Experimental result of back-streaming white neutron beam characterization at Chinese spallation neutron source

Abstract

The Chinese spallation neutron source was completed in May 2018 and then subsequently commissioned. The Back-streaming white neutron beam line can be used in neutron nuclear data measurement, neutron physics research, and nuclear technology. In these experiments, it is necessary to know the neutron energy spectrum, the neutron flux, and the neutron beam profile of the neutron beam. In this paper, we present the preliminary measurements of these parameters. The neutron energy spectrum and neutron flux are measured by the time-of-flight method with a fission chamber equipped with <sup>235</sup>U and <sup>238</sup>U samples and a <sup>6</sup>Li-Si detector. The neutron beam profile is measured by a scintillator-CMOS detection system. The preliminary experimental measurements of the beam line are obtained. Among them, the energy spectrum measurement range of white neutrons is from eV to more than 100 MeV, which also gives an uncertainty analysis; the neutron fluence rate gives the full power value of the two experimental halls; the collimated white neutron beam spot is given under a diameter of 60 mm. The future plan is also given. The results of these experimental parameters can serve as the foundation for the future nuclear data measurement and detector calibration experiments of the beam line.

Detector calibration based on secondary protons of Back-n white neutron source

“…Back-n是 我国第一台高性能白光中子源, 与CSNS同步建 成, 可以提供0.5 eV-200 MeV能区的连续能量中 子 [5−8] . 目前已经测定的能谱如图1所示, 能谱峰 值位于MeV附近 [9] . 反角白光中子源有两个实验 厅, 实验厅一及实验厅二的中心位置距离散裂中子 源的钨靶分别约55和76 m. 通过调节中子开关以 及准直器一、准直器二的孔径的组合, 可以得到不 同束斑尺寸及束流通量的白光中子束流.…”

“…在散裂中 子源的质子束流打靶功率为100 kW时, 使用束斑 直径F60的孔径组合, 在实验厅一的中心位置(距 离钨靶55 m)的束流通量为1.75 × 10 7 s -1 •cm -2 , 实验厅二的中心位置(距离钨靶76 m)的束流通量 为7.03× 10 6 s -1 •cm -2 [10] . 由于Back-n的中子能量最高可达200 MeV [9,10] ,…”

“…随产生 g -flash [8] , 可以利用 g -flash来标定中子的起 [12] , 而 12 C(n, p) 12 B, 12 C(n, d) 11 B, 12 C(n, t) 10 B, 12 C(n, 3 He) 10 Be, 12 C(n, a) 9 Be等反 应道的截面数据来源于Talys1.9程序 [13] 计算结 果. 相较于其他反应道, 1 H(n,el), FENDL-3.1c 12 C(n,p) 12 B, Talys1.9 12 C(n,d) 11 B, Talys1.9 12 C(n,t) 10 B, Talys1.9 12 C(n, 3 He) 10 Be, Talys1.9 12 C(n,) 9 Be, Talys1.9 1 H(n,) 2 H, FENDL-3.1c 鉴别 [14−16] . 在搭建及使用带电粒子望远镜时, 需要 使用带电粒子来进行测试及标定.…”

“…. Cross sections of the 1 H(n, el), 12 C(n, p) 12 B, 12 C(n, d)11 B, 12 C(n, t) 10 B, 12 C(n, 3 He)10 Be, 12 C(n, a)9 Be and 1 H(n, g) 2 H reactions.…”

Measurement of total neutron cross section of natural lithium at China Spallation Neutron Source Back-n facility

“…针对天然锂和 7 Li的中子反应数据, 从20世 纪30年代就开展了实验测量. 采用的中子源主要 是基于 7 Li(p, n), 9 Be(a, n), 13 C(a, n), T(p, n) 3 He 等核反应的单能中子源, 实验数据集中在快中子能 区, 而慢中子能区的天然锂中子全截面数据相对较 少 . 在 实 验 核 反 应 数 据 库 (experimental nuclear reaction data, EXFOR) [5] 中收录的天然锂慢中子 能区实验数据有三家, 分别是1935年Dunning等 [6] 基于Rn-Be放射性中子源测量的天然锂0.025 eV 的中子全截面; 1946年Havens等 [7] 基于哥伦比亚 大学回旋加速器中子谱仪测量的0.0169-60.5 eV LiF样品中子全截面; 1950年Hibdon [8] 本工作基于中国散裂中子源反角白光中子束 线(CSNS Back-n) [9−12] , 利用中子全截面测量谱 仪(NTOX) [13]…”