Low-energy Electron Beam Research Articles

Wavelength Measurements of Electron Cyclotron Harmonic Waves in Earth's Magnetotail

AbstractElectron cyclotron harmonic (ECH) waves, potential drivers for diffuse aurora precipitation, have been extensively investigated for decades. The generation mechanism of ECH waves, however, remains an open question. Theoretical work in 1970s has demonstrated that ECH waves can be excited by loss cone distributions of hot plasma sheet electrons. Recent THEMIS spacecraft observations, however, indicate that the waves can also be excited by low energy electron beams. Utilizing interferometry techniques to analyze the phase difference between electric potentials measured by individual probes on Electric Field Instrument antenna pairs on THEMIS spacecraft, we compute the wavenumber of both beam‐driven ECH waves and loss‐cone‐driven ECH waves. These wavenumber measurements as well as other wave properties obtained from spacecraft measurements prove to be consistent with expectation from linear instability analysis. This provides us with independent verification of the generation mechanism and linear dispersion relation of beam‐driven and loss‐cone‐driven ECH waves. Our statistical results demonstrate that the median value of the wave vectors of beam‐driven ECH waves, characterized by wave normal angles () less than 80°, is 0.011 m−1; and that of loss‐cone‐driven ECH waves, characterized by wave normal angles larger than 85°, is 0.00765 m−1. Direct wavenumber measurements of ECH waves allow us to better understand the interaction between ECH waves and electrons in Earth's magnetosphere.

Kinetic control of self-assembly using a low-energy electron beam

Self-assembly and on-surface synthesis are vital strategies used for fabricating surface-confined 1D or 2D supramolecular nanoarchitectures with atomic precision. In many systems, the resulting structure is determined by the kinetics of the processes involved, i.e., reaction rate, on-surface diffusion, nucleation, and growth, all of which are typically governed by temperature. However, other external factors have been only scarcely harnessed to control the on-surface chemical reaction kinetics and self-assembly. Here, we show that a low-energy electron beam can be used to steer chemical reaction kinetics and induce the growth of molecular phases unattainable by thermal annealing. The electron beam provides a well-controlled means of promoting the elementary reaction step, i.e., deprotonation of carboxyl groups. The reaction rate increases with the increasing electron beam energy beyond the threshold energy of 6 eV. Our results offer the novel prospect of controlling self-assembly, enhancing the rate of reaction steps selectively, and thus altering the kinetic rate hierarchy.

Fiber-Optic Based Laser Wakefield Accelerated Electron Beams and Potential Applications in Radiotherapy Cancer Treatments

Ultra-compact electron beam technology based on laser wakefield acceleration (LWFA) could have a significant impact on radiotherapy treatments. Recent developments in LWFA high-density regime (HD-LWFA) and low-intensity fiber optically transmitted laser beams could allow for cancer treatments with electron beams from a miniature electronic source. Moreover, an electron beam emitted from a tip of a fiber optic channel could lead to new endoscopy-based radiotherapy, which is not currently available. Low-energy (10 keV–1 MeV) LWFA electron beams can be produced by irradiating high-density nano-materials with a low-intensity laser in the range of ~1014 W/cm2. This energy range could be useful in radiotherapy and, specifically, brachytherapy for treating superficial, interstitial, intravascular, and intracavitary tumors. Furthermore, it could unveil the next generation of high-dose-rate brachytherapy systems that are not dependent on radioactive sources, do not require specially designed radiation-shielded rooms for treatment, could be portable, could provide a selection of treatment energies, and would significantly reduce operating costs to a radiation oncology clinic.

Comparison of the microbicidal effectiveness of 150 kV x-rays and cobalt-60 gamma rays

The radiation response, quantified by the dose-log survival curve, of spores of Bacillus pumilus subjected to irradiation in a 150 kV x-ray beam was examined and compared with the response obtained by irradiation in a reference cobalt-60 beam. The spores were irradiated at doses ranging from 2 kGy to 11 kGy. The response was the same for both beam qualities within measurement uncertainties. Combining these findings with our previously published data, the radiation resistance of B. pumilus spores is determined to be independent of beam quality for low and high energy x-rays, low and high energy electron beams, and cobalt-60 gamma beams.

