Neutron beam monitors are an essential diagnostic component of neutron scattering facilities. They are used to measure neutron flux, calibrating experiments performed on the instruments, allowing measurement of facility performance, understanding of the effect on the neutrons of beam-line components (such as choppers), calibration of detectors and tracking of beam stability. Ideally beam monitors should not perturb the beam. Previous work shows commercial beam monitors attenuate the beam by a few percent in the worst case due to the 1–2 mm thick aluminium entrance and exit windows and the material inside. Parasitic methods of neutron beam diagnostics, where there is no beam monitor directly in the beam, would be preferable. This paper presents the concept of a parasitic method of monitoring the beam which can be used for neutron chopper phasing. This is achieved by placing a gamma detector close to a rotating chopper and measuring a signal proportional to the flux absorbed by the chopper. Neutrons interact with the boron absorber on the chopper disc leading to gamma emission at 480 keV. Detection of these gamma rays is used to determine the chopper phasing and timing. Potentially information on the flux of the beamline can be extracted. Results from a proof of concept implementation show that diagnosis of neutron chopper phases is feasible.

中子束监视器是中子散射设备的重要诊断组件。它们用于测量中子通量，在仪器上进行的校准实验，允许测量设施性能，了解束线组件（例如斩波器）对中子的影响，检测器的校准以及束稳定性的跟踪。理想情况下，光束监控器不应干扰光束。先前的工作表明，在最坏的情况下，由于1-2 mm厚的铝制进出口窗和内部材料，商用光束监控器会将光束衰减百分之几。最好采用中子束诊断的寄生方法，即在束中没有束监测器。本文提出了一种可用于中子斩波器定相的寄生束监视方法的概念。这可以通过将伽马探测器放置在旋转的斩波器附近并测量与斩波器吸收的通量成比例的信号来实现。中子与斩波盘上的硼吸收剂相互作用，导致480 keV的伽马发射。这些伽马射线的检测用于确定斩波器的相位和定时。可以提取关于光束线通量的潜在信息。概念验证实施的结果表明，中子斩波器相的诊断是可行的。可以提取关于光束线通量的潜在信息。概念验证实施的结果表明，中子斩波器相的诊断是可行的。可以提取关于光束线通量的潜在信息。概念验证实施的结果表明，中子斩波器相的诊断是可行的。