中子辐照法合成新型纳米结构材料

放射化学与纳米科学的交叉,既是放射化学在新兴前学科的应用,也是放射化学本身在前沿领域的发展.本文通过介绍反应堆中子催化引起的富勒烯反应,特别是聚合反应的设计方法、分离纯化过程,产物分析和结构表征等研究,建立了堆中子合成伞碳富勒烯二聚体C121,C131和C141的方法,探索开辟利用中子等放射性辐射技术,发展新型纳米结构物质,如全碳富勒烯二聚体、三聚体、甚至四聚体的新方法.全碳富勒烯二聚体既是碳元素的一种新的同分异构体,也是合成富勒烯高聚物的起始物,因此倍受关注.它们在人工光合成、分子电子器件和超分子化学领域有广阔的应用前景.     

以中子管为激发源的中子活化分析系统慢化屏蔽体设计

应用MCNP程序,通过对中子输运过程的模拟计算,得到了以14 MeV D-T中子管为激发源,在慢化屏蔽材料选取不同组合时的热中子注量率分布,热化比及镉比随铅层厚度的变化,以及屏蔽体外几处关键点的生物剂量率。根据模拟计算的数据,设计了活化分析系统的慢化屏蔽体,为开展以14MeV D-T中子管为激发源的中子活化分析工作奠定了基础。     

核燃料棒235U富集度均匀性扫描装置中的中子慢化系统计算

对于核燃料棒235U富集度均匀性扫描装置,为了合理有效地利用252Cf中子源,提高检测灵敏度,需要合理选择中子慢化材料,优化中子慢化过程。本文利用Monte Carlo方法对中子慢化系统进行了优化计算,在保证慢化中子(En<1MeV)通量密度较高和235U与238U的裂变反应几率比R5/8也较高的前提下,给出了几种慢化材料及其组合的结果。     

First Experiment of Measuring the Strains of Metallic Materials by Neutron Diffraction in China

The presence of residual stresses in engineering components can significantly affect their load carrying capacity, resistance to fracture and corruption, dimension stability, operation life, etc. The measurement of residual stress has played an important role in various fields, such as machine manufacturing, irrigation works, aviation, war industry, nuclear industry, petrochemical industry, transportation and so on. Analysis of the residual stress is extremely required during the process of developing new materials and fabricating new components.     

Neutron Cross Section Covariances for Structural Materials and Fission Products

We describe neutron cross section covariances for 78 structural materials and fission products produced for the new US evaluated nuclear reaction library ENDF/B-VII.1. Neutron incident energies cover full range from ¹⁰−5 eV to 20 MeV and covariances are primarily provided for capture, elastic and inelastic scattering as well as (n,2n). The list of materials follows priorities defined by the Advanced Fuel Cycle Initiative, the major application being data adjustment for advanced fast reactor systems. Thus, in addition to 28 structural materials and 49 fission products, the list includes also ²³Na which is important fast reactor coolant. Due to extensive amount of materials, we adopted a variety of methodologies depending on the priority of a specific material. In the resolved resonance region we primarily used resonance parameter uncertainties given in Atlas of Neutron Resonances and either applied the kernel approximation to propagate these uncertainties into cross section uncertainties or resorted to simplified estimates based on integral quantities. For several priority materials we adopted MF32 covariances produced by SAMMY at ORNL, modified by us by adding MF33 covariances to account for systematic uncertainties. In the fast neutron region we resorted to three methods. The most sophisticated was EMPIRE-KALMAN method which combines experimental data from EXFOR library with nuclear reaction modeling and least-squares fitting. The two other methods used simplified estimates, either based on the propagation of nuclear reaction model parameter uncertainties or on a dispersion analysis of central cross section values in recent evaluated data files. All covariances were subject to quality assurance procedures adopted recently by CSEWG. In addition, tools were developed to allow inspection of processed covariances and computed integral quantities, and for comparing these values to data from the Atlas and the astrophysics database KADoNiS.     

Influence of Materials and Counting-Rate Effects on 3He Neutron Spectrometry

The high energy resolution of the Cuttler-Shalev 3He neutron spectrometer causes spectral measurements with this instrument to be strongly susceptible to artifacts caused by the presence of scattering or absorbing materials in or near the detector or the source, and to false peaks generated by pileup coincidences of the rather long-risetime pulses from the detector. These effects are particularly important when pulse-height distributions vary over several orders of magnitude in count rate versus channel. A commercial pile-up elimination circuit greatly improves but does not eliminate the pileup problem. Previously reported spurious peaks in the pulse-height distributions from monoenergetic neutron sources have been determined to be due to the influence of the iron in the detector wall.     

压水堆候选耐事故包壳材料的中子经济性分析

对候选耐事故包壳材料304SS、310SS、FeCrAl、APMT和SiC进行中子经济性分析。结果表明,中子经济性由高到低排序为:SiCZrFeCrAlAPMT304SS310SS;为达到与Zr包壳相同的燃耗寿期[60000MW·d/t(U)],铁基合金包壳厚度取0.4mm且保持包壳外径不变时,燃料富集度增加量不超过0.5%,而SiC在包壳厚度不变的情况下富集度降低约0.12%。     

自给能中子探测器关键材料及元件的研制进展

本文介绍了我国在运核电机组的基本状况以及国内核电自给能中子探测器的发展形势.详细分析了自给能中子探测器的结构特点、原理和应用,以及三代核电技术堆内核测系统的需求和使用寿命.阐述了自给能中子探测器用关键材料的国内外研制进展,重点分析了钒丝、铑丝和铠装信号电缆的制备工艺难点以及性能要求,阐明了钒丝、铑丝的高纯化与微量元素控...     

