Depth dose dependence of the mouse bone using kilovoltage photon beams: A Monte Carlo study for small-animal irradiation

This study investigated the dose enhancement due to the presence of mouse bone irradiated by the kilovoltage (kV) photon beams. Dosimetry of the bone associated with soft and lung tissue was determined by Monte Carlo simulations using the EGSnrc-based code in millimeter scale. Two inhomogeneous phantoms with 2 mm of bone layer sandwiched by: (1) water and lung (bone–lung phantom); and (2) water (bone–water phantom), were used. Relative depth doses along the central beam axes in the phantoms and dose enhancement ratios (bone dose in the above inhomogeneous phantoms to the dose at the same point in the water phantom) were determined using the 100 and 225 kVp photon beams. For the 100 kVp photon beams, the depth dose gradient in the bone was significantly larger compared to that in a water phantom without the bone. This is due to the beam hardening effect that some low-energy photons were filtered out in the deeper depth, resulting in less photoelectric interactions and hence energy depositions in the bone. Moreover, dose differences between the top and downstream (bottom) bone edges at depths of 1–5 mm were 168–192% and 149–166% for the bone–lung and bone–water phantom, respectively. These differences were larger than 21–27% (bone–lung) and 12–23% (bone–water) for the 225 kVp photon beams. The maximum dose enhancement ratio in the bone for the bone–lung and bone–water phantoms in various depths was about 5.7 using the 100 kVp photon beams. This ratio was larger than two times of that (2.4) for the 225 kVp photon beams. It is concluded that, apart from the basic beam characteristics such as attenuation and penumbra, which are related to the photon beam energy in the mouse irradiation, the bone dose is another important factor to consider when selecting the beam energy in the small-animal treatment planning, provided that the bone dose enhancement is a concern in the preclinical model.     

Asymmetry of bremsstrahlung from transversely polarized electrons

By using an electron-photon coincidence method the photon emission asymmetry in the elementary process of bremsstrahlung from transversely polarized electrons was measured. For an electron beam of 300 keV incident on a gold target the asymmetry for spin up and down of the primary beam was measured for fixed direc-tions of the outgoing electrons and photons as a function of the energy split. Asymmetries up to 30% were found. The measurements are a proper test for theories going beyond the first Born approximation.     

Target thickness dependence of bremsstrahlung from solid films

We report initial results of a study of the target thickness dependence of bremsstrahlung from solid film targets. The electron beam energy is 50 keV and bremsstrahlung is observed at 90°. Targets are aluminium and gold. Target thicknesses from 50 μg/cm², where single interaction conditions apply, to twice the electron range, where a multiple interaction model applies, were studied. We observe the transition from thin to thick film spectra. The purpose is to investigate whether the polarization bremsstrahlung contribution may be suppressed in solid film targets.     

Effects of electron beam irradiation on the photoelectrochemical properties of TiO2 film for DSSCs

TiO₂ has been widely utilized for various industrial applications such as photochemical cells, photocatalysts, and electrochromic devices. The crystallinity and morphology of TiO₂ films play a significant role in determining the overall efficiency of dye-sensitized solar cells (DSSCs). In this study, the preparation of nanostructured TiO₂ films by electron beam irradiation and their characterization were investigated for the application of DSSCs. TiO₂ films were exposed to 20–100 kGy of electron beam irradiation using 1.14 MeV energy acceleration with a 7.46 mA beam current and 10 kGy/pass dose rates. These samples were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS) analysis. After irradiation, each TiO₂ film was tested as a DSSC. At low doses of electron beam irradiation (20 kGy), the energy conversion efficiency of the film was approximately 4.0% under illumination of simulated sunlight with AM 1.5 G (100 mW/cm²). We found that electron beam irradiation resulted in surface modification of the TiO₂ films, which could explain the observed increase in the conversion efficiency in irradiated versus non-irradiated films.     

