MeV Energy Electrons Research Articles

Measurements of continuous spectra of photons from 4/6 MeV dual energy e-LINAC

The continuous spectra of photons originated due to bombardment of 4 MeV, 6 MeV and dual energy (4 MeV ＋ 6 MeV) electrons on a thick Tungsten target have been measured for a recently developed 4/6 MeV dual energy electron-LINAC. The energy of incident electrons was deduced from the end-point energy of the measured bremsstrahlung spectrum. The experimental value of the incident electrons energy was found to be 4.10 ± 0.15 MeV and 6.15 ± 0.17 MeV, which are in good agreement with the expected value 4.00 MeV and 6.00 MeV, respectively, from the tuned operational parameters of the e-LINAC. The fractional intensity contribution due to 4 MeV and 6 MeV electrons in the continuous spectrum of photons from dual energy mode has been extracted to be 0.43 ± 0.11 (4 MeV) ＋ 0.57 ± 0.11 (6 MeV).

Electron Flux Variability and Ultra‐Low Frequency Wave Activity in the Outer Radiation Belt Under the Influence of Interplanetary Coronal Mass Ejections and High‐Speed Solar Wind Streams: A Statistical Analysis From the Van Allen Probes Era

AbstractThe ultra‐low frequency (ULF) waves can stochastically accelerate radiation belt electrons. Radial diffusion is a well‐established mechanism that can enhance or reduce the electron population in combination with other processes. Using data from the Van Allen Probes, we investigated the response of the 2.10 MeV energy electrons and ULF waves to two types of solar wind structures interacting with Earth's magnetosphere, namely, interplanetary coronal mass ejections (ICMEs) and High‐Speed solar wind streams (HSS). We use measured electron differential flux and ULF waves in the Pc4–Pc5 frequency range from October 2012 to May 2019. We examine 155 events with changes in the outer radiation belt electron differential flux. Results considering all ICMEs and HSSs during the Van Allen Probes era show that for both solar wind structures, solar wind interplanetary magnetic field Bz, solar wind proton density, and speed are related to the outer radiation belt relativistic electrons' response. The persistent ULF power is present during enhancement cases, while for reduction, the ULF waves power is concentrated at the initial reduction on the outer radiation belt electron flux.

Indium Tin Oxide with High Carrier‐Collection Capacity and Radiation Resistance for GaInP Solar Cell

The crystal structure, light transmittance, and contact resistivity of transparent conducting indium‐tin‐oxide (ITO) films for a III–V solar cell are studied. The optical transparency of ITO can reach 96% under appropriate annealing conditions. ITO and n+‐GaAs can form Ohmic contacts having a lower contact resistance than those formed with ITO and n+‐GaInP. A specially designed solar cell structure is fabricated to grow the ITO film as the front electrode and thus prevent oxidation of the AlInP window layer. Three different GaInP solar cells with pure ITO and ITO/metal grid electrode structures are designed and compared. The results indicate that the ITO electrode has good carrier‐collection ability. After irradiation with 1 MeV energy electrons with an electron fluence of 1 × 1015 e cm−2, the remaining factor of the GaInP solar cells with a pure ITO electrode is ≈98%. The results indicate that ITO films have significant application potential in space solar cell manufacturing.

Space low earth orbit environment simulator for ground testing materials and devices

The design and operation of an experimental installation are described, used for simulating those factors that most greatly affect the properties of materials and microelectronic devices in conditions of the near Earth (Low Earth Orbit) environment. The simulator apparatus is in the form of a cylindrical metal vacuum chamber constructed and mounted to the electron accelerator facility of the Center for the Advancement of Natural Discoveries using Light Emission Synchrotron Research Institute (Armenia) which allows the production of accelerated electrons with the following parameters: ultra-short pulse duration (τ = 4·10−13 s), electron energy 3.5 MeV, pulse current intensity 60 A/cm2, pulse frequency 12 Hz. A comparison may be made with conventional electron accelerators, which employ micro-second pulse duration, and a far lower current intensity of 2∙10−3 A/cm2. Thus, the specific features of this installation enable the simulation of ultra-fast processes as occur in cosmic space or under other extreme conditions. Here, we present the initial results obtained, concerning the influence of high-density electron irradiation on the behavior of the electro-physical properties of silicon crystals. Peculiarities and differences are presented between the results obtained from silicon crystals irradiated by electrons with an energy of 3.5 MeV and a pulse duration of τ = 4·10−13 s, and those from silicon samples irradiated with 7.5 MeV or 50 MeV energy electrons, using conventional electron accelerators.

