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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - High performance x-ray source using point-typed CNT field emitter
摘要： The high performance cold cathode x-ray source was fabricated by using the point-typed CNT field emitter. The cold cathode x-ray source consists of the CNT point emitter, the metal mesh gate electrode, the metal hole focusing lens and the tungsten target anode electrode. To fabricate x-ray source, such components were mounted in a SUS vacuum chamber. The fabricated CNT x-ray source showed a good resolution of x-ray images at a low anode current and at a low anode voltage, and also indicated stable operation. We evaluated x-ray images according to the tube voltage and the tube current, respectively.
关键词： point-typed field emitter,carbon nanotube field emitter,metal mesh gate electrode,x-ray image,cold cathode x-ray source,tungsten anode electrode
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - CNT field emitter based high performance x-ray source
摘要： We fabricated the cold cathode x-ray source composed of point-type CNT field emitter, mesh gate electrode, e-beam focusing lens and W anode. The point-type CNT field emitter was made by CNT film with a triangular tip shape. Field emission properties measured in triode configuration showed the low turn-on and threshold electric fields, the high emission current and focused electron beam spot. The CNT field emitter based cold cathode x-ray source reveals high resolution x-ray images. We demonstrated that the point-type CNT emitter is suitable candidate for the high performance cold cathode x-ray sources.
关键词： cold cathode x-ray source,triode structure,field emission,carbon nanotube filed emitter
更新于2025-09-23 15:21:21
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A Monte Carlo based dosimetric characterization of Esteya <sup>?</sup> , an electronic surface brachytherapy unit
摘要： The purpose of this work is threefold: First, to obtain the phase-space of an electronic brachytherapy (eBT) system designed for surface skin treatments. Second, to explore the use of some efficiency enhancing (EFEN) strategies in the determination of the phase-space. Third, to use the phase-space previously obtained to perform a dosimetric characterization of the Esteya eBT system. Methods: The Monte Carlo study of the 69.5 kVp x-ray beam of the Esteya? unit (Elekta Brachytherapy, Veenendaal, The Netherlands) was performed with PENELOPE2014. The EFEN strategies included the use of variance reduction techniques and mixed Class II simulations, where transport parameters were fine-tuned. Four source models were studied varying the most relevant parameters characterizing the electron beam impinging the target: the energy spectrum (mono-energetic or Gaussian shaped), and the electron distribution over the focal spot (uniform or Gaussian shaped). Phase-spaces obtained were analyzed to detect differences in the calculated data due to the EFEN strategy or the source configuration. Depth dose curves and absorbed dose profiles were obtained for each source model and compared to experimental data previously published. Results: In our EFEN strategy, the interaction forcing variance reduction (VRIF) technique increases efficiency by a factor ~ 20. Tailoring the transport parameters values (C1 and C2) does not increase the efficiency in a significant way. Applying a universal cutoff energy EABS of 10 keV saves 84% of CPU time whilst showing negligible impact on the calculated results. Disabling the electron transport by imposing an electron energy cutoff of 70 keV (except for the target) saves an extra 8% (losing in the process 1.2% of the photons). The Gaussian energy source (FWHM = 10%, centered at the nominal kVp, homogeneous electron distribution) shows characteristic K-lines in its energy spectrum, not observed experimentally. The average photon energy using an ideal source (mono-energetic, homogeneous electron distribution) was 36.19 ± 0.09 keV, in agreement with the published measured data of 36.2 ± 0.2 keV. The use of a Gaussian-distributed electron source (mono-energetic) increases the penumbra by 50%, which is closer to the measurement results. The maximum discrepancy of the calculated percent depth dose with the corresponding measured values is 4.5% (at the phantom surface, less than 2 % beyond 1 mm depth) and 5% (for the 80% of the field) in the dose profile. Our results agree with the findings published by other authors and are consistent within the expected Type A and B uncertainties. Conclusions: Our results agree with the published measurement results within the reported uncertainties. The observed differences in PDD, dose profiles and photon spectrum come from three main sources of uncertainty: inter-machine variations, measurements and Monte Carlo calculations. It has been observed that a mono-energetic source with a Gaussian electron distribution over the focal spot is a suitable choice to reproduce the experimental data.
关键词： simulation efficiency,Monte Carlo simulation,electronic brachytherapy,surface treatment,dosimetry,x-ray source
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Field Emission from Oxide Nanowires: Mechanism and Applications
摘要： In this invited talk, our recent progresses in the research of field emission from several oxide nanowires and their applications in vacuum microelectronic devices will be reviewed. Field emission properties from of CuO, WO3-x and ZnO nanowires were studied and their field emission mechanism were discussed. Applications of nanowire field emitter in gated field emitter, flat panel x-ray source and imaging detector were explored. Prototype of flat panel X-ray source using ZnO nanowire field emitters was fabricated and its high resolution imaging capability was demonstrated. The feasibility of a large area high-sensitive detector using ZnO nanowire field emitters is also verified.
