Research on system performance of a bandwidth limiting neutron chopper at CSNS

Abstract

BackgroundBandwidth limiting (BWL) neutron chopper is one of the important devices installed on the time-of-flight neutron scattering spectrometer. The BWL chopper can select the wavelength range of neutrons and filter the pulse period overlapping background by means of the periodically rotating disk, so as to improve the signal-to-noise ratio.PurposeThis study aims to verify whether the performance of the BWL choppers installed on the neutron scattering spectrometer of China Spallation Neutron Source (CSNS) meets the engineering requirements; on the other hand, it can provide reference for the design of BWL chopper on to be constructed.MethodsFirst of all, based on the BWL chopper system installed on the general purpose powder diffractometer (GPPD) of CSNS, the performances of the BWL chopper were systematically studied by theoretical calculation. Then, Monte Carlo simulation software McStas was employed to calculate the performance of BWL with the physical parameters of neutron choppers. Finally, neutron beam experiments were carried out to measure the actual working performance of the BWL choppers.ResultsThe results show that the actual wavelength bandwidth is about 0.478 nm with less than 0.5% relative error to the target bandwidth of 0.48 nm. The BWL chopper has a significant effect on the filtering long-wave neutron background.ConclusionsThe BWL neutron chopper installed on GPPD of CSNS satisfies engineering needs, and can provide a reference for the design and improvement of the BWL in the neutron scattering spectrometer to be built in the future.

Keywords

• bandwidth limiting neutron chopper, disk,
• mcstas, neutron beam experiments