High-energy Electron Irradiation Research Articles

IL-1 Generated Subsequent to Radiation-induced Tissue Injury Contributes to the Pathogenesis of Radiodermatitis

IL-1 Generated Subsequent to Radiation-induced Tissue Injury Contributes to the Pathogenesis of Radiodermatitis

Assembly of suspended graphene on carbon nanotube scaffolds with improved functionalities

With self-assembly being an efficient and often preferred process to build micro- and nano-materials into ordered macroscopic structures, we report a simple method to assemble monolayer graphene onto densified vertically aligned carbon nanotube (CNT) micropillars en route to unique functional three-dimensional microarchitecture. This hybrid structure provides new means of studying strain induced in suspended graphene. The strain induced could be controlled by the size and number of supporting microstructures, as well as laser-initiated localised relaxation of the graphene sheet. The assembled structure is also able to withstand high-energy electron irradiation with negligible effect on the electrical properties of the hybrid system. The hybrid system was further functionalised with quantum dots on the CNTs with the assembled top graphene layer as a transparent electrode. Significant improvements in photocurrent were achieved in this system.

Irradiation-induced valence conversion of samarium ions in Na2SO4

Na2SO4: Sm phosphors were synthesized by heating pure sodium sulphate with a small amount of SmF3 at 950 degrees C. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements show that the particle size of as-synthesized phosphors is 58 and 60 nm, respectively. The samples were irradiated by Co-60 gamma-rays with irradiation doses of 10-50 kGy at room temperature and by electrons with a total fluence of 6.7 x 10(16) e/cm(2) at a flux of 7.8 x 10(11) e/cm(2).sec. After exposure to gamma-ray and high energy electron irradiations, as-synthesized phosphors show the conversion of Sm3+ -> Sm2+. The photoluminescence (PL) spectra of as-synthesized, gamma-ray, and electron-irradiated phosphors obtained under 375 nm excitation consist of narrow emission bands with peaks at 563, 598, 644, and 704 nm, assigned to the (4)G(5/2) -> H-6(J) (J = 5/2, 7/2, 9/2, and 11/2) transitions within 4f(5) electronic configuration of Sm3+. The PL spectra of irradiated phosphors under 570 nm excitation at room temperature consist of a broad band with a peak at 695 nm and an emission line at 685.9 nm on the broad band. The broad band is assigned to the 4f (5)5d -> 4f 6 (7FJ) transition and the emission line to the D-5(0). F-7(0) transition within Sm2+. The PL and photoexcitation (PE) spectra at 10 K were well assigned to energy levels of Sm2+. Annealing at 473 K (200 degrees C) completely erased the Sm2+ emission band within the detection limit at room temperature.

Electrical characterization of defects introduced in n‐Si during electron beam deposition of Pt

AbstractWe have used deep level transient spectroscopy (DLTS) and high resolution DLTS to characterize the defects introduced in epitaxially grown n‐type, P‐doped, Si during electron beam deposition (EBD) of Pt for Schottky contact formation. The identity of some of these defects could be established by comparing their properties to those of well‐known defects introduced by high energy electron irradiation of the same material. The most prominent EBD‐induced defects thus identified were the E‐center (VP center), the A‐center (VO center), interstitial carbon (Ci), and the interstitial carbon–substitutional carbon (CiCs) pair. EBD also introduced some defects that were not observed after high energy electron irradiation. DLTS depth profiling revealed that the main defects, VO and VP, could be detected up to 0.5 µm below the metal–Si interface. Shielding the sample from particles originating in the region of the electron beam significantly reduced defect introduction and resulted in Schottky contacts with improved rectification properties. Finally, we have found that exposing the sample to EBD conditions, without actually depositing metal, introduced a different set of electron traps, not introduced by the EBD process.

