Electron Beam Fluence Research Articles

Secondary radiation dose modeling in passive scattering and pencil beam scanning very high energy electron (VHEE) radiation therapy.

Electrons with kinetic energy up to a few hundred MeV, also called very high energy electrons (VHEE), are currently considered a promising technique for the future of radiation therapy (RT) and in particular ultra-high dose rate (UHDR) therapy. However, the feasibility of a clinical application is still being debated and VHEE therapy remains an active area of research for which the optimal conformal technique is also yet to be determined. In this work, we will apply two existing formalisms based on analytical Gaussian multiple-Coulomb scattering theory and Monte Carlo (MC) simulations to study and compare the electron and bremsstrahlung photon dose distributions arising from two beam delivery systems (passive scattering with or without a collimator or active scanning). We therefore tested the application of analytical and MC models to VHEE beams and assessed their performance and parameterization in the energy range of 6-200MeV. The optimized electron beam fluence, the bremsstrahlung, an estimation of central-axis and off-axis x-ray dose at the practical range and neutron contributions to the total dose, along with an extended parameterization for the photon dose model were developed, together with a comparison between double scattering (DS) and pencil beam scanning (PBS) techniques. MC simulations were performed with the TOPAS/Geant4 toolkit to verify the dose distributions predicted by the analytical calculations. The results for the clinical energy range (between 6 and 20MeV) as well as for higher energies (VHEE range between 20 and 200MeV) and for two treatment field sizes (5×5 and 10×10 cm2 ) are reported, showing a reasonable agreement with MC simulations with mean differences below 2.1%. The relative contributions of photons generated in the medium or by the scattering system along the central-axis (up to 50% of the total dose) are also illustrated, along with their relative variations with electron energy. The fast analytical models parametrized in this study allow an estimation of the amount of photons produced behind the practical range by a DS system with an accuracy lower than 3%, providing important information for the eventual design of a VHEE system. The results of this work could support future research on VHEE radiotherapy.

Electron irradiation-induced paramagnetic and fluorescent defects in type Ib high pressure–high temperature microcrystalline diamonds and their evolution upon annealing

Defects introduced to synthetic type Ib diamond micrometer-size particles by electron-beam irradiation were studied by electron paramagnetic resonance and photoluminescence (PL) spectroscopy as a function of e-beam fluence and post-irradiation thermal annealing. Increasing electron-beam fluence causes a substantial reduction of the substitutional nitrogen (P1) content, accompanied by progressively higher concentrations of paramagnetic negatively charged vacancies (V−) and triplet interstitials (R1/R2). Annealing results in a drastic decrease in the V− and R1/R2 content and an increase in the negatively charged nitrogen-vacancies (NV− or W15). Analysis of PL spectra allows for identification of color centers in the irradiated diamond samples and following their evolution after annealing. These data facilitate understanding of different factors contributing to the formation of color centers in diamond and promote efforts toward controlled engineering of optical centers in fluorescent diamond particles.

Irradiation of W and K-Doped W Laminates without or with Cu, V, Ti Interlayers under a Pulsed 6 MeV Electron Beam.

Small multilayered laminated samples consisting of stacks of W (or K-doped W) foils without an interlayer or with interlayers from Cu, V, and Ti were exposed to a pulsed electron beam with an energy of 6 MeV in several irradiation sessions. All samples maintained their macroscopic integrity, suggesting that the W-metal laminate concept is compatible with high heat flux applications. The surface of the samples was analyzed using a scanning electron microscope (SEM) before and after each irradiation session. The experimental results indicate that electron beam irradiation induces obvious modifications on the surface of the samples. Morphological changes such as the appearance of nanodroplets, nanostructures, and melting and cracking, depending on the sample type and the electron beam fluence, are observed. The irradiation is carried out in a vacuum at a pressure of 2 to 4 × 10−2 torr, without active cooling for the samples. The structures observed on the surface of the samples are likely due to electron beam heating and vaporization followed by vapor condensation in the volume adjacent to the surface.

Precipitation of Pt Nanoparticles inside Ion-Track-Etched Capillaries

Ion-track-etched capillaries containing nanoparticles of precious metals (e.g., Pt, Au, and Ag) can be applied to plasmonic absorber materials. The precipitation of homogeneous and highly dispersed precious metal nanoparticles inside capillaries represents a key process. Ion-track-etched capillaries (diameter: ~500 nm, length: ~25 μm) were created in polyimide film by 350 MeV Xe irradiation (3 × 107 ions/cm2) and chemical etching (using a sodium hypochlorite solution). The films with capillaries were immersed in an aqueous solution containing 0.1–10 mmol/L H2PtCl6 and 0.5 vol% C2H5OH, and then irradiated with a 2 MeV electron beam up to a fluence of 1.4 × 1016 e/cm2. The Pt particles inside the capillaries were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The precipitation of Pt nanoparticles and isolated aggregates inside the capillaries was confirmed by TEM. The Pt nanoparticles tended to aggregate under increasing concentrations of H2PtCl6 in the aqueous solution; meanwhile, no changes in nanoparticle size were noted under increasing electron beam fluence. The results suggest that the proposed method can be used to form metal nanoparticles in nanosized capillaries with a high aspect ratio.