Neutron Yield Increase by Simulated Pyroelectric Crystal Neutron Source

In this work, we initially simulated a pyroelectric crystal neutron source and calculated its neutron yield. Then in order to carry out its validation, we compared our results with experimental results. Afterwards with changes in the pyroelectric crystal shape, we could reduce the ion beam radius and followed by its convergence; the neutron gain increased. In the following, we compounded the convergence model and two crystal systems that caused more neutron gains. Finally, by using various materials as the target, we tried to offer materials with high neutron producing ability.     

基于扩展型多球中子谱仪的中子能谱测量

为了有效地测量加速器辐射场的中子能谱,论文通过FLUKA模拟的辐射场中子能谱和探测器能量响应选择出合适的扩展型多球中子谱仪、利用基于少道解谱理论的解谱程序来得到实验能谱以及积分注量统计。并通过计算与实验计数率的对比证明了该方法测量中子能谱的可行性,同时分析了实验的不足并给出了改进的建议。     

核材料中子辐照损伤的团簇动力学模拟综述

核材料中子辐照损伤是影响核能装置安全性和稳定性的关键问题之一。由于难以开展大量的中子辐照实验来评估核材料的损伤机理,因此相关理论模拟至关重要。介观尺度团簇动力学（CD）模型由于不受时间和空间尺度的限制,是一种研究材料中子辐照损伤长时间演化的有效方法。本文综述了CD的模型、数值算法和最新进展,重点介绍了CD在典型核材料的中子辐照问题中的系列应用,并对CD的未来发展进行了展望。     

单次脉冲中子源方法测量瞬发中子衰减常数

瞬发中子衰减常数α是核系统的重要标志性特征参数,该值的准确测量对于核临界安全具有重要意义。本工作采用单次脉冲中子源的方法测量了某次临界核系统的瞬发中子衰减常数,获得了几种不同次临界状态下的瞬发中子衰减常数,测量结果与²⁵²Cf随机脉冲源法测量结果一致。     

医院中子照射器中子束流出口处热中子注量率的测量

医院中子照射器是基于微型反应堆而设计的专门用于硼中子俘获治疗（BNCT）的核反应堆装置,其额定功率为30 kW。在堆芯相对两侧分别设有一条热中子束流和超热中子束流用于病人照射,在热中子束流内引出一条实验用热中子束流,用于瞬发γ法测量病人血硼浓度。本工作利用²³⁵U裂变靶和白云母探测片测量了热、超热和实验用热中子束流出口处的热中子绝对注量率。结果显示,在30 kW额定功率运行时,热、超热和实验用热中子束流出口处的热中子注量率分别为1.67×10⁹、2.44×10⁷和3.03×10⁶ cm^-2•s^-1。以上结果达到了BNCT设计要求,并能满足瞬发γ测量血硼浓度的要求。     

Detection of Fissioning Materials Using a Neutron Source Based on a Compact Betatron

The possibility of using a neutron source based on a 10 MeV compact betatron and 1 kg heavy water or 3.3 kg beryllium in the betratron bremsstrahlung beam is investigated. The ²³⁵U detection limit in a 358 mm in diameter and 782 mm high container with probability 0.997 in an experimental apparatus with one epithermal-neutron detector is 40 mg with exposure 10 min. Increasing the mass of the neutron target to 10 kg heavy water and the number of neutron counters to 25 could decrease the ²³⁵U detection limit to 3 mg. A neutron detector based on a compact betatron can be expected to give ²³⁵U detection sensitivity 10^–8 g/g.     

Measurement of Neutron Life in a D2O-System by Neutron Fluctuation

The neutron life has been determined in a D₂O system by combining observation of the inherent fluctuations which occur in the neutron population and reactivity measurements by period method.

The ratio of variance to mean number of counts was measured as a function of counting intervals. Short counting-time intervals were chosen in the experiment to eliminate contribution of delayed neutrons. Also, the variance was measured in the subcritical state, to eliminate the counting loss due to the dead time of the detector.

The decay constant for the critical state has been determined by extrapolation of the observed relation between the decay constant and reactivity.     

Measurements of Neutron Thermalization Time Constant of Light Water by Pulsed Neutron Method

The thermalization parameters of light water have been measured using a pulsed neutron source and non-l/v absorbers (Cd, Gd and Sm). The pulsed neutron source utilizing the D-D reaction was placed at the center of an effectively infinite system of water poisoned with non-1/v; absorbers. The time dependent capture γ-rays from these absorbers were detected by a Nal(Tl) scintillation counter. The neutron thermalization time constant of light water was determined to be 5.3 ± 0.3,μsec from the difference of the decaying reaction rates of the γ-rays, expressed as the sum of two asymptotical exponential components. The resulting value was larger than that of Möller's experiment (4.1 ± 0.4μsec), but agreed fairly well with the theoretical value of 5.6μsec, calculated by Hoshino based on the Nelkin model. A supplementary experiment was performed using thick neutronic filters of Cd and Ag.     

居里级Am-Be中子源产生的热中子通量密度分布

实验室中的同位素Am-Be中子源在有关中子活化方法研究以及在核反应堆中子测量系统研制过程中的调试和刻度等方面都有着非常重要的作用.为使这些应用更有效并得到更准确的实验结果,需要知道Am-Be中子源在周围慢化介质中热中子通量密度的分布.用蒙特卡罗方法并结合中子源发射率计算得到了居里级Am-Be中子源在圆柱形水池中不同半径...