Effect Of High-energy Electron Irradiation Research Articles

High-energy electron irradiation and B coordination in Na2O–B2O3–SiO2 glass

The effects of high-energy electron irradiation and the fractions of B atoms in particular sites in a Na borosilicate glass have been studied using time resolved electron energy loss spectroscopy in a scanning transmission electron microscope. Conversion of B atoms from the tetrahedral into trigonal coordination under irradiation has been observed. A mechanism for high-energy electron irradiation processes in Na borosilicate glasses is proposed based on the evolution of the near-edge fine structures of the B K, Si L and O K-edges.

Structural changes and phase behavior of electron-irradiated poly(vinylidene-trifluoroethylene) copolymers

The effect of high-energy electron irradiation on poly(vinylidene-trifluoroethylene) P(VDF-TrFE), copolymer of 56/44 comonomer molar ratio is studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and thermally stimulated depolarization current (TSDC). DSC results show that the energy necessary to process ferroelectric transition decreases after irradiation, which indicates that high-energy electron irradiation makes ferroelectric phase less stable, causing transition to paraelectric phase at a temperature below melting point. XRD data show that the peak at 2 θ=19° gradually disappears with the increase of absorbed dose, which indicates that the transition from all-trans ferroelectric state to a trans-gauche amorphous conformation takes place. It is found that both the peak temperature and released charge carrier density decrease with the irradiation doses in TSDC spectra, demonstrating less dipoles and crystalline regions in the irradiated copolymer films during ferro-paraelectric (F–P) transition. The results of TSDC measurements are related to the morphological changes induced by electron beam (EB) irradiation as well as the presence of local polar ordering and decrease of crystallinity revealed in DSC and XRD results.

Structural evolution and dielectric relaxation behavior of electron-irradiated poly(vinylidene fluoride–trifluoroethylene) 80/20 mol % copolymers

The effect of high-energy electron irradiation on poly(vinylidene fluoride-trifluoroethylene) 80/20 mol % copolymers has been studied in a broad dose ranging from 0 to 120 Mrad. It was found that the copolymers transformed from a normal ferroelectric to a relaxor ferroelectric phase (RFE) at high electron doses. For copolymers irradiated at the dose above 90 Mrad, they exhibited typical dielectric behavior of RFE, e.g., whose dielectric constant peaks show strong frequency dispersion. X-ray diffraction patterns showed that the irradiation induced a coexistence of the polar and nonpolar phase in the crystalline regions, leading to nanosized coherent regions in the irradiated copolymer films. Differential scanning calorimetery and polarization hysteresis loops also revealed the reduction in the crystallinity and stability of the ferroelectric state, reflecting significant changes in the ferroelectric-to-paraelectric phase transition due to the effect of high-energy electron irradiation.

The electron irradiation effects on silicon gate dioxide used for power MOS devices

The work provides experimental results of high energy electron irradiation effects on silicon dioxide used for power MOS devices. A systematic increase of the threshold voltage has been observed in irradiated IGBT and VDMOS devices processed on Si 〈1 0 0〉 and Si 〈1 1 1〉 , respectively. The threshold voltage shift has been interpreted as a result of the accumulated charge in the gate oxide. Single event gate rupture has been observed and attributed to the recoil ion interaction with the gate SiO 2. The result has been corroborated by reliability stress tests. After electron irradiation, an increase in breakdown voltage appeared on all devices which was attributed to a change in the surface impact ionisation coefficient. The change is most notable in devices processed on Si substrate with 〈1 1 1〉 orientation.

Evolution of transitional behavior and structure of electron-irradiated poly(vinylidene fluoride–trifluoroethylene) copolymer films

The effect of high-energy electron irradiation on poly(vinylidene fluoride– trifluoroethylene) (PVDF–TrFE) copolymer is investigated in a broad range of electron doses in light of a recent finding of the relaxor ferroelectric behavior and large electrostriction in the material. It is shown that although irradiation reduces both the crystalline and polar ordering, the two are not directly related to each other. In contrast to differential scanning calorimetery (DSC) and X-ray results which show that the copolymer becomes amorphous for higher irradiation dose, the dielectric data still exhibit relaxation peak which follows the Vogel–Fulcher law, indicating the presence of local polar ordering.

Quantitative analysis of structural, relaxational and electrostrictive properties of PVDF-TRFE/PMMA films irradiated with high-energy electrons

In this paper, the effect of high-energy electron irradiation on the transitional and electromechanical responses of PVDF-TRFE/PMMA (poly (vinylidene nuoride-trinuoroethylene)/polymethylmethacrylate) blend films is investigated in the light of a recent finding of large electrostrictive strain and high electromechanical response of PVDF-TXFE copolymer films after high-energy electron irradiation. Due to the decrease in crystallinity, both the dielectric and polarization responses were found to decrease with PMMA content. Interestingly, the presence of PMMA is found to affect the crystal-amorphous interface properties strongly in irradiated polyblend films. The field-induced strain which could be due to electrostriction and Maxwell stress for a blend system is found to come mainly from electrostriction. At room temperature, the contribution to the total strain from the Maxwell stress is found to be <20% while this contribution increases markedly with increasing temperature, especially for 7 %wt PMMA polyblend films.

