Measurement of the prompt neutron spectrum from thermalneutron-induced fission in U-235 using the recoil proton method

A measurement of the ^235U prompt fission neutron spectrum (PFNS) by the recoil proton method was performed at the Institute of Nuclear Physics and Chemistry, China. Details of the method, which include the calculation and validation of the response matrix, are presented. The PFNS for ^235U in the energy range 1–12 MeV, induced by thermal neutrons, was obtained. The measured spectrum in the low-energy region was in good agreement with previous work and the ENDF/B-VII library, except for minor differences. In the high-energy region, however, the relative height of the measured spectrum was greater, and an analysis of the experiment indicated uncertainties of 13% at 10 MeV and 24% at 12 MeV. Experimental results showed that the recoil proton method could be used to measure prompt fission neutron spectra. Some directions for future work are included.

Analysis of prompt fission neutron spectrum and multiplicity for ^(237)Np(n, f) in the frame of multi-modal Los Alamos model

The improved version of Los Alamos model with the multi-modal fission approach is used to analyse the prompt fission neutron spectrum and multiplicity for the neutron-induced fission of 237Np. The spectra of neutrons emitted from fragments for the three most dominant fission modes （standard Ⅰ, standard Ⅱ and superlong） are calculated separately and the total spectrum is synthesized. The multi-modal parameters contained in the spectrum model are determined on the basis of experimental data of fission fragment mass distributions. The calculated total prompt fission neutron spectrum and multiplicity are better agreement with the experimental data than those obtained from the conventional treatment of the Los Alamos model.

Prompt neutron multiplicity distribution for ^(235)U(n,f) at incident energies up to 20 MeV

For the n＋235U fission reaction, the total excitation energy partition of the fission fragments, the average neutron kinetic energy ε （A） and the total average energies Eˉγ（A） removed by γ rays as a function of fission fragment mass are given at incident energies up to 20 MeV. The prompt neutron multiplicity as a function of the fragment mass, ν（A）, for neutron-induced fission of 235U at different incident neutron energies is calculated. The calculated results are checked with the total average prompt neutron multiplicities νˉ and compared with the experimental and evaluated data. Some prompt neutron and γ emission mechanisms are discussed.

Study on element detection and its correction in iron ore concentrate based on a prompt gamma-neutron activation analysis system

A prompt gamma-neutron activation analysis(PGNAA) system was developed to detect the iron content of iron ore concentrate. Because of the self-absorption effect of gamma-rays and neutrons, and the interference of chlorine in the neutron field, the linear relationship between the iron analytical coefficient and total iron content was poor, increasing the error in the quantitative analysis. To solve this problem, gamma-ray self-absorption compensation and a neutron field correction algorithm were proposed, and the experimental results have been corrected using this algorithm. The results show that the linear relationship between the iron analytical coefficient and total iron content was considerably improved after the correction. The linear correlation coefficients reached 0.99 or more.

Calculation of Prompt Fission Neutron from ^(233)U(n, f) Reaction byMulti-Modal Los Alamos Model

An attempt is made to improve the evaluation of the prompt fission neutron emis- sion from 233U（n, f） reaction for incident neutron energies below 6 MeV. The multi-modal fission approach is applied to the improved version of Los Alamos model and the point by point model. The prompt fission neutron spectra and the prompt fission neutron as a function of fragment mass （usually named ＂sawtooth＂ data） v（A） are calculated independently for the three most dominant fission modes （standard I, standard II and superlong）, and the total spectra and v（A） are syn- thesized. The multi-modal parameters are determined on the basis of experimental data of fission fragment mass distributions. The present calculation results can describe the experimental data very well, and the proposed treatment is thus a useful tool for prompt fission neutron emission prediction.