Giant electrocaloric effect in ferroelectric poly(vinylidenefluoride-trifluoroethylene) copolymers near a first-order ferroelectric transition

We present directly measured electrocaloric effect (ECE) from the poly(vinylidenefluoride-trifluoroethylene) 65/35 mol. % copolymer. The data reveal a large difference in the ECE between that measured in applying and in removing the electric field. The difference is significantly reduced by modifying the copolymer with 20 Mrad of high energy electron irradiation. Moreover, an isothermal entropy change ΔSint = 160 J kg−1 K−1 and an adiabatic temperature change ΔTint = 35 °C can be induced in the irradiated copolymer. These results demonstrate the promise of achieving a significant ECE in ferroelectric polymers near first-order ferroelectric-paraelectric transition where multiple intermediate phases can exist.

Electrical and Optical Characterization of n-GaN by High Energy Electron Irradiation

The effect of high energy electron irradiation on the electrical and optical properties of n-GaN is studied. Hall and photoluminescence measurements are carried out on the samples irradiated with different doses. The results obtained from Hall measurements show that electron concentration and mobility are proportional to electron irradiation doses. The PL results show that the near-band-edge intensity and yellow luminescence intensity decrease continually with the increasing electron irradiation. However, it is found that the ratio of the yellow luminescence intensity to the near-band-edge intensity increases with the increasing of electron irradiation dose. To interpret this phenomenon, we propose two theoretical models based on the charge transport mechanism and rate equations, respectively, and they are in good agreement with the experimental observations.

Relaxor Properties and Tunability of Electron-Irradiated Thin Poly(vinlidene fluoride-trifluoroethylene) Copolymer Film

The effect of high energy electron irradiation on poly(vinlidene fluoride-trifluoroethylene) copolymer film with thickness about 180 nm has been studied. Both dielectric spectroscopy investigation and X-Ray Diffraction show that all-trans conformation of pre-irradiated films is transformed to trans-gauche conformation after irradiation. The relaxor behavior of irradiated sample obeys the modified Curie-Weiss and Vogel-Fulcher law. And the tunability is increased from 42% to 63% after irradiation.

Comparison of measured with calculated dose distribution from a 120‐MeV electron beam from a laser‐plasma accelerator

To evaluate the dose distribution of a 120-MeV laser-plasma accelerated electron beam which may be of potential interest for high-energy electron radiation therapy. In the interaction between an intense laser pulse and a helium gas jet, a well collimated electron beam with very high energy is produced. A secondary laser beam is used to optically control and to tune the electron beam energy and charge. The potential use of this beam for radiation treatment is evaluated experimentally by measurements of dose deposition in a polystyrene phantom. The results are compared to Monte Carlo simulations using the geant4 code. It has been shown that the laser-plasma accelerated electron beam can deliver a peak dose of more than 1 Gy at the entrance of the phantom in a single laser shot by direct irradiation, without the use of intermediate magnetic transport or focusing. The dose distribution is peaked on axis, with narrow lateral penumbra. Monte Carlo simulations of electron beam propagation and dose deposition indicate that the propagation of the intense electron beam (with large self-fields) can be described by standard models that exclude collective effects in the response of the material. The measurements show that the high-energy electron beams produced by an optically injected laser-plasma accelerator can deliver high enough dose at penetration depths of interest for electron beam radiotherapy of deep-seated tumors. Many engineering issues must be resolved before laser-accelerated electrons can be used for cancer therapy, but they also represent exciting challenges for future research.

Defects in an Electron-Irradiated 6H-SiC Diode Studied by Alpha Particle Induced Charge Transient Spectroscopy: Their Impact on the Degraded Charge Collection Efficiency

Defects in electron-irradiated 6H-SiC diodes have been studied by single alpha particle induced charge transient spectroscopy and deep level transient spectroscopy (DLTS) in order to identify critical defects responsible for the charge collection efficiency (CCE) decreased by high-energy electron irradiation. The defect X2 detected by the charge transient spectroscopy and the electron trap Ei detected by the DLTS had a similar activation energy of around 0.50 eV. In addition, the annealing at 200oC completely removed defects X2 and Ei, and restored the CCE. The defect X2 is attributed to the electron trap Ei, and responsible for the decreased CCE.