Estimation of neutron yields produced from SS316L, CuCrZr, and graphite targets for MeV-energy electrons toward JT-60 Tokamak fusion device

Estimation of neutron yields produced from SS316L, CuCrZr, and graphite targets of the mainly In-vessel components of a Tokamak fusion device for MeV-energy electrons has been performed by neutronics analysis using a 3D Monte Carlo code [PHITS], including an electron-gamma shower M.C. code [EGS 5]. Neutronics analysis for Tokamak fusion devices is performed mainly with neutrons and photons using evaluated nuclear data libraries with energy up to 20 MeV energy. Furthermore, we have experience of photoneutron emission due to runaway electrons at several hydrogen discharges in Tokamak fusion device. The energy of the runaway electrons reaches at several tens of MeV energy. A 3D Monte Carlo code [PHITS + EGS5] suitable for electron and photon transport at energies greater than 20 MeV is very attractive for the photoneutron analysis of Tokamak fusion devices.

Quantifying the Precipitation Loss of Radiation Belt Electrons During a Rapid Dropout Event

AbstractRelativistic electron flux in the radiation belt can drop by orders of magnitude within the timespan of hours. In this study, we used the drift‐diffusion model that includes azimuthal drift and pitch angle diffusion of electrons to simulate low‐altitude electron distribution observed by POES/MetOp satellites for rapid radiation belt electron dropout event occurring on 1 May 2013. The event shows fast dropout of MeV energy electrons at L > 4 over a few hours, observed by the Van Allen Probes mission. By simulating the electron distributions observed by multiple POES satellites, we resolve the precipitation loss with both high spatial and temporal resolutions and a range of energies. We estimate the pitch angle diffusion coefficients as a function of energy, pitch angle, and L‐shell and calculate corresponding electron lifetimes during the event. The simulation results show fast electron precipitation loss at L > 4 during the electron dropout, with estimated electron lifetimes on the order of half an hour for MeV energies. The electron loss rate shows strong energy dependence with faster loss at higher energies, which suggest that this dropout event is dominated by quick and localized scattering process that prefers higher energy electrons. The improved temporal and spatial resolutions of electron precipitation rates provided by multiple low‐altitude observations can resolve fast‐varying electron loss during rapid electron dropouts (over a few hours), which occur too fast for a single low‐altitude satellite. The capability of estimating the fast‐varying electron lifetimes during rapid dropout events is an important step in improving radiation belt model accuracy.

Size Control of Cu Nanoparticles in Ion-Exchanged Soda-Lime Glass by 6 MeV Electron Irradiation and Its Application in Biofilm Inhibition

ABSTRACT A few soda-lime glass samples with a 1 cm2 area and 0.1 cm thickness were dipped into a molten salt bath of copper sulfate and sodium sulfate in a molar ratio of 54:46 at 545°C for 10 min. These samples were irradiated with 6 MeV energy electrons in the fluence range from 10 × 1014 to 40 × 1014 electrons/cm2 and annealed at 400°C. The optical properties and the corresponding induced effects were characterized by techniques such as ultraviolet-visible (UV-Vis), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The UV-Vis absorption spectra showed two peaks, one at 754 nm and other centered at 533 nm. The absorption peak at 754 nm was ascribed to Cu+2 ions, and the one at 553 nm corresponded to the surface plasmon resonance (SPR) band of nanocrystalline copper clusters. The intensity and the full-width at half maximum (FWHM) of the optical absorption peaks increased with an increase in the electron fluence. The XRD spectra showed a peak at 2θ positi...

