Abstract
The C<sub>6</sub>D<sub>6</sub> detection system coupling with the pulse height weighting technique is widely used for experimentally measuring the neutron capture cross section. The thickness of sample used in the experiment directly affects the neutron beam time and the reliability of the experimental data. In the present work, we compare the lutetium (Lu) neutron capture reaction cross sections among the samles with different thickness, obtained by the C<sub>6</sub>D<sub>6</sub> detection system of the back-streaming white neutron beam line at China spallation Neutron Source (CSNS back-n). The light response of the detection system is simulated with the consideration of the sample thickness by GEANT4 Monte Carlo simulation code. The 4<sup>th</sup> order polynomial pulse weight functions for different samples are determined by using the above light response function. In the experiment, the high precision capture yield distributions in the resonance energy region are obtained by measuring the longer flight distance and background. The experimental resonance parameters are deduced by analyzing the capture yield distribution with the R-matrix theory. The comparisons of the results of capture yield and the resonance parameters between the two groups show that the resonance curve of 1.06mm <sup>nat</sup>Lu sample changes due to its thickness effect, and there is a large difference between the experimental resonance parameters and ENDF/B-VIII.0 database. However, the experimental results of 0.207mm <sup>nat</sup>Lu sample can well accord with the ENDF/B-VIII. 0 data.
Highlights
Pink, and blue arrows indicate the energies of the 175Lu,176Lu, and 181Ta resonances, respective
通过比较不同厚度的 natLu 靶(n,γ)反应实验结果发现,厚靶在大部分强共振峰 位置的产额均出现了饱和现象,薄靶则没有。厚靶因其自屏蔽效应等问题,共振 能量间隔较小的位置不能明显的给出共振结构,并且共振曲线也出现了扭曲现象。 利用多级 R 矩阵 SAMMY 分析程序从实验俘获产额中提取了共振参数。对比了 实验与 ENDF/B-VIII.0 数据库的共振因子,结果发现较薄 natLu 样品实验结果能够 很好的再现 ENDF/B-VIII.0 评价库和文献数据。鉴于本实验结果,建议今后同类 实验研究中尽量选择较薄的样品为佳。
Summary
摘 要 C6D6 闪烁体探测系统结合脉冲权重技术被广泛应用于中子俘获反应截面 测量研究。实验中采用的样品厚度直接影响中子束流时间,同时也影响 实验数据的可靠性。基于中国散裂中子源反角白光束线(CSNS Back-n) C6D6 探测系统,对比研究了不同厚度的镥(Lu)样品中子俘获反应截面的 实验测量。利用 GEANT4 蒙特卡罗程序模拟了考虑样品厚度的探测系统 光响应,计算出精确的脉冲权重函数。实验中,通过采用较长中子飞行 距离和本底测量,得到了高精度的共振区产额分布。通过 R 矩阵理论分 析产额分布,得到了相应的实验共振参数。结果发现,较厚 Lu 样品因其 厚度效应导致共振曲线发生变化,实验共振参数与 ENDF/B-VIII.0 评价 数据库差距较大 ; 然 而 , 较 薄 Lu 样品实验结果能够很好的再现 ENDF/B-VIII.0 评价数据。 关键词:中子俘获反应截面,中国散裂中子源,共振参数分析 PACS: 29.25.Dz, 02.70.Uu, 52.70.La, 01.52.+r 前国际上主要有五大评价中子核数据库,分别是中国 CENDL[4]、美国 ENDF/B[5]、 日本 JENDL[6]、欧洲 JEFF[7]和俄罗斯 BROND[8]。中子俘获截面数据是核数据的 主要组成部分之一,在核装置与核能系统设计、运行及核物理基础研究中具有重 要的参考价值和实际用途[1,2,3]。 中国散裂中子源(CSNS)已于2018年建成,是我国“十一五”期间重点建设的 大科学装置,属于世界四大脉冲散裂中子源之一[9]。CSNS加速器具有双束团和单 束团两种脉冲模式,质子束流功率为100kW,能量为1.6GeV,平均流强为64uA, 脉冲重复频率为25Hz,脉冲宽度为41ns,中子产额可高达2.0×1016s-1。反角白光 束线(Back-n)是CSNS的重要实验平台之一,主要用于中子核数据实验测量工作。 反角白光束线位于CSNS质子束流反角(180 ̊)方向,束线全长80 m,共有两个实验 终端,分别在距离散裂靶约55 m(实验一厅)和76 m(实验二厅)处。为降低实验二 厅的本底,在通道与二厅的连接处安装有1m厚的聚乙烯、铅等材质制作成的屏蔽
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
