中子与9Be和6,7Li反应的次级中子发射谱实验研究

测量了8.17MeV与10.27MeV中子与⁹Be和^6,7Li作用的次级中子双微分截面. 对于10.27MeV, 为了消除从D(d,np)破裂反应来的源破裂中子对双微分截面测量结果的影响, 采用了常规多探测器快中子飞行时间谱仪和非常规多探测器快中子飞行时间谱仪相结合的办法. 用Monte-Carlo方法对实验测量得到的飞行时间谱进行了详细的模拟, 通过测量谱与模拟谱的比较, 得到了实验测量的次级中子双微分截面. 实验测量结果以n-p(常规谱仪)和n-C(非常规谱仪)弹性散射微分截面作为归一. 测量结果与评价数据以及其他测量数据进行了比较. 用一个基于Hauser-Feshbach和激子模型的轻核核反应理论模型对^6,7Li的次级中子双微分截面进行了计算, 理论计算结果与实验结果符合得较好.     

浦项中子装置上~(209)Bi中子全截面测量（英文）

在浦项中子装置(PNF)的100 Me V电子直线加速器上利用透射法和飞行时间法测量了209Bi的0.1～100 e V的中子全截面。文中对于实验装置特点、用吸收片法拟合本底、拟合中子飞行距离和时间零点的处理过程做了较为详细的描述。测量结果与以前发表的实验数据以及评价数据ENDF/B-VII.1做了比较,比较结果符合得较好。     

浦项中子装置上209Bi中子全截面测量(英文)

在浦项中子装置(PNF) 的100 MeV电子直线加速器上利用透射法和飞行时间法测量了209Bi 的0.1~100 eV的中子全截面。文中对于实验装置特点、用吸收片法拟合本底、拟合中子飞行距离和时间零点的处理过程做了较为详细的描述。测量结果与以前发表的实验数据以及评价数据ENDF/B-VII.1 做了比较,比较结果符合得较好。     

光中子源上吸收片功能研究

15 MeV电子直线加速器驱动的光中子源装置,将用于中国科学院战略性先导科技专项“钍基熔盐堆”中的核数据初步测量工作、中子探测器的研制和反应堆相关材料的辐照研究等。光中子源的中子能谱是连续的,中子能量通过中子飞行时间法测量得到,需要利用吸收片确认中子吸收峰,刻度飞行时间,计算等效飞行距离,扣除实验本底等,而实验本底的扣除对最终总截面计算有很大的影响。因此通过Geant4蒙特卡罗模拟软件构建了包括中子源、吸收片在内的模拟实验环境;研究了不同吸收片的吸收谱和吸收片厚度的关系,同理论计算值进行了比较,给出了推荐的吸收片厚度值;模拟计算了中子飞行时间谱,并和实验测量结果比较,确定中子等效飞行距离为5.70 m。Geant4的理论计算也可以模拟出多吸收片本底函数曲线,可用于实验数据的本底扣除和误差分析。实验测量、模拟分析以及理论公式计算的吸收片厚度和中子飞行时间参数得到了完全一致的结果,验证了实验测量的可靠性。A photo-neutron source driven by a 15 MeV electron LINAC is built for the "Strategic Priority Research Program" of the Chinese Academy of Sciences-the "thorium-based molten salt reactor" project to conduct the nuclear data measurement work,develop neutron detector and carry out reactor material irradiation studies.Since the neutron energy spectrum is continuous,the neutron energy is measured by the time of flight (TOF) method,and neutron filters are needed to confirm absorption peaks,calibrate the TOF,calculate the equivalent flight distance,and remove the experimental background which has great influence on the calculation accuracy of the total cross section.Based on the Monte Carlo simulation tool,Geant4 a simulation environment is set up,including neutron source and neutron filters,to study the energy absorption spectra and thickness of different filters and recommended data for the thickness are provided.The neutron TOF spectra are simulated and compared with experimental measurement,deciding the equivalent TOF distance to be 5.7 m.Geant4 can also simulate the background curve of multiple filters and be used to remove background and analyze errors for the experimental data.All the experiments,simulation and theoretical calculation show consistent results on filter thickness and neutron TOF parameters,indicating the accuracy of the measurement.     