DEVELOPMENT AND APPLICATIONS OF AN ON-LINE THERMAL NEUTRON PROMPT-GAMMA ELEMENT ANALYSIS SYSTEM

This paper introduces the principles, instrumentation, implementation, and industrial applications of an on- line thermal neutron prompt- gamma element analysis system (using a 252Cf neutron source, Am- Be neutron source, or neutron generator). The energy resolution of the system at the H prompt- gamma full- energy photopeak (2.22325 MeV) is 3.6 keV. The concentration measurement error of A12O3, Fe2O3, CaO and SiO2 is ±0.3%,±0.1%.±0.4% and ±0.4%, respectively.The system has been tested on- site at both the Shandong and the Zhengzhou Aluminum Works. Our preliminary on- site measurements confirm that the stability, reliability, measurement range, and accuracy of the system can meet the requirements of the aluminum production process. Facilitation of this measurement at aluminum plants is expected to reduce plant costs by over 3 million dollars annually through reduced energy consumption, more rapid qualification of pulps being mixed during the production process, and in reduced labor costs.

Progress of neutron induced prompt gamma analysis technique in 1988～2003

This paper described new development of the neutron induced prompt gamma-ray analysis(NIPGA) technology in 1988-2003.The pulse fast-thermal neutron activation analysis method,which utilized the inelastic reaction and capture reaction jointly,was employed to measure the elemental contents more efficiently.Lifetime of the neutron generator was more than 10000h and the performance of detector and MCA reached a high level.At the same time,Monte Carlo library least-square method was used to solve the nonlinearity problem in the NIPGA.

Overview of Industrial Materials Detection Based on Prompt Gamma Neutron Activation Analysis Technology

Prompt gamma neutron activation analysis (PGNAA) is a non-destructive online measurement nuclear analysis method. With its unique advantages, it has been widely used in online analysis of industrial materials such as coal, cement, and minerals in recent years. However, there are many kinds of literature on PGNAA in the field of industrial materials detection, and there are still a few concluding articles. To this end, based on the principle of PGNAA online analysis, the status quo and development of the real-time online detection of industrial material components in the field are reviewed and discussed by consulting a large number of domestic and foreign PGNAA related literature and data, to facilitate the reference of relevant scientific researchers.

Design of a prompt-gamma neutron activation analysis system on China Advanced Research Reactor

In this paper,computational methods are used to optimize the design of a prompt-gamma neutron activation analysis(PGNAA) system on China Advanced Research Reactor(CARR).Approaches are adopted for obtaining accurate neutron beam parameter and saving the computing time.For the radiation shielding design,the optimizing factors include the cost,weight,volume,machining convenience and background radiation at the detector position.Low background spectrum and high sensitivity are expected.The simulation results,and experiences from international PGNAA community,were used in the design of the CARR PGNAA system.

中国先进研究堆瞬发γ元素成像技术研究

无损分析样品内部的元素分布,对于材料、考古、地质科学等领域的研究具有重要意义。基于瞬发γ活化分析方法,结合中子照相技术,分析了模拟样品的结构和对称性,首次利用中国先进研究堆(CARR)水平孔道聚焦的微束中子束流,开展样品瞬发γ扫描分析和材料内部元素分布研究。通过蒙特卡罗软件(MCNP)对样品元素分布实验模型进行分析,模拟结果获得了样品不同区域的铜、铁、铝元素分布,基本实现了元素空间分辨。MCNP计算结果表明在瞬发γ扫描分析中,优化准直几何参数和提高中子通量能进一步提高元素空间分辨和元素测量准确度。

