Secondary Electron Production Research Articles

Effects of electromagnetic and plasma drag forces on the orbit evolution of dust in planetary magnetospheres

We have considered the evolution of dust orbits in a gravitational and electromagnetic field like that in the magnetosphere of Saturn. The orbits evolve due to the action of plasma drag and gyrophase drag (Lorentz force combined with a delay in charging of the dust). We calculate the average relative change in the semimajor axis, 〈 a dot /a 0〉 , and the average change in eccentricity, 〈 e dot 〉 , for different initial orbits and different plasma conditions, including cases with constant temperature and density and cases with gradients in temperature and density. Finally, we adopted a plasma model which may be appropriate for the E-ring plasma of today. This model has a cold and hot electron component and the production of secondary electrons is important, contrary to the other cases considered. It appears possible that the E-ring dust particles, if injected by Encleadus at low eccentricities, will keep their low eccentricities in today's plasma environment. This would imply that the orbits would drift slowly outward mainly due to plasma drag. Using an extensive set of different parameters, we show that in some circumstances the perturbing forces may be strongly dependent on global or local plasma conditions and/or dust properties. This implies that even moderate environmental changes could have significant effects on the evolution of Saturn's E-ring, and emphasizes the need for better in situ measurements in order to understand this diffuse ring phenomenon.

Modified Sternglass theory for the emission of secondary electrons by fast-electron impact.

The Sternglass theory [Sternglass, Phys. Rev. 108, 1 (1957)] for fast-ion-induced secondary-electron emission from metals has been modified to predict the secondary-electron yield from metals impacted by energetic (several keV to about 200 keV) electrons. The primary modification of the theory accounts for the contribution of the backscattered electrons to the production of secondary electrons based on a knowledge of the backscattered-electron energy distribution. The modified theory is in reasonable agreement with recent experimental data from gold targets in the 6--30-keV electron energy range.

Solar cycle dependence of spacecraft charging in low Earth orbit

Recent experimental evidence has shown that Defense Meteorological Satellite Program (DMSP) polar orbiting spacecraft at 840 km can develop electric potentials as severe as −1430 V while at high magnetic latitudes. To explore this charging region, an analysis of DMSP F6, F7, F8, and F9 satellite precipitating particle and ambient plasma measurements taken during periods of high, medium, and low solar flux is performed. One hundred eighty‐four charging events ranging from −46 to −1430 V are identified, and an extreme solar cycle dependence is found as charging is most frequent and severe during solar minimum. Satellite measurements and time‐dependent ionospheric model (TDIM) output are used to determine the cause of the solar cycle dependence and to characterize the environments which generate and inhibit these potentials. The electron precipitation associated with various DMSP charging levels is analyzed; it is suggested that precipitating electrons as low as 2 to 3 keV may contribute to charging though higher‐energy electrons make greater contributions. Secondary electron production due to incident electrons below 1 keV is shown to inhibit charging. The energetic electron fluxes shown to generate charging do not vary significantly over the solar cycle. Instead, DMSP ambient plasma data and TDIM generated results identify a variation in plasma density over 1 or more orders of magnitude as the cause of the solar cycle dependence, and an ambient plasma density of less than 104 cm−3 is found necessary for significant negative charging (≥100 V) to occur.

Use of spin polarized metastable atom deexcitation spectroscopy to probe the dynamics of metastable atom-surface interactions

Spin-labelling techniques, specifically the use of electron-spin-polarized metastable atoms in conjunction with spin analysis of the ejected electrons, are used to probe the dynamics of metastable atom-surface interactions. Studies of clean and adsorbate covered metallic, semiconductor and insulating surfaces show that the electron ejection processes are more complex than suggested by conventional models of metastable atom deexcitation at surfaces and that effects such as secondary electron production, inelastic spin-flip scattering, and perturbation of the incident atom by the surface must also be considered.

Track structure model for damage to mammalian cell cultures during solar proton events.

