Simulation and optimization for a 30-MeV electron accelerator driven neutron source

A neutron source driven by electron accelerator is proposed in Shanghai Institute of Applied Physics (SINAP). The facility is planned for the study of nuclear data in Thorium-Uranium cycling system, and for material research. A detailed simulation of the neutron source is performed for the program to get the neutron generation maximum economically. Several parameters of the facility, which affect the neutron yield and the neutron escape from outer surface of the target, are analyzed respectively. Besides, the yielding neutron spectrum and the escaping neutron angular distribution are calculated and discussed.     

Optimization study of some neutron imaging parameters in a reactor based neutron radiography facility

Neutron imaging technique can be used as a means of material Non-Destructive testing. One of common neutron sources for neutron radiography is nuclear research reactor. In this work, several neutron imaging parameters such as aperture distance and the radiography plane location from the neutron source as well as the aperture diameter have been computationally optimized to deliver a proposed neutron beam. According to the results, the aperture diameter of 3.5–4 cm which was located at 55–85 cm from the outer layer of reactor core and the position of image plane at 300–400 cm fulfills delivering of the suitable neutron flux and other required conditions. W, Fe and Pb walls with an identified length formed the convergent-divergent collimator and shielded the neutron and gamma out of beam path. Bi and Fluental filters with an optimal dimension were used to efficiently improve the neutron beam profile at a sample position.     

用活化法测量自成靶陶瓷中子管的中子发生率

以自成靶陶瓷中子管内Ｄ、Ｔ离子束流高斯型分布为依据，建立了中子管中子发生率与中子场中某一点通量密度之间的理论联系，采用活化法间接测量得φ６０ｍｍ自成靶陶瓷中子管的中子发生率为２．２×１０＾８／ｓ。     

中子发生器产额的测量

用铁片活化法和长计数管测量中子发生器的中子产额，给出了测量方法和结果。     

MgO single-crystal as an efficient thermal neutron filter

A formula is given which, for neutron energies in the range 10⁻⁴ < E < 10 eV, permits calculation of the nuclear capture, thermal diffuse and Bragg scattering cross-sections as a function of magnesium oxide (MgO) temperature and crystal parameters. Computer program has been developed to calculate the total neutron cross-section and transmission through mono-crystalline MgO. The calculated neutron transmission and effective attenuation coefficient values for MgO-single crystal at different temperatures are compared with measured ones. An overall agreement is indicated between the formula fits and experimental data. A feasibility study for the use of MgO-single crystal is discussed in terms of the optimum MgO-single crystal thickness, mosaic spread, temperature and cutting plane for efficient transmission of thermal-reactor neutrons, and also for rejection of the accompanying fast neutrons and gamma rays.     

散裂中子源靶站和中子散射谱仪的概念设计

本文介绍了可应用于多学科应用的散裂中子源(CSNS)靶站和中子散射谱仪概念设计的进展。CSNS靶站将由重水冷却多片钨靶,铍/铁反射体和铁/重混凝土生物屏蔽体组成。采用三个WING型慢化器:水(室温),液体甲烷(100K)和液体氢(20K),设有18个水平中子孔道。MonteCarlo模拟显示优化的靶截面高宽比为1:2.5左右。额定的100kW核功率的质子束轰击后,慢化器处钨靶溢出的脉冲中子通量约为2.4×1016cm?2·s?1。有限元方法计算表明,钨靶体内的总发热量是47kJ/s。即使使用截面较小的钨靶,在通常的水冷速率下,靶体温度也仅略高于90°C。靶体的热应力形变最大不超过0.2mm。根据经济实用原则选择建造粉末衍射仪、小角散射仪、反射仪及直接几何非弹性散射仪等四类有代表性的中子散射谱仪,就能覆盖>80%的中子散射研究领域。     

Modelling effects on axial neutron flux in a Tokamak device

Using Monte Carlo N-Particle (MCNP5), three different Tokamak models using different geometries were simulated, maintaining some basic parameters from the ITER design. The neutron flux and the reaction rates were obtained over different volumes: FW, divertor and along the different device walls. The three geometries were compared under the same conditions. The results showed the behaviour of the neutron flux spectra along the different walls, as well as, the most suitable model taking in consideration the different analyses and the final purpose of adding a transmutation layer. Finally, the chosen geometry will be used to analyse the burnup, buildup, decay, and processing of material under irradiation.     

