Anwendung nuklearer Verfahren in der ungarischen Tonerdeindustrie

Der Beitrag gibt einen zusammenfassenden Überblick über die in der ungarischen Tonerdeindustric verwendeten nuklearen Versuchsmethoden.

Anhand von Beispielen werden die an Betriebsapparaturen durchgeführten Durchlauf- und Verteiungsmessungen sowie die unter Laborbedingungen vorgenommenen reaktionskinetischen Untersuchungen, die auf die Klärung verschiedener Prozesse der Tonerdeherstellung gerichlet waren, veranschaulicht.

Weiterhin werden analytische Anwendungen der Neutronenaktivierungs- und Röntgenfluoreszenzmethode sowie Meß- und Regelungseinrichtungen, die auf der Strahlenabsorption beruhen, bekanntgemacht.     

Aktivierungsanalytische Untersuchung von Zirkoniumlegierungen

Durch Aktivierungsanalyse mit Reaktorneutronen (zerstörungsfrei und mit chemischer Aufarbeitung) sowie mittels zerstörungsfreier Untersuchungen an einem Neutronengenerator wurden O, Al, Si, P, Mn, Cu, Nb, Mo, Cd, Ti, Cr und Hf in Zirkoniumlegierungen bestimmt.     

THERMAL NEUTRON ACTIVATION ANALYSIS—AN IMPORTANT ANALYTICAL TOOL

ABSTRACT

This review is intended to present an introduction to the use of thermal neutron activation analysis (TNAA) as an analytical technique for the determination of elements in almost all kinds of matrices. This method of analysis is generally multi-element and experimental conditions can be designed to be nondestructive to the sample. This review will focus on thermal neutron activation as this technique allows determination of approximately two-thirds of the elements on the periodic chart. There are also more and wider spread facilities in the United States that offer these services. The available facilities are located across the United States and are generally accessible to everyone. The review will also detail the advantages and disadvantages of TNAA compared to other common spectroscopic methods. An outline of the general procedure for performing the analysis of the elements using activation analysis is presented to emphasize the ease of using this technique. The outline is divided into sections that give the general procedure, how to choose the correct nuclear reaction and reaction product, and the main sources of errors that can affect the results of the study. These sources of error are subdivided into general types of errors. The general types of errors are divided into those related to pre-chemistry, problems associated with the irradiation of the samples, errors associated with the use of nuclear constants (cross sections, half-lives, transition probabilities, etc.), the choice of the correct reaction and reaction product, and those associated with the counting of the irradiated samples. The general theory of activation analysis is presented and summarizes the derivation of the equations used and the development of the comparator method of analysis. The comparator method is used to simplify the method by irradiating samples along with standards. This reduces the need for using the nuclear constants and thus reducing errors. The use of radiochemical separations to isolate analytes of choice from the radioactive matrix is also described. Some current literature is also included to give a feel for current applications of the use of thermal neutron activation analyses. The summary also describes some of the different matrices that have been used for analyses.     

Environmental radioactivity of soils and sediments: Egyptian sector of the Nile valley

The activity concentrations of natural ⁴⁰K, ²³²Th, and ²³⁸U in 89 soil and 84 sediment samples collected over the entire Egyptian Nile River basin including the Nile delta are reported based on the results of epithermal neutron activation analysis. The average activity concentrations of ⁴⁰K, ²³²Th, and ²³⁸U equal to 15.3?±?6.6, 15.6?±?11.1 and 220?±?31 Bq/kg, respectively, are significantly lower than those reported for the Upper Continental Crust, World Average Sediments as well as World Average Soils, suggesting the presence of a considerable portion of mafic material, most probably originating from the Ethiopian High Plateau. Their average activity concentrations are statistically the same in soil and sediments, indicating that the Nile sediments and soil material are of the same origin. The main goal of this study was not only to estimate the radiological hazards but also to show the influence of sedimentary material transportable by the Blue Nile from the Ethiopian High Plateau. The different hazard indices like the radium equivalent, gamma index, external hazard as well as the internal hazard show a low radiological exposure either on direct contact or if local mud bricks are used in the construction of dwellings.     

随机中子动力学及其数值模拟研究进展

随机中子动力学是核动力设计和核反应堆安全中的重要课题,本文从随机中子动力学的基础概念和研究方法出发,介绍随机中子动力学研究的历史发展和研究现状.裂变中子与光子的多重性是反应堆零功率中子噪声主要来源,对中子涨落的方程描述及其求解,演化出零功率中子噪声与功率反应堆噪声的随机理论.随机中子动力学的重要应用包括反应性微观测量、功率反应堆噪声测量和分析、核临界漂移分析和核材料识别与检测等.在半个多世纪的研究中,以脉冲堆点火过程的脉冲爆发等待时间分布为代表的随机性,一直缺乏定量分析方法和工具.直到近几年,模拟随机中子动力学过程的广义半马尔科夫过程模拟方法取得了重要进展,很好地揭示了脉冲堆实验中子点火规律.最后讨论随机中子动力学研究中有待解决的研究课题.     

