X射线硬化对面密度测量灵敏度的影响

利用蒙特卡罗方法分别研究了3种能量X光机的光子穿透不同厚度铝的硬化情况及3种能量光机作为光源测量面密度的过程,并开展了相关实验研究,根据模拟结果对比分析了不同能量光机X射线硬化对面密度测量灵敏度的影响,结果表明:对同种能量光机的光子而言,随着面密度变大,射线硬化程度越严重,导致测量灵敏度下降;光子能量越低,测量灵敏度随面密度变大下降越快,反之亦然;对于某一范围面密度被测物,调整X光机电压使X光子刚好穿透并形成有效图像,可获得最理想的测量灵敏度。     

TL and OSL dosimetric properties of Opal gemstone for gamma radiation dosimetry

In this work, the response of the natural material Opal was studied in relation to its thermoluminescence (TL) and optically stimulated luminescence (OSL), after exposure to the gamma radiation of a ⁶⁰Co source. The structure of the powdered Opal was verified using the X-ray diffraction, scanning electronic microscopy and energy-dispersive X-ray spectroscopy techniques. The material, in its stone form, was turned into powder and mixed to Teflon (also in powder) in three different concentrations, and then pellets were manufactured. The aim of this work was to evaluate the response of these pellets in high-doses of gamma radiation beams, and to observe their possible application as dosimeters, using the TL and OSL techniques. The dosimetric properties of the samples were analyzed by means of different tests, as: TL emission curves and OSL signal decay curves, reproducibility of TL and OSL response, minimum detectable dose, TL and OSL dose–response curves (5 Gy–10 kGy), and fading. The results obtained in this work, for the TL and OSL phenomena, demonstrated that the pellets of Opal + Teflon present an adequate performance e possibility of use as dosimeters in beams of high-dose gamma radiation.     

Review on applications of synchrotron-based X-ray techniques in materials characterization

Synchrotron radiation (SR), as a result of its high-intensity, brilliant, monochromatic, and collimated beams, is becoming one of the most crucial components of research in various fields of materials science such as nanomaterials, biomaterials, and energy materials. SR-based characterization methods can be employed to analyze different systems such as powders, thin films, and bulk forms having complex crystalline or amorphous structures. In this review, peculiarities of SR are briefly explained. Moreover, various techniques carried out utilizing this instrument for material characterization such as X-ray powder diffraction, grazing-incidence X-ray diffraction, small/wide-angle X-ray scattering, X-ray absorption spectroscopy, different techniques of X-ray imaging, X-ray photoelectron spectroscopy, and X-ray microprobes/nanoprobes are presented. As a result, by shedding light on the advantages of SR and its superiority to the equivalent laboratory experiments, researchers are recommended to exploit the capabilities of this invaluable tool in their materials characterization.     

强吸收介质内部低Z材料结构的X射线显微成像研究

惯性约束核聚变靶室靶丸位置的原位无损检测是目前的研究热点和难点.针对此需求,建立了强吸收介质包裹的低Z材料X射线显微成像物理模型.通过计算机模拟和实验,较为系统地考察了光子能量、成像距离以及强吸收介质尺度等参量对成像质量的影响.结果表明,利用X射线相衬成像技术来实现惯性约束核聚变靶室靶丸的高分辨无损检测是可行的. 关键词： X射线显微 位相衬度 核聚变靶 无损检测     

Evaluation of the dosimetric characteristics of a radiophotoluminescent glass dosimeter for high-energy photon and electron beams in the field of radiotherapy