Solar proton events (SPEs) occur infrequently and unpredictably, thus representing a potential hazard to interplanetary space missions. Biological damage from SPEs will be produced principally through secondary electron production in tissue, including important contributions due to delta rays from nuclear reaction products. We review methods for estimating the biological effectiveness of SPEs using a high energy proton model and the parametric cellular track model. Results of the model are presented for several of the historically largest flares using typical levels and body shielding.

Detection of energy-selected secondary electrons in coincidence with energy-loss events in thin carbon foils.

The ultimate resolution in secondary-electron images obtained in a scanning transmission electron microscope depends strongly on secondary-electron-production mechanisms. In such a microscope, equipped with an electron-energy-loss spectrometer as well as secondary-electron-energy analyzer, coincidences have been achieved between secondary electrons and energy-loss electrons. This has resulted in additional information on the origin of secondary electrons in thin carbon films. The average probability for the production of secondary electrons of a given kinetic energy rises linearly with the energy lost by the primary electrons minus this kinetic energy and a few eV. These secondary electrons seem to appear from a cascade which was started by the original energy-loss event. Since most of these events are volume-plasmon excitations, volume-plasmon decay followed by a cascade contributes strongly to the secondary-electron emission. The linear relation seems to break down at energy losses of more than \ensuremath{\approxeq}125 eV. Energy losses associated with surface plasmons give a high probability for emission and detection of secondary electrons with a kinetic energy of 2--3 eV. For losses which are about 11 eV higher than the kinetic energy of the secondary electrons, an enhanced probability of emission exists. This enhancement is attributed to direct ionization from the valence band. The results are obtained in non-ultrahigh-vacuum conditions but show one of the many possibilities of coincidence spectroscopy in a scanning transmission electron microscope.

Impact ionization in the presence of strong electric fields in silicon dioxide

Abstract This paper reports the results of Monte Carlo transport calculations for electrons in strong electric fields in silicon dioxide based on new choices for the deformation potential in acoustic phonon scatter and for the ionization threshold. Impact ionization is described on the basis of cross sections derived from many body dielectric theory coupled to a model insulator. The electron-acoustic and electron-elastic scattering rates are matched at 8 eV in order to provide appropriate limitation on the electron-phonon scattering. The sensitivity of secondary electron production to these parameters is described. Also described is the important role of bulk trapped negative charge in affecting secondary electron production by changing the local field value. The results show that suitable choices for these parameters lead to appropriate levels of impact ionization and vacuum emission spectra.

The effects of a universal wedge and beam obliquity upon the central axis dose buildup for 6‐MV x rays

In a number of clinical situations, the dose to the skin and the superficial tissues is of concern. Both beam obliquity and a beam modifier will modify the dose delivered to these regions due to changes in the scattering geometry, scattered photon and secondary electron production, and changes in the energy spectrum of a polyenergetic beam. Some linear accelerators use a single universal wedge mounted within the treatment head. Because such a wedge is at an extended distance from the patient, its contribution to the beam contaminants incident to the skin will be limited. Measurements of the ionization in the buildup region have been performed in a polystyrene phantom irradiated with a 6-MV x-ray beam from a linear accelerator equipped with a universal wedge. The variation of the buildup dose with obliquity, universal wedging, and distance from the source has been measured for angles of incidence between 0 degrees and 60 degrees and for effective wedge angles between 0 degrees and 45 degrees. The results indicate that the percentage buildup has a much stronger dependence upon the angle of incidence than upon the effective wedge angle. For distances approaching the treatment head, it is shown that the universal wedge generates secondary electrons that elevate the surface dose, but that this contribution decreases with distance.

Secondary electrons induced by fast ions under channeling conditions. I. Production and emission of secondary electrons.

Energy spectra of ion-induced secondary electrons emitted from Si and GaAs single crystals have been measured for various ions with a velocity of 3.75 MeV/amu. A simple {ital Z}{sub 1}{sup 2}-scaling behavior of the electron yields indicates that the observed keV electrons stem from simple binary collisions between the ions and the target electrons. Measurements for GaAs crystals preamorphized with 2-keV Ar{sup +} ions provide evidence for the localization of the binary collisions near the surface region under channeling incidence conditions. Furthermore, these measurements are used to determine the effective target thicknesses both for channeling and random incidence conditions.

