共查询到18条相似文献,搜索用时 178 毫秒
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准直器是中子照相装置的关键组件之一.利用石墨为慢化剂.铋为γ过滤器。采用光阑直径、准直器长度、石墨塞长度可调以实现准直比和镉比的大幅度调节.钢结构水箱快门完成了SPRR—300准直系统设计。实验结果显示设计是合理的.成像质量达ASTM-86达二级以上.能满足不同成像技术和不同样品的中子照相需求。 相似文献
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利用不同材料的中子质量衰减系数不同而获取样品内部的结构潜像,属于吸收散射衬度成像;而相衬成像是基于中子的波动性,当中子波穿过样品时,由于样品对中子的折射,不同厚度、不同材质引入的相位差不同,从而导致波前畸变,畸变的波前在穿过样品后作为次波源互相干涉成像,从而获取样品内部结构潜像。研究工作通过数值模拟方法分析了中子相衬成像过程,并基于反应堆中子照相装置进行了不同条件下的多色热中子相衬成像实验。模拟与实验结果表明,在适当准直比条件下,铝材料边缘将出现明显的边缘增强效应,该效应与准直比、样品与转换屏之间的距离密切相关。 相似文献
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对于一台中子散射谱仪,中子导管对中子的传输性能很重要,文中利用Mcstas程序对中子小角散射谱仪中平行中子导管和锥形中子导管以及平行中子导管的几种准直长度对中子的传输性能进行了模拟计算,通过对样品台处束流轮廓和中子注量率的计算,可以看出,相对于锥形中子导管,平行中子导管为中子传输性能更优良的排列模式,平行中子导管模式下几种准直长度具有不同的中子的传输效率,设计时要兼顾准直度和注量率这两个因素。 相似文献
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本文综合考虑几何不锐度和探测系统固有不锐度的影响,把准直比、样品与转换屏间距离、转换屏和CCD(CMOS)相机分辨率等关键参数引入到系统脉冲响应函数,推导出更准确和全面的中子照相系统整体空间分辨率计算公式,探讨了公式中各参数与分辨的定量关系和影响规律。利用该公式对中国先进研究堆实时中子成像探测系统在不同准直比条件下的整体空间分辨率进行了计算与分析,讨论了如何优化调整各影响因素以提高中子照相装置的整体测试性能。为中子照相装置的优化设计以及确定特定样品的测试方案,提供了重要的理论依据。 相似文献
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中子照相的数值模拟在中子照相技术研究中有着重要的作用。介绍了MCNP程序在数值模拟中子照相中的应用,给出了样品的模拟图像结果,并利用MCNP模拟分析了散射中子对中子照相成像结果的影响,对以后的中子照相实验具有指导意义。 相似文献
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《等离子体科学和技术》2020,22(8):84004
The time-of-flight enhanced diagnostics(TOFED) neutron spectrometer has been installed in TOFED house, which is a newly-built neutron diagnostic lab outside the EAST experimental hall. The line of sight(LOS) of TOFED is defined by the collimator going through the 150 cm biological shielding wall, which can reduce background neutrons very effectively for the neutron spectral measurements. The Monte Carlo code MCNP5 is used in the simulations to characterize collimation effects and the radiation safety of the new house. The collimator makes neutron flux almost fully perpendicular to S1 detectors. In addition, the proportion of scattered neutrons in the LOS of the TOFED is obtained for the measured spectral data interpretation. The simulation results show that the TOFED house satisfies the requirement for the TOFED operations at EAST and gives a safe environment for personnel access during the EAST operation. 相似文献
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In relation to the establishment of thermal neutron radiography as a measurement method with high accuracy and reliability, this paper reviewed the present status on the development of high-frame-rate neutron radiography with a steady thermal neutron beam and its application to multiphase flow researches. This review included also the present progress on the quantification of neutron radiographic image at Kyoto University, i.e. (1) quantitative method to measure void fraction of two-phase flow with thermal neutron radiography (Σ-scaling method), (2) influence of scattered neutrons on void fraction measured by neutron radiography, (3) measurement error of neutrons in a low neutron flux field, (4) error in void fraction measurement due to low gray level, and (5) measurement error due to low imaging speed Moreover, a new experimental approach on a total macroscopic cross section for thermal neutrons measurement by neutron radiography was presented. This paper revealed neutron radiography to be a promising visualization and measurement method in thermal hydraulic research. 相似文献
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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. 相似文献
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Mohamed H. Hassan 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(15):2545-2549