Electron beam damage of perfluorosulfonic acid studied by soft X-ray spectromicroscopy

Scanning transmission X-ray microscopy (STXM) was used to study chemical changes to perfluorosulfonic acid (PFSA) spun cast thin films as a function of dose imparted by exposure of a 200 kV electron beam in a Transmission Electron Microscope (TEM). The relationship between electron beam fluence and absorbed dose was calibrated using a modified version of a protocol based on the positive to negative lithography transition in PMMA [Leontowich et al, J. Synchrotron Rad. 19 (2012) 976]. STXM was used to characterize and quantify the chemical changes caused by electron irradiation of PFSA under several different conditions. The critical dose for CF2-CF2 amorphization was used to explore the effects of the sample environment on electron beam damage. Use of a silicon nitride substrate was found to increase the CF2-CF2 amorphization critical dose by ∼x2 from that for free-standing PFSA films. Freestanding PFSA and PMMA films were damaged by 200 kV electrons at ∼100 K and then the damage was measured by STXM at 300 K (RT). The lithography cross-over dose for PMMA was found to be ∼2x higher when the PMMA thin film was electron irradiated at 120 K rather than at 300 K. The critical dose for CF2-CF2 amorphization in PFSA irradiated at 120 K followed by warming and delayed measurement by STXM at 300 K was found to be ∼2x larger than at 300 K. To place these results in the context of the use of electron microscopy to study PFSA ionomer in fuel cell systems, an exposure of 300 e−/nm2 at 300 K (which corresponds to an absorbed dose of ∼20 MGy) amorphizes ∼10% of the CF2-CF2 bonds in PFSA. At this dose level, the spatial resolution for TEM imaging of PFSA is limited to 3.5 nm by radiation damage, if one is using a direct electron detector with DQE = 1. This work recommends caution about 2D and 3D morphological information of PFSA materials based on TEM studies which use fluences higher than 300 e−/nm2.

Plasmonic Nanopore Fabrication for Single Molecule Bio Sensor By Using Electron Beam Irradation

Recently the portable device called MINion for single molecule analysis was developed by Oxford Nanopore Technology. The electrical detection technique for the solid state device was utilized for single molecule detection . However, the large error rates were reported by several journals, even though the significant error reduction was developed after the invention of the portable nanopore device. In this report, we introduce the optical nanopore fabrication by using plasmonic optical enhancement effect. First, the Au thin films were vacuum-deposited on the nanometer thin SiN film, followed by removal of SiN film and by drilling Au apertures by using focused ion beam (FIB) technique. Then, electron beam irradiations on the specimens either by using low energy field emission electron beam microscopy (FESEM) or high energy Transmission electron beam microscopy (TEM). In addition, the periodic grooves, or the periodic Au aperture array were fabricated on the Au sample in order to provide strong plamonic optical enhancements. During the electron irradiation on the fabricated Au surface, we observed the diffused binary Au-C membrane due to Ostwald ripening and also the unstable Au-C mixed phase change via spinodal decomposition. We also found that the Au cluster diffusion would depend upon the electron beam fluence. However, the exact understanding of this phenomenon is still on-going investigation. Figure 1

A surface analysis of polypropylene/clay nanocomposites exposed to electron irradiation

AbstractThe effects of electron irradiation in air at various doses on surface chemical composition of nanofilled polypropylene were explored by X‐ray photoelectron spectroscopy. An organically modified nanoclay ingredient along with a functional compatibilizer was employed for this purpose. The nanocomposite formation was confirmed by means of transmission electron microscopy, where in presence of compatibilizer, an exfoliated structure was brought about. Medium irradiation dose was established to be considerably effective in raising surface oxygen content, while at very high electron beam fluence, the ablation (etching) predominated. The optimal electron beam intensity was also found with respect to the extent of the functionalization. Various moieties of ether, ester, and alcohol characteristics were produced after exposure which could act as functional, active precursors being suitable for subsequent functionalization reactions. Furthermore, it could be understood that the electron irradiation spur organoclay migration toward surface layers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Increase in individual absorption bands of MgF2 under electron irradiation

Decomposition of the induced absorption spectra of a MgF2 crystal into individual bands made it possible to construct the dependences of their intensity, and hence, the intrinsic defect concentration, on the electron beam fluence (energy density). The features of these dependences and their possible consequences are analyzed.