We aimed to evaluate the suitability of a glass dosimeter (GD) for high-energy photon and electron beams in experimental and clinical use, especially for radiation therapy. We examined the expanded dosimetric characteristics of GDs including dose linearity up to 500 Gy, uniformity among GD lots and for individual GDs, the angular dependence, and energy dependence of 4 therapeutic x-ray qualities. In addition, we measured the dosimetric features (dose linearity, uniformity, angular dependence, and energy dependence) of the GD for electron beams of 10 different electron energy qualities. All measurements with the exception of dose linearity for photon beam were performed in a water phantom. For high-energy photon beams, dose linearity has a linear relationship for a dose ranging from 1 to 500 Gy with the coefficient of determination; R² of 0.998. The uniformity of each GD of dose measurements was within ±0.5% for four GD lots and within ±1.2% for 80 GDs. In terms of the effects of photon beam angle, lower absorbed doses of within 1.0% were observed between 60° and 105° than at 90°. The GD energy dependence of 4 photon beam energy qualities was within ±2.0%. On the other hand, the result of the dose linearity for high-energy electron beams showed well fitted regression line with the coefficient of determination; R² of 0.999 between 6 and 20 MeV. The uniformity of GDs exposed to the nominal electron energies 6, 9, 12, 16, and 20 MeV was ±1.2%. In terms of the angular dependence to electron beams, absorbed doses were within 2.0% between 60° and 105° than at 90°. In evaluation of the energy dependence of the GD at nominal electron energies between 5 and 20 MeV, we obtained responses between 1.1% and 3.5% lower than that for a cobalt-60 beam. Our results show that GDs can be used as a detector for determining doses when a high-energy photon beam is used, and that it also has considerable potential for dose measurement of high-energy electron beam.     

Theory of Z-scan technique using Gaussian-Bessel beams with a phase object

This paper reports the theoretical study of combining Z-scan technique with Gauss-Bessel (GB) beams beside a phase object (PO) to measure the third-order nonlinear susceptibility components.By using this method,the sign of refractive index which depends on the shape of the close aperture Z-scan curve can be easily determined.Meanwhile,the magnitude of nonlinear coefficients can also be deduced by theoretical fit.The proposed method is advantageous for high sensitivity and imposes a lower stress in the cases of fragile materials,since small pulse energy is enough for the measurement of nonlinear coefficients.Predictions of the models are compared with Gaussian Z-scan measurement and GB Z-scan measurement.By using GB beams with a PO,the sensitivity of Z-scan measurements is found to be a factor of over 60 times greater than for Gaussian beams and 2 times greater than for Gaussian-Bessel beams.     

Towards one machine, two purposes: using a common SC linac for XFEL and ERL simultaneously

The linac based XFEL and ERL are advanced (or, say, 4th generation) light sources, with different electron beam parameters and different advantages. However, the linac used for XFEL and ERL should provide very advanced beams with high energy, high peak and/or average current, very low emittance and low energy spread, thus making the linac very complicated and expensive. To share the XFEL and ERL advantages and save the construction-operation budget, a proposal of using a common superconducting electron linac for hard X-ray XFEL and ERL is described in this paper. The interactions between the XFEL and ERL beams via the accelerating structure are studied and the result is positive.     

Ce:KNSBN晶体衍射特性研究

在非同时读出条件下测量了Ce:KNSNB晶体两波耦合体光栅衍射效率随写入光强比、写入光偏振态和写入光夹角的变化关系,并与同时读出条件下衍射效率变化规律的测量结果进行了比较,发现二者基本一致.利用耦合波理论对实验结果进行了理论分析和拟合,拟合结果和实验数据较好的吻合.     

激光高能X射线成像中探测器表征与电子影响研究

基于激光尾场加速电子的高能X射线源具有高光子能量与小源尺寸的特点,在高空间分辨无损检测方面发挥着十分重要的作用.在X光机上测量了CsI针状闪烁屏、锗酸铋(BGO)闪烁阵列与DRZ闪烁屏的本征空间分辨率,并模拟了三类探测器对高能X射线的能量沉积响应,其中CsI针状闪烁屏的空间分辨率高达8.7 lp/mm.采用Ta转换靶产生的高能X射线开展透视照相,能够分辨最高面密度33.0 g/cm~2的两层客体结构.开展了X射线照相、X射线与电子混合照相以及电子照相三种情况的比对实验,在X射线产额不足或探测效率不够情况下采用X射线与电子混合透视照相的方案,以牺牲对比度为代价,能较大程度地提高图像信号强度.     

