Electron Beam Spot Research Articles

Electron Beam Additive Manufacturing of SS316L with a Stochastic Scan Strategy: Microstructure, Texture Evolution, and Mechanical Properties

This study examines the microstructure, crystallographic texture evolution, and mechanical properties of stainless steel 316L fabricated through electron beam melting using a stochastic scan strategy at a preheat temperature of 1123 K. X-ray diffraction confirmed the presence of a pure austenitic phase in the fabricated material. Equiaxed cellular structures were observed in the center of the melt pool regions and elongated cellular structures observed at the melt pool overlap regions. A finite element-based numerical model was employed to estimate the thermal gradients and solidification rates within the melt pool of an electron beam spot. Microstructural analysis indicated a generation of columnar grains from the bottom to the top of the build owing to high thermal gradients. A crystallographic texture investigation showed a generation of strong <110> fiber texture along the build direction of the material and reported that the stress distributions within the melt pool led to a strong crystallographic texture driven by the stress evolution observed from thermokinetic computational modelling of the electron beam-melting process. Mechanical properties were assessed using profilometry-based indentation plastometry, demonstrating strain hardening at a high temperature of 773 K.

Design and performance of a low-emittance electron gun for electron beam probe

An Electron Beam Probe (EBP) is preferable to provide a non-interceptive measurement of the transverse distribution of a dense bunched ion beam. During EBP operation, it was observed that the electron beam spot subjects to expansion when scanned across the ion beam due to the strong space charge field of the ion bunch, leading to significant degradation of spatial resolution. To mitigate this effect, a small electron beam spot is beneficial as demonstrated in previous research. This paper presents design details of a low-emittance, small-spot, and long-work-distance electron gun. Geometry optimization of the gun and focus lens is conducted using a multiobjective genetic algorithm (MOGA) interfaced with space charge simulation codes to maintain normalized thermal emittance within an acceptable increase and achieve a small spot at a long work distance. The emittance is measured using a slit-screen technique, resulting in a norm. rms emittance of 0.046(+-0.005) um*rad under low beam current conditions (50 nA). In high-resolution mode, a beam spot size of 0.6 mm (rms) is achieved at a work distance of 1.2 m with the combination of Einzel lens and solenoid. The gun has been successfully operated as part of EBP experiments for accurate and high-resolution measurement of ion beam width, demonstrating excellent agreement with wire scanner measurements with relative deviation not exceeding 1%.

Properties of Electrons Accelerated by the Ganymede‐Magnetosphere Interaction: Survey of Juno High‐Latitude Observations

AbstractThe encounter between the Jovian co‐rotating plasma and Ganymede gives rise to electromagnetic waves that propagate along the magnetic field lines and accelerate particles by resonant or non‐resonant wave‐particle interaction. They ultimately precipitate into Jupiter's atmosphere and trigger auroral emissions. In this study, we use Juno/JADE, Juno/UVS data, and magnetic field line tracing to characterize the properties of electrons accelerated by the Ganymede‐magnetosphere interaction in the far‐field region. We show that the precipitating energy flux exhibits an exponential decay as a function of downtail distance from the moon, with an e‐folding value of 29°, consistent with previous UV observations from the Hubble Space Telescope (HST). We characterize the electron energy distributions and show that two distributions exist. Electrons creating the Main Alfvén Wing (MAW) spot and the auroral tail always have broadband distribution and a mean characteristic energy of 2.2 keV while in the region connected to the Transhemispheric Electron Beam (TEB) spot the electrons are distributed non‐monotonically, with a higher characteristic energy above 10 keV. Based on the observation of bidirectional electron beams, we suggest that Juno was located within the acceleration region during the 11 observations reported. We thus estimate that the acceleration region is extended, at least, between an altitude of 0.5 and 1.3 Jupiter radius above the 1‐bar surface. Finally, we estimate the size of the interaction region in the Ganymede orbital plane using far‐field measurements. These observations provide important insights for the study of particle acceleration processes involved in moon‐magnetosphere interactions.