Secondary electrons from charged particle collisions with atoms and molecules

Since a large fraction of the energy transfer in energetic atomic collisions is in the production of secondary electrons, most of the radiation effects are a result of this process. Therefore, a knowledge of the energy spectrum (and for some purposes the angular distribution) of secondaries is crucial in understanding the interaction of charged particles with matter. Semi-empirical models for the differential cross sections for secondary electron production by proton and electron impact on atoms and molecules have been developed which summarize a large amount of information in the form of analytical equations with a few parameters for each target species.

Mechanisms for secondary electron production in ion-atom collisions

Electron angular distributions provide a sensitive probe of ionization mechanisms in ion-atom collisions. At high energy, two broad classes of mechanisms, namely, single collision and double collision mechanisms, operate. The former produce electrons in the binary encounter peak while the latter are pertinant everywhere else in the electron energy and angular distributions. Low energy electrons, cusp electrons, and ridge electrons all manifest some aspects of double collision mechanisms.

Secondary-electron emission from metals impacted by high-velocity particles: molecular-effect deviations from a single-particle picture

Experiments have been performed to study the influence of projectile molecular effects on the production of secondary electrons in the MeV/amu energy regime. Secondary-electron yields from Au, Ta and A1 2O 3 surfaces were measured using charged-particle projectiles provided by Van de Graaff accelerators (H + at 1.5–6 MeV, H 2 + at 2–6 MeV, H 3 + at 3–6 MeV, 3He + at 13–22 MeV, 3He 2+ at 13–33 MeV, 4He + at 18–22 MeV, and 4He 2+ at 18–33 MeV) and scanning electron microscopes (electrons at 0.8–30 keV). For low projectile velocities, the total electron yield due to a composite projectile is less than the sum of the yields of the individual components of that projectile. This “molecular effect” is attributed to interference effects between the individual components of the projectile which lessen each component's ability to produce secondary electrons. As the projectile velocity is increased, these interference effects are reduced and the projectile as a whole becomes more effective in producing secondary electrons. Secondary electrons produced by backscattered electrons were also studied and found to constitute 60–80% of the total number of secondary electrons emitted from Au and Ta and ~ 40% of those emitted from Al 2O 3. These results are interpreted in terms of existing theories of secondary-electron emission. Ongoing computer simulations are contributing to an understanding of the particle dynamics of the secondary-electron emission process for composite projectiles and are showing qualitative agreement with experiment.

A study of proximity effects at high electron-beam voltages for x-ray mask fabrication part 1: Additive mask processes

Proximity effects can be reduced when exposing x-ray mask membranes by increasing the electron-beam accelerating voltage. Forward scattering in the resist is reduced and exposure due to backscattered electrons is also reduced since the more energetic electrons are able to pass through the electroplating base and thin mask membrane. In this paper, a detailed study of the proximity effect at high electron-beam voltages for additive process x-ray mask fabrication will be discussed. The main contributors to the proximity effect at high beam voltages were found to be backscattering from the x-ray mask membrane, fast secondary electron production by the incident beam, backscattering from the Au/Cr plating base, and finite beam size. The proximity effect was found to still be significant at 75 kV; but, greatly reduced compared to the measured effect at 50 kV. A Monte Carlo simulation program which included the effects of fast secondary electron production was used to analyze the experimental results. Simulated radial absorbed energy distributions were found to agree well with experimental data from x-ray mask structures. The use of proximity correction parameters, determined from the Monte Carlo data, in a proximity correction program predicted that correction will be necessary at 75 and 100 kV. The reduction in proximity effect gained by using 100 kV was found to be quite small compared to the reduction gained by using 75 kV instead of 50 kV.

