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.     

一种测量次级中子能谱的新方法

采用双飞行时间法创建了一台非常规快中子飞行时间谱仪,排除了用D(d,n)3He中子源测量8-13MeV能区次级中子双微分截面时源中破裂中子群对次级中子能谱测量的干扰.结合常规快中子飞行时间谱仪的测量,实现了用D(d,n)3He中子源开展8-13MeV中子能区次级中子双微分截面的测量.     

一种测量次级中子能谱的新方法

采用双飞行时间法创建了一台非常规快中子飞行时间谱仪，排除了用D（d,n)^3He中子源测量8－13MeV能区次级中子双微分截面时源中破裂中子群对次级中子能谱测量的干扰，结合常规快中子飞行时间谱仪的测量，实现了用D（d,n)^3He中子源开展8－13MeV中子能区次级中子双微分截面的测量。     

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。     

聚变中子能谱测量系统脉冲中子灵敏度的实验研究

为多种复杂环境下的稳态和脉冲DT聚变中子能谱测量建立了一种灵敏度优化反冲质子磁谱仪. 使用成像板和同位素α源测量了谱仪的反冲质子能量-位置投影关系. 利用稳态加速器中子源平台、通过单粒子计数方法结合三维带电粒子输运程序模拟,研究了谱仪脉冲中子灵敏度能量响应. 通过高探测效率参数设置使谱仪对DT中子的探测效率达到2×10^-5 cm²水平,从而在较弱中子源上获得了较高统计精度实验数据. 程序模拟结果与谱仪α粒子刻度和DT中子标定实验结果取得了良好的一致性,可由此发展精细解谱技术,以提高脉冲中子能谱测量的灵敏度和能量分辨. 关键词： 聚变中子能谱 磁反冲质子 脉冲中子灵敏度 粒子输运     

非弹性中子散射谱仪

非弹性中子散射是利用中子与材料晶格或自旋散射发生能量和动量交换来测量材料动力学性质的实验技术.非弹性中子散射谱仪可以直接测量声子谱、自旋波、晶体场等性质,且能量和动量分辨率高,在物理、材料、化学、生物等领域有广泛应用,是前沿科学研究中重要的实验仪器.本文概述了非弹性中子散射的发展过程、基本理论、散射谱仪及应用范例.     

一种宽能谱多球中子谱仪能量响应的MC模拟

利用蒙特卡罗程序FLUKA模拟计算了聚乙烯慢化球和辅助材料慢化球对低能中子到高能中子的响应函数曲线。结果表明,对纯聚乙烯球来说,随着聚乙烯层厚度的增加,响应曲线峰逐步右移,峰值在高能区有所下降,对20 Me V以上的中子,无论纯聚乙烯球的尺寸有多大,其响应均下降到很低的程度;对辅助材料慢化球来说,中子能量小于1 Me V时,辅助材料慢化球与聚乙烯慢化球的响应曲线相似,但当中子能量大于20 Me V时,中子与辅助材料层发生(n,xn)反应,慢化球的响应呈显著上升趋势。分析计算结果,最终能够确定宽能谱多球中子谱仪的尺寸组合。     

14.7MeV中子在C和Be核上小角弹性散射测量

利用快中子位置灵敏谱仪和伴随粒子飞行时间方法、测量了14.7MeV中子在C和Be核上的弹性散射微分截面.用蒙特卡罗方法对中子在样品中的通量衰减、多次散射作了修正.实验数据与他人结果作了比较和讨论.     

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.     

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.     

Measurement of 232Th (n,γ) cross section at the CSNS Back-n facility in the unresolved resonance region from 4 keV to 100 keV

The neutron capture cross section of ²³²Th was measured at the neutron time-of-flight facility Back-n of China Spallation Neutron Source (CSNS) for the first time. The measurement was performed with 4 hydrogen-free deuterated benzene C₆D₆ liquid scintillation detectors, in the ES#2 experiment station on the beam line, at a distance of about 76 m from the neutron-production assembly. The total energy detection principle in combination with the pulse height weighting technique (PHWT) was applied to analyze the measured data. Results of the ²³²Th (n,γ) reaction cross section in the unresolved resonance region from 4 keV to 100 keV were obtained, which shows a good agreement with the existing experimental data from EXFOR, as well as with the evaluated data from the ENDF/B-VIII.0 and CENDL-3.1. In addition, the excitation function of ²³²Th (n,γ)²³³Th reaction in the unresolved resonance region was theoretically calculated by using the code TALYS-1.95. By fitting the experimental cross section and theoretical data, the average parameters in the unresolved resonance region were extracted. The datasets are openly available at http://dx.doi.org/10.11922/sciencedb.j00113.00015.     