关键词： flat panel X-ray source,field emission,ZnO nanowire
更新于2025-09-23 15:21:21
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Performance of assembled X-ray optics consisted of a polycapillary X-ray optics and a monocapillary X-ray optics for micro X-ray fluorescence spectrometry
摘要： A micro X-ray fluorescence (μ-XRF) spectrometry instrument based on an assembled X-ray optics was constructed in the laboratory. The assembled X-ray optics consisted of a polycapillary slightly focusing X-ray lens and a tapered monocapillary X-ray lens (TMXRL). The output X-ray beam of the polycapillary slightly focusing X-ray lens was focused again by the TMXRL. A TMXRL with output aperture of 12.01 μm was drawn by a nested glass tube. To evaluate the performance of the instrument, a performance comparison between different capillary X-ray optics was conducted. The intensity of the Fe Kα from an iron plate was used to indicate the analysis efficiency of the μ-XRF instrument. The relative gain of the instrument was corrected by comparing the intensity per unit area for a pinhole aperture. Compared with TMXRL single used, the assembled X-ray optics also had a micro focal spot. Furthermore, the relative gain of the assembled X-ray optics and the intensity of the Fe Kα from the iron plate obtained by the assembled X-ray optics were approximately 5 times those of the TMXRL single used. This highly intense micro X-ray beam with several diameters obtained by the assembled X-ray optics will be useful for μ-XRF analysis.
关键词： Capillary X-ray optics,Micro X-ray focusing,Micro X-ray fluorescence,Laboratory X-ray source
更新于2025-09-23 15:19:57
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Exploring phase contrast imaging with a laser-based K?± x-ray source up to relativistic laser intensity
摘要： this study explores the ability of a hard Kα x-ray source (17.48 keV) produced by a 10 TW class laser system operated at high temporal contrast ratio and high repetition rate for phase contrast imaging. For demonstration, a parametric study based on a known object (PET films) shows clear evidence of feasibility of phase contrast imaging over a large range of laser intensity on target (from ~1017 W/cm2 to 7.0 × 1018 W/cm2). To highlight this result, a comparison of raw phase contrast and retrieved phase images of a biological object (a wasp) is done at different laser intensities below the relativistic intensity regime and up to 1.3 × 1019 W/cm2. this brings out attractive imaging strategies by selecting suitable laser intensity for optimizing either high spatial resolution and high quality of image or short acquisition time.
关键词： biological imaging,laser intensity,phase contrast imaging,high repetition rate,Kα x-ray source
更新于2025-09-23 15:19:57
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Temporal evolution of photo-induced thermal strain in InSb probed by ultra-short laser produced Cu Kα x-rays
摘要： Development and characterization of a wire target based kHz rep rate Cu Kα x-ray source using a Ti:sapphire laser system and its use in time resolved x-ray diffraction (TXRD) of the InSb (111) sample are presented. The observed Kα x-ray photon flux is ～3.2 × 109 photons sr?1 s?1 at a laser intensity of ～3.5 × 1016 W cm?2. TXRD signal from the InSb (111) crystal pumped by an ultrashort Ti:sapphire laser pulse (fluence ～ 13 mJ cm?2) shows a lattice expansion due to heating on a multipicosecond time scale. The crystal gradually cools down and recovers at ～1.5 ns after the laser excitation. The observed strain variation in the crystal matches well with the simulated results. The study of full recovery of the sample will be helpful for the development of InSb based devices.
关键词： Cu Kα x-ray source,time resolved x-ray diffraction,ultrashort laser pulses,thermal strain,InSb
更新于2025-09-11 14:15:04
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Graphene paper as an emitter for low-power X-ray sources
摘要： Carbon materials are known to be one of the most suitable platforms for the development of cold electron emitters. Here we explore field emission (FE) performance of so-called graphene paper that is a micrometer-thick foil obtained by stacking chemically exfoliated graphene layers. We find, that shaped into triangular form, graphene paper exhibits competitive FE characteristics, such as high-current density stable in time, and low threshold fields. In addition, we study the degradation of such graphene-based emitters under high emissions currents and discuss possible application for a transmission-type X-ray source.
关键词： field emission,graphite emitter,x-ray source
更新于2025-09-10 09:29:36
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Beam simulation and experiment of multi-focal spot electron gun for distributed X-ray sources
摘要： Distributed X-ray sources provide a solid foundation for the invention of new-generation computed tomography (CT). This study proposes a novel multi-focal spot electron gun scheme for distributed X-ray sources. The source in this study uses a dispenser cathode as the electron emitter, a mesh grid to control emission current, and two electrostatic lenses for beam shaping, focusing, and deflecting. Novel focusing and deflecting electrodes were designed to increase the number of focal spots in the distributed source. It consists of two identical half-rectangle opening electrodes by adjusting the potential of the two electrodes to control the trajectory of the electron beam and then obtain multi-focal spots on the anode target. The number of X-ray sources in the distributed source is limited by the amount of cathodes. The multi-focal spot electron gun can break this limitation and provide more possibilities and options for distributed X-ray sources and stationary CT. Experimental results reflect the excellent repeatability of the multi-spot electron gun. The dynamic effective focal spot sizes of the deflected (deflected amplitude, 10.5mm) and non-deflected electron beams at full with half max (FWHM) are 1.30mm×0.60mm and 1.15mm×0.55mm, respectively (anode voltage, 160kV; beam current, 30mA).
关键词： Stationary CT,Distributed X-ray source,Multi-spot electron gun,Dispenser cathode
更新于2025-09-09 09:28:46
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Optical and Gamma-Ray Variability of the vRL NLSy1 Galaxy, 1H 0323+342
摘要： 1H 0323+342 was one of the ?rst vRLNLSy1 galaxies detected at gamma-rays with the Fermi-LAT and is one of the brightest of this class observed at optical wavelengths. We report the results of monitoring the optical ?ux, polarization and the gamma-ray ?ux of 1H 0323+342 during the past ~5 years. In some cases, the optical ?ux has been monitored on timescales as short as ~minutes simultaneously with two telescopes, demonstrating, for the ?rst time, the reality of microvariability events with durations as short as ~15 min for this object.
关键词： gamma-ray source,blazar,narrow line seyfert 1 galaxy
更新于2025-09-09 09:28:46