Fast neutron radiography opened up a new range of possibilities to image extremely dense objects. The removal of the scattering effect is one of the most challenging problems in neutron imaging. Neutron scattering in fast neutron radiography did not receive much attention compared with X-ray and thermal neutron radiography. The purpose of this work is to investigate the behavior of the Point Scattered Function (PScF) as applied in fast neutron radiography.The PScF was calculated using MCNP as a spatial distribution of scattered neutrons over the detector surface for one emitting source element. Armament and explosives materials, namely, Rifle steel, brass, aluminum and trinitrotoluene (TNT) were simulated. Effect of various sample thickness and sample-to-detector distance were considered. Simulated sample geometries included a slab with varying thickness, a sphere with varying radii, and a cylinder with varying base radii. Different neutron sources, namely, Cf-252, DT as well as DD neutron sources were considered. Neutron beams with zero degree divergence angle; and beams with varying angles related to the normal to the source plane were simulated.Curve fitting of the obtained PScF, in the form of Gaussian function, were given to be used in future work using image restoration codes. Analytical representation of the height as well as the Full Width at Half Maximum (FWHM) of the obtained Gaussian functions eliminates the need to calculate the PScF for sample parameters that were not investigated in this study. 相似文献
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Maria Ines Silvani Gevaldo L. de Almeida Rosanne C.A.A. Furieri 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2007,263(1):253-257
The impact of the divergence of a thermal neutron beam and the scattered neutrons on the quality of tomographic images acquired by transmission have been evaluated by using a third generation tomographic system incorporating neutron collimators under several different arrangements. The system equipped with a gaseous position sensitive detector has been placed at the main channel outlet of the Argonauta Research Reactor in Instituto de Engenharia Nuclear (CNEN-Brazil) which furnishes a thermal neutron flux of 2.3 × 105 n cm−2 s−1. Experiments have then been conducted using test-objects with well-known inner structure and composition to assess the influence of the collimators arrangement on the quality of the acquired images. Both, beam divergence and scattering - expected to spoil the image quality - have been reduced by using properly positioned collimators between the neutron source and the object, and in the gap between the object and the detector, respectively. The shadow cast by this last collimator on the projections used to reconstruct the tomographic images has been eliminated by a proper software specifically written for this purpose. Improvement of the tomographic images has been observed, demonstrating the effectiveness of the proposed approach to improve their quality by using properly positioned collimators. 相似文献
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基于强流氘氚中子源科学装置HINEG设计了一套快中子照相准直屏蔽系统。采用中子输运设计与安全评价软件系统SuperMC和ENDF/B-Ⅶ.0数据库计算了准直中子束的中子能谱及注量率、γ射线能谱及注量率、直射中子注量率与γ射线注量率比值(φd/φγ)、直射与散射中子注量率比值(φd/φs)、准直束中子注量率的不均匀度等特性参数,并采用MCNP5程序进行了对比验证。研究了准直屏蔽系统的内衬材料、尺寸等对特性参数的影响规律,并通过优化获取了最优设计方案。计算结果显示,在同等计算条件下,SuperMC计算结果与MCNP计算结果相对偏差小于1%,准直屏蔽系统的φd/φγ为50.1,φd/φs为5.7,在Φ30 cm视野范围内的中子注量率为4.80×107 cm-2•s-1,其中直射中子注量率为4.09×107 cm-2•s-1,中子注量率不均匀度为5.8%,满足快中子照相对准直束特性参数的要求。 相似文献
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A study has been made of the spectra of cold neutrons inelastically scattered by benzene, diphenyl, and unirradiated and irradiated polyethylene. A beryllium filter was used to separate the cold neutron spectral line,and the energy of the scattered neutrons was analyzed by the time of flight method. The measurements were made at the sample temperature 20° C. The resulting data are compared with the results of optical studies on the spectra of the materials used.Translated from Atomnaya Énergiya, Vol. 14, No. 3, pp. 257–263, March, 1963 相似文献