Materials Research with X-ray Micro-beams at the Advanced Photon Source

X-ray scattering has had a rich and prominent place in the history of materials research. For samples that are large single crystals, X-ray diffraction provides very detailed, high-quality information about the atomic structure of almost every kind. However, most engineering materials are not a large single crystal, but mixtures of materials or a poly-crystalline material. Still, X-ray diffraction using X-ray beams significantly larger than the structures being investigated has produced much excellent information. Examples of this are powder diffraction, texture analysis, strain analysis, etc. While these types of analyses have been very useful in providing a microscopic understanding, they do not provide the microscopic information that we really want. What we really want to have is this useful X-ray diffraction information for every volume element in our sample; not just the diffraction information about small volume elements, but all of the volume elements, exactly where they are in our sample, and how each one diffracts. This detailed spatial and structural information is what is needed for a full understanding of the source of the properties that we find in engineering materials.     

Holography with guided optical waves

This paper deals with “waveguide holograms” recorded in a layer of storage material covering a planar dielectric waveguide. Reference and read-out waves are guided modes of the waveguide. Their field in the storage medium is evanescent. A theory of the diffraction efficiencies of these waveguide holograms is presented fors-polarized wavefields. To calculate the hologram structure the attenuation of the reference wave caused by absorption in the light-sensitive storage material is taken into account. Analytical expressions for the local and the overall diffraction efficiencies and for the intensity profiles of the diffracted fields are derived. The dependence of these quantities on experimental parameters (the waveguide thickness, the mode numbers of the reference and read-out waves, and the angle of incidence of the plane object wave) is presented graphically, i.e., by computer plots. Grating couplers for integrated optics can be made by waveguide holography. We consider this application to be interesting because incoupling efficiencies for Gaussian beams of up to 96% can be achieved theoretically.     

Structure functions at HERA

HERA provides the key facility for the measurement of proton structure functions. Formalism and methods are outlined for the measurement and interpretation of inclusive structure functions, including the use of polarised e ^± beams. The measurement of charm, beauty and photon structure functions is discussed, together with special runs at low proton energy for measurement of the longitudinal structure function. Finally, the functions accessed using polarised beams on polarised targets are indicated.     

On the passive electrode signal in X-ray detectors based on superconducting tunnel junctions

X-ray detectors based on superconducting tunnel junctions with the multilayer electrode structure described by the formula Ti/Nb/Al, AlO _x /Al/Nb/NbN were studied. The main signal arose during X-ray absorption in the top electrode and had an energy resolution of ∼90 eV at the 5.9-keV line. The bottom passive Ti/Nb electrode provided rapid absorption of excess quasiparticles. The residual signal of the passive electrode was from 7 to 17% of the main signal amplitude. The dependences of the amplitude of this signal on the voltage and the absorbed X-ray energy were measured for detectors with different thicknesses of the top and bottom electrodes. The rate of quasiparticle trapping by the energy trap in the Ti/Nb bilayer was estimated. The main mechanisms of the formation of the passive electrode signal formation were considered and methods for its suppression were proposed.     

Response matrix of an extended range Bonner sphere spectrometer for the characterization of collimated neutron beams

Accelerator-based neutron beams are becoming popular tools for material testing, radiation hardness and soft errors studies. The characterization of these beams in terms of dosimetric and spectrometric quantities is a challenging task, mainly due to their wide energy interval (from thermal up to hundreds MeV) and, in certain facilities like VESUVIO @ ISIS (RAL, UK), to their small dimension (few cm in radius). Extended Range Bonner Sphere Spectrometers (ERBSS) would be a valuable tool, due to their wide energy range, good photon discrimination and possibility to choose among different central detectors according to the intensity, photon component and time structure of the field. Nevertheless, the non-uniform irradiation of the spheres could lead to important systematic errors. With the aim of bringing the advantages of ERBSS into the characterization of collimated beams, a dedicated study was performed using the VESUVIO spallation-based collimated beam at ISIS (Rutherford Appleton Laboratory, Oxford). Here a 3.21 cm radius collimated beam was characterized using a Dysprosium activation foil-based ERBSS whose response matrix was recalculated for this specific beam diameter. Besides the results of the experimental campaign, this paper presents the calculation of the response matrix and its dependence on the beam dimension.     