Time-resolved spectroscopy at the picosecond laser-triggered electron accelerator ELYSE

ELYSE is a fast kinetics center created for pulse radiolysis with picosecond time-resolution. The facility is a 4–9 MeV electron accelerator using a subpicosecond laser pulse to produce an electron pulse from a Cs₂Te semiconductor photocathode and RF gun technology for the electron acceleration. The pulse duration is around 5 ps at low charge (<2 nC) and high energy (9 MeV), and is under routine conditions 10 ps at higher charge (5 nC) and >8 MeV. The dark current at the target is less than 1% of the pulse photocurrent.Time-resolved absorbance measurements in cells placed in front of the electron beam are achieved using pulsed laser diodes, or a xenon flash lamp as light sources, and photodiodes connected to a 3 GHz transient digitizer or a streak camera (250–800 nm range and 3.7 ps time resolution) as detection instruments. In addition, the synchronization between the laser beam and the electron beam is exploited to measure the absorbance by a pump-probe set-up, the pump being the electron pulse produced by the laser pulse, and the probe being part of the laser beam (120 fs–3 ps) delayed by a variable optical line.     

Large-scale synthesis of silver nanoparticles using Ag(I)–S12 polymer through electron beam irradiation

Size-controlled large scale synthesis of silver nanoparticles was performed using Ag(I)–S12 inorganic-organic hybrid polymer with supramolecular structures though electron beam irradiation. The Ag(I)–S12 polymer was simply prepared by mixing dodecanethiol with the solution of silver salts. The silver nanoparticles with various sizes were prepared from Ag(I)–S12 polymer with an electron beam voltage from 0.3 MeV to 2 MeV, current from 0.06 mA to 0.48 mA, and/or irradiation time from 1 to 10 min. The morphology and chemical composition of the irradiated samples were characterized by transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR).     

Molecular patterning with a two-dimensional network polymer LB film 2: Drawing patterns by an electron beam

Electron beam lithography was investigated using a cross-linkable polymer Langmuir–Blodgett (LB) film. Cross-linking reaction occurs in the LB film with electron beam irradiation as well as UV light irradiation and the irradiated LB film becomes insoluble in the organic solvents to form a two-dimensional network in the LB film. The sensitivity and contrast of the cross-linkable polymer LB film are 3 μC cm^-2 and 0.64, respectively. The limiting resolution of patterning is 0.2 μm line-and-space. The electron beam lithography using the cross-linkable polymer LB film is applicable to the future nanotechnology.     

Bremsstrahlung from gas atom targets: Study of background processes

Recent absolute bremsstrahlung cross section experiments on gas targets of Ne, Ar, Kr and Xe at 28 and 50 keV have shown a significant polarization bremsstrahlung (PB) contribution, in contrast with previous thin-film experiments where no PB has been seen. Recently, Obolensky and Pratt have considered ways to improve the PB model, but the theory is still about 20% below the data. While a more complete theoretical calculation is certainly needed, we consider two additional background processes, not corrected in the experiment, that depend on the background photon spectrum in the beam line produced by electron interaction with collimators in the beam. We compare an estimate of both backgrounds with that from beam electrons elastically scattered by the gas into the cell window or wall and discuss initial efforts to measure these backgrounds.     

Modelling of phenol removal in aqueous solution depending on the electron beam energy

This paper deals with the influence of the electron beam energy (E=1.2–3 MeV; I=20–125 μA; D_R=1.3–8.3 kGy s⁻¹) on the degradation of phenol in aqueous solution. The decomposition of phenol and the concentration of its principal by-products are significantly influenced by the energy of the electron beam. The degradation yield increases with the electron energy. A simplified phenomenologic model of the reactor was proposed to describe the results.     

Experimental results on 2–30 keV bremsstrahlung from thick and thin targets

The recent experimental investigations on electron bremsstrahlung produced from impact of 2–30 keV electrons with thick solid and thin gaseous targets are reviewed. The theoretical models describing the energy and angular distributions of bremsstrahlung photons are discussed with their brief outlines and formulations to explain the experimental data. The results on thick target bremsstrahlung (TTB) spectra produced by keV electrons have suggested that there is a need to develop a comprehensive theory for accounting the solid state effects. It is further noted that the prediction of the modified KKD formula gives a reasonable agreement with the TTB data, whereas a semi-empirical formula gives a better fit to the data for thick targets. The available experimental data for dependence of double differential cross-sections of emitted photons on impact energy and their emission angles for gaseous atoms and molecules exhibit a good agreement with the theoretical calculations of Kissel et al., [1983. Shape functions for atomic-field bremsstrahlung from electrons of kinetic energy 1–500 keV on selected neutral atoms 1<Z<92. Atom. Data Nucl. Data Tables 28, 381–460].     