Effect of high-energy electron irradiation on forsterite laser crystals

The effect of 21-MeV electron irradiation on the optical absorption characteristics of Czochralski-grown forsterite (Mg2SiO4) single crystals (both undoped and chromium-doped) has been investigated. The irradiation is found to induce additional optical absorption (AOA) in the crystals in the range of 225–1200 nm due to the formation of color centers based on intrinsic host point defects and the change in the oxidation state of chromium ions. The AOA spectra have been decomposed into elementary bands. The influence of the chromium concentration in crystals, the oxygen content in the growth atmosphere, and additional doping with lithium on the behavior of these bands has been analyzed. A possible structure of the color centers responsible for the AOA is discussed. It is shown that the electron irradiation somewhat decreases the intensity of the characteristic absorption bands of tri- and tetravalent chromium ions and gives rise to a new absorption band in Mg2SiO4:Cr and Mg2SiO4:Cr,Li crystals heavily doped with chromium.

Formation of Si nanocrystals in ion implanted Si-SiO2 structures by MeV electron irradiation

Si-SiO2 structures implanted with Si+ or O+ ions were studied after high-energy (MeV) electron irradiation. 15 keV silicon or 10 keV oxygen ions with doses of 1.5×1012 cm−2 were implanted in n-type Si-SiO2 structures. The ion-beam energy was chosen so that the maximum number of the implanted ions would be deposited close to or at the Si-SiO2 interface. The reference (non-implanted) and ion implanted samples were simultaneously irradiated by 20 MeV electrons with a flux of about 1×1015 cm−2. The MeV electron irradiation effect on the redistribution of the implanted ions in Si-SiO2 structures was studied using RBS spectroscopy. The SiO2 surface roughness changes induced by ion implantation and high-energy electron irradiation of the structures were observed by atomic force microscopy (AFM).

Effect of high-energy electron irradiation in an electron microscope column on fluorides of alkaline earth elements (CaF2, SrF2, and BaF2)

The effect of high-energy (150 eV) electron irradiation in an electron microscope column on crystals of fluorides of alkaline earth elements CaF2, SrF2, and BaF2 is studied. During structural investigations by electron diffraction and electron microscopy, the electron irradiation causes chemical changes in MF2 crystals such as the desorption of fluorine and the accumulation of oxygen in the irradiated area with the formation of oxide MO. The fluorine desorption rate increases significantly when the electron-beam density exceeds the threshold value of ∼2 × 103 pA/cm2). In BaF2 samples, the transformation of BaO into Ba(OH)2 was observed when irradiation stopped. The renewal of irradiation is accompanied by the inverse transformation of Ba(OH)2 into BaO. In the initial stage of irradiation of all MF2 compounds, the oxide phase is in the single-crystal state with a lattice highly matched with the MF2 matrix. When the irradiation dose is increased, the oxide phase passes to the polycrystalline phase. Gaseous products of MF2 destruction (in the form of bubbles several nanometers in diameter) form a rectangular array with a period of ∼20 nm in the sample.

Effects of high-energy electron irradiation on blue luminescence of unintentionally doped GaN heterostructure

The unintentionally doped epitaxial GaN was grown on (0001) sapphire by metal organic chemical vapor deposition (MOCVD). The effects of 2MeV electron irradiation with the doses of 1×1015/cm2 and 5×1015/cm2 on the GaN epilayers were investigated by photoluminescence (PL) and Rutherford backscattering spectroscopy (RBS). The blue luminescence (BL) from the GaN epitlayers decreases significantly after the dose of 1×1015/cm2 electron irradiation. This is attributed to complex formation of BL-related defects with other point defects. On the contrary, the BL intensity from the GaN epilayers subjected to electron irradiation with the dose of 5×1015/cm2 increases beyond the BL intensity from the low-dose irradiated one. It is deduced that the surplus gallium vacancies in 1− charge state (VGa1-) could lead to the BL intensity rebounding as electron irradiation damage accumulated.