Influence of Grid Aperture Ratio on Electron Transmittance and Electron Beam Spot Size in Field Emission Processes of Carbon Nanotubes

Field emission is an important work mode for electron sources, and carbon nanotubes (CNTs) have been extensively studied for their good emission properties. It is well known that the parameters of the grid deeply influence the field emission performance of CNTs, a relationship that requires further elucidation. Therefore, in this study, the relationship between the grid aperture ratio and electron transmittance was studied through simulations and experiments. This study’s results indicate that the electron transmittance improved as the grid aperture ratio increased. Meanwhile, electron beam spot simulations and imaging experiments indicate that an increased grid aperture ratio will expand the cathode electron divergence, leading to a larger electron beam spot size. These results demonstrate that there is a trade-off in maintaining the grid aperture ratio between high electron transmittance and relatively small electron beam spot size, and the optimum grid aperture ratio is between 75% and 85%. These results will provide a reference for the design and optimization of X-ray tubes and other electron sources.

Mechanisms for removing impurities in a single crystal superalloy by electron beam drip melting

The development of clean and green manufacturing of superalloys has attracted widespread attention. The returned scrap of superalloys, however, contains a significant amount of oxygen (O), nitrogen (N), and inclusions, which cannot be used effectively, and thus resulting in substantial waste generation. In this study, the electron beam drip melting (EBDM) is used to deeply remove the O, N and inclusions in a single crystal superalloy. The concentration of O and N can be reduced to 0.57 and 0.55 ppmw after drip melting, with removal rates of 97.9 % and 83.8 % respectively. The number density of inclusions experienced a significant decrease, dropping from 12.90 to 0.18 mm−2, representing a reduction of 98.6 %. The intense Marangoni convection will gather the surface inclusions in the central area of the electron beam spot. The inclusions get close to each other to form cavities, and thus the aggregation reaction occurs to form inclusion clusters. Due to the dissolution and decomposition reactions caused by the local overheating and bombardment of electron beam, the inclusions can be removed effectively. The generated O and N are eliminated through mass transfer and evaporation reactions, while the remaining inclusions on the surface can be artificially removed. The electron beam drip melting can be used for the preparation of superalloys with extremely low levels of O, N and inclusions.

Numerical investigation of the impact of thermoelectric effect on electron beam welding of dissimilar materials

Electron beam welding of GH4169 and Ni is required in the manufacture of the regenerative cooling system of the liquid rocket motor. The thermoelectric effect is observed during the welding of dissimilar metals; however, there has been a lack of investigation into the influence of this effect on electron beam welding joint formation and its dependence on test plate thickness. The thermoelectric effect of electron beam welding between GH4169 and Ni with varying thicknesses, as well as the influence of induced magnetic fields on electron beam trajectories, are investigated through the establishment of a numerical model incorporating thermal-electric-magnetic coupling.The results show that when the test plate increases from 2.5 mm to 10 mm the peak current density increases from 5.1 × 106 A/m2 to 7.6 × 106 A/m2, and the maximum magnetic flux density increases from 1.49× 10−2 T to 1.77 × 10−2 T. The increase in magnetic flux density results in a greater displacement of the electron beam spot away from the interface between the two materials, thereby causing incomplete fusion defects in the joints. This study elucidates the fundamental physical principles underlying the occurrence of incomplete fusion defects in electron beam welding joints, thereby furnishing essential theoretical underpinnings for enhancing the quality of dissimilar metal electron beam weld joints.

Optimization of vertically aligned carbon nanotube beam trajectory with the help of focusing electrode in the microchannel plate

The focusing electrode plays an important role to reduce the electron beam trajectory with low dispersion and high brightness. This article summarizes the importance of the vertically aligned multi-walled carbon nanotube effect with the focusing electrode. First of all, the effect of electron beam trajectory is studied with the different heights, hole sizes, and applied voltage of the focusing electrode by the opera 3D simulation. The field emission electron beam spot is captured in the microchannel plate which helps to reduce the signal noise effect and damage of CNT tips by the joule heating effect. The high-dense bright spot is optimized at the focusing electrode hole size of 2 mm, and the height of 1 mm from the gate mesh electrode at the low bias voltage of − 200 V without the loss of current. The FWHM of the electron beam is calculated 0.9 mm with its opening angle of 0.9° which could be applicable in high-resolution multi-electron beam microscopy and nano-focused X-ray system technology.