Beam dynamics in dielectric laser acceleration

We discuss recent developments and challenges of beam dynamics in Dielectric Laser Acceleration (DLA), for both high and low energy electron beams. Starting from ultra-low emittance nanotip sources the paper follows the beam path of a tentative DLA light source concept. Acceleration in conjuction with focusing is discussed in the framework of Alternating Phase Focusing (APF) and spatial harmonic ponderomotive focusing. The paper concludes with an outlook to the beam dynamics in laser driven nanophotonic undulators, based on tilted DLA grating structures.

Effect of electrode separation and electrode backscatter thickness of a parallel plate ionization chamber on the measurement of dose to tissue in beta radiation fields

Plane parallel plate ionization chamber (PPC) is used in dosimetry especially for beta particles and low energy electron beam. The response of the PPC is affected by the electrode separation, thickness and material of backscatterer. The effect of electrode separation arises due to the well-known inscattering effect of electron which causes fluence perturbation inside the chamber cavity. The perturbation is caused due to reduced electron scattering in the chamber cavity compared to an ideal phantom material and it depends on the thickness of the cavity. Furthermore, the response of PPC also gets affected by the material behind the air cavity. Variation in the response depends on the thickness and the atomic number of the material behind collecting electrode of the PPC. The theoretical studies on the effect of collecting electrode backscatter thickness and electrode separation on the response of a PPC used as a transfer standard in ISO 6980 reference beta radiation field from 85Kr, 90Sr–90Y and 106Ru–106Rh radionuclides are presented. Multi-particle transport code FLUKA is used for the studies. The Polymethyl Methacrylate (PMMA) plate having 3.5 mm thickness is found to provide full backscatter for the above beta radionuclides. It is also observed that even for a well-guarded PPC, as the chamber electrode separation increases, the measured depth dose curve deviates from the ideal depth dose curve and the effective point of measurement (EPOM) of the PPC shifts towards downward direction from chamber reference point. It is also observed that the deviation between ideal and measured depth dose curve (related to EPOM shift) depends on the cavity thickness of the PPC. In the present work, optimization of design parameters of a PPC is carried out to establish it as a transfer standard in compliance with ISO 6980 for the standardization of reference beta radiation fields from 85Kr, 90Sr–90Y and 106Ru–106Rh radionuclide.

A gas curtain beam profile monitor using beam induced fluorescence for high intensity charged particle beams

A minimally invasive transverse beam profile monitor based on supersonic gas curtain technology and beam-induced fluorescence has been developed and demonstrated. The concept presented can be used to measure both the profile of the proton beam in the Large Hadron Collider (LHC) and the concentricity of the electron and the proton beams in the LHC hollow electron lens. In this Letter, the performance of such a monitor for a low energy electron beam is discussed, which paves the way for its wider implementation.

Cracking During the Formation of Chromium-Based Surface Alloys by a Low-Energy High-Current Electron Beam

Cracking During the Formation of Chromium-Based Surface Alloys by a Low-Energy High-Current Electron Beam

Study on osteoinductive activity of biotin film by low-energy electron beam deposition.

Biotin film was prepared by low-energy electron beam deposition (LEBD). The molecular structure, chemical composition and micromorphology of the biotin film were investigated by 1HNMR, FTIR, XPS, AFM and SEM. The results showed the molecular structure of a monolayer of biotin film is fully consistent with the molecular structure of the initial biotin powders. The contact angle test showed that the biotin film exhibit good hydrophilicity. The release kinetics of biotin film was tested by UV-Vis method. It was found that the film was almost completely released in about two weeks. The cell viability of MC3T3-E1 cells on the surface of the biotin film was attaining 100.54±1.7% (P<0.05), showing excellent biocompatibility and biosafety. Titanium implant with surface of biotin film was implanted into the femoral head of rabbits as experimental group. The animals were euthanized after four weeks. Compared with the control group, mature lamellar bone formation was observed with dense trabecular bone, and the expression of Coll-I, Runx2 and BMP-2 was better. The results showed that the repair effect of bone defect in the experimental group was excellent.