铟活化诊断氘氘中子产额不确定度分析

介绍了铟活化诊断氘氘中子产额的测量原理,分析了中子产额测量不确定度的来源及评定方法。中子产额测量不确定度主要由灵敏度标定不确定度、活化射线净计数不确定度、立体角测量不确定度及测量系统的随机误差等构成。评估了灵敏度标定过程中加速器中子与聚变中子能量差异、大厅散射中子本底等因素对灵敏度标定的影响,并评估了宇宙射线本底对活化射线净计数测量的影响。分析了中子产额处于不同量级时起主要作用的不确定度分量,提出了减小灵敏度标定不确定度的方法。以实验数据为基础,对具体的实验数据进行了分析计算。结果表明:利用伴随粒子法在加速器中子源上标定出铟活化测量系统灵敏度的相对标准不确定度为4.3%。中子产额低于1010时,产额测量不确定度大于7%,活化射线净计数误差是产额测量误差的主要来源;产额大于1010时,测量不确定度好于7%,中子产额测量不确定度主要由灵敏度标定不确定度引起。     

中国散裂中子源反角白光中子束流参数的初步测量

中国散裂中子源(CSNS)已于2018年5月建设完工,随后进行了试运行.其中的反角白光中子束线(Back-n)可用于中子核数据测量、中子物理研究和核技术应用等多方面的实验.本文报道对该中子束的品质参数测量实验过程以及最终实验结果.实验主要采用中子飞行时间法,利用~(235)U,~(238)U裂变室和~6Li-Si探测器测量了中子能谱和中子注量率,又利用闪烁体-互补金属氧化物半导体探测系统测量了中子束斑的剖面,得到了该束线的初步实验测量结果.其中白光中子的全能谱测量范围eV—100 MeV,给出了不确定度分析;给出了中子注量率两个实验厅位置的满功率值;给出了白光中子在直径60 mm情况下的全能区束斑.通过与模拟结果的比较探讨了以上结果的合理性,并提出了改进计划.这些实验结果为以后该束线的核数据测量和探测器标定实验奠定了基础.     

用直接中子法测量（n, 2n）反应截面的实验方法研究

在中国原子能科学研究院HI-13 串列加速器上的非常规多探测器快中子飞行时间谱仪上,采用直接中子法测量了14.3 MeV 中子与169Tm作用的(n,2n) 反应截面。用蒙特卡罗方法模拟了次级中子的产生,以对实验数据进行中子注量率衰减、多次散射和有限几何修正,同时结合SUNF 方法得到的评价能谱,给出了(n,2n) 反应截面的实验测量结果。测量截面以中子弹性散射微分截面作为标准截面来归一,并用反冲质子望远镜测量n-p 反应的反冲质子,以监视中子注量率。用直接中子法测量得到的结果与评价数据进行了比较,讨论了采用这种方法测量(n,2n) 反应截面的可行性。(n,2n) reaction cross section from 169Tm at 14.3 MeV was measured with the direct emittedneutron coincidence detecting method, using abnormal fast neutron TOF spectrometer on the HI-13 Tandem Accelerator at CIAE. Monte-Carlo method was used to simulate the generation of secondary neutron and correct the experimental data considering neutron flux attenuation, multiple scattering and finite geometry correction. Combining with evaluated spectra given by SUNF program, the experimental measurement results of the (n,2n) reaction cross sections were given. Cross sections of measurements were normalized by using neutron elastic scattering differential cross section as a standard section, and a recoil proton telescope was used to measure recoiling proton from the n-p reaction to monitor neutron flux rate. After comparing the experimental results with evaluated data, the feasibility of the direct emitted-neutron coincidence detecting method is discussed.     

天然核素Ta和In的快中子俘获截面测量

本工作测量了Ta和In在0.34—1.68MeV能区的中子俘获截面.实验中使用大液体闪烁探测器测量瞬发俘获γ辐射,用长中子计数器监测中子能量.为了降低测量中的本底采用了快符合电路和飞行时间技术.截面测量为相对测量,以金的俘获截面作为标准.最后对结果进行了比较和讨论.     

基于裂变γ标识技术的瞬发裂变中子谱测量新方法

瞬发裂变中子谱（prompt fission neutron spectrum,PFNS）是用于核实验诊断过程中十分重要的参数数据,传统的测量主锕系核素（U,Pu）PFNS的技术手段是采用裂变室,利用裂变碎片标识裂变中子,通过中子飞行时间技术获得裂变中子谱.目前出现了一种新的用于PFNS测量的技术,其原理是基于如下的物理事实：在一次裂变过程中,释放中子的同时伴随着释放7–8个γ射线光子,而非弹性散射效应产生的γ射线光子只有1–2个.据此,可以通过裂变γ射线的多重性将裂变中子和其他杂散中子甄选出来,达到测量PFNS的目的.本文建立了基于裂变γ标识技术的PFNS测量实验系统.利用该系统对²⁵²Cf中子源的PFNS进行了实验测量,测量结果与传统的裂变碎片标识法及ENDF/B-VⅡ数据库的标准谱进行了比较,对新方法的裂变标识率以及实验不确定度也一并进行了分析.     

