Evaluation of a method for time-of-flight, wavelength and distance calibration for neutron scattering instruments by means of a mini-chopper and standard neutron monitors
L. Vergara, M. Arai, R. Woracek, M. Olsson, A. Quintanilla, S. Alcock, J. Nilsson, K. Kanaki, P. M. Kadletz, O. Kirstein, R. Hall-Wilton, N. Tsapatsaris
Accurate conversion of neutron time-of-flight (TOF) to wavelength, and its uncertainty, is of fundamental importance to neutron scattering measurements. Especially in cases where instruments are highly configurable, the determination of the absolute wavelength after any change must always be performed. Inspired by the manner with which neutron spectrometers determine the absolute wavelength, we evaluate for the first time, in the author's knowledge, a commonly used method for converting TOF to neutron wavelength, the distance of a monitor from the source of neutrons and we analytically calculate the uncertainty contributions that limit the precision of the conversion. The method was evaluated at the V20 test beamline at the Helmholtz Zentrum Berlin (HZB), emulating the ESS source with a pulse of 2.86 ms length and 14 Hz repetition rate, by using a mini-chopper operated at 140 Hz, beam monitors (BMs) and data acquisition infrastructure. The mini-chopper created well-defined neutron pulses and the BM was placed at two positions, enabling the average wavelength of each of the pulses created to be determined. The used experimental setup resulted in absolute wavelength determination at the monitor positions with a $δλ_{mean} / λ_{mean}$ of $\sim$1.8% for $λ>4$ Å. With a modest increase of the distance between the reference monitor positions a $δλ_{mean} / λ_{mean}$ of below 0.5% can be achieved. Further improvements are possible by using a thinner monitor, smaller chopper disc openings and a higher rotational speed chopper. The method requires only two neutron measurements and doesn't necessitate the use of crystals or complex fitting, and could constitute a suitable addition to imaging, diffraction, reflectometers and small angle neutron scattering instruments, at spallation sources, that do not normally utilise fast choppers.
Multi-Grid Detector for Neutron Spectroscopy: Results Obtained on Time-of-Flight Spectrometer CNCS
多栅极探测器技术已经从原理验证和表征阶段发展而来。在这里，我们报告的性能的多栅极探测器，MG.CNCS原型，已安装和测试的冷中子斩波器谱仪，CNCS在SNS。这允许在操作仪器上与$^3$ He探测器的性能进行并排比较。演示器的有效面积为0.2 m $^2$。它是专门针对CNCS的规格定制的。该探测器于2016年6月安装，并从那时起开始运行，与CNCS的He-3探测器并行收集中子散射数据。在本文中，我们提出了一个全面的分析，这些数据，特别是仪器的能量分辨率，速率能力，背景和相对效率。稳定性，伽马射线和快中子灵敏度也进行了研究。在探测器组件中的散射的效果已经被测量，并提供输入比较的蒙特卡罗模拟。所有的数据进行比较，测量的$^3$ He探测器同时，显示所有的功能记录的一个探测器也记录了其他。能量分辨率非常匹配。我们发现，多网格是能够匹配的数据收集的$^3$他，并看到一个相当大的优势，在计数率能力的迹象。基于这些结果，我们相信，多重网格探测器将能够利用ESS前所未有的中子通量在斩波器谱仪上产生高质量的科学数据。
Design development and implementation of an irradiation station at the neutron time-of-flight facility at CERN
一个新的寄生式、混合场、中子为主的辐照站最近已在欧洲粒子物理实验室（CERN）投入使用。该站安装在中子飞行时间设施中，利用中子散射靶产生的二次辐射。新的台站允许在更接近于粒子加速器运行期间所遇到的辐照条件下进行辐射损害研究;在台站进行的辐照试验将补充通常用伽马源进行的材料标准试验。样品将每年暴露于MGy范围内的中子剂量，对n TOF设施运行的影响最小。该工作站有24个辐照位置，每个位置可容纳多达100 cm 3的样品材料。鉴于其接近nTOF靶，在保护屏蔽内，考虑到人员的安全并避免对nTOF设施和实验的操作产生任何不必要的影响，已经仔细地开发了辐照站及其操作程序。由于nTOF靶周围的整个区域和辐照样品的残留放射性，即使当nTOF设施不运行时，也禁止人类操作员进入辐照站。机器人用于远程安装和取回样品，并根据辐射防护条例和最大限度地减少人员剂量的目的，对处理程序进行了其他优化。