Spatiotemporal characterization of evaporated atoms during electron beam melting additive manufacturing by advanced laser diagnostics

Electron powder bed fusion (E-PBF) is an additive manufacturing technology used to produce parts layer-wise for advanced aerospace, biomedical, and other applications. Precise control over the energy transferred to the powder by the electron beam is key to further process improvements. Here, we used tunable diode laser absorption spectroscopy to characterize the evaporated titanium atoms above the molten area of a TA6V powder alloy, and, thus, the effects of the energy transferred to it by the electron beam. This unconventional diagnostic tool achieves analyses at very high temporal (<1 μs) and spatial (<100 μm) resolutions, thus, offering valuable information on the microsecond-scale dynamics of the micro-melting zone and the effectiveness of the electron beam spot at diameters as small as ∼200 μm. Our measurements highlighted sharp fluctuations during the evaporation process that were independent of the power and scan speed of the electron beam; instead, the molten pool surface itself seems to drive these fluctuations. Our analysis also documented the shape and density of the vapor plume, which was oriented perpendicular to the surface under common E-PBF conditions.

Beam Trajectory Analysis of Vertically Aligned Carbon Nanotube Emitters with a Microchannel Plate

Vertically aligned carbon nanotubes (CNTs) are essential to studying high current density, low dispersion, and high brightness. Vertically aligned 14 × 14 CNT emitters are fabricated as an island by sputter coating, photolithography, and the plasma-enhanced chemical vapor deposition process. Scanning electron microscopy is used to analyze the morphology structures with an average height of 40 µm. The field emission microscopy image is captured on the microchannel plate (MCP). The role of the microchannel plate is to determine how the high-density electron beam spot is measured under the variation of voltage and exposure time. The MCP enhances the field emission current near the threshold voltage and protects the CNT from irreversible damage during the vacuum arc. The high-density electron beam spot is measured with an FWHM of 2.71 mm under the variation of the applied voltage and the exposure time, respectively, which corresponds to the real beam spot. This configuration produces the beam trajectory with low dispersion under the proper field emission, which could be applicable to high-resolution multi-beam electron microscopy and high-resolution X-ray imaging technology.

Characteristics of the cylindrical reflex triode driven by a four-stage linear transformer driver.

A cylindrical reflex triode was designed and directly driven by a four-stage linear transformer driver to generate high intensity pulsed warm x rays. We developed a numerical model of the cylindrical reflex triode and simulated and studied the experimental electron distribution and the radiation characteristics. The working voltage of the cylindrical reflex triode is 220kV, and the current is about 600kA. Under the voltage pulse with a rise time of 100ns, the electron beam spot is uniform, and the duration of the gap without short circuit reaches 200ns. The x-ray dose is 385rad (Si), with an irradiation area of 615cm2 and a uniformity of less than 2:1. The radiation field distribution is basically consistent with the simulation results. Compared with the two-stage series diode on the Flash-II accelerator, the x-ray conversion efficiency of the cylindrical reflex triode is increased about 1.6 times.

A probabilistic approach for determining Monte Carlo beam source parameters: II. Impact of beam modeling uncertainties on dosimetric functions and treatment plans

Objective. The Monte Carlo method is recognized as a valid approach for the evaluation of dosimetric functions for clinical use. This procedure requires the accurate modeling of the considered linear accelerator. In Part I, we propose a new method to extract the probability density function of the beam model physical parameters. The aim of this work is to evaluate the impact of beam modeling uncertainties on Monte Carlo evaluated dosimetric functions and treatment plans in the context of small fields. Approach. Simulations of output factors, output correction factors, dose profiles, percent-depth doses and treatment plans are performed using the CyberKnife M6 model developed in Part I. The optimized pair of electron beam energy and spot size, and eight additional pairs of beam parameters representing a 95% confidence region are used to propagate the uncertainties associated to the source parameters to the dosimetric functions. Main results. For output factors, the impact of beam modeling uncertainties increases with the reduction of the field size and confidence interval half widths reach 1.8% for the 5 mm collimator. The impact on output correction factors cancels in part, leading to a maximum confidence interval half width of 0.44%. The impact is less significant for percent-depth doses in comparison to dose profiles. For these types of measurement, in absolute terms and in comparison to the reference dose, confidence interval half widths less than or equal to 1.4% are observed. For simulated treatment plans, the impact is more significant for the treatment delivered with a smaller field size with confidence interval half widths reaching 2.5% and 1.4% for the 5 and 20 mm collimators, respectively. Significance. Results confirm that AAPM TG-157's tolerances cannot apply to the field sizes studied. This study provides an insight on the reachable dose calculation accuracy in a clinical setup.