X射线散射对面密度测量结果影响的数值模拟研究

定性分析了X射线散射对面密度测量结果的影响,给出了面密度测量结果偏差的评估表达式。利用蒙特卡罗方法数值模拟了不同照相布局、不同光源能量和不同材料类型情形下X射线散射对测量结果的影响。模拟结果表明:在无防护窗情形下,被测物自身散射将导致测量结果偏小;在有防护窗情形下,前窗散射对测量结果的影响不大,后窗散射对测量结果的影响与接收介质离被测物的距离有关,具体表现为距离越小影响越大;在一定光子能量范围内,光源能量越低散射导致的测量偏差越大;被测物的原子序数和密度越大,散射导致的测量偏差越大。     

Autoholography and possibility of direct phase measurement in X-ray diffraction analysis

A method for direct experimental measurement of phases of scattered waves in X-ray diffraction analysis has been proposed. To determine these phases, an unconventional holographic exposure technique (hereinafter, “autoholography”) is used, wherein a beam scattering on an object completely identical to the one being investigated, but spatially shifted and rotated in a certain manner relative to the latter, is used as a reference beam. In principle, autoholography method does not require a very high coherence of the radiation beams used since the reference beam allows to compensate for its absence to a certain extent in this case. Therefore, X-ray radiation used for X-ray diffraction analysis is also perfectly suitable for the autoholography.     

9MeV电子直线加速器X射线测量

 高能工业CT采用9MeV电子加速器产生轫致辐射，利用高能X射线能够有效地穿透物质以及同物质对射线吸收和散射不同这一原理来检查物体内部缺陷或内部结构。加速器电子束的焦点、X射线的最高能量、X射线剂量及均匀性与工业CT成像的质量和速度密切相关；对探测器的电子线路部分进行的X射线屏蔽关系到探测器的使用寿命。X射线测量结果表明，所用9MeV电子直线加速器满足高能工业CT检测的要求。     

Control of parameters of micropinches formed in current-carrying plasma jet

The temporal evolution and spatial pattern of X-ray emission from a laser-induced vacuum discharge of moderate power has been investigated. It was found that micropinches in the initial stage of the cathode jet expansion into the vacuum ambient were formed. They generated a soft X-ray radiation and beams of accelerated electrons; therewith these phenomena occurred just when both amplitude of the discharge current and energy of the initiating laser pulse lied in the specified ranges of values. Parameters of the micropinch, namely, its position within the interelectrode gap and also, intensity of the X-ray radiation and beams of the accelerated electrons emitted from the micropinch are variable over a wide range of values through changes of energy of the laser pulse and/or amplitude of the discharge current.     

Optimization of the design for beamline with fast polarization switching elliptically polarized undulators

Fast switching of X‐ray polarization with a lock‐in amplifier is a good method for acquiring weak signals from background noise for X‐ray magnetic circular dichroism (XMCD) experiments. The usual way to obtain a beam with fast polarization switching is to use two series of elliptically polarized undulators (tandem twin EPUs). The two EPUs generate two individual beams. Each beam has a different polarization and is fast switched into the beamline. It is very important to ensure that the energy resolution, the flux and the spot size at the sample of the two beams are equal in XMCD experiments. However, it is difficult in beamline design because the distances from the two EPUs to the beamline optics are different and the beamline is not switchable. In this work, a beamline design without an entrance slit for fast polarization switching EPUs is discussed. The energy resolution of the two beams can be tuned to be equal by minor rotation of the optics in the monochromator. The flux of the two beams can be balanced through separation blades X, Y in the exit slit, and by adjusting the position of the X blades along the beam. The spot size of the two beams can be adjusted to be equal by shifting the sample as well.     

Simultaneous diffraction of two waves at a reflection volume hologram

Based on the theory of coupled waves the simultaneous diffraction of two waves at a plane dielectric reflection volume hologram is described. By analogy to the transmission volume grating the intensities of the output beams strongly depend on the phase shift between the incident waves and the phase shift of the grating with respect to the interference structure of the read-out waves. This gives the possibility of transferring the incident energy from one wave into the other and can be used for the modulation or deflection of the reconstructed beams. The separate determination of the different kinds of phase shifts by intensity or phase measurements is discussed.