堆用中子探测器校验装置设计

本文采用MCNP4c程序,对影响堆用中子探测器校验装置的各项参数进行计算,确定了装置慢化体厚度、引出孔径等一系列参数.对装置的屏蔽性能进行了计算,结果表明装置屏蔽性能满足标准要求.     

基于旋叶式被动静电探测方法的研究

对于贴地飞行的空中目标,一般都处于雷达的盲区,且由于地面的其它干扰不利于对目标特性信号的提取。空中运动目标带电量高且难以去除,为静电探测系统提供了可靠性和实用性。介绍了旋叶式静电探测系统的基本工作原理,分析了探测装置屏蔽参数的影响并对探测装置的屏蔽单元做出仿真,利用目标在探测器位置的场强变化提出了旋叶式静电探测感应电流的近似公式,通过仿真模拟实验验证了近似公式的正确性和实用性,对探测装置进行实验,进而验证了探测装置的可行性。     

Background of a “<Emphasis Type="Italic">dE + E</Emphasis>” phoswich detector

A method for estimating the γ-ray background of a phoswich detector of the “dE + E” type is discussed. The phoswich detector is composed of an outer thin detector and an inner total-absorption detector and is used for β-ray spectrometry. The calculated background of the phoswich detector with an area 40 cm² inside 5-cm-thick lead shielding is shown to be 0.095 ± 0.019 counts/s. The contribution of the high-energy background to the total level is 77%.     

A collimator for hot plasma x-ray diagnostics in ion sources

We present a collimator configuration for measuring energy resolved x-ray plasma volume bremsstrahlung emitted, e.g., by an ECRIS. Special attention we paid to shielding the detector against interfering Compton scattered radiation and wall bremsstrahlung stemming from the collimator entrance aperture. We estimate the efficiency for shielding of Compton scattered radiation at least attainable by this arrangement.     

Measurement of the high energy component of the x-ray spectra in the VENUS electron cyclotron resonance ion source

High performance electron cyclotron resonance (ECR) ion sources, such as VENUS (Versatile ECR for NUclear Science), produce large amounts of x-rays. By studying their energy spectra, conclusions can be drawn about the electron heating process and the electron confinement. In addition, the bremsstrahlung from the plasma chamber is partly absorbed by the cold mass of the superconducting magnet, adding an extra heat load to the cryostat. Germanium or NaI detectors are generally used for x-ray measurements. Due to the high x-ray flux from the source, the experimental setup to measure bremsstrahlung spectra from ECR ion sources is somewhat different from that for the traditional nuclear physics measurements these detectors are generally used for. In particular, the collimation and background shielding can be problematic. In this paper, we will discuss the experimental setup for such a measurement, the energy calibration and background reduction, the shielding of the detector, and collimation of the x-ray flux. We will present x-ray energy spectra and cryostat heating rates depending on various ion source parameters, such as confinement fields, minimum B-field, rf power, and heating frequency.     

Construction and testing of the instrument for neutron holographic study at the Budapest Research Reactor

Neutron scattering device dedicated to neutron holography experiments is described. The device is operating at a constant wavelength prepared by a double focusing monochromator. It is equipped by highly efficient shielding, proper collimator, Eulerian cradle, monitor detector, gamma-ray, and neutron detectors as well. Relevant software serves as control for the measurement and data collection. The harmonized application of the components enumerated above makes our device extremely efficient and unparalleled. Two atomic resolution neutron holographic experiments carried out illustrate the efficiency and power of the instrument.     

An upgraded x-ray spectroscopy diagnostic on MST

An upgraded x-ray spectroscopy diagnostic is used to measure the distribution of fast electrons in MST and to determine Z(eff) and the particle diffusion coefficient D(r). A radial array of 12 CdZnTe hard-x-ray detectors measures 10-150 keV Bremsstrahlung from fast electrons, a signature of reduced stochasticity and improved confinement in the plasma. A new Si soft-x-ray detector measures 2-10 keV Bremsstrahlung from thermal and fast electrons. The shaped output pulses from both detector types are digitized and the resulting waveforms are fit with Gaussians to resolve pileup and provide good time and energy resolution. Lead apertures prevent detector saturation and provide a well-known etendue, while lead shielding prevents pickup from stray x-rays. New Be vacuum windows transmit >2?keV x-rays, and additional Al and Be filters are sometimes used to reduce low energy flux for better resolution at higher energies. Measured spectra are compared to those predicted by the Fokker-Planck code CQL3D to deduce Z(eff) and D(r).     