How the absorption-band intensities in high-purity quartz glasses depend on the electron-beam fluence

To study the formation of defects in quartz glasses of type KS-4V, KU-1, and Corning 7980 under the action of an electron beam (EB), the induced absorption spectra is decomposed into individual bands (IBs) with maxima at 163.5, 183.5, 213, 225, 244, and 260 nm. In all the glasses, the intensities of most of the IBs saturated at doses around 90 MGy as the EB fluence increased. The steady-state absorption at 260, 213, and 183 nm was a factor of 2–4 less in KS-4V than in KU-1. The intensity of the bands at 163 nm virtually coincided in these glasses and monotonically increased with increasing EB fluence. This indicates an impact mechanism for the throughput of the oxygen-deficient centers responsible for this band.

The effects of incident electron current density and temperature on the total electron emission yield of polycrystalline CVD diamond

The effects of temperature and incident electron current density on the total electron emission yield (TEEY) of polycrystalline diamond deposited by the chemical vapour deposition technique (CVD) were investigated at low electron beam fluence. It was found that the TEEY reversibly increases with the temperature and reversibly decreases with the current density. This behaviour is explained on the basis of a dynamic competition between the accumulation of holes (positive space charge), which internally reduces the secondary electron emission, and the thermally activated conductivity that tends to reduce the space charge formation.

Thermoluminescence from a dosimeter sheet irradiated with accelerated electron beams

Ultra-low intensity electron beams generated from an electron linear accelerator have been applied to the investigation of the response of the thermoluminescence (TL) sheet for irradiation. The TL image has been measured with a high-sensitivity TL imaging system developed by using a two-dimensional photon counter. The imaging system was expected to be a profile monitor for ultra-low intensity electron beams and to be a high-sensitivity electron beam monitor having a wide dynamic range. In the present work the TL images of the electron beam profile has been observed on the TL sheet irradiated with the beam. There has been the linear relation between the number of TL photons emitted from the sheet and the electron beam fluence in the fluence range over five orders of magnitude. From the results for irradiation at energies of 6 and 10 MeV the cause of the TL due to the irradiation is discussed.

G-SIMS of crystallisable organics

In this study, the gentle SIMS (G-SIMS) concept has been applied to the crystallisable organic materials of Irganox 1010, caffeine, cholesterol, glucose, poly- l-lysine and bovine serum albumin. These are chosen to represent as wide a range of material types as possible. For each case, the G-SIMS spectra are considerably simpler than the static SIMS, enabling direct interpretation and identification. It is demonstrated that the amount of fragmentation in the mass spectrum may be controlled numerically and this information can be used to re-assemble the parent molecule. Wherever possible, the use of dual column ion beams is recommended to eliminate alignment requirements. Additionally, the total electron beam fluence should be kept below 6×10 18 electrons/m 2 to prevent electron damage.

Optical absorption spectra of 10-MeV electron-irradiated paratellurite single crystals

Optical absorption spectra of TeO2 crystals, irradiated at room temperature by up to 2·1018 cm−2 10-MeV electrons and subsequently annealed to 575K, are studied. The dependence of Urbach absorption edge parameters in TeO2 on the electron beam fluence is discussed. The irradiation-induced near-edge broad (2.5–3.5eV) absorption band is shown to be related to oxygen vacancies, annealing at 475–525K.

Optimization of conformal electron beam therapy using energy‐ and fluence‐modulated beams

Fluence modulation of multiple electron beams of various energies has been used to optimize the delivered dose distribution during electron beam radiation therapy. By maximizing the probability of achieving tumor control without causing severe complications electron beam fluence profiles have been optimized for superficial target volumes. It is possible to use several equiportal fluence-modulated electron beams to modify the energy deposition with depth in a controlled manner making it possible to use the technique as an alternative to bolus. The technique was tested in two representative phantom geometries and in three clinical patient geometries using a set of five and two different energies. The local maxima in dose for the plans with five energies were typically lower than with the conventional or advanced bolus techniques. The principles for how the technique could be carried out in the future with a fourth generation radiotherapy accelerator are also indicated.

Measurements of deep penetration of low-energy electrons into metal-oxide-semiconductor structure

A polycrystalline Si-SiO2-Si metal-oxide-semiconductor (MOS) transistor covered with thick insulation and passivation layers of SiO2 was examined to measure the threshold voltage shifts as a function of electron energy over the range of from 5 to 18 keV. The electron-beam fluence was varied over six orders of magnitude from 2×10−9 to 2×10−3 C/cm2. From the experimental data, the fraction of the incident electron energy deposited in the gate oxide was determined. The result shows a deep penetration of low-energy electrons beyond the electron range.

Pulsed electron beam induced recrystallization and damage in GaAs

Single-pulse electron-beam irradiations of 300-keV 1015Kr+/cm2 or 300-keV 3×1012 Se+/cm2 implanted layers in unencapsulated 〈100〉 GaAs are studied as a function of the electron beam fluence. The electron beam pulse had a mean electron energy of ≃20 keV and a time duration of ?10−7 s. Analyses by means of MeV He+ channeling and TEM show the existence of narrow fluence window (0.4–0.7 J/cm2) within which amorphous layers can be sucessfully recrystallized, presumably in the liquid phase regime. Too high a fluence produces extensive deep damage and loss of As.