Heliospheric effects on cosmic-ray electrons

view Abstract Citations (34) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Heliospheric Effects on Cosmic-Ray Electrons Moraal, H. ; Jokipii, J. R. ; Mewaldt, R. A. Abstract Motivated by the success of current modulation models in interpreting the solar modulation of Galactic cosmic-ray nuclei, several effects on cosmic-ray electrons which are new or which have not yet been fully explored are considered. Among these are the contribution of Galactic positrons to the total electron flux, the production of secondary electrons from solar system objects, and the possibility of electrons being accelerated at the solar wind termination shock. It is found that the first of these provides a natural interpretation of the time variations of Galactic cosmic-ray electrons. Jovian electrons and thermal solar wind electrons may be accelerated to cosmic-ray energies at the termination shock. Such acceleration effects may alter the time-intensity profiles of electrons at earth, further modifying the interpretation of the electron modulation. Publication: The Astrophysical Journal Pub Date: January 1991 DOI: 10.1086/169617 Bibcode: 1991ApJ...367..191M Keywords: Electron Acceleration; Galactic Cosmic Rays; Heliosphere; Milky Way Galaxy; Solar Electrons; Solar Wind; Magnetic Field Configurations; Solar Cycles; Solar System; Space Radiation; COSMIC RAYS: GENERAL; PARTICLE ACCELERATION full text sources ADS |

A study of proximity effects at high electron-beam voltages for x-ray mask fabrication. I. Additive mask processes

Proximity effects can be reduced when exposing x-ray mask membranes by increasing the electron-beam accelerating voltage. Forward scattering in the resist is reduced and exposure due to backscattered electrons is also reduced since the more energetic electrons are able to pass through the electroplating base and thin mask membrane. In this article, a detailed study of the proximity effect at high electron-beam voltages for additive process x-ray mask fabrication will be discussed. The main contributors to the proximity effect at high beam voltages were found to be backscattering from the x-ray mask membrane, fast secondary electron production by the incident beam, backscattering from the Au/Cr plating base, and finite beam size. The proximity effect was found to still be significant at 75 kV; but, greatly reduced compared to the measured effect at 50 kV. A Monte Carlo simulation program which included the effects of fast secondary electron production was used to analyze the experimental results. Simulated radial absorbed energy distributions were found to agree well with experimental data from x-ray mask structures. The use of proximity correction parameters, determined from the Monte Carlo data, in a proximity correction program predicted that correction will be necessary at 75 and 100 kV. The reduction in proximity effect gained by using 100 kV was found to be quite small compared to the reduction gained by using 75 instead of 50 kV.

Cross Sections for Production of Secondary Electrons by Charged Particles

Abstract The availability of cross sections for the production of secondary electrons from ion or electron collisions is reviewed from the point of view of a potential user. Some recent measurements and empirical models are pointed out. New models are proposed which give differential and total cross sections for proton and electron impact.

Cross Sections for Production of Secondary Electrons by Charged Particles

Cross Sections for Production of Secondary Electrons by Charged Particles

Auger electron and secondary electron yields induced by surface-channeled protons

The Auger electron and secondary electron emission from a (2 × 1)-Si(001) surface induced by surface-channeled 75 and 150 keV protons have been studied. The measured yield profiles have very different shapes. They are explained by calculated flux density distributions of the channeled protons taking into acount the different impact parameter dependence of Auger and secondary electron production.

Observation of auroral secondary electrons in the Jovian magnetosphere

Localized enhancements in the flux of suprathermal electrons were observed by the Voyager 1 Plasma Science instrument near the outer boundary of the Io plasma torus between L ∼7.5 and L ∼10. This localization, which occurs within the general region of hot electrons noted by Sittler and Strobel (1987), and the spectral characteristics of the observed electrons are consistent with secondary (backscattered) electron production by intense Jovian auroral energetic particle precipitation and support the hypothesis that such electrons may contribute to the processes that heat the plasma in this region of the magnetosphere.

Secondary electron production and the millimeter to gamma-ray continuum of emission-line quasi-stellar objects

A model is outlined to explain the multifrequency continua of active galactic nucleus (AGN) and QSOs based on synchrotron and Compton emission of secondary electrons. 3C 273 is used as a particular guide for observational constraints since it so well observed from radio to gamma-ray photon energies. In this model the large blue bump and blue bump Compton components arise in the innermost region near a supermassive compact object with strong magnetic field. Infrared synchrotron emission and infrared Compton components arise in the low-field region. The model results in bumps, wiggles, and inflections in the multifrequency continuum that correspond to those observed. 47 refs.