中子活化分析在环境研究中的应用

一 引言 活化分析是重要的核分析技术之一,它可分为中子活化分析、带电粒子活化分析和γ射线活化分析。中子活化分析技术已有50多年的历史,应用非常广泛,其分析基础是对活化了的同位素进行放射性测量,这些同位素是直接由待测元素的核产生的。中子活化分析具有灵敏度高,选择性强、准确度高,并能在大浓度范围内同时测定大量元素。 中子活化分析目前主要应用在生物学、地质学和环境科学,此外,在金属和半导体、考古以及刑事侦察等方面亦有应用。在中子活化分析中,热中子活化法应用较多,一方面     

中子活化分析参量化的进一步研究——Ⅰ.裂变干扰的参量法校正

112个活化分析感兴趣的(n,γ)反应k_0值的建立,已经使得63种元素的参量法堆中子活化测定成为可能。然而,为了实现堆中子活化分析的全面参量化,尚需进一步解决几个问题。作者对实现裂变干扰和阈反应干扰的参量化修正,以及“远”、“近”测量几何效率的参量化归一提出一些新的建议。 本工作基于~(235)U(n,f)反应在热中子能区的截面服从1/v定律且具有小的Q_0(I_0/σ_0)值,首次建议了“组合核常数”Ik_0,从而实现了堆中子活化分析中裂变干扰的参量法校正。在我院3座反应堆的6个照射孔道上测定了8个主要裂变干扰反应的Ik_0值。这些Ik_0值的堆中子谱无关性质。证实了本法的可靠性。     

INIS数据库核分析技术的文献检索

研究了INIS数据库中核分析技术(例如中子活化分析(NAA)、X射线荧光分析(XRF)、质子诱导X射线发射分析(PJXF))的文献检索的适用性。从1976年到1988年7月,数据库收集储存了约9700个NAA及其它形式的活化分析文件,约3500个XRE文献和1200个PIXE文     

同位素中子源活化瞬发分析装置

一、基本原理自六十年代中期以来,中子活化瞬发γ射线元素分析技术(PNAA)得到人们广泛重视。与通常的中子活化分析(NAA)技术相比,它分析的是样品中的主要成分,若用同位素中子源,还可进行实时在线连续测定及现场分析。PNAA技术是用热中子与待测元素发生中子俘获反应,处于激发态的产物核在瞬间     

大样品中子活化分析的理论依据和误差修正

中子活化分析(NAA)是最重要的核分析技术之一。目前,国内和国际上绝大多数NAA实验室只能对小样品(mg～g或μL～mL)进行分析。本工作概要介绍大样品中子活化分析的原理,重点介绍了由于体积增大而带来的中子注量率自屏蔽、γ射线自吸收等修正因子的算法,以及对样品不均匀性的修正方法。     

快中子活化分析

活化分析作为核技术的一种应用,正在成为日益推广应用的一种新的分析技术。根据照射粒子(即活化粒子)的种类不同,可分为中子活化分析、带电粒子活化分析和γ光子活化分析。在中子活化分析中,根据中子能量的不同,一般又分为热中子活化分析和快中子活化分析。     

第一次活化分析会议简讯

在全国科学大会精神鼓舞下,我国第一次活化分析会议于1978年7月13月～20日在北京召开。参加这次会议的有来自全国各有关部门和地区的四十八个单位,一百多名代表。提交大会的八十多篇成果报告中,包括反应堆中子活化分析、14MeV 中子活化分析、同位素中子源活化分析、带电粒子活化分析、质子激发 X 荧光分析、瞬发γ和带电粒子核反应分析以及其它核分析方法。此外,还有七篇关于活化分析中几个不同领域的评述文章和三篇关于活     

