Development of a new Fourier chopper with laser pickup system for neutron beam modulation in correlation RTOF diffractometry

IF 1.4 3区物理与天体物理 Q3 INSTRUMENTS & INSTRUMENTATION

Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment Pub Date : 2025-09-15 DOI:10.1016/j.nima.2025.171025

Gizo Bokuchava, Valery Zhuravlev, Igor Papushkin, Alexander Kruglov

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引用次数: 0

Abstract

For the further development of the RTOF (reverse time-of-flight) method, a unique Fourier chopper with a fundamentally improved design and enhanced technical specifications has been developed and put into operation at the FSD Fourier diffractometer on the IBR-2 pulsed reactor (FLNP JINR, Dubna, Russia). The chopper consists of a multi-slit rotor–stator system housed in a dedicated vacuum chamber and mounted on a precision translation platform, enabling rapid switching between TOF (high intensity) and RTOF (high resolution) operational modes.

The new chopper introduces advanced capabilities that provide promising potential for further improvement of the RTOF method. In particular, it implements a set of six different frequency window functions, which enable detailed studies of diffraction peak profiles and residual intensity oscillations caused by the finite value of the maximum neutron beam modulation frequency. Additionally, the device supports measurements of individual Fourier harmonics forming the diffraction peak at various constant chopper speeds across the entire accessible TOF-scale range.

An innovative feature of the chopper is the presence of 1024 physical radial slits (each ∼0.7 mm wide), precisely cut into both the stator plate and rotor disc, which reduces neutron absorption and scattering by the chopper material. Furthermore, this work demonstrates for the first time the feasibility of generating pickup signals using a 1550 nm infrared laser beam passing through the slits in both the rotor and stator (Laser Pickup System – LPS). This approach enables direct measurement of the actual transmission function of the chopper, precisely matching the neutron beam modulation profile. As a backup pickup signal source, a standard incremental optical encoder, mounted on the motor shaft, is also used. Experimental results show that high-resolution RTOF diffraction spectra measured using the LPS system exhibit a high signal-to-noise ratio and are comparable to those obtained with the optical encoder.

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相关RTOF衍射中用于中子束调制的新型傅立叶斩波激光拾取系统的研制

为了进一步发展RTOF（反向飞行时间）方法，开发了一种独特的傅立叶斩波器，从根本上改进了设计和增强了技术规格，并在IBR-2脉冲反应堆（FLNP JINR, Dubna，俄罗斯）的FSD傅立叶衍射仪上投入使用。斩波器由一个多缝转子-定子系统组成，该系统安装在专用真空室中，并安装在精密平移平台上，能够在TOF（高强度）和RTOF（高分辨率）操作模式之间快速切换。新的斩波器引入了先进的功能，为进一步改进RTOF方法提供了有希望的潜力。特别是，它实现了一组六种不同的频率窗函数，可以详细研究衍射峰轮廓和由最大中子束调制频率有限值引起的剩余强度振荡。此外，该设备支持在整个可访问的tof尺度范围内以各种恒定斩波速度形成衍射峰的单个傅立叶谐波的测量。斩波器的一个创新特点是存在1024个物理径向狭缝（每个宽约0.7毫米），精确地切割到定子板和转子盘上，从而减少了斩波器材料对中子的吸收和散射。此外，这项工作首次证明了利用1550 nm红外激光束通过转子和定子的狭缝产生拾取信号的可行性（激光拾取系统- LPS）。这种方法可以直接测量斩波器的实际传输函数，精确地匹配中子束调制剖面。作为备用拾取信号源，还使用安装在电机轴上的标准增量光学编码器。实验结果表明，LPS系统测量的高分辨率RTOF衍射光谱具有较高的信噪比，与光学编码器测量的高分辨率RTOF衍射光谱相当。

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来源期刊

Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment 物理-光谱学

CiteScore

3.20

自引率

21.40%

发文量

787

审稿时长

1 months

期刊介绍： Section A of Nuclear Instruments and Methods in Physics Research publishes papers on design, manufacturing and performance of scientific instruments with an emphasis on large scale facilities. This includes the development of particle accelerators, ion sources, beam transport systems and target arrangements as well as the use of secondary phenomena such as synchrotron radiation and free electron lasers. It also includes all types of instrumentation for the detection and spectrometry of radiations from high energy processes and nuclear decays, as well as instrumentation for experiments at nuclear reactors. Specialized electronics for nuclear and other types of spectrometry as well as computerization of measurements and control systems in this area also find their place in the A section. Theoretical as well as experimental papers are accepted.