A probabilistic approach for determining Monte Carlo beam source parameters: I. Modeling of a CyberKnife M6 unit

Objective. During Monte Carlo modeling of external radiotherapy beams, models must be adjusted to reproduce the experimental measurements of the linear accelerator being considered. The aim of this work is to propose a new method for the determination of the energy and spot size of the electron beam incident on the target of a linear accelerator using a maximum likelihood estimation. Approach. For that purpose, the method introduced by Francescon et al (2008 Med. Phys. 35 504–13) is expanded upon in this work. Simulated tissue-phantom ratios and uncorrected output factors using a set of different detector models are compared to experimental measurements. A probabilistic formalism is developed and a complete uncertainty budget, which includes a detailed simulation of positioning errors, is evaluated. The method is applied to a CyberKnife M6 unit using four detectors (PTW 60012, PTW 60019, Exradin A1SL and IBA CC04), with simulations being performed using the EGSnrc suite. Main results. The likelihood distributions of the electron beam energy and spot size are evaluated, leading to and . Using these results and a 95% confidence region, simulations reproduce measurements in 13 out of the 14 considered setups. Significance. The proposed method allows an accurate beam parameter optimization and uncertainty evaluation during the Monte Carlo modeling of a radiotherapy unit.

Process monitoring of electron-beam based writing of semiconductor mask patterns

As mask capabilities advance to support optical lithography, mask-making processes become more complex and therefore require more sophisticated monitoring to ensure manufactured masks are defect-free. We present a methodology that aggregates process signatures from writings of different mask patterns under nominal process conditions and detects anomalous process behaviors during writings of new mask patterns. The new approach was demonstrated using simulated electron beam writing of integrated circuit patterns subjected to inconsistent electron beam dosage and spot size. Anomalous process behaviors were detected and tracked quantitatively even if new mask patterns were unlike past mask patterns.

Evolution of dielectric surface potential induced by electron beam radiation

<p indent=0mm>Spacecrafts operate in a complex space plasma environment and are constantly exposed to cosmic ray radiation. The charging and discharging phenomena that occur on the dielectric surfaces result in major reliability issues for the spacecraft’s normal operation. Secondary electron emission (SEE) caused due to electron radiation is the primary inducement of dielectric surface charging, and the SEE level severely affects the charging and discharging status. In this paper, to discover the dynamic evolution process of dielectric surface charging under the circumstances of electron beam irradiation, we have conducted a systematic study on the surface potential and SEE behaviors under various irradiation situations. First, we fitted the secondary electron yield (SEY) curves for three dielectric materials with high resistance, namely MgO, Al₂O₃, and ZnO, and extracted the two critical energies (<italic>E</italic>₁ and <italic>E</italic>₂, where the SEY value equals 1 for the first and second time, respectively), SEY peak values, and the corresponding primary electron energy of the SEY peak value from the three SEY curves. Then, for the situation of electron beam radiating dielectric materials, we developed a physical model and simulated the dynamic evolution processes of the dielectric surface potential. The radiation source is a pulsed electron beam, and some radiating conditions include the following: The intensity of the beam current is set as 1 × <sc>10⁻⁹ A,</sc> the diameter of the electron beam spot is 1 × <sc>10⁻⁸ m,</sc> the width of a single pulse is 0.9 × <sc>10⁻⁹ s,</sc> and the period duration of a single pulse is 1 × <sc>10⁻⁹ s.</sc> We calculated the charge accumulating amount after pulse radiation and the corresponding variation quantity of the surface potential based on these assumed radiation parameters and the ideal charging situation without charge leakage. We discovered the evolution regularities of the potential variation rate, potential level, and potential balanced duration for the three irradiated materials by calculating the transient surface potential. Furthermore, we have simulated the dependence of surface potential on the radiation energy (<italic>E</italic>_p) of the electron beam. Several conclusions are summarized by analyzing the simulation and calculation results. First, the SEE characteristics of dielectric materials, particularly the two critical energy values <italic>E</italic>₁ and <italic>E</italic>₂, are the two key factors that affect positive or negative charging, as well as the balanced duration and balanced surface potential level. Second, the negative balanced surface potential induced by low energy electrons (<italic>E</italic>_p><italic>E</italic>₂) is only a few tens of volts; the balanced time is a few hundred pulses, and the surface potential variation rate first increases and then decreases. Third, the negative balanced surface potential induced by the high energy electrons (<italic>E</italic>_p><italic>E</italic>₂) is relatively high and its magnitude can reach <sc>10000 V;</sc> moreover, the balanced duration is relatively long (about several tens of thousands pulse duration). Fourth, because the positive balanced surface potential induced by the middle energy electrons (<italic>E</italic>₁<<italic>E</italic>_p<<italic>E</italic>₂) is extremely low, and the balanced time is short (less than a few tens of seconds), the variation rate of the positive surface potential rapidly decreases. Fifth, the dielectric material with a higher <italic>E</italic>₂ value exhibits a lower negative balanced surface potential and a long balanced duration, and this property makes the dielectric material with a high <italic>E</italic>₂ value play a more significant role in the suppression of surface charging. In this paper, we have discussed in detail the dynamic evolution regularities of surface potential when the dielectric is irradiated by an electron beam, which is beneficial for further analysis about dielectric surface charging, discharging, and further research on the charging defense.