Structure and residual stress distribution in TiNi substrate after fabrication of surface alloy using electron-beam treatments

In this work, an origin of the residual stresses formed in the sublayer of TiNi substrate adjacent to the [Ti-Ni-Ta-Si] surface alloy (SA) was proposed. The as-cast SA was fabricated through an additive thin-film electron-beam synthesis using a low-energy high current electron beam (LEHCEB) treatment of the [Ti60Ta30Si10 (at. %)/TiNi] system. An additional post-LEHCEB treatment was employed for the SA synthesis (denoted as EB-treated SA) in order to reduce the value of residual stresses. Based on the XRD, TEM/SEM/EDS data, it has been found that the transition zone between the outer SA zone and the TiNi substrate exhibits several sublayers: eutectic B2+Ti3Ni4, martensitic and heat-affected zone (HAZ). However, the martensitic interlayers formed beneath the as-cast and EB-treated SAs possess different types of martensitic structures. Indeed, in the as-cast SA the sublayer of TiNi substrate is a Ni-rich (Ti<50Ni>50) one, so the martensitic transformation В2→R takes place in this sublayer. In turn, in the EB-treated SA the TiNi sublayer shows the composition close to equiatomic (Ti∼50Ni∼50) one, therefore the В2→B19′ martensitic transformation has occurred. The formation of martensitic phases led to a partial decrease (by a factor of ∼1.5–2) of the residual stresses in the underlying HAZ of TiNi substrates. The mechanism of B2 phase stabilization in the HAZ is closely related with a substructural hardening accompanied by formation of dense dislocation structures and residual elastic stresses that could be relaxed through short-term annealings induced by electron beam treatments.

Quantitative evaluation of dosimetric uncertainties associated with small electron fields

IntroductionAlthough many studies have investigated small electron fields, there are several dosimetric issues that are not well understood. This includes lack of charged particle equilibrium, lateral scatter, source occlusion and volume averaging of the detectors used in the measurement of the commissioning data. High energy electron beams are also associated with bremsstrahlung production that contributes to dose deposition, which is not well investigated, particularly for small electron fields. The goal of this work has been to investigate dosimetric uncertainties associated with small electron fields using dose measurements with different detectors as well as calculations with eMC dose calculation algorithm. MethodsDifferent dosimetric parameters including output factors, depth dose curves and dose profiles from small electron field cutouts were investigated quantitatively. These dosimetric parameters were measured using different detectors that included small ion chambers and diodes for small electron cutouts with diameters ranging from 15-50mm mounted on a 6 × 6cm2 cone with beam energies from 6-20MeV. ResultsLarge deviations existed between the output factors calculated with the eMC algorithm and measured with small detectors for small electron fields up to 55% for 6MeV. The discrepancy between the calculated and measured doses increased 10%-55% with decreasing electron beam energy from 20 MeV to 6 MeV for 15mm circular field. For electron fields with cutouts 20mm and larger, the measured and calculated doses agreed within 5% for all electron energies from 6-20MeV. For small electron fields, the maximal depth dose shifted upstream and becomes more superficial as the electron beam energy increases from 6-20MeV as measured with small detectors. DiscussionLarge dose discrepancies were found between the measured and calculated doses for small electron fields where the eMC underestimated output factors by 55% for small circular electron fields with a diameter of 15 mm, particularly for low energy electron beams. The measured entrance doses and dmax of the depth dose curves did not agree with the corresponding values calculated by eMC. Furthermore, the measured dose profiles showed enhanced dose deposition in the umbra region and outside the small fields, which mostly resulted from dose deposition from the bremsstrahlung produced by high energy electrons that was not accounted for by the eMC algorithm due to inaccurate modeling of the lateral dose deposition from bremsstrahlung. ConclusionElectron small field dosimetry require more consideration of variations in beam quality, lack of charged particle equilibrium, lateral scatter loss and dose deposition from bremsstrahlung produced by energetic electron beams in a comprehensive approach similar to photon small field dosimetry. Furthermore, most of the commercially available electron dose calculation algorithms are commissioned with large electron fields; therefore, vendors should provide tools for the modeling of electron dose calculation algorithms for small electron fields.

Characterization of a Radiofluorogenic Polymer for Low-Energy Electron Beam Penetration Depth Visualization.