Mineralization of aqueous phenolate solutions: A combination of irradiation treatment and wet oxidation

Wet oxidation (high-temperature, high-pressure oxidation of organic wastes in aqueous solution) and radiation technology were combined in γ-ray and electron beam induced oxidation of 4×10^?4–1×10^?2 mol dm^?3 Na-phenolate solutions in a wide O₂ concentration (1–20 bar pressure) and absorbed dose (0–50 kGy) range. Most experiments were made in stainless steel high pressure autoclave equipped with magnetic stirrer. The rate of oxidation was followed by chemical oxygen demand and total organic carbon content measurements. The rate was similar in γ-ray and pulsed electron beam irradiation and increased with O₂ concentration in the liquid.     

Characterization of a power bipolar transistor as high-dose dosimeter for 1.9–2.2 MeV electron beams

Results of the characterization studies on a power bipolar transistor investigated as a possible radiation dosimeter under laboratory condition using electron beams of energies from 2.2 to 8.6 MeV and gamma rays from a ⁶⁰Co source and tested in industrial irradiation plants having high-activity ⁶⁰Co γ-source and high-energy, high-power electron beam have previously been reported. The present paper describes recent studies performed on this type of bipolar transistor irradiated with 1.9 and 2.2 MeV electron beams in the dose range 5–50 kGy. Dose response, post-irradiation heat treatment and stability, effects of temperature during irradiation in the range from –104 to +22 °C, dependence on temperature during reading in the range 20–50 °C, and the difference in response of the transistors irradiated from the plastic side and the copper side are reported. DLTS measurements performed on the irradiated devices to identify the recombination centres introduced by radiation and their dependence on dose and energy of the electron beam are also reported.     

Advanced oxidation process by electron-beam-irradiation-induced decomposition of pollutants in industrial effluents

Electron-beam irradiation considered on advanced oxidation process induces the decomposition of pollutants in industrial effluent. Experiments were conducted using a radiation dynamics electron beam accelerator with 1.5 MeV energy and 37 kW power. The effluent samples from an industrial complex were irradiated using the IPEN's liquid effluent irradiation pilot plant. The experiments were conducted using one sample from each of eight separate industrial units and five samples of a mixture of these units. The physical–chemical characterization of these samples is presented. The electron beam irradiation was efficient in destroying the organic compounds delivered in these effluents, mainly, chloroform, dichloroethane, methyl isobutyl ketone, toluene, xylene and phenol. The necessary dose to remove 90% of the most organic compounds from industry effluent was 20 kGy. The removal of organic compounds from this complex mixture was explained by the destruction G value (Gd) that was obtained for those compounds with different initial concentrations and was compared with literature.     

Continuous X-rays produced in light-ion–atom collisions

Continuous X-rays produced in light-ion–atom collisions producing continuous backgrounds and therefore determining the detection limit of PIXE, have been experimentally and theoretically studied. It is shown that the experimental results over the wide range of projectile-ion energy from 0.5 to 40 MeV are well explained by four sources of radiative processes: nuclear bremsstrahlung (NB), atomic bremsstrahlung (AB) (or polarization bremsstrahlung), secondary-electron bremsstrahlung (SEB), and quasi-free-electron bremsstrahlung (QFEB).     

Cr cluster deposition by plasma—gas-condensation method

Transmission electron microscopy observation was carried out for nanometric Cr clusters deposited on microgrids at room temperature using plasma–gas-condensation (PGC) method. In order to obtain optimum conditions for monodisperse cluster formation we have studied effects of an Ar gas pressure, an Ar gas flow rate, and a mixing rate of He gas with Ar gas on the size distribution of formed clusters. It has been found that monodisperse clusters with the size rage of 9–13 nm in diameter are producible at a low Ar gas pressure (≤1.3 Torr) and a low Ar gas flow rate (≤600 sccm). The mean cluster size decreases with decreasing Ar gas pressure, while it is not sensitive to the Ar gas flow rate. When He gas is mixed with Ar gas, the mean cluster size further decreases to 6 nm and the cluster beam intensity becomes stronger probably because He gas with the high thermal conductivity enhances supersaturation for cluster nucleation.     