High-energy electron irradiation effects in C60 films

We report here the high-energy (1 MeV) electron irradiation effects on C60 films. Fourier transform infrared spectroscopy, Raman spectroscopy, and x-ray diffraction results are consistent and provide clear evidence of the nondestruction of C60 molecules upon irradiation. The presence of C60 signature peaks in the spectra of all three techniques indicates that the C60 films have not been transformed into a hitherto proposed structure of amorphous carbon for low-energy irradiation. A very short collision time mechanism has been proposed to explain the observation.

Electron irradiation effects in AlGaAs/GaAs single heterojunction bipolar transistors

The effects of high-energy electron irradiation on the dc characteristics of polyimide passivated AlGaAs/GaAs HBTs of different base thicknesses and different emitter sizes are investigated. The devices show gain degradation for doses greater than 10/sup 15/ e/cm/sup 2/. The gain degradation of the passivated devices decreases (1) with increase in the base thickness, (2) with increase in the perimeter to area ratio of the emitter, and (3) with increase in the base current. Our results suggest that the observed gain degradation due to electron irradiation is mainly caused by an increase in the emitter-base junction space charge region recombination.

Polarization and structural properties of high-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer films

The effect of high-energy electron irradiation on structural and polarization properties of 50/50 mol % copolymer of poly(vinylidene fluoride-trifluoroethylene) was investigated for both mechanically stretched and unstretched films. Although stretching can significantly enhance the polarization and dielectric responses in unirradiated films, it was observed that this enhancement was not significant in irradiated films. In addition, the polarization in both types of films after irradiation can be described quite well by a logarithmic mixing law of composites, which consist of crystallites embedded in an amorphous matrix with nearly the same fitting parameters. On the other hand, the enhancement of the mechanical properties from stretching persists after the irradiation, and the elastic modulus along the stretching direction remains high after irradiation in comparison with unstretched films. It was found that the dielectric dispersion in both types of films after irradiation fits well to the Vogel–Fulcher law. It was also observed that the crystallinity decreases and the crosslinking coefficient increases continuously with dose. However, there was no direct one to one type relationship between the crystallinity and the crosslinking coefficient. Although stretching can reduce the rate of crosslinking, the reduction of crystallinity with dose for stretched and unstretched films does not show a marked difference.

Electron irradiation effects in polyimide passivated InP/InGaAs single heterojunction bipolar transistors

In this paper, we report the effects of high-energy electron irradiation on the DC characteristics of polyimide passivated InP/InGaAs single heterojunction bipolar transistors. In contrast with the results of electron irradiation of unpassivated devices, the polyimide-passivated devices show much less degradation of current gain and no change in the collector output conductance. The decrease of collector current in the active regime is found to be typically /spl sim/ 9 percent for a cumulative equivalent 1-MeV dose of 2.7/spl times/10/sup 16/ e/cm/sup 2/ (/spl sim/620 Mrad (InGaAs)). For low base currents, the devices show an increase in the current gain for smaller doses (<2.5/spl times/10/sup 15/ e/cm/sup 2/) followed by a decrease at the higher doses. The increase in the current gain at low doses is attributed to the trapped charge in the polyimide layer near the periphery of the B-E junction. The most significant effect of electron irradiation on the passivated devices is a-decrease in the slope of the I/sub C/-V/sub CE/ characteristics of some devices in the saturation regime. We believe this decrease in slope is caused by an increase in the collector series resistance after irradiation. Finally, devices with smaller emitter size are shown to have less radiation degradation than the larger emitter devices. This is explained by the smaller radiation damage at the junction peripheries of the passivated devices.

Special Structures of Graphite Steels After High-Energy Electron Irradiation

The effect of high-energy electron irradiation on the structure and properties of the graphite steels was investigated. It was shown that singleand multicycle irradiation allows the improvement of hardness and ductility twice). A partial dissolution of the graphite, carbides redistribution, and refinement of the grain size allow the formation of the favorable surface structure after irradiation. .