Sensitivity of a new-developed neutron detector

We develop a kind of neutron detector, which consists of a polyethylene thin film and two PIN semiconductors connected face-to-face. The detector is insensitive to γ-rays. Its sensitivity to neutron has been calculated with MCNP program and calibrated by experiments, and the results indicate that the neutron sensitivity of the compensation detector will vary with polyethylene convel‘ter. The compensation PIN detector can be employed to measure pulse neutron in neutron and gamma mixture radiation field.     

固体径迹探测器测量束流装置内的中子通量密度

在微型反应堆零功率装置上搭建了硼中子俘获治疗拟采用的热中子束流装置。利用固体径迹探测器(SSNTD)测量了束流装置中心轴线上不同位置处的中子通量密度。结果显示,在束流装置入口处中子通量密度为5.39×107cm–2·s–1时,出口处热中子通量密度为5.63×104cm–2·s–1,热中子通量密度衰减到入口处的1/957。而利用热释光(TLD)方法和MCNP/4B程序测量和计算结果分别为1/1032和1/972。     

On the neutron diffraction in crystals in the field of a standing sound wave

The diffraction of neutrons is considered in crystals under the influence of a standing sound wave. The scattering probability is calculated for the elastic neutron-crystal interaction, whereas the neutron-standing sound wave interaction can be either elastic and inelastic. The possibility of short-wave (high-energy) neutrons diffraction is illustrated. It is shown that the Debye-Waller factor can be changed and tuned. The analysis of conservation laws are adduced both for thermal and short-wave neutrons. The formation of a “sublattice” is shown in the process of neutrons elastic diffraction with respect to standing sound wave. The analogous to the Kapitza-Dirac effect is considered for neutrons.The problem is solved within the frame of non-stationary S-matrix theory, where the neutron-phonon interaction is described by the Fermi pseudopotential, which is considered as a perturbation.     

On the neutron diffraction in a crystal in the field of a standing laser wave

The possibility of high-energy neutron diffraction in a crystal is shown by applying the solution of time-dependent Schrödinger equation for a neutron in the field of a standing laser wave. The scattering picture is examined within the framework of non-stationary S-matrix theory, where the neutron-laser field interaction is considered exactly and the neutron-crystal interaction is considered as a perturbation described by Fermi pseudopotential (Farri representation).The neutron-crystal interaction is elastic, and the neutron-laser field interaction has both inelastic and elastic behaviors which results in the observation of an analogous to the Kapitza-Dirac effect for neutrons. The neutron scattering probability is calculated and the analysis of the results are adduced. Both inelastic and elastic diffraction conditions are obtained and the formation of a “sublattice” is illustrated in the process of neutron-photon-phonon elastic interaction.     

快中子转换屏发光性能研究

以中子转换屏发光机理建立数学模型,计算了LiF-ZnS中子转换屏的各项参数对成像性能的影响。用不同种类荧光粉制备了多块不同厚度和材料成分的快中子转换屏进行性能测试,实验结果显示,14 MeV快中子转换屏最佳厚度为3 mm左右,ZnS和粘合剂的最佳重量比为1:1–2:1。对快中子转换屏和塑料闪烁体等中子探测屏的性能进行了实验测试和对比,给出了各种探测屏的性能差异和适用范围。     

中子反射谱仪前端导管优化

基于两种中子反射谱仪设计(A:前端为8.0 m垂直聚焦导管,入口200mm,出口40 mm;B:前端为1.6+3.4m水平偏转垂直聚焦导管,入口100mm,出口50mm),对其前端偏转/聚焦导管进行了中子束模拟,结果表明:1)在特征波长为0.4 nm的冷中子导管末端,没有必要再次偏转束流以减低本底;2)与建议方案相比,概念设计中的注量下降了52.8%,而水平方向发散度增大了24.1%,垂直方向发散度减小60.7%;3)聚焦导管长度应不低于6.0 m,导管聚焦超镜m值在2.0-2.5最佳,两侧超镜m值对束流几乎无影响,使用中子束高度应不低于150mm可达到较好的注量率和发散度.     