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.     

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.     

New experimental measurement of natSe(n, γ) cross section between 1 eV to 1 keV at the CSNS Back-n facility

The ⁷⁴Se is one of 35 p-nuclei, and ⁸²Se is a r-process only nucleus, and their (n, γ) cross sections are vital input parameters for nuclear astrophysics reaction network calculations. The neutron capture cross section in the resonance range of isotopes and even natural selenium samples has not been measured. Prompt γ-rays originating from neutron-induced capture events were detected by four C₆D₆ liquid scintillator detectors at the Back-n facility of China Spallation Neutron Source (CSNS). The pulse height weighting technique (PHWT) was used to analyze the data in the 1 eV to 100 keV region. The deduced neutron capture cross section was compared with ENDF/B-VIII.0, JEFF-3.2, and JENDL-4.0, and some differences were found. Resonance parameters were extracted by the R-matrix code SAMMY in the 1 eV-1 keV region. All the cross sections of ^natSe and resonance parameters are given in the datasets. The datasets are openly available at http://www.doi.org/10.11922/sciencedb.j00113.00019.     

Measurement of the fast neutron scattering and total cross sections of141Pr

The differential elastic neutron scattering cross sections of¹⁴¹Pr were measured at the incident neutron energies of 1.2, 1.7 and 1.9 MeV in the angular range between 25 and 150 degrees. At 1.7 MeV the differential inelastic neutron scattering cross sections corresponding toQ=?1122 keV, and at 1.9 MeV the ones corresponding toQ=?1122, andQ=?1295 keV were also determined. In a transmission experiment, the total cross section was measured between 0.50 and 2.42 MeV. The total and differential cross sections were calculated using the nuclear optical model. The calculated results were compared with the experimental data.     

Initial years' neutron-induced cross-section measurements at the CSNS Back-n white neutron source

The Back-n white neutron source(known as Back-n) is based on back-streaming neutrons from the spallation target at the China Spallation Neutron Source(CSNS).With its excellent beam properties,e.g.,a neutron flux of approximately 1.8×10~7 n/cm~2/s at 55 m from the spallation target,energy range spanning from 0.5 eV to 200 MeV,and time-of-flight resolution of a few per thousand,along with the equipped physical spectrometers,Back-n is considered to be among the best facilities in the world for carrying out nuclear data measurements.Since its completion and commencement of operation in May 2018,five types of cross-section measurements concerning neutron capture cross-sections,fission cross-sections,total cross-sections,light charged particle emissions,in-beam gamma spectra,and more than forty nuclides have been measured.This article presents an overview of the experimental setup and result analysis on the neutron-induced cross-section measurements and gamma spectroscopy at Back-n in the initial years.     

75As中子辐射俘获截面的实验测量及蒙特卡罗修正

在四川大学2.5 MV静电加速器上， 用活化法测量了29—1 100 keV 能区中子引起的75As(n， γ)76As反应截面， 并用MCNP 4C程序对实验中由中子的多次散射、 注量率衰减效应等引起的偏差进行了修正， 最后将所得结果与已有数据进行了比较。 We have measured the neutron radiative capture cross section of 75As in the energy range of En=29—1 100 keV using the activation technique at 2.5 MV electrostatic accelerator of Sichuan University. The experimental data were then corrected for multiple scattering and self shielding effects with MCNP 4C code. We also compared our results， with the existing measurement， calculation and evaluated data in ENDF/B Ⅵ.     

Cross section for <Superscript>246</Superscript>Cm subbarrier fission

The cross section for ²⁴⁶Cm fission induced by neutrons of energy in the range 0.1 eV-20 keV was measured by the neutron lead slowing-down spectrometer (LSDS-100) of the Institute for Nuclear Research (INR, Russian Academy of Sciences, Moscow). The parameters of the resonance area and of the fission width were evaluated for several low-lying s-wave neutron resonances. The parameters of the intermediate structure in the cross section for the subbarrier fusion of ²⁴⁶Cm nuclei were found. The results obtained in this way were compared with available experimental data and with recommended evaluated data.     

Resonance neutron capture in 56Fe

The neutron capture cross section of ⁵⁶Fe has been measured with 0.2–0.3% energy resolution from 2.5 keV up to the inelastic neutron scattering threshold. Results are compared with recent total cross-section data and average parameters are derived for s-, p- and d-wave resonances. The low correlation coefficient observed between the s-wave reduced neutron and radiative widths is consistent with the minor contribution of the valence capture mechanism as calculated in the framework of the optical model. Broad E1 and M1 doorway states for s-, p- and d-wave resonances are postulated to explain the cross-section data and γ-ray spectra up to 1 MeV.