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The effect of high-energy electron irradiation on ferritin/haemosiderin cores (in an iron-overloaded human liver biopsy), its mineral analogue; six-line ferrihydrite (6LFh), and iron phosphate dihydrate (which has similar octahedral ferric iron to oxygen coordination to that in ferrihydrite and ferritin/haemosiderin cores) has been investigated using electron energy-loss spectroscopy (EELS). Fe L2,3-ionisation edges were recorded on two types of electron microscope: a 200 keV transmission electron microscope (TEM) and a 100 keV scanning transmission electron microscope (STEM), in order to investigate the damage mechanisms in operation and to establish a methodology for minimum specimen alteration during analytical electron microscopic characterisation. A specimen damage mechanism dominated by radiolysis that results in the preferential loss of iron co-ordinating ligands (O, OH and H2O) is discussed. The net result of irradiation is structural re-organisation and reduction of iron within the iron hydroxides. At sufficiently low electron fluence and particularly in the lower incident energy, finer probe diameter STEM, the alteration is shown to be minimal. All the materials examined exhibit damage which as a function of cumulative fluence is best fitted by an inverse power-law, implying that several chemical and structural changes occur in response to the electron beam and we suggest that these are governed by secondary processes arising from the primary ionisation event. This work affirms that electron fluence and current density should be considered when measuring mixed valence ratios with EELS.

Effect of High-Energy Electron Irradiation of Chicken Meat on Thiobarbituric Acid Values, Shear Values, Odor, and Cooked Yield

Experiments were conducted to determine whether electron-beam irradiation would affect shear values, yield, odor, and thiobarbituric acid (TBA) values of chicken tissues. Broiler breasts (pectoralis superficialis) and whole thighs were irradiated with an electron-beam accelerator at levels to produce adsorbed doses of 100, 200, and 300 krads on the surface of the sample. The thigh samples were stored for 2, 4, and 8 days before testing for TBA values. The depth to which the radiation had penetrated the pectoralis superficialis muscle was also determined.Radiation penetrated 22 mm into slices of pectoralis superficialis muscle when 100 krad was absorbed by the surface of the tissue. The dose absorbed beneath the tissue surface to a depth of 10 mm was larger than the dose absorbed at the surface. The absorbed dose decreased as the depth of penetration increased.For cooked breast tissue, the shear values and moisture content were not affected by the absorbed radiation. Cooking losses of aged breast tissue were not affected by irradiation, but cooking losses were reduced in breast tissue that had not been aged. Irradiating uncooked thigh and uncooked breast samples produced a characteristic odor that remained after the thighs were cooked but was not detectable after the breast samples were cooked. With two exceptions, no significantly different TBA values were found that could be attributed to irradiation.

Effects of High-Energy Electron Irradiation of Chicken Meat on Salmonella and Aerobic Plate Count

Four experiments were used to determine the effects of high-energy irradiation on the number of aerobic microorganisms and Salmonella on broiler breasts and thighs. Irradiation ranging from 100 to 700 kilorads (krads) was provided by a commercial-scale, electron-beam accelerator. Irradiation of broiler breast and thigh pieces with electron beams at levels of 100, 200, 300, 400, 500, and 600 krads showed that levels as low as 100 krads would eliminate Salmonella. When 33 thighs were tested after irradiation at 200 krads, only one thigh tested presumptive positive. The total number of aerobic organisms was reduced by 2 to 3 log10 cycles at irradiation levels of 100, 200, 300, 400, 500, 600, and 700 krads. Increasing the dose above 100 krads gave little if any additional benefit.

Physical and dielectric properties of irradiated polypropylene and poly(ethylene terephthalate)

The effect of high-energy electron irradiation in air and in nitrogen on the physical and dielectric properties of polypropylene and poly(ethylene terephthalate) has been studied by measurements of electric strength, dielectric constant, dissipation factor, tensile strength, gel fraction and molecular weight distribution. Electric strength of polypropylene was improved by irradiation, while dielectric properties of poly(ethylene terephthalate) were virtually unaffected by irradiation of 1.0–20 Mrad. Possible mechanisms for increasing electric strength are discussed from the point of view of degradation and oxidation taking place simultaneously with crosslinking of polypropylene. The maximum dose level to improve the electric strength of polypropylene is determined to be about 5 Mrad.

Radiation resistance of InP solar cells under light illumination

The demonstration of superior radiation resistance of InP solar cells during solar cell operation is reported. High-energy electron irradiation effects on InP n+-p junction solar cells under light illumination are compared with those under dark conditions. The InP solar cells under light illumination are found to have less degradation in solar cell properties. This is explained by minority-carrier injection enhanced annealing of radiation-induced defects, analyzed using deep level transient spectroscopy, in the p-InP layer.

Defect clustering induced by secondary collisions in Pt(C) alloys during high-voltage-electron-microscope irradiation

To obtain information about the stability of interstitial solid solutions under irradiation, we have studied various aspects of radiation-induced microstructure changes in model alloys, such as Pt-based alloys containing C. Some interesting effects of high-energy electron irradiation observed in this alloy system are reported in the present paper.

Ionization enhanced crystallization in amorphous germanium

The effect of high-energy electron irradiation upon the kinetics of crystallization of amorphous germanium layers has been studied, using conductivity measurements, during isochronal and isothermal warm-up. An increase in the growth rate of crystallization, induced at the surface or in the bulk, has been observed. It is suggested that this increase is the consequence of the recombination of electron-hole pairs created by the irradiation.