用NAA研究清凉寺窑和张公巷窑青瓷胎的原料特征及来源

为研究清凉寺窑汝瓷胎和张公巷窑青瓷胎的原料特征及来源, 选取37个清凉寺窑汝瓷胎样品(32个汝官瓷胎和5个汝民瓷胎)、 32个张公巷窑青瓷胎样品以及14个岩石样品, 用中子活化分析 （NAA）方法测得每个样品中的23种元素含量; 使用散布分析及主成分分析方法处理NAA数据。 结果表明: 元素Fe, Ce, Ba, Ta, Th, La, Sm和Cr可作为区分汝官瓷胎和张公巷窑青瓷胎原料产地的指纹元素; 汝官瓷胎原料产地较集中, 来源相对稳定; 清凉寺窑汝民瓷胎料产地与汝官瓷基本相同, 均为就地取材; 张公巷窑青瓷胎原料产地较为分散, 与汝官瓷不同, 但二者距离相近。 关     

14MeV中子引起的核反应截面测量中监督反应的研究

讨论了14MeV中子引起的核反应截面测量中监督反应对测量结果的影响,同时列出了常用的一些监督反应及参数,利用截面的评价值给出了一些监督反应的截面随中子能量变化的关系曲线,并对^27Al（n,p）^27Mg反应做了定性分析,说明了监督反应的选取对反应截面测量的重要性。 It was discussed in this article that the effects of different monitors in the cross section measurements of nuclear reactions induced by 14 MeV neutrons, at the same time some monitors and correlative parameters were listed. The excitation functions of monitors are taken from the evaluatied cross sections, and a qualitative analysis has been performed for ^27Al（n,p） ^27Mg reaction. It indicates that the choice of monitor is very important for cross section measurements     

Neutron diffraction study of the magnetic ordering in the series R 2 BaNiO 5 (R = Rare Earth)

A neutron diffraction study, as a function of temperature, of the title compounds is presented. The whole family (space group Immm, a ≈ 3.8?, b ≈ 5.8?, c ≈ 11.3?) is structurally characterised by the presence of flattened NiO₆ octahedra that form chains along the a-axis, giving rise to a strong Ni-O-Ni antiferromagnetic interaction. Whereas for Y-compound only strong 1D correlations exist above 1.5 K, presenting the Haldane gap characteristic of 1D AF chain with integer spin, 3D AF ordering is established simultaneously for both R and Ni sublattices at temperatures depending on the rare earth size and magnetic moment. The magnetic structures of R₂BaNiO₅ ( R = Nd, Tb, Dy, Ho, Er and Tm) have been determined and refined as a function of temperature. The whole family orders with a magnetic structure characterised by the temperature-independent propagation vector = (1/2, 0, 1/2). At 1.5 K the directions of the magnetic moments differ because of the different anisotropy of the rare earth ions. Except for Tm and Yb (which does not order above 1.5 K), the magnetic moment of the R³⁺ cations are close to the free-ion value. The magnetic moment of Ni²⁺ is around 1.4 , the strong reduction with respect to the free-ion value is probably due to a combination of low-dimensional quantum effects and covalency. The thermal evolution of the magnetic structures from T _N down to 1.5 K is studied in detail. A smooth re-orientation, governed by the magnetic anisotropy of R³⁺, seems to occur below and very close to T _N in some of these compounds: the Ni moment rotates from nearly parallel to the a-axis toward the c-axis following the R moments. We demonstrate that for setting up the 3D magnetic ordering the R-R exchange interactions cannot be neglected. Received 19 July 2001     

BNCT优化网格设计及相关算法研究

用MCNP蒙特卡罗程序模拟了硼中子俘获治疗(BNCT)3种国际基准网格模型, 并与 修正的Snyder椭球模型进行了比较. 在此基础上, 给出了一种保质量守恒、内存量少、易于产生输入文件的4种基本材料成分的BNCT网格模型. 计算结果表明, 在4mm网格下, 新模型可以达到基准模型的精度; 根据解析模型剂量随深度的变化规律, 研究构造了多网格组合模型, 在重要区域计算精度不损失的条件下, 计算时间大大缩短. 最后研究给出了一个既保证精度、又在可接受的时间内完成剂量计算的模型、样本数和相应的算法, 它基本上满足临床BNCT的要求.     

CSR外靶实验终端中子流测量的模拟

随着兰州重离子加速器冷却储存环(HIRFL-CSR)外靶实验终端中子墙的建立, 为实验测量高能中子提供了机遇. 为确定CSR外靶实验终端对中子流测量的可行性, 基于BUU理论模型分别对对称系统(Ni+Ni, Pb+Pb)和非对称系统(Pb+Ni)进行了模拟计算, 发现当系统能量达到几百MeV/u时, 中子流信号相当明显, 并与碰撞参数有明显的依赖关系. 模拟结果表明, 在前角20°的覆盖范围内, 可以较好地实现中子流测量所需要的反应平面确定及碰撞参数选择. 对双击事件及其对中子流的影响进行了简单的讨论.