Study of X-ray Emission from a Compact Diode Operated by a High-Inductance Capacitor Discharge

A compact diode comprising a flat plate anode and a sharp-edged cathode (a piece of razor blade) energized by 0.5 F capacitor charged to 30 kV is investigated for optimization of X-rays emission vis-à-vis separation between electrodes and width of the cathode, which is responsible for electron emission by impact of electric field. It is a high-inductance system, the parasitic inductance is found to be 353 ± 5 nH, and the recorded peak discharge current is just 35 ± 02 kA. The maximum X-ray emission is observed for a 2-mm-wide cathode with an interelectrode separation of 3 mm. The X-ray yield in 4-geometry is found to be 34 ± 3 mJ with a wall-plug efficiency of 0.015 ± 0.001%. The X-ray emission occurs about 200 ns after the application of high voltage, synchronized with the dip in current wave form. The low efficiency of the system for X-ray generation is attributed to high parasitic inductance.     

Characterization of dose delivery in a hard X-ray irradiation facility

The Radiation Bioengineering Laboratory at Seoul National University (SNU) operates a user-constructed hard X-ray irradiation facility for radiation biology and radiation therapy physics studies. The system package of YXLON model 450-D08 operating at the anode voltage of up to 450 kV is a key part of the facility, which enables in vitro cell irradiation and animal irradiation for in vivo studies. In this article, dose delivery in the hard X-ray irradiation facility was characterized in terms of the dose vs. operational parametric combination of the facility. The operational parameters included beam tube anode voltage, beam tube current, irradiation time, and beam exit-to-sample distance. Bremsstrahlung X-rays at energy below approximately 20 keV were filtered out by a 3 mm-thick aluminum plate fitted over the 5 mm-thick beryllium window. Gafchromic EBT films were used as radiation sensor materials in dose measurement. The characterization was validated via experimental observation of the in vitro biological responses of cells to radiation exposure. The biological responses obtained using the new hard X-ray irradiator were highly comparable with those obtained using a commercial gamma-ray irradiator.     

大束流场发射阴极X射线管的阳极设计

采用蒙特卡罗软件和有限元分析软件分析了固定阳极X射线管中电子轰击阳极靶的能量沉积和热量传输过程,固定阳极由铜棒和钨片组成。研究了在不同形状、尺寸和占空比的电子束脉冲轰击下,阳极靶面不同厚度的钨片和相邻铜棒的温度上升过程。结果表明,钨片厚度存在最优值,但最优值与具体使用条件相关;在脉冲成像方式下,固定阳极靶能承受更强束流强度的轰击。因此,采用固定阳极靶方案,研制140 kV高压、10 mA以上电流、直径1 mm以下有效焦点的场发射阴极X射线管是可行的。     

Low-Energy Plasma Focus as a Tailored X-Ray Source

A low-energy (2.3 kJ) plasma focus energized by a single 32-F capacitor charged at 12 kV with filling gases hydrogen, neon, and argon is investigated as an X-ray source. Experiments are conducted with a copper and an aluminum anode. Specifically, attention is given to tailoring the radiation in different windows, e.g., 1.2–1.3 keV, 1.3–1.5 keV, 2.5–5 keV, and Cu-K line radiation. The highest X-ray emission is observed with neon filling and the copper anode in the 1.2–1.3 keV window, which we speculate to be generated due to recombination of hydrogenlike neon ions with a few eV to a few 10s of eV electrons. The wall-plug efficiency of the device is found to be 4%. The other significant emission occurs with hydrogen filling, which exhibits wall-plug efficiency of 1.7% for overall X-ray emission and 0.35% for Cu-K line radiation. The emission is dominated by the interaction of electrons in the current sheath with the anode tip. The emission with the aluminum anode and hydrogen filling is up to 10 J, which corresponds to wall-plug efficiency of 0.4%. The X-ray emission with argon filling is less significant.     

Investigation of optimal scanning protocol for X-ray computed tomography polymer gel dosimetry

X-ray computed tomography is one of the potential tool used to evaluate the polymer gel dosimeters in three dimensions. The purpose of this study is to investigate the factors which affect the image noise for X-ray CT polymer gel dosimetry. A cylindrical water filled phantom was imaged with single slice Siemens Somatom Emotion CT scanner. The imaging parameters like tube voltage, tube current, slice scan time, slice thickness and reconstruction algorithm were varied independently to study the dependence of noise on each other. Reductions of noise with number of images to be averaged and spatial uniformity of the image were also investigated. Normoxic polymer gel PAGAT was manufactured and irradiated using Siemens Primus linear accelerator. The radiation induced change in CT number was evaluated using X-ray CT scanner. From this study it is clear that image noise is reduced with increase in tube voltage, tube current, slice scan time, slice thickness and also reduced with increasing the number of images averaged. However to reduce the tube load and total scan time, it was concluded that tube voltage of 130 kV, tube current of 200 mA, scan time of 1.5 s, slice thickness of 3 mm for high dose gradient and 5 mm for low dose gradient were optimal scanning protocols for this scanner. Optimum number of images to be averaged was concluded to be 25 for X-ray CT polymer gel dosimetry. Choice of reconstruction algorithm was also critical. From the study it is also clear that CT number increase with imaging tube voltage and shows the energy dependency of polymer gel dosimeter. Hence for evaluation of polymer gel dosimeters with X-ray CT scanner needs the optimization of scanning protocols to reduce the image noise.     

