentration of Cu atoms before annihilation. These experimental results are investigated theoretically by performing calculations of the "image-potential" Positron surface states and annihilation characteristics of the surface trapped Positrons with relevant Fe and Cu core-level electrons for the clean Fe(100) and Cu(100) surfaces and for the Fe(100) surface with quantum-dot like Cu nanoparticles embedded in the top atomic layers of the host substrate. Estimates of the Positron binding energy and Positron annihilation characteristics reveal their strong sensitivity to the nanoparticle coverage. Computed core annihilation probabilities are compared with experimental ones estimated from the measured Auger peak intensities. The observed behavior of the Fe and Cu PAES signal intensities is explained by theoretical calculations as being due to trapping of Positrons in the regions of Cu nanoparticles embedded in the top atomic layers of Fe. © 2009 American Institute of Physics
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Studies of the Auger spectrum from the (100) surface of GaAs using Positron annihilation induced Auger electron spectroscopy
2020Co-Authors: Starnes S., Weiss A., Fry J.Abstract:Measurements of the first high-resolution Positron annihilation induced Auger spectrum from GaAs(100) are presented. The spectrum displays six As and three Ga Auger peaks below 110 eV, including a strong As M4,5VV peak at 28 eV and a less intense Ga M2,3M4,5M4,5 peak at 53 eV. The Auger peak intensities are used to obtain experimental annihilation probabilities for relevant core-level electrons. Experimental results are compared with first-principles calculations of Positron surface states and annihilation characteristics of surface trapped Positrons. Copyright (C) 2000 Elsevier Science Ltd. | Measurements of the first high-resolution Positron annihilation induced Auger spectrum from GaAs(100) are presented. The spectrum displays six As and three Ga Auger peaks below 110 eV, including a strong As M4,5VV peak at 28 eV and a less intense Ga M2,3M4,5M4,5 peak at 53 eV. The Auger peak intensities are used to obtain experimental annihilation probabilities for relevant core-level electrons. Experimental results are compared with first-principles calculations of Positron surface states and annihilation characteristics of surface trapped Positrons
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Positron annihilation induced Auger electron spectroscopic studies of reconstructed semiconductor surfaces
2020Co-Authors: Fazleev N., Starnes S., Reed J., Weiss A.Abstract:The Positron annihilation induced Auger spectrum from GaAs(100) displays six As and three Ga Auger peaks below 110 eV corresponding to M4,5VV, M2M4V, M2,3M4,5M4,5 Auger transitions for As and M2,3M4,5M4,5 Auger transitions for Ga. The integrated Auger peak intensities have been used to obtain experimental annihilation probabilities of surface trapped Positrons with As 3p and 3d and Ga 3p core level electrons. PAES data is analyzed by performing calculations of Positron surface and bulk states and annihilation characteristics of surface trapped Positrons with relevant Ga and As core level electrons for both Ga- and As-rich (100) surfaces of GaAs, ideally terminated, non-reconstructed and with (2×8), (2×4), and (4×4) reconstructions. The orientation-dependent variations of the atomic and electron densities associated with reconstructions are found to affect localization of the Positron wave function at the surface. Computed Positron binding energy, work function, and annihilation characteristics demonstrate their sensitivity both to chemical composition and atomic structure of the topmost layers of the surface. Theoretical annihilation probabilities of surface trapped Positrons with As 3d, 3p, and Ga 3p core level electrons are compared with the ones estimated from the measured Auger peak intensities. © 2011 American Institute of Physics
R Diehl - One of the best experts on this subject based on the ideXlab platform.