Thermoluminescence and photoluminescence study of caso4: Dy nanophosphor for 6 mev energy electron dosimetry

Nanoparticles of CaSO 4 : Dy with size around 25 nm, were synthesized by the chemical co-precipitation method for the purpose of high energy electron dosimetry. The nanocrytstalline samples were irradiated with 6 MeV energy electrons having fluence varied from 3 × 10 14 to 2 × 10 15 e/cm 2 .The pre and post irradiated samples were characterized by the XRD, SEM, PL and TL techniques. The XRD spectra show the orthorhombic phase and do not change with the electron fluence. Moreover, the particle size found to be around 25 nm and marginally increased from 25 nm to 34 nm with the increase in the electron fluence. SEM image confirms the existence of the nanoparticle around 30 to 40 nm. In PL emission spectra, a shift towards lower wavelength has been observed with decrease in particle size from micrometer to nanometer. This mainly attributes to the extension in the band gap of Dy 3+ ions. The TL spectra exhibit four peaks at around 437,545,638, and 748 K respectively. The TL response curve shows that the peak intensity initially increased with electron fluence, and at a fluence of 9 × 10 14 e/cm 2 saturates then decreased with increase in the electron fluence. It is mainly due to the generation of different kinds of trapping centers. The present study indicates that the CaSO 4 : Dy phosphor can be used for the measurement of dose of 6 MeV energy electrons over a range varying from 1 kGy to 25 kGy.

Simulation of MeV electron energy deposition in CdS quantum dots absorbed in silicate glass for radiation dosimetry

We are currently developing 2D dosimeters with optical readout based on CdS or CdS/CdSe core-shell quantum-dots using commercially available materials. In order to understand the limitations on the measurement of a 2D radiation profile the 3D deposited energy profile of MeV energy electrons in CdS quantum-dot-doped silica glass have been studied by Monte Carlo simulation using the CASINO and PENELOPE codes. Profiles for silica glass and CdS quantum-dot-doped silica glass were then compared.

Radio Spectral Evolution of an X‐Ray–poor Impulsive Solar Flare: Implications for Plasma Heating and Electron Acceleration

We present radio and X-ray observations of an impulsive solar flare that was moderately intense in microwaves, yet showed very meager EUV and X-ray emission. The flare occurred on 2001 October 24 and was well observed at radio wavelengths by the Nobeyama Radioheliograph (NoRH), the Nobeyama Radio Polarimeters (NoRP), and the Owens Valley Solar Array (OVSA). It was also observed in EUV and X-ray wavelength bands by the TRACE, GOES, and Yohkoh satellites. We find that the impulsive onset of the radio emission is progressively delayed with increasing frequency relative to the onset of hard X-ray emission. In contrast, the time of flux density maximum is progressively delayed with decreasing frequency. The decay phase is independent of radio frequency. The simple source morphology and the excellent spectral coverage at radio wavelengths allowed us to employ a nonlinear χ2-minimization scheme to fit the time series of radio spectra to a source model that accounts for the observed radio emission in terms of gyrosynchrotron radiation from MeV-energy electrons in a relatively dense thermal plasma. We discuss plasma heating and electron acceleration in view of the parametric trends implied by the model fitting. We suggest that stochastic acceleration likely plays a role in accelerating the radio-emitting electrons.

Nonlinear Thomson scattering from relativistic laser plasma interaction

Nonlinear Thomson scattering radiation has been observed from relativistic laser plasma interaction. We found that this radiative process is dominant for very high intensity at which point the relativistic scattering of the laser light originates from MeV energy electrons inside the plasma

X-ray radiation from nonlinear Thomson scattering of an intense femtosecond laser on relativistic electrons in a helium plasma.

We have generated x-ray radiation from the nonlinear Thomson scattering of a 30 fs/1.5 J laser beam on plasma electrons. A collimated x-ray radiation with a broad continuous spectrum peaked at 0.15 keV with a significant tail up to 2 keV has been observed. These characteristics are found to depend strongly on the laser strength parameter a(0). This radiative process is dominant for a(0) greater than unity at which point the relativistic scattering of the laser light originates from MeV energy electrons inside the plasma.