Influences of surfactant (PVA) concentration and pH on the preparation of copper nanoparticles by electron beam irradiation

Electron beam irradiation method was successfully applied to the preparation of Cu nanoparticles in aqueous solution under room temperature and ambient pressure using polyvinyl alcohol (PVA) as the surfactant. The influences of the pH on the products were studied by X-ray diffraction (XRD), and those of the surfactant PVA concentration on the particle size and agglomeration by ultraviolet–visible spectrophotometry (UV–vis) and laser scattering particle size distribution analysis (LSPSDA). The products were characterized by XRD and transmission electron microscopy (TEM). The results showed that the grain size of Cu nanoparticles, within a certain range, can decrease with increasing PVA concentration. Pure Cu nanoparticles with the grain size distribution of 5–50 nm were prepared when the pH was adjusted between 5.0 and 9.0, and the PVA concentration was 2.20 g/100 mL.     

Reinforcement of natural rubber/high density polyethylene blends with electron beam irradiated liquid natural rubber-coated rice husk

Coating of rice husk (RH) surface with liquid natural rubber (LNR) and exposure to electron beam irradiation in air were studied. FTIR analysis on the LNR-coated RH (RHR) exposed to electron beam (EB) showed a decrease in the double bonds and an increase in hydroxyl and hydrogen bonded carbonyl groups arising from the chemical interaction between the active groups on RH surface with LNR. The scanning electron micrograph showed that the LNR formed a coating on the RH particles which transformed to a fine and clear fibrous layer at 20 kGy irradiation. The LNR film appeared as patches at 50 kGy irradiation due to degradation of rubber. Composites of natural rubber (NR)/high density polyethylene (HDPE)/RHR showed an optimum at 20–30 kGy dosage with the maximum stress, tensile modulus and impact strength of 6.5, 79 and 13.2 kJ/m², respectively. The interfacial interaction between the modified RH and TPNR matrix had improved on exposure of RHR to e-beam at 20–30 kGy dosage.     

Catalytic conversion of CO2–CH4 mixture into synthetic gas—Effect of electron-beam radiation

The radiolysis of methane (0.7 MeV electron beam) was studied as a function of its concentration at two doses: 5 and 20 kGy. In both cases the G (–CH₄) value raised with the increase of the substrate concentration. Thereby the yields observed at 20 kGy are much lower, because of recombination processes. Results are also reported on the conversion of the gas mixture CH₄:CO₂:He=1:1:1 into synthetic gas (H₂/CO) at 500 °C, using two catalysts : (N5) and (N20), containing 5 wt% Ni and 20 wt% Ni, respectively, supported on γ-Al₂O₃. In an experimental series the catalysts (N5) and (N20) were treated by irradiation (4 MGy dose) before use. The highest conversion yields (above 35%) were observed by implementation of N5 and N20 catalyst at 500 °C under the influence of electron beam radiation.     

Control factors and by-products during decomposition of butane in electron beam irradiation

This research was conducted to determine the removal characteristics of butane, using an electron beam. Influential factors, such as an initial concentration, background gases (nitrogen, air, and helium), and absorbed doses (kGy) were investigated. The decomposition efficiencies of background gases showed that oxidation caused by radicals formed from gases, such as N₂ and O₂, had a greater influence on results than oxidation from primary electrons for butane removal. Removal efficiencies were 40% at 2.5 kGy and 66% at 10 kGy, when the initial concentration of butane was 60 ppmC. When the initial concentration was lower, the energy efficiency of butane removal by electron beam was higher. By-products, including CO₂, CO, acetaldehyde, and acetone, formed after electron beam irradiation. Concentrations of CO₂ and CO tended to increase when absorbed doses increased as butane was decomposed by the electron beam through an advanced oxidation.