中子场空间分布特性研究

采用Monte-Carlo方法,以高斯聚变中子谱和麦克斯韦裂变中子谱为源谱,进行了中子在大气中输运的理论模拟,给出了不同源高度,空问不同位置处的中子注量、能谱和吸收剂量,并总结了中子场的空问分布特性。     

Supermirror neutron guide system for neutron resonance spin echo spectrometers at a pulsed neutron source

A neutron guide system for neutron resonance spin echo spectrometers has been constructed at BL06 of the Japan Proton Accelerator Research Complex, Materials and Life Science Experimental Facility. The spectrometers consist of two types of neutron spin echo instruments, a modulated intensity by zero effort instrument (MIEZE) and a neutron resonance spin echo instrument (NRSE), to cover a wide energy range for various sample environments. A neutron beam from the moderator is deflected by supermirror neutron guides, split, and separately guided into the MIEZE and NRSE. The characteristic wavelengths of the neutron guide tube for the MIEZE and NRSE are 2.9 and 4.9 Å, respectively. The cross sections of the exit of the MIEZE and NRSE guides are 15 mm × 50 mm and 30 mm × 50 mm, respectively. The neutronics and shielding design were optimized by using the heavy ion transport code system (PHITS), and the absolute average neutron fluxes at the exits of the MIEZE and NRSE guides are estimated to be 2.7 × 10⁸ and 6.9 × 10⁸ n/cm²/s/MW, respectively. The measured fluxes of the MIEZE and NRSE neutron guides are 0.56 and 0.95 times the calculated values, respectively.     

中子残余应力谱仪静态屏蔽体表面辐射剂量率初算

中子残余应力谱仪静态屏蔽体主要用于对谱仪装置的附加闸门、中子导管等组件的辐射剂量的屏蔽,使装置操作人员可以安全地在装置周围活动。通过MCNP5程序对谱仪装置静态屏蔽体的屏蔽能力进行了计算,可为该方案的改进、优化提供依据,以便最终制造出满足辐射剂量要求的屏蔽体。     

微型堆辐照座内快中子通量谱的测定

用Ａｌ，Ｆｅ，Ｉｎ和Ｎｉ作探测片，用阈探测片活化法测定了中国原子能科学研究院微型堆内，外辐照孔道的快中子能量。用平均截面法求得内外辐照孔道的快中子与热中子能量比分别为０．１９８和０．０７７，用有效阈能法计算了不同能量区间的快中子通量，同时也对四个内辐照等之间及内、外辐照管内径向和轴向快中子通量的不均匀度进行了测定。     

利用中子散射研究生物材料

中子散射是一种研究生物大分子结构及动力学运动规律的重要手段.通过测量散射中子的强度函数可以得到生物大分子的体积、质量、形状、回转半径、生物大分子中的原子成分,特定原子所处的位置及分布,生物大分子动力学运动的信息等.测量中子在生物样品上的动量和能量转移,可以得到动力学结构因子.结合理论模型分析计算可以得到生物大分子内原子、原子团快速运动和生物大分子慢的集体运动的信息,提取生物大分子中原子的涨落行为,生物分子构象变化及生物大分子材料的柔性等信息.中子散射能识别出生物物质中轻的元素及同位素.和X射线方法相比,中子散射法对生物材料的损伤较小.     

中子衍射残余应力分析技术及其应用

中子衍射方法可以用来测量材料内部的三维残余应力分布,是一种重要的无损检测分析手段.本文概述了中子衍射残余应力分析的基本原理、特点和发展现状,并简要介绍了其在工程和材料科学领域的应用情况与前景.