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an asymmetric distribution of Positrons in the galactic disk revealed by gamma rays
Nature, 2008Co-Authors: G Weidenspointner, P. Jean, Gerry Skinner, J Knodlseder, Peter Von Ballmoos, G F Bignami, R Diehl, A W StrongAbstract:Antimatter is not an exotic rarity found only in the depths of the Universe: there are large quantities in our own Galaxy. We know this because we see the 511-keV γ-ray emission line, a signature of electron–Positron annihilation, coming from the general direction of the Galactic Centre. The origin of the Positrons has remained a mystery, but the distribution of the annihilation line radiation provides a clue. Astronomers now have the tools that can work out that distribution, and analysis of more than four years of spectroscopic data from the INTEGRAL satellite reveals an unexpected distribution of the 511-keV γ-ray emission from the inner Galactic disk, suggesting that the Positrons originate in binary stars containing black holes or neutron stars. Gamma-ray line radiation at 511 keV is the signature of electron–Positron annihilation, which comes from the general direction of the Galactic centre, but the origin of the Positrons was a mystery. This paper reports a distinct asymmetry in the 511 keV line emission coming from the inner Galactic disk, which resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies >20 keV, indicating that they may be the dominant origin of the Positrons. Gamma-ray line radiation at 511 keV is the signature of electron–Positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre1, but the origin of the Positrons has remained a mystery. Stellar nucleosynthesis2,3,4, accreting compact objects5,6,7,8, and even the annihilation of exotic dark-matter particles9 have all been suggested. Here we report a distinct asymmetry in the 511-keV line emission coming from the inner Galactic disk (∼10–50° from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies >20 keV (‘hard’ LMXBs), indicating that they may be the dominant origin of the Positrons. Although it had long been suspected that electron–Positron pair plasmas may exist in X-ray binaries, it was not evident that many of the Positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511-keV line. For these models, our result implies that up to a few times 1041 Positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter.
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an asymmetric distribution of Positrons in the galactic disk revealed by gamma rays
Nature, 2008Co-Authors: G Weidenspointner, P. Jean, Gerry Skinner, J Knodlseder, G F Bignami, Peter Von Ballmoos, R DiehlAbstract:Gamma-ray line radiation at 511 keV is the signature of electron-Positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the Positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles have all been suggested. Here we report a distinct asymmetry in the 511-keV line emission coming from the inner Galactic disk ( approximately 10-50 degrees from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies >20 keV ('hard' LMXBs), indicating that they may be the dominant origin of the Positrons. Although it had long been suspected that electron-Positron pair plasmas may exist in X-ray binaries, it was not evident that many of the Positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511-keV line. For these models, our result implies that up to a few times 10(41) Positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter.
Prasanta Chatterjee - One of the best experts on this subject based on the ideXlab platform.
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dynamics of the Positron acoustic waves in electron Positron ion magnetoplasmas
Indian Journal of Physics, 2017Co-Authors: Asit Saha, Prasanta ChatterjeeAbstract:Dynamics of the Positron acoustic waves in electron–Positron–ion (e–p–i) magnetoplasmas with \(\kappa \)-distributed hot electrons and Positrons is investigated in the frameworks of the Kadomtsev–Petviashili (KP) and modified Kadomtsev–Petviashili (mKP) equations. Employing the reductive perturbation technique, the KP and mKP equations are derived. Using the bifurcation theory of planar dynamical systems, the Positron acoustic solitary wave solutions, the kink and anti-kink wave solutions are obtained. Considering an external periodic perturbation in the electron–Positron–ion magnetoplasmas, the perturbed KP and mKP equations are studied via some qualitative and quantitative approaches. To corroborate in the fact that the perturbed KP and mKP equations can indeed give rise to the quasiperiodic and chaotic motions, the phase plane plots, time series plots, and the Poincare section are used. The quasiperiodic and developed chaos can be observed for the perturbed Positron acoustic waves. The frequency (\(\omega \)) of the external periodic perturbation plays the role of the switching parameter in chaotic motions of the perturbed Positron acoustic waves through quasiperiodic route to chaos. This work can be useful to understand the dynamics of nonlinear electromagnetic perturbations in space and laboratory plasmas consisting of \(\kappa \)-distributed hot electrons and Positrons.