基于中国散裂中子源反角白光中子束线的天然锂中子全截面测量

锂是熔盐堆燃料载体盐的主要材料之一,其中子核反应截面数据是熔盐堆芯中子物理设计及堆芯长期安全运行中的重要基础数据.本工作基于中国散裂中子源反角白光中子束线(CSNS Back-n)飞行时间谱仪,利用中子全截面测量谱仪(NTOX),采用透射法测量了天然锂中子全截面.实验中,中子飞行距离约为76.0 m,采用15.0 mm和8.00 mm两种厚度的天然锂金属样品,在0.4 e V—20 Me V中子能量范围内测得了统计计数较好的中子全截面.特别是在ke V及以下能区增补了实验数据,为锂的核数据评价工作提供了更加丰富和可靠的实验数据.在此基础上,采用1/v律和R矩阵理论对Me V以下能区的新测量数据进行了理论分析,获得了7Li和6Li在260 ke V能量附近的中子共振参数.     

锂玻璃探测器中子探测效率的刻度

为了精确测量keV能区的中子俘获截面,中国原子能科学研究院正在建造一台4π 全吸收型γ 探测装置---GTAF,锂玻璃探测器将会作为中子束流监视器测量中子能谱。利用5SDH-2 加速器刻度了锂玻璃探测器在两个入射中子单能点(250 和565 keV) 的探测效率,并使用EANT4 和MCNP 程序模拟计算了锂玻璃探测器的相对探测效率。通过归一化实验数据和模拟结果,得到了锂玻璃探测器在10keV~1 MeV 能区的中子探测效率曲线。对于把锂玻璃探测器测量得到的飞行时间谱转化为中子束流能谱,是一项非常重要的工作,同时为探测器效率刻度提供了新方法。In order to accurately measure the neutron capture cross section in the energy range of keVMeV, 4 πgamma-ray total absorption facility (GTAF) is being constructed at China Institute of Atomic Energy (CIAE). The lithium glass detector will be used as a neutron beam monitor for GTAF. The detection efficiency of the lithium glass detector at two incident neutron energy points (250, 565 keV) was calibrated in 5SDH-2 accelerator, and the relative detection efficiency was simulated by GEANT4 and MCNP code. By the normalization of the experimental data and simulation result, the neutron detection efficiency curve of the lithium glass detector between 10 keV and 1 MeV was obtained. This work will be important to convert the Time-of-flight spectrum that be measured by Li-glass detector to the energy spectrum of neutron beam, and provide the new method for calibration of detection efficiency.     

基于HI-13串列加速器的中子俘获反应截面测量方法

利用BaF₂晶体对γ射线探测效率高、时间分辨率好的特点,研制了国内首套由40个BaF₂探测器单元组成的γ全吸收型探测装置,用于在线测量中子俘获反应截面。在HI-13串列加速器上建立250～850 keV的中子源,其0°角的源强约为5.09×106 n/（Sr·s）,使用γ全吸收型探测装置,通过瞬发γ射线法测量了93Nb、197Au、natC和空样品的实验数据。根据BaF₂探测器信号的特征,采用了基线补偿、软件阈值设置、时间窗限定、脉冲幅度积分增长率设置和快慢成分比设置等多种数字化波形分析方法,剔除噪声信号以提高效应本底比。以197Au样品数据为标准,natC样品数据为样品相关性本底,空样品数据为样品无关性本底,采用相对测量法得到了93Nb的中子俘获反应截面实验数据。通过与ENDF评价库数据的比较,验证了测量装置和技术方法的可行性。     

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial reso-lution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.     

Determinations of niobium and palladium resonance cross-sections by time-of-flight transmission experiment

The neutron total cross-sections and resonance parameters of Niobium (Nb) and Palladium (Pd) were measured in the neutron energy regions from 0.1 eV to 100 eV by using the time-of-flight method at the Pohang Neutron Facility, Korea, which consists of an electron linear accelerator, a water-cooled Tantalum (Ta) target with a water moderator, and a 12.06 m long time-of-flight path. A ⁶Li-ZnS(Ag) scintillator with a diameter of 12.5 cm and a thickness of 1.6 cm was used as a neutron detector, and high purity natural Nb and Pd metallic sheets with thickness of 15 mm (0.0833 atoms/barn) and 1 mm (0.0068 atoms/barn) respectively, were used for the neutron transmission measurements. The notch filters composed of Cobalt (Co), Indium (In), and Cadmium (Cd) were used to estimate the background level and also to calibrate energy. In order to reduce the gamma-ray background from Bremsstrahlung and from neutron capture, we employed a neutron-gamma separation system based on their different pulse shapes. The resonance parameters of ^natNb and ^natPd were obtained from the transmission ratio by using the SAMMY code, which utilizes both Doppler and resolution broadening effects and Bayes’ generalized least squares technique. The present measurements were compared with the existing experimental and the evaluated reactions data files.     