Low Energy Plasma Focus as an Intense X-ray Source for Radiography

Study on X-ray emission from a low energy (1.8 kJ) plasma focus device powered by a 9 μF capacitor bank, charged at 20 kV and giving peak discharge current of about 175 kA by using a lead-inserted copper-tapered anode is reported. The X-ray yield in different energy windows is measured as a function of hydrogen filling pressure. The maximum yield in 4π-geometry is found to be (27.3±1.1) J and corresponding wall plug efficiency for X-ray generation is 1.52±.06%. X-ray emission, presumably due to bombarding activity of electrons in current sheath at the anode tip was dominant, which is confirmed by the pinhole images. The feasibility of the device as an intense X-ray source for radiography is demonstrated.     

Fine structures of divergence of polycapillary X-ray optics

The divergence of the beam focused by polycapillary X-ray optics (PXRO) varied at different distances from the exit of the PXRO. This distance dependence of the divergence of the PXRO was defined as the fine structures of the divergence of the PXRO. The fine structures of the divergence of the PXRO were presented in order to use them fully. There were main three types of the PXRO, such as polycapillary parallel X-ray lens (PPXRL), polycapillary focusing X-ray lens (PFXRL) and polycapillary slightly focusing X-ray lens (PSFXRL). For the PPXRL, the divergence decreased near its exit. The reason for this might be that the divergence near the exit of the PPXRL depended mainly on the X-rays traversing directly through the monocapillaries in the center of the PPXRL without total reflection. For the PFXRL and PSFXRL, they both had respectively a focal depth over which the beam sizes at different output distances remained acceptably small. For the 8 keV X-rays, the focal depth and divergence over the focal depth of the PFXRL were about 300 μm and 25.0 mrad, respectively. At the same energy of 8 keV, the focal depth and divergence over the focal depth of the PSFXRL were about 500 μm and 12.5 mrad, respectively. The divergence of the PFXRL and the PSFXRL depended mainly on the angles between axes of monocapillaries that composed them.     

The Columbia University proton-induced soft x-ray microbeam

A soft X-ray microbeam using proton-induced X-ray emission (PIXE) of characteristic titanium (K_α 4.5 keV) as the X-ray source has been developed at the Radiological Research Accelerator Facility (RARAF) at Columbia University. The proton beam is focused to a 120 μm × 50 μm spot on the titanium target using an electrostatic quadrupole quadruplet previously used for the charged particle microbeam studies at RARAF. The proton induced X-rays from this spot project a 50 μm round X-ray generation spot into the vertical direction. The X-rays are focused to a spot size of 5 μm in diameter using a Fresnel zone plate. The X-rays have an attenuation length of (1/e length of ∼145 μm) allowing more consistent dose delivery across the depth of a single cell layer and penetration into tissue samples than previous ultrasoft X-ray systems. The irradiation end station is based on our previous design to allow quick comparison to charged particle experiments and for mixed irradiation experiments.     

X-Ray Measurement and Enhancement of SBUPF1 Plasma Focus Device in Different Ar Pressures and Operating Voltages

In this paper, best condition of filling gas pressure and operating voltage for SBUPF1 plasma focus device to have maximum intensity of hard and soft X-ray emission has been reported. For time resolved X-ray detection, PIN detector and fast plastic Scintillator detector with appropriate filters have been used and for time integrated X-ray emission measurement, radiography films with appropriate filter masks have been used. Rogowski coil has been used for pinch detection. The highest hard X-ray emission has been observed at the pressure of 0.45 mbar of Argon and discharge voltage about 23.5 kV. The highest Soft X-ray emission has been observed at the pressure of 0.35 mbar of Argon and discharge voltage about 23.5 kV. For enhancement of hard X-ray emission intensity, lead disk was placed in copper anode tip and measurements were repeated. Results have shown that hard X-ray emission has been enhanced about 23% and soft X-ray emission has been enhanced about 33% with inserting a high atomic number metal disk like lead. Results from integral X-ray measurement have shown presence of dominant peaks in ranges 13.2–15, 21–21.9 and 23.4–24.3 keV with significant spectral components in the range of 0–50 keV. Pinch size has measured with pin hole camera and it is about 0.6 mm × 2.12 mm. Captured images with SBUPF1 have confirmed that it is a suitable source for introspective imaging with capability of showing very fine details.     