Design of an Einzel Lens with Square Cross-Section

In this paper, the results of modeling and simulation of a microcolumn are presented. The microcolumn is part of a developed miniature MEMS electron microscope equipped with a miniature MEMS high-vacuum micropump. Such an arrangement makes this device the first stand-alone miniature electron-optical device to operate without an external high-vacuum chamber. Before such a device can be fabricated, research on particular elements must be carried out to determine the working principles of the device. The results of the calculations described in this article help us to understand the work of a microcolumn with square holes in the electrodes. The formation of an electron beam spot at the anode is discussed. Further calculations and results show the dependence of the Einzel lens size on the electron beam spot diameter, electron beam current, and microcolumn focusing voltage. The results are used to define the optimal design of the developed MEMS electron microscope.

Multi‐Scale Lipid Membrane Flow by Electron Beam‐Induced Electrowetting

AbstractThis study proposes a new technique for control of lipid membrane flow using an electron beam (EB)‐induced virtual cathode (VC). A spot 2.5 keV EB is indirectly irradiated onto supported lipid bilayers (SLBs) which are formed on a 100‐nm‐thick silicon nitride (SiN) membrane, and then a focused electric field around the EB spot (that is, the VC) causes membrane flow of the SLBs due to a voltage drop across them and electrowetting effects between them and the SiN membrane. This VC technique is shown to be able to change membrane shapes by small‐ and large‐scale controls of lipid membrane flow. For SLBs consisting of a single component, a spot VC can achieve small‐scale control of membrane flow; and the edge of the SLBs is demonstrated to change only around the spot VC. It is also shown that the spot VC can cause large‐scale deformation of SLBs consisting of ternary components by inducing a surface instability phenomenon known as Saffman–Taylor instability. The obtained results indicate that the proposed VC technique can achieve multi‐scale control of lipid membrane flow, which will contribute to on‐demand control of network topology in biomolecular devices based on artificial lipid membranes.

Field-emission electron gun for a MEMS electron microscope

This article presents a field-emission electron gun intended for use in a MEMS (microelectromechanical system) electron microscope. Its fabrication process follows the technology of a miniature device under development built from silicon electrodes and glass spacers. The electron gun contains a silicon cathode with a single very sharp protrusion and a bundle of disordered CNTs deposited on its end (called a sharp silicon/CNT cathode). It was tested in diode and triode configurations. For the diode configuration, a low threshold voltage <1000 V and a high emission current that reached 90 µA were obtained. After 30 min of operation at 900 V, the emission current decreased to 1.6 µA and was stable for at least 40 min, with RMS fluctuation in the anode current lower than 10%. The electron beam spot of the source was observed on the phosphor screen. In the diode configuration, the spot size was the same as the emission area (~10 µm), which is a satisfactory result. In the triode configuration, an extraction electrode (gate) control function was reported. The gate limited the emission current and elongated the lifetime of the gun when the current limit was set. Moreover, the electron beam current fluctuations at the anode could be reduced to ~1% by using a feedback loop circuit that controls the gate voltage, regulating the anode current. The developed sharp silicon/CNT cathodes were used to test the MEMS electron source demonstrator, a key component of the MEMS electron microscope, operating under atmospheric pressure conditions. Cathodoluminescence of the phosphor layer (ZnS:Ag) deposited on the thin silicon nitride membrane (anode) was observed.