Neutron dosimetry in low-earth orbit using passive detectors

This paper summarizes neutron dosimetry measurements made by the USF Physics Research Laboratory aboard US and Russian LEO spacecraft over the past 20 years using two types of passive detector. Thermal/resonance neutron detectors exploiting the 6Li(n,T) alpha reaction were used to measure neutrons of energies <1 MeV. Fission foil neutron detectors were used to measure neutrons of energies above 1 MeV. While originally analysed in terms of dose equivalent using the NCRP-38 definition of quality factor, for the purposes of this paper the measured neutron data have been reanalyzed and are presented in terms of ambient dose equivalent. Dose equivalent rate for neutrons <1 MeV ranged from 0.80 microSv/d on the low altitude, low inclination STS-41B mission to 22.0 microSv/d measured in the Shuttle's cargo bay on the highly inclined STS-51F Spacelab-2 mission. In one particular instance a detector embedded within a large hydrogenous mass on STS-61 (in the ECT experiment) measured 34.6 microSv/d. Dose equivalent rate measurements of neutrons >1 MeV ranged from 4.5 microSv/d on the low altitude STS-3 mission to 172 microSv/d on the ~6 year LDEF mission. Thermal neutrons (<0.3 eV) were observed to make a negligible contribution to neutron dose equivalent in all cases. The major fraction of neutron dose equivalent was found to be from neutrons >1 MeV and, on LDEF, neutrons >1 MeV are responsible for over 98% of the total neutron dose equivalent. Estimates of the neutron contribution to the total dose equivalent are somewhat lower than model estimates, ranging from 5.7% at a location under low shielding on LDEF to 18.4% on the highly inclined (82.3 degrees) Biocosmos-2044 mission.     

LS301快中子探测器的效率刻度

主要介绍了利用252Cf标准裂变中子能谱刻度快脉冲LS301型液闪中子探测器的探测效率的实验方法和结果, 简要介绍了实验数据的处理过程, 得到了阈值分别为0.5, 0.7, 1.0和1.6 MeV, 以及中子能量在10 MeV以下的探测器效率, 并对测量结果进行了误差分析。同时为了检验实验结果的准确性, 将实验结果与理论计算结果进行比较, 两者在不确定度范围内符合得很好。Neutron detection efficiency of LS301 fast neutron detector was calibrated by measuring the neutron energy spectrum of 252Cf source, which has a standard fission neutron spectrum. A low mass, fast ionization chamber is used as the fission fragments detector in the time of flight(TOF) spectrometer and afforded the start signal of neutron flight. The stop signal was offered by the anode of LS301. A measured TOF spectrum was turned to the neutron energy spectrum which will be compared with the standard one. Consequently, the fast neutron detection efficiency of LS301 was obtained. Calibration procedures of experimental and data processing was given. Relative detection efficiencies were obtained separately for threshold settings of 0.5, 0.7, 1.0 and 1.6 MeV for neutron energies under 10 MeV. Experimental results accorded with theoretical efficiency curves which were calculated with the Monte Carlo code NEFF50.     

液体闪烁体探测器测量皮秒激光脉冲中子源能谱

在星光Ⅲ实验装置上开展皮秒激光脉冲中子源实验,使用液体闪烁体探测器测得较好的中子信号,利用飞行时间法获得中子的能量/时间分布,通过示波器电压时间积分与阻抗之比得到不同能量段的电荷值。建立液体闪烁体探测器Geant4计算模型,通过实际打靶情况与标定情况下液体闪烁体探测器出光口收集到的可见光光子数之比,结合标定的灵敏度数据,获得液体闪烁体探测器对不同能量中子的灵敏度。计算得到源发射的中子能谱,能量在1 MeV以上的液体闪烁体探测器方向测得的中子产额为1.04108 sr-1。     

基于脉冲中子源法的CiADS反应性测量蒙卡模拟分析

脉冲中子源法(PNS)是加速器驱动次临界系统反应性测量的一种重要技术.利用蒙卡软件建立CiADS次临界反应堆模型,模拟注入脉冲质子束的过程,获得的中子通量的时间演化谱.采用Python语言编程实现脉冲叠加过程,给出稳定缓发中子本底,实现脉冲中子源法的次临界反应堆的反应性测量模拟,给出脉冲周期注入下堆芯不同位置处的中子变...