Evolution of High-Energy Electron Beam Irradiation Effects on Zeolite Supported Catalyst: Metal Nanoprecipitation

The high-energy electron irradiation effects on Fe-loaded, zeolite-supported catalyst were examined by transmission electron microscopy. In the original sample under little beam irradiation, no nanoparticles larger than 1 nm can be observed, and about half of the loaded Fe is identified as being in a positive ion state (i.e., iron oxides). Metal Fe nanoparticles in neutral state Fe0 were then found to precipitate quickly under beam illumination with an electron dose of ∼2.4 × 107 nm–2 or above at room temperature. Since electron microscopy is widely applied in the characterization of all sorts of catalysts supported on zeolites, the current observations could be treated as a model system to distinguish the metal nanoparticles existing in the original catalyst from those precipitated by electron beam irradiation. It was the ionization effect of electron radiation, other than temperature rise, that played an important role in the formation and growth of the metal precipitates. In the current system, the induced nanoprecipitations were identified as pure Fe metal clusters by electron energy loss spectroscopy (EELS), high-resolution transmission electron microscopy (HRTEM), and electron diffraction. As in current modeling system, although only metal Fe nanoparticles can be observed by EELS if the irradiation effect is ignored at the first place, the functional component in the loaded catalyst is actually a mixture of Fe-oxide and Fe.

Environment Exposure Tests of Electron-Emitting Film for Spacecraft Charging Mitigation

A new electron-emitting device operating in completely passive manner has been developed to prevent spacecraft charging and discharging. It is named as electron-emitting film (ELF) for spacecraft charging mitigation. This emitter (ELF) utilizes the field enhancement at the triple junction formed at the interface where metal and insulator are met and exposed to vacuum. ELF emits prebreakdown emission current that might lead to arcing at the triple junction. Hence, it balances the input and output currents to the spacecraft during substorm. After ensuring the robustness of this ELF against ground handling and in-orbit contamination, laboratory experiment confirmed continuous electron emission for 100 accumulated hours to assure the endurance. In this paper, its durability against high-energy electron and proton irradiation equivalent to ten solar years in GEO is reported. Effect of heat cycling (-150 °C-100 °C) and vacuum ultraviolet irradiation in GEO on this emitter is also completed. Postemissions of this ELF confirm the durability under those harsh space environments.

Effect of high-energy electron irradiation of a multilayer W-Mo system on the spectral characteristics of thermowave processes

A method is developed to analyze the state of the interface in a multilayer metallic system; it is based on spectral analysis of a heat-transfer coefficient. A coefficient of correlation is used to find the relation between the spectral characteristics and the thermal conductivity of the interphase interface. The change in the coefficient of correlation induced by 10-MeV electron irradiation of a multilayer W-Mo system is studied.

Contribution of incoherent effects to bremsstrahlung of fast particles in crystals

Incoherent radiation of high-energy electrons in crystals is due to the thermal spread of atoms about their equilibrium positions in lattices. The procedure for modeling incoherent radiation developed previously makes it possible to interpret some results of recent experiments conducted on the Mainz microtron (abbreviated MAMI).

Polysilicon on Insulator Structures for Sensor Application at Electron Irradiation & Magnetic Fields

The effects of high energy electron irradiation and high magnetic fields (up to 14 T) on the electrical characteristics of recrystallized p-type polysilicon-on-insulator layers were studied. The aim of the paper is to obtain the material suitable to create the sensors operating in harsh conditions.

Lifetime Control of 4.5 kV SiCGT by High-Energy Electron Irradiation

The measured turn-off waveforms of 4.5 kV SiCGTs by using electron irradiation with various electron doses are reported. The turn-off time decreased with an increase in the electron dose. Furthermore, the turn-off characteristics of SiCGTs with p-type drift layer, which assumed the various trap concentrations, are simulated. The relation between the turn-off characteristics and the trap is also investigated. The simulated results show good correlation to measured data and the simulated turn-off times decrease with an increase in the electron dose as well as measured data.

Observation of Bistable Defects in Electron Irradiated N-Type 4H-SiC

DLTS measurements show bistable behavior of the previously reported EH5 peak in low- and high-energy electron irradiation 4H-SiC. Both reconfiguration processes (A ! B and B ! A) take place above 700 ±C. By isothermal annealing, the reconfiguration rates were determined and the reconfiguration energy was calculated to EA = 2.4±0.2 eV. Since the defect is present already after low-energy electron irradiation, which mainly affects the C atom in SiC, the EH5 peak may be related to defects associated with C-vacancies or C-interstitials