Measurements of the fast electron bremsstrahlung emission during electron cyclotron resonance heating in the HL-2A tokamak

A fast electron bremsstrahlung (FEB) diagnostic technique based on cadmium telluride (CdTe) detector has been developed recently in the HL-2A tokamak for measurements of the temporal evolution of FEB emission in the energy range of 10-200 keV. With a perpendicular viewing into the plasma on the equatorial plane, the hard x-ray spectra with eight different energy channels are measured. The discrimination of the spectra is implemented by an accurate spectrometry. The system also makes use of fast digitization and software signal processing technology. An ambient environment of neutrons, gammas, and magnetic disturbance requires careful shielding. During electron cyclotron resonance heating, the generation of fast electrons and the oscillations of electron fishbone (e-fishbone) have been found. Using the FEB measurement system, it has been experimentally identified that the mode strongly correlates with the electron cyclotron resonance heating produced fast electrons with 30-70 keV.     

A compact, multiangle electron spectrometer for ultraintense laser-plasma interaction experiments

Experiments on the multiterawatt (MTW) laser at the Laboratory for Laser Energetics will study the effect of the focal-spot shape on the forward acceleration and collimation of electrons. A compact electron spectrometer has been developed to record the energy spectra of electrons ejected in the interaction of the laser at multiple angular locations simultaneously. The modular system with replaceable magnets provides an adjustable energy band, currently 0.2-6 MeV. The detector is an array of imaging plates. The device is designed to operate in the high-noise environment (bremsstrahlung and Compton x rays, gamma rays, and scattered electrons), while being compact enough to fit in the 30 cm radius MTW target chamber. The detector geometry and shielding were optimized with the particle/radiation transport code GEANT4. Calibration was performed with beta sources. The required dynamic range, sensitivity, and resolution were confirmed with initial MTW experimental data.     

Design criteria of the bolometer diagnostic for steady-state operation of the W7-X stellarator

A bolometric diagnostic system with features necessary for steady-state operation in the superconducting stellarator W7-X was designed. During a pulse length of 1800 s with an ECRH (electron cyclotron resonance heating) power of 10 MW, the components suffer not only from a large thermal load but also from stray radiation of the nonabsorbed isotropic microwaves. This paper gives an overview of the technical problems encountered during the design work and the solutions to individual problems to meet the special requirements in W7-X, e.g., component thermal protection, detector offset thermal drift suppression, as well as a microwave shielding technique.     

Optimization of energy window for gamma densitometer based backscatter method in oil industry

In this paper, we describe the results of various calculations performed for a design of the interference gauges that use the gamma-ray backscattering method with different scatter windows. The Pb barrier as shielding placed between 4 mCi ¹³⁷Cs sealed radioactive source and a NaI (Tl) scintillation detector (1 inch in diameter—2 inch in height). Upon interaction with the material the scattered radiation, due to Compton process, was measured by NaI(Tl) detector. Using Compton scattered photons and review of the scattered photons in substance, by measuring of gamma-ray photons distributed, the density of materials can be obtained accurately. The results present for different scatter energy windows which 39–273 and 39–390 keV scatter windows have the best ΔX, STD and signal to noise.     

保护气体对高氮钢焊接熔滴过渡模式和气孔缺陷的影响研究

采用激光-电弧复合热源对8 mm厚的高氮钢板进行焊接试验,研究不同保护气体组成对焊缝形貌、熔滴过渡特征和气孔缺陷的影响。结果表明,采用纯氩做保护气体时,熔滴过渡模式以射流过渡为主,并伴有少量排斥过渡;保护气体成分为Ar+N₂混合气体时,熔滴过渡模式为短路过渡;保护气体成分为Ar+N₂+O₂混合气体时,熔滴过渡模式为射流过渡。保护气体的组成对焊缝气孔缺陷也存在一定的影响,保护气体为纯氩时,焊缝气孔率最大,其值为2.52%;保护气体为90% Ar+10% N₂时,气孔率最低,仅为0.16%;Ar+N₂中添加1%的O₂后,气孔率略有升高,但与纯氩时相比,气孔率仍下降明显。采用Ar+N₂+O₂三元混合气作为保护气体时,能够有效抑制焊缝内气孔数量,同时可以改善熔滴过渡模式,提高焊接过程稳定性。     

微波电路结构设计中的电磁兼容性

指出微波电路电磁兼容性设计的重要性,对电磁干扰机理进行了具体分析;通过具体事例,阐述微波电路结构设计过程中的注意事项和采取的措施,以及所能达到的电磁兼容的效果;介绍一些常用屏蔽材料的特点和选用时的注意事项,详细给出了一些屏蔽材料在结构设计中的具体运用.     