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dynamic behavior of ion acoustic waves in electron Positron ion magnetoplasmas with superthermal electrons and Positrons
Physics of Plasmas, 2014Co-Authors: Nikhil Pal, Asit Saha, Prasanta ChatterjeeAbstract:The dynamic behavior of ion acoustic waves in electron-Positron-ion magnetoplasmas with superthermal electrons and Positrons has been investigated in the framework of perturbed and non-perturbed Kadomtsev-Petviashili (KP) equations. Applying the reductive perturbation technique, we have derived the KP equation in electron-Positron-ion magnetoplasma with kappa distributed electrons and Positrons. Bifurcations of ion acoustic traveling waves of the KP equation are presented. Using the bifurcation theory of planar dynamical systems, the existence of the solitary wave solutions and the periodic traveling wave solutions has been established. Two exact solutions of these waves have been derived depending on the system parameters. Then, using the Hirota's direct method, we have obtained two-soliton and three-soliton solutions of the KP equation. The effect of the spectral index κ on propagations of the two-soliton and the three-soliton has been shown. Considering an external periodic perturbation, we have presented the quasi periodic behavior of ion acoustic waves in electron-Positron-ion magnetoplasmas.
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head on collision of ion acoustic solitary waves in electron Positron ion plasma with superthermal electrons and Positrons
European Physical Journal D, 2011Co-Authors: Prasanta Chatterjee, Uday Narayan GhoshAbstract:The head-on collision of ion acoustic solitary waves are studied in an electron-Positron-ion plasma composed of superthermal electrons, superthermal Positrons, and cold ions using the extended Poincare-Lighthill-Kuo (PLK) method. The effects of the ratio of electron to Positron temperature, the spectral index of electron and Positron, and the concentration of Positron component on the phase shift are studied. It is found that the presence of superthermal electrons and superthermal Positrons play a significant role on the collision of ion acoustic solitary waves. It is also been observed that the temperature ratio plays a significant role on the collision of ion acoustic solitary waves.
G F Bignami - One of the best experts on this subject based on the ideXlab platform.
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an asymmetric distribution of Positrons in the galactic disk revealed by gamma rays
Nature, 2008Co-Authors: G Weidenspointner, P. Jean, Gerry Skinner, J Knodlseder, Peter Von Ballmoos, G F Bignami, R Diehl, A W StrongAbstract:Antimatter is not an exotic rarity found only in the depths of the Universe: there are large quantities in our own Galaxy. We know this because we see the 511-keV γ-ray emission line, a signature of electron–Positron annihilation, coming from the general direction of the Galactic Centre. The origin of the Positrons has remained a mystery, but the distribution of the annihilation line radiation provides a clue. Astronomers now have the tools that can work out that distribution, and analysis of more than four years of spectroscopic data from the INTEGRAL satellite reveals an unexpected distribution of the 511-keV γ-ray emission from the inner Galactic disk, suggesting that the Positrons originate in binary stars containing black holes or neutron stars. Gamma-ray line radiation at 511 keV is the signature of electron–Positron annihilation, which comes from the general direction of the Galactic centre, but the origin of the Positrons was a mystery. This paper reports a distinct asymmetry in the 511 keV line emission coming from the inner Galactic disk, which resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies >20 keV, indicating that they may be the dominant origin of the Positrons. Gamma-ray line radiation at 511 keV is the signature of electron–Positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre1, but the origin of the Positrons has remained a mystery. Stellar nucleosynthesis2,3,4, accreting compact objects5,6,7,8, and even the annihilation of exotic dark-matter particles9 have all been suggested. Here we report a distinct asymmetry in the 511-keV line emission coming from the inner Galactic disk (∼10–50° from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies >20 keV (‘hard’ LMXBs), indicating that they may be the dominant origin of the Positrons. Although it had long been suspected that electron–Positron pair plasmas may exist in X-ray binaries, it was not evident that many of the Positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511-keV line. For these models, our result implies that up to a few times 1041 Positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter.
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an asymmetric distribution of Positrons in the galactic disk revealed by gamma rays
Nature, 2008Co-Authors: G Weidenspointner, P. Jean, Gerry Skinner, J Knodlseder, G F Bignami, Peter Von Ballmoos, R DiehlAbstract:Gamma-ray line radiation at 511 keV is the signature of electron-Positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the Positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles have all been suggested. Here we report a distinct asymmetry in the 511-keV line emission coming from the inner Galactic disk ( approximately 10-50 degrees from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies >20 keV ('hard' LMXBs), indicating that they may be the dominant origin of the Positrons. Although it had long been suspected that electron-Positron pair plasmas may exist in X-ray binaries, it was not evident that many of the Positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511-keV line. For these models, our result implies that up to a few times 10(41) Positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter.