Electron beam probe: The analysis of the electron beam spot expansion and a prototype development at IMP

Non-interceptive diagnostic techniques are essential for high beam power accelerators. An Electron Beam Probe (EBP) is preferable to measure the beam distribution of a dense beam bunch in which a low-intensity and low-energy electron beam sweeps across the ion beam and the deflection angle exerted on each electron by the space charge field of ion beam reflecting the local density distribution of the ion beam. In this paper, the design and setup of an EBP system, together with preliminary beam experiment result, are presented. A dedicated multi-particle simulation algorithm is developed which reproduces the expansion effect of electron beam spot in a dense ion bunch as observed by several Labs, and a theoretical interpretation is given with a preliminary solution being proposed. In the future, an improved version of EBP will supply non-interceptive diagnostics for Booster Ring (BRing) of the High Intensity heavy ion Accelerator Facility (HIAF), of which a fast scanning system will be implemented with the parallel electron beam optics configured.

Secondary electron yield suppression using millimeter-scale pillar array and explanation of the abnormal yield–energy curve**Project supported by the National Natural Science Foundation of China (Grant Nos. U1832190, 61501364, U1537211, and 11705142).

The phenomenon of secondary electron emission is of considerable interest in areas such as particle accelerators and on-board radio frequency (RF) components. Total secondary electron yield (TSEY) is a parameter that is frequently used to describe the secondary electron emission capability of a material. It has been widely recognized that the TSEY vs. primary electron energy curve has a single-hump shape. However, the TSEY–energy curve with a double-hump shape was also observed experimentally—this anomaly still lacks explanation. In this work, we explain this anomaly with the help of a millimetre-scale (mm-scale) silver pillar array fabricated by three-dimensional (3D) printing technology. The TSEY–energy curve of this pillar array as well as its flat counterpart is obtained using sample current method. The measurement results show that for the considered primary electron energy (40–1500 eV), the pillar array can obviously suppress TSEY, and its TSEY–energy curve has an obvious double-hump shape. Through Monte Carlo simulations and electron beam spot size measurements, we successfully attribute the double-hump effect to the dependence of electron beam spot size on the primary electron energy. The observations of this work may be of help in determining the TSEY of roughened surface with characteristic surface structures comparable to electron beam spot size. It also experimentally confirms the TSEY suppression effect of pillar arrays.

Estimation of Dosimetric Parameters based on KNR and KNCSF Correction Factors for Small Field Radiation Therapy at 6 and 18 MV Linac Energies using Monte Carlo Simulation Methods.

Estimating dosimetric parameters for small fields under non-reference conditions leads to significant errors if done based on conventional protocols used for large fields in reference conditions. Hence, further correction factors have been introduced to take into account the influence of spectral quality changes when various detectors are used in non-reference conditions at different depths and field sizes. Determining correction factors (KNR and KNCSF) recommended recently for small field dosimetry formalism by American Association of Physicists in Medicine (AAPM) for different detectors at 6 and 18 MV photon beams. EGSnrc Monte Carlo code was used to calculate the doses measured with different detectors located in a slab phantom and the recommended KNR and KNCSF correction factors for various circular small field sizes ranging from 5-30 mm diameters. KNR and KNCSF correction factors were determined for different active detectors (a pinpoint chamber, EDP-20 and EDP-10 diodes) in a homogeneous phantom irradiated to 6 and 18 MV photon beams of a Varian linac (2100C/D). KNR correction factor estimated for the highest small circular field size of 30 mm diameter for the pinpoint chamber, EDP-20 and EDP-10 diodes were 0.993, 1.020 and 1.054; and 0.992, 1.054 and 1.005 for the 6 and 18 MV beams, respectively. The KNCSF correction factor estimated for the lowest circular field size of 5 mm for the pinpoint chamber, EDP-20 and EDP-10 diodes were 0.994, 1.023, and 1.040; and 1.000, 1.014, and 1.022 for the 6 and 18 MV photon beams, respectively. Comparing the results obtained for the detectors used in this study reveals that the unshielded diodes (EDP-20 and EDP-10) can confidently be recommended for small field dosimetry as their correction factors (KNR and KNCSF) was close to 1.0 for all small field sizes investigated and are mainly independent from the electron beam spot size.