On the solar wind control of Pc5 ULF pulsation power at mid‐latitudes: Implications for MeV electron acceleration in the outer radiation belt

On the basis of observations made at six sites (L shell range 3.75–6.79) belonging to the International Monitor for Auroral Geomagnetic Events (IMAGE) magnetometer array, we provide a statistical study of the relationship of solar wind speed to daily ULF pulsation power for 1995, 1996, and 1997, an interval corresponding to the declining phase of solar cycle 22. We find a very strong positive correlation between solar wind speed and dayside magnetospheric pulsation power across the entire L shell range studied. In addition, we identify a number of geomagnetic storm onset days on the basis of Dst variations and demonstrate that on these days large‐amplitude ULF pulsation activity can be driven during only moderate solar wind speed conditions. Removing the onset day population improves the correlation of pulsation power to solar wind speed and demonstrates how an improved solar wind speed proxy based on pulsation power can be determined by considering Dst. We also demonstrate an exponential decay of 1–10 mHz Pc5 wave power with decreasing L shell, the decay rate increasing with solar wind speed, thus indicating a stronger dependence of pulsation power on solar wind speed at higher L shells in the range L=3.75–6.79. Further, the L shell range studied is consistent with that over which storm‐time enhancements of MeV electron fluxes have been observed in the outer radiation belt, and we discuss the implications of the dependence of PcS ULF wave power on both solar wind speed and L shell for mechanisms which implicate large‐amplitude ULF pulsations in the acceleration of storm‐time MeV energy electrons.

Nonthermal Flare Emission from MeV‐Energy Electrons at 17, 34, and 86 GHz

We present analyses of two solar flares observed with high spatial resolution at 86 GHz with the BIMA millimeter-wavelength telescope and at 17 and 34 GHz with the Nobeyama radioheliograph. The flares were observed on 1998 November 24 and 1999 May 1. At millimeter wavelengths these are impulsive events, and therefore they must be produced by MeV-energy electrons. The present study using simultaneous observations of two flares at 86, 34, and 17 GHz provides an excellent opportunity to study high-energy electrons with high spatial resolution observations at three optically thin frequencies. The morphology of millimeter emission can reveal both the properties of the MeV-energy electrons and the nature of the coronal magnetic field lines where they radiate. One of the two events we present is the first clear case of a λ = 3 mm source in which both footpoints of a loop are detected. In the second event the polarization image at 17 GHz also suggests a bipolar or looplike morphology. Such morphological observations can be used to constrain the nature of the magnetic field in the solar corona.

Multiple Components in the Millimeter Emission of a Solar Flare

We analyze a small flare using imaging data at millimeter, microwave, and soft X-ray wavelengths and microwave and hard X-ray spectral observations. The remarkable aspect of this flare is evidence for the presence of MeV-energy electrons, which are responsible for the nonthermal millimeter emission, at a time when no hard X-rays from lower energy electrons are detected. This occurs during a smoothly varying phase, which is seen at radio wavelengths to last several minutes and is the brightest phase at millimeter wavelengths but is undetected in hard X-rays: it follows a brief spike of emission at flare onset, which has the more usual properties of impulsive events and features nonthermal microwave, millimeter, and hard X-ray emission. We interpret the phase that is brightest at millimeter wavelengths as being due to efficient trapping of a relatively small number of nonthermal electrons, whereas during the hard X-ray emission, trapping is much less efficient, and the decay time is much shorter at all energies, which leads to a larger ratio of hard X-ray flux to radio flux. As in many previous events studied at millimeter wavelengths, there is a discrepancy between the electron energy spectral indices inferred from the milllimeter and hard X-ray data during the impulsive phase when both are detected: again it appears that the energy spectrum at 1 MeV must be significantly flatter than at several hundred keV and below. However, there are problems in reconciling quantitatively the energy spectra for the hard X-ray-emitting and radio-emitting components: based on the most plausible parameters, the radio-emitting electrons should produce most of the hard X-rays. One solution to this contradiction is to invoke a coronal magnetic field stronger than seems likely based on the photospheric magnetic field.