微堆超热中子活化分析在地学样品测定中的应用

微型中子源反应堆(简称微堆)是以高浓铀(235 U)作燃料的轻水欠慢化型反应堆,辐照孔道内存在有较大份额的超热中子和快中子,适合进行超热中子活化分析(ENAA)的实验研究。地质样品成分复杂,在用普通的中子活化分析时,基体元素影响了部分元素的准确测定。为降低基体成分的本底干扰、改善目标元素的测量精密度和检出限,可采用超热中子活化分析的方法。本文利用微堆上安装的屏蔽材料为镉的超热中子辐照孔道,测定了元素周期表中67种元素的约130个核素的镉比,讨论了在超热中子活化分析中某些元素的有利因子及铀裂变和(n,p)反应的干扰情况,验证了微堆ENAA方法在地质科学样品检测中的实际应用,证实利用本方法可测定地学样品中20余种元素,其检出限、精密度和准确度均得到了较明显的改善。该法是常规活化分析方法必要的、有益的补充。     

中子活化分析法测定古瓷参考物质

中子活化分析用于研究陶瓷中元素的组成已经有一段时间了,这种现代分析技术用于瓷器的分析和鉴定有以下几个优点:分析灵敏度高,通常可达10~(-3)—10~(-10)g/g;所需样品量少,通常只需0.1g左右;由于测量技术的自动化和采用计算机处理数据,分析的效率高,同时可以进行样品的多元素分析。在对古陶瓷研究中采用活化分析技术以后,有可能定量地测出陶瓷中的微量元素(ppm数量级),陶瓷中这样少量的一些元素往往代表着陶土或瓷土的     

砂岩中25种元素的中子活化分析—绝对法测定

应用常规活化分析方法处理并辐照岩石及标准样品。照射后的样品用Ge(Li)探测器作无损定量分析,元素的含量用两种方法计算:(1)用标准Au、Co活性求解热中子和超镉中子通量后,利用文献给出的中子截面等核常数计算,即绝对法;(2)为检查绝对法中因引用核参数造成的误差,制备了Ta、U、W、Na、La、Fe、Hf、Ce、K、Lu等元素标准伴随照射,用     

层状壳聚糖水凝胶的制备与性能

通过两步低温辐射和冷冻/解冻循环相结合的方法制备聚乙烯醇/聚氧乙烯(PVA/PEO)为基层,聚乙烯醇/壳聚糖(PVA/CS)为上层抗菌功能层的层状壳聚糖水凝胶。通过对吸收剂量、电子束流、聚合物溶液浓度等的研究确定最佳制备工艺,并通过溶胀性能、力学性能、抗菌性能及红外光谱和扫描电镜表征所得层状水凝胶的结构与性能。结果表明,该方法制备的层状壳聚糖水凝胶具有明显的层状结构,层间结合紧密,壳聚糖结构未改变;层状水凝胶的溶胀性能随着壳聚糖含量增大而逐渐增大,60%CS含量平衡溶胀度达到2 200%;层状水凝胶力学强度随着壳聚糖含量增加而先增大后减小,40%CS含量下层状水凝胶从PVA/PEO凝胶的0.35MPa提高到0.47 MPa;抗菌性能测试表明层状水凝胶对大肠杆菌和金黄色葡萄球菌均具有明显的抑菌效果,抑菌性能随着壳聚糖含量的提高而增大。     

The positron distribution in a layered stack sample studied with the use of positron lifetime spectroscopy

Computer simulation using GEANT4 codes indicates an enhancement of the fraction of implanted positrons stopped in the denser regions of a layered sample. However, positron lifetime measurements performed for layers of pure aluminum, silver and gold foils do not reveal this effect, indicating instead that backscattering plays an important role in determining the positron implantation profile in layered and/or heterogeneous samples.     

Approach to Safety Assessment of Methods for Handling Liquid Radioactive Wastes from Nuclear Fuel Cycle Enterprises

The application of the concept of deeply layered protection, which was developed for nuclear power plants, to modern methods for handling liquid radioactive wastes is examined. It is shown that this concept can be used successfully for assessing the safety status of different types of storage sites. It is concluded that it is desirable to develop for domestic nuclear fuel cycle objects a multilevel safety concept based on the principle of deeply layered protection and later to prepare on this basis the standardization documentation.     