Low-energy (80–300 keV) electron beam accelerators are gaining in importance in the radiation processing industry due to their ease of use and wide range of applications (e.g. product surface sterilizations or polymer curing and cross-linking). Due to their very low penetration depth (tens to hundreds of microns), currently used film dosimeters exhibit dose gradients over their thickness and do not resolve the dose response in the first microns of the irradiated material. Hence, the surface dose, defined as the dose in the first micron Dµ, cannot be measured directly. This study presents a polymer material as a dosimeter candidate for high-dose low-energy electron beam irradiations. The readout of the dose-dependent fluorescence intensity, originating from a pararosaniline dye reaction when irradiated, is measured using fluorescence microscopy. So far, no in-depth characterization of the material has been performed, leaving the stability and fluorescence properties of the material not fully optimized. We describe the improvements in polymer composition and the fabrication method, and characterize the material properties in terms of the thermal stability, glass transition temperature, refractive index, hardness, rheological behavior, and water affinity. All of these create a complex set of requirements a polymer needs to fulfill to become an effective dosimeter when measuring using confocal microscopy. The fluorescence readout procedure will be addressed in further studies.

Photon yield of superradiant inverse Compton scattering from microbunched electrons

Compact x-ray sources offering high-brightness radiation for advanced imaging applications are highly desired. We investigate, analytically and numerically, the photon yield of superradiant inverse Compton scattering from microbunched electrons in the linear Thomson regime, using a classical electrodynamics approach. We show that for low electron beam energy, which is generic to inverse Compton sources, the single electron radiation distribution does not match well to collective amplification pattern induced by a density modulated electron beam. Consequently, for head-on scattering from a visible laser, the superradiant yield is limited by the transverse size of typical electron bunches driving Compton sources. However, by simultaneously increasing the electron beam energy and introducing an oblique scattering geometry, the superradiant yield can be increased by orders of magnitude.

Oxidation behavior of TiCr and TiMo alloys formed by low-energy pulsed electron beam impact

The titanium-based alloys with 2–3 at.% of chromium (TiCr) and molybdenum (TiMo) were produced on the top of titanium samples by means of the high-intense pulsed electron beam impact on the titanium with preliminary deposited Cr and Mo coatings. The TiCr and TiMo alloys were subjected to oxidation in open air atmosphere at temperature 600 °C. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-disperse X-ray microanalysis (EDX) were used for structure and elemental composition determination in the samples. The analysis of oxygen depth profiles showed the increase in oxygen penetration depth in the case of TiCr alloy in comparable to pure titanium. The oxygen concentration corresponding to stoichiometry of the oxide phase TiO2 was found on the depth equaled to the thickness of the TiCr alloy that shows the enhancement of the diffusion of oxygen in the modified layer. The diffusion of oxygen at the temperature of 600 °C is enhanced by decomposition of the solid solutions based on bcc β-Ti phase with free chromium and molybdenum atoms releasing. The free molybdenum atoms take part in the stabilization of TiO2 anatase phase while the free chromium atoms form intermetallic compound TiCr2 preventing the sample from oxidation.

Beam dynamics simulation study for longitudinal bunch length measurement of RF modulated thermionic electron gun at VECC, Kolkata

A superconducting electron linac (e-linac) photo-fission driver is under construction at VECC for the upcoming rare isotope beam facility called ANURIB. Electron gun and straight low energy beam transport (LEBT) line has been installed and is operational at a test area, delivering electron beam of 100 keV. We discuss beam dynamics and analytical calculations leading to optimal parameters of analysing section of LEBT line and RF deflector cavity that will be used for measuring longitudinal characteristics for the low energy electron beam.

Low-energy electron beam generation in inductively coupled plasma via a DC biased grid

Low-energy electron beam generation using a DC biased grid was investigated in an inductively coupled plasma (ICP). The electron beam was measured in argon gas at various pressures, ICP source powers, and substrate voltages (V sub). At a low ICP source power (50 W), an electron beam was generated even at small values of V sub (10 V), however at a high ICP source power (200 W), an electron beam was only generated when a higher voltage (30 V) was applied due to the short sheath thickness on the grid surface. The sheath on the grid surface is an important factor for generating electron beams because low-energy electrons are blocked. If the sheath thickness to small, a high voltage should be applied to generate an electron beam, as accelerate regions cannot exist without the sheath. At high pressure, since electrons experience numerous neutral collisions, a high substrate voltage is needed to generate an electron beam. However, if the applied substrate voltage becomes too high (40 V) at high pressure, high-energy electrons result in secondary plasma under the grid. Therefore, maintaining a low pressure and low ICP source power is important for generating electron beams.

