Neutron beam monitor based on a boron-coated GEM

A new thermal neutron beam monitor with a Gas Electron Multiplier (GEM) is developed to meet the needs of the next generation of neutron facilities. A prototype chamber has been constructed with two 100 mm×100 mm GEM foils. Enriched boron-10 is coated on one surface of the aluminum cathode plate as the neutron convertor. 96 channel pads with an area of 8 mm×8 mm each are used for fast signal readout. In order to study the basic characteristics of a boron-coated GEM, several irradiation tests were carried out with α source ²³⁹Pu and neutron source ²⁴¹Am(Be). The signal induced by the neutron source has a high signal-to-noise ratio. A clear image obtained from α source ²³⁹Pu is presented, which shows that the neutron beam monitor based on a boron-coated GEM has a good two-dimensional imaging ability.     

Reinvestigation of the high spin states in ^（161）Er and enhanced E1 transitions in the N=93 isotones

High-spin states in ¹⁶¹Er have been studied experimentally using the ¹⁵⁰Nd(¹⁶O, 5n) reaction at a beam energy of 86 MeV. The relatively enhanced E1 transitions between the 5/2⁺[642] and 3/2^-[521] bands are observed in ¹⁶¹Er, and the B(E1) values are extracted experimentally. The systematics of the R(E1) values in the N=93 isotones are presented. It is found that the strength of the E1 transitions obviously exhibits angular momentum dependence, and the occurrence of the relatively enhanced E1 transitions could be attributed to octupole softness.     

Exploring nuclear symmetry energy with isospin dependence in neutron skin thickness of nuclei

We propose an alternative way to constrain the density dependence of the symmetry energy from the neutron skin thickness of nuclei which shows a linear relation to both the isospin asymmetry and the nuclear charge with a form of Z^2/3. The relation of the neutron skin thickness to the nuclear charge and isospin asymmetry is systematically studied with the data from antiprotonic atom measurement, and with the extended Thomas-Fermi approach incorporating the Skyrme energy density functional. An obviously linear relationship between the slope parameter L of the nuclear symmetry energy and the isospin asymmetry dependent parameter of the neutron skin thickness can be found, by adopting 70 Skyrme interactions in the calculations. Combining the available experimental data, the constraint of -20 MeV L 82 MeV on the slope parameter of the symmetry energy is obtained. The Skyrme interactions satisfying the constraint are selected.     

Chemical composition of the lunar surface from neutron leakage fluxes

The neutron leakage fluxes from the lunar surface are calculated by Monte Carlo transport code based on Geant4. The integral fluxes of fast neutrons, epi-thermal neutrons and thermal neutrons are analyzed. Numerical results for 20 kinds of lunar soils and 7 minerals show that the fast neutron fluxes are linearly related to the average atomic mass numbers of the lunar materials used in simulations. Meanwhile, the average atomic mass numbers are strongly modulated by the abundances of iron (Fe) and titanium (Ti), and a linear relationship between the average atomic mass numbers and the abundances of Fe and Ti is found. Furthermore, the results show that the ratios of epi-thermal to thermal fluxes for lunar soils are linearly related to the macroscopic absorption cross sections of lunar materials, and that the macroscopic absorption cross sections monotonically increase with the abundances of Fe and Ti by a simple function. Then we reach the conclusion that the neutron fluxes can provide the information about the Fe and Ti contents.     

Design and performance analysis of a compact magnetic proton recoil spectrometer for DT neutrons

A magnetic proton recoil (MPR) spectrometer is a novel instrument with superior performance, including high energy resolution, high count rate and good signal-to-noise ratio (SNR) for measurements of neutron spectra from inertial confinement fusion (ICF) experiments and high power Tokomaks. In this work, the design of a compact MPR spectrometer (cMPR) was evaluated for deuteron-tritium (DT) neutron spectroscopy. The characteristics of the spectrometer were analyzed using 2-D beam transport simulations, 3-D particle transport calculations and Monte-Carlo simulations. Based on the theoretical results, an instrument design that satisfies special experimental requirements is proposed. The energy resolution and efficiency of the spectrometer are also evaluated. The results indicate that the proposed cMPR spectrometer would achieve a detection efficiency and energy resolution of approximately 10^-8 and 4%, respectively, for DT neutrons.     

中子三轴谱仪的原理、技术与应用

中子作为一种具有独特性质的亚原子粒子,在很多研究领域都具有重要且无法替代的优势.中子三轴谱仪通过能量守恒和动量守恒原理就可以测量某一系统的弹性或非弹性散射性质,从而获得该系统的结构或动力学信息.中子三轴谱仪得名于其3个核心部分:单色器、样品和分析器,每一部分都可以独立转动.由于三轴谱仪在物理学尤其是凝聚态物理学研究中所发挥的重要作用,中国科学院物理研究所将联合中国原子能科学研究院,在后者新建成的中国先进研究堆搭建一台现代化的热中子三轴谱仪.文章结合该谱仪,介绍了中子三轴谱仪的基本原理、技术以及应用范围.     

中子活化分析在鄂尔多斯地区元素分析中的应用

利用中子活化对鄂尔多斯盆地油气田上方的地质样品进行了某些元素的检测,通过实验分析,得到了该地区岩石中某些元素的含量,并对该地区的放射性元素作出了评价,绘制了样品的稀土配分模式图和评价了当地的金属矿产资源情况.结果表明,在油气田的上方,放射性元素铀呈现出负异常;钍和钾无明显异常;岩石中的其它元素和中国大陆地壳元素丰度基本...     

D-T中子与平板型聚乙烯材料作用的次级中子角度谱实验研究

基于反冲质子法建立了一种测量D-T中子与平板型宏观样品作用的次级中子角度谱的实验方法.为保证探测器的能量线性并在较低的中子有效测量下阈(0.5 MeV)情况下获得好的中子-伽马射线甄别性能,采用高、低能段分别测量的方法.采用事件记录法,同时记录了次级中子和伴随伽马射线的脉冲形状甄别和脉冲幅度二维信息,利用基于ROOT数据分析平台编写的离线数据分析程序,完成了伴随伽马射线的挑选和扣除,以及高、低两能段反冲质子谱的拼接,并成功的将神经网络技术应用于中子能谱的解谱,获得了D-T中子与9和18 cm厚平板型聚乙烯材料作用的0.5-15 MeV的次级中子角度谱实验结果.实验模型的MC模拟由MCNP5完成,数据库采用ENDF-VI,实验结果和MC计算结果在实验不确定度范围内一致. 关键词： D-T中子 积分中子学 反冲质子法 次级中子能谱     

D+离子束轰击时间对氘钛靶特性的影响

利用ZF-300keV中子发生器,采用伴随粒子法研究了氘钛靶的中子产额随D⁺离子束轰击时间的变化特性;利用慢正电子湮没技术和扫描电镜分别研究了D⁺离子束轰击前后靶辐射损伤特性和表面形貌特征.结果表明,束流轰击引起氘钛靶缺陷结构和表面形貌的改变 ,但轰击时间的不同并未引起氘钛靶的中子产额、缺陷结构和表面形貌有明显差异;数值模拟了D⁺离子束在氘钛靶的辐射损伤特性和能量损失规律并与实验结果进行了比照分析和讨论. 关键词： 中子发生器 氘钛靶 伴随粒子法 慢正电子湮没技术     

QCD 揭秘

 俗称为QCD 的量子色动力学是强相互作用的现代理论。从历史上看,它源于原子核物理及对常规物质的描述--理解质子和中子是什么以及它们是如何相互作用的。如今QCD 被用来描述大部分高能加速器中发生的现象。