低场核磁共振射频场屏蔽效能的计算与研究

采用有限元方法计算了圆柱形屏蔽体的屏蔽效能和屏蔽体对螺线管内部磁场的影响，得到屏蔽效能和螺线管内部磁场随屏蔽体尺寸变化的曲线。并用Matlab对球形屏蔽体的屏蔽效能进行了计算，二者基本一致。结果表明，屏蔽效能随圆柱体半径的增加而缓慢增加，随圆柱体厚度的增加而迅速增加，但是当厚度大于1．5mm以后，几乎保持不变。     

6063铝合金型材插箱的设计与验证

为了实现插箱的简单制造,提升插箱的屏蔽效能,插箱采用2种6063铝合金型材,铣切后拼装而成。文中介绍了型材和插箱的设计,给出了型材强度和化学成分检测结果,着重介绍了插箱的电磁屏蔽影响因素,实测和比对了2种插箱的屏蔽效能。结果表明型材插箱的屏蔽效能基本达到了3级要求。型材插箱继承了原有企标插箱的安装结构要素,实现了升级换代,能满足标准化、模块化、系列化的要求。     

微域保护气对金属微滴喷射过程影响机制研究

金属微滴喷射3D打印过程需在低氧环境(氧含量低于50 ppm)下进行,现有设备常采用带除氧系统的密闭手套箱来维持低氧环境,但因其空间受限,操作不便,很难适应该技术向应用领域拓展。在微滴喷射出口处构建微域低氧环境,既可保护微滴喷射时不被氧化,又能扩大该技术应用范围并提高操作灵活性,是促进金属微滴喷射3D打印技术工程化应用的一个关键。但施加保护气会产生气流扰动,不利于微滴稳定喷射和精确沉积。为解决现有微域保护技术不足,设计开发一种新型环形射流微域保护装置,结合微域保护下的锡合金微滴喷射试验与微域气流流场模拟,揭示氧化和气流动力学对微滴喷射过程作用机制。研究发现当保护气供应不足时,金属射流由于氧化表面张力降低、黏度增大(即Oh数增大),会断裂为带锥形拖尾的单颗熔滴;当保护气供应过大时,气流在射流根部产生二次涡,使射流二次断裂,并生成多颗熔滴。最终在合适参数下打印出较长沉积距离熔合良好、堆叠整齐的锡合金立柱和尺寸均匀、落点准确的凸点阵列,证实环形射流微域保护装置的有效性。研究成果可为金属微滴喷射3D打印技术的推广应用提供关键技术支持和理论基础。     

Fabrication and measurement of the performance of a printed EMI shielding mesh filter on PET film

In this paper, Electromagnetic interference (EMI) shielding mesh filter films are fabricated using the screen printing method. An EMI shielding mesh filter requires fine line patterns under 30 μm, therefore, the screen masks with fine-line screen mesh, as well as suitable ink composed of fine metal particles are required. Moreover, because the printed EMI shielding filter has to be fabricated on a PET film, the ink should be sintered at a temperature below 150°C not to deform the film. For the purposes of this study, a screen mesh with a mask of 20 μm line, and ink made nano silver paste with a sintering temperature of 140°oC, which could guarantee fine-line patterning on the PET, were used. The ink had a viscosity of 90,000–12,000 cps and metal content of 85% in weight. The printed EMI shielding mesh had a line width of about 24 μm and a thickness of about 2.5 μm. The measured surface resistance was 0.5∼0.7 ω/□, offering good electrical performance as an EMI mesh. A simple measurement system was used to evaluate the electrical shielding performance of the printed EMI shielding mesh. A comparison of the printed EMI shielding mesh with pure film without mesh and copper sheet revealed that the printed EMI shielding mesh is indeed capable of providing good electrical performance.     

Computer simulation of the vertex detector of the CLAS12 facility

The CLAS International Collaboration is preparing the CLAS detector for updating in 2013, because the energy of the CEBAF electron accelerator will be raised to 12 GeV. The new facility will be called the CLAS 12. An SVT vertex detector will be one of new units of the CLAS 12. This paper presents the results of computer simulation of the vertex detector using the GEANT4 package. Estimates of the detector counting rate and the expected accuracy of determining coordinates and momenta are obtained. The dependence of the efficiency of operation of the vertex detector on different external conditions is studied.     

地面雷达屏蔽导热机箱设计

同时满足屏蔽、密封和导热三个指标,是电子设备机箱设计的一大难题。三者之间往往会产生矛盾,尤其是屏蔽和密封、导热和密封之间。解决这些矛盾,并进行优化处理,是电磁屏蔽机箱设计中的关键问题。介绍了某型号雷达屏蔽导热机箱的设计思路,主要针对屏蔽、密封和导热三个指标进行了详细考量,并进行结构设计优化,使其满足各项指标要求。最后通过仿真和具体试验验证了结构设计的合理性,该机箱的设计成功对同类机箱的设计提供了一种有效的解决思路。     

铝合金材料中微量金属对电磁屏蔽的影响

根据某通讯产品屏蔽单元盒对高频电性能技术指标的试验,研究、分析了铝合金材料中所含的微量金属元素对电磁屏蔽的影响。结果表明,铝合金材料中含铜量的多少对电磁屏蔽的效果影响最大,四种铝合金材料的电磁屏蔽效果好差顺序为：LY12、ZL105、LF2、LF21。