Electron acceleration in Nd-laser plasma beat-wave experiments

The beating between two colinear Nd-YLF (λ = 1.053 μm, τ = 90 ps) and Nd-YAG (λ = 1.064 μm, τ = 160 ps) lasers in a homogeneous plasma (ne = 1017 cm−3) generates intense relativistic plasma waves associated with a high longitudinal electric field of the order of 1 GVm−1. In the conditions of the experiment, these electron plasma waves couple with ion waves in the regime of modulational instability as it has been demonstrated by electric field amplitude and saturation time measurements by Thomson scattering.When 3 MeV energy electrons are injected into the plasma, several hundreds of electrons accelerated up to 3.7 MeV are observed in correlation with the Thomson scattering signal associated to the plasma waves. This result is in agreement with a numerical simulation which takes into account the relative focussing geometry of electron and laser beams.

Electron acceleration in Nd-laser plasma beat-wave experiments.

The beating between two colinear Nd-YLF (λ = 1.053 μm, τ = 90 ps) and Nd-YAG (λ = 1.064 μm, τ = 160 ps) lasers in a homogeneous plasma (ne = 1017 cm−3) generates intense relativistic plasma waves associated with a high longitudinal electric field of the order of 1 GVm−1. In the conditions of the experiment, these electron plasma waves couple with ion waves in the regime of modulational instability as it has been demonstrated by electric field amplitude and saturation time measurements by Thomson scattering. When 3 MeV energy electrons are injected into the plasma, several hundreds of electrons accelerated up to 3.7 MeV are observed in correlation with the Thomson scattering signal associated to the plasma waves. This result is in agreement with a numerical simulation which takes into account the relative focussing geometry of electron and laser beams.

Passage of MeV-energy electrons through monocrystals

A wave equation for electrons channeled in a crystal which allows for incoherent scattering on thermal vibrations, is derived. The wave function evolution for electrons penetrating into axial and planar channels of a Si crystal and the output angular electron distributions are investigated. The possibility of a band structure calculation for channeling electrons without solving the eigenvalue problem is shown. The theoretical results prove to be in good agreement with experimental ones.

Effects of electron irradiation on N on P silicon solar cells

Radiation tests on bare N/P silicon solar cells and solar cells with various cover materials were performed with 1 MeV energy electrons for integrated fluxes up to 10 16 e/cm 2. The effect of electron irradiation upon the physical, electrical, optical, and thermal characteristics of the cells were analyzed and are presented in parametric form wherever practical. In particular, the changes with electron flux in the electrical output, and the temperature coefficients of the electrical output as well as the effect of the angle of incident radiation upon the output, have been investigated. The variations of spectral transmittance of cover materials and the spectral reflectance at angles of incidence between zero and 75 degrees were measured and the data compared to the electrical measurements results. The solar absorptance as a function of angle of incidence and the hemispherical emittance were calculated. All electrical measurements were performed under illumination closely approximating the spectrum of solar irradiation in outer space, and at the intensity of the solar constant. This is of particular importance when studying the effects of charged particle radiation, since the data thus obtained can be directly utilized for spacecraft solar array design.

Effects of Electron Irradiation on N on P Silicon Solar Cells

Radiation tests on bare N/P silicon solar cells and solar cells with various cover materials were performed with 1 Mev energy electrons for integrated fluxes up to 1016 e/cm2. The effect of electron irradiation upon the physical, electrical, optical, and thermal characteristics of the cells were analyzed and are presented in parametric form wherever practical. In particular, the changes with electron flux in the electrical output, and the temperature coefficients of the electrical output as well as the effect of the angle of incident radiation upon the output, have been investigated. The variations of spectral transmittance of cover materials and the spectral reflectance at angles of incidence between zero and 75 degrees were measured and the data compared to the electrical measurement results. The solar absorptance as a function of angle of incidence and the hemispherical emittance were calculated. All electrical measurements were performed under illumination closely approximating the spectrum of solar irradiation in outer space, and at the intensity of the solar constant. This is of particular importance when studying the effects of charged particle radiation, since the data thus obtained can be directly utilized for spacecraft solar array design.