Ultra fast electron beam X-ray computed tomography for two-phase flow measurement

Electron beam X-ray CT is a new technique for a fast measurement of multiphase flows with frame rates of 1000 images per second and more. It gives, in principle, quantitatively accurate images of the flow at high spatial resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated by X-rays. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement studies, we devised and built a fast scanned electron beam X-ray tomography scanner. The scanner consists of an electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current, with the required electron optics for beam adjustment, beam focusing and beam deflection unit and a fast circular CZT detector comprising 240 elements of 1.5 mm × 1.5 mm × 1.5 mm active pixel area. X-ray radiation is produced on a circular water cooled tungsten target. The CT system achieves up to 7000 frames per second with a spatial resolution of 1 mm. First two-phase flow experiments have been carried out on gas-water flows in bubble columns. Further, a vertical test section made of titanium alloy has been installed at the TOPFLOW facility and will be used in future to study the evolution of two-phase gas-water pipe flow at high pressures and temperatures.     

重复频率亚纳秒硬X射线源研制及应用

为获得一种多用途X射线源,满足核辐射探测器研制、脉冲成像等多任务应用需要,本文研制出具备重复频率、超快、高稳定性、便于连续调节脉冲电压和脉宽等的多用途X射线源,其上升沿达98.6 ps,运行电压达425 kV,10 cm处峰值注量率高达2.07×10¹⁸ cm^-2•s^-1,为开展相关应用研究提供了理想的辐射条件。     

Design of an ion extractor system for a prototype ion source experiment for SST-1 neutral beam injector

An ion extractor system has been designed for the steady state superconducting tokamak (SST-1) neutral beam injector (NBI) for an experiment using a prototype ion source with fully integrated regulated high voltage power supply (RHVPS) and data acquisition and control system (DACS) developed at Institute for Plasma Research (IPR) to obtain experience of NB operation. The extractor system is capable of extracting positive hydrogen ion beam of ∼10 A current at ∼20 kV. This paper presents the beam optics study for detailed design of an ion extraction system which could meet this requirement. It consists of 3 grid accel-decel system, each of the grid has 217 straight cylindrical holes of 8 mm diameter. Grids are placed on a specially designed G-10 block; a fiber reinforc plastic (FRP) isolator of outer diameter of 820 mm and 50 mm thickness. Provisions are made for supplying high voltage to the grid system through the embedded feed-throughs. Extractor system has been fabricated, mounted on the SST-1 neutral beam injector and has extracted positive hydrogen ion beam of 4 A at 20 kV till now.     

Simulation of Secondary Electron and Backscattered Electron Emission in A6 Relativistic Magnetron Driven by Different Cathode

Prticle-in-cell(PIC) simulations demonstrated that,when the relativistic magnetron with diffraction output(MDO) is applied with a 410 kV voltage pulse,or when the relativistic magnetron with radial output is applied with a 350 kV voltage pulse,electrons emitted from the cathode with high energy will strike the anode block wall.The emitted secondary electrons and backscattered electrons affect the interaction between electrons and RF fields induced by the operating modes,which decreases the output power in the radial output relativistic magnetron by about 15%(10%for the axial output relativistic magnetron),decreases the anode current by about 5%(5%for the axial output relativistic magnetron),and leads to a decrease of electronic efficiency by 8%(6%for the axial output relativistic magnetron).The peak value of the current formed by secondary and backscattered current equals nearly half of the amplitude of the anode current,which may help the growth of parasitic modes when the applied magnetic field is near the critical magnetic field separating neighboring modes.Thus,mode competition becomes more serious.     

X射线空气比释动能(治疗水平)标准装置的建立

为开展X射线在治疗水平剂量率下的量值溯源与传递工作,依据IEC 60731—1997标准的要求,建立了管电压为10~250 kV、剂量率范围为1.0×10^-3~10 Gy/h的X射线空气比释动能(治疗水平)标准装置。其中10~60 kV X射线空气比释动能(治疗水平)标准装置在1.0 m处非均匀性小于1%的辐射野为ø60 mm,散射对辐射场贡献小于1.2 %,在距离放射源1~5 m范围内反平方律在2.5 %内符合,使用标准电离室测得装置的稳定性为1.8％、重复性为0.1％。60~250 kV X射线空气比释动能(治疗水平)标准装置在1.0 m处非均匀性小于1%的辐射野为ø80 mm,散射对辐射场贡献小于1.2 %,在距离放射源1~5 m范围内反平方律在1.5 %内符合,使用标准电离室测得装置的稳定性为1.7％、重复性为0.03％。标准装置辐射场空气比释动能率的相对扩展不确定度为3.0％ (k=2),经测量,装置的各项性能指标均满足治疗水平剂量检测仪器的检定/校准要求。     