Multiple Dielectric Relaxation Times in an Irradiated Transmission Line

The theory of multiple dielectric relaxation times in an irradiated transmission line is developed in detail for strip lines and coaxial lines. The problem of deposition profiles, photo-Compton currents, and dielectric properties which vary arbitrarily is treated first; then the treatment is specialized to layered dielectrics. A numerical scheme is given for solving the resulting system of equations describing wave propagation on a line with layered dielectrics. The generalization to a shielded strip line (a three-conductor line) is also presented.     

基于地基土等效线性的三维厂址反应分析

随着核电厂选址条件的日趋复杂化,土-结构相互作用（SSI）成为核电厂抗震分析需要考虑的重要因素之一。目前经典的自由场厂址反应分析采用的是一维层状地基土的分析,比如SHAKE91、EERA和SASSI等,很难考虑土层的非均质层状因素。因此随着核电安全的监管要求越来越高,抗震的精细化分析成为趋势。本文采用有限元程序ABAQUS编写的UMAT材料子程序,实现了基于地基土材料的等效线性,开展均质层状土的三维自由场厂址反应分析。其计算分析结果与SHAKE91计算结果进行对比表明,在均质层状土条件下吻合较好。因此,本研究为求解复杂非均质地基条件的SSI分析提供了良好的工程适用性。      

Red layered medieval stained glass window characterization by means of micro-PIXE technique

Red layered medieval stained glass windows on a transparent greenish substrate are characteristic of European medieval cathedrals, but few compositional analyses have been performed on the coloured layers. The PIXE technique has been performed on a red layered stained glass window obtained during the restoration works carried out in Las Huelgas Monastery in Burgos (Spain). Protons of 3 MeV with a beam of 4 × 5 μm² were used to acquire elemental maps of a cross section of the sample, in order to observe the homogeneity of the layered structure and its substrate.In our work, copper was detected as in other layered glasses but a correspondence with lower amounts of zinc has also been determined. Both elements appear enriched in the red coloured layers, while the other quantified elements have the same relative composition along the sample. Corrosion layers, due to the lead supporting structure of the window, were also found.     

Calculation of depth-dependent elemental concentration with X-ray fluorescence using a layered calibration method

Depth-dependent elemental concentration can be assessed using either multiple-angle or confocal X-ray fluorescence (XRF) measurements. This work presents a different approach based on a layered calibration method. The depth-dependent elemental concentration was modeled as multiple layers of uniform elemental concentrations. The unknown elemental concentration in each layer can be calculated using a single-angle XRF measurement, layered calibration data, and a priori knowledge of the concentration behavior as a function of depth. The method was verified using a commercial portable X-ray spectrometer and four-layer stacks of polyester resin discs doped with various concentrations of arsenic. This approach is particularly suitable for quantitative in vivo measurements of arsenic and selenium concentrations in the human skin since minimal ionizing radiation exposure constrains the number of XRF measurements.     

Seismic response analysis of soil-structure interactive system using a coupled three-dimensional FE-IE method

This paper proposes a slightly new three-dimensional radial-shaped dynamic infinite elements fully coupled to finite elements for an analysis of soil-structure interaction system in a horizontally layered medium. We then deal with a seismic analysis technique for a three-dimensional soil-structure interactive system, based on the coupled finite-infinite method in frequency domain. The dynamic infinite elements are simulated for the unbounded domain with wave functions propagating multi-generated wave components. The accuracy of the dynamic infinite element and effectiveness of the seismic analysis technique may be demonstrated through a typical compliance analysis of square surface footing, an L-shaped mat concrete footing on layered soil medium and two kinds of practical seismic analysis tests. The practical analyses are (1) a site response analysis of the well-known Hualien site excited by all travelling wave components (primary, shear, Rayleigh waves) and (2) a generation of a floor response spectrum of a nuclear power plant. The obtained dynamic results show good agreement compared with the measured response data and numerical values of other soil-structure interaction analysis package.     

Vibrations of a rigid disc on a layered viscoelastic medium

A method of obtaining the dynamic impedance functions for a rigid circular foundation placed on a layered viscoelastic half-space is presented. Both hysteretic and Voigt models of internal damping are considered. The results obtained indicate that the presence of internal damping introduces important changes in the dynamic response of the foundation for vertical, rocking and horizontal steady-state excitation.