Coherent Terahertz Emission Using Metasurfaces to Intercept a Flat Electron Beam

Terahertz electromagnetic radiation is one of the hottest research topics thanks to its promising applications in diverse scientific and technological fields. Using a uniformly moving electron beam to interact with a metallic or dielectric surface is an efficient tool for the generation of high-power terahertz waves. In the present paper, we demonstrate enhanced coherent terahertz emission theoretically and experimentally by using a metasurface formed by an array of Fabry-Perot-like resonators to obliquely intercept a low-energy flat electron beam. We illustrate that the mechanism is one of modified coherent Smith-Purcell radiation rather than the expected transition radiation. More notably, this metasurface overcomes the inherent restriction imposed by the decay length in conventional beam-wave interactions, greatly enhancing the radiation efficiency and intensity. This emission promises an attractive way of developing high-power terahertz sources.

Impact of low energy electron beam on black pepper (&lt;i&gt;Piper nigrum&lt;/i&gt; L.) microbial reduction, quality parameters, and antioxidant activity

&lt;abstract&gt; &lt;p&gt;Low energy electron beam (e-beam) has the ability to decontaminate or reduce bioburden and enhance the food product's safety with minimal quality loss. The current study aimed to evaluate the efficacy of e-beam on natural microbiota and quality changes in black peppercorns. The black pepper was exposed to e-beam at doses from 6–18 kGy. The microbial quality, physicochemical attributes, total phenolic compounds, and antioxidant activity were evaluated. Results demonstrated the microbial population in black pepper decreased with increasing e-beam treatment doses. Significant inactivation of Total Plate Count (TPC), yeasts, and molds were observed at dose 6 kGy by 2.3, 0.7, and 1.3 log CFU g&lt;sup&gt;−1&lt;/sup&gt;, respectively, while at 18 kGy the reduction level was 6, 2.9, and 4.4 log CFU g&lt;sup&gt;−1&lt;/sup&gt;, respectively. Similarly, 18 kGy of e-beam yielded a reduction of 3.3 and 3.1 log CFU g&lt;sup&gt;−1&lt;/sup&gt; of &lt;italic&gt;Salmonella&lt;/italic&gt; Typhimurium and coliform bacteria, respectively. A significant difference (&lt;italic&gt;p&lt;/italic&gt; &amp;lt; 0.05) was noted between doses 12, 15, and 18 kGy on &lt;italic&gt;Bacillus cereus&lt;/italic&gt; and &lt;italic&gt;Clostridium perfringens&lt;/italic&gt; in black pepper. During e-beam doses, the values &lt;italic&gt;L&lt;/italic&gt;&lt;sup&gt;*&lt;/sup&gt;, &lt;italic&gt;a&lt;/italic&gt;&lt;sup&gt;*&lt;/sup&gt; and &lt;italic&gt;b&lt;/italic&gt;&lt;sup&gt;*&lt;/sup&gt; of black peppercorn were not noticeably altered up to 18 kGy dose. No significant (&lt;italic&gt;p&lt;/italic&gt; &amp;gt; 0.05) difference in moisture, volatile oil, and piperine content upon (6–18 kGy) treatments in comparison to the control. A slight difference in the bioactive compound, retaining &amp;gt; 90% of total phenolic compounds and antioxidant activity. Results revealed that e-beam doses ≥ 18 kGy were influential for inactivating natural microbes and foodborne pathogens without compromising the physicochemical properties and antioxidant activity of black peppercorns.&lt;/p&gt; &lt;/abstract&gt;

Uniform Irradiation of Eggs with Low-Energy Electron Beams

Uniform Irradiation of Eggs with Low-Energy Electron Beams

О порогах плавления системы «пленка - подложка» при облучении низкоэнергетическим сильноточным электронным пучком

The effect of film material thermal conductivity on the melting threshold of the film-substrate system depending on the film thickness during a low-energy high-current electron beam (LEHCEB) irradiation was analyzed based on the numerical solution of the one-dimensional unsteady heat equation with a volumetric thermal source. Experimentally obtained oscillograms of the beam current at the collector and the accelerating voltage were used to simulate the heating source. Numerical variations of the film thermal conductivity were carried out within a wide range, overlapping the entire range for real materials. The dependence of the melting threshold of a homogeneous material on thermal conductivity was determined. The general regularities of the behavior of film and substrate melting thresholds depending on the film thickness were also established.