X-ray tomography system for industrial applications

X-ray radiography and tomography are two of the most used non-destructive testing techniques both in industrial and cultural heritage fields. However, the inspection of heavy materials or thick objects requires X-ray energies larger than the maximum energy provided by commercial X-ray tubes (600 kV). For this reason, and owing to the long experience of the INFN-Gruppo Collegato di Messina in designing and assembling low energy electron linacs, a 5 MeV electron linac based X-ray tomographic system has been developed at the Dipartimento di Fisica, Università di Messina. The X-ray source, properly designed, provides a 16 cm diameter X-ray spot at the sample position, and a beam opening angle of about 3.6 degree. Optimization of the parameters influencing the e-γ conversion and the X-ray beam characteristics have been studied by means of the MCNP-4C2 (Monte-Carlo-N-Particle, version 4C2) code. The image acquisition system consists of a CCD camera and a scintillator screen. Preliminary radiographies and tomographies showing the high quality performances of the tomographic system have been acquired. Finally, the compactness of the accelerator system is one of the advantages of the discussed tomography device which could be made transportable.     

复杂X射线能谱构造方法研究

本文提出了基于最小二乘法的复杂X射线能谱构造方法,介绍了其构造原理,设计了由35~100 kV加速电压条件下的14个X射线过滤谱组成的构造子谱组。目标能谱模拟构造结果表明,构造能谱与目标能谱总体的相对偏差基本控制在10%以内;影响其偏差的主要因素包括构造子谱数量与形态,目标能谱的非连续可微以及射线源特征X射线。     

Versatile plasma ion source with an internal evaporator

A novel construction of an ion source with an evaporator placed inside a plasma chamber is presented. The crucible is heated to high temperatures directly by arc discharge, which makes the ion source suitable for substances with high melting points. The compact ion source enables production of intense ion beams for wide spectrum of solid elements with typical separated beam currents of ∼100-150 μA for Al⁺, Mn⁺, As⁺ (which corresponds to emission current densities of 15-25 mA/cm²) for the extraction voltage of 25 kV. The ion source works for approximately 50-70 h at 100% duty cycle, which enables high ion dose implantation. The typical power consumption of the ion source is 350-400 W. The paper presents detailed experimental data (e.g. dependences of ion currents and anode voltages on discharge and filament currents and magnetic flux densities) for Cr, Fe, Al, As, Mn and In. The discussion is supported by results of Monte Carlo method based numerical simulation of ionisation in the ion source.     

Evaluation of radiation dose and positioning accuracy on X-ray volume imaging system for image-guided radiotherapy

Linear accelerators equipped with X-ray volumetric cone-beam Imaging (XVI) system enable verification of location of patients and displacement of tumors for image-guided radiotherapy (IGRT). The objective of this study is to evaluate the positioning accuracy using the XVI system for image-guided patient setup and to establish a lower-dose imaging protocol without sacrificing positioning accuracy for routine treatment courses. Several low-dose imaging protocols are proposed by modifying tube voltage from 120 to 100 kV and lowering tube current from 40 to 10 mA. The positioning accuracy of both bone and gray value registration methods provided by XVI system were also evaluated. Phantom study revealed that the gray value algorithm was more accurate than the bone algorithm in position and registration. However, both translational and rotational accuracies were less than 0.15 mm and 0.8^° at all dimensions, which were considered negligible in clinical applications. In addition, the lower-dose protocol (100 kV, 10 mA) produced relative much less radiation dose compared to the default CBCT protocol in the XVI system. In conclusion, our proposed lower-dose protocol results in significant radiation dose reduction without compromising positioning accuracy and may have the potential to be adopted for clinical usage in the future.     

Cluster formation, evolution and size distribution in Fe-Cu alloy: Analysis by XAFS, XRD and TEM

Fe-Cu alloys containing 1.3 at.% copper were studied as model systems for cluster formation in reactor pressure vessel steels. The samples were annealed at 775 K for different times and subsequently analyzed using X-ray absorption fine structure spectroscopy at the Cu-K-edge, X-ray diffraction and transmission electron microscopy. The results show that copper cluster formation might occur even with short annealing times. These clusters of about 1 nm size can switch easily from bcc iron-like structures to fcc copper, if the local copper concentration is high enough. While a short annealing time of 2.5 h at 775 K maintains a good dilution of copper in the bcc iron matrix, annealing for 312 h leads to large fcc copper precipitates. A linear combination analysis suggests that in the sample annealed 8 h, copper clusters are mostly formed with the same structure as the matrix. A co-existence of bcc and fcc clusters is obtained for 115 h of annealing. Transmission electron microscopy indicates the presence of precipitates as large as 60 nm size for an annealing time of 312 h, and X-ray diffraction provided complementary data about the clusters size distributions in all of the four samples.