反应堆瞬发γ活化成像技术研究进展

瞬发γ活化成像技术(Prompt Gamma Activation Imaging,PGAI)是基于瞬发γ中子活化分析技术(Prompt Gamma Neutron Activation Analysis,PGAA)的一种新型元素成像技术,具有PGAA非破坏性、高灵敏度的多元素分析特点,同时可研究大体积样品内元素含量的三维分布情况。与移动中子源(如同位素中子源、加速器中子源)相比,反应堆中子源具有高通量的冷/热中子,因此,基于反应堆中子源的PGAI装置具有更加广阔的应用前景。鉴于PGAI技术的重要性,主要介绍了PGAI技术原理和测量方法、列举了国内外具有代表性的PGAI装置及特点,并指出当前PGAI技术研究现状与应用进展。其中,与中子层析成像(Neutron Tomography,NT)结合的PGAI是目前研究的重点。随着国内高通量中子反应堆的持续稳定运行以及PGAI装置的建立和技术发展,相信未来PGAI技术能在我国更多领域得到广泛和深入应用。

基于可移动中子源的瞬发γ活化成像研究进展

瞬发γ活化成像技术基于瞬发γ射线中子活化分析,结合准直测量或者伴随粒子测量手段,以实现对样品内部中元素位置分布的测量。当前大多数相关研究都是基于大型中子源开展的,这限制了该技术的应用场景,可移动小型化中子源是该技术现场应用的必然要求。基于可移动中子源的瞬发伽马活化成像技术按照准直方式可分为基于单孔准直、编码孔准直及伴随粒子测量三类,对其技术原理、研究进展及仍存在的问题进行介绍与讨论。目前的技术在空间分辨率上还需要进一步提升,未来将进一步结合图像处理算法提高成像质量并降低测量时间。

基于瞬发伽马谱学的元素重建算法

质子治疗中的瞬发伽马射线是质子和靶标之间核反应的产物,瞬发伽马射线的特征能量和强度可以用来确定靶中元素的种类和数量,在之前的实验中已经证明,无论反应截面多么复杂,一旦确定了被照射元素和入射质子的能量,元素浓度与伽马射线光子数之间就存在一定的线性关系。然而,这种线性关系很难应用于医学成像,而且氢的非线性行为迄今尚未研究。将这种线性关系推广到包括氢等非线性情况的混合元素材料,并提出了一种通用的数学形式,即基于瞬发伽马谱学的重建算法(PGSRA)。PGSRA的基本假设是样品材料的PGS与元素的每摩尔伽马射线有某种关系。对于碳和氧,这种关系是线性的,而对于氢,这种关系是非线性的。由于2.23 MeV的伽马线来源于中子吸收辐射,研究氢非线性行为,利用蒙特卡罗模拟验证碳、氧和氢的不同组合,如聚甲基丙烯酸甲酯(PMMA)、戊二醇和乙醇二醇的线性和非线性关系。所有样品材料的碳、氧相对误差均小于4%。基于氢的非线性特性,其相对误差约为10%。此外,样品密度的相对误差对所有样品材料都小于3.5%。开发的PGSRA法可能是PGS和医学成像之间的第一座桥梁。

中子诱发伽马产生截面测量中的谱分析技术

在中子反应截面测量中,瞬发γ射线法是一种通过测量核反应放出的特征γ射线来得到截面数据的方法,这种方法能够避免竞争反应道产生的干扰.但是瞬发γ射线法为在线实验,本底来源丰富,造成了在线实验谱分析难度大,结果不确定性高.本文研究了使用瞬发γ射线法测量中子诱发伽马产生截面的谱分析技术,总结了中子诱发伽马产生截面测量中不同特征峰形成的物理过程,降低了在线实验谱处理过程中计算效应峰净面积的不确定度.通过采用各种响应函数来对全能峰、本底以及干扰因素进行拟合的方法,精确提取了效应峰的净面积.针对弱峰的净面积,本方法可将峰区域选取引起的波动从30%降低到1%以内,且净面积拟合值与理论值的差距与统计不确定度相当;对于解重峰,本方法所得结果与理论值差距显著低于1%.通过效率曲线分析、拟合优度计算等方法同时验证了谱分析方法的可靠性.

Monte-Carlo simulation of cement neutron field distribution characteristics in PGNAA

The distribution characteristics of the neutron field in cement was simulated using the MCNP code to comply with the requirements of an online Prompt Gamma Neutron Activation Analysis system.Simulation results showed that the neutron relative flux proportion reduced with increasing cement thickness.When the cement thickness remains unchanged,the reduced proportion of thermal neutrons increases to a small extent,but the epithermal, intermediate,and fast neutrons will decrease according to the geometric progression.H element in the cement mainly affects the reduction of fast neutrons and other single-substance elements,e.g.,O,Ca,56Fe,Si,and Al.It also slows down the reduction of the fast neutrons via inelastic scattering.O contributes more than other elements in the reduction of fast neutrons.Changing the H content affects the thermal,epithermal,intermediate,and fast neutrons, while changing the Ca,Fe,and Si contents only influences the thermal,epithermal,and intermediate neutrons;hence, there is little effect on the reduction of fast neutrons.

MC simulation of thermal neutron flux of large samples irradiated by 14 MeV neutrons

The response of a 14 MeV neutron-based prompt gamma neutron activation analysis (PGNAA) system,i.e.the prompt gamma-rays count rate and the average thermal neutron flux,is studied with a large concrete sample and with a homogeneous large sample,which is made of polyethylene and metal with various concentrations of hydrogen and cadmium using the MCNP-5 (Monte Carlo N-Particle) code.The average thermal neutron flux is determined by the analysis of the prompt gamma-rays using the thermal neutron activation of hydrogen in the sample,and the thermal and fast neutron activation of carbon graphite irradiation chamber of the PGNAA-system.Our results demonstrated that the graphite irradiation chamber of the PGNAA-system fairly operates,and is useful to estimate the average thermal neutron flux of large samples with various compositions irradiated by 14 MeV neutrons.

Analysis of prompt supercritical process with heat transfer and temperature feedback

The prompt supercritical process of a nuclear reactor with temperature feedback and initial power as well as heat transfer with a big step reactivity (ρ0>β) is analyzed in this paper. Considering the effect of heat transfer on temperature of the reactor, a new model is set up. For any initial power, the variations of output power and reactivity with time are obtained by numerical method. The effects of the big inserted step reactivity and initial power on the prompt supercritical process are analyzed and discussed. It was found that the effect of heat transfer on the output power and reactivity can be neglected under any initial power, and the output power obtained by the adiabatic model is basically in accordance with that by the model of this paper, and the analytical solution can be adopted. The results provide a theoretical base for safety analysis and operation management of a power reactor.

瞬发中子衰减常数测量模拟程序

为研究瞬发中子衰变常数α的实验方法和改进相关测量技术,在中子输运程序的基础上,开发了α测量的模拟程序。可以模拟中子输运和α测量的全过程,利用该程序对球形金属装置的测量全过程进行了模拟,模拟结果均与设定的值一致。该程序实现了Rossi-α法的A/C值的计算和Feynman法测量过程模拟,从而弥补了普通中子输运程序的不足。

A brief introduction to neutron activation analysis in China―history,major achievements,and future perspectives

The history,the major achievements in both methodology and applications,the current trends and future perspectives of neutron activation analysis (NAA) in China are briefly described.

复杂地形对核爆炸瞬发中子辐射场的影响

通过分析地面附近核爆炸瞬发辐射的不同来源,选择一系列能反映局部或区域地形起伏对辐射场影响的特征参数,应用数字高程模型建立了地形特征计算方法,通过相关性分析和统计分析的方法,定量研究了地形特征对辐射场的具体影响。研究结果表明,指向和背离爆心方位的地形开阔度与辐射场增强或削弱程度成高度线性相关;地形坡面越陡,“阳坡”辐射场越易受到增强,而“阴坡”则越易受到削弱;地形可视性对中子吸收剂量场的影响较小,而对次级γ吸收剂量场则会造成显著影响,地形的完全遮挡将会显著削弱次级γ辐射场。