ZEMAX模拟中子相衬成像研究

相衬成像是中子成像领域内的前沿技术,它的成像机理基于中子束的波动性.进行中子相衬成像研究,有必要对这一过程进行仿真计算,但目前尚无模拟中子波动行为的程序出现,本文探讨了利用光学仿真软件ZEMAX对热中子相衬成像过程进行模拟的可行性,介绍了具体的模拟过程和结果,研究了不同的物源距离、物屏距离、点中子源尺寸以及样品尺寸对最终成像结果的影响.仿真结果和理论较为接近,这表明使用该软件模拟中子相衬成像是具有一定的可行性的.     

SPRR-300反应堆中子照相装置准直系统的研制

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。     

热中子相衬成像技术的初步探索

介绍了中子相衬成像原理及其特点,对中子相衬成像中的同轴轮廓法进行了重点论述,讨论了相衬成像的条件及实验技术,简介了SPRR-300拟进行的相衬成像技术研究方法。     

光学相衬成像技术在中子照相中的应用

介绍了中子相衬成像原理及其特点,对中子相衬成像中的同轴轮廓法进行了重点论述,讨论了相衬成像的条件及实验技术,简介了SPRR-300拟进行的相衬成像技术研究方法.     

中子全息术中孪生像消除模拟

在中子全息照相的记录过程中,参考波与物波近似沿同一方向传播至全息屏,并在重建时形成不可分离的原像和共轭像,在特定波长下,两者可能干涉相消,产生孪生像现象。受制于中子探测效率和单色器能量分辨率,目前中子全息成像中孪生像的消除技术尚未得到系统的理论和实验研究。本文采用数值方法对已成功应用于X射线全息孪生像消除的两种全息记录及重建技术展开模拟,讨论基于研究堆的中子全息成像技术实现孪生像消除的可行性,并从实验效率和重建质量出发,对单色器分辨率、波数记录间隔、波数记录范围等关键参数进行定量分析和优化选取。结果表明,在研究堆中子源相对较低的单色器分辨率和较窄的可选能区条件下,通过记录2~4个不同能点的全息图即可获取较理想的中子全息重建结果。     

中子学积分实验前级准直系统的设计

积分实验是检验评价中子核数据可靠性和精准度的重要手段,效应/本底比是衡量积分实验数据品质的重要参数。为了获得更高的效应/本底比,对中国原子能科学研究院积分实验使用的前级准直系统进行了设计,该系统主要由前级准直器和阴影锥组成。利用MCNP-4C程序对不同条件下的本底谱进行了模拟,结果显示,加上前级准直系统之后,效应/本底比有非常明显的改善。     

近场条件下X射线位相衬度成像方法及其模拟

近场条件下的类同轴法位相衬度成像具有边缘突出效应，其强度分布与相位分布的拉普拉斯算子有直接关系。在近场成像过程中，成像距离决定了成像质量的好坏。本工作通过一维模拟几种具有特定几何构型样品的菲涅耳衍射图样，得到近场条件下最适宜的成像距离，并通过二维模拟验证了此结论。      

中国先进研究堆间接中子照相方法的初步研究

中国先进研究堆（CARR）的建成为我国间接中子照相技术的发展及应用提供了重要的实验平台。本文基于CARR开展了间接中子照相方法的初步研究。首先利用蒙特卡罗方法计算分析了基于CARR开展间接中子照相测量的条件;然后根据这些条件,通过解析计算确定了间接成像两次曝光过程的实验参数;最后利用CARR的热中子孔道,以核燃料元件模拟件为样品进行了间接中子照相实验,并研究了间接中子照相成像数据的处理及分析方法。     

热中子层析照相的仿真技术探索研究

热中子照相技术在检测含氢材料、重金属样品等方面是X射线等其它无损检测技术的有益补充,热中子层析技术研究在国内尚是空白,实验研究条件欠缺且代价高昂,通过仿真研究再过渡到实验研究,将有效降低研究成本,提高研究效率.文章根据中子层析照相基本原理,设计模拟样品,采用MCNP仿真计算的方法获取了样品中子投影图像,利用C++Builedr研发中子层析数据获取程序和反投影滤波算法层析重建程序,重建了样品二维断面图像,样品二维断面图像与实际样品一致,证明了所采用的仿真研究流程合理可行,为中子层析照相技术的深入研究奠定了基础.     

中子照相系统整体空间分辨率计算与分析

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。     

On neutron phase contrast imaging

Improving the spatial resolution conditions in a neutron imaging experiment enables the detection of phase-based contrast in addition to attenuation contrast. Addressing not only the amplitude but also the phase of radiation in an imaging experiment allows for obtaining additional information about the sample. The so-called neutron phase contrast method improves imaging results mainly by edge enhancement which increases the visibility of sub-resolution structures and of low attenuation contrast materials. These effects have been found at high intensity synchrotron X-ray sources before and have been applied to neutron imaging recently. However, the excellent coherence conditions and spatial resolution of imaging instruments at state-of-the-art synchrotron sources can hardly be compared to neutron imaging. Nevertheless, edge enhancement has been found for increased resolution (coherence) conditions in neutron experiments as well. As for X-ray instruments the effects have been explained by diffraction, although typical interference fringes have never been recorded. In contrast this article will explain the effects measured with neutron radiation by refraction and total reflection. Both of these do not require high spatial coherence. Therefore improved resolution and not increased coherence will be considered as precondition to obtain the reported signals and to understand the results. Considerations concerning relaxed collimation requirements for improved detector resolutions will be presented as a consequence.     

快中子照相的实验研究

快中子照相是一种优良的无损检测技术,它有着X射线、热中子照相等所不具有的独特优势。本文介绍了作者分别采用^241Am-Be同位素中子源和中子发生器进行的快中子照相研究,并利用自制的Gd2O2S：Tb快中子转换发光屏进行探测,成功实现照相。     

14 MeV快中子照相用光纤转换屏研究

快中子照相技术因其超强的样品透视能力而成为射线无损检测技术近年来研究的热点,转换屏是中子照相装置的关键部件。光纤转换屏是一种新型的快中子照相转换屏,较大程度兼顾了光纤阵列的高探测效率和荧光屏的高成像质量,具有很好的应用前景。本文以D-T加速器为中子源,用ZnS和环氧树脂以及光纤研制了快中子照相光纤转换屏,耦合科学级CCD数字成像系统,进行了快中子数字照相技术研究,获取了不同光纤排列方式的光纤转换屏积分曝光图像,同时测量了快中子荧光屏和塑料闪烁体等其他快中子照相用转换屏的发光效率,实验结果表明,光纤转换屏的发光效率高于其他类型转换屏的。     

Point Scattered Function (PScF) for fast neutron radiography

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.     

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。     

基于中子IP板的核燃料元件间接中子CT实验方法研究

中子照相作为一种无损检测技术是分析和确定核燃料元件缺陷的重要手段。中国原子能科学研究院中子照相团队依托中国先进研究堆（CARR）中子照相测试平台,搭建了核燃料元件间接中子CT装置,并开展核燃料元件模拟件的间接三维中子成像技术研究。本文首先采用蒙特卡罗模拟方法优化确定了样品环境转移屏蔽容器的关键参数并研制出屏蔽容器,并基于该装置开展了核燃料元件模拟件的间接中子CT照相实验,从获得的三维实验数据可观测到尺寸约0.35 mm模拟芯块缺陷。实验结果表明,该装置可满足核燃料元件的间接中子CT实验检测。同时初步研究了基于IP板的间接中子成像数据处理的制约因素和方法,为后续进一步利用金属转换屏替代中子IP板等技术,真正实现乏燃料元件无损检测应用提供实验指导。     

冷中子差分成像模拟研究

冷中子照相利用穿透样品的中子和荧光屏~6Li反应产生的α带电粒子与荧光材料发光,从而在探测器上记录光强度的分布.本文简单介绍了冷中子照相的特点,给出了铍与钛金属宏观总截面随能量的变化,设计特定的样品采用MCNP模拟不同能量下的中子图像,中子图像显现Bragg吸收限上下两幅图像的对比度差异,采用差分成像对两幅中子图像进行处理,凸现了冷中子照相的优点.     

Television Imaging System for Fast Neutron Radiography Using Baby Cyclotron

Abstract

A television imaging system for fast neutron radiography (FNR-TV) developed using the fast neutron source reactor YAYOI was applied to the baby-cyclotron based fast neutron source to get images of thick objects quickly. In the system the same technique as a current television imaging system of thermal neutron radiography was applied, while the luminescent converter was used to detect fast neutrons.

Using the CR39 track etch method it took about 7 h to get an image, while the FNR-TV only 20 s enough for taking the same object. However the FNR-TV imaging result of the simulation model of a large explosive device for the space launch vehicle of H-2 type was not so good as the image taken with the CR39 track etch method. The reason was that the luminescence intensity of the FNR-TV converter was a